Effects of axitinib and lenvatinib on cardiovascular function and haemodynamic

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): EU Horizon 2020 Research and Innovation programme, under the Marie Skłodowska-Curie European Training Network

Background

The introduction of novel anticancer treatments, targeting vascular endothelial growth factor receptors (VEGFRs), has changed the therapeutic approach in oncology. However, with their introduction in clinical practice, unanticipated cardiovascular complications emerged, including hypertension, left ventricular dysfunction and thromboembolism [1]. Even though these therapeutics strongly affect haemodynamic balance in patients, the pathophysiological mechanisms by which they impair cardiovascular function are still largely unknown, leading to a reduction of therapeutic dosage or to a temporary or permanent treatment interruption [2].

Purpose

The severity of cardiovascular complications following the treatment with VEGFR inhibitors, along with the lack of antihypertensive strategies able to adequately manage these events, require an unequivocal and urgent assessment of their cardiovascular safety. This study aims to determine the extent to which VEGFR inhibitors impact on cardiovascular function, profiling their effect on regional haemodynamic responses. Their cardiovascular assessment represents a valuable opportunity to investigate the mechanisms underlying cardiovascular toxicities induced by these novel antiangiogenic treatments.

Methods

This study evaluated the haemodynamic effects of selected receptor tyrosine kinase inhibitors (RTKIs), namely axitinib and lenvatinib, in conscious and freely moving rats using the Doppler Flowmetry technique. Male Sprague Dawley Rats (350-450 g) were chronically implanted with pulsed Doppler flow probes (around the renal and mesenteric arteries, and the descending abdominal aorta) and catheters (jugular vein and distal abdominal aorta) [3]. Haemodynamic parameters were measured over 4 days, before and after daily administration of axitinib (3 and 6 mg/kg, 3 and 6 mg/kg/h for 1 h, i.v.), or lenvatinib (3 and 6 mg/kg, 3 and 6 mg/kg/h for 1 h, i.v.).

Results

Both axitinib and lenvatinib evoked a significant hypertensive response, which progressively increased over the 4 days. This pressor effect was associated with a notable decrease of vascular conductance in the hindquarters. Lenvatinib caused a more marked vasoconstriction in mesenteric and renal vessels when compared to axitinib, which only elicited a renal vasoconstrictive effect at the highest dose used.

Conclusions

This study showed that the axitinib- and lenvatinib-induced hypertensive response is associated with regionally selective vasoconstrictions, which consistently occur in the hindquarters vascular bed. However, their vasoconstrictive profile differs in the renal and mesenteric vasculature. In addition, the Doppler Flowmetry model showed to be a translational approach to predict the detrimental cardiovascular effects of these anticancer drugs, since the increase in blood pressure observed with this method reflects the hypertensive response reported in clinical practice.

The effect of EMAT coil geometry on the Rayleigh wave frequency behaviour

Understanding of optimal signal generation and frequency content for electromagnetic acoustic transducers (EMATs) is key to improving their design and signal to noise ratio. Linear and meander coil designs are fairly well understood, but other designs such as racetrack or focused coils have recently been proposed. Multiple transmission racetrack coil EMATs, with focused and unfocused designs, were constructed. The optimum driving frequency for maximum detected signal was found to range between 1.1 and 1.4 MHz on aluminium for a 1.5 mm width coil. A simple analytical model based on the instantaneous velocity of a wave predicts a maximum signal at 1.44 MHz. Modelling the detection coil as a spatial square wave agrees with this, and predicts a general relation of f_P=0.761v/L between the optimum frequency f_P, the wave velocity v, and the coil width L. A time domain model of the detection coil predicts a 1.4-1.5 MHz peak for continuous wave excitation, with a frequency that decreases as the length of the wavepacket is decreased, consistent with the experimental data. Linear coil modelling using the same technique is shown to be consistent with previous work, with improving detection at lower wave frequencies, and signal minima at every integer multiple of the wavelength. Finite Element Analysis (FEA) is used to model the effects of the spatial width of the racetrack generation coil and focused geometry, and no significant difference is found between the focused and the unfocused EMAT response. This highlights the importance of designing the EMAT coil for the correct lift-off and desired frequency of operation.

Structure-based exploration and pharmacological evaluation of N-substituted piperidin-4-yl-methanamine CXCR4 chemokine receptor antagonists

Using the available structural information of the chemokine receptor CXCR4, we present hit finding and hit exploration studies that make use of virtual fragment screening, design, synthesis and structure-activity relationship (SAR) studies. Fragment 2 was identified as virtual screening hit and used as a starting point for the exploration of 31 N-substituted piperidin-4-yl-methanamine derivatives to investigate and improve the interactions with the CXCR4 binding site. Additionally, subtle structural ligand changes lead to distinct interactions with CXCR4 resulting in a full to partial displacement of CXCL12 binding and competitive and/or non-competitive antagonism. Three-dimensional quantitative structure-activity relationship (3D-QSAR) and binding model studies were used to identify important hydrophobic interactions that determine binding affinity and indicate key ligand-receptor interactions.

More inclusive bipolar mixed depression definition by permitting overlapping and non-overlapping mood elevation symptoms

OBJECTIVE

The objective of this study was to assess the strengths and limitations of a mixed bipolar depression definition made more inclusive than that of the Diagnostic and Statistical Manual of Mental Disorders Fifth Edition (DSM-5) by counting not only 'non-overlapping' mood elevation symptoms (NOMES) as in DSM-5, but also 'overlapping' mood elevation symptoms (OMES, psychomotor agitation, distractibility, and irritability).

METHODS

Among bipolar disorder (BD) out-patients assessed with the Systematic Treatment Enhancement Program for BD (STEP-BD) Affective Disorders Evaluation, we assessed prevalence, demographics, and clinical correlates of mixed vs. pure depression, using more inclusive (≥3 NOMES/OMES) and less inclusive DSM-5 (≥3 NOMES) definitions.

RESULTS

Among 153 depressed BD, counting not only NOMES but also OMES yielded a three-fold higher mixed depression rate (22.9% vs. 7.2%) and important statistically significant clinical correlates for mixed compared to pure depression (more lifetime anxiety disorder comorbidity, more current irritability, and less current antidepressant use), which were not significant using the DSM-5 threshold.

CONCLUSION

To conclude, further studies with larger numbers of patients with DSM-5 bipolar mixed depression assessing strengths and limitations of more inclusive mixed depression definitions are warranted, including efforts to ascertain whether or not OMES should count toward mixed depression.

More inclusive bipolar mixed depression definitions by requiring fewer non-overlapping mood elevation symptoms

OBJECTIVE

Assess strengths and limitations of mixed bipolar depression definitions made more inclusive than that of the Diagnostic and Statistical Manual of Mental Disorders Fifth Edition (DSM-5) by requiring fewer than three 'non-overlapping' mood elevation symptoms (NOMES).

METHOD

Among bipolar disorder (BD) out-patients assessed with Systematic Treatment Enhancement Program for BD (STEP-BD) Affective Disorders Evaluation, we assessed prevalence, demographics, and clinical correlates of mixed vs. pure depression, using less inclusive (≥3 NOMES, DSM-5), more inclusive (≥2 NOMES), and most inclusive (≥1 NOMES) definitions.

RESULTS

Among 153 depressed BD, compared to less inclusive DSM-5 threshold, our more and most inclusive thresholds, yielded approximately two- and five-fold higher mixed depression rates (7.2%, 15.0%, and 34.6% respectively), and important statistically significant clinical correlates for mixed compared to pure depression (e.g. more lifetime anxiety disorder comorbidity, more current irritability), which were not significant using the DSM-5 threshold.

CONCLUSION

Further studies assessing strengths and limitations of more inclusive mixed depression definitions are warranted, including assessing the extent to which enhanced statistical power vs. other factors contributes to more vs. less inclusive mixed bipolar depression thresholds having more statistically significant clinical correlates, and whether 'overlapping' mood elevation symptoms should be counted.

Detection of the secondary, low-affinity β1 -adrenoceptor site in living cells using the fluorescent CGP 12177 derivative BODIPY-TMR-CGP

Background and Purpose

CGP 12177 not only inhibits agonist effects mediated through the catecholamine site of the β₁-adrenoceptor with high affinity, but also exhibits agonist effects of its own at higher concentrations through a secondary, low-affinity β₁-adrenoceptor site or conformation. β-blocker affinities for this ‘CGP 12177’ site of the human β₁-adrenoceptor have thus far only been characterized in functional studies. Here, we used the fluorescent CGP 12177 analogue BODIPY-TMR-CGP to directly investigate receptor–ligand interactions at the secondary binding site of the β₁-adrenoceptor.

Experimental Approach

The human β₁-adrenoceptor was stably expressed in CHO cells containing a cAMP response element (CRE)-secreted placental alkaline phosphatase (SPAP) reporter gene construct. Functional responses of BODIPY-TMR-CGP were determined in the CRE-SPAP reporter gene assay, and manual and automated confocal microscopy platforms used to investigate the binding properties of BODIPY-TMR-CGP.

Key Results

BODIPY-TMR-CGP displayed a pharmacological profile similar to that of CGP 12177, retaining agonist activity at the secondary β₁-adrenoceptor site. In confocal microscopy studies, specific BODIPY-TMR-CGP binding allowed clear visualization of β₁-adrenoceptors in live cells. Using a wider concentration range of labelled ligand in a high-content fluorescence-based binding assay than is possible in radioligand binding assays, two-site inhibition binding curves of β-adrenoceptor antagonists were revealed in CHO cells expressing the human β₁-adrenoceptor, but not the β₂-adrenoceptor.

Conclusions and Implications

The fluorescent CGP 12177 analogue allowed the detection of the β₁-adrenoceptor secondary site in both functional and binding studies. This suggests that BODIPY-TMR-CGP presents an important and novel fluorescent tool to investigate the nature of the secondary β₁-adrenoceptor site.

Quantitative analysis of neuropeptide Y receptor association with beta-arrestin2 measured by bimolecular fluorescence complementation

BACKGROUND AND PURPOSE

beta-Arrestins are critical scaffold proteins that shape spatiotemporal signalling from seven transmembrane domain receptors (7TMRs). Here, we study the association between neuropeptide Y (NPY) receptors and beta-arrestin2, using bimolecular fluorescence complementation (BiFC) to directly report underlying protein-protein interactions.

EXPERIMENTAL APPROACH

Y1 receptors were tagged with a C-terminal fragment, Yc, of yellow fluorescent protein (YFP), and beta-arrestin2 fused with the complementary N-terminal fragment, Yn. After Y receptor-beta-arrestin association, YFP fragment refolding to regenerate fluorescence (BiFC) was examined by confocal microscopy in transfected HEK293 cells. Y receptor/beta-arrestin2 BiFC responses were also quantified by automated imaging and granularity analysis.

KEY RESULTS

NPY stimulation promoted association between Y1-Yc and beta-arrestin2-Yn, and the specific development of BiFC in intracellular compartments, eliminated when using non-interacting receptor and arrestin mutants. Responses developed irreversibly and were slower than for downstream Y1 receptor-YFP internalization, a consequence of delayed maturation and stability of complemented YFP. However, beta-arrestin2 BiFC measurements delivered appropriate ligand pharmacology for both Y1 and Y2 receptors, and demonstrated higher affinity of Y1 compared to Y2 receptors for beta-arrestin2. Receptor mutagenesis combined with beta-arrestin2 BiFC revealed that alternative arrangements of Ser/Thr residues in the Y1 receptor C tail could support beta-arrestin2 association, and that Y2 receptor-beta-arrestin2 interaction was enhanced by the intracellular loop mutation H155P.

CONCLUSIONS AND IMPLICATIONS

The BiFC approach quantifies Y receptor ligand pharmacology focused on the beta-arrestin2 pathway, and provides insight into mechanisms of beta-arrestin2 recruitment by activated and phosphorylated 7TMRs, at the level of protein-protein interaction.

Antagonist selective modulation of adenosine A1 and A3 receptor pharmacology by the food dye Brilliant Black BN: evidence for allosteric interactions

Allosteric binding sites on the adenosine receptor family represent potential therapeutic targets for a number of conditions involving metabolic stress. This study has identified Brilliant Black BN as a novel allosteric modulator of the adenosine A(1) and A(3) receptors. In addition to being a food dye and pharmaceutical excipient, Brilliant Black BN is commonly used within calcium mobilization assays to quench extracellular fluorescence. Brilliant Black BN (5-500 microM) had no significant effect on the calcium mobilization stimulated by the nonselective adenosine receptor agonist 5'-(N-ethylcarboxamido)adenosine in Chinese hamster ovary cells stably transfected with the human adenosine A(1) or A(3) receptor. Likewise, calcium mobilization and radioligand binding assays found that Brilliant Black BN (5-500 microM) did not significantly influence the antagonism mediated by 8-cyclopentyl-1,3-dipropylxanthine (100 nM) at the A(1) receptor. In contrast, the affinity of N-[9-chloro-2-(2-furanyl)[1,2,4]-triazolo[1,5-c]quinazolin-5-yl]benzene acetamide (MRS1220) at the A(3) receptor and xanthine amine congener (XAC) and XAC-X-BY630 at the A(1) and A(3) receptors was significantly decreased in the presence of 500 muM Brilliant Black BN. A reduction in XAC potency at the A(1) and A(3) receptor was achieved within 1 min of Brilliant Black BN addition, despite receptors having been pre-equilibrated with antagonist. Dissociation kinetics of the fluorescent XAC derivative, XAC-X-BY630, revealed that the decrease in affinity is probably due to a significant increase in dissociation rate of the antagonist in the presence of Brilliant Black BN. Taken together, these results suggest that Brilliant Black BN can act allosterically to modify ligand affinity at A(1) and A(3) receptors.

Audio-visual presentation of information for informed consent for participation in clinical trials

BACKGROUND

Informed consent is a critical component of clinical research. Different methods of presenting information to potential participants of clinical trials may improve the informed consent process. Audio-visual interventions (presented for example on the Internet, DVD, or video cassette) are one such method.

OBJECTIVES

To assess the effects of providing audio-visual information alone, or in conjunction with standard forms of information provision, to potential clinical trial participants in the informed consent process, in terms of their satisfaction, understanding and recall of information about the study, level of anxiety and their decision whether or not to participate.

SEARCH STRATEGY

We searched: the Cochrane Consumers and Communication Review Group Specialised Register (searched 20 June 2006); the Cochrane Central Register of Controlled Trials (CENTRAL), The Cochrane Library, issue 2, 2006; MEDLINE (Ovid) (1966 to June week 1 2006); EMBASE (Ovid) (1988 to 2006 week 24); and other databases. We also searched reference lists of included studies and relevant review articles, and contacted study authors and experts. There were no language restrictions.

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials comparing audio-visual information alone, or in conjunction with standard forms of information provision (such as written or oral information as usually employed in the particular service setting), with standard forms of information provision alone, in the informed consent process for clinical trials. Trials involved individuals or their guardians asked to participate in a real (not hypothetical) clinical study.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed studies for inclusion and extracted data. Due to heterogeneity no meta-analysis was possible; we present the findings in a narrative review.

MAIN RESULTS

We included 4 trials involving data from 511 people. Studies were set in the USA and Canada. Three were randomised controlled trials (RCTs) and the fourth a quasi-randomised trial. Their quality was mixed and results should be interpreted with caution. Considerable uncertainty remains about the effects of audio-visual interventions, compared with standard forms of information provision (such as written or oral information normally used in the particular setting), for use in the process of obtaining informed consent for clinical trials. Audio-visual interventions did not consistently increase participants' levels of knowledge/understanding (assessed in four studies), although one study showed better retention of knowledge amongst intervention recipients. An audio-visual intervention may transiently increase people's willingness to participate in trials (one study), but this was not sustained at two to four weeks post-intervention. Perceived worth of the trial did not appear to be influenced by an audio-visual intervention (one study), but another study suggested that the quality of information disclosed may be enhanced by an audio-visual intervention. Many relevant outcomes including harms were not measured. The heterogeneity in results may reflect the differences in intervention design, content and delivery, the populations studied and the diverse methods of outcome assessment in included studies.

AUTHORS' CONCLUSIONS

The value of audio-visual interventions for people considering participating in clinical trials remains unclear. Evidence is mixed as to whether audio-visual interventions enhance people's knowledge of the trial they are considering entering, and/or the health condition the trial is designed to address; one study showed improved retention of knowledge amongst intervention recipients. The intervention may also have small positive effects on the quality of information disclosed, and may increase willingness to participate in the short-term; however the evidence is weak. There were no data for several primary outcomes, including harms. In the absence of clear results, triallists should continue to explore innovative methods of providing information to potential trial participants. Further research should take the form of high-quality randomised controlled trials, with clear reporting of methods. Studies should conduct content assessment of audio-visual and other innovative interventions for people of differing levels of understanding and education; also for different age and cultural groups. Researchers should assess systematically the effects of different intervention components and delivery characteristics, and should involve consumers in intervention development. Studies should assess additional outcomes relevant to individuals' decisional capacity, using validated tools, including satisfaction; anxiety; and adherence to the subsequent trial protocol.

Agonist-occupied A3 adenosine receptors exist within heterogeneous complexes in membrane microdomains of individual living cells

G protein-coupled receptors are known to be organized within different membrane compartments or microdomains of individual cells. Here, we have used a fluorescent A3 adenosine receptor (A3-AR) agonist, ABEA-X-BY630, and the technique of fluorescence correlation spectroscopy (FCS) to investigate the diffusional characteristics of functional agonist-occupied A3-AR complexes in single living cells. In Chinese hamster ovary cells expressing the human A3-AR, the fluorescent A3-AR agonist was able to inhibit forskolin-stimulated [3H]cAMP production (pEC50=8.57), and this was antagonized by the A3-selective antagonist MRS1220 (pK(B)=9.32). The fluorescent ligand also stimulated phosphoinositide hydrolysis (pEC50=7.34). Ligand binding to the A3-AR on the membranes of single cells and subsequent increases in single cell [Ca2+]i were monitored simultaneously in real time using confocal microscopy. FCS measurements in small-membrane microdomains (approximately 0.2 microm2) revealed two agonist-occupied A3-AR components with differing diffusion characteristics (diffusion coefficients=2.65x10(-8) and 1.19x10(-9) cm2/s, respectively). The binding of ligand to these two components was reduced from 5.1 and 14.9 to 2.6 and 3.3 receptors/microm2, respectively, by MRS1220 (100 nM). These data provide direct evidence for at least two populations of agonist-occupied A3-receptor complexes, showing different motilities within the membrane of single living cells.

Isolation and the characterization of the degradation products of the mediator ABTS-derived radicals formed upon reaction with polyphenols

Two degradation products were obtained from the incubation of the widely used 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), ABTS, radical cations with the polyphenols, (+)-catechin, (-)-epicatechin, and phloroglucinol in acetate buffer (pH 5). The products were purified by reversed-phase chromatography and characterized by UV-visible detection, mass spectrometry, and (1)H NMR spectroscopy. The data allowed us to identify the degradation products as 3-ethyl-6-sulfonate benzothiazolinone imine and the corresponding sulfoxide, 3-ethyl-6-sulfonate benzothiazolone. Elemental composition strongly supported the proposed structures. Our results unequivocally demonstrated that ABTS radicals are not as stable as usually claimed because they could be degraded upon interaction with polyphenols, in addition to being reduced by these antioxidants back to the parent compound. Therefore, it is concluded that caution must be exercised in using ABTS radicals as a basis for the evaluation of antioxidant capacities of pure compounds and/or complex mixtures.

Echocardiographic abnormalities in primary antibody deficiency

OBJECTIVE

To document cardiac abnormalities secondary to pulmonary disease in primary antibody deficiency.

PATIENTS AND METHODS

A cross sectional audit study of patients from a regional immunology centre. Subjects undergoing two dimensional and Doppler transthoracic echocardiography were reviewed. Ventricular dimensions and function, valvular competence, and estimated pulmonary artery pressure were recorded. Data were compared with clinical variables, pulmonary function tests, and thoracic computed tomography data.

RESULTS

Nineteen patients with common variable immunodeficiency and one with IgG(2) subclass deficiency were included, mean age at diagnosis 37.5 years, mean estimated diagnostic delay 10.94 years. Left ventricular impairment was found in 15% and right heart dilatation in 20%. Pulmonary hypertension (mean pulmonary artery pressure >25 mm Hg) was found in 45% (9/20), graded as moderate (40-60 mm Hg) in 44% of cases. Pulmonary function was obstructive in 47% (9/19). Fifty five percent of the patients with computed tomography data within the last five years (10/18) had confirmed bronchiectasis. Patients with right heart dilatation and/or moderate pulmonary hypertension (n = 6) had a more prolonged diagnostic delay (p = 0.04) and more severe lung disease.

CONCLUSION

Echocardiographic abnormalities are common in primary antibody deficiency, associated with diagnostic delay and pulmonary complications. Pulmonary hypertension should be considered in those with severe lung disease and can be confirmed by echocardiography.

Quantitative analysis of the formation and diffusion of A1-adenosine receptor-antagonist complexes in single living cells

The A1-adenosine receptor (A1-AR) is a G protein-coupled receptor that mediates many of the physiological effects of adenosine in the brain, heart, kidney, and adipocytes. Currently, ligand interactions with the A1-AR can be quantified on large cell populations only by using radioligand binding. To increase the resolution of these measurements, we have designed and characterized a previously undescribed fluorescent antagonist for the A1-AR, XAC-BY630, based on xanthine amine congener (XAC). This compound has been used to quantify ligand-receptor binding at a single cell level using fluorescence correlation spectroscopy (FCS). XAC-BY630 was a competitive antagonist of A1-AR-mediated inhibition of cAMP accumulation [log10 of the affinity constant (pKb) = 6.7)] and stimulation of inositol phosphate accumulation (pKb = 6.5). Specific binding of XAC-BY630 to cell surface A1-AR could also be visualized in living Chinese hamster ovary (CHO)-A1 cells by using confocal microscopy. FCS analysis of XAC-BY630 binding to the membrane of CHO-A1 cells revealed three components with diffusion times (tauD) of 62 micros (tauD1, free ligand), 17 ms (tauD2, A1-AR-ligand), and 320 ms (tauD3). Confirmation that tauD2 resulted from diffusion of ligand-receptor complexes came from the similar diffusion time observed for the fluorescent A1-AR-Topaz fusion protein (15 ms). Quantification of tauD2 showed that the number of receptor-ligand complexes increased with increasing free ligand concentration and was decreased by the selective A1-AR antagonist, 8-cyclopentyl-1,3-dipropylxanthine. The combination of FCS with XAC-BY630 will be a powerful tool for the characterization of ligand-A1-AR interactions in single living cells in health and disease.

Modelling of signalling via G-protein coupled receptors: pathway-dependent agonist potency and efficacy

A mathematical model is constructed to study promiscuous coupling of receptors to G-proteins and to simulate events leading to the activation of multiple effector pathways within a cell. The model is directed at a better understanding of the factors that determine the efficacy and potency of a drug. Assuming that the receptors can exist in multiple conformational states, and allowing for agonist specific conformation, a system of ordinary differential equations is constructed and subsequently pathway-dependent agonist efficacy and potency order is predicted. A simple case of the compartmentalization of receptors and G-proteins is also given, using the current model to illustrate the effects of spatial heterogeneity on the predicted response.

Reporter-gene systems for the study of G-protein-coupled receptors

Reporter-gene assays offer an alternative to biochemical assays for following signal transduction pathways from receptors at the cell surface to nuclear gene transcription in living cells. Specific reporter-gene systems are now available for the study of ligand activity at G alpha(i/o), G alpha(s) and G alpha(q) G-protein-coupled receptors. In recent years reporter genes have been applied in academia and industry to the study of ligand efficacy and affinity in recombinant and primary cell lines using a variety of colour, fluorescent or luminescent read-outs.

Evaluation of the effect of data pre-treatment procedures on classical pattern recognition and principal components analysis: a case study for the geographical classification of tea

A simple transformation that uses the half-range and central value has been used as a data pre-treatment procedure for principal component analysis (PCA) and pattern recognition techniques. The results obtained have been compared with the results from classical normalisation of data (mean normalisation, maximum normalisation and range normalisation), autoscaling and the minimum-maximum transformation. Three data sets were used in the study. The first was formed by determining 17 elements in 53 tea samples (901 pieces of data). The second and third data sets arose from two long-term drift studies performed to examine instrumental stability at standard and robust conditions. The instruments used were an inductively coupled plasma atomic emission spectrometer and an inductively coupled plasma mass spectrometer. Each drift diagnosis experiment consisted of replicate determinations of a test solution containing 15 analytes at 10 mg l-1 over 8 h without recalibration. Twenty-nine emission lines were determined 99 times, thus, each data set was formed by 2881 pieces of data. Data pre-treatment was applied to the three data sets prior to the use of principal component analysis, cluster analysis, linear discrimination analysis and soft independent modelling of class analogy. The study revealed that the half-range and central value transformation resulted in a better classification of the tea samples than that achieved using the classical normalisation. The loadings in the PCA for the long-term stability study, under both standard and robust conditions, were found to be similar to the drift trends only when the minimum-maximum transformation and the mean or maximum normalizations were used as data pre-treatments.

Modulation by cellular cholesterol of gene transcription via the cyclic AMP response element

The effect of rapid changes in cellular cholesterol content on adenosine 3',5'-cyclic monophosphate (cAMP) response element-mediated gene transcription was investigated. The study was carried out in Chinese hamster ovary (CHO-K1) cells permanently expressing the human beta(2)-adrenoceptor. Gene transcription was quantified using a reporter gene (secreted placental alkaline phosphatase) under the transcriptional control of cAMP response element (CRE) sequences. Cellular cholesterol was reduced by 42% or elevated by 47% by incubating cells for 1 hr with methyl-beta-cyclodextrin alone or methyl-beta-cyclodextrin complexed with cholesterol, respectively. There was a significant negative correlation between the free cholesterol content of the cells and CRE-mediated gene expression in response to 10(-6) M isoprenaline (slope = -4.57 +/- 0.73, P < 0.001), indicating that beta(2)-adrenoceptor-mediated activation of the CRE is inhibited by cholesterol. Cyclic AMP accumulation in response to isoprenaline (10(-12) to 10(-5) M) was also inhibited in cholesterol-enriched cells and enhanced in cholesterol-depleted cells compared to controls (P < 0.05, two-way ANOVA). Cholesterol also inhibited serum-mediated enhancement of CRE-driven gene expression, and we present data suggesting that the pathway activated by serum and inhibited by cholesterol could be independent of adrenoceptor activation and protein kinase A. We conclude that in CHO-K1 cells cholesterol inhibits at least two processes that can stimulate CRE-mediated gene expression. One is isoprenaline activation of cAMP synthesis, the other is activated by serum. These findings demonstrate that activation of gene transcription by extracellular stimuli could be influenced by cellular cholesterol content.

Role of protein kinase Calpha in signaling from the histamine H(1) receptor to the nucleus

Stimulation of histamine H(1) receptors produced a marked activation of inositol phospholipid hydrolysis, intracellular calcium mobilization, and stimulation of the c-fos promoter in CHO-H1 cells expressing the H(1) receptor at a level of 3 pmol/mg protein. The latter response was determined using a luciferase-based reporter gene (pGL3). This response to histamine was not sensitive to inhibition by pertussis toxin but could be completely attenuated by the protein kinase C (PKC) inhibitor Ro-31-8220, or by 24-h pretreatment with the phorbol esters phorbol 12,13-dibutyrate or phorbol-12-myristate-13-acetate. Several isoforms of PKC can be detected in CHO-H1 cells (alpha, delta, epsilon, mu, iota, zeta) but only PKCalpha and PKCdelta were down-regulated by prolonged treatment with phorbol esters. Of the two isoforms that were down-regulated, only protein kinase Calpha was translocated to CHO-H1 cell membranes after stimulation with either histamine or phorbol esters. The PKC inhibitor Gö 6976, which inhibits PKCalpha but not PKCdelta, was also able to significantly attenuate the c-fos-luciferase response to histamine. The mitogen-activated protein kinase kinase inhibitor PD 98059 markedly inhibited the response to histamine, suggesting that the likely major target for PKCalpha was the mitogen-activated protein kinase pathway. These data suggest that the histamine H(1) receptor can signal to the nucleus via PKCalpha after activation of phospholipase Cbeta.

Influence of receptor number on functional responses elicited by agonists acting at the human adenosine A(1) receptor: evidence for signaling pathway-dependent changes in agonist potency and relative intrinsic activity

Activation of A(1) adenosine receptors leads to the inhibition of cAMP accumulation and the stimulation of inositol phosphate accumulation via pertussis toxin-sensitive G-proteins. In this study we have investigated the signaling of the A(1) adenosine receptor in Chinese hamster ovary (CHO) cells, when expressed at approximately 203 fmol/mg (CHOA1L) and at approximately 3350 fmol/mg (CHOA1H). In CHOA1L cells, the agonists N(6)-cyclopentyladenosine (CPA), (R)-N(6)-(2-phenylisopropyl)adenosine, and 5'-(N-ethylcarboxamido)adenosine (NECA) inhibited cAMP production in a concentration-dependent manner. After pertussis toxin treatment, the agonist NECA produced a stimulation of cAMP production, whereas CPA and (R)-N(6)-(2-phenylisopropyl)adenosine were ineffective. In CHOAIH cells, however, all three agonists produced both an inhibition of adenylyl cyclase and a pertussis toxin-insensitive stimulation of adenylyl cyclase. All three agonists were more potent at inhibiting adenylyl cyclase in CHOA1H cells than in CHOA1L cells. In contrast, A(1) agonists (and particularly NECA) were less potent at stimulating inositol phosphate accumulation in CHOA1H cells than in CHOA1L cells. After pertussis toxin treatment, agonist-stimulated inositol phosphate accumulation was reduced in CHOA1H cells and abolished in CHOA1L cells. The relative intrinsic activity of NECA in stimulating inositol phosphate accumulation, compared to CPA (100%), was much greater in the presence of pertussis toxin (289.6%) than in the absence of pertussis toxin (155.2%). These data suggest that A(1) adenosine receptors can couple to both pertussis toxin-sensitive and -insensitive G-proteins in an expression level-dependent manner. These data also suggest that the ability of this receptor to activate different G-proteins is dependent on the agonist present.

Non-competitive antagonism of beta(2)-agonist-mediated cyclic AMP accumulation by ICI 118551 in BC3H1 cells endogenously expressing constitutively active beta(2)-adrenoceptors

Constitutive activity of the beta(2)-adrenoceptor, which is sensitive to inhibition by an inverse agonist such as ICI 118551, has been readily demonstrated in recombinant systems expressing constitutively-active mutant receptors or over-expressing the wild-type beta(2)-adrenoceptor. Here we demonstrate the presence of constitutive beta(2)-adrenoceptor activity in BC3H1 cells which endogenously express this receptor. In BC3H1 cells, only ICI 118551 behaved as an inverse agonist at beta(2)-adrenoceptors, while propranolol, ICI 118551, atenolol and, to a lesser extent, alprenolol exhibited inverse agonism in CHO-beta(2)4 cells transfected with cDNA for the human beta(2)-adrenoceptor (310 fmol. mg protein(-1)). The level of expression of beta2-adrenoceptors in BC3H1 cells was not high (78 fmol.mg protein-1) and the efficiency of receptor - effector coupling in this cell line was much lower than in the recombinant CHO-beta(2)4 cells (as judged by the partial agonist nature of both salbutamol and clenbuterol). ICI 118551 (log K(D)-9.73+/-0.07) and propranolol (log K(D)-9.25+/-0.12) both behaved as conventional competitive antagonists of isoprenaline-stimulated cyclic AMP accumulation in high expressing CHO-beta(2)4 cells. In contrast, ICI 118551 appeared to act as a non-competitive antagonist in BC3H1 cells and in low expressing CHO-beta(2)6 cells (50 fmol.mg protein(-1)). This non-competitive effect of ICI 118551 in BC3H1 cells was also observed when either salbutamol was used as agonist, or the incubation period with isoprenaline was extended to 30 min. The possibility that these effects of ICI 118551 are due to an interaction with different affinity states (R, R* and R') of the receptor is discussed.

Genotoxic, cytotoxic and developmental effects of tributyltin oxide (TBTO): an integrated approach to the evaluation of the relative sensitivities of two marine species

Adopting an integrated approach the potential genotoxic, cytotoxic and developmental effects of tributyltin oxide (TBTO), a known endocrine-disrupting agent for neogastropods, have been evaluated in two ecologically relevant invertebrates: Mytilus edulis (blue mussel) and Platynereis dumerilli (rag worm). Following determination of the maximum tolerated dose (MTD) in terms of developmental and survival effects, the embryo-larval stages of these organisms were exposed to a range of concentrations of TBTO, and analysed for cytotoxic (proliferation rate index) and genotoxic (sister chromatid exchanges and chromosomal aberrations) effects. The study suggested that: (1) TBTO is both toxic and genotoxic to embryo-larval stages of both species; (2) at comparable concentrations, for developmental and genotoxic effects, P. dumerilii (non-target species) is more sensitive compared to M. edulis (target species); and (3) genotoxic effects are more closely tied with the development and survival of the organisms. The study emphasises the need of the evaluation of genotoxic potential of other endocrine-disrupting agents in different taxonomic groups.

Conference formats in family practice residencies

BACKGROUND

This study was intended to establish national baseline data of the current structure of conferences at family practice residencies and to determine if there are differences in conference formats among types of residencies.

METHODS

An author-developed survey was mailed to 331 programs stratified by type and randomly selected. Statistical analysis included chi-square tests and non-parametric tests.

RESULTS

The response rate was 84%. The average time devoted to lectures was 4.5 hours a week, with the noon hour the most common time. Most speakers were from within the program, and community-based family physicians were rarely present. Structural changes were frequent.

CONCLUSIONS

Results indicate that a variety of formats are implemented for meeting Residency Review Committee requirements in the structure of family practice residencies' conferences. Program settings do influence how conferences are structured. More research is needed on this neglected area of formal resident education.

A preliminary clinical investigation into the potential of blood lead levels to measure bone resorption in patients with skeletal metastases, using ICP-MS

A simple, accurate and precise method to measure lead levels in whole blood by inductively coupled plasma-mass spectrometry (ICP-MS) has been developed. Blood samples were diluted (1 + 9) with 0.1% v/v Triton X-100 and 0.1% v/v nitric acid, and gave a limit of detection of 0.06 microgram/l (3sn). Spiking experiments demonstrated recoveries of 100 +/- 10% and verification against Seronorm reference and BCR certified reference materials gave experimental values in close agreement to the reference values. The methodology was used to conduct a feasibility study, involving a preliminary clinical investigation to assess the potential of whole blood lead levels as biochemical markers to measure bone resorption in patients with skeletal metastases and receiving treatment. The results from this feasibility study showed that the method remained under analytical control, giving inter and intra assay coefficients of variation of < 5%. This feasibility study also showed that the changes in the blood lead levels within individual patients were measurable and in many cases the patient's observed clinical performance demonstrated similar trends to the blood lead levels measured over time. Overall the results were encouraging and showed promise. Further and more detailed investigations into the use of lead and other trace metals as biomarkers of bone resorption is warranted.

Determination of beryllium in a stream sediment by high-performance chelation ion chromatography

High-performance chelation ion chromatography (HPCIC), involving a chelating silica substrate bonded with aminomethylphosphonic acid, has been developed as a novel technique for the quantitative determination of beryllium in complex matrices. An isocratic separation method, using an eluent containing 1 M KNO3, 0.5 M HNO3 and 0.08 M ascorbic acid, allowed the Be2+ to elute away from the sample matrix peak in under 6 min in a sample containing in excess of 800 mg l(-1) matrix metals. A detection limit of 35 microg l(-1) Be(II) was found using a post-column reaction involving Chrome Azurol S (CAS), 1 M hexamine and 10 mM EDTA buffered at pH 6. The standard addition curve gave excellent linearity (R2>0.999). The procedure was applied to the determination of trace beryllium in a certified sediment sample. The results obtained compared well with the certified value for beryllium.

Methodologies for determination of antimony in terrestrial environmental samples

Methodologies for the environmental analysis of total antimony and aqueous chemical speciation are critically reviewed, including preparation techniques for aqueous and solid matrices and the determination of solid state partitioning and recommendations are given for future research directions. Concentrations of total antimony commonly present in aqueous and solid environmental samples are readily determined using present day analytical techniques. This has resulted primarily from technological advances in microwave digestion for solid matrices and the development of plasma based analyte detection systems. ICP-AES and ICP-MS techniques are both utilised for the environmental analysis of total antimony concentrations. However, ICP-MS is increasingly favoured as a result of reduced spectral interferences and the potential for analyte detection in the pg mL(-1) range. Determination of aqueous antimony speciation presents a number of complex analytical challenges and highly selective separation and identification techniques are required prior to detection. The majority of published techniques including common applications of hydride generation are insufficiently selective for the determination of intrinsic chemical speciation and often only oxidation state data are obtained. The recent in-line applications of HPLC-ICP-MS offer the potential for highly selective separations of aqueous antimony species and determination of detailed chemical speciation data. However, considerable development work is required to optimise chromatographic separations and identify uncharacterised species resident in environmental systems. Analytical techniques to aid the determination of antimony's associations with solid environmental matrices include the application of chemical extraction procedures and leaching experiments. To date, this area of analytical research has received little attention and further studies are required to elucidate this aspect of antimony's environmental chemistry.

Detection of genotoxins in the marine environment: adoption and evaluation of an integrated approach using the embryo-larval stages of the marine mussel, Mytilus edulis

In genetic ecotoxicology or eco-genotoxicology, there is lack of well-validated systems which could demonstrate the utility of multiple endpoints in environmental quality assessment. For an evaluation of genotoxic potential of heterogeneous marine sediment samples collected from a small fishing harbour in the UK, an in vivo test system using embryo-larval stages of the common mussel, Mytilus edulis was validated against direct and indirect acting reference mutagens. The system appeared to be sensitive and reproducible for cytogenetic endpoints analysed (sister chromatid exchanges (SCEs) and chromosomal aberrations (CAbs)). Following validation and chemical characterisation of the environmental samples, multiple endpoints were measured. Determination of the maximum tolerated dose (MTD) was carried out as a measure to determine cytotoxic effects as a confounding factor for genotoxicity, based on developmental and cytotoxic (in terms of proliferative rate index or PRI) effects. Evaluation of the genotoxic potential of the samples gave a positive response for all the endpoints tested, linking different levels of biological organisation (i.e., chromosomal, cellular and organismal) for the observed effects. The study also emphasises the need for the assessment of the short and long-term impacts of dredge disposal on marine biota by including laboratory-based bioassays and incorporating an integrated approach which could yield as much useful information as possible in overall hazard and risk assessment for aquatic genotoxicity.

Tributyltin induces cytogenetic damage in the early life stages of the marine mussel, Mytilus edulis

Using an integrated approach, the genotoxic potential of bis(tri-n-butyltin), an antifouling agent known to disrupt endocrine system in marine invertebrates, has been evaluated in the embryo-larval stages of the edible mussel, Mytilus edulis. While evaluating the genotoxic potential, the toxicity of tributyltin was also taken into account by determining the maximum tolerated dose. The study suggested that tributyltin is capable of inducing cytogenetic damage (sister chromatid exchanges and chromosomal aberrations) in this target species. The study emphasises the need for further investigations of the potential genotoxic effects of this and other endocrine disrupters on ecologically relevant aquatic invertebrates, which contribute to the maintenance of ecosystems and that could potentially be harmful to human health via the food chain.

Large-amplitude undulatory fish swimming: fluid mechanics coupled to internal mechanics

The load against which the swimming muscles contract, during the undulatory swimming of a fish, is composed principally of hydrodynamic pressure forces and body inertia. In the past this has been analysed, through an equation for bending moments, for small-amplitude swimming, using Lighthill's elongated-body theory and a ‘vortex-ring panel method’, respectively, to compute the hydrodynamic forces. Those models are outlined in this review, and a summary is given of recent work on large-amplitude swimming that has (a) extended the bending moment equation to large amplitude, which involves the introduction of a new (though probably usually small) term, and (b) developed a large-amplitude vortex-ring panel method. The latter requires computation of the wake, which rolls up into concentrated vortex rings and filaments, and has a significant effect on the pressure on the body. Application is principally made to the saithe (Pollachius virens). The calculations confirm that the wave of muscle activation travels down the fish much more rapidly than the wave of bending.

Reduced IL-4 and interferon-gamma (IFN-gamma) expression by CD4 T cells in patients with chronic lymphocytic leukaemia

CD7 co-expression by CD4 T cells has been reported to be higher in the Th1 compared with the Th2 functional subset. Clinical immunodeficiency and immune dysregulation are more prevalent in the advanced stages of B cell chronic lymphocytic leukaemia (B-CLL). To analyse this further 25 patients with B-CLL and 11 healthy subjects were examined for cell surface CD7 and intracellular IFN-gamma and IL-4 expression in the peripheral blood CD4+ T helper cell population. Significantly decreased CD7, IFN-gamma and IL-4 expression was observed in the patients with B-CLL (P < 0.001). While CD7 negativity and IL-4 expression were more frequent in the later stages of the disease, this did not attain statistical significance. These results suggest a possible explanation for the reduced cellular and humoral immunity in B-CLL.

Gi-Protein alpha-subunit mRNA antisense oligonucleotide inhibition of Gi-coupled receptor contractile activity in the epididymis of the guinea-pig

We have used a reversible permeabilization method to facilitate the entry of Gialpha1, 2 and 3 G-protein subunit mRNA antisense or mismatch oligonucleotides into intact tissue, to investigate the G-protein alpha-subunit coupling of alpha2-adrenoceptors, neuropeptide Y (NPY) Y1, and A1 adenosine receptors in preparations of the epididymis of the guinea-pig. The alpha2-adrenoceptor agonist, xylazine, elicited concentration dependent contractions from preparations of phenylephrine (3 microM)-stimulated epididymis (pEC50 value 6.52+/-0.39, maximum response 236+/-41 mg force). Compared to respective mismatch controls the incubation of preparations with Gialpha2, but not with Gialpha1 or Gialpha3 mRNA antisense oligonucleotides (30 microM) reduced the maximal xylazine-potentiation of phenylephrine (3 microM)-stimulated contractility (to 51+/-12% of Gialpha2 mismatch control). The oligonucleotide incubations had no effect upon the pEC50 values of xylazine. The A1 adenosine receptor agonist, cyclopentyladenosine (CPA) elicited concentration dependent contractions from preparations of phenylephrine (3 microM)-stimulated epididymis (pEC50 value 7.66+/-0.57, maximum response 208+/-54 mg force). Incubation of preparations of epididymis with Gialpha1, but neither Gialpha2 nor Gialpha3 antisense oligonucleotides reduced the maximal CPA-potentiation of phenylephrine (3 microM)-stimulated contractions (to 55+/-17% of Gialpha1 mismatch control), pEC50 values were not affected. The incubation of preparations with Gialpha2 antisense mRNA oligonucleotides reduced the maximal NPY-potentiation of phenylephrine (3 microM)-stimulated contractions (to 62+/-15% of Gialpha mismatch control). Compared with Gialpha2 mismatch controls, the incubation of preparations with Gialpha1 and Gialpha3 oligonucleotides also reduced the NPY-potentiation of phenylephrine (3 microM)-stimulated contractions. These studies indicate that, in the guinea-pig epididymis, alpha2-adrenoceptors and A1 adenosine receptors preferentially couple to effectors through Gialpha2 and Gialpha1 subunits respectively. In contrast NPY receptors may elicit effects through either Gialpha1, 2 or 3 subunits.

Nonselective effects of the putative phospholipase C inhibitor, U73122, on adenosine A1 receptor-mediated signal transduction events in Chinese hamster ovary cells

Adenosine A1 receptors can signal, through Gi/o proteins, to inhibit adenylyl cyclase activity and also to stimulate phosphoinositide hydrolysis and the subsequent release of intracellular Ca2+ stores. The aminosteroid U73122 (1-[6-1[17beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1 H-pyrrole-2,5-dione) has been widely used as an inhibitor of phospholipase C, the enzyme mediating phosphoinositide hydrolysis. Using U73122, we sought to selectively block signalling through the phospholipase C pathway, in Chinese hamster ovary (CHO-K1) cells heterologously expressing human adenosine A1 receptors. U73122 inhibited A1 receptor-mediated phosphoinositide hydrolysis, as measured by total inositol phosphate accumulation, over the concentration range 1-15 microM. However, over the same concentration range, it also appeared to inhibit A1 receptor-mediated inhibition of forskolin-stimulated cyclic AMP accumulation, A1 receptor agonist-promoted [35S]GTP-gammaS binding, and at the higher concentrations (10-15 microM) produced marked morphological changes, leading to cytolysis. The structural analogue of U73122, U73343 (1-[6-[[17beta-3-methoxyestra-1,3,5(10-trien-17-yl]amino]hexyl]-2, 5-pyrrolidone-dione), typically used as an inactive control compound, had little effect on these events. The data suggest that U73122 is not a selective inhibitor of phospholipase C activity, interfering with adenosine A1 receptor signalling generally, either at the pre-effector level involving Gi/o proteins, or as a consequence of the morphological changes it induces.

Potentiation of adenosine A1 receptor-mediated inositol phospholipid hydrolysis by tyrosine kinase inhibitors in CHO cells

1. The effect of protein tyrosine kinase inhibitors on human adenosine A1 receptor-mediated [3H]-inositol phosphate ([3H]-IP) accumulation has been studied in transfected Chinese hamster ovary cells (CHO-A1) cells. 2. In agreement with our previous studies the selective adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) stimulated the accumulation of [3H]-IPs in CHO-A1 cells. Pre-treatment with the broad spectrum tyrosine kinase inhibitor genistein (100 microM; 30 min) potentiated the responses elicited by 1 microM (199+/-17% of control CPA response) and 10 microM CPA (234+/-15%). Similarly, tyrphostin A47 (100 microM) potentiated the accumulation of [3H]-IPs elicited by 1 microM CPA (280+/-32%). 3. Genistein (EC50 = 13.7+/-1.2 microM) and tyrphostin A47 (EC50 = 10.4+/-3.9 microM) potentiated the [3H]-IP response to 1 microM CPA in a concentration-dependent manner. 4. Pre-incubation with the inactive analogues of genistein and tyrphostin A47, daidzein (100 microM; 30 min) and tyrphostin A1 (100 microM; 30 min), respectively, had no significant effect on the accumulation of [3H]-IPs elicited by 1 microM CPA. 5. Genistein (100 microM) had no significant effect on the accumulation of [3H]-IPs produced by the endogenous thrombin receptor (1 u ml(-1); 100+/-10% of control response). In contrast, tyrphostin A47 produced a small augmentation of the thrombin [3H]-IP response (148+/-13%). 6. Genistein (100 microM) had no effect on the [3H]-IP response produced by activation of the endogenous Gq-protein coupled CCK(A) receptor with the sulphated C-terminal octapeptide of cholecystokinin (1 microM CCK-8; 96+/-6% of control). In contrast, tyrphostin A47 (100 microM) caused a small but significant increase in the response to 1 microM CCK-8 (113+/-3% of control). 7. The phosphatidylinositol 3-kinase inhibitor LY 294002 (30 microM) and the MAP kinase kinase inhibitor PD 98059 (50 microM) had no significant effect on the [3H]-IP responses produced by 1 microM CPA and 1 microM CCK-8. 8. These observations suggest that a tyrosine kinase-dependent pathway may be involved in the regulation of human adenosine A1 receptor mediated [3H]-IP responses in CHO-A1 cells.

Influence of receptor number on the stimulation by salmeterol of gene transcription in CHO-K1 cells transfected with the human beta2-adrenoceptor

1. The beta2-agonist salmeterol is a potent relaxant of airway smooth muscle with a long duration of action. Previous studies of cyclic AMP accumulation, however, have indicated that salmeterol is a low efficacy beta2-agonist when compared to isoprenaline. Here we have compared the properties of salmeterol and isoprenaline as stimulants of gene transcription in CHO-K1 cells transfected with the human beta2-adrenoceptor to different levels (50 and 310 fmol mg protein(-1)). 2. Gene transcription was monitored using a secreted placental alkaline phosphate (SPAP) reporter gene under the transcriptional control of six cyclic AMP response element (CRE) sequences. 3. In the lower expressing cells (CHO-beta2/6), salmeterol produced a maximal cyclic AMP response that was only 22% that of that obtained with isoprenaline. In contrast in the higher expressing cells (CHO-beta2/ 4), the two maxima were of similar magnitude. 4. Salmeterol was a more potent stimulant of gene transcription, producing the same maximal response as isoprenaline in both cell lines. Furthermore, in the CHO-beta2/4 cells, Salmeterol was 50 fold more potent as a stimulant of SPAP secretion than of cyclic AMP accumulation. In contrast, isoprenaline was 24 fold less sensitive as a stimulant of SPAP secretion than of cyclic AMP accumulation. In the presence of serum (10%), the effects of both salmeterol and isoprenaline on gene transcription were augmented. 5. These data suggest that the low efficacy and/or long duration of action of salmeterol, favours a potent stimulation of gene transcription when compared to more efficacious but shorter-lived agonists such as isoprenaline.

A1 and A2 adenosine receptor modulation of contractility in the cauda epididymis of the guinea-pig

1. The effects of adenosine receptor agonists upon phenylephrine-stimulated contractility and [3H]-cyclic adenosine monophosphate ([3H]-cyclic AMP) accumulation in the cauda epididymis of the guinea-pig were investigated. The alpha1-adrenoceptor agonist, phenylephrine elicited concentration dependent contractile responses from preparations of epididymis. In the absence or presence of the L-type Ca2+ channel blocker, nifedipine (10 microM) the non-selective adenosine receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA, 1 microM) shifted phenylephrine concentration-response curves to the left (4 and 5 fold respectively). Following the incubation of preparations with pertussis toxin (200 ng ml(-1) 24 h) NECA shifted phenylephrine concentration-response curves to the right (5.7+/-0.9 fold). 2. In the presence of phenylephrine (1 microM), NECA and the A1 adenosine receptor selective agonists, N6-cyclopentyladenosine (CPA) and (2S)-N6-[2-endo-norbornyl]adenosine ((S)-ENBA) elicited concentration-responses dependent contractions from preparations of epididymis (pEC50 values 8.18+/-0.19, 7.79+/-0.29 and 8.15+/-0.43 respectively). The A3 adenosine receptor agonists N6-iodobenzyl-5'-N-methylcarboxamido adenosine (IBMECA) and N6-2-(4-aminophenyl) ethyladenosine (APNEA) mimicked this effect (but only at concentrations greater than 10 microM). In the presence of 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 30 nM) CPA concentration-response curves were shifted, in parallel to the right (apparent pKB 8.75+/-0.88) and the maximal response to NECA was reduced. 3. In the presence of DPCPX (100 nM) the adenosine agonist NECA and the A2A adenosine receptor selective agonist, CGS 21680 (2-p-(2-carboxyethyl)-phenethylamino-N-ethylcarboxamido adenosine), but not CPA, inhibited phenylephrine (20 microM) stimulated contractions (pIC50 7.15+/-0.48). This effect of NECA was blocked by xanthine amine congener (XAC, 1 microM) and the A2A adenosine receptor-selective antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-++ +ylamino]ethyl)phenol (ZM 241385; 30 nM). 4. (S)-ENBA (in the absence and presence of ZM 241385, 100 nM), but not NECA or CPA inhibited the forskolin (30 microM)-stimulated accumulation of [3H]-cyclic AMP in preparations of the epididymis of the guinea-pig (by 17+6% of control). In the presence of DPCPX (100 nM) NECA and CGS 21680, but not (S)-ENBA, increased the accumulation of [3H]-cyclic AMP in preparations of epididymis (pEC50 values 5.35+/-0.35 and 6.42+/-0.40 respectively), the NECA-induced elevation of [3H]-cyclic AMP was antagonised by XAC (apparent pKB 6.88+/-0.88) and also by the A2A adenosine receptor antagonist, ZM 241385 (apparent pKB 8.60+/-0.76). 5. These studies are consistent with the action of stable adenosine analogues at post-junctional A1 and A2 adenosine receptors in the epididymis of the guinea-pig. A1 Adenosine receptors potentiate alpha1-adrenoceptor contractility, an effect blocked by pertussis toxin, but which may not be dependent upon an inhibition of adenylyl cyclase. The epididymis of the guinea-pig also contains A2 adenosine receptors, possibly of the A2A subtype, which both inhibit contractility and also stimulate adenylyl cyclase.

Involvement of G-protein betagamma subunits in coupling the adenosine A1 receptor to phospholipase C in transfected CHO cells

In transfected Chinese hamster ovary (CHO-A1) cells the human adenosine A1 receptor directly stimulates pertussis toxin-sensitive increases in inositol phosphate production and potentiates (synergistically) the inositol phosphate responses mediated by Gq-coupled P2Y2 purinoceptor and CCK(A) receptors. In the present study we have investigated the role of Gbetagamma subunits in mediating adenosine A1 receptor effects on phospholipase C activation (both direct and synergistic) by transiently transfecting CHO-A1 cells with a scavenger of Gbetagamma subunits: the C-terminus of beta-adrenoceptor kinase 1 (beta ark1 residues 495-689). [3H]inositol phosphate responses to the selective adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA; 1 microM) were inhibited (41 +/- 1%) in CHO-A1 cells transiently transfected with the Gbetagamma scavenger, beta ark1 (495-689). Expression of beta ark1 (495-689) protein was confirmed by Western blotting. In contrast, adenosine A1 receptor-mediated inhibition of forskolin stimulated [3H]cyclic AMP accumulation was unaffected by transient expression of beta ark1 (495-689). Beta ark1 (495-689) expression had no significant effect on the [3H]inositol phosphate responses produced by activation of the endogenous P2Y2 purinoceptor (100 microM UTP; 92 +/- 0.8% of control). [3H]inositol phosphate accumulation in response to adenosine A receptor activation was also attenuated in CHO-K1 cells co-transfected with the beta ark1 (495-689) minigene (59 +/- 4% inhibition of control response to 1 microM CPA). Finally, transient expression of beta ark1 (495-689) in CHO-A1 cells inhibited the augmentation of [3H]inositol phosphate responses resulting from co-activation of adenosine A1 receptors and P2Y2 purinoceptors. These experiments indicate that Gbetagamma subunits are involved in the direct coupling the adenosine A1 receptor to phospholipase C and that they also participate in the augmentation of P2Y2 purinoceptor-mediated [3H]inositol phosphate responses by the adenosine A1 receptor.

Human adenosine A1 receptor and P2Y2-purinoceptor-mediated activation of the mitogen-activated protein kinase cascade in transfected CHO cells

1. The mitogen-activated protein (MAP) kinase signalling pathway can be activated by a variety of heterotrimeric Gi/Go protein-coupled and Gq/G11 protein-coupled receptors. The aims of the current study were: (i) to investigate whether the Gi/Go protein-coupled adenosine A1 receptor activates the MAP kinase pathway in transfected Chinese hamster ovary cells (CHO-A1) and (ii) to determine whether adenosine A1 receptor activation would modulate the MAP kinase response elicited by the endogenous P2Y2 purinoceptor. 2. The selective adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) stimulated time and concentration-dependent increases in MAP kinase activity in CHO-A1 cells (EC50 7.1+/-0.4 nM). CPA-mediated increases in MAP kinase activity were blocked by PD 98059 (50 microM; 89+/-4% inhibition), an inhibitor of MAP kinase kinase 1 (MEKI) activation, and by pre-treating cells with pertussis toxin (to block Gi/Go-dependent pathways). 3. Adenosine A1 receptor-mediated activation of MAP kinase was abolished by pre-treatment with the protein tyrosine inhibitor, genistein (100 microM; 6+/-10% of control). In contrast, daidzein (100 microM), the inactive analogue of genistein had no significant effect (96+/-12 of control). MAP kinase responses to CPA (1 microM) were also sensitive to the phosphatidylinositol 3-kinase inhibitors wortmannin (100 nM; 55+/-8% inhibition) and LY 294002 (30 microM; 40+/-5% inhibition) but not to the protein kinase C (PKC) inhibitor Ro 31-8220 (10 microM). 4. Activation of the endogenous P2Y2 purinoceptor with UTP also stimulated time and concentration-dependent increases in MAP kinase activity in CHO-A1 cells (EC50=1.6+/-0.3 microM). The MAP kinase response to UTP was partially blocked by pertussis toxin (67+/-3% inhibition) and by the PKC inhibitor Ro 31-8220 (10 microm; 45+/-5% inhibition), indicating the possible involvement of both Gi/Go protein and Gq protein-dependent pathways in the overall response to UTP. 5. CPA and UTP stimulated concentration-dependent increases in the phosphorylation state of the 42 kDa and 44 kDa forms of MAP kinase as demonstrated by Western blotting. 6. Co-activation of CHO-A1 cells with CPA (10 nM) and UTP (1 microM) produced synergistic increases in MAP kinase activity which were not blocked by the PKC inhibitor Ro 31-8220 (10 microM). 7. Adenosine A1 and P2Y2 purinoceptor activation increased the expression of luciferase in CHO cells transfected with a luciferase reporter gene containing the c-fos promoter. However, co-activating these two receptors produced only additive increases in luciferase expression. 8. In conclusion, our studies have shown that the transfected adenosine A1 receptor and the endogenous P2Y2 purinoceptor couple to the MAP kinase signalling pathway in CHO-A1 cells. Furthermore, co-stimulation of the adenosine A1 receptor and the P2Y2 purinoceptor produced synergistic increases in MAP kinase activity but not c-fos mediated luciferase expression.

A1 adenosine receptor modulation of electrically-evoked contractions in the bisected vas deferens and cauda epididymis of the guinea-pig

1. The effects of adenosine receptor agonists upon both electrically-evoked and phenylephrine-induced contractile responses were investigated in the bisected vas deferens and the cauda epididymis of the guinea-pig. Electrical field-stimulation (10 s trains of pulses at 9 Hz, 0.1 ms duration, supramaximal voltage) elicited biphasic and monophasic contractile responses from preparations of bisected vas deferens and cauda epididymis, respectively; these responses were abolished by tetrodotoxin (300 nM). 2. In the prostatic half of the vas deferens the A1 selective adenosine receptor agonists, N6-cyclopentyladenosine (CPA) and (2S)-N6-[2-endo-norbornyl]adenosine ((S)-ENBA) and the non-selective A1/A2 adenosine receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA) inhibited electrically-evoked contractions (pIC50+/-s.e.mean values 6.15+/-0.24, 5.99+/-0.26 and 5.51+/-0.24, respectively). The responses to CPA were blocked by the A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine, DPCPX (100 nM). 3. In the epididymal half of the vas deferens NECA potentiated (at < or = 100 nM) and inhibited (at > or = 1 microM) electrically-evoked contractions. In the presence of the non-selective alpha-adrenoceptor antagonist phentolamine (3 microM), the alpha1-adrenoceptor antagonist, prazosin (100 nM), or at a reduced train length (3 s) NECA inhibited electrically-evoked contractions (pIC50 values 6.05+/-0.25, 5.97+/-0.29 and 5.71 +/-0.27, respectively). CPA (at 10 microM) also inhibited electrically-evoked contractions in this half of the vas deferens. In the presence of prazosin (100 nM), CPA also inhibited electrically-evoked contractions (pIC50 6.14+/-0.67); this effect was antagonized by DPCPX (30 nM, apparent pK(B) 8.26+/-0.88). In the presence of the P2 purinoceptor antagonist, suramin (300 microM), CPA (up to 1 microM) potentiated electrically-evoked contractions. 4. NECA, CPA and APNEA potentiated electrically-evoked contractions in preparations of cauda epididymis (pEC50 values 7.49+/-0.62, 7.65+/-0.74 and 5.84+/-0.86, respectively), the response to CPA was competitively antagonized by DPCPX (100 nM) with an apparent pK(B) value of 7.64+/-0.64. 5. The alpha1-adrenoceptor agonist phenylephrine elicited concentration-dependent contractile responses from preparations of bisected vas deferens and cauda epididymis. NECA (1 microM) potentiated responses to phenylephrine (< or = 1 microM) in the epididymal, but not in the prostatic half of the vas deferens. In preparations of epididymis NECA (1 microM) shifted phenylephrine concentration response curves to the left (4.6 fold). In the presence of a fixed concentration of phenylephrine (1 microM), NECA elicited concentration-dependent contractions of preparations of the epididymal half of the vas deferens and of the epididymis (pEC50 values 7.57+/-0.54 and 8.08+/-0.18, respectively). NECA did not potentiate responses to ATP in either the epididymal half of the vas deferens or the epididymis. 6. These studies are consistent with the action of stable adenosine analogues at prejunctional A1 and postjunctional A1-like adenosine receptors. The prejunctional A1 adenosine receptors only inhibit the electrically-evoked contractions of purinergic origin (an effect predominant in the prostatic half of the vas deferens). At the epididymis, where electrically-evoked contractions are entirely adrenergic, the predominant adenosine receptor agonist effect is a potentiation of alpha1-adrenoceptor-, but not of ATP-induced contractility.

Human 5-HT1B receptor stimulated inositol phospholipid hydrolysis in CHO cells: synergy with Gq-coupled receptors

We have previously reported that the transfected Gi/Go protein-coupled human adenosine A1 receptor (expressed at 200 fmol/mg of protein) and the endogenous 5-HT1B receptor (not detectable using radioligand binding) suppress forskolin-stimulated cyclic AMP accumulation and stimulate increases in [Ca2+]i in Chinese hamster ovary cells (CHO). In addition, co-activation of the adenosine A1 receptor (but not the 5-HT1B receptor) potentiates the hydrolysis of inositol phospholipids elicited by receptors coupled to Gq-proteins (Dickenson and Hill, 1996. Eur. J. Pharmacol. 320, 141-151). In order to establish whether this difference in ability to modulate Gq-coupled receptor responses is a consequence of low 5-HT1B receptor density, we have stably transfected CHO-KI cells with the human 5-HT1Dbeta cDNA (the human homologue of the rodent 5-HT1B receptor). We initially isolated a clonal cell line (designated CHO5-HT1B cells) displaying moderate specific [3H]5-HT binding (pKd of 8.17+/-0.07 and a Bmax of 140 fmol/mg protein). In CHO5-HT1B cells, the selective human 5-HT1B/1D receptor agonist sumatriptan produced a concentration-dependent inhibition of forskolin-stimulated cyclic AMP accumulation (pEC50=7.92+/-0.04). Sumatriptan also elicited a moderate and pertussis toxin-sensitive increase in [3H]inositol phosphate formation in CHO-5HT1B cells (pEC50=6.51+/-0.05). Finally, sumatriptan synergistically enhanced P2U purinoceptor stimulated [3H]inositol phosphate accumulation through a pertussis toxin-sensitive mechanism. These findings clearly show the significance of 5-HT1B receptor expression level in determining whether 5-HT1B receptor activation can modulate the accumulation of [3H]inositol phosphates elicited by a Gq-protein coupled receptor. The observation that 5-HT1B receptor activation can potentiate Gq-coupled receptor stimulated second messenger responses may have an important physiological role in the regulation of vascular smooth muscle contraction.

Enzyme-inducing effects of bicalutamide in mouse, rat and dog

1. Bicalutamide, a non-steroidal antiandrogen, produced dose-related increases in total cytochrome P450 (P450) and aldrin epoxidase, but had no effect on ethoxyresorufin O-deethylase, when administered for 10 weeks at 0, 25, 75 and 150 mg/kg/day to the male dog. 2. In the male and female mouse, bicalutamide, administered orally at 75 mg/kg/day for 3 months, produced marked induction of total P450, ethoxycoumarin O-deethylase, pentoxyresorufin O-dealkylase and aldrin epoxidase. Immunoblotting showed that bicalutamide produced substantial induction of CYP2B isoforms, with lower increases in CYP3A. Immunohistochemistry of mouse liver sections also showed marked increases in the level of CYP2B isoforms, with an increase in the extent of distribution from centrilobular to panlobular; CYP3A isoforms were also increased, but to a lesser degree. 3. Bicalutamide, administered as 14 daily oral doses (250 mg/kg) to groups of male rats, produced increases primarily in ethoxycoumarin O-deethylase and erythromycin N-demethylase, together with smaller increases in ethoxyresorufin O-deethylase and pentoxyresorufin O-dealkylase; these changes were reversible within 7 days. Immunoblotting of microsomes and immunocytochemistry of liver sections showed that bicalutamide markedly induced CYP3A1, but had little effect on CYP2B1 in rat. Compared with dexamethasone, bicalutamide is a more selective inducer of CYP3A1 in rat. 4. Bicalutamide, administered to rats as 14 daily oral doses of 10 mg/kg, induced its own metabolism by stimulating both aromatic hydroxylation and direct glucuronidation. This effect was apparently offset by a concomitant decrease in hydrolysis of bicalutamide, resulting in no marked change in total amounts of dose eliminated over 2 days. 5. Although the secondary effects of enzyme induction result in thyroid hypertrophy and adenoma in rat and hepatocellular carcinoma in mouse following chronic administration of bicalutamide, these changes are considered to have little clinical relevance. In any case, bicalutamide does not produce enzyme induction in man at clinically relevant dose levels.

G protein-coupled-receptor cross-talk: the fine-tuning of multiple receptor-signalling pathways

Signalling via the large family of G protein-coupled receptors (GPCRs) can lead to many cellular responses, ranging from regulation of intracellular levels of cAMP to stimulation of gene transcription. Members of this receptor family have been grouped into different categories dependent on the particular G protein subtypes that they predominantly interact with. Thus, receptors that couple to GS proteins will stimulate adenylate cyclase in many cells, while Gq/11-coupled receptors can mobilize intracellular Ca2+ via activation of phospholipase C. There is accumulating evidence, however, that activation of one particular signalling pathway by a GPCR can amplify intracellular signalling within a parallel but separate pathway. In this article Lisa Selbie and Stephen Hill review some of the evidence for these synergistic interactions and suggest that they may have an important role in finetuning signals from multiple receptor signalling pathways.

Receptor-stimulated phospholipase C activity in human umbilical artery cultured endothelial cells grown in a low oxygen environment

Endothelial cells of the human umbilical blood vessels are widely cultured in an oxygen tension (21%) far above that in which they exist in vivo (3%). This study investigates the effect of the long term culture (ca. 1 month) of human umbilical artery endothelial cells in a reduced oxygen environment (3%: HUAEC3) in comparison to cells grown in a 'normoxic' environment (21%: HUAEC21). Despite reports of altered metabolic pathways and reduced membrane integrity in other cell types, the characteristics of HUAEC3 were found to be similar to those of HUAEC21 with respect to morphology, immunocytochemical profile and in vitro growth rates. Cellular glutathione was maintained in these cells although ATP levels in HUAEC3 were found to be significantly lower than those observed in HUAEC21. The phosphoinositide responses of the HUAEC3 to a variety of agonists were also found to be of similar magnitude to those observed in HUAEC21. In addition, the pharmacological characteristics of the phospholipase C-linked histamine H1 and P2y2 (P2U) receptors were not changed by culture of cells in a low oxygen environment.

Neuropeptide Y (NPY) and peptide YY (PYY) effects in the epididymis of the guinea-pig: evidence of a pre-junctional PYY-selective receptor

1. The effects of peptide YY (PYY), neuropeptide Y (NPY) and structurally related peptides upon field stimulation-induced and phenylephrine-mediated contractile responses in the cauda epididymis of the guinea-pig were investigated. 2. Preparations of cauda epididymis responded to field stimulation with contractions which were completely attenuated by both the neurotoxin, tetrodotoxin (500 nM), and also by the alpha-adrenoceptor antagonist, phentolamine (3 microM). PYY (n=7) and the truncated peptide analogue PYY(3-36) (n=5) inhibited field stimulation-induced contractions (pIC50+s.e.mean: 8.9+/-0.2 and 9.4+/-0.2, respectively). Pancreatic polypeptide (PP, up to 1 microM, n=6), NPY (up to 100 nM, n=6) and the NPY analogues [Leu31,Pro34]NPY (n=6) and NPY(13-36) (both up to 1 microM, n=5) had no significant effect. 3. The NPY Y1 receptor antagonist BIBP3226 ((R)-N2-(diphenylacetyl)-N[(4-hydroxyphenyl)-methyl]-argininami de) at 750 nM (n=6) and 7.5 microM (n=6) did not affect the PYY-mediated inhibition of field stimulation-induced contractions (pIC50 8.9+/-0.3 and 9.0+/-0.3, respectively). In the presence of BIBP3226 (7.5 microM), NPY (n=6) inhibited field stimulation-induced contractions (pIC50 8.0+/-0.2). 4. NPY, PYY and PYY(3-36) inhibited [3H]-noradrenaline release from preparations of epididymis (pIC50 values 7.9+/-0.7, 9.6+/-0.8 and 10.0+/-0.9, respectively, all n=6). The agonists PP and [Leu31,Pro34]PYY (both up to 100 nM) were without significant effect (both n=6). 5. In preparations of cauda epididymis, stimulated with threshold concentrations of the alpha1-adrenoceptor agonist, phenylephrine (1 microM), both NPY (n=6) and PYY (n=7) elicited concentration-dependent increases in contractile force (with pEC50 values of 8.9+/-0.2 and 8.6+/-0.1, respectively). The effects of both NPY (n=6) and PYY (n=6) were antagonized by preincubation with BIBP3226 (75 nM; apparent pK(B)+/-s.e. values 8.3+/-1.0 and 8.2+/-0.6, respectively). The peptide analogues NPY(13-36) (n=5), PYY(3-36) (n=7) and [Leu31,Pro34]NPY (n=5) did not significantly augment responses to threshold concentrations of phenylephrine. 6. These results are consistent with the proposal that distinct NPY receptors mediate the (prejunctional) inhibition of field stimulation-induced contractions and the (postjunctional) potentiation of responses to phenylephrine in the cauda epididymis of the guinea-pig. The rank order of agonist potency (NPY > or = PYY >> NPY(13-36), [Leu31,Pro34]NPY and PYY(3-36) and the high potency of BIBP3226 indicate that the postjunctional receptor may be Y1-like. The rank orders of agonist potency in inhibiting field stimulation-induced contractile responses and [3H]-noradrenaline release (PYY(3-36) > or = PYY > NPY >> PP, NPY(13-36), [Leu31,Pro34]NPY and PYY(3-36) > or = PYY > NPY >> PP, [Leu31,Pro34]PYY, respectively) are consistent with the action of these peptides at a PYY-preferring receptor subtype, which may be distinct from the presently characterized NPY receptor subtypes.

Role of G-protein beta gamma subunits in the augmentation of P2Y2 (P2U)receptor-stimulated responses by neuropeptide Y Y1 Gi/o-coupled receptors

Neuropeptide Y (NPY) significantly potentiates the constrictor actions of noradrenaline and ATP on blood vessels via a pertussis toxin (PTX)-sensitive mechanism involving Gi/o (alpha beta gamma) protein subunits (Gi/o, GTP-binding proteins sensitive to PTX). In Chinese hamster ovary K1 (CHO K1) cells expressing specific receptors for these neurotransmitters, stimulation of Gi/o protein-coupled receptors for NPY and other neurotransmitters can augment the Gq/11-coupled (Gq/11, GTP-binding proteins insensitive to PTX) alpha 1B adrenoceptor- or ATP receptor-induced arachidonic acid (AA) release and inositol phosphate (IP) production (early events which may precede vasoconstriction). In this study, we have assessed the role of G beta gamma subunits in the synergistic interaction between Gi/o- (NPY Y1, 5-hydroxytryptamine 5-HT1B, adenosine A1) and Gq/11- [ATP P2Y2 (P2U)]-coupled receptors on AA release by using the specific abilities of regions of the beta-adrenergic receptor kinase (beta ARK1 residues 495-689) and the transducin alpha subunit to associate with G-protein beta gamma subunit dimers and to act as G beta gamma subunit scavengers. Transient expression of beta ARK1(495-689) in CHO K1 cells heterologously expressing NPY Y1 receptors had no significant effect on the PTX-insensitive ability of ATP to stimulate AA release. Stimulation of NPY Y1 receptors (as well as the endogenous 5-hydroxytryptamine 5-HT1B receptor and the transiently expressed human adenosine A1 receptor) resulted in a PTX-sensitive augmentation of ATP-stimulated AA release, which was inhibited by expression of both G beta gamma subunit scavengers. Expression of beta ARK1(495-689) similarly inhibited NPY Y1 receptor augmentation of ATP-stimulated IP production (a measure of phospholipase C activity), a step thought to precede the NPY Y1 receptor-augmented protein kinase C-dependent AA release previously observed in these cells. These experiments demonstrate that G beta gamma subunits, as inhibited by two different G beta gamma scavengers, significantly contribute to the synergistic interaction between NPY Y1 Gi/o- and Gq/11-coupled receptor activity, and are required for the augmentation of IP production and AA release observed in this model cell system.

Beta-adrenoceptor-mediated inhibition of alpha 1-adrenoceptor-mediated and field stimulation-induced contractile responses in the prostate of the guinea pig

1. The prostate of the guinea pig responds to electrical field-stimulation (2 s trains, 0.1 ms pulses at 3-60 Hz, supramaximal voltage) with contractile responses. At 18 Hz these responses were inhibited (82 +/- 2%) by the L-type Ca2+ channel blocker, nifedipine (10 microM) and (by 100%) by the neurotoxin, tetrodotoxin (500 nM). The alpha 1A-selective adrenoceptor antagonist, 5-methylurapidil, inhibited responses to field stimulation in the absence and presence of nifedipine (10 microM) with -log molar (p) IC50 (+/- s.e. mean) values of 7.95 +/- 0.14 and 7.01 +/- 0.07, respectively. 2. The non-selective beta-adrenoceptor agonist, isoprenaline, reduced (56 +/- 8%) field stimulation induced contractile responses (pEC50 6.91 +/- 0.11). The non-selective beta-adrenoceptor antagonist propranolol (50 nM) and the beta 1-adrenoceptor selective antagonist, atenolol (3 microM), but not the beta 2-adrenoceptor antagonist ICI 118,551 ((+/-)-1 -[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxyl]-3-[1-methylethyl)amino ]-2-butanol HCl; 100 nM) antagonized this effect (apparent pKB values 8.44 +/- 0.22 and 6.92 +/- 0.21, respectively) indicating an effect mediated through beta 1-like adrenoceptors. In the presence of nifedipine (10 microM) isoprenaline (up to 10 microM) did not inhibit the remaining response to field-stimulation. 3. Phenylephrine elicited contractile responses (pEC50 4.47 +/- 0.30) from preparations of guinea pig prostate which were reduced (63 +/- 25%) by nifedipine (10 microM). This response was antagonized by 5-methylurapidil (100 nM, apparent pKB 8.24 +/- 0.33), but was not affected by preincubation chloroethylclonidine (50 microM, 30 min). Responses to phenylephrine (30 microM) were inhibited (by up to 52 +/- 5%) by isoprenaline (pIC50 6.40 +/- 0.35, the beta 2-adrenoceptor selective agonist, salbutamol was weakly effective). Propranolol (300 nM), ICI 118,551 (100 nM) and atenolol (3 microM) shifted isoprenaline concentration-response curves to the right (apparent pKB +/- s.e. values 7.68 +/- 1.10; 8.00 +/- 0.72 and 6.62 +/- 0.95, respectively). In the presence of nifedipine (10 microM) responses to phenylephrine (30 microM,) were inhibited (by up to 51 +/- 4%) by isoprenaline (pIC50 6.88 +/- 0.17): propranolol (300 nM) and ICI 118,551 (100 nM), but not atenolol (3 microM) antagonized this effect (apparent pKB values 8.85 +/- 1.53 and 8.35 +/- 1.18, respectively). Thus beta 1-like and beta 2-like adrenoceptors may be involved in the isoprenaline-stimulated inhibition of phenylephrine concentration-response curves. 4. Phenylephrine stimulated [3H]-inositol phosphate accumulation (pEC50 4.47 +/- 0.83), an effect insensitive to chloroethylclonidine pre-treatment (50 microM, 30 min) and to nifedipine (10 microM), but inhibited by 5-methylurapidil (apparent pKD 7.90 +/- 0.22). Isoprenaline (up to 1 microM) did not affect the phenylephrine-stimulated maximal increase in [3H]-inositol phosphates but did increase [3H]-cyclic adenosine monophosphate ([3H]-cAMP) accumulation (pEC50 6.77 +/- 0.66); propranolol (30 nM) and ICI 118,551 (110 nM), but not atenolol (up to 3 microM), antagonized this effect. These responses may therefore be mediated through beta 2-like adrenoceptors. 5. These results show that the alpha 1-adrenoceptor mediated and field stimulation-induced contractions of the guinea pig prostate are partly dependent upon intracellular and extracellular sources of Ca2+. We conclude that both beta 1- and beta 2-like adrenoceptors inhibit responses to phenylephrine in the prostate of the guinea pig. The beta 1-like adrenoceptor-mediated inhibition of these responses is evident upon the field stimulation-induced and nifedipine-sensitive component of the response to phenylephrine and may not involve the activation of adenylyl cyclase. The beta 2-like adrenoceptor may inhibit both nifedipine sensitive and insensitive components of the response to phenylephrine, possibly through the activation of adenylyl cyclase, but not through the i

An endogenous A2B adenosine receptor coupled to cyclic AMP generation in human embryonic kidney (HEK 293) cells

1. Cyclic AMP generation by adenosine analogues was examined in human embryonic kidney (HEK 293) cells by use of a [3H]-adenine pre-labelling methodology. 2. Adenosine analogues showed the following rank order of potency (pD2 value): 5'-N-ethylcarboxamidoadenosine (NECA, 5.24)>2-chloroadenosine (4.41) > or = adenosine (4.19)= N6-(2-(4-aminophenyl)-ethylamino)adenosine (APNEA, 4.11). The A2A-selective agonist CGS21680 failed to elicit a significant stimulation of cyclic AMP generation at concentrations below 30 microM. 3. Of these agents, NECA was observed to exhibit the greatest intrinsic activity, while in comparison maximal responses to adenosine (76+/-8% NECA response), 2-chloroadenosine (70+/-6%) and APNEA (40+/-3%) were significantly reduced. 4. Antagonists of the NECA-evoked cyclic AMP generation showed the rank order of apparent affinity (apparent pA2 value): CGS 15943 (7.79)=XAC (7.74)>DPCPX (7.01)=PD115199 (6.93) 8FB-PTP (6.80)>KF 17837 (5.98)>3-propylxanthine (5.13). 5. Agarose gel electrophoresis of the products of the polymerase chain reaction, with cDNA generated from HEK 293 cell total RNA showed virtually identical patterns and nucleotide sizes in comparison with the vector for the full length human brain A2B adenosine receptor. 6. We concluded that HEK 293 cells express an endogenous adenosine receptor coupled to cyclic AMP generation which is of the A2B subtype.