Identification of genes associated with platinum drug sensitivity and resistance in human ovarian cancer cells

Platinum-based chemotherapeutic regimens are ultimately unsuccessful due to intrinsic or acquired drug resistance. Understanding the molecular basis for platinum drug sensitivity/resistance is necessary for the development of new drugs and therapeutic regimens. In an effort to identify such determinants, we evaluated the expression of approximately 4000 genes using cDNA microarray screening in a panel of 14 unrelated human ovarian cancer cell lines derived from patients who were either untreated or treated with platinum-based chemotherapy. These data were analysed relative to the sensitivities of the cells to four platinum drugs (cis-diamminedichloroplatinum (cisplatin), carboplatin, DACH-(oxalato)platinum (II) (oxaliplatin) and cis-diamminedichloro (2-methylpyridine) platinum (II) (AMD473)) as well as the proliferation rate of the cells. Correlation analysis of the microarray data with respect to drug sensitivity and resistance revealed a significant association of Stat1 expression with decreased sensitivity to cisplatin (r=0.65) and AMD473 (r=0.76). These results were confirmed by quantitative RT–PCR and Western blot analyses. To study the functional significance of these findings, the full-length Stat1 cDNA was transfected into drug-sensitive A2780 human ovarian cancer cells. The resulting clones that exhibited increased Stat1 expression were three- to five-fold resistant to cisplatin and AMD473 as compared to the parental cells. The effect of inhibiting Jak/Stat signalling on platinum drug sensitivity was investigated using the Janus kinase inhibitor, AG490. Pretreatment of platinum-resistant cells with AG490 resulted in significant increased sensitivity to AMD473, but not to cisplatin or oxaliplatin. Overall, the results indicate that cDNA microarray analysis may be used successfully to identify determinants of drug sensitivity/resistance and future functional studies of other candidate genes from this database may lead to an increased understanding of the drug resistance phenotype.

Chronic Pseudomonas aeruginosa infection definition: EuroCareCF Working Group report

Chronic pulmonary infection with P. aeruginosa develops in most patients with cystic fibrosis (CF); by adulthood 80% of patients are infected and chronic P. aeruginosa infection is the primary cause of increased morbidity and mortality in CF. Chronic infection is preceded by an intermittent stage of infection. The initial stage is characteristically followed by the gradual emergence of mucoid variants of the colonizing strains and a rise in anti-Pseudomonas antibodies. In addition to optimizing existing therapeutic strategies, effective new agents need to be identified. Studies in patients with CF are particularly challenging: the progressive nature of the disease and the wide variation in severity influence considerably the outcome of drug testing. A validated, universally accepted, and clinically useful classification of patients infected with P. aeruginosa, particularly those chronically infected, is needed that can be used as both a criterion for patient selection for clinical trials and as a study endpoint.

Transmission of colistin-resistant Pseudomonas aeruginosa between patients attending a pediatric cystic fibrosis center

We report on an outbreak of colistin-resistant Pseudomonas aeruginosa (CRPA) that occurred in a United Kingdom pediatric cystic fibrosis (CF) unit and involved six children over a period of 5 years. All CRPA-positive children had received aerosolized colistin therapy before first isolation of resistant organisms (mean duration, 3.1 years). Four of the 6 had also received courses of intravenous colistin in the year before the first isolation of CRPA. No impact of CRPA acquisition on respiratory function, clinical condition, or radiological parameters could be demonstrated. Four of the 6 children carried isolates of CRPA indistinguishable on genotyping. Two of these 4 children were sisters. The other 2 were on the same ward together at time of first isolation, and subsequently shared overlapping admissions with one of the sisters. While there is no conclusive evidence for the route of transmission, the frequency of overlapping in-patient admissions between 3 of these patients is suggestive of patient-to-patient transfer in the nosocomial setting.CF clinicians should be aware that colistin resistance can occur in P. aeruginosa, and some of these strains are capable of spread within CF units.

The 2018 rift eruption and summit collapse of Kīlauea Volcano

In 2018, Kīlauea Volcano experienced its largest lower East Rift Zone (LERZ) eruption and caldera collapse in at least 200 years. After collapse of the Pu'u 'Ō'ō vent on 30 April, magma propagated downrift. Eruptive fissures opened in the LERZ on 3 May, eventually extending ~6.8 kilometers. A 4 May earthquake [moment magnitude (M _w) 6.9] produced ~5 meters of fault slip. Lava erupted at rates exceeding 100 cubic meters per second, eventually covering 35.5 square kilometers. The summit magma system partially drained, producing minor explosions and near-daily collapses releasing energy equivalent to M _w 4.7 to 5.4 earthquakes. Activity declined rapidly on 4 August. Summit collapse and lava flow volume estimates are roughly equivalent-about 0.8 cubic kilometers. Careful historical observation and monitoring of Kīlauea enabled successful forecasting of hazardous events.

Characterisation of human melatonin mt(1) and MT(2) receptors by CRE-luciferase reporter assay

A cyclic AMP response element (CRE)-luciferase reporter gene assay was used to characterise the functional responses of human melatonin mt(1) and human melatonin MT(2) receptors, stably expressed in the human embryonic kidney cell line HEK293, to a series of six naphthalenic analogues of melatonin. By comparison to the observed melatonin-mediated inhibition of stimulated luciferase levels the naphthalenic series was identified as comprising agonists, partial agonists and one antagonist of melatonin mt(1) and melatonin MT(2) receptor function. Three of the agonist/partial agonist members of this series were also identified as displaying a functional selectivity for the melatonin MT(2) receptor. Competitive displacement of 2-[125I]iodomelatonin binding to the ovine pars tuberalis melatonin ML(1) receptor demonstrated a close correlation to the observed functional luciferase responses of the human melatonin mt(1) receptor. We conclude that the CRE-luciferase reporter gene assay provides an effective functional screening method for the pharmacological characterisation of human melatonin receptor subtypes.

Opioid kappa receptors and the secretion of prolactin (PRL) and growth hormone (GH) in the rat. I. Effects of opioid kappa receptor agonists bremazocine and U-50,488 on secretion of PRL and GH: comparison with morphine

The effects of bremazocine and U-50,488, two selective opioid kappa receptor agonists, and the preferential mu receptor agonist morphine on the secretion of PRL and GH were compared in conscious male rats bearing permanent right atrial cannulae for serial blood sampling and drug delivery. All three opioids stimulated PRL secretion in a dose-related manner, but the kappa agonists differed from morphine in several respects. They were considerably more potent than morphine in triggering a PRL response, but were unable to elevate PRL levels to more than 100 ng/ml, whereas morphine, at the highest dose (4.5 mg/kg), induced an almost twice larger response. Also their PRL-releasing effect was inhibited more strongly by the preferential kappa receptor antagonist Mr-2266 than by naloxone, whereas Mr-2266 and naloxone, which are equipotent as antagonists of the mu receptors, were equipotent in suppressing the PRL-stimulating effect of morphine, a mu agonist. In a complete contrast to morphine, which effectively stimulated GH secretion, the kappa agonists had no effect on GH release at lower doses and suppressed it at higher doses. It is concluded that the PRL-releasing effect of the kappa agonists is mediated by the kappa receptors which may participate with the mu receptors in regulation of PRL secretion by opioids. The GH-inhibiting effect of the kappa agonists requires further clarification.

The roles of valine 208 and histidine 211 in ligand binding and receptor function of the ovine Mel1a beta melatonin receptor

Site-directed mutagenesis was used to study two residues, valine 208 and histidine 211, in transmembrane domain 5 of the ovine Mel1a beta melatonin receptor. A series of 4 mutants were constructed (V208A, V208L, H211F, H211L), and each engineered to contain a FLAG-epitope. Immunocytochemistry demonstrated that all the mutants were expressed in COS-7 cells at levels comparable to the FLAG-epitope tagged wild-type Mel1a beta receptor (approximately 120 fmol/mg protein). Ligand binding revealed however that all mutants had reduced affinities for 2-[125I]-iodomelatonin (Kd wild-type 139 pM, Kd mutants 320 to 989 pM). Competition studies, with a series of melatonin analogues, identified a probable interaction between histidine 211 and the 5-methoxy group of melatonin. The wild-type receptor and both valine 208 mutants displayed a dose-dependent melatonin mediated inhibition of cyclic AMP levels in HEK293 cells, with IC50 values in the same rank-order as their melatonin binding affinities. Both H211F and H211L, however, did not display any melatonin mediated effects and may suggest that histidine 211 is critical for melatonin mediated receptor activation.

Cloning and functional analysis of a polymorphic variant of the ovine Mel 1a melatonin receptor

We have isolated a novel variant of the Mel 1a melatonin receptor from an ovine PT cDNA library. Relative to the reported sequence for the Mel 1a melatonin receptor there are 8 changes in the DNA sequence. Only 3 of these result in amino acid substitutions, one in extracellular loop 3 and two in the carboxy-terminal tail. We have designated the novel variant of the sheep Mel 1a receptor Mel 1a(beta), and correspondingly the previously reported variant Mel 1a(alpha). As minor changes in the primary amino acid sequence of G-protein-coupled receptors can influence their functional characteristics we have accordingly characterized this novel variant of the Mel 1a melatonin receptor. This melatonin receptor displays high affinity binding and inhibits the cAMP second messenger pathway in transfected L-cells demonstrating that this receptor is fully functional. PCR analysis shows Mel 1a(beta) is present in several breeds of sheep and suggests that the Mel 1a(beta) receptor was established early in the evolution of the sheep species.

The prognostic value of DNA ploidy combined with histologic substaging for incidental carcinoma of the prostate gland

Although current methods of histologic substaging for incidental prostatic carcinoma are useful, they offer only general indications of potential tumor behavior. To further define the biologic tendencies of stage A cancers, an examination was made of the role of DNA ploidy combined with histologic staging in archival material selected to achieve both a representative sample and long-term follow-up. With histology alone, 36% of stage A2 cancers and 9% of A1 neoplasms were progressive. Adding DNA flow cytometry to histology resulted in a significant improvement in the capacity of pathologic evaluation to predict outcome. Progression occurred in 67% of aneuploid stage A2 prostate cancers and in none of the nonaneuploid stage A1 tumors. Despite current limitations in the interpretation of DNA histograms from archival tissue, flow cytometry has significant potential in the pathologic evaluation of incidental prostatic carcinomas.

Retrospective DNA analysis of head and neck squamous cell carcinoma

Abnormal cellular DNA content, a hallmark of malignancy, is known to occur in squamous cell carcinoma of the head and neck. The significance of this finding has yet to be elucidated. Paraffin-embedded blocks from 46 squamous cell carcinomas of the head and neck were sectioned, dewaxed, and made into a suspension of bare nuclei by mechanical mincing and enzymatic digestion. The nuclei were stained with propidium iodide, and quantitative DNA measurements were obtained with flow cytometry. The results were compared with existing prognostic factors: DNA aneuploidy was identified in 41% of the specimens and was significantly correlated with tumor size and surgical stage; the relationship between DNA aneuploidy and anatomic site approaches statistical significance. There was no correlation with histologic grade or presence or absence of cervical metastasis.

Safety and efficacy of tenecteplase in patients with wake-up stroke assessed by non-contrast CT (TWIST): a multicentre, open-label, randomised controlled trial

BACKGROUND

Current evidence supports the use of intravenous thrombolysis with alteplase in patients with wake-up stroke selected with MRI or perfusion imaging and is recommended in clinical guidelines. However, access to advanced imaging techniques is often scarce. We aimed to determine whether thrombolytic treatment with intravenous tenecteplase given within 4·5 h of awakening improves functional outcome in patients with ischaemic wake-up stroke selected using non-contrast CT.

METHODS

TWIST was an investigator-initiated, multicentre, open-label, randomised controlled trial with blinded endpoint assessment, conducted at 77 hospitals in ten countries. We included patients aged 18 years or older with acute ischaemic stroke symptoms upon awakening, limb weakness, a National Institutes of Health Stroke Scale (NIHSS) score of 3 or higher or aphasia, a non-contrast CT examination of the head, and the ability to receive tenecteplase within 4·5 h of awakening. Patients were randomly assigned (1:1) to either a single intravenous bolus of tenecteplase 0·25 mg per kg of bodyweight (maximum 25 mg) or control (no thrombolysis) using a central, web-based, computer-generated randomisation schedule. Trained research personnel, who conducted telephone interviews at 90 days (follow-up), were masked to treatment allocation. Clinical assessments were performed on day 1 (at baseline) and day 7 of hospital admission (or at discharge, whichever occurred first). The primary outcome was functional outcome assessed by the modified Rankin Scale (mRS) at 90 days and analysed using ordinal logistic regression in the intention-to-treat population. This trial is registered with EudraCT (2014-000096-80), ClinicalTrials.gov (NCT03181360), and ISRCTN (10601890).

FINDINGS

From June 12, 2017, to Sept 30, 2021, 578 of the required 600 patients were enrolled (288 randomly assigned to the tenecteplase group and 290 to the control group [intention-to-treat population]). The median age of participants was 73·7 years (IQR 65·9-81·1). 332 (57%) of 578 participants were male and 246 (43%) were female. Treatment with tenecteplase was not associated with better functional outcome, according to mRS score at 90 days (adjusted OR 1·18, 95% CI 0·88-1·58; p=0·27). Mortality at 90 days did not significantly differ between treatment groups (28 [10%] patients in the tenecteplase group and 23 [8%] in the control group; adjusted HR 1·29, 95% CI 0·74-2·26; p=0·37). Symptomatic intracranial haemorrhage occurred in six (2%) patients in the tenecteplase group versus three (1%) in the control group (adjusted OR 2·17, 95% CI 0·53-8·87; p=0·28), whereas any intracranial haemorrhage occurred in 33 (11%) versus 30 (10%) patients (adjusted OR 1·14, 0·67-1·94; p=0·64).

INTERPRETATION

In patients with wake-up stroke selected with non-contrast CT, treatment with tenecteplase was not associated with better functional outcome at 90 days. The number of symptomatic haemorrhages and any intracranial haemorrhages in both treatment groups was similar to findings from previous trials of wake-up stroke patients selected using advanced imaging. Current evidence does not support treatment with tenecteplase in patients selected with non-contrast CT.

FUNDING

Norwegian Clinical Research Therapy in the Specialist Health Services Programme, the Swiss Heart Foundation, the British Heart Foundation, and the Norwegian National Association for Public Health.

On the mechanism of growth hormone autofeedback regulation: possible role of somatostatin and growth hormone-releasing factor

To determine the role of somatostatin (SRIF) and GH-releasing factor (GRF) in GH autofeedback, 20 micrograms rat GH in 2 microliter were injected into the third ventricle (IVT) 1 or 3 h before injection of the alpha 2-receptor stimulator clonidine (50 micrograms/kg, iv), which elevates plasma GH and TSH levels in normal rats. GH preinjected 1 or 3 h before clonidine significantly suppressed the clonidine-induced GH surge, whereas TSH release was not affected by GH. Preinjection of ovine LH IVT following the same protocol did not inhibit the clonidine-induced GH surge, suggesting a specific effect of IVT GH. Passive immunization with 400 microliters sheep antisomatostatin serum did not reverse the inhibition of the clonidine-induced GH surge by exogenous GH administered IVT either 1 or 3 h before clonidine. The TSH response was augmented by this procedure. Furthermore, IVT GH did not reduce the surges of GH and TSH elicited by GRF (250 ng/kg, iv) and TRH (150 ng/kg, iv) administered 1 or 3 h after IVT rat GH. These results suggest that GH autofeedback is mediated by reduced GRF secretion, rather than enhanced SRIF release.

Perceived body image and eating behavior in young adults with cystic fibrosis and their healthy peers

Treatment aimed at achieving an ideal nutritional status is an integral part of the management of patients with cystic fibrosis (CF). Emphasis is continually placed upon dietary intake and weight. The effects of this on eating behavior and self-perceptions are unclear. This work compared male and female CF adults with a healthy male and female control population with regard to (a) clinical variables, (b) actual, perceived, and desired body shape/body mass index (BMI), and (c) body satisfaction, eating behaviors and attitudes, and self-esteem. Clinical data were recorded for 221 adults with CF and 148 healthy controls. All subjects completed BMI Charts (perception of body weight/BMI), the Eating Attitudes Test, and scales of body satisfaction and self-esteem. CF patients had poorer lung function and nutritional status than controls. Control males accurately perceived their body shape/BMI and were content with it, whereas CF males viewed their BMI as greater than it actually was and desired to be much heavier. Control females viewed their body shape/BMI as less than it actually was and desired to be even slimmer, in comparison with CF females, who perceived their BMI as less than it actually was but were happy with their perceived shape/weight. Control subjects, especially females, dieted to a greater extent and were more preoccupied with food (with binge eating and intended vomiting) than CF patients. Conversely, those with CF reported greater pressure from others to eat than did controls. More problems with food/eating behavior were associated with less body satisfaction and reduced self-esteem. In comparison with a healthy control population, the perceptions and behaviors of CF adults relating to eating, weight, and body image are not abnormal. Indeed, females with CF have fewer problems than their healthy peers.

‘Cepacia syndrome’ with Burkholderia multivorans, 9 years after initial colonization

A 16-year-old boy with cystic fibrosis developed 'cepacia syndrome' 9 years after the first isolation of Burkholderia multivorans. It is important to recognise that 'cepacia syndrome' is not restricted to those infected with genomovar type III strains and that rapid, irreversible clinical decline can occur many years after the 1st isolation of Burkholderia cepacia complex (Bcc).

The ovine melatonin-related receptor: cloning and preliminary distribution and binding studies

A melatonin-related receptor was cloned from an ovine genomic library. The sequenced gene has a similar structure to that of the melatonin receptor gene family and consists of two exons separated by an intron of approximately 3 kb. Exon 1 and exon 2 of the ovine melatonin-related receptor encode a protein of 575 amino acids which is 73.8% homologous to the human melatonin-related receptor and shows 40.9% homology with the ovine Mel1a melatonin receptor. COS-7 cells transiently expressing ovine melatonin-related receptors did not bind 2-[125]iodomelatonin or 3H-melatonin. Reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization studies revealed expression of the ovine melatonin-related receptor in the hypothalamus, pituitary, retina and retinal pigment epithelium. Furthermore, expression of the ovine melatonin-related receptor is shown to be coincident with Mel1a and 2-[125I]iodomelatonin binding in the pituitary and serotonin N-acetyl transferase (arylalkylamine N-acetyl transferase, AANAT) expression in the retina. Expression patterns and similarity with the melatonin receptor gene family suggest a role for this novel G protein-coupled receptor in control and regulation of endocrine function and retinal physiology.

Catecholamine synthesis inhibitors acutely modulate [3H]estradiol binding by specific brain areas and pituitary in ovariectomized rats

Drugs known to alter endogenous levels of catecholamines were administered to adult ovariectomized rats to assess catecholaminergic effects on estradiol (E2) uptake and binding in nuclear and supernatant fractions of pituitary and specific brain regions and on cytoplasmic E2 receptor numbers and affinities. Specific (i.e. diethylstilbestrol-blockable) binding in vivo was measured 1 h after the iv injection of [3H]E2 (1 micrograms/kg). Administration of the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine (alpha MPT) 2 h before [3H]E2, to reduce levels of dopamine (DA), norepinephrine (NE), and epinephrine (Ep), decreased total and specific [3H]E2 binding by 36-56% in the nuclear fraction of the anterior pituitary, basal hypothalamus, and anterior hypothalamus. The dopamine-beta-hydroxylase inhibitor diethyldithiocarbamate (DDC), administered 2 h before [3H]E2 to reduce levels of only NE and Ep, increased the total and specific uptake of [3H]E2 by 62-140% in nuclear and supernatant fractions of the anterior pituitary and also increased uptake in several brain areas. In vitro analysis of hypothalamic and pituitary cytoplasms showed that in vivo administration of DDC increased E2 binding. Scatchard analysis showed that DDC increased receptor numbers 18-29%, with no change in the dissociation constant in pituitary cytoplasms. At the same time, plasma PRL levels were reduced by DDC treatment, indicating that DDC had increased DA output. Phenoxybenzamine (a blocking agent at alpha 1 postsynaptic binding sites) and a high dose of clonidine (a pre- and postsynaptic alpha-receptor agonist) did not significantly alter specific uptake in the cell nuclear fraction of any tissue, suggesting that postsynaptic alpha-receptors do not play a major role in modulating [3H]E2 uptake. No drug altered plasma levels of radioactivity. Because alpha-methyl-p-tyrosine and DDC both inhibit synthesis of NE and Ep, it is suggested that their opposite effects on uptake of [3H]E2 are related to their opposite effects on DA output. This interpretation is compatible with our previous observations that DA agonists increase [3H]E2 uptake in brain and pituitary in ovariectomized rats.

Chimeric melatonin mt1 and melatonin-related receptors. Identification of domains and residues participating in ligand binding and receptor activation of the melatonin mt1 receptor

Melatonin receptors bind and become activated by melatonin. The melatonin-related receptor, despite sharing considerable amino acid sequence identity with melatonin receptors, does not bind melatonin and is currently an orphan G protein-coupled receptor. To investigate the structure and function of both receptors, we engineered a series of 14 chimeric receptor constructs, allowing us to determine the relative contribution of each transmembrane domain to ligand binding and receptor function. Results identified that when sequences encoding transmembrane domains 1, 2, 3, 5, or 7 of the melatonin mt(1) receptor were replaced by the corresponding domains of the melatonin-related receptor, the resultant chimeric receptors all displayed specific 2-[(125)I]iodomelatonin binding. Replacement of sequences incorporating transmembrane domains 4 or 6, however, resulted in chimeric receptors that displayed no detectable 2-[(125)I]iodomelatonin binding. The subsequent testing of a "reverse" chimeric receptor in which sequences encoding transmembrane domains 4 and 6 of the melatonin-related receptor were replaced by the corresponding melatonin mt(1) receptor sequences identified specific 2-[(125)I]iodomelatonin binding and melatonin-mediated modulation of cyclic AMP levels. To further investigate these findings, site-directed mutagenesis was performed on residues within transmembrane domain 6 of the melatonin mt(1) receptor. This identified Gly(258) (Gly(6.55)) as a critical residue required for high affinity ligand binding and receptor function.

Impact of a cleaner-burning cookstove intervention on blood pressure in Nicaraguan women

Few studies have evaluated the cardiovascular-related effects of indoor biomass burning or the role of characteristics such as age and obesity status, in this relationship. We examined the impact of a cleaner-burning cookstove intervention on blood pressure among Nicaraguan women using an open fire at baseline; we also evaluated heterogeneity of the impact by subgroups of the population. We evaluated changes in systolic and diastolic blood pressure from baseline to post-intervention (range: 273-383 days) among 74 female cooks. We measured indoor fine particulate matter (PM(2.5); N = 25), indoor carbon monoxide (CO; N = 32), and personal CO (N = 30) concentrations. Large mean reductions in pollutant concentrations were observed for all pollutants; for example, indoor PM(2.5) was reduced 77% following the intervention. However, pollution distributions (baseline and post-intervention) were wide and overlapping. Although substantial reductions in blood pressure were not observed among the entire population, a 5.9 mmHg reduction [95% confidence interval (CI): -11.3, -0.4] in systolic blood pressure was observed among women aged 40 or more years and a 4.6 mmHg reduction (95% CI: -10.0, 0.8) was observed among obese women. Results from this study provide an indication that certain subgroups may be more likely to experience improvements in blood pressure following a cookstove intervention.

Identification of Mel1a melatonin receptors in the human embryonic kidney cell line HEK293: evidence of G protein-coupled melatonin receptors which do not mediate the inhibition of stimulated cyclic AMP levels

Binding assays using 2-[125I]iodomelatonin revealed high-affinity, guanosine 5'-O-(3-thiotriphosphate) sensitive, melatonin binding sites (B(max) 1.1 fmol/mg protein) in the human embryonic kidney cell line HEK293. Competition studies using the selective melatonin receptor antagonist luzindole and RT-PCR techniques identified these sites as human Mel1a melatonin receptors. Challenge of HEK293 cells with 1 microM melatonin had no effect on forskolin stimulated cyclic AMP levels, whereas in HEK293 cells engineered to stably over-express the human Mel1a melatonin receptor (B(max) > 400 fmol/mg protein) melatonin dose-dependently inhibited stimulated cyclic AMP levels (IC50 7.7 pM). These data may indicate that certain tissues, expressing low levels of G protein-coupled melatonin receptors, do not display melatonin mediated inhibition of cAMP.

Interaction between norepinephrine and serotonin in the neuroendocrine control of growth hormone release in the rat

Both alpha 2-adrenergic (alpha 2) and serotonergic (5HT) neurons are associated with stimulation of GH secretion via GRH release. The object of this study was to determine whether the 5HT system is involved in the stimulation of GH secretion by alpha 2-receptor agonists. There are two parts of this study. In the first, the relationship between alpha 2-5HT systems were analyzed by determining if alpha 2-stimulated GH release is mediated by 5HT. In this model, systemically administered alpha 2-agonists [clonidine (CLON) or UK14,304] were tested against 5HT antagonists (meterogoline or cyproheptadine) or 5HT synthesis inhibitors (p-chlorophenylalanine methylester hydrochloride). In the second, sites of 5HT-GRH interaction were determined by testing the response to CLON after 5HT neurotoxin [5,7-dihydroxytryptamine (5,7-DHT)] microinjection at specific hypothalamic nuclei. In both experiments sequential blood samples were withdrawn from silastic jugular cannulas in unanesthetized, freely moving animals. Metergoline (0.045 and 0.135 mg/kg, iv) and cyproheptadine (0.969 micrograms/kg, iv) suppressed, in a dose-dependent manner, the CLON (33 or 66 micrograms/kg, iv)-induced GH surge that was detected 15-30 min after injection in control animals. Both cyproheptadine (0.969 micrograms/kg, iv) and p-chlorophenylalanine (300 mg/kg, ip) effectively suppressed the UK14,304 (220 micrograms/kg, iv)-induced GH surge that occurred 15-30 min after injection in control animals. These data suggest that an intact 5HT system is required for alpha 2-stimulated GH release. 5,7-DHT neurotoxin microinjected into the midline arcuate nucleus (6 micrograms/mg,iv) or bilaterally into the ventromedial nucleus or perifornical area (4 micrograms/0.2 microliter) 5 days previously suppressed the CLON (30 micrograms/kg)-induced GH surge only in animals with arcurate nucleus lesions. To determine if the suppression was mediated by inhibition of GH-releasing hormone (GRH) or stimulation of somatostatin (SRIF), an additional experiment was conducted including 5,7-DHT arcuate nucleus-lesioned animals injected with anti-SRIF. Inasmuch as anti-SRIF failed to reverse the 5,7-DHT suppression of GH secretion, the results of this experiment suggest that GRH mediates NE-5HT-induced GH secretion. In conclusion, these data suggest that alpha 2 activation of GH secretion requires intact serotonergic terminals in the arcuate nucleus and most likely involves GRH rather than SRIF, release.

Serine residues 110 and 114 are required for agonist binding but not antagonist binding to the melatonin MT(1) receptor

Site-directed mutation of serine 110 (Ser(3.35)) and serine 114 (Ser(3.39)) in the human melatonin MT(1) receptor to alanine residues reduced ligand binding affinities of seven known melatonin receptor agonists and partial agonists by 3- to 15-fold. These mutants also displayed a relative reduction in their affinities for melatonin-mediated functional responses of 30- and 14-fold, respectively. In contrast to the observed effects of the agonists and partial agonists, the melatonin receptor antagonist luzindole was found to bind to mutants Ser(3.35)Ala and Ser(3.39)Ala with affinities equivalent to that determined for the wild-type melatonin MT(1) receptor. Luzindole was subsequently confirmed as an antagonist of melatonin-mediated functional responses for both mutant receptors. These studies have identified that in the human melatonin MT(1) receptor, Ser(3.35) and Ser(3.39), in transmembrane domain 3, are critical for the formation of the high-affinity ligand binding site for agonists and partial agonists but not for the antagonist luzindole.

Opioid kappa receptors and the secretion of prolactin (PRL) and growth hormone (GH) in the rat. II. GH and PRL release-inhibiting effects of the opioid kappa receptor agonists bremazocine and U-50,488

An analysis of the GH release-inhibiting action of the opioid kappa receptor agonists bremazocine and U-50,488, established earlier, was attempted by testing the agonists against activation of GH secretion by morphine or clonidine in male rats bearing right atrial cannulae for serial blood sampling and drug delivery. Both kappa agonists inhibited the effect of subsequent administration of clonidine in a dose-related manner. Bremazocine was approximately ten times more potent than U-50,488, a ratio corresponding to the known affinities of the two compounds for the kappa receptors. The inhibiting action of bremazocine was more strongly reversed by the preferential kappa receptor antagonist Mr-2266 than by naloxone, neither of which interfered with the GH-stimulating effect of clonidine. Bremazocine, however, did not alter the activation of GH secretion by exogenous growth hormone releasing factor. Thus, the inhibiting effect of bremazocine and probably U-50,488 seems to be derived from stimulation of the kappa receptors which in turn activates a GH release inhibiting mechanism of unknown identify which, however, does not involve release of somatostatin. Both kappa agonists also inhibited the effect of morphine, but in this case U-50,488 was approximately hundred times less effective than bremazocine. Since bremazocine and U-50,488 are antagonists of the delta receptors, which seem to mediate the GH-releasing effect to morphine, their inhibiting effect in this instance may be related to this property rather than to an action on the kappa receptors. Bremazocine, but not U-50,488, was also highly effective in inhibiting stimulation of PRL secretion by morphine.(ABSTRACT TRUNCATED AT 250 WORDS)