Oncostatin M suppresses EGF-mediated protein tyrosine phosphorylation in breast cancer cells

The effect of oncostatin M (OM) on epidermal growth factor (EGF)-mediated protein tyrosine phosphorylation in an infiltrating ductal breast carcinoma cell line, H3922, was investigated by Western blot analysis. Pretreatment of H3922 cells with OM for 72 h suppressed EGF-stimulated protein tyrosine phosphorylation signals by 77%. Interestingly, pretreatment with OM for 6 or 48 h had little effect on these signals. EGF-mediated tyrosine phosphorylation of EGF receptor (EGFR) was suppressed by 55% in 72-h OM pretreated H3922 cells. No reduction in EGFR protein expression was detected in these cells. Flow cytometric analysis verified that OM does not suppress EGFR expression. The effect of OM could not be attributed to induction of protein tyrosine phosphatases. An H3922 subclone cell line, designated H3922-8, was found to exhibit no proliferative response to treatment with EGF. However, EGF-mediated protein tyrosine phosphorylation was detected in these cells. Radioligand EGF binding studies comparing H3922 to H3922-8 cells indicated that the clonal cells apparently lack high affinity EGF receptors. The mechanism by which OM suppresses EGF-mediated tyrosine phosphorylation has not been completely characterized. However, the suppressive effect occurs regardless of whether the cells are acutely responsive (H3922) or virtually unresponsive (H3922-8) to EGF stimulation of cell growth.

Effects of cyclopentyladenosine on isoproterenol response in adult and senescent cardiac tissue from Fischer 344 rats

To characterize age-related changes in beta-adrenergic responsiveness and to test the hypothesis that an increase in the effects of adenosine contribute to impaired beta-adrenergic responsiveness, Fischer 344 rat right atria (RA), left atria (LA), and left ventricular trabeculae carnae were exposed to the beta-receptor agonist isoproterenol (ISO), followed by four doses of the selective adenosine A(1) receptor agonist cyclopentyladenosine (CPA). Spontaneous contractile rates of adult RA were inhibited more than senescent RA by CPA. Contractility (+dF/dt) of adult LA was reduced more than senescent LA by CPA. Left trabeculae carnae tissue responded weakly to CPA, but senescent tissue was less responsive than adult tissue. Senescent atrial A(1) receptor density was 56% greater than in adult tissue, whereas the density in senescent ventricles was 39% lower than in adult tissue. No significant difference in antagonist affinities (K(d)) of A(1) receptor was observed between adult and senescent atria. In addition, agonist competition curves indicated a significant increase in senescent atrial and a decrease in senescent ventricular tissue in the affinity of agonist for high-affinity A(1) receptors with no difference in dissociation constant (K(i)). No significant age-related differences in atrial or ventricular tissues occurred in either the antagonist affinity (K(d)) or density (B(max)) of the beta-adrenergic receptors. CPA was found to inhibit ISO-stimulated adenylate cyclase activity more in senescent than in adult atrial and ventricular membrane preparations. We conclude that age-related differences in functional response to ISO and CPA, A(1) receptor density, and ISO-stimulated adenylate cyclase activity differ in atrial and ventricular myocardium.

Cloning and characterization of human oncostatin M promoter

Oncostatin M (OSM), an IL-6 subfamily cytokine, inhibits proliferation and causes morphological changes in many tumor cell lines. GM-CSF, phorbol-12-myristate-13-acetate (PMA), and lipopolysaccharide (LPS) induce OSM expression. To investigate the mechanisms governing OSM promoter activity, we have cloned and partially sequenced an 8.5 kb fragment of human genomic DNA immediately 5' of the OSM coding region and mapped the transcription start site. Transient transfection assays with a series of 5' deletion plasmids demonstrated maximal reporter activity in U937 cells with a minimum 304 bp construct. The 5'-proximal region of the human OSM gene contains a C/EBP consensus element around -45 bp and several GC-rich regions around -60, each of which is responsible for basal promoter activity. Electrophoretic mobility shift assay coupled with supershift analysis confirmed the presence of a cis -acting binding site for activated STAT5 complexes following GM-CSF treatment. Furthermore, transient transfection studies demonstrated a loss of GM-CSF responsiveness in reporter constructs containing mutations within this STAT element. Our results establish that C/EBP and an as yet unidentified GC-rich binding transcription factor are responsible for basal OSM promoter activity, while GM-CSF-stimulated OSM expression is driven by activated STAT5 complexes binding to a cis -acting STAT element on the OSM promoter.

Inhibition of human liver cytochrome P-450 1A2 by the class IB antiarrhythmics mexiletine, lidocaine, and tocainide

Mexiletine, lidocaine, and tocainide are class IB antiarrhythmic drugs that are used for the treatment of ventricular arrhythmias and are known to inhibit drug metabolism. The objectives of this study were to characterize the inhibitory effects of mexiletine, lidocaine, and tocainide on cytochrome P-450 1A2 (CYP1A2) activity in human liver microsomes and to evaluate their relative inhibitory potencies by using a molecular model of this P-450 isozyme. The inhibitory effect of mexiletine, lidocaine, and tocainide on cytochrome CYP1A2 in human liver microsomes was examined with methoxyresorufin O-demethylase activity as an index of the catalytic activity of this P-450 isozyme. The kinetic inhibition types and Ki values were determined by Lineweaver-Burk plots and Dixon plots, respectively. Molecular modeling was used to assess the interaction of these agents with the CYP1A2 active site. Methoxyresorufin O-demethylase activity was inhibited 67 +/- 8%, 20 +/- 5%, and 7 +/- 4% by 2 mM mexiletine, lidocaine, and tocainide, respectively. Mexiletine and lidocaine exhibited competitive inhibition with Ki values of 0.28 +/- 0.12 mM and 1.54 +/- 0.74 mM, respectively, whereas the inhibition type of tocainide could not be determined because of its weak potency. A charge interaction between mexiletine and the Asp313 side chain in the CYP1A2 active site was found, and varying degrees of hydrogen bond formation between these three compounds and the CYP1A2 active site were observed. The in vitro inhibitory potencies in human liver microsomes (mexiletine > lidocaine > tocainide) are consistent with the structural interactions found in a molecular model of the active site of CYP1A2.

Adenosine A1 receptor-dependent and -independent effects of the allosteric enhancer PD 81,723

The 2-amino-3-benzoylthiophene PD 81,723 has been shown to exhibit allosteric enhancement of adenosine A1 receptor binding and function. The aim of this study was to clarify the mechanism of this effect using membranes purified from rat brain and Chinese hamster ovary (CHO)-A1 cells that stably express the rat adenosine A1 receptor as well as intact CHO-A1 and nontransfected CHO cells. In membranes containing 100 microM magnesium, (2-amino-4, 5-dimethyl-3-thienyl)-[3-(trifluoromethyl)phenyl]methanone (PD 81, 723) significantly increased the affinity of the adenosine A1 receptor agonist, cyclopentyladenosine, for the low-affinity receptor without affecting high-affinity binding or Bmax. In intact cells, PD 81,723 inhibited basal adenylyl cyclase (AC) activity as well as forskolin-, cholera toxin-, and pertussis toxin-stimulated AC activity in CHO-A1 and CHO cells. Basal AC activity was inhibited 49% in CHO and 82% in CHO-A1 cells by 30 microM PD 81,723. In CHO-A1 cells, half-maximal inhibition of forskolin-stimulated AC occurred at 5 microM PD 81,723 compared to 10 microM in CHO cells. Cholera toxin-stimulated AC was reduced 90% in both CHO and CHO-A1 cells by 30 microM PD 81,723. At the same concentration of PD 81,723, pertussis toxin-stimulated AC activity was reduced 86% (CHO-A1) and 77% (CHO). [3H]forskolin was displaced from purified rat liver AC by PD 81,723 with an IC50 of 96 microM. These results demonstrate that two mechanisms appear to contribute to the observed effects of PD 81, 723. One mechanism is allosteric enhancement of adenosine A1 receptor function. Results from transfected and nontransfected cells suggest that PD 81,723 also inhibits AC directly by binding to the catalytic unit at or near the forskolin-binding site.

Comparative inhibition of human cytochromes P450 1A1 and 1A2 by flavonoids

Flavonoids are a class of dietary phytochemicals that modulate various biological activities. The effects of flavone and five hydroxylated derivatives on the methoxyresorufin O-demethylase activity catalyzed by cDNA-expressed human cytochromes P450 (CYP)1A1 and 1A2 were examined. Flavone was a less potent inhibitor of CYP1A1 (IC50 = 0.14 microM) than CYP1A2 (IC50 = 0.066 microM). Four hydroxylated flavone derivatives (3-hydroxy-, 5-hydroxy-, 7-hydroxy-, and 3,7-dihydroxyflavone) were also potent inhibitors of CYP1A1 (IC50 < 0.1 microM) and CYP1A2 (IC50 < 0.3 microM). For CYP1A1, 7-hydroxyflavone exhibited a competitive mode of inhibition, with a Ki value of 0.015 microM and 6-fold selectivity for CYP1A1 over CYP1A2. 3,5,7-Trihydroxyflavone (galangin) showed the highest potency toward CYP1A2. The inhibition by galangin of the methoxyresorufin O-demethylase activity of CYP1A2 was mixed-type, with a Ki value of 0.008 microM. Galangin showed 5-fold selectivity in its inhibition of CYP1A2 over CYP1A1. The results indicate that some flavonoids have high potencies and selectivities for inhibition of CYP1A isozymes. This may have important implications for cancer prevention, as well as other pharmacological and toxicological effects of these compounds.

Inhibition of human cytochrome P450 1A2 by flavones: a molecular modeling study

Cytochrome P450 1A2 metabolizes a number of important drugs, procarcinogens, and endogenous compounds. Several flavones, a class of phytochemicals consumed in the human diet, have been shown to differentially inhibit human P450 1A2-mediated methoxyresorufin demethylase. A molecular model of this P450 was constructed in order to elucidate the molecular basis of the P450-flavone interaction. Flavone and its 3,5,7-trihydroxy and 3,5,7-trimethoxy derivatives were docked into the active site to assess their mode of binding. The site is hydrophobic and includes several residues that hydrogen bond with substituents on the flavone nucleus. The binding interactions of these flavones in the modeled active side are consistent with their relative inhibitory potentials, namely 3,5,7-trihydroxylflavone > flavone > 3,5,7-trimethoxylflavone, toward P450 1A2-mediated methoxyresorufin demethylation.

Inhibition of methoxyresorufin demethylase activity by flavonoids in human liver microsomes

Flavonoids are a class of dietary phytochemicals with anticarcinogenic properties. A series of ten structurally related flavonoids were evaluated for their effect on methoxyresorufin O-demethylase (MROD) activity in human liver microsomes. All compounds inhibited this cytochrome P450 1A2 (CYP1A2) mediated activity. 3,5,7-Trihydoxyflavone (galangin) was the most potent inhibitor, followed by 3-hydroxyflavone and flavone. The relative inhibitory potency of flavonoids is related to their structures. The results suggest that flavonoids may modulate pharmacological and toxicological effects mediated by CYP1A2.

CD40 is functionally expressed on human breast carcinomas: variable inducibility by cytokines and enhancement of Fas-mediated apoptosis

The CD40 molecule, a member of the TNF receptor gene family, has been intensively studied with respect to regulation of B cell proliferation and survival. Although CD40 is also expressed on carcinoma cell lines, information concerning the biological function of CD40 on cells of epithelial origin is limited. In this study we detected constitutive CD40 on human breast carcinoma cell lines and an increase in CD40 expression following treatment with cytokines IL-1alpha and IFN-gamma. CD40 ligation was also found to increase MHC II expression in cells pretreated with IFN-gamma. In contrast to normal B cells, where CD40 signaling provides a potent survival signal, we observed that CD40 ligation in breast carcinoma cells results in growth inhibition and enhanced susceptibility to Fas-mediated apoptosis. Enhanced apoptosis appears to be attributable, at least in part, to an up-regulation of Fas expression caused by CD40 ligation. These results suggest a potentially important role for CD40 in breast tumor biology.

Oncostatin M-specific receptor expression and function in regulating cell proliferation of normal and malignant mammary epithelial cells

Oncostatin M (OSM) is a cytokine produced by activated T lymphocytes and macrophages. OSM is structurally and functionally related to leukaemia inhibitory factor (LIF), another cytokine in the interleukin 6 (IL-6) family. The biological activities of OSM are mediated through two types of receptor complexes, the LIF/OSM shared receptor (type I) and OSM-specific receptor (OSM-R, type II), which is composed of gp130 as a binding subunit and a newly identified affinity conversion subunit, OSM-R beta. Previous research conducted in the authors' laboratory has shown that OSM inhibits the growth of several breast cancer cell lines. To investigate whether OSM has a similar effect in primary normal human mammary epithelial (HME) cells, the activity of OSM in HME cells derived from four donors was examined. OSM produced a dose-dependent inhibition of DNA synethesis in these cells. In order to determine the receptor subtypes mediating OSM activity in HME and breast cancer cells, flow cytometry analysis using anti-gp130mAb and anti-OSM-R beta mAb was performed. In these studies, the authors were able to examine expressions of gp130 and OSM-R beta. In addition, quantitative RT-PCR assays were conducted to measure expressions of the mRNAs of the subunits for type I and type II OSM receptor. The results show that HME cells and most breast cancer cell lines express both the type I and the type II OSM receptors. However, type II, OSM-specific receptors are expressed at a higher levels than type I, OSM/LIF shared receptors. Accordingly, we compared the growth regulatory activities of OSM with LIF in HME cells and in breast cancer cells. In contrast to the inhibitory activity of OSM, LIF stimulated the growth of breast cancer cells, whereas it had no effect on normal mammary epithelial cell growth. Together, these data suggest that OSM plays an inhibitory role in normal and malignant mammary epithelial cell growth in vitro. OSM activity is mediated by the OSM-specific receptor (type II), not by the OSM/LIF shared receptor.

Liver LDL receptor mRNA expression is decreased in human ApoB/CETP double transgenic mice and is regulated by diet as well as the cytokine oncostatin M

We have investigated liver LDL receptor mRNA expression in nontransgenic, human cholesteryl ester transfer protein (CETP) transgenic, and human apolipoprotein (Apo) B/CETP double transgenic mice fed a normal chow diet and a high fat, high cholesterol diet (HFHC). Three weeks of HFHC feeding increased total serum cholesterol 1.5-fold in the nontransgenic, 3.1-fold in the CETP transgenic, and 3.4-fold in the ApoB/CETP double transgenic mice. To examine the liver LDL receptor mRNA expression among the different groups of mice fed the normal diet or fed the HFHC diet, we developed a quantitative reverse-transcribed polymerase chain reaction assay in which the LDL receptor mRNA level was normalized with the beta-actin mRNA. The results show that on the normal chow diet, the LDL receptor mRNA expression levels were lower in the ApoB/CETP mice than in the nontransgenic mice and the human CETP transgenic mice. Liver LDL receptor gene expression was lower in all groups of mice fed the HFHC diet, with the lowest level of expression in the ApoB/CETP mice. Similar results were obtained by Northern blot analysis. In addition, we have previously shown that the cytokine oncostatin M (OM) increases LDL receptor gene expression in HepG2 cells. In this study, we used the ApoB/CETP mice as the model system to examine the in vivo activity of OM on liver LDL receptor gene expression. Our data show that OM increased the level of liver LDL receptor mRNA up to 80% to 90% when the animals were fed the HFHC diet. The results from these studies demonstrate that the expression of the liver LDL receptor in the ApoB/CETP mice is suppressed compared with nontransgenic mice and that the expression of the hepatic LDL receptor gene in these mice is subjected to the normal cholesterol feedback regulation. In addition, LDL receptor gene expression in these mice is also inducible by a positive regulator.

Aging and pharmacology

Research on aging and pharmacology in humans has been termed geriatric clinical pharmacology, which is an established subdiscipline within the broad field of clinical pharmacology. This article reviews information relevant to clinical cancer research and the care of older patients with cancer. Accordingly, the current state of knowledge on drug utilization, pharmacokinetics, pharmacodynamics, adverse drug events, drug interactions, polypharmacy, adherence to treatment, and clinical research considerations are reviewed. Although a review of the literature on aging and cancer chemotherapy is not included in this particular presentation, information is very sparse. Thus, there is significant potential for valuable contributions from clinical research through partnerships between geriatric clinical pharmacologists and medical oncologists.

Novel mechanism of transcriptional activation of hepatic LDL receptor by oncostatin M

In this paper we describe a sterol-independent regulation of low density, lipoprotein receptor (LDLR) transcription by the cytokine oncostatin M (OM) in HepG2 cells. We show that OM-induced expression is independent of cholesterol regulation and occurs at the transcriptional level. To elucidate regulatory mechanism(s), we constructed a luciferase reporter system comprising either the native LDLR promoter including repeats 1, 2, and 3, or a synthetic promoter vector containing repeats 2+3 only, allowing us to directly examine OM effects on individual elements. Specific mutants in repeats 1, 2, and 3 were made to facilitate the mapping of the OM effect on the promoter. Wildtype and mutant constructs were assayed for cholesterol and OM regulation. The results show that mutation within the core SRE-1 element of repeat 2 totally abolished cholesterol regulation but had no effect on OM inducibility. More interesting, a mutation within repeat 1 reduced basal transcription activity to 10% of the native promoter, but OM induction was unaltered. However, the identical mutation engineered in repeat 3 significantly decreased OM induction of LDLR promoter activity. These results suggest a novel regulatory role for the repeat 3 element in LDLR transcription.

Aging and pharmacology

Research on aging and pharmacology in humans has been termed geriatric clinical pharmacology, which is an established subdiscipline within the broad field of clinical pharmacology. This article reviews information relevant to clinical cancer research and the care of older patients with cancer. Accordingly, the current state of knowledge on drug utilization, pharmacokinetics, pharmacodynamics, adverse drug events, drug interactions, polypharmacy, adherence to treatment, and clinical research considerations are reviewed. Although a review of the literature on aging and cancer chemotherapy is not included in this particular presentation, information is very sparse. Thus, there is significant potential for valuable contributions from clinical research through partnerships between geriatric clinical pharmacologists and medical oncologists.

Oncostatin M-mediated transcriptional suppression of the c-myc gene in breast cancer cells

Oncostatin M (OM) inhibits proliferation of H3922, a human breast cancer cell line derived from a ductal infiltrating carcinoma. We have found that treatment of H3922 cells with OM for 72 h lowers the steady-state level of c-myc mRNA to 16% of that seen in control cells. Our present study showed that down-regulation of c-myc mRNA levels was both dose and time dependent. Results from nuclear run-off analysis and mRNA stability studies established that a major component of the observed OM-induced down-regulation of c-myc mRNA occurs at the transcriptional level. OM treatment of H3922 cells reduced the abundance of actively transcribed c-myc mRNAs to approximately 25% of that observed in control cells. These data were supported by our finding that OM did not significantly affect the half-life of c-myc mRNA in actinomycin-treated H3922 cells. Taken together, these data demonstrate that the suppressive effect of OM on c-myc gene expression in H3922 cells occurs at the transcriptional level.

Oncostatin M-specific receptor mediates inhibition of breast cancer cell growth and down-regulation of the c-myc proto-oncogene

Human oncostatin M (OM) is a M(r) 28,000 glycoprotein that has been shown to regulate cell proliferation and differentiation. The biological activities of OM can be mediated by two different heterodimeric receptor complexes, the leukemia inhibitory factor (LIF)/OM shared receptor and the OM-specific receptor. In this study, we have examined the growth-regulatory effect of OM on 10 breast cancer cell lines derived from human tumors. The cellular proliferation of seven of these breast cancer cell lines was inhibited by OM. The three cell lines that did not respond to OM treatment lacked the expression of OM receptors. The growth-inhibitory activity of OM is examined further in the H3922 breast cancer cell line, which expresses the high-affinity OM receptor at a relatively higher level. We found that the cellular proliferation of H3922 cells was induced strongly by extrogenous epidermal growth factor (EGF), EGF-like factor, and basic fibroblast growth factor. The proliferative activities of these growth factors can be abolished totally by cotreatment of H3922 cells with OM. Treatment of H3922 cells with OM for 24 h did not block EGF binding or the induction of EGF receptor tyrosine phosphorylation. This finding suggests that OM interferes with the mitogenic signal at steps distal to the EGF receptor. Examination of proto-oncogene expression demonstrated that OM down-regulates the c-myc gene in H3922 cells. The biological effects reported herein are not shared by the OM-related cytokines interleukin 6 or LIF, as demonstrated by the inability of these proteins to inhibit cell growth or modulate c-myc gene expression in breast cancer cells. Additionally, the high-affinity binding of labeled OM cannot be displaced by LIF. Together, these data suggest that OM is a growth inhibitor for breast cancer cells. The inhibitory activity is mediated predominantly through the OM-specific receptor, and activation of this receptor abrogates growth factor stimulation and down-regulates the c-myc proto-oncogene.

Aging and drug interactions. III. Individual and combined effects of cimetidine and cimetidine and ciprofloxacin on theophylline metabolism in healthy male and female nonsmokers

The individual and combined effects of cimetidine and ciprofloxacin on theophylline metabolism were examined in healthy young and elderly male and female nonsmokers. Single-dose studies of theophylline pharmacokinetics were performed at base line and on the fifth day of each of three treatment regimens consisting of 400 mg cimetidine every 12 hr, 500 mg ciprofloxacin every 12 hr and the combination of cimetidine and ciprofloxacin. Base-line theophylline plasma clearance and formation clearance of theophylline metabolites decreased with age in both gender groups to a similar extent (20% less in elderly men than in young men; 24% less in elderly women than in young women). Individually, cimetidine and ciprofloxacin produced proportionate declines in plasma theophylline clearance that were similar among the four groups (range, 23.4-32.7% decrease). The combined regimen yielded further impairment in theophylline elimination compared with each agent alone (range, 35.9-42.6% decrease). Cimetidine was a nonselective inhibitor of theophylline metabolic pathways in young men, but it exerted a greater inhibitory effect on N-demethylation pathways in the other groups. Ciprofloxacin inhibited N-demethylations of theophylline to a greater extent than the hydroxylation pathway. Coadministration of these two inhibitors further reduced the formation of theophylline metabolites. The proportionate reduction in formation clearance of theophylline metabolites was similar among the four groups. Thus, the response to inhibition of theophylline metabolism by cimetidine and ciprofloxacin is not influenced by age or gender.

Acetylator phenotype in relation to age and gender in the Baltimore Longitudinal Study of Aging

This study investigated in healthy Caucasians the possible occurrence of age and gender-associated differences in NAT2 acetylator phenotype. Acetylator phenotype was determined after a single oral dose of 100 mg dapsone during testing of oral glucose tolerance in 510 Caucasian volunteers aged from 19 to 93 years, 339 men and 171 women, from the Baltimore Longitudinal Study of Aging. Participants were classified as slow or rapid acetylators according to the ratio of monoacetyldapsone to dapsone concentration in plasma. The ratio dividing the two groups, 0.30, was chosen after inspection of a probit plot and histogram of the monoacetyldapsone/dapsone ratios. Fifty-one percent of the participants were slow acetylators and 49% were rapid acetylators. Because there was no significant difference between the sexes in the monoacetyl-dapsone/dapsone ratios, all 510 participants were pooled into a single group for further analysis. In the combined analysis, there was a small decline in the prevalence of the slow acetylator phenotype with age, but this age effect accounted for less than 1% of the total variance in the monoacetyldapsone/dapsone ratio (r2 = 0.009). Also, it was shown in a group of 20 participants that administration of glucose with dapsone does not influence the determination of acetylator phenotype. In a large healthy Caucasian. American population, there was no biologically important effect of age or sex on the distribution of NAT2 acetylator phenotype.

Age-related pharmacokinetics of daunorubicin and daunorubicinol following intravenous bolus daunorubicin administration in the rat

Age-related differences in pharmacokinetics may be important in determining altered anthracycline cardiotoxicity in the senescent rat and also in older humans. This study examined the effect of aging on daunorubicin pharmacokinetics in the Fischer 344 rat. Daunorubicin 7.5 mg/kg was administered i.v. to 6- and 24-month-old male Fischer 344 rats and plasma and tissue sampling was performed over 168 h for assay of daunorubicin and daunorubicinol concentrations by high-performance liquid chromatography. Systemic clearance of daunorubicin was decreased in older compared to younger animals (56 +/- 4 versus 202 +/- 17 ml min-1 kg-1; P < 0.05). In addition, the area under the plasma daunorubicinol concentration/time curve was significantly increased in older rats. In the heart, the area under the concentration/time curve was significantly increased in senescence both in the case of daunorubicin (201 +/- 12 versus 86 +/- 4 micrograms h g-1; P < 0.05) and daunorubicinol (1347 +/- 118 versus 182 +/- 4 micrograms h g-1; P < 0.05). Furthermore, the peak mean concentrations of daunorubicin were increased in older compared to younger rats both in plasma (1078 +/- 82 versus 663 +/- 66 ng ml-1; P < 0.05) and in heart (27 +/- 1 versus 10 +/- 1 micrograms g-1; P < 0.05). This also was true for daunorubicinol in plasma (284 +/- 39 versus 168 +/- 27 ng ml-1; P < 0.05) and in myocardium (8.6 +/- 0.6 versus 2.4 +/- 0.2 micrograms g-1; P < 0.05). Following daunorubicin injection, the ratio of daunorubicinol to daunorubicin concentrations in tissues increased with time, particularly in plasma and heart in senescent rats. Thus, there are significant age-related changes in daunorubicin and daunorubicinol kinetics in the rat that could alter susceptibility to acute systemic toxicity and to chronic cardiotoxicity.

Relation between plasma and saliva concentrations of enoxacin, ciprofloxacin, and theophylline

To assess the reliability of predicting plasma concentrations of enoxacin, ciprofloxacin, and theophylline from drug concentrations in saliva, six healthy volunteers received single oral doses of enoxacin, ciprofloxacin, and theophylline administered in combination on each of four separate study days, with different, doses separated by at least 5 days. Drug concentrations were determined by a newly developed high-performance liquid chromatography (HPLC) assay, which could measure simultaneously all three drugs in plasma or saliva. Saliva data from the postabsorptive phase after drug administration were used to minimize the effects of variation in absorption. There were good correlations between saliva and plasma concentrations of enoxacin, ciprofloxacin, and theophylline (r = 0.91, 0.88, and 0.98, respectively). The mean (+/-SD) saliva-to-plasma (S/P) ratio for theophylline was 0.63 +/- 0.06 with a coefficient of variation (CV) of 7.9 +/- 2.7%. In contrast, the S/P ratios and CV values for enoxacin and ciprofloxacin were 0.72 +/- 0.21 and 28.9 +/- 11.1%, and 0.58 +/- 0.15 and 25.3 +/- 6.7%, respectively. Because of the large inter- and intraindividual variability, saliva concentrations of enoxacin and ciprofloxacin are not reliable for predicting plasma concentrations. However, saliva may be used reliably for predicting plasma concentrations of theophylline.

Aging increases the cardiotoxicity of daunorubicin and daunorubicinol in the rat

This study examined effects of aging on the cardiac response in vitro to daunorubicin, a cancer chemotherapeutic agent that causes cardiotoxicity. Left ventricular trabeculae carneae from adult (aged 6-9 months) and old (aged 24-28 months) Fischer 344 rats were placed in oxygenated, physiological buffer. Preparations were treated with daunorubicin (175 microM) or saline (controls) over a 210-minute study period. Daunorubicin-induced decline in contractility (DS and dS/dt) was greater in old compared to adult myocardium (p < .02). Similarly, cardiac relaxation (90% relaxation time) was more impaired by daunorubicin in older preparations (p < 01). Although daunorubicin concentrations were unaffected by age, daunorubicinol concentrations in ventricular strips increased with time to a greater extent in the older group (p < .05). This study suggests that senescence increases the acute in vitro cardiotoxicity of daunorubicin and that the metabolite, daunorubicinol, may contribute to this toxicity.

Age-related characterization of atrial adenosine A1 receptor activation: direct effects on chronotropic and inotropic function in the Fischer 344 rat

Adenosine, an endogenously produced nucleoside, has direct negative chronotropic and inotropic effects on right and left atrial tissues, respectively. Age-related differences in the effects of A1 adenosine receptor activation on atrial rhythmic and contractile function were investigated in adult (6-8 months) and senescent (23-24 months) Fischer 344 (F344) rats. Senescent right atria (RA) were more sensitive to the negative chronotropic effects of R-phenylisopropyladenosine (R-PIA), a selective A1 receptor agonist, than adult RA (EC50: 4.8 +/- 0.7 vs 10.8 +/- 1.5 nM). However, senescent left atria (LA) were 15.4% less responsive to the maximal negative inotropic effects of R-PIA than adult LA. R-PIA did not significantly change resting force from basal values in either age group, but 90% relaxation time was prolonged threefold in senescent LA compared with adults. Radioligand binding experiments with 1,3-[3H]dipropyl-8-cyclopentylxanthine, a selective adenosine A1 receptor antagonist, showed a 56% greater density (Bmax) of adenosine A1 receptor in senescent than adult without differences in affinities (Kd). The increased sensitivity of senescent RA to the negative chronotropic effects of adenosine A1 receptor stimulation suggests a role for adenosine in abnormal sinus node function that occurs more frequently with age. Adenosine A1 receptor stimulation has more effect on relaxation than contraction in senescent LA compared with LA from adult F344 rats. However, the increase in density of adenosine A1 receptors suggests a functional dissociation between the availability of binding sites and receptor activation.

Quantification of the voltage-response relationship between punctate and field electrical stimulation and the function of isolated rat left atria and papillary muscles

The effects of varying the electrical stimulation voltage on the noradrenergic tone and systolic and diastolic cardiac function of isolated rat cardiac preparations is unknown. If a wide range of voltages substantially alters the basal noradrerengic tone of isolated cardiac preparations, highly variable responses may complicate the interpretation of the cardiac effects of interventions, such as drugs or toxins. This study was designed to determine whether field or punctate electrode stimulation altered systolic and diastolic cardiac function of isolated rat atrial and ventricular muscle preparations through a beta-adrenergic receptor-mediated mechanism. Isolated left atria and right ventricular papillary muscles from adult Sprague-Dawley rats were stimulated to contract isometrically in Krebs bicarbonate buffer (30 degrees C, pH 7.4, 0.5 Hz). Cardiac muscle function was assessed by determining cardiac contractility (dF/dt), relaxation (80% relaxation time), and muscle stiffness (changes in resting force). Muscles were electrically stimulated to contract using either punctate or field electrodes. Basal values of cardiac function were determined at threshold voltages, and voltage was increased in stepwise fashion, over a wide range, to obtain a voltage response-relation to cardiac function. In left atrial preparations, both punctate and field electrical stimulation caused a 200% increase in cardiac contractility. The greatest changes in contractility occurred at near threshold voltages (less than 5 volts for punctate and 19 volts for field stimulation). The voltage-dependent increases in cardiac contractility were attenuated or abolished by pretreatment with atenolol (10 micromol/L; selective beta 1-antagonist) or reserpine (5 mg/kg i.p., 24 hr before euthanasia). In contrast to left atrial preparations, neither field or punctate electrical stimulation had any effect on the cardiac contractility of papillary muscle preparations. Neither field or punctate electrical stimulation had any effect on cardiac relaxation (80% relaxation time) or muscle stiffness (changes in resting force) of left atrial or papillary muscle preparations. This study demonstrates that punctate and field electrical stimulation can significantly increase cardiac contractility of rat left atrial preparations at near threshold voltages by increasing noradrenergic tone. Thus, control of the voltage range may be required to reduce variation in cardiac function of isolated rat left atrial preparations.

Relative potency of mexiletine, lidocaine, and tocainide as inhibitors of rat liver CYP1A1 activity

Mexiletine and tocainide are lidocaine congeners that share similar chemical structures. Clinical studies suggest that the in vivo inhibitory effect of mexiletine on the CYP1A family of isoforms is substantially greater than that of tocainide. We investigated the inhibitory property of mexiletine, lidocaine, and tocainide on the in vitro activity of the cytochrome P4501A1 (CYP1A1) isozyme in the rat. Hepatic microsomes were prepared from rat livers induced with 3-methylcholanthrene. The rate of ethoxyresorufin-O-dealkylation (EROD) was used as an index of CYP1A1 activity. Vmax and KM of the reactions were determined from Lineweaver-Burk plots. The Ki values for the inhibitors were derived from Dixon plots. Results showed that mexiletine is a competitive inhibitor, lidocaine is a mixed inhibitor, and tocainide is a noncompetitive inhibitor of EROD. The Ki values for mexiletine and tocainide were 0.30 +/- 0.02 mM and 12.4 +/- 0.7 mM, respectively. Two Ki values for lidocaine were determined. They were 0.65 +/- 0.07 mM and 4.1 +/- 1.3 mM, respectively. The relative inhibitory potency of these agents on rat CYP1A1 activity is mexiletine > lidocaine > tocainide. This difference in potency, which is most likely attributable to the change in the chemical composition in the aliphatic chain among the compounds, suggests that these compounds may be useful probes for studying the mechanism of the interaction with the active site of CYP1A1.

Age-related effects in rabbit hearts of N6-R-phenylisopropyladenosine, an adenosine A1 receptor agonist

Interventions known to increase cytoplasmic Ca2+ appear to amplify age-related impairment of cardiac function. In addition, increased release of interstitial adenosine, an endogenous nucleoside, has been suggested to mediate the diminished beta-adrenergic responsiveness in senescent heart. However, the direct effects of adenosine A1 receptor activation on senescent myocardium have not been investigated thoroughly. Therefore, the effects of N6-R-phenylisopropyladenosine (R-PIA), an A1 agonist, on atrial rate and contractility (+dF/dt) in adult (6-8 months) and senescent (5-7 years) New Zealand White rabbits were compared in spontaneously beating right atria and electrically stimulated isolated right papillary muscles. Although senescent right atria appeared to be more sensitive to the negative chronotropic-effects of R-PIA, the effective concentrations producing 50% of the maximum response (EC50 values) of R-PIA were not significantly different between adult (26 nM, 95% confidence limits: 12-52 nM) and senescent (13 nM; 95% confidence limits: 10-16 nM). However, senescent right ventricular papillary muscles were more sensitive to the negative inotropic effects of R-PIA. For example, at 90 contractions/min, 100 nM R-PIA decreased +dF/dt 25.3 +/- 7.4% and 61.9 +/- 4.8% in adult and senescent papillary muscles, respectively. To investigate whether R-PIA might alter sarcoplasmic reticulum (SR) function as a mechanism of decreased inotropy, we determined the inotropic effects of R-PIA on steady-state and 30-s postrest-potentiated contractions (PRP; an index of SR Ca2+ release) of left atria. R-PIA did not selectively decrease contractility of PRP compared to steady state in either adult or senescent left atria.(ABSTRACT TRUNCATED AT 250 WORDS)

Impaired bronchodilator response to albuterol in healthy elderly men and women

BACKGROUND

Lymphocytes of normal elderly subjects and young asthmatics display dysfunctional beta-adrenoceptors. If beta-adrenoceptor dysfunction were found in senescent airways, it might help explain the pathogenesis of late onset asthma.

METHODS

The bronchodilatory effects of albuterol after methacholine-provoked bronchoconstriction were compared in 17 healthy young (age 20 to 36 years) and 17 healthy elderly (age 60 to 76 years) volunteer subjects. Albuterol was inhaled via dosimeter (initially 7.8 micrograms, doubling every 7.5 min) with forced expiratory flow at 50% vital capacity (FEF50) measured prior to each dose. Albuterol sensitivity was expressed as the cumulative logarithm of the area under the FEF50 recovery curve (AUC); a greater AUC meant lower sensitivity. On another study day, spontaneous recovery from methacholine was assessed similarly.

RESULTS

There was no intergroup difference in spontaneous recovery. Despite lower methacholine doses provoking similar (35%) FEF50 falls in elderly subjects, albuterol AUC was greater in elderly subjects (6,552%.min.microgram) than young subjects (3,922%.min microgram; p = 0.03). Multiple regression showed that AUC and age were related (p = 0.02).

CONCLUSION

Airway beta 2-adrenoceptor responsiveness is diminished in old age, suggesting that airway beta-adrenoceptor dysfunction may be implicated in late-onset asthma.

Simultaneous determination of theophylline, enoxacin and ciprofloxacin in human plasma and saliva by high-performance liquid chromatography

A simple reversed-phase high-performance liquid chromatographic method has been developed for the simultaneous determination of theophylline, ciprofloxacin and enoxacin in plasma and saliva. The biological fluid samples were extracted with methylene chloride-isopropyl alcohol prior to isocratic chromatography on a Waters C18 mu Bondapak column. Ultraviolet detection was carried out at 268 nm. The assay is linear for ciprofloxacin and enoxacin (0.05-10 micrograms/ml), and theophylline (0.1-20 micrograms/ml). The assay can be used to investigate the interaction of these two fluoroquinolones with theophylline.

Pharmacokinetic optimisation of drug therapy in elderly patients

With increasing age, there are a number of physiological changes that affect the handling of drugs in the human body. Increases in body fat percentage as well as decreases in lean body mass, hepatic metabolism and renal elimination capacity are of particular clinical significance. It is important to take these changes into account when choosing drug therapy for older patients in order to minimise adverse effects and maximise potential benefits. This is particularly important when prescribing drugs with a narrow therapeutic index such as digoxin, theophylline, phenytoin, lidocaine (lignocaine) or warfarin. When available, monitoring of plasma concentrations can assist in the optimisation of drug dosage.

Characterization of the independent and combined effects of two inhibitors on oxidative drug metabolism in rat liver microsomes

To evaluate how two inhibitors influence oxidative drug metabolism, this study investigated the inhibitory effects of mexiletine with cimetidine and mexiletine with lidocaine, both individually and in combination, on the oxidative metabolism of two probe substrates, aminopyrine and aniline in rat liver microsomes. Mexiletine was a competitive inhibitor of aminopyrine N-demethylation, whereas cimetidine was a mixed type of inhibitor (Ki = 2.00 +/- 0.04 and 0.20 +/- 0.02 mM, respectively). For aniline hydroxylation, mexiletine exhibited a mixed type of inhibition, whereas lidocaine was a noncompetitive inhibitor (Ki = 0.60 +/- 0.07 and 8.50 +/- 0.12 mM, respectively). The combined inhibition of either mexiletine with cimetidine or mexiletine with lidocaine on aminopyrine and aniline metabolism was close to the fully additive effects of the individual compounds when their individual concentrations were below a 2-fold Ki concentration, regardless of the apparent kinetic inhibition type. The combined inhibition was less than fully additive when the individual concentrations were twice the Ki or above. These results demonstrate that, when two inhibitors of oxidative drug metabolism are combined, both the Ki values and the concentrations of inhibitors play important roles in determining the extent of additive inhibition of enzyme activity.

Theophylline metabolism in healthy nonsmokers and in patients with insulin-dependent diabetes mellitus

This study examined the pharmacokinetics of theophylline and formation of its metabolites in patients with insulin-dependent diabetes mellitus (IDDM) and in sex-, age-, and weight-matched healthy nonsmokers (n = 8 per group). Subjects received a single dose of 5 mg/kg theophylline intravenously. The pharmacokinetic parameter values of theophylline (plasma clearance, elimination half-life, and volume of distribution) and the formation clearance of theophylline metabolites (3-methylxanthine, 1-methyluric acid, and 1,3-dimethyluric acid) were similar between the two groups. Plasma free fraction of theophylline was higher in the subjects with diabetes than in the healthy subjects (0.61 +/- 0.04 versus 0.56 +/- 0.02; p < 0.001). In the group of subjects with diabetes, there was a positive correlation between hemoglobin A1c values and plasma theophylline clearance (r = 0.76; p < 0.05), formation clearance of 1,3-dimethyluric acid (r = 0.78; p < 0.05), and formation clearance of 1-methyluric acid (r = 0.71; p < 0.05). These results suggest that patients with IDDM and poor glycemic control are more likely to have an increased rate of theophylline metabolism.

Oncostatin M activates low density lipoprotein receptor gene transcription in sterol-repressed liver cells

Oncostatin M (OM), a cytokine produced by macrophages and activated T cells, has been shown to be a potent inducer of liver low density lipoprotein receptor (LDLR) activity by increasing LDL uptake and cell surface LDLR number in HepG2 cells. To investigate whether OM regulates the transcription of the LDLR gene and if the effect is independent of the sterol pathway, we examined the effects of OM on the promoter activity of the LDLR gene and the expression of LDLR mRNA. HepG2 cells were transfected with hybrid genes containing three different lengths of DNA fragments from the 5' flanking region of the LDLR gene that were fused to the coding region of the chloramphenicol acetyltransferase (CAT) gene. OM induced an approximately 3-fold increase in CAT activities in pLDLR-CAT vector-transfected cells that were incubated in lipoprotein-depleted medium and a 6-fold increase in CAT activities when the transfected cells were treated with sterols. OM stimulated similar increases in CAT activities in HepG2 cells transfected with pLDLR-CAT 234, pLDLR-CAT 1563, and pLDLR-CAT 6500, suggesting that the essential cis-acting element that mediates the OM effect is located within the 177 base pairs upstream of the transcription start site of the LDLR gene. Examination of the regulation of the endogenous LDLR mRNA expression by OM gave results similar to those in transfected cells. OM increased the levels of mRNA of LDLR, regardless of the presence or absence of lipoprotein and sterols. These data suggest that the up-regulation of the LDLR by OM is at the transcriptional level through a nonsterol mediated mechanism.

Streptococcus pneumoniae-induced pulmonary hypertension and systemic hypotension in anesthetized sheep

Because some patients with Streptococcus pneumoniae bacteremia may present with shock, we reasoned that this organism may produce substances that cause shock. To test this hypothesis, type III pneumococcus supernatant, suspended in 10 ml of sterile water, was infused over 1 min in 8 adult anesthetized sheep. Normal saline was used as a control and had no effect on any of the hemodynamic parameters. Infusion of supernatant resulted in a precipitous fall in cardiac output from a control value of 4.25 +/- 0.54 to 2.80 +/- 0.43 (SE) l/min, a fall in mean systemic arterial pressure from 70 +/- 4 to 49 +/- 8 mmHg, and an increase in the mean pulmonary arterial pressure from 13 +/- 2 to 23 +/- 4 mmHg within 1 min after the infusion was completed. The peak hemodynamic effects were observed at approximately 3 min and returned to normal within 10 min after the infusion was completed. The thromboxane B2 level increased from a control value of 10 +/- 5 to 156 +/- 43 pg/ml at 3 min after the infusion was completed and decreased to 63 +/- 34 pg/ml at 20 min. A second identical dose of pneumococcal supernatant, repeated within 2 h of the first dose, had no effect on hemodynamic variables. Pretreatment with indomethacin, 5 mg/kg body wt, completely blocked the hemodynamic effects of pneumococcal supernatant (n = 3 sheep). Thus, we conclude that S. pneumoniae supernatant contains substances that cause septic shock syndrome through the synthesis of arachidonic acid metabolites and that a sublethal dose of the supernatant causes rapid tachyphylaxis.

A solid-phase radioimmunoassay for cyclic AMP

A solid-phase radioimmunoassay for cAMP in tissues, body fluids, and cultured cells has been developed using 125I-2'-O-monosuccinyl adenosine-3':5'-cyclic monophosphate tyrosyl methyl ester and High Binding EIA microtiter strips coated overnight at 4 degrees C with a rabbit or sheep polyclonal anti-cAMP antibody. After washing and blocking of wells, samples or standards were added, followed by the addition of radiolabel. Bound 125I-cAMP was separated from free by washing with phosphate buffer containing Tween 20. Bound 125I-cAMP was inversely proportional to cAMP in samples or standards. Cyclic AMP content of unknowns was calculated from a standard curve run concurrently with each assay. Both antibodies showed sensitivity of approximately 1 fmol, an assay range between 15 and 1,000 fmol, a maximum displacement ratio of up to 11-12, and no cross-reactivity with other cyclic nucleotides. Recoveries were 86.5%-106.8%, intraassay coefficients of variation were 2.4%-6.0%, and interassay coefficients of variation were 7.4%-10.2% for both antibodies. The cAMP content of tissues (brain > heart > kidney, liver > muscle) from rat, rabbit, and guinea pig, cultured rat lymphocytes from three lymphoid tissues, and human serum and urine were tested. This solid-phase RIA is a reliable, sensitive, rapid, and relatively inexpensive method for determination of cAMP.

Peripheral mononuclear leucocyte beta adrenoceptors and non-specific bronchial responsiveness to methacholine in young and elderly normal subjects and asthmatic patients

BACKGROUND

As beta adrenoceptor dysfunction occurs in both the normal elderly subject and in young asthmatic patients, the hypothesis was examined that age related beta adrenoceptor changes are important in the pathogenesis of late onset asthma in old age.

METHODS

Subjects were non-smokers who comprised 17 young normal subjects of mean (SE) age 29.4 (1.3) years, 17 elderly normal subjects of 67.2 (1.3) years, seven young asthmatic patients of 31.0 (2.8) years, and 17 elderly asthmatic patients of 68.5 (1.4) years. All asthmatic patients withheld inhalers for 12 hours and oral treatment for 24 hours before each study day. Subjects underwent an inhaled methacholine challenge (Newcastle dosimeter method) on two nonconsecutive days. The slope of the flow at 50% of the vital capacity (FEF50) dose-response curve was derived from the percentage fall in FEE50 divided by methacholine dose (sFEF50). Beta-adrenoceptor density (Bmax) and affinity (%KH) were determined with (125I)iodocyanopindolol as the radioligand in membranes prepared from mononuclear leucocytes.

RESULTS

Log sFEF50 was shown to be reproducible (repeatability coefficient 0.41) on the two study days and was inversely related to %KH but not to Bmax. Multiple regression analysis (all 58 subjects, overall R2 = 0.57) revealed an inverse relation between log sFEF50 and %KH, and between log sFEF50 and Bmax. The inverse relation between log sFEF50 and %KH was preserved whereas that between log sFEF50 and Bmax was lost when young asthmatic subjects or when all asthmatic subjects were excluded from multiple regression analysis.

CONCLUSIONS

The beta adrenoceptor dysfunction observed in late onset asthma may be similar to that seen during ageing. Thus late onset asthma may represent the extreme of a spectrum of age associated beta adrenoceptor dysfunction.

Species comparison of adenosine and beta-adrenoceptors in mammalian atrial and ventricular myocardium

The antagonist radioligand 1,3-[3H]dipropyl-8-cyclopentylxanthine ([3H]DPCPX) was used to characterize adenosine A1 receptors in membrane preparations from atrial and ventricular myocardium of rat, rabbit, guinea pig and pig. Kd values in crude membranes from guinea pig atria and ventricles (3.3 and 3.0 nM) were higher than those in the other species (ranges, 1.5-1.8 and 1.5-1.9 nM). Bmax values were greater in atria than in ventricles in all four species, and in atria and ventricles of guinea pig (76 and 34 fmol/mg), than in the other species (ranges, 15-17 and undetectable to 12 fmol/mg). In contrast, guinea pig Kd and Bmax values for beta-adrenoceptors, which were labelled with (-)3-[125I]iodocyanopindolol, fell within the range of values for the other three mammalian species. In semipurified membrane preparations from pig, [3H]DPCPX and the agonist radioligand [125I]-N6-4-aminobenzyladenosine appeared to label a similar population of receptors and gave comparable Kd values in atria (0.73 and 0.66 nM) and in ventricles (0.57 and 0.70 nM). In semipurified preparations from pig, the agonist R-(-)-N6-(2-phenylisopropyl)adenosine (R-PIA) displaced [3H]DPCPX in a manner consistent with the presence of both high- and low-affinity adenosine A1 receptors. The data from this study indicate that the density of adenosine A1 receptors in atria is greater than in ventricles, but similar Kd values suggest that the A1 receptor population is the same in the two cardiac tissues. Also, the data demonstrate that the [3H]DPCPX antagonist binding characteristics of guinea pig myocardium differ from those in rat, rabbit and pig.

Aging and the response to inhibition and induction of theophylline metabolism

The twofold to threefold higher incidence of adverse drug reactions in elderly as opposed to younger patients is due mainly to more severe disease and the requirement for more complex drug treatment regimens. The incidence of adverse drug reactions increases with the number of prescribed drugs. Because of multiple drug use by the elderly, the potential for drug interactions is greater in this patient group. Surprisingly, the effect of age on the clinical pharmacology of drug interactions has not been thoroughly investigated. Our studies have shown that cimetidine inhibits and phenytoin induces the metabolism of theophylline to a similar extent in healthy male nonsmokers and smokers. Preliminary analysis of the results of a study to investigate the inhibition of theophylline metabolism by cimetidine and ciprofloxacin administered in combination to healthy male and female nonsmokers also does not show an age difference in response. Additional careful studies are needed to evaluate further the pharmacology and clinical importance of pharmacokinetic and pharmacodynamic drug interactions in the elderly.

Effect of adenosine on heart rate in isolated muskrat and guinea pig hearts

The purpose of this study was to compare the responses of isolated hearts of the diving muskrat with the nondividing guinea pig (GP) to determine the contribution of adenosine (ADO) to the profound bradycardia that was seen in isolated muskrat hearts during exposure to hypoxia. Muskrat hearts were more sensitive than GP hearts to the heart rate-lowering effects of exogenously applied ADO or a stable ADO analogue, (R)-N6-(phenylisopropyl)adenosine. The hearts of both species were unpaced, and the bradycardia appeared to be due to high degree of atrioventricular block. Radioligand binding with 8-cyclopentyl-1,3-[3H]dipropylxanthine to A1-ADO receptors was greater in cardiac membranes prepared from GP hearts than from muskrat hearts. Nucleoside transporter antagonist binding was also greater in GP hearts compared with muskrats. This was determined by membrane binding of [3H]-nitrobenzylthioinosine, an antagonist of nucleoside transport. Both muskrat and GP hearts responded to 30 min of hypoxic perfusion by releasing ADO into the coronary effluent; however, the muskrat hearts released approximately five times more than the GP hearts. When hearts were subjected to hypoxia in the presence of ADO deaminase, theophylline, or 8-(p-sulfophenyl)theophylline, the hypoxia-induced bradycardia was blocked in the GP hearts and either slightly reduced or not affected in muskrat hearts. In contrast to GP hearts, muskrat hearts release larger amounts of ADO during hypoxia and are more sensitive to the negative chronotropic effects of exogenously administered ADO; yet the hypoxia-induced bradycardia does not appear to be exclusively mediated by ADO in the muskrat as it is in the isolated GP heart.

The effect of tocainide on theophylline metabolism

The effect of 5 days of oral tocainide (400 mg every 8 h) on the kinetics of theophylline given as a single 5 mg kg-1 i.v. infusion over 30 min was investigated in eight healthy male nonsmokers. Treatment with tocainide decreased the plasma clearance of theophylline from 37.5 +/- 6.9 (mean +/- s.d.) to 33.7 +/- 5.0 ml kg-1 h-1 (difference -3.8, 95% CI, -1.7 to -5.9; P = 0.004) and increased its terminal elimination half-life from 9.7 +/- 2.5 to 10.4 +/- 2.1 h (difference 0.7, 95% CI, 0.2 to 1.2; P = 0.011). Tocainide decreased the formation clearances of 3-methylxanthine and 1-methyluric acid, but the formation clearance of 1,3-dimethyluric acid was unaltered. These data indicate that tocainide exerts a modest inhibitory effect on theophylline metabolism. The magnitude of this change is substantially smaller than that reported to be produced by mexiletine.

Cardiac functional responses to adenosine by PD 81,723, an allosteric enhancer of the adenosine A1 receptor

Adenosine, a locally released and rapidly metabolized nucleoside, protects the heart from damage during ischemia by reducing oxygen demand and increasing oxygen supply. The aminothiophene derivative (2-amino-4,5-dimethylthien-3-yl)[3-(trifluoromethyl)phenyl]-met hanone (PD 81,723) has been shown to act as an allosteric enhancer of the adenosine A1 receptor in brain membranes and thyroid cells. The present study investigates the effects of PD 81,723 in spontaneously contracting right atria and electrically stimulated left atria isolated from Sprague-Dawley rats. N6-cyclopentyladenosine (CPA), an adenosine A1 receptor agonist, produced concentration-dependent inhibition of heart rate in right atria and contractile parameters in left atria. In the right atrium, 5 microM of PD 81,723 significantly shifted the concentration-response curves for CPA to the left, both in the absence and presence of a nonselective adenosine receptor antagonist, 8-(p-sulfophenyl)theophylline (8-SPT, 10 microM). In the left atrium, PD 81,723 also shifted the concentration-response curves for CPA to the left, but only in the presence of 8-SPT. Potentiation of CPA-induced negative chronotropic and inotropic responses with PD 81,723, although not significant, was also observed in the presence of a selective adenosine A1 receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 1 nM). These results demonstrate that PD 81,723 enhances the direct negative chronotropic and inotropic effects of adenosine A1 receptor activation in rat atria.

Effects of adenosine in combination with calcium channel blockers in patients with primary pulmonary hypertension

OBJECTIVES

The purpose of this study was to evaluate the effects of vasodilator combination therapy in patients with primary pulmonary hypertension.

BACKGROUND

Calcium channel blockers and adenosine have each been shown to be effective in reducing pulmonary artery pressure and pulmonary vascular resistance in patients with primary pulmonary hypertension. However, the effects of combining these vasodilators have not been studied.

METHODS

To test the combination, 12 patients were placed on oral nifedipine and 3 on diltiazem therapy, using a dose titrated to maximal effect (mean nifedipine dose 103 +/- 24 mg, mean diltiazem dose 300 +/- 49 mg). Patients were then given maintenance doses of the calcium channel blocker at half the cumulative loading dose at 6-h intervals. One hour after the maintenance dose of calcium blocker, all patients received an infusion of adenosine, starting with 50 micrograms/kg per min and increasing by 50 micrograms/kg per min at 2-min intervals to a maximally tolerated dose (180 +/- 63 micrograms/kg per min).

RESULTS

Ten patients responded to calcium channel blockers (defined as a > or = 20% decrease in pulmonary vascular resistance), with a 16% decrease in mean pulmonary artery pressure (p = 0.057), a 39% decrease in pulmonary vascular resistance (p = 0.002) and a 24% increase in stroke volume (p = 0.007). Five patients were nonresponders, with no significant changes in pulmonary artery pressure, pulmonary vascular resistance, cardiac index or stroke volume. In the calcium channel blocker responders, the combination of adenosine and calcium blocker reduced pulmonary vascular resistance by 49%, increased stroke volume by 33% and decreased mean pulmonary artery pressure by 14% compared with drug-free baseline values. In nonresponders, combination therapy resulted in nonsignificant changes in pulmonary artery pressure and pulmonary vascular resistance.

CONCLUSIONS

Adenosine has the ability to further decrease pulmonary artery pressure and pulmonary vascular resistance in patients with primary pulmonary hypertension who respond to calcium channel blockers. Those who fail to respond to these agents have little added effect from adenosine.

Acute metabolic effects of clonidine and adenosine in man

Insulin resistance may contribute to non-insulin-dependent diabetes mellitus, hypertension, and dyslipidemia; increased free fatty acid concentrations could both promote and maintain this state of insulin resistance. Therefore, agents that inhibit lipolysis and decrease plasma concentrations of free fatty acids could be of therapeutic interest. We have measured metabolic effects of clonidine, an alpha 2 adrenergic agonist, and adenosine in healthy human subjects since human fat cells have alpha 2 and adenosine A1 receptors, which inhibit lipolysis in vitro. Clonidine, as expected, significantly lowered systolic and diastolic blood pressure; clonidine also decreased the plasma concentration of free fatty acids. Although clonidine caused a transient mild increase in plasma glucose, insulin and triglyceride concentrations were unchanged. The metabolic effects of adenosine were examined with two protocols. In the first study, volunteers received a graded infusion of adenosine (at 0, 10, 20, 50 and 100 micrograms/kg.min for 30 min/dose), and glucose, insulin, free fatty acids, as well as respiratory rate, systolic and diastolic blood pressures, and heart rate were measured. There was no change in glucose, insulin, or free fatty acid concentrations. In the second study a graded infusion was used and was maintained at 100 micrograms/kg/min for 120 minutes. Heart rate and respiratory rate significantly increased. Glucose and free fatty acid concentrations were unchanged, while insulin concentrations were significantly increased. All subjects had significant symptomatic complaints (dyspnea, chest pressure) during the adenosine infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Impaired beta-adrenoceptor function, increased leukocyte respiratory burst, and bronchial hyperresponsiveness

Inflammatory processes have potential importance in the pathogenesis of bronchial hyperresponsiveness and asthma. Because beta-adrenoceptor function may be impaired in asthma, we studied regulation of the leukocyte respiratory burst using blood samples from subjects with bronchial hyperresponsiveness to methacholine. Leukocytes from hyperresponsive subjects were less responsive to the beta-agonist isoproterenol than were leukocytes from healthy control subjects. The magnitude of the respiratory burst was increased in cells from hyperresponsive subjects and correlated with the degree of methacholine responsiveness. These results demonstrate that peripheral leukocytes reflect a functional impairment in beta-adrenergic responsiveness that parallels airway hyperresponsiveness. Because untreated subjects demonstrated a reduction in beta-adrenergic response, the impairment in beta-adrenoceptor function was not a result of drug therapy and may be associated with the pathogenesis of asthma.

Relationship between nonspecific bronchial responsiveness to methacholine and peripheral mononuclear leukocyte beta-adrenergic receptor function in young drug-naive subjects

Asthma is associated with dysfunction of the beta-adrenergic receptor adenylyl cyclase signal transduction pathway. It has been argued that this results from receptor down-regulation by beta-agonist therapy. This study examined the relationship between nonspecific bronchial responsiveness (NSBR) to methacholine (Newcastle dosimeter method) and beta-adrenergic receptor density (Bmax) and affinity (%KH) in membranes from peripheral blood mononuclear leukocytes (MNL) in 12 male (27.3 +/- 1.7 yr old) and 14 female (31.4 +/- 1.7 yr old) drug-naive subjects with and without symptoms of mild intermittent wheezing. None had ever smoked or received any antiasthma medication. "Hyperresponsive" subjects were defined as those (n = 11) whose simplified slope of FEF50 (calculated as the percent fall in FEF50 divided by the dose of methacholine) was more than one SD above the mean for asymptomatic subjects. The log of the slope was reproducible (repeatability coefficient = 0.43) on two nonconsecutive days. Multiple regression analysis (overall R2 = 0.57) revealed negative relationships between the log of the slope and both Bmax (p = 0.016) and %KH (p = 0.011). Analysis of variance confirmed a lower mean (+/- SEM) value of %KH in "hyperresponsives" (45.7 +/- 5.5%) than in "normoresponsives" (60.4 +/- 4.1%, p = 0.04) with a similar trend for Bmax (hyperresponsives = 33.5 +/- 4.1 fmol/mg, normoresponsives = 45.9 +/- 7.1 fmol/mg, p = 0.18). These relationships between bronchial responsiveness, Bmax, and %KH cannot be explained by drug therapy, and they provide further evidence that there is an intrinsic impairment in the function of beta-adrenergic receptors on peripheral MNLs from subjects with high levels of nonspecific bronchial responsiveness.

Reduced subjective awareness of bronchoconstriction provoked by methacholine in elderly asthmatic and normal subjects as measured on a simple awareness scale

BACKGROUND

Asthma death rates are rising, with the greatest rise and highest death rates in old age. A reduced cardiovascular response in the elderly may lead to the underestimation by physicians of the severity of acute asthma attacks. This would be compounded if elderly patients had reduced awareness of bronchoconstriction.

METHODS

Methacholine provoked bronchoconstriction was compared in 34 elderly (17 asthmatic, 17 normal; age 60-83, mean 68 years) and 33 young subjects (16 asthmatic, 17 normal; 20-46, mean 30 years). None were smokers. All underwent inhaled methacholine challenge by the Newcastle dosimeter method, monitored by maximal expiratory flow-volume loops (MEFVL). The endpoints were a 35% fall in forced expiratory flow at 50% vital capacity or cumulative inhalation of 6.4 mg methacholine. The one second forced expiratory volume (FEV1) was derived from MEFVL. After challenge and before bronchodilatation subjects graded awareness of respiratory discomfort from 1 (no symptoms) to 4 (pronounced symptoms needing immediate treatment).

RESULTS

Despite a greater fall in FEV1 in elderly asthmatic patients (mean (SE) 27.4% (2.2%)) than in young asthmatic patients (21.5% (1.7%)) elderly patients were less aware of bronchoconstriction (awareness score 2.00 (SE 0.15) than young patients (3.06 (0.11)). Similar differences in awareness score were seen between elderly normal subjects (1.53 (0.17)) and young normal subjects (2.76 (0.22)), despite no difference in degree of bronchoconstriction.

CONCLUSIONS

Reduced awareness of moderate acute bronchoconstriction in old age may delay self referral in acute asthma and contribute to higher asthma mortality in the elderly.