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Biomedical subjects

W H Newman

Publications and source records attributed to W H Newman.

At least 37 records · Page 2Linked to original sources
PubMed1994

Thromboxane A2/prostaglandin H2-stimulated mitogenesis of coronary artery smooth muscle cells involves activation of mitogen-activated protein kinase and S6 kinase.

Prostaglandin H2 (PGH2) and thromboxane A2 (TXA2) are potent activators of platelets and vascular smooth muscle whose responses are mediated through a common G-protein coupled receptor (TXA2/PGH2 receptor). Despite the many studies describing their ability to aggregate platelets and contract vascular smooth muscle, little is known concerning the potential mitogenic capabilities of these autocoids. Mitogen-activated protein kinases (MAP kinases) and ribosomal S6 kinases are well characterized intracellular mediators involved in proliferation of cells. The present study was designed to examine the activation of MAP kinase and S6 kinase in guinea pig coronary artery smooth muscle cells (CASMC) in response to stimulation by a TXA2/PGH2 mimetic, I-BOP ([1S-(1 alpha,2 beta(5Z),3 alpha(1E,3R*),4 alpha)]-7-[3-(3-hydroxy-4-(4'- iodophenoxy)-1-butenyl)-7-oxabicyclo-[2.2.1]heptan-2-yl]-5-h eptenoic acid). Equilibrium radioligand binding assays using [125I]BOP defined a single class of high affinity TXA2/PGH2 receptors on monolayers of guinea pig CASMC (Kd = 0.18 +/- 0.03 nM; 26,476 +/- 3,600 sites/cell; 0.08 +/- 0.01 pmol/mg of protein; n = 12). I-BOP produced a concentration-dependent increase in [3H]thymidine incorporation in these cells (EC50 = 0.3 nM) which was inhibited by a series of TXA2/PGH2 receptor antagonists as well as by verapamil and staurosporine. I-BOP also produced a time-dependent increase in the activation of kinases phosphorylating myelin basic protein (MBP; a substrate for MAP kinase) and RRLSSLRA (S6 peptide; a substrate for pp85rsk kinase), reaching a peak activation between 5 and 10 min. Stimulated MBP kinases were identified as ERK1 and ERK2. The activation of these kinases by I-BOP was inhibited by the TXA2/PGH2 receptor antagonist SQ29548 and also by staurosporine. These results indicate that I-BOP, a TXA2/PGH2 mimetic, produces growth of coronary artery vascular smooth muscle cells, which is preceded by activation of MAP kinase and S6 kinase.

Animals↗
PubMed1994

Correlation between vascular and cellular responses to atrial natriuretic peptide and to sodium nitroprusside.

Atrial natriuretic peptide (ANP) and sodium nitroprusside (SNP) increase cGMP in vascular smooth muscle cells and act as vasodilators in some, but not all, blood vessels. In this present study, we attempted to correlate the ability of these two agents to dilate blood vessels with the ability to increase cGMP in cultured vascular smooth muscle cells. In the isolated guinea pig heart, SNP dose-dependently increased coronary flow while ANP was ineffective. In smooth muscle cells cultured from the coronary system, SNP increased intracellular cGMP in a dose-dependent manner while ANP had no effect on cGMP in these cells. In isolated guinea-pig thoracic aorta, precontracted with K+, both ANP and SNP produced relaxation and ANP was the more potent. In smooth muscle cells cultured from the aorta, ANP and SNP increased cGMP and the potency relationship was similar to the intact vessel. These results support the view that phenotypic properties of vascular smooth muscle cells can account for differences in the response of blood vessels to vasodilators.

Analysis of Variance↗
PubMed1994

Variability of response to atrial natriuretic peptide and sodium nitroprusside in cultured vascular smooth muscle cells from three blood vessels.

OBJECTIVES: Vascular beds vary in their responses to atrial natriuretic peptide and sodium nitroprusside. Both of these agents dilate blood vessels by increasing intracellular guanosine 3',5'-cyclic monophosphate (cyclic-GMP) but activate different enzymes in the vascular smooth muscle cell. We aimed to determine if the response of intracellular cyclic-GMP to atrial natriuretic peptide and sodium nitroprusside varies in smooth muscle cells cultured from different vascular beds. DESIGN: Prospective, repeated measures analysis of concentration-response curves. SETTING: Anesthesia research laboratory of an academic medical center. SUBJECTS: Guinea pigs: Cultured guinea pig smooth muscle cells were obtained from three different blood vessels. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Intracellular cyclic-GMP was measured by radioimmunoassay and concentration-response curves of cyclic-GMP to atrial natriuretic peptide and sodium nitroprusside were determined. Cells from the thoracic aorta were the most responsive to atrial natriuretic peptide. Atrial natriuretic peptide (1 microM) increased cyclic-GMP concentrations to 72 +/- 5 pmol/mg (20-fold increase) with a 50% effective concentration of 3 nM. The concentration-response curve in epicardial coronary smooth muscle cells was to the right with an 50% effective concentration for atrial natriuretic peptide of 20 nM and a maximum response of a ten-fold increase in cyclic-GMP. Coronary resistance vessel cells were unresponsive to atrial natriuretic peptide. In response to sodium nitroprusside, the concentration-response curve in coronary resistance vessel cells was significantly to the left of either thoracic aorta cells or the epicardial coronary cells. The 50% effective concentration for sodium nitroprusside in coronary resistance vessel smooth muscle cells was approximately 1 microM, while in both thoracic aortic cells and epicardial coronary cells, the 50% effective concentration was ten times higher. Coronary resistance cells were the most responsive with a 62-fold increase in cyclic-GMP in response to 1 mM of sodium nitroprusside. The maximum response in thoracic aorta cells and epicardial cells was 20- and 30-fold, respectively. CONCLUSIONS: Smooth muscle cells respond differently to vasodilators. The response of these cultured cells mimics the response of the intact vascular bed from which they were obtained. These findings suggest that phenotypic properties of smooth muscle cells within a blood vessel contribute to the responsiveness of the vessel.

Analysis of Variance↗
PubMed1994

Incidence and clinical significance of hemidiaphragmatic paresis in patients undergoing carotid endarterectomy during cervical plexus block anesthesia.

This study was designed to investigate the incidence and clinical consequences of hemidiaphragmatic paresis in patients undergoing carotid endarterectomy using cervical plexus block anesthesia. In 28 patients, diaphragmatic motion was evaluated by fluoroscopy 20 min after cervical plexus block with 1% mepivacaine. In 61% of the patients abnormalities of diaphragmatic motion were detected. These motion anomalies were associated with a statistically significant elevation of PaCO2. Gender, age, and whether the block was on the left or right side did not appear to affect the incidence of motion abnormalities after cervical plexus block anesthesia.

Aged↗
PubMed1994

Thermal diffusion probe and instrument system for tissue blood flow measurements: validation in phantoms and in vivo organs.

A minimally invasive probe and instrument system for real-time measurements of temperature, thermal conductivity and tissue blood flow has been designed for research and clinical use. The essence of the probe is a thermistor, located at the tip of catheters or glass and steel needles, and operating in transient self-heated mode at constant temperature increment. Thermal conductivity and tissue blood flow are determined by use of a coupled tissue-probe thermal model. The effects of temporal baseline temperature shifts are minimized by a novel, automatic, analog compensation circuit. Very short heating periods (3 s) and cooling periods (12 s) provided near-continuous measurements (4/min). Calibration experiments performed in media of known thermal conductivity exhibit a linear response with respect to thermal conductivity. In vitro experiments performed in isolated perfused dog liver preparations are presented to evaluate this instrument system. In vivo experiments performed in cat brain, dog liver, and human tumor demonstrate the ability of this instrument system to perform physiologically valid measurements (comparison inter-subjects and intra-subjects). The minimally invasive probes (0.8 mm OD) are capable of long term measurements (several months), with minimal tissue reactions (0.3 mm around the probe).

Animals↗
PubMed1994

The effect of pertussis toxin on the growth of vascular smooth muscle cells stimulated by serum or platelet-derived growth factor.

The involvement of a Gi- or G(o)-related G-protein as a regulator of the growth of guinea pig thoracic aorta smooth muscle (TASM) cells was studied by investigating the effects of pertussis toxin (PTX) on the growth of these cells. PTX treatment decreased the growth rate of TASM cells by 70-100%. This effect was apparent within 24 h after exposure to the toxin and persisted for at least 10 days after starting the treatment. The effect of the toxin appeared to be the result of the inactivation of a G-protein because 1) TASM cell membranes contained a 40-kilodalton substrate for the toxin in in vitro assays that was absent in membranes prepared from cells pretreated with toxin; and 2) the effect required both the enzymatic component (A-protomer) of the toxin that inactivates Gi/G(o)-related G-proteins and its B-oligomer necessary for binding and internalization of the A-protomer. The effect of the toxin was not due to an increased level of intracellular cAMP brought about by inactivation of a G-protein that normally inhibits adenylyl cyclase activity. Further, the toxin did not merely make some unknown mitogen rate limiting, because neither increasing concentrations of serum in the growth medium nor supplementation with platelet-derived growth factor could overcome its inhibition of TASM cell growth. Instead, some unknown process regulated by a PTX-sensitive G-protein appears to be required for the normal growth of these cells.

Adenosine Diphosphate Ribose↗
PubMed1994

Tolerance to nitroglycerin in vascular smooth muscle cells: recovery and cross-tolerance to sodium nitroprusside.

Treatment with nitric oxide (NO)-producing vasodilators such as nitroglycerin (NTG) and sodium nitroprusside (SNP) causes tolerance. Both NTG and SNP relax blood vessels by increasing guanosine 3',5'-cyclic monophosphate (cGMP) in vascular smooth muscle. We determined the effect of treatment with NTG on cGMP production in cultured pig coronary smooth muscle cells (CSM). Cells incubated for 1 h with 10 microM NTG were desensitized to the effect of NTG on cGMP, but 100 microM NTG was required to induce cross-tolerance to SNP. Acute concentration-response curves of cGMP to NTG and to SNP were determined in cells pretreated for 1 h with 100 microM NTG and compared to response curves in untreated cells. In untreated cells, both NTG and SNP increased cGMP concentration dependently. SNP (1 mM) increased cGMP to 575 +/- 22 pmol/mg vs 55 +/- 4 pmol/mg for 1 mM NTG (P < 0.01, n = 8). Pretreated cells were unresponsive to acutely applied NTG but remained responsive to SNP, although the concentration-response curve to SNP was significantly depressed by approximately 60%. After washout of the NTG pretreatment, the cGMP response to SNP returned to control within 48 h while response to NTG required 72 h. These results show that smooth muscle cells exposed to NTG become tolerant to the effect of NTG on cGMP, and that cross-tolerance to SNP required a 10-fold higher concentration of NTG. The cGMP concentration-response curves of these tolerant cells to rechallenge with NTG or SNP were different.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Regulation of atrial natriuretic peptide receptors in vascular smooth muscle cells: role of cGMP.

We tested the hypothesis that intracellular guanosine 3',5'-cyclic monophosphate (cGMP) regulates atrial natriuretic peptide (ANP) receptors. The effect of chronic exposure to ANP, sodium nitroprusside (SNP), and 8-bromo-cGMP (8-BrcGMP) on ANP receptors and cGMP formation was determined in guinea pig thoracic aorta smooth muscle cells (TASM) and in coronary artery smooth muscle cells (CASM). TASM express both the ANP-activated guanylyl cyclase (B-receptor) and the clearance receptor (C-receptor) and respond to ANP with increased cGMP. CASM exhibit only the ANP C-receptor. In TASM, 24-h treatment with 1 microM atriopeptin (AP) III [rat ANP-(103-126)] caused a sixfold increase in basal cGMP levels, which were unaltered in CASM. In AP III-treated TASM, maximal binding of 125I-labeled AP III (Bmax) was reduced 40% while affinity [dissociation constant (KD)] was unaltered. In CASM, Bmax and KD were not affected. In treated TASM, washed free of AP III, acute dose-response curves of cGMP to AP III were not different from that in untreated cells. In both TASM and CASM, basal cGMP levels were elevated and Bmax was decreased by 6-h treatment with SNP. SNP did not alter the acute response of cGMP to AP III. In both cell types, 8-BrcGMP for 6 h caused reduction in Bmax. These findings support the conclusion that elevated cGMP was necessary for ANP-induced downregulation of receptors. The unaltered responsiveness of cGMP to AP III suggests the B-receptor was not altered and the reduced Bmax was due to decreased C-receptor.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1993

Tolerance to sodium nitroprusside. Studies in cultured porcine vascular smooth muscle cells.

BACKGROUND: Tolerance to nitrovasodilators, including sodium nitroprusside (SNP), is a clinical problem. SNP causes vasodilatation by releasing nitric oxide, which stimulates intracellular guanosine 3':5'-cyclic monophosphate (cGMP) accumulation in smooth muscle cells. This study examined tolerance to SNP in coronary smooth muscle cells by measuring intracellular cGMP formation. METHODS: Smooth muscle cells were isolated from pig coronary vessels. Intracellular cGMP formation in response to SNP, nitroglycerine, and atrial natriuretic peptide (ANP) was quantitated by radioimmunoassay before and after chronic pretreatment. RESULTS: The detection of tolerance of cells rechallenged with SNP required exposure to a minimum concentration of 1 microM for SNP for at least 60 min. In untreated cells, acutely applied 100 microM SNP increased the cGMP concentration to 300 +/- 8.6 pmol/mg protein (mean +/- SEM). The cGMP concentration in cells pretreated with 1 microM SNP for 60 min increased to 213 +/- 11 pmol/mg in response to 100 microM SNP (P < 0.01, compared to untreated cells). The pretreatment of cells for 60 min with increasing concentrations of SNP caused a sequential reduction in the acute concentration-response curves of cGMP to SNP. After a 6 h washout period, cGMP accumulation in response to a rechallenge with SNP returned to control levels. The acute concentration-response curve of cGMP to SNP in cells pretreated with 100 microM nitroglycerine for 60 min was reduced significantly. Pretreatment with 100 microM SNP for 60 min did not change the response of cAMP accumulation to isoproterenol or forskolin. However, the response of cGMP formation to ANP was potentiated after pretreatment. In addition, elevation of basal cAMP or cGMP concentrations, induced with isoproterenol or ANP, respectively, did not alter the response of cGMP formation to SNP. CONCLUSION: The study yielded the following findings: (1) reversible tolerance to SNP was induced in cultured vascular smooth muscle cells; (2) chronic exposure to nitroglycerine induced cross-tolerance to SNP; (3) cells that were tolerant to SNP showed a potentiated response to ANP.

Animals↗
PubMed1992

Inhibition of endothelial cell clearance of atrial natriuretic peptide by cyclic GMP treatment.

In a previous study, we reported that cyclic GMP (cGMP) selectively down-regulates the clearance receptor (C-receptor) for atrial natriuretic peptide (ANP) in the cultured bovine pulmonary artery endothelial (CPAE) cell line. The present study was undertaken in order to examine the effect of cGMP on the internalization of the ANP-receptor complex in CPAE cells. Maximum binding of [125I]APIII to the cells significantly decreased following the treatment with 1 mM 8-bromo-cGMP for 48 or 72 h. Scatchard analysis of the binding assay data from the treated cells showed a decrease in Bmax (616 to 411 fmol/mg protein) without a significant change in Kd. Removal of cell surface-bound APIII by acetic acid revealed that not only the surface binding, but also the internalization of APIII significantly decreased in 8-bromo-cGMP-treated cells, indicating a decrease in receptor-mediated uptake of ANP into the cells. These results suggest that cGMP regulates the clearance of ANP by vascular endothelial cells.

Analysis of Variance↗
PubMed1992

Difference in effect of atrial natriuretic peptide on cGMP in aortic and coronary smooth muscle cells.

Blood vessels show a heterogeneous response to the atrial natriuretic peptide (ANP). In our experiments thoracic aorta from the guinea pig relaxed in response to atriopeptin III (AP; rat ANP-103-126) and to sodium nitroprusside (SNP). In contrast, in perfused guinea pig hearts, AP III produced no change in coronary flow, while SNP increased flow. In smooth muscle cells cultured from the coronary system (CASM) and from the thoracic aorta (TASM), we compared receptor binding and the effects on guanosine 3',5'-cyclic monophosphate (cGMP) production of AP III. AP III bound specifically with equal affinity and with equivalent numbers of binding sites in both cell types. AP III produced a dose-dependent increase in cGMP in TASM (50% effective concentration approximately 3 nM) with a maximum 11-fold increase over basal at 1 microM AP III. In contrast, in CASM, AP III failed to increase cGMP. Nitroprusside increased cGMP in both cell types. Autoradiograms of 125I-labeled AP III linked to cell membranes showed bands at 70 kDa (ANP-C receptor) in both cell types. A second band at 140 kDa (ANP-B receptor) was only seen in TASM. These results suggest that smooth muscle cells of coronary resistance vessels of the guinea pig do not express the particulate guanylyl cyclase that is activated by ANP.

Animals↗
PubMed1991

Differential effect of pertussis toxin on adenosine and muscarinic inhibition of cyclic AMP accumulation in canine ventricular myocytes.

Cyclic AMP regulation by muscarinic and adenosine receptors was investigated in isolated canine ventricular myocytes. Both the muscarinic receptor agonist, carbachol, and the adenosine receptor agonist, phenylisopropyladenosine, decreased isoproterenol-stimulated cyclic AMP accumulation in a concentration-dependent manner. Carbachol was more potent than phenylisopropyladenosine and had a greater inhibitory effect. At 10(-6) M, carbachol reduced isoproterenol-stimulated cyclic AMP by 73 +/- 5% while 10(-3) M phenylisopropyladenosine was required to decrease cyclic AMP accumulation by 54 +/- 8%. Pretreatment of myocytes with pertussis toxin to inactivate the inhibitory guanine nucleotide binding protein, Gi, completely abolished the effect of phenylisopropyladenosine to reduce cyclic AMP stimulation. In comparison, pertussis toxin treatment blunted the response to carbachol and shifted the dose-effect curve to the right but did not eliminate the inhibitory action of carbachol. In toxin-treated myocytes, 10(-3) M carbachol produced a 26 +/- 6% reduction of isoproterenol-induced cyclic AMP accumulation. This pertussis toxin-insensitive action of carbachol was antagonized by atropine and pirenzepine and was prevented when either of two different phosphodiesterase inhibitors. RO-20-1724 or isobutylmethylxanthine, was included in the incubation medium. The results indicate that adenosine receptor-mediated inhibition of hormone-stimulated cyclic AMP accumulation in ventricular myocytes occurs by a single, Gi-dependent mechanism while muscarinic inhibition appears to involve both Gi-dependent and Gi-independent mechanisms. The Gi-independent mechanism may reflect enhanced phosphodiesterase activity which results from the activation of muscarinic receptors.

Animals↗
PubMed1991

Atrial natriuretic peptide inhibits oxidant-induced increases in endothelial permeability.

Chemically and enzymatically generated oxidants alter endothelial cell shape, increase macromolecular permeability across endothelial cell monolayers, and increase lung microvascular permeability. We examined the effect of ANP (atrial natriuretic peptide) on oxidant-induced injuries to bovine aortic endothelial cell monolayers and to isolated, perfused rabbit lungs. Treatment of cultured endothelial monolayers with glucose oxidase (1.4 U/ml) caused changes in cell shape characterized by a retraction of cells and the formation of numerous intercellular gaps. Glucose oxidase treatment also caused a reduction in F-actin stress fibers visualized by rhodamine-phalloidin fluorescence. Pretreatment (5 min) of the endothelial monolayers with ANP (10(-7) M) attenuated the oxidant-induced changes in cell shape and reduction in F-actin staining. In addition, ANP significantly (P less than 0.05) reduced increases in endothelial monolayer permeability to albumin resulting from glucose oxidase treatment. Oxidant-induced injury of isolated, perfused rabbit lungs produced pulmonary edema measured as an increase in lung weight. This increase in weight was significantly (P less than 0.05) inhibited by pretreatment of lungs with ANP (10(-7) M). Collectively, these results suggest that ANP may act to preserve endothelial barrier function and reduce edema formation caused by oxidant injury.

Animals↗
PubMed1990

Atrial natriuretic peptide regulation of endothelial permeability is mediated by cGMP.

Previous studies in our laboratory showed that ANP inhibits increases in endothelial monolayer permeability to macromolecules induced by thrombin. In this present study, we investigated the second messenger system involved in the influence of ANP on monolayer permeability. In bovine aortic endothelial cells (BAEC), ANP (100 nM) caused increased cGMP levels which were measurable at 30 sec and maximal at 3 min. Addition of 8-bromo cGMP (1 mM) to BAEC monolayers mimicked the actions of ANP by inhibiting thrombin- mediated increases in permeability to [125I]-labeled bovine serum albumin. Inhibition of increases in permeability by lower concentrations of ANP was enhanced by the cGMP-selective phosphodiesterase inhibitor, M&B 22948 (100 microM). The use of ANP structural analogs which stimulate cGMP production (AP III or BNP) prevented thrombin-induced increases in monolayer permeability, whereas AP-I, which does not increase cGMP levels, was ineffective.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1989

Atriopeptin inhibition of thrombin-mediated changes in the morphology and permeability of endothelial monolayers.

To determine the role of endothelial atriopeptin (AP) receptors, we examined the effect of AP-III on the morphology and macromolecular permeability of monolayer cultures of bovine aortic endothelial cells. AP-III alone (10(-9)-10(-6) M) had no observable effect on the morphology of the monolayers or their permeability to 125I-labeled albumin. However, incubation of the endothelial monolayers with AP-III (10(-8)-10(-6) M) antagonized thrombin-induced (1 unit/ml) cell-shape change and the formation of intercellular gaps. AP-III also opposed the effect of thrombin on the distribution of actin filaments in the endothelial cytoskeleton. Further, thrombin caused a 2-fold increase in monolayer permeability to 125I-labeled albumin, which was abolished by 10(-8)-10(-6) M AP-III pretreatment. Taken together with the findings that AP-III exhibited specific and saturable binding in these cells, these data suggest that AP regulates endothelial permeability through a receptor-mediated process.

Actins↗
PubMed1989

Persistent desensitization of the heart to the inotropic action of isoproterenol by adenosine.

Isolated guinea pig hearts were perfused with Krebs buffer in the absence or presence of 10 microM adenosine for 60 to 120 min followed by a 15 min washout with adenosine-free buffer. The effects of isoproterenol on left ventricular dP/dt and heart rate were then determined. Perfusion with adenosine for a minimum of 90 min followed by washout resulted in a 40% depression of the dose-response curve of left ventricular dP/dt to isoproterenol. This depressed inotropic responsiveness persisted for at least 1 hr after cessation of adenosine perfusion. The heart rate response to isoproterenol was unaffected. Also, adenosine perfusion had no effect on ouabain inotropism. Measurement of adenosine in coronary effluent and in ventricular tissue by radioimmunoassay verified that no residual elevated adenosine remained following perfusion and washout. Moreover, isoproterenol-induced release of adenosine into the coronary effluent did not differ between control and adenosine-treated hearts. Addition of 100 microM theophylline, an adenosine receptor antagonist, to the adenosine containing buffer during perfusion prevented the depressed response to isoproterenol. In membrane fractions prepared from ventricles, beta receptors were assessed by (-) [125] iodocyanopindolol binding and neither the density of these receptors nor their affinity for agonists or antagonists was altered by adenosine perfusion. However, activation of adenylate cyclase by isoproterenol (10 microm) was significantly depressed in membranes from adenosine perfused hearts. These findings are consistent with a receptor mediated action of adenosine to produce persistent depression of catecholamine inotropism. Such an effect may be important in heart failure where myocardial levels of adenosine are elevated and circulating levels of catecholamines are high.

Adenosine↗
PubMed1988

Endothelium-mediated coronary dilatation by adenosine does not depend on endothelial adenylate cyclase activation: studies in isolated guinea pig hearts.

Adenosine, applied to the coronary system of guinea pigs at up to 10(-6) M, elicits dilatation solely via an endothelium-mediated process. We investigated the role of coronary A2 receptors in this dilation, since the coronary endothelium possesses adenosine A2-receptors with a stimulatory action on the adenylate cyclase. In situ, A2 receptor stimulation can be assessed by prelabeling the coronary endothelial adenine nucleotide pool with 3H-adenosine and subsequently determining the rate of release of radiolabeled cAMP induced by A2 agonists. Thus, perfusion of isolated hearts with 5'-N-ethylcarboxamidoadenosine (NECA) dose-dependently increased coronary flow and the release of 3H-cAMP from the endothelium. In the presence of 50 microM 2',5'-dideoxyadenosine (ddA), a P-site agonist which inhibits the catalytic activity of adenylate cyclase, coronary flow increases induced by both adenosine and NECA were unaffected. In contrast, ddA reduced the release of labeled cAMP in response to NECA by about 60%. In cultured endothelial cells, ddA likewise inhibited cAMP accumulation due to NECA by about 70%. Moreover, ddA antagonized the adenylate cyclase mediated flow response due to the PGI2 analogue, iloprost, as well as the positive chronotropic and inotropic actions of isoproterenol. The dissociation elicited by ddA between the coronary flow response and the release of cAMP strongly indicates that the endothelial A2 receptors which are linked to adenylate cyclase are not causally involved in endothelium-dependent coronary dilatation induced by adenosine.

Adenosine↗