cardiovascular-agents and 8-(4-sulfophenyl)theophylline

1. This study investigated the mechanism of prolonged relaxation to ATP in the rat isolated perfused mesenteric arterial bed. 2. In methoxamine pre-constricted preparations, ATP elicited dose-dependent, endothelium-dependent, rapid relaxation at 5 pmol - 0.05 micromol (R(max) 76+/-5.6%, pD(2) 9.2+/-0.2), and contraction, followed by prolonged endothelium-independent vasorelaxation at 0.05, 0.5 and 5 micromol (56+/-3.0, 87+/-2.9 and 85+/-4.6%). Suramin (100 microM), attenuated rapid (pD(2) 7.8+/-0.1) and prolonged relaxation to ATP. The selective P2 receptor antagonist PPADS (10 microM) reduced prolonged, but not rapid relaxation. Neither phase of relaxation was affected by 8-sulphophenyltheophylline (1 microM) or indomethacin (10 microM). 3. alpha,beta-methylene ATP (alpha,beta-meATP; 10 microM) attenuated prolonged relaxation to ATP (relaxations at 0.05 and 0.5 micromol were 25+/-8.3 and 48+/-9.0%, respectively). alpha,beta-meATP blocked contractions and revealed rapid relaxation to ATP at 0.05 - 5 micromol. 4. Capsaicin pre-treatment did not affect either phase of vasorelaxation to ATP. alpha,beta-meATP (10 microM) had no effect on vasorelaxation mediated by electrical stimulation of capsaicin-sensitive sensory nerves. 5. High K(+) (25 mM) attenuated prolonged relaxation to ATP (21+/-2.6 and 64+/-5.8%, at 0.05 and 0.5 micromol, respectively), but had no effect on rapid relaxation. Ouabain (1 mM), an inhibitor of Na(+)/K(+)-ATPase, and glibenclamide (10 microM), an inhibitor of K(ATP) channels, also attenuated prolonged relaxation to ATP. Charybdotoxin (100 nM), a selective inhibitor of K(Ca) channels, and tetraethylammonium (10 mM) had no effect on rapid or prolonged relaxations. 6. These results show that the prolonged phase of vasorelaxation to ATP in the rat isolated mesenteric arterial bed, which may be mediated by P2Y receptors, is endothelium-independent, involves activation of Na(+)/K(+)-ATPase and K(ATP) channels, and is inhibited by alpha,beta-meATP. Neither prolonged nor rapid vasorelaxation to ATP involves capsaicin-sensitive sensory nerves, adenosine P1 receptors, prostanoids or K(Ca) channels.

Topics: Adenosine Triphosphate; Animals; Capsaicin; Cardiotonic Agents; Cardiovascular Agents; Charybdotoxin; Drug Interactions; Electric Stimulation; Endothelium, Vascular; Glyburide; In Vitro Techniques; Indomethacin; Isotonic Solutions; Male; Mesenteric Arteries; Neurons, Afferent; Ouabain; Pyridoxal Phosphate; Rats; Rats, Wistar; Suramin; Tetraethylammonium; Theophylline; Vasodilation

We examined pial arteriolar reactivity to a partially endothelial nitric oxide synthase (eNOS)-dependent vasodilator ADP as a function of chronic estrogen status. The eNOS-dependent portion of the ADP response was ascertained by comparing ADP-induced pial arteriolar dilations before and after suffusion of a NOS inhibitor, N(omega)-nitro-L-arginine (L-NNA; 1 mM) in intact, ovariectomized (Ovx), and 17beta-estradiol (E2)-treated Ovx females. We also examined whether ovariectomy altered the participation of other factors in the ADP response. Those factors were the following: 1) the prostanoid indomethacin (Indo); 2) the Ca2+-dependent K+ (K(Ca)) channel, iberiotoxin (IbTX); 3) the ATP-regulated K+ (K(ATP)) channel glibenclamide (Glib); 4) the K(Ca)-regulating epoxygenase pathway miconazole (Mic); and 5) the adenosine receptor 8-sulfophenyltheophylline (8-SPT). In intact females, the eNOS-dependent (L-NNA sensitive) portion of the ADP response represented approximately 50% of the total. The ADP response was retained in the Ovx rats but L-NNA sensitivity disappeared. On E2 replacement, the initial pattern was restored. ADP reactivity was unaffected by Indo, Glib, Mic, and 8-SPT. IbTX was associated with 50-80% reductions in the response to ADP in the intact group that was nonadditive with L-NNA, and 60-100% reductions in the Ovx group. The present findings suggest that estrogen influences the mechanisms responsible for ADP-induced vasodilation. The continued sensitivity to IbTX in Ovx rats, despite the loss of a NO contribution, is suggestive of a conversion to a hyperpolarizing factor dependency in the absence of E2.

Topics: Adenosine Diphosphate; Adenosine Triphosphate; Animals; Antifungal Agents; Arterioles; Calcium; Cardiovascular Agents; Endothelium, Vascular; Estrogens; Female; Glyburide; Hypoglycemic Agents; Indomethacin; Miconazole; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Ovariectomy; Peptides; Pia Mater; Potassium Channels; Rats; Rats, Sprague-Dawley; Theophylline; Vasodilation

Adenosine is an important regulatory metabolite in the heart where it has a cardioprotective function. In the ventricle, the cardioprotective action of adenosine is mediated through the adenosine A1 receptor and inhibition of adenylyl cyclase. In order to investigate the effect of age on adenosine signal transduction in the heart, the effect of specific adenosine A receptor agonists on adenylyl cyclase activity was measured in crude cardiac ventricular membranes isolated from 1-, 6- and 24-month-old Fisher 344 rats. There were no differences in basal cyclase activity with age. Consistent with observations from other laboratories, isoproterenol- and forskolin-stimulated cyclase activity decreased with age. In addition, there was an age-related decline in the capacity of adenosine to inhibit stimulated adenylyl cyclase. The specific A1 adenosine receptor agonists, N6-cyclopentyladenosine (CPA) and N6-p-sulfophenuladenosine (SPA) inhibited isoproterenol- and forskolin-stimulated adenylyl cyclase activity in cardiac membranes from 1-month and 6-month-old rats; however, CPA and SPA did not inhibit adenylyl cyclase in membranes from 24-month-old rats. These data indicate that in addition to the age-related decline in beta-adrenergic receptor function with age, there is also a decrease in adenosine A; receptor-mediated responses. In contrast, carbachol acting through muscarinic receptors, caused the same inhibition of adenylyl cyclase at all ages. Therefore, the age-related decline in inhibitory signal transduction is specific to the adenosine A1 receptor. The age-related defect is probably at the level of the adenosine/receptor interaction and/or the receptor/guanine nucleotide binding protein interaction.

Topics: Adenosine; Adenylyl Cyclase Inhibitors; Adenylyl Cyclases; Adrenergic beta-Agonists; Age Factors; Animals; Carbachol; Cardiovascular Agents; Cell Membrane; Colforsin; Heart; Isoproterenol; Male; Muscarinic Agonists; Myocardium; Purinergic P1 Receptor Agonists; Rats; Rats, Inbred F344; Receptors, Purinergic P1; Sulfonic Acids; Theophylline