15-hydroxy-11-alpha-9-alpha-(epoxymethano)prosta-5-13-dienoic-acid and diadenosine-tetraphosphate

Diadenosine tetraphosphate (AP4A) is a vasoactive mediator that may be released from platelet granules and that may reach higher plasma concentrations during coronary ischemia-reperfusion. The objective of this study was to analyze its coronary effects in such conditions. To this, rat hearts were perfused in a Langendorff preparation and the coronary response to Ap4A (10(-7)-10(-5) M) was recorded. In control hearts, Ap4A produced concentration-dependent vasodilatation both at the basal coronary resting tone and after precontracting coronary vasculature with 11-dideoxy-1a,9a-epoxymethanoprostaglandin F2α (U46619), and this vasodilatation was reduced by reactive blue 2 (2×10(-6) M), glibenclamide (10(-5) M), H89 (10(-6) M), U73122 (5×10(-6) M) and endothelin-1 (10(-9) M), but not by L-NAME (10(-4) M), isatin (10(-4) M), GF109203x (5×10(-7) M), or wortmannin (5×10(-7) M). After ischemia-reperfusion, the vasodilatation to Ap4A diminished, both in hearts with basal or increased vascular tone, and in this case the relaxation to Ap4A was not modified by reactive blue 2, L-NAME, glibenclamide, isatin, H89, GF109203x or wortmannin, although it was reduced by U73122 and endothelin-1. UTP produced coronary relaxation that was also reduced after ischemia-reperfusion. These results suggest that the coronary relaxation to Ap4A is reduced after ischemia-reperfusion, and that this reduction may be due to impaired effects of KATP channels and to reduced response of purinergic P2Y receptors.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Androstadienes; Animals; Coronary Vessels; Dinucleoside Phosphates; Endothelin-1; Estrenes; Glyburide; Heart; In Vitro Techniques; Indoles; Isatin; Isoquinolines; Male; Maleimides; NG-Nitroarginine Methyl Ester; Perfusion; Pyrrolidinones; Rats; Rats, Sprague-Dawley; Reperfusion Injury; Rest; Sulfonamides; Triazines; Vasoconstriction; Wortmannin

By use of front-surface fluorometry and fura-2-loaded medial strips of the porcine coronary artery, cytosolic Ca++ concentration ([Ca++]i) and force development were monitored simultaneously to determine the mechanisms of vasorelaxation induced by the diadenosine polyphosphates (APnA) diadenosine 5',5'''-P1, P4-tetraphosphate (AP4A) and diadenosine 5',5'''-P1,P5-pentaphosphate (AP5A). APnA concentration-dependently inhibited the sustained elevations of [Ca++]i and force induced by U-46619, a thromboxane A2 analog, in the presence of extracellular Ca++. APnA shifted the [Ca++]i-force relation curves of contractions induced by various concentrations of high K+ to the right. The AP4A-induced decreases in [Ca++]i and force were largely attenuated by tetrabutylammonium. The AP4A-induced decreases in force were attenuated by 4-aminopyridine and charybdotoxin. The AP5A-induced decreases in [Ca++]i and force were attenuated by tetrabutylammonium, 4-aminopyridine and charybdotoxin. In the absence of extracellular Ca++, APnA did not inhibit the transient elevations of [Ca++]i induced by histamine or caffeine. Both AP4A and AP5A increased intracellular cAMP content. We thus conclude that AP4A and AP5A relax the porcine coronary artery by decreasing [Ca++]i, possibly through the activation of K+ channels, but not through inhibition of intracellular Ca++ release and by decreasing the Ca++ sensitivity of the contractile machinery. These effects were considered to be mediated by cAMP.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Caffeine; Calcium; Coronary Vessels; Cyclic AMP; Cyclic GMP; Dinucleoside Phosphates; Histamine; In Vitro Techniques; Muscle, Smooth, Vascular; Potassium Channel Blockers; Swine; Vasodilation