Differential responses to ATPγS in the mesenteric and hindlimb vascular bed of the cat

The mechanism by which the purinergic agonist adenosine 5′-O-(3 thiotriphosphate) (ATPγS) decreases vascular resistance was investigated in the mesenteric and hindlimb vascular beds of the cat. Injections of ATPγS into the hindlimb perfusion circuit elicited dose-dependent decreases in perfusion pressure while injections into the mesenteric circuit produced a biphasic response with an initial vasopressor response followed by a vasodepressor response. In the mesenteric vascular bed the pressor response to ATPγS was blocked by a P2X₁ receptor antagonist. Also an inhibitor of nitric oxide synthase enhanced the vasoconstrictive responses to ATPγS. However, the vasodepressor response in the mesenteric bed was not altered by the administration of an alpha adrenergic receptor antagonist, a cyclooxygenase inhibitor, a P2Y₁ receptor antagonist, or a K⁺_ATP channel blocking agent. These data suggest that the vasopressor response to ATPγS in the mesenteric vascular bed of the cat is mediated via P2X₁ receptor activation. The differential responses to ATPγS in the hindlimb and mesentery suggest differences in purinergic receptor distribution in the vascular system of the cat. In addition, the results suggest that prostaglandin synthesis, P2Y₁ receptor activation, alpha receptor inhibition, and K⁺_ATP channels activation play little to no role in mediating the vascular response to ATPγS in the mesentery of the cat.