Renal Vascular Reactivity to P₂-Purinoceptor Activation in Spontaneously Hypertensive Rats

This study was performed to determine the possible contribution of an imbalance between P(2X) (vasoconstriction) and P(2Y) (vasodilation)-purinergic reactivity to the increased vascular resistance of spontaneously hypertensive rats (SHR). The vasoactive responses to alpha,beta-methylene ATP and 2-methylthio ATP specific agonists, respectively, for P(2X) and P(2Y) purinergic receptors were characterized in isolated perfused kidneys from Wistar Kyoto (WKY) and SHR. To analyze P(2X)- and P(2Y)-purinergic reactivity we used phenylephrine and barium chloride, or acethylcholine (ACh) and sodium nitroprusside (NP) as reference compounds, respectively. The renal vasculature from SHR showed markedly enhanced reactivity to alpha,beta-methylene ATP, phenylephrine and barium chloride. The dose-response curves were characterized by a similar threshold, with a greater maximal response. There were no significant differences in the dose-response curves or in maximal vasodilation to 2-methylthio ATP, ACh or NP when both groups were compared, except at the dose of 10(-6) g/g kidney weight of NP in which the SHR group showed an increased responsiveness. The results indicate that the increased responsiveness of kidneys from SHR to alpha,beta-methylene ATP may be due to nonspecific functional changes in the renal vasculature rather than to a specific alteration in the activity of renal P(2X)-purinoceptors. Our results also indicate that P(2Y)-purinergic reactivity, nitric oxide-induced vasodilation and the cGMP-dependent mechanisms of vasodilation are well preserved in SHR.