Pressure-mediated vasoconstriction of juxtamedullary afferent arterioles involves P-2-purinoceptor activation

This study was conducted to examine the hypothesis that P-2 purinoceptors contribute to pressure-induced autoregulatory adjustments of afferent arteriolar caliber. Experiments were performed in vitro using the blood-perfused juxtamedullary nephron technique. Afferent arteriolar diameter averaged 19.2 +/- 0.6 mu m (n = 51) at control perfusion pressure of 100 mmHg and decreased when perfusion pressure was increased. Desensitization of Pt purinoceptors abolished the alpha,beta-methylene ATP-mediated afferent vasoconstriction and prevented pressure-dependent autoregulatory adjustments in afferent diameter. P-2-purinoceptor saturation significantly decreased afferent caliber and attenuated pressure-induced autoregulatory responses. To block P-2 receptors, afferent arterioles were treated with the P-2-purinoceptor antagonists, pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid or suramin. P-2-receptor blockade prevented the afferent arteriolar vasoconstriction evoked by increasing perfusion pressure from 100 to 130 and 160 mmHg. These data demonstrate that inhibition of P-2 purinoceptor-dependent responses through receptor desensitization, receptor saturation, or purinoceptor blockade impairs normal autoregulatory behavior in rat juxtamedullary afferent arterioles. The results are consistent with the hypothesis that P-2 purinoceptors participate in mediating autoregulatory adjustments in afferent arteriolar diameter.