PRESSURE-MEDIATED VASOCONSTRICTION OF JUXTAMEDULLARY AFFERENT ARTERIOLES INVOLVES P-2-PURINOCEPTOR ACTIVATION

This study was conducted to examine the hypothesis that P-2 purinocept ors contribute to pressure-induced autoregulatory adjustments of affer ent arteriolar caliber. Experiments were performed in vitro using the blood-perfused juxtamedullary nephron technique. Afferent arteriolar d iameter averaged 19.2 +/- 0.6 mu m (n = 51) at control perfusion press ure of 100 mmHg and decreased when perfusion pressure was increased. D esensitization of Pt purinoceptors abolished the alpha,beta-methylene ATP-mediated afferent vasoconstriction and prevented pressure-dependen t autoregulatory adjustments in afferent diameter. P-2-purinoceptor sa turation significantly decreased afferent caliber and attenuated press ure-induced autoregulatory responses. To block P-2 receptors, afferent arterioles were treated with the P-2-purinoceptor antagonists, pyrido xal-phosphate-6-azophenyl-2',4'-disulfonic acid or suramin. P-2-recept or blockade prevented the afferent arteriolar vasoconstriction evoked by increasing perfusion pressure from 100 to 130 and 160 mmHg. These d ata demonstrate that inhibition of P-2 purinoceptor-dependent response s through receptor desensitization, receptor saturation, or purinocept or blockade impairs normal autoregulatory behavior in rat juxtamedulla ry afferent arterioles. The results are consistent with the hypothesis that P-2 purinoceptors participate in mediating autoregulatory adjust ments in afferent arteriolar diameter.