The effects of neuropeptide Y (NPY) were studied in the isolated rat kidney, which was perfused at constant perfusion pressure with a synthetic medium. In this preparation NPY produced concentration (1-100 nM)-dependent inhibition of renin release and vasoconstriction. In kidneys perfused at constant flow, inhibition of renin release by NPY was even more pronounced, excluding a flow-dependent washout effect. The simultaneous infusion of the calcium channel antagonist methoxyverapamil (2 microM) or of the calmodulin inhibitor calmidazolium (1 microM) did not prevent these effects of NPY, suggesting that calcium-dependent reactions are not primarily involved. Inhibition of renin release by NPY was also observed in tissue pieces prepared from the hydronephrotic rat kidney, in which tubular elements are lacking. This indicates that inhibition of renin release by NPY is not dependent on the presence of macula densa cells or on changes of intrarenal hemodynamics. In isolated kidneys from rats pretreated with pertussis toxin (2 micrograms/100 g ip) both effects of NPY, renal vasoconstriction and inhibition of renin release, were almost completely abolished. The pertussis toxin-sensitive factor mediating the effects of NPY is most likely the Ni-coupling protein of the adenylate cyclase complex. Accordingly, our data suggest that NPY induces renal vasoconstriction and inhibits renin release by inhibition of adenylate cyclase activity in vascular smooth muscle and renin-producing cells.