Inhibition of renal vasoconstriction by elevated ureteral pressure

These experiments were prompted by the observation that elevated ureteral pressure inhibited renal vasoconstrictions elicited by electrical stimulation of "defense regions" of the central nervous system (DNS) in cats. Experiments were designed to detect the relative contributions to this inhibition of CNS reflexes and interactions between autoregulatory and neural controls of the renal circulation. Cats were anesthetized with either chloralose or pentobarbital. Renal blood flow was measured electromagnetically. Elevated ureteral pressure lowered prestimulus renal vascular resistance. Renal vasoconstrictions elicited by electrical stimulation of the CNS or the peripheral renal nerves and by infusion of catecholamines into the renal artery were equally inhibited by elevated ureteral pressure. Equal inhibition of CNS and renal nerve-evoked vasoconstrictions suggested that a reflex was not involved. Equal inhibition of vasoconstrictions elicited by renal nerve stimulation and by catecholamine infusions suggested that elevated ureteral pressure acted primarily at a postsynaptic site. Inhibition of prostaglandin synthesis by indomethacin diminished, but did not abolish, the ureteral pressure-induced inhibition of neurogenic vasoconstrictions.