Time dependence of mechanisms in the renin response to renal nerve stimulation

The renin release responses to 1 and 5 min of renal nerve stimulation were determined. The left kidneys of alpha-chlorolose-anesthetized cats were pump perfused with blood while stimulating the decentralized renal nerves at different frequencies (0.5 ms, 10 V). With renal blood flow (RBF) held constant, 1 min of renal nerve stimulation increased renin secretion rate (RSR) at 1.0 (128%), 4.0 (168%) and 12.0 (160%) Hz. After 5 min of stimulation the responses were not different. Propranolol pretreatment prevented the increase in RSR at 1.0 Hz, and resulted in decreased RSR at 4.0 and 12.0 Hz. This response pattern occurred after 1 and 5 min of renal nerve stimulation. When renal perfusion pressure (RPP) was held constant, RSR at 1 min into the stimulation period was similar to that found in the constant RBF group. However, after 5 min the 4.0 Hz and 12.0 Hz responses were significantly greater than the 1 min responses (242% and 508%). Propranolol pretreatment resulted in renin responses after 1 min of stimulation which were similar to the beta-blocked constant RBF group. After 5 min of stimulation at 4.0 and 12.0 Hz RSR was greater than control levels. The results illustrate that renal nerve evoked renin release is time-dependent under constant RPP conditions. The data indicate the presence of 3 mechanisms in these responses. A beta-adrenergic receptor operates at all frequencies to increase renin release. When renal vasoconstriction occurs additional mechanisms are involved. One is inhibitory, independent of renal hemodynamic conditions and rapidly activated. The second is excitatory, occurs only under constant RPP conditions, and is activated slowly.