Renal Nerves Modulate Renin Secretion during Autoregulation

Efferent stimulation of the renal nerves at a very low frequency (0.25 Hz) which is subthreshold for changes in renal blood flow (RBF), urinary sodium excretion (U_NaV), and renin secretion has been shown to augment the renin secretion response to reduction in renal arterial pressure to 50 mm Hg by aortic constriction. The present experiments determined whether this modulating influence on renin secretion could be demonstrated during aortic constriction when both RBF and glomerular filtration rate (GFR) were autoregulated. In 9 dogs with renal nerves sectioned, aortic constriction reduced renal arterial pressure from 131 to 98 mm Hg and U_NaV from 68 ± 15 to 29 ± 6 μeq/min, did not change RBF or GFR, and significantly increased renin secretion (82 ± 26 to 606 ± 206 ng/min). Aortic constriction during low frequency renal nerve stimulation (0.25 Hz) resulted in similar increases in renin secretion (245 ± 130 to 691 ± 298 ng/min). In 10 dogs with innervated and contralateral dener-vated filtering kidneys, aortic constriction reduced renal arterial pressure from 131 to 99 mm Hg without changing RBF or GFR and equally decreasing U_NaV in innervated and dener-vated kidneys. Renin secretion increased significantly more (P < 0.05) from innervated (1363 ± 669 ng/min) than from denervated kidneys (647 ± 399 ng/min). These results support the view that the prevailing nerve activity which passes to the kidney during aortic constriction exceeds 0.25 Hz of electrical nerve stimulation and is sufficient to augment the renin secretion response to aortic constriction when RBF and GFR are autoregulated.