Carotid baroreflex regulation of plasma renin levels.

The influence of carotid sinus pressure (CSP) on plasma renin activity (PRA) was studied in vagotomized, alpha-chloralose-anesthetized salt-deprived (<1 meq Na+/day) or salt-loaded (100-125 meq Na+day) cats. Changes in renal vascular resistance were produced by varying the pressure in the isolated perfused carotid sinus while maintaining renal blood flow constant in one kidney. Renal flow-pressure determinations were made at high, medium, and low CSP. Venous blood samples were withdrawn for PRA determination by radioimmunoassay after 10 min at each CSP. Low CSP resulted in an increased renal resistance and a dramatic elevation of the PRA in both groups. High CSP also resulted in an increase in PRA (due to contralateral variable-flow kidney) accompanied by a decrease in renal vascular resistance. No difference was found between PRA during medium CSP ad initial control PRA. Propranolol blocked the increase in PRA during low CSP but had no effect on the elevated PRA during high CSP. It is concluded that low CSP produced an increase in PRA that was associated with a reflex activation of renal sympathetic nerves.