Sympathetic activation cannot fully account for increased plasma renin levels during water deprivation

This study was designed to determine if the increase in plasma renin activity (PRA) that occurs during water deprivation is mediated by the renal sympathetic nerves or adrenomedullary catecholamine release. Male Sprague-Dawley rats were studied while conscious and unrestrained. In intact or sham-operated rats, 48 h of water deprivation resulted in at least a threefold increase in PRA and plasma renin concentration (PRC) but no significant change in plasma norepinephrine or epinephrine concentration. Renal denervation decreased basal PRA, reduced the magnitude of the dehydration-induced PRA increase by 33%, and abolished the renin-suppressing effect of l-propranolol infusion in water-deprived rats. Adrenal demedullation also reduced basal and water-deprived PRA and PRC. However, even the combination of renal denervation and adrenal demedullation did not prevent a significant renin response to dehydration (control PRA of 1.8 +/- 0.6 ng.ml(-1).h(-1) to dehydration PRA of 6.8 +/- 1.3 ng.ml(-1).h(-1), P < 0.05). Therefore, some mechanism in addition to sympathoadrenomedullary activation plays a major role in mediating increased PRE during water deprivation.