Responses of plasma renin activity and dopamine-beta-hydroxylase to increased intravascular volume

Circadian variations of plasma renin activity, plasma dopamine-beta-hydroxylase, and urinary aldosterone excretion were measured in man under conditions of high- and low-sodium intake. Plasma renin activity and urinary aldosterone excretion were maximal at 8 a.m. Plasma DBH shows small, biologically insignificant circadian fluctuations. In three subjects on low-salt diets, the values were lower than those in the same subjects on high-salt diets. Expansion of intravascular volume in supine normal volunteers lowered plasma renin and DBH activity, and also resulted in a significant natriuresis. The decline in DBH activity probably reflects a decrease in its release from autonomic nerve endings and thus demonstrates in man an effect of decreasing autonomic activity.