Effects of saline and albumin on plasma and urinary catecholamines in dogs

Volume expansion by infusion of saline and 25% albumin has been compared in dogs to differentiate volume- and salt-induced catecholamine changes previously observed in humans. Plasma and urinary norepinephrine (NE) and epinephrine (E) decreased following both saline (urinary) NE+E, from 17.3 +/- 3.4 to 6.8 +/- 1.5 ng/min; P less than 0.005) and albumin (from 29.9 +/- 3.4 to 12.5 +/- 2; P less than 0.001) infusion. Urinary dopamine increased in saline-expanded dogs (from 3.4 +/- 0.6 to 4.4 +/- 0.8 ng/min, P less than 0.05), but did not significantly change in control and albumin-expanded dogs; whereas plasma free dopamine remained uninfluenced by saline or albumin. The mean renal clearance of dopamine more than doubled (from 110 +/- 37 to 272 +/- 96 ml/min; P less than 0.05) in response to saline expansion, but did not significantly change in response to albumin expansion or in control animals. A significant correlation between the increase of urinary dopamine and the tubular rejection fraction of sodium was found in saline-expanded dogs (P less than 0.05), or when all experiments (saline, albumin expansion, and control dogs) were considered together (P less than 0.001). The data indicate that : 1) the increase in urinary dopamine excretion (concomitant with sodium excretion) is related to the saline infusion rather than to the suppression of the sympathetic nervous system induced by plasma volume expansion; 2) this increased urinary dopamine originates probably in the kidney. Dopamine may thus be somehow related to regulation of urinary sodium excretion, either as an endogenous natriuretic factor or a response reflecting natriuresis.