[Sympathomimetic component of dopamine renal action in water-saline depletion]

In 20 healthy subjects hydro-saline depletion was achieved by a 4-day natriuretic treatment associated with hypo-saline diet. Dopamine (DA) was infused in subpressor dose (.1 microgram . kg-1 . min-1) during sustained hypotonic polyuria induced by 5% glucose infusion. Four 15-min clearance periods were performed. DA was infused during the 2nd and the 3rd period. The effective renal plasma flow (RPF) as well as the glomerular filtration rate (GFR) were calculated by PAH and creatinine clearances, respectively. In our experimental conditions DA produced: a) an increase in the abnormally isoosmotic sodium reabsorption as % of sodium distal load; b) a decrease in both sodium and osmolar clearance; c) an early increase in free water clearance. RPF and GFR decreased not significantly. The present results indicate that DA in hydro-saline depletion helps to preserve the extracellular fluid volume in minimizing the salt and water loss associated with hypotonic polyuria. These effects on sodium excretion may be related to sympathomimetic properties acquired by DA in this experimental condition.