[Dopamine hydro-natriuresis. - II) Interactions of dopamine and expansion of extracellular liquid volume].

We have observed that in the presence of salt retention (DOCA pretreatment) dopamine (DA) promoted a hydro-natriuretic effect; in contrast in salt depletion (natriuretic pretreatment) the changes in sodium tubular reabsorption and in urinary flow were non significant. The present study was designed to identify the possible mechanisms underlying the hydro-natriuretic effect. DA was infused at a subpressor rate (0,1 microgram/kg . min) during induced hypotonic polyuria. 19 healthy human subjects at different degree of salt retention were studied. The results demonstrate that the tubular inhibitory effects produced by DA on the % sodium reabsorptions (total as % of sodium filtered load, anisosmotic as % of sodium distal load) are the higher the lower are the control values of these reabsorptions. Hence DA appears to act by enhancing the inhibitory tubular response elicited by salt retention. Moreover these inhibitory effects are positively related with the simultaneous DA-induced haemodynamic effects. This suggests that the decrease in sodium reabsorptions during DA infusion is haemodynamically mediated.