[Dopamine as a regulator of natriuresis. Experimental bases and their implications].

Renal effects of dopamine (DA) infused i.v. in a subpressor dose (0.1 microgram. kg.-1 min-1) were investigated in healthy human subjects during steady hypotonic polyuria. In each experiment four clearance (cl.) periods of 15 min were performed; DA was administered during the second and the third cl. periods. The glomerular filtration rate and renal effective plasma flow were estimated as endogenous creatinine and PAH clearances. Moreover the following variables were evaluated: a) sodium total and sodium isosmotic reabsorption as a % of sodium filtered load (s.f.l.); b) sodium anisosmotic reabsorption as a % of sodium distal load (s.d.l.); c) total renal vascular resistance (RT), arteriolar afferent (RA) and efferent (RE) resistances. Three groups of experiments were performed: A) in hydro-saline retention by DOCA pretreatment (24 subjects); B) in hydro-saline depletion by natriuretic pretreatment (20 subjects); C) in hydro-saline depletion and beta-adrenergic blockade induced by natriuretic and propranolol pretreatments (9 subjects). In A experimental condition DA significantly increased renal plasma flow, glomerular filtration rate, urinary flow, urine sodium concentration and osmolarity; on the contrary DA significantly decreased RT, RA, sodium total and isosmotic reabsorption, % of s.f.l., and sodium anisosmotic reabsorption, % of s.d.l. In B condition no significant changes were observed during DA infusion in either haemodynamic parameters or urinary flow; on the other hand DA significantly blunted urinary osmolarity, urinary sodium concentration and sodium excretion rate suggesting an increased sodium anisosmotic reabsorption (% of s.d.l.). In C condition the vasodilating and hydrosaluretic effects of DA were restored. Our results suggest that DA activates, besides "dopaminic" vascular receptors, the presynaptic facilitory beta-adrenergic receptors in renal adrenergic pathways. Thus the renal action of DA depends on renal adrenergic activity.