EFFECTS ON RENAL HEMODYNAMIC AND SEGMENTA L RENAL HANDLING OF SODIUM BY AMINO-ACIDS ADMINISTRATION - DIFFERENCES BETWEEN NITRIC-OXIDE SYNTHESIS PRECURSORS AND NON PRECURSORS

intravenous amino acid infusion has been reported to produce an increa se oi glomerular filtration (GF) and plasma renal flow (PRF). Experime ntally, the nitric oxide (NO) agonists induce renal effects similar to that of amino acid. In this study we tested the hypothesis that renal effects of amino acids require the presence oi L-arginine, a precurso r of NO synthesis. To this end, we compared the renal and hormonal res ponses to intravenous administration of two isomolar essential amino a cid solutions, one without L-arginine (EA) and another with L-arginine (EA + L-ARG) in seven healthy subjects. Renal production of Na was as sessed by radioimmunoassay of urinary excretion of cGMP. The blood ami no acid levels increased after the two solutions (EA + L-ARG: 1,946 +/ - 201 vs 1,655 +/- 114 mu mol/l, p < O.05; EA: 2,550 +/- 448 vs 1,879 +/- 270 mu mol/l, p < 0.071 whereas the blood L-arginine levels only i ncreased after L-arginine infusion (109 +/- 8 vs 82 +/- 9 mu mol/l, p < 0.05), the amount of aminoacid filtered increased during EA+L-ARG (2 35 +/- 24 vs 175 +/- 25 mu mol/l/min/1.73 m(2), p < 0.01) and EA (307 +/- 61 vs 197 +/- 34 mu mol/min/1.73 m(2), p < 0.07) but their tubular reabsortion increases too, so no significant urinary amino acid excre tion changes were observed after any of two solutions (EA + L-ARG 12 /- 4 vs 10 +/- 3 mu mol/min; EA 17 +/- 5 vs 75 +/- 4 mu mol/min). No c hanges in RPF were observed either after EA + L-ARG or EA. Both amino acid solutions induced a significant increase in GF (EA + L-ARG 121 +/ - 6 vs 103 +/- 6 ml/min/1.73 m(2), p < 0.05; EA 118 +/- 6 vs 102 +/- 6 ml/min/1.763 m(2), p < 0.05) when compared with values obtained in 5 control subjects treated with saline solution. This effect was higher and earlier after EA + L-ARG administration. Natriuresis increased sig nificantly during EA + L-ARG (356 +/- 42 vs 244 +/- 34 mu mol/min, p < 0.01) and EA (373 +/- 50 vs 313 +/- 43 mu mol/min/ p < 0.05). The EA + L-ARG infusion induced a significant increase in sodium fractional e xcretion (2.1 +/- 0.3 vs 1.7 +/- 0.3%, p < 0.01) and a significant dec rease in fractional distal sodium reabsortion (93.3 +/- 0.9 vs 94.5 +/ - 0.9%, p < 0.05) as studied by lithium clearance. The blood levels of insulin, dopamine, growth hormone, glucagon, atrial natriuretic facto r and urinary excretion of cGMP and PGF2 alpha were not significantly affected by EA + L-ARG nor EA. Plasma renin activity and plasma aldost erone decreased after EA + L-ARG infusion. These results indicate that intravenous administration of an isomolar essential amino acid soluti on induces, by unknown mechanisms, an increase of glomerular filtratio n not related to volume expansion. This effect is greater when the ami no acid solution contains L-arginine. L-arginine administration produc es an additional natriuretic renal response through tubular mechanisms .