Effect of two regimens of intravenous amino acid infusion on renal haemodynamics, renal tubular function and sodium and water homeostatic hormones in healthy humans

The effect of two different regimens of intravenous infusion of amino acids on glomerular filtration rate (GFR), renal plasma flow (RPF), tubular sodium and water handling judged from the clearance of lithium (CLi), and plasma concentrations of angiotensin II (Ang II), aldosterone (Aldo), arginine vasopressin (AVP), atrial natriuretic peptide (ANP), growth hormone (GH), and glucagon was investigated in healthy humans. In the first protocol (n = 11) the infusion lasted 90 min; both GFR and RPF increased significantly (median increase 7.1% and 9.1% respectively, P less than 0.05 both). In the second protocol (n = 13) the infusion lasted 30 min; both GFR and RPF tended to increase (median increase 3.5% and 7.4%) but the change did not reach significance. The changes in tubular sodium and water handling were similar in the two protocols. Absolute reabsorption rates in the proximal tubules were unaltered, resulting in an increased output into the distal tubules that was totally compensated for by an increased distal reabsorption. Thus no changes in urinary excretion of sodium and water were observed. Ang II, Aldo, AVP, ANP and GH were unchanged by amino acid infusion, but glucagon increased. It is suggested that the alterations in renal haemodynamics and distal tubular reabsorption may be mediated by glucagon.