Effect of plasma amino acid and hormone concentrations on renal plasma flow and glomerular filtration rate.

The effect of amino acid infusion on renal hemodynamics was examined in 13 healthy subjects. Seven subjects participated in the first experimental protocol: study 1 - amino acids were infused for 3 h to increase plasma amino acid levels 2- to 3-fold above baseline; study 2 - amino acids were infused with somatostatin and peripheral replacement of insulin, glucagon and growth hormone; and study 3 - somatostatin and hormones were infused as in study 2, but no amino acids were infused. During study 1 both glomerular filtration rate (GFR) and renal plasma flow (RPF) increased by 20%. In contrast, when amino acids were infused with somatostatin (study 2), neither GFR nor RPF changed from baseline. In study 3, somatostatin alone had no effect on GFR and RPF. In a second experimental protocol, 6 subjects were maintained for 7 days on a low protein diet (40 g/day); amino acids were infused as in study 1 before and after the protein restriction. Baseline GFR and RPF both decreased significantly after protein restriction. The response to amino acid infusion was not changed. These results indicate that: (1) hyperaminoacidemia causes a rise in both GFR and RPF; (2) the increase is likely to be mediated by some hormones whose secretion is inhibited by somatostatin, and (3) protein restriction causes a decline in GFR and RPF but fails to alter the renal hemodynamic response to amino acid infusion.