RENAL RESPONSES TO AMINO-ACIDS IN THE SHEEP FETUS

Adult animals and humans are known to increase renal blood flow and gl omerular filtration rate (GFR) in response to an acute protein load or amino acid infusion; however, the ontogeny of this phenomenon is not known. This study was designed to test the hypothesis that, despite no rmally high baseline amino acid levels in the fetus, increases in plas ma amino acids stimulate increases in GFR before birth. Eight chronica lly instrumented fetal sheep (126 +/- 1 days gestation) were infused w ith a mixture of amino acids (0.15 and 0.30 mmol . kg(-1). min(-1) iv) . Plasma alpha-amino nitrogen levels increased significantly from 7.1 +/- 0.3 to 13.0 +/- 0.9 and 25.5 +/- 2.1 mg/dl, respectively, in respo nse to the two doses, and GFR increased significantly from 3.2 +/- 0.4 to 4.0 +/- 0.5 and 4.6 +/- 0.5 ml/min, respectively. Arterial pressur e did not change. Renal amino acid reabsorption was significantly incr eased at all time points during the amino acid infusion, reaching a va lue nearly five times that of control by the last clearance period. Na + reabsorption was also increased throughout the infusion. Na+, K+, an d Cl- excretions increased significantly only at the very last time po int. These data indicate that the mechanism or mechanisms responsible for amino acid-induced hyperfiltration are present and functional even before birth in the sheep. Because maternal eating patterns and prote in intake are known to change maternal plasma amino acid levels and am ino acids are actively transported across the placenta, our findings s uggest that both acute and chronic changes in maternal protein intake may alter fetal renal function.