AJP - Regulatory, Integrative and Comparative Physiology, Vol 269, Issue 4 888-R895, Copyright © 1995 by American Physiological Society
Effect of oral protein loading on renal hemodynamics in human pregnancy
W. M. Barron and M. D. Lindheimer
Department of Obstetrics and Gynecology, University of Chicago, Illinois 60607, USA.
Glomerular filtration rate (GFR) and ERPF increase approximately 50% in
human pregnancy. To determine if pregnant women have additional "renal
reserve," inulin and p-aminohippurate clearances (Cin, CPAH) were measured
in maximally hydrated women before and after a 300-g steak meal, once
during late gestation, and again > or = 3 mo postpartum. Protein loading
increased Cin [106 +/- 5 (SE) to 119 +/- 4 ml/min, P < 0.003], but not
CPAH (587 +/- 35 to 624 +/- 32 ml/min, NS) in the nonpregnant state, but
neither clearance was altered during gestation (Cin: 156 +/- 7 to 160 +/-
9.6 ml/min, NS; CPAH: 831 +/- 36 to 899 +/- 37 ml/min, NS). A natriuresis
occurred only postpartum (+142 mu eq/min, P < 0.02), which could be
explained by the increased GFR alone, since indexes of filtrate delivery
and reabsorption (V/GFR, CH2O/GFR, CH2O/V) and fractional sodium excretion
changed little. Dopamine excretion, uninfluenced by protein, did not
correlate with increments in GFR. A carbohydrate meal (time controls) had
no effect on the above described parameters. We make the following
conclusions. If protein and pregnancy achieve hyperfiltration by similar
mechanisms, these pathways appear "exhausted" in gestation. Also, oral
protein loading does not measure maximal renal reserve, since basal GFR in
late gestation was substantially greater than that measured after protein
feeding in nonpregnant subjects.
