Effect of amino acid infusion as an index of renal vasodilatory capacity in pregnant rats.

Experiments were performed in midterm pregnant and virgin Munich-Wistar rats to investigate how the chronically vasodilated kidney of a gravid animal would respond to a further acute vasodilatory stimulus, in the form of a 90-min intravenous infusion of the amino acid glycine (at 0.167 mmol.kg-1.min-1). In young adult midterm pregnant rats studied in the base-line state, glomerular filtration rate (GFR), single-nephron GFR, renal plasma flow (RPF), and glomerular plasma flow were significantly greater (by approximately 30%) than in virgins due to a gestational renal vasodilation. Despite the underlying chronic renal vasodilation of pregnancy, the kidney of the gravid rat displays a marked further renal vasodilation (with consequent further increases in GFR and RPF) in response to acute glycine loading; the percent increase in GFR and RPF was similar to that seen in the relatively vasoconstricted virgin. This ability to further acutely increase the GFR in the pregnant rat was not limited to animals maintained on a normal protein diet but was also seen in older pregnant rats subjected to the additional chronic vasodilatory stimulus of long-term high-protein feeding, although in these older animals the gestational vasodilation was blunted.