The effect of pregnancy on glomerular filtration rate and salt and water reabsorption in the rat.

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Abstract
Glomerular filtration rate (GFR) and salt and H2O reabsorption were measured in age-matched (12-13 wk old) virgin rats and rats at different stages of pregnancy and infused with saline at 37.5 and 200 .mu.l/min. GFR and salt and H2O reabsorption were significantly higher in early pregnancy and remained at steady, high values until at least mid-pregnancy. GFR was slightly lower close to term, but Na and H2O reabsorption remained significantly enhanced. Significant expansion of extracellular fluid volume (ECFV) was first apparent during mid-pregnancy, indicating that ECFV expansion could not be directly responsible for the early increase in GFR. Proximal tubules were significantly elongated 5-6 days after mating until term, indicating that an increased reabsorptive area in the proximal tubule may be at least partly responsible for the increased reabsorption in pregnancy.