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

Abstract

1. Glomerular filtration rate (G.F.R.) and salt and water reabsorption were measured in age-matched (12- to 13-week-old) virgin rats and rats at different stages of pregnancy and infused with saline at 37.5 and 200 microliters/min. 2. G.F.R. and salt and water reabsorption were significantly higher in early pregnancy and remained at steady, high values until at least mid-pregnancy. G.F.R. was slightly lower close to term, but sodium and water reabsorption remained significantly enhanced. 3. Significant expansion of extracellular fluid volume (e.c.f.v) was first apparent during mid-pregnancy, indicating that e.c.f.v. expansion could not be directly responsible for the early increase in G.F.R. 4. Proximal tubules were significantly elongated 5- 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.