Changes in renal haemodynamics and kidney weight during pregnancy in the unanaesthetized rat

1. Glomerular filtration rate ([(3)H]inulin clearance) and renal plasma flow (PAH clearance) were measured in unanaesthetized Sprague-Dawley rats early in pregnancy (8-10 days) and near term (18-20 days); the results were compared with studies in virgin litter-mates. Evidence of kidney growth was sought by analysing renal dry weights as well as [(14)C]choline incorporation into membrane phospholipids of renal cortical slices.2. Inulin clearances were similar early in pregnancy (pregnant 2.36 +/- 0.12 (S.E. of mean) vs. non-pregnant 2.33 +/- 0.10 ml./min) but near term values were significantly increased (pregnant 2.80 +/- 0.05 vs. non-pregnant 2.39 +/- 0.05 ml./min, P < 0.001). PAH clearances were similar in pregnant and litter-mate control animals at each stage of the study.3. Total renal weight increased significantly both early and late in pregnancy, but renal dry weights as well as [(14)C]choline incorporation were similar in pregnant and non-pregnant animals both at 8-10 days gestation and near term.4. Data confirm our previous findings on renal haemodynamics in anaesthetized rats. Observations that renal dry weight and [(14)C]choline incorporation into phospholipids are similar in litter-mate pregnant and control animals suggests that renal enlargement in this species is due to increments in water content and not to accelerated growth.