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

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Abstract
1. Glomerular filtration rate ([3H]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 [14C]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 [14C]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 [14C]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.