Glomerular filtration rate and salt and water reabsorption during pregnancy in the conscious rat.

1. Glomerular filtration rate (g.f.r.) and salt and water reabsorption were measured in age-matched conscious virgin rats and rats at different stages of pregnancy that were infused with saline at 40 and 200 microliters min-1. 2. G.f.r. and salt and water reabsorption were significantly higher at all stages of pregnancy irrespective of the the rate of infusion. 3. The similarity in both time course and magnitude, of changes in renal function between conscious and anaesthetized rats at the two infusion rates suggests that the detection of differences in the anaesthetized rat during pregnancy is not dependent on either the anaesthetic/surgery employed or the rate of expansion of the extracellular fluid volume. 4. During the induction of the diuresis in 20-day pregnant rats infused at 40 microliters min-1 urine flow was higher and osmolality lower than in virgin rats and rats at earlier stages of pregnancy, suggesting that late-pregnant rats have an altered ability for elaborating concentrated or dilute urine.