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

1. Glomerular filtration rate (G.F.R.) and salt and water reabsorption were measured in age-matched virgin rats and rats at different stages of pseudopregnancy and post-pseudopregnancy. 2. Tubular reabsorption and G.F.R. were significantly higher in later pseudopregnancy. Values at mid-pseudopregnancy were intermediate between virgin controls and late-pseudopregnancy. In post-pseudopregnancy G.F.R. and reabsorption had returned to values not different from the virgins. 3. Expansion of extracellular fluid volume (e.c.f.v.) and elongation of proximal tubules were observed during pseudopregnancy. In post-pseudopregnancy increased tubular length was still apparent but e.c.f.v. was not. 4. The remarkable similarity in the changes in e.c.f.v. and renal functions and structure during pseudopregnancy to those in early pregnancy suggests that the feto-placental unit is not necessary for the pregnancy changes. 5. The differences between the time course of change in plasma progesterone and the time courses of changes in e.c.f.v., renal functions and tubular morphology in late pseudopregnancy suggest that progesterone is not directly involved.