Acute and chronic effects of progesterone and prolactin on renal function in the rat.

The renal effects of acute and chronic progesterone and prolactin administration were investigated in rats. Acute progesterone treatment caused a reduced urinary potassium excretion compared to controls (0.80 +/- 0.03 vs. 1.30 +/- 0.04 mumole min-1; P less than 0.01). No other renal changes were apparent. Acute prolactin administration produced no significant changes in renal function. Chronic progesterone treatment reduced urinary potassium output by increasing tubular reabsorption. Absolute reabsorption (mumole min-1) for controls was 4.70 +/- 0.42 and for progesterone treatment, 6.40 +/- 0.57 (P less than 0.05 comparing the two). No other renal changes were apparent. Animals made pseudopregnant by chronic prolactin administration showed a significant (16%) elevation in glomerular filtration rate, similarly enhanced fluid and solute reabsorption, and a significant (16%) increase in proximal tubule length. This would imply a role for prolactin in early rat pregnancy and pseudopregnancy when similar renal changes are evident and circulating hormone levels high.