Potassium regulation and progesterone-aldosterone interrelationships in human pregnancy: a prospective study.

Little is known about the intrinsic renal and hormonal regulation of potassium excretion in pregnancy despite major alterations in many of the potassium regulatory factors. Forty primigravid women on an unrestricted diet were studied during the second and third trimesters and exhibited constant absolute and fractional potassium excretion despite a significant increase in plasma aldosterone concentration between these stages. The plasma progesterone level rose significantly between studies but closer analysis showed no correlation between individual changes in plasma aldosterone concentration and progesterone between trimesters. In the 14 subjects studied post partum, baseline absolute potassium excretion was not significantly altered but filtered potassium fell and fractional potassium excretion tended to rise. After dietary sodium manipulation at these stages, absolute potassium excretion, fractional potassium excretion, and progesterone were unaltered despite significant changes in plasma aldosterone concentration and sodium excretion. These results suggest that potassium excretion is held constant throughout pregnancy and that renal tubular potassium reabsorption adjusts appropriately to the increased filtered potassium load. Progesterone does not appear to be involved in the acute regulation of potassium or sodium excretion but may have effects on sodium and potassium excretion that are constant, proportional to its placental production, and unresponsive to endogenous changes in mineralocorticoid production.