Role of aldosterone in sodium retention of pregnancy in the rat

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Abstract
Whether the absence or inhibition of aldosterone would alter the Na retention of pregnancy in the rat was tested. Metabolic balance studies were performed during the last 2 wk of the 3 wk rat pregnancy in the following 4 groups of saline-drinking rats: nonpregnant, sham adrenalectomized; pregnant sham adrenalectomized; nonpregnant, adrenalectomized; and pregnant adrenalectomized. Significant net Na retention was not found during the 2nd wk in any of the groups. During the final week, both pregnant groups retained between 8 and 11 meq Na more than their respective control groups. Plasma aldosterone concentration was measured in these rats at term. The mineralocorticoid was not detectable in the nonpregnant adrenalectomized rats but was present in the pregnant adrenalectomized rats at a concentration of about 50% of that found in the pregnant sham-adrenalectomized rats. Serial measurements revealed that aldosterone was measurable by day 18 and nondetectable by 2 days postpartum in these pregnant adrenalectomized rats. Comparable balance studies were also performed in 3 groups of water-drinking rats: nonpregnant, and pregnant rats that received large daily doses of spironolactone. During the 3rd wk both pregnant groups were in significant positive Na balance. Net Na retention for untreated pregnant rats was 8.4 meq and for the spironolactone treated, 6.9 meq, values that were not significantly different. It is unlikely that aldosterone plays a critical role in the Na retention found during rat pregnancy.

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