REGULATION OF ALDOSTERONE IN THE RAT EFFECT OF OESTROUS CYCLE, PREGNANCY, AND SODIUM STATUS

Abstract

Summary Whole blood concentrations of aldosterone and corticosterone were measured in female rats on a moderate sodium diet (1‐2 mmol/day) during diestrus, proestrus, oestrus and on days 4, 12, 18 of pregnancy. At diestrus, the aldosterone (5·6 ± 4·9 ng/100 ml., n = 4) and corticosterone (10·4 ± 10·7 μg/100 ml, n = 4) concentrations were significantly lower (P < 0·01) than at oestrus when aldosterone and corticosterone concentrations were respectively 15·2 ± 7·8 ng/100 ml (n = 6) and 27·2 ± 12·2 μg/100 ml (n = 6). The blood aldosterone concentration of day‐12 pregnant rats, 33·9 ± 7·8 ng/100 ml (n = 8), was significantly higher than the values at oestrus and remained elevated at day 18. (Parturition occurs at day 21‐22.) Corticosterone values were not elevated during pregnancy, compared to values at oestrus. Sodium loading (7‐8 m mol/day) did not suppress blood aldosterone concentrations in non‐pregnant rats, but did significantly (P < 0·05) suppress values in the 18‐20 day pregnant rat. Plasma renin concentration (PRC), plasma renin substrate (PRS) and derived plasma renin activity (PRA) did not vary significantly during the oestrous cycle, being respectively (18·3 ± 10·7) × 10 ‐5 Goldblatt Units/ml, 0·416 ± 0·199 μg/ml, and 5·0 ± 2·6 ng/ml/h in 21 samples. PRC increased significantly by day 11 of gestation, while PRS decreased significantly at day 11 (P < 0·05) and even further by days 18‐20 (P < 0·001). The derived PRA was elevated only in 11‐14 day pregnant rats (P < 0.05). It is concluded that factors other than renin are responsible for the increase in aldosterone in pregnancy.