REGULATION OF ALDOSTERONE IN THE GUINEA‐PIG — EFFECT OF OESTRUS CYCLE, PREGNANCY AND SODIUM STATUS

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Abstract
The blood concentrations of aldosterone, corticosterone and cortisol were measured in conscious, non-stressed guinea-pigs using a double isotope dilution derivative assay procedure. Aldosterone levels in the guinea-pig were high when compared with those of other species. The concentration of aldosterone, 379. 159 ng/100 ml ( SD), and cortisol, 318 101 g/100 ml, found in non-pregnant females on a moderate sodium intake was significantly greater than in males (aldosterone 222 24 ng/100 ml and cortisol 193 57 g/100 ml). There was no sex difference in corticosterone concentration; females, 025 006 g/100 ml and males, 023 010 g/100 ml. The oestrus cycle had no effect on levels of the three steroids measured. Two thirds of the way through the 68-day gestation period aldosterone levels were significantly elevated compared with non-pregnant values (687 509 ng/100 ml versus 379 159 ng/100 ml, p < 005). Values at day 20 (332 117 ng/100 ml) and day 60 of gestation (519 217 ng/100 ml) were similar to those of non-pregnant animals. Cortisol and corticosterone levels were significantly elevated at 20 days gestation and they continued to rise until, at day 60, cortisol was 9 times and corticosterone 4 times higher than the non-pregnant values. Compared with a moderate Na intake, salt loading suppressed aldosterone levels and Na restriction raised them.

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