Regulation of aldosterone in the guinea-pig--effect of oestrus cycle, pregnancy and sodium status.

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, 37-7 +/- 15-9 ng/100 ml (x +/- SD), and cortisol, 31-8 +/- 10-1 mug/100 ml, found in non-pregnant females on a moderate sodium intake was significantly greater than in males (aldosterone 22-2 +/- 2-4 ng/100 ml and cortisol 19-3 +/- 5-7 mug/100 ml). There was no sex difference in corticosterone concentrations; females, 0-25 +/- 0-06 mug/100 ml and males, 0-23 +/- 0-10 mug/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 (68-7 +/- 50-9 ng/100 ml, p less than 0-05). Values at day 20 (33-2 +/- 11-7 ng/100 ml) and day 60 of gestation (51-9 +/- 21-7 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.