Regulation of Aldosterone in the Guinea‐pig — Effect of Oestrus Cycle, Pregnancy and Sodium Status

Abstract

Summary. 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, 37-9, ± 15-9 ng/100 ml {x ± SD), and cortisol, 31-8 ± 10-1 ng/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 ng/100 ml). There was no sex difference in corticosterone concentration; females, 0-25 ± 0-06 ttg/100 ml and males, 0-23 ± 0-10 Mg/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 versus 37-9 ± 15-9 ng/100 ml, p < 0-05). Values at day 20 (33-2 ± 11-7 ng/100 ml) and day 60 of gestation (51-9 i 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.

Ascorbate depletion prevents aldosterone stimulation by sodium deficiency in the guinea pig

“…inner mitochondrial membranes in adreno¬ cortical cells) cannot be excluded, our results do not support the idea of an indirect protection against oxygen radical species by vitamin C via the regenera¬ tion of vitamin E. Plasma concentrations of cortisol and aldosterone in our control animals are high compared to other species. This species difference has been reported before (24)(25)(26) and may be explained in part by a low affinity of the glucocorticoid receptor to cortisol. The affinity of the guinea pig mineralocorticoid receptor (type 1) to aldosterone is the same as in the rat and may not explain high aldosterone plasma concentrations in this species (27).…”

Role of Testosterone in the Sexual Dimorphism of Adrenal Activity at Puberty in the Guinea-Pig

“…Indeed Diamond et al (1969) have found higher plasma cortisol levels in adult females than in male guinea-pigs and they have described how plasma cortisol levels in adult females reach their highest level just at the time of oestrus and decrease after testosterone treatment. However, Whipp, Wintour, Coghlan & Scoggins (1976) found no variations of plasma cortisol levels during the oestrous cycle.…”

Evidence for isoforms of 11β-hydroxysteroid dehydrogenase in the liver and kidney of the guinea pig

“…The MC receptor of the guinea pig, however, shows no difference from that of other species (Myles & Funder 1994). Since free plasma cortisol levels are much higher in the guinea pig than in the human, while plasma aldosterone is in the same range in both species (Whipp et al 1976), it seems reasonable to assume that a highly efficient mechanism exists to exclude cortisol from the MC receptors in the guinea pig. One of these mechanisms could be 11 ß-HSD-II with a high activity in MC target tissues (Keightley & Fuller 1996), as in the human.…”