Pituitary-adrenal function in pseudopregnant rats.

Pseudopregnancy inhibited plasma corticosterone response to stress. The production of corticosterone by adrenal slices in vitro was also discussed; no changes in adrenal 5 alpha-reductase activity were observed. Secretion of corticosterone in the adrenal venous blood was decreased as well, without changes in dehydrocorticosterone or tetrahydrocorticosterone secretion rates. Treatment with ACTH increased the secretion rates of corticosterone to the range observed in control rats. Steady state secretion and metabolism of corticosterone was unchanged. The data indicate that the diminished responses in plasma concentrations, in vitro production, and secretion rates of corticosterone obtained in pseudopregnant rats after stress, are secondary to changes on the release of ACTH from the pituitary gland rather than to adrenal steroid secretion per se or handling of corticosterone by the liver. The expected rise in plasma prolactin observed in cycling rats after stress was absent in pseudopregnant rats. The data suggest that an inhibition of the prolactin release mechanisms similar to that observed with the release of ACTH may have occurred after stress. The dynamics involved in the changes affecting the release of pituitary hormones in pseudopregnant rats are still unclear.

Postnatal endocrine dysfunction resulting from prenatal exposure to carbofuran, diazinon or chlordane.

Prenatal exposure to pesticides of three different classes initiated persistent postnatal endocrine dysfunction. Adrenal function and hepatic metabolism of corticosterone were studied in adult hybrid mice exposed during development to either an organophosphate (Diazinon), a carbamate (Carbofuran), or an organochlorine (Chlordane). Animals were exposed to relatively low levels of the toxins in utero and neonatally via the mothers' milk. Exposure to lower doses of the anticholinesterase compounds, Diazinon or Carbofuran, resulted in impairment of hepatic metabolism of corticosterone in vitro due to a loss in reductive capacity per unit liver weight. Plasma levels of corticosterone were also elevated in these animals, but without a concomitant increase in adrenal steroidogenesis in vitro. The effects of exposure to Chlordane were more complex. In male animals, exposure to lower doses of chlordane resulted in an increase in plasma corticosterone levels without an apparent increase in hepatic metabolism of corticosterone or adrenal steroidogenesis. In contrast, side-chain metabolism of corticosterone was decreased in female mice exposed to Chlordane. Similar effects on pituitary-adrenal function were not evident for the offspring of mice exposed to higher doses of the toxins. Possible mechanisms for this non-linear dose-response are discussed.

Postnatal endocrine dysfunction induced by prenatal methylmercury or cadmium exposure in mice.

The subtle and delayed effects of two heavy metals, cadmium and mercury, on the pituitary-adrenal axis of mice were examined. Exeprimental animals were exposed to the toxins both in utero and neonatally via treated mothers' milk. Plasma levels of corticosterone, adrenal production of corticosterone in vitro, and the capacity of the liver to metabolize corticosterone in vitro were studied in these animals as adults. Exposure to methylmercury resulted in diminished hepatic metabolism of corticosterone in vitro due to a loss of liver mass. Adrenal function and plasma levels of corticosterone were unaffected by treatment. Cadmium-exposed animals examined at 277 days of age showed no significant differences when compared to untreated controls. However, when studied at 460-480 days of age, a sex difference in the response to cadmium exposure was noted. In males, the major effect was enhancement of hepatic reductive capacity, while in females, adrenal secretory capacity was enhanced. Possible mechanisms of action and consequences of these effects are discussed.

Estimation of pregnenolone synthesis in rat adrenal homogenates: some cofactor requirements: effects of stress, hypophysectomy, cortisone and ACTH.

Pregnenolone synthesis was estimated in whole adrenal homogenates incubated in the presence of cyanoketone (2alpha-cyano-4,4,17alpha-trimethyl-androst-5-en-17beta-ol-3-one). The yield of pregnenolone depended on the type of incubation medium employed. Both Ca++ and bovine serum albumin (BSA) markedly stimulated the rate of pregnenolone synthesis as did NADPH or NADPH generating system. Aminoglutethimide added in vitro inhibited cholesterol sidechain cleavage activity. Ether stress in vivo stimulated pregnenolone synthesis in vitro, and hypophysectomy of 24 hours duration resulted in a decrease. Cortisone administration for 8 days reduced the formation of pregnenolone by rat adrenal homogenates, an effect prevented by concomitant treatment with ACTH. Similarly, hypophysectomy of 8 days duration resulted in a marked diminution of pregnenolone synthesis and ACTH replacement reversed this effect. Changes in pregnenolone synthesis were paralleled by changes in corticosterone and total steroid production.

Effects of melatonin and an aqueous pineal extract on adrenal secretion of reduced steroid metabolites in female rats.

The effects of melatonin and an aqueous extract of bovine pineal glands on adrenal function were studied in pinealectomized, ovariectomized and hypophysectomized rats. Melatonin (50 microgram i.p., twice daily for 1 week) stimulates adrenal 5 alpha-reductase activity in intact animals and after ovariectomy. A corresponding enhancement in the secretion of the principal 5 alpha-reduced metabolites of corticosterone (B), dihydrocorticosterone (DHB) and tetrahydrocorticosterone (THB), occurs in vivo. As a result, proportional output of B declines. In contrast, an aqueous pineal extract (360 mg bovine pineal tissue/day for 1 week) fails to alter reductase activity or to produce the secretory changes associated with increased reductive metabolism of B. Melatonin also stimulates adrenal reductase activity in hypophysectomized rats. The results suggest that melatonin is a potential contributor to the physiologic regulation of adrenal steroidogenesis.

Effects of pinealectomy on adrenal function in vivo and in vitro in female rats.

Female rats were ovariectomized and either sham-pinealectomized or pinealectomized on day 24 of age and exposed to a photoperiod of 12 h light: 12 h dark. In vivo and in vitro measures of adrenocortical function were made at 6, 7, and 8 weeks of age (18, 25, and 32 days post-pinealectomy, respectively). Pinealectomy diminished the post-castration rise in adrenal 5alpha-reductase activity in all age groups (P less than .05). The proportionate secretion of corticosterone (compared with the total steroid output) by adrenal slices was likewise enhanced (P less than .05) although the secretion and production of corticosterone in vitro was not altered. Pinealectomy substantially diminished (P less than .05) the in vivo secretion rates of reduced metabolites of corticosterone (dihydrocorticosterone and tetrahydrocorticosterone) without altering corticosterone secretion. Consequently, proportionate secretion of corticosterone in vivo was also enhanced (P less than .05). These findings are consistent with the notion that in ovariectomized rats removal of the pineal gland diminishes adrenal 5alpha-reductase activity without affecting ACTH secretion. However, in rats with ovaries intact, estrogen modified the effects of pinealectomy. Not only was the intra-adrenal metabolism of corticosterone diminished (higher proportionate output), but also resting levels of plasma corticosterone (P less than .01), corticosterone production in vitro (P less than .05), and total adrenal steroidogenesis in vitro (P less than .01) were increased. Thus, ACTH secretion may be enhanced following pineal removal in the presence of estrogen. The data suggest that the pineal gland, together with the ovaries, plays a role in the modulation of adrenal steroidogenesis.

Role of adrenal 5alpha-reductase activity in determining the responsiveness of hypophysectomized rats to ACTH.

Studies were conducted to examine the contribution of adrenal 5alpha-reductase to the phenomenon of diminished adrenal "responsiveness" to ACTH after hypophysectomy in rats. Rats hypophysectomized for 1 week secreted small amounts of corticosterone (B), 5alpha-dihydrocorticosterone (DHB) and 3beta,5alpha-tetrahydrocorticosterone (R) acutely after ACTH. Adrenal reductase activity in vitro at that time was high. After replacement with ACTH for 24 h, B,DBH, and R secretion increased slightly. Reductase activity remained high. Treatment with ACTH for 2 days further stimulated secretion of DHB and R but not B. Reductase activity was unaffected. Enzyme activity declined at 3 days concomitant with a proportionately greater increase in B than DHB and R secretion. Only after 7 days of ACTH did B secretion exceed DHB and R output. At that time, reductase activity was still lower. The results establish the functional significance of 5alpha-reductase activity as a regulatory site for the action of ACTH in determining the composition of adrenocortical secretory products in hypophysectomized rats.