Effects of aminoglutethimide, metyrapone, and ascorbic acid on testicular metabolism of cholesterol

Testosterone production in mature scorbutic mutant rats unable to synthesize ascorbic acid

The effect of a deficiency of ascorbic acid (AsA) on in-vivo testosterone production in mature male rats was investigated using a mutant strain of rats (ODS rats) unable to synthesize AsA. Male 60-day-old rats were fed AsA-deficient lab chow for 28 days with [ODS(+)] or without [ODS(-)] AsA supply. The AsA levels in the liver of ODS(-) rats were undetectable and those in the testes decreased to about 25% of those in ODS(+) rats by day 28. Plasma LH levels in ODS(-) rats decreased to about 30% of those in ODS(+) rats by day 28. However, there were no significant differences in the plasma levels of testosterone, or in the relative weights of seminal vesicles and ventral prostates between ODS(+) and ODS(-) rats. Plasma levels of testosterone in ODS(-) rats after a single injection of 200 IU hCG changed similarly to that in ODS(+) rats. The metabolic clearance rate of testosterone was also the same at 60 min after an intravenous injection of [3H]testosterone in both groups. These results indicate that AsA-deficiency in adult rats causes no significant change in basal plasma levels of testosterone or in the response to hCG, despite decreased plasma LH levels.

Superoxide dismutase as a regulatory switch in mammalian testicular steroidogenesis

The delta 4-pathway of testosterone biosynthesis in leydig cells, widely believed to proceed through pregnenolone--greater than pregnenedione--greater than progesterone route catalyzed by 5 delta-3 beta-hydroxysteroid dehydrogenase and delta 5-delta 4-isomerase respectively is shown to pass through an alternate pathway mediated by superoxide dismutase and peroxidase. A built-in regulatory switch is incorporated in this route, with the superoxide dismutase inducible upon LH-stimulation of the leydig cells.

Biosynthesis of androgens by pheochromocytomas

Homogenates from four adrenal pheochromocytomas converted 4-14C-labeled pregnenolone, 17-hydroxyprogesterone, and dehydroepiandrosterone into androstenedione and testosterone. In addition to these androgens, labeled pregnane substrates were also transformed into corticosteroids, as previously reported, and this conversion occurred in even higher yield. The formation of labeled metabolites of either pathway was greater in homogenates from intraadrenal pheochromocytomas than in those derived from an extraadrenal tumor, but less than in preparations of hyperplastic adrenal cortex. Incubations of subcellular fractions isolated from an adrenal pheochromocytoma showed that the enzyme activities involved in androgen formation from the radioactive substrates studied were associated with the microsomes and required exogenous cofactors. In contrast to adrenocortical tissue, chromaffin cell preparations uniformly failed to convert substrate [4-14C] cholesterol into either androgens or corticosteroids. The data available demonstrate the presence in chromaffin tissue of all of the enzyme activities required for the biosynthesis of androgens and corticosteroids except for those involved in the side-chain scission of cholesterol.

Effect of adrenocorticotropin and dietary ascorbic acid on cutaneous basophil hypersensitivity to phytohemagglutinin in chickens

Two trials were conducted to assess the effects of adrenocorticotropin (ACTH) and dietary ascorbic acid (AA) on cutaneous basophil hypersensitivity (CBH) to phytohemagglutinin (PHA-P) in chickens. Broiler chicks received AA at levels of 0, 150, or 300 mg/kg of feed (ppm) continuous from hatching. At 6 to 7 wk of age, birds from each AA group received either 2 IU ACTH/100 g of body weight, 4% gelatin, or no ACTH or gelatin injections. Injections were given 12 h prior to, at the time of, and at 12 and 24 h after an intradermal wattle injection with PHA-P. Responses to PHA-P were determined as wattle indices. Injections of ACTH reduced body weight gain in both trials and decreased relative bursa weight in Trial 1. Injections of ACTH and dietary AA increased plasma cholesterol in both trials. Peak CBH wattle response occurred at 24 h post PHA-P injection. Injections of ACTH decreased mean wattle index at 18 and 36 h post PHA-P injection in Trial 1 and 18 and 24 h post PHA-P injection in Trial 2. The addition of AA ameliorated the ACTH-mediated suppression of CBH in a dose-related manner.

Modulation of estrogen-induced carcinogenesis by chemical modifications

The mechanism of carcinogenesis by estrogens is still unknown. Uncontrolled stimulation of cell proliferation, an endocrine imbalance, or metabolic activation of estrogens to reactive intermediates capable of tissue injury have previously been proposed. In an attempt to gain insight into mechanistic details of estrogen-induced carcinogenesis in male Syrian hamsters, fluorine substituted estrogens, which were impaired in their capacity to be transformed into catechols, have been tested for their carcinogenic activity. 2-Fluoroestradiol was found to be non-carcinogenic in Syrian hamsters despite its estrogenic potency. In a second unrelated experiment, ascorbic acid, which reduced diethylstilbestrol quinone to cis- and trans-diethylstilbestrol in vitro, was administered to estradiol or diethylstilbestrol-treated hamsters. A lowered incidence of kidney tumors in vivo was found in animals receiving ascorbic acid vs estrogen-treated control animals. These results were taken as evidence for a role of estrogen metabolites (catechols formed from estradiol or quinone formed from diethylstilbestrol) in estrogen-induced tumorigenesis. A mechanistic model of metabolic activation of estrogens followed by damage to cellular macromolecules is proposed.

Effect of pharmacological doses of ascorbic acid on the hepatic microsomal haemoproteins in the guinea-pig

1. Ascorbic acid deficiency results in a reduction in the activity of the hepatic mixed function oxidase systems in the guinea-pig. In this study, male Dunkin-Hartley guinea-pigs were given 0, 50, 100, 200 or 300 mg ascorbic acid/d in two equal doses in buffered sucrose solution (200 g/l) for 4 d. Controls received an equal volume of sucrose solution. 2. A dose of 50 mg ascorbic acid/d resulted in a significant rise in the specific activities of both cytochromes P-450 and b5. At doses of 200 and 300 mg ascorbic acid/d the concentration of both haemoproteins was significantly lower than the control values. These effects were mirrored by total microsomal haem concentration. 3. These results suggest that when given in large doses, ascorbic acid ceases to act simply as a vitamin and should be considered a drug competing for substrates and cofactors with co-administered drugs and endogenous substrates such as cholesterol.

The role of ascorbic acid in the regulation of cholesterol metabolism and in the pathogenesis of artherosclerosis

Strong clinical and experimental evidence suggests that chronic latent vitamin C deficiency leads to hypercholesterolaemia and the accumulation of cholesterol in certain tissues. Ascorbic acid supplementation of the diet of hypercholesterolaemic humans and animals generally results in a significant reduction in plasma cholesterol concentration. While most studies relating ascorbic acid to atherosclerosis have used the rabbit as a model, those concerned with elucidating the role of ascorbic acid in the regulation of cholesterol metabolism have generally used the guinea pig. Comparatively little use has been made of the non-human primates. A significant advance in recent years has been the development of a model of chronic latent scurvy in the guinea pig. Chronic dietary inadequacy of vitamin C may influence the pathogenesis of atherosclerosis as it affects not only plasma cholesterol and triglyceride concentrations but also the integrity of the vascular wall. Ascorbic acid is involved in the regulation of cholesterol metabolism in several ways. Dietary inadequacy of vitamin C is associated indirectly with a lowering of cholesterol absorption, this effect resulting from a reduction in the availability of bile acids, monoglycerides and fatty acids. The excretion of cholesterol as neutral steroids, however, appears not to be affected by ascorbic acid. Although much of the evidence for the involvement of ascorbic acid in cholesterol synthesis is equivocal, it seems likely that cholesterol synthesis is decreased in vitamin C deficiency. A series of studies using guinea pigs with chronic latent vitamin C deficiency has provided clear evidence that bile acid synthesis is reduced in this condition. Indirect evidence strongly suggests that this results from a decrease in the activity of the microsomal enzyme cholesterol 7 alpha-hydroxylase. However, some evidence suggests that the mitochondrial reactions of bile acid synthesis require ascorbic acid. The role of ascorbic acid in the regulation of steroidogenesis appears to involve selective inhibitory and stimulatory effects on the desmolase, hydroxylase and dehydrogenase reactions which lead to the formation of pregnenolone and its subsequent conversion to steroid hormones.