alpha-Tocopherol depletion eliminates the regional differences in adrenal mitochondrial lipid peroxidation

Species differences in adrenal lipid peroxidation: role of alpha-tocopherol

Previous reports have noted high levels of lipid peroxidation (LP) in vitro in a variety of adrenocortical preparations. However, we have observed that susceptibility to adrenal LP seems to vary considerably from species to species. The current study was done to confirm these apparent species differences in adrenal LP in vitro and to determine if they were attributable to differences in alpha-tocopherol content. Incubation of mitochondrial or microsomal preparations from guinea pig or rabbit adrenal glands with ferrous ion (Fe2+) caused a time-dependent increase in the formation of thiobarbituric acid reactive substances (TBARS) accompanied by depletion of alpha-tocopherol. By contrast, incubation of adrenal mitochondria or microsomes from rats or monkeys with Fe2+ had little or no detectable effect on TBARS and basal adrenal alpha-tocopherol levels were five to ten-fold greater than those in guinea pigs or rabbits. In addition, there was little change in alpha-tocopherol concentrations during incubation of rat or monkey adrenal tissue. Dietary alpha-tocopherol deficiency in rats reduced adrenal alpha-tocopherol to concentrations approximating those in guinea pigs. Incubation with Fe2+ induced high levels of TBARS in adrenal mitochondria and microsomes from the alpha-tocopherol deficient rats. Conversely, dietary alpha-tocopherol supplementation in rabbits increased adrenal alpha-tocopherol levels and prevented Fe2+ induced TBARS formation in mitochondria and microsomes. The results indicate that there are large species differences in adrenal susceptibility to LP in vitro and that these differences are at least partly attributable to species differences in adrenal alpha-tocopherol concentrations.

Effects of adrenocorticotropic hormone and dexamethasone on adrenal and hepatic alpha-tocopherol concentrations

Studies were done to determine the effects of ACTH treatment on adrenal alpha-tocopherol (alpha-T) concentrations in female rats. Administration of dexamethasone (DEX) to inhibit endogenous ACTH secretion increased whole adrenal alpha-T levels as well as the fractional amount in adrenal cytosol. Adrenal ascorbic acid (AA) concentrations were unaffected by DEX. DEX treatment also had no effect on hepatic AA content but decreased alpha-T concentrations in the liver. The subcellular distribution of alpha-T in the liver was not altered by DEX. Administration of ACTH to DEX-treated animals decreased adrenal alpha-T content and restored the pattern of subcellular distribution to that seen in controls. ACTH had no effect on hepatic alpha-T concentrations or subcellular distribution. ACTH treatment also had no effect on AA concentrations in adrenals or livers. The results demonstrate that ACTH has a role in the regulation of adrenal alpha-T but the mechanism(s) involved remain to be determined. The data also indicate that glucocorticoids such as DEX directly influence hepatic alpha-T levels independent of their effects on ACTH secretion.

Regulation of adrenal and hepatic alpha-tocopherol content by androgens and estrogens

Previous studies demonstrated that alpha-tocopherol concentrations were far greater in adrenal glands and in livers from female rats than in those from males. Studies were done to investigate the role of androgens and estrogens in the regulation of adrenal and hepatic alpha-tocopherol content. In males and females, adrenal concentrations of alpha-tocopherol were approx. 10-fold greater than those in liver and the highest concentrations of alpha-tocopherol were in the crude mitochondrial fractions in both organs. Castration of female rats decreased alpha-tocopherol concentrations in adrenals and in livers. Proportionately similar declines occurred in both organs and in all subcellular fractions. The effects of castration were prevented by estradiol replacement at the time of surgery. Gonadectomy in male rats had effects opposite to those in females, increasing adrenal and hepatic alpha-tocopherol concentrations. Testosterone administration to castrated males prevented the increases in adrenal and hepatic alpha-tocopherol content. Neither castration nor gonadal hormone replacement in either sex had any effect on plasma alpha-tocopherol levels or on cytosolic ascorbic acid concentrations in adrenals or livers. The results indicate a role for estrogens and androgens in the regulation of adrenal and hepatic concentrations of alpha-tocopherol. The opposing effects of androgens and estrogens fully account for the sex differences in tissue alpha-tocopherol levels in rats.