Studies were done to assess the contribution of alpha-tocopherol to the regional differences in microsomal lipid peroxidation (LP) and steroid metabolism in the guinea pig adrenal cortex. In normal guinea pigs, ferrous ion (Fe2+)- and ascorbic acid-induced LP are far greater in microsomal preparations from the inner adrenal zone (zona reticularis) than in those from the outer zones (zona fasciculata plus zona glomerulosa). The amounts of unsaturated fatty acids, substrates for LP, are similar in the two zones, but alpha-tocopherol concentrations are 4-5 times greater in outer than inner zone microsomes. Tocopherol depletion by dietary deprivation had little effect on LP in vitro in inner zone microsomes, but substantially increased LP in outer zone preparations. As a result, tocopherol deficiency eliminated the zonal differences in microsomal LP. Unsaturated FFA concentrations were lower in tocopherol-deficient microsomal preparations than in those from tocopherol-sufficient animals, suggesting peroxidative losses in vivo. Tocopherol deficiency decreased steroid C-17,20 lyase activity in outer zone microsomes, but had no effect on activity in inner zone preparations, eliminating the normal zonal difference in activity (outer greater than inner). The results indicate that alpha-tocopherol is a major determinant of adrenal LP and is responsible for the regional differences in microsomal LP in guinea pig adrenal cortex; the effects of ascorbic acid on LP in each zone are also affected by alpha-tocopherol. alpha-Tocopherol may influence the functional zonation of the adrenal cortex by selectively protecting outer zone steroidogenic enzymes from oxidative degradation.

1. 14C-Diethylene glycol (DEG), administered orally to rats at 1, 5, and 10 ml/kg, gave elimination half-lives of 6, 6, and 10 h, respectively, from urinary excretion data. Half-logarithmic plots of urinary 14C excretion rates versus time indicated zero-order elimination for the first 9 and 18 h after oral doses of 5 and 10 ml of 14C-DEG/kg, respectively. 14C-DEG urinary elimination kinetics changed into first-order 6, 9, and 18 h after oral doses of 1, 5, and 10 ml/kg, with a half-life of 3 h. 2. After oral doses of 3 and 5 ml ethylene glycol (EG)/kg, half-lives of 4.5 and 4.1 h were estimated from cumulative urinary excretion data for non-metabolized EG. A half-life of 2 h was determined from half-logarithmic plots of urinary excretion rates of non-metabolized EG after the same oral doses of EG. 3. The urinary concentrations of non-metabolized DEG and its metabolite, 2-hydroxyethoxyacetic acid (2-HEAA), determined by high-resolution n.m.r. spectroscopy in the urine of rats doses with DEG were 61-68% and 16-31% dose, respectively. 4. Urinary concentrations of non-metabolized EG and its metabolite, glycolic acid (GA), determined by n.m.r., gave 62-67% for non-metabolized EG and 28.7% for GA following oral doses of EG. 5. Oxidation of DEG and EG in rats was accompanied by a change of urinary pH, reflecting metabolic acidosis. 6. Comparison of the KM for DEG oxidation in vitro by ADH with that of ethanol oxidation, showed a 680-fold difference in substrate affinity. DEG inhibited ethanol oxidation non-competitively, the Ki being 0.44 M.

Oral doses of 1 and 5 ml/kg 14C-diethylene glycol (DEG) given to rats were rapidly and almost completely absorbed, the invasion constants being 2.95 h-1 and 4.24 h-1. The kinetics of invasion were determined with the method of residuals (Rowland and Tozer 1989) and by reconstruction of the invasion curves according to Kübler (1970). 14C-DEG was rapidly distributed from the blood into the organs and tissues in the order kidneys > brain > spleen > liver > muscle > fat, i.e. the same order as the blood flow. The relative volume of distribution, app. VD, was determined at 298 ml, indicating distribution over the whole body. After oral doses of 1, 5, and 10 ml 14C-DEG/kg 64, 87, and 91% of 14C activity in rat blood disappeared in 12-16 h with a half-life of 3.4 h and the remaining 9, 5, and 4% with half-lives of 39 h, 45 h, and 49 h. A total of 73-96% of 14C activity in blood was excreted with the urine and 0.7-2.2% with the faeces. From the cumulative urinary excretion kinetics half-lives of 6 h were determined for doses of 1 and 5 ml/kg and 10 h for the dose of 10 ml/kg. After doses of 5 ml/kg and 10 ml/kg 14C-DEG semi-logarithmic plots of elimination rate versus time were constant for 5 and 9 h, respectively, indicating that DEG accelerated its renal elimination by inducing osmotic diuresis. Thereafter urinary excretion followed first order kinetics with elimination half-lives of 3.6 h. After oral doses of 5 ml/kg 14C-DEG given to rats of 336 g body weight with an app. VD of 297 ml, the total clearance of 14C activity was determined at 63 ml/h, and the renal clearance of unmetabolized DEG was 66 ml/h. The ratio of ClDEG to Cl(inulin) = 0.64 indicated that DEG and its metabolite 2-hydroxyethoxyacetate (2-HEAA) were reabsorbed from the tubuli into the blood capillaries. DEG produced metabolic acidosis, which was completely balanced after doses of 1 and 5 ml/kg, but doses greater than 10 ml/kg produced non-compensated metabolic acidosis, hydropic degeneration of the tubuli, oliguria, anuria, accumulation of urea-N, and death in uraemic coma.

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