Zonal differences in adrenocortical lipid peroxidation: Role of α-tocopherol

Abstract

Studies were done to evaluate the relationship between α-tocopherol (α-T) concentrations and lipid peroxidation (LP) in vitro in microsomal preparations from the inner (zona reticularis) and outer (zona fasciculata plus zona glomerulosa) zones of the guinea pig adrenal cortex. Microsomes were incubated with ferrous ion (Fe 2+) to promote free radical production, and α-T levels and LP were monitored after various incubation times. α-T concentrations were far lower in inner than outer zone preparations and were rapidly depleted from inner zone microsomes by incubation with Fe 2+. Coinciding with α-T depletion was a large and rapid increase in LP. With outer zone microsomes, α-T depletion required more than 30 min, and very little LP was demonstrable during this period. However, once α-T depletion occurred, LP was rapidly initiated and reached levels similar to those obtained with inner zone preparations. Inhibition of LP by MnCl 2 prevented the Fe 2+-induced declines in α-T in both zones. The results demonstrate the importance of α-T as a modulator of adrenal LP and indicate that the zonal differences in LP are largely attributable to the differences in α-T concentrations.