Effects of hypophysectomy and administration of growth and thyroid hormones on the hydroperoxide-induced calcium release process and glutathione levels in rat liver mitochondria

Abstract

In order to investigate the effects of growth and thyroid hormones on Ca 2+ transport in liver mitochondria, Ca 2+ release and other accompanying changes induced by t-butylhydroperoxide were measured in mitochondria from hypophysectomized and hormone-injected rats. Mitochondria from normal and hypophysectomized rats showed similar rates of Ca 2+ uptake (40 nmol · min · −1 mg protein −1) and ruthenium red-insensitive release (3 nmol · min · −1 mg protein −1). However, the t-butylhydroperoxide (0.5 m m)-induced release of 90% of the added Ca 2+ required 1027 ± 98 and 560 ± 35 s in the hypophysectomized and normal groups, respectively, and the difference was independent of Ca 2+. The release was accompanied by a loss of membrane potential, large amplitude swelling, the oxidation of NAD(P)H and stimulation of respiration. At conditions of equivalent release rates, the rate and extent of swelling as well as the stimulation of respiration were lower in mitochondria from hypophysectomized rats than those in the normal group. These results were confirmed by electron microscopy and provided evidence for a dissociation between the release of Ca 2+ and the increase of membrane permeability. The administration of bovine growth hormone and/or 3,5,3′-triiodo- l-thyronine to hypophysectomized rats decreased the Ca 2+ release times by different degrees and thyroid hormone was more effective than growth hormone. Hypophysectomy doubled the GSH content and hormone injections decreased it and the Ca 2+ release times in parallel. Indeed, a high degree of correlation ( r = 0.96) was obtained between mitochondrial GSH and the release times from groups of differing hormone status. Differences in the groups in the time required for oxidation of 80–90% of GSH were correlated with the differences in the times for release of 90% Ca 2+. Therefore, these results demonstrated that growth and thyroid hormones can alter both the hydroperoxide-induced Ca 2+ release and the metabolism of GSH in liver mitochondria, suggesting that the two processes are related. It is proposed that the effects of these hormones on Ca 2+ transport may result from the promotion of its efflux from mitochondria and its mobilization into the cytosol.