Role of lysosomotrophic reagents in glucocorticoid hormone action

Abstract

Administration of (10 mg/200 g) methylamine or chloroquine to adrenalectomized rats for 2 days followed by a single injection of either cortisol (2.5 mg/200 g) or dexamethasone (0.5 mg/200 g) resulted in a significant enhancement of the tyrosine aminotransferase enzymatic activity in rat liver versus rats given a single injection only of either steroid. Lysosomotrophic reagents were unable to induce tyrosine aminotransferase when administered alone. Cytosols from rat liver treated with lysosomotrophic reagents in vivo had approx. 20–30% more specific binding to [ 3H]dexamethasone as compared to the control, untreated rats. This enhanced binding was due to an increase in the concentration of the receptor rather than change in the affinity of the hormone for the receptor. Rat livers perfused with and homogenized in 10 mM Tris-HCl/0.25 M sucrose buffer (pH 7.5) containing about 5 mM lysosomotrophic reagents showed optimum stabilization of the steroid unbound glucocorticoid receptor in vitro at both 4°C and 25°C. These reagents had no effect on in vitro transformation of [ 3H]dexamethasone-receptor complex or on the binding of the thermally transformed receptor to the nuclei. It is concluded from these studies that lysosomotrophic reagents (a) enhance tyrosine aminotransferase induction by glucocorticoids and (b) stabilize unbound glucocorticoid receptor both in vivo and in vitro without any effect on in vitro transformation of the steroid-receptor complex.