Effects of Hypophysectomy on Rat Adrenal Corticosteroidogenesis in Vivo

Abstract

The biosynthesis of corticosterone from cholesterol by the rat adrenal gland was investigated in the eviscerated rat with cholesterol-4-C14 administered intravenously. The adrenal uptake of cholesterol-4-Cl4 was increased considerably by preincubation of the radioactive cholesterol with serum prior to administration. Hypophysectomy led to a decrease in the conversion of labeled cholesterol to corticosterone in parallel with a decrease in the adrenal concentration of corticosterone. The de novo formation of radioactive corticosterone was still observed at 96 hr. after hypophysectomy, but at a greatly reduced rate compared to controls. Corticosterone, detectable in adrenal glands of hypophysectomized rats, reflects a continuing synthesis of the hormone, rather than residual glandular storage of the hormone. The specific activity (cpm/)[mu]g) of corticosterone in the decapsulated gland is higher in 96 hr.-hypophysectomized rats than in eviscerated controls. These results are discussed with regard to the pool system(s) of "active" precursor cholesterol. The reduction of corticosteroidogenesis by hypophysectomy is much greater in the decapsulated gland than in the capsular gland, supporting the view that the capsular or glomerulosa zone is much less dependent upon ACTH control.