Effects of altered endocrine function on biliary metabolites of [4-14C]androst-4-ene-3,17-dione in rats. Possible utility as a model for identifying anti-atherosclerotic agents.

ABSTRACT

Atherosclerosis, coronary artery disease and elevated serum cholesterol are frequently associated with an abnormal pattern of androgen metabolites, especially an elevation of etiocholanolone (E) and/or epiandrosterone (EA) relative to androsterone (A). Therapeutic correction of these metabolic defects may lower serum cholesterol. We have attempted to reproduce this metabolic syndrome in rats by altering their endocrine status. Intact male rats excreted very little A or E in their bile; more than 80% of the [4-14C]A-dione was excreted as unknown polar compounds. Adrenalectomy, thyroidectomy or streptozotocin diabetes induced little or no change in the excretion of both E and A and did not alter the A/E ratio. Hypophysectomy (hypox), however, resulted in a huge increase in E excretion and a 10-fold decrease in the A/E ratio. Treatment of hypophysectomized males with bovine growth hormone (bGH) but not testosterone or thyroxine restored the pattern of androgen metabolites to that of intact male rats. Intact female rats excreted mainly A, and this was decreased by ovariectomy. Hypophysectomy, however, resulted in a marked increase in E and a corresponding large decrease in A excretion. Treatment of hypox females with estradiol or triiodothyronine did not correct the metabolic defects in A and E production, whereas GH resulted in a pattern of A-dione metabolism resembling that of intact males; i.e., primarily polar metabolites with low A and E. Hypophysectomy thus results in a dramatic increase in 5 beta-reductase activity in male and female rats. GH therapy restores the metabolic pathway to that seen in intact males. Our objective had been to find a model capable of detecting substances which would increase A and decrease E production. The male rat (regardless of endocrine status) has little 5 alpha-reductase activity. The intact female rat, however, has high 5 alpha-reductase activity, and retains significant 5 alpha-reductase in the absence of the ovaries. In hypox females, 5 alpha-reductase was much reduced while 5 beta-reductase was increased. Furthermore, serum cholesterol was elevated in hypox females but could be lowered by exogenous androsterone. Thus the hypox female rat appears to offer the best model for identifying non-hormonal agents which could enhance the production of A and/or decrease the production of E. Such agents might favorably influence cholesterol metabolism.