On serum concentrations of testosterone and dihydrotestosterone and testicular 3β-hydroxysteroid dehydrogenase activity in intact and hypophysectomized diabetic rats

Abstract

Adult male Sprague-Dawley rats were made diabetic with streptozotocin (40 mg/kg BW). The effect of treatment with insulin, LH, or both hormones during the experimental period on serum levels of testosterone (T) and dihydrotestosterone (DHT), as well as testicular Δ5-3β-hydroxysteroid dehydrogenase (3β-HSD) activity was measured 15 days (intact rats) or 10 days (hypophysectomized rats) after the induction of diabetes. In intact rats, diabetes resulted in a marked reduction in serum hormone levels and testicular 3β-HSD activity. Insulin or LH treatment significantly increased hormone levels and testicular 3β-HSD activity in diabetic rats. The administration of both hormones to diabetic rats resulted in a rise in enzyme activity to values similar to those in the normoglycemic controls, with a concomitant increase in serum hormone levels. In hypophysectomized diabetic rats, insulin resulted in testicular 3β- HSD activity and serum hormone concentrations similar to those in normoglycemic hypophysectomized rats. Treatment with LH significantly increased 3β-HSD activity and the serum levels of T and DHT in hypophysectomized normoglycemic and hypophysectomized diabetic animals compared to those in the hypophysectomized untreated controls. When the results were expressed in terms of 3β-HSD activity per testis weight, it became evident that treatment of diabetic hypophysectomized rats with both hormones increased 3β-HSD activity to levels similar to those obtained in the normoglycemic hypophysectomized animals treated with LH alone. In both experiments, the stimulatory effects of insulin and LH on the serum levels of T and DHT followed a pattern similar to that the effects of insulin and LH on the activity of the testicular 3β-HSD. The results of this study serve as further evidence of testicular failure in diabetic rats and suggested that an inadequate steroidogenesis in the testes of diabetic rats may be due, at least in part, to decreased 3β-HSD ctivity. Based on the parameters studied, a synergistic action could be observed after daily treatment with insulin and LH. This fact supports previous findings of a stimulatory effect of insulin on LH receptors in the testis of the diabetic rat and suggests that in the testes, 3β-HSD is regulated by LH and insulin.