Effect of streptozotocin diabetes on the pituitary-testicular axis in the rat.

The pituitary-testicular axis was investigated in the streptozotocin diabetic male rat to determine the relationship between hormonal alterations and steroidogenic activity. Male Sprague-Dawley rats weighing 250-300 g were used in all experiments. Diabetes was induced by intraperitoneal injection (40 mg/kg body wt.) of streptozotocin and they were studied with non-diabetic controls. The observations on these animals were compared to those from diabetic rats treated with 1-5 IU protamine zinc insulin. Steroidogenic activity was determined by measuring the per cent of [4-14C]-cholesterol converted to [4-14C]-pregnenolone and [4-14C]-progesterone. Plasma concentrations of LH, FSH and prolactin were measured by RIA. Streptozotocin induced diabetes resulted in significantly reduced plasma LH (34%, p less than 0.20) and prolactin (53%, p less than 0.001) but did not modify FSH concentrations. Insulin treatment completely and partially restored abnormal LH and prolactin release. The activity of the enzyme cleaving the side-chain of cholesterol (rate limiting step in steroidogenesis) was considerably reduced in the diabetic state (59%, p less than 0.002) and insulin treatment restored it to even supranormal levels (not significant). Our findings suggest that insulin may play a physiological and differential role in regulating the secretory activity of the anterior pituitary. The insulin is needed for normal LH and prolactin release and Leydig cells function but its role in FSH release and Sertoli cells function is not clear.