Adrenal Involvement in the Diabetes-induced Loss of Growth Hormone and Prolactin Receptors in the Livers of Female Rats

Streptozotocin-induced diabetes causes a decrease in growth hormone and prolactin receptors in the livers of female rats, and in the serum concentration of somatomedin-C/insulin-like growth factor-I, concomitantly with an increase in the serum testosterone levels. In this study, a possible role for adrenal androgens in the loss of receptors was examined. Rats were adrenalectomised bilaterally 3 days after the induction of diabetes with streptozotocin (100 mg/kg intravenously), and livers were removed 3 days later. Adrenalectomy had no effect on binding of ovine prolactin or bovine growth hormone to liver microsomal membranes from non-diabetic rats, but in diabetic rats it entirely abolished the 56% decrease in prolactin binding and significantly reversed the 66% decrease in growth hormone binding and the parallel fall in serum levels of somatomedin-C/insulin-like growth factor-I (p less than 0.05). Adrenalectomy also prevented the diabetes-induced rise in serum testosterone. Daily injection of testosterone to normal and diabetic rats for 12 days significantly reduced both prolactin and growth hormone binding (p less than 0.001), with the effect of diabetes being additive upon the testosterone effect. Implantation of testosterone-filled silastic capsules at the time of adrenalectomy (i.e. for 3 days) did not prevent the adrenalectomy-induced restoration of both growth hormone and prolactin receptors. The resulting high serum testosterone level did not reduce binding to growth hormone receptors in control rats over the 3 day period, and caused no further decrease in diabetic rats. However, binding to prolactin receptors was reduced by 47% in control animals with no further loss in diabetic animals (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)