Continuous Subtherapeutic Insulin Counteracts Hypothalamopituitary-Gonadal Alterations in Diabetic Rats

In experimental animal models, gonadal axis lesions are probably responsible for reproductive disorders associated with diabetes mellitus. The pathogenesis of these disorders is not yet known, but it is assumed that insulin deficiency plays an important role. To check this hypothesis, we have investigated the hypothalamopituitary-gonadal axis of insulin-treated streptozocin-induced diabetic (STZ-D) rats and compared it with that of untreated diabetic and control animals. Insulin was delivered by subcutaneously implanted osmotic minipumps. Furthermore, to determine whether possible beneficial insulin effects are selectively limited to the gonadal axis or act generally, we also studied retinal microangiopathy. The hypothalamopituitary-gonadal axis of insulin-treated diabetic animals was almost unchanged. On the contrary, retinal microangiopathy was only slightly influenced by subtherapeutic insulin doses. In conclusion, continuous administration of insulin at subtherapeutic doses can successfully counteract most of the effects of diabetes on the gonadal axis. Thus, the gonadal-axis impairment in STZ-D animals appears to be related to the fall of plasma insulin below a critical level. Furthermore, the various organ systems may respond to different plasma insulin threshold levels.