Central insulin administration maintains reproductive behavior in diabetic female rats

Diabetic female rats have decreased ovulation, reproductive behavior and luteinizing hormone surges. Peripheral insulin treatment restores the phenotype to normal and also corrects many of the metabolic changes. To further evaluate the role of insulin in the specific maintenance of reproductive behavior, rather than administering it peripherally, we gave insulin intracerebroventricularly (ICV) at doses that did not correct the peripheral metabolic changes associated with diabetes such as hyperglycemia. During the experiment, we assessed the general activity and reproductive behavior of gonadectomized, estrogen- and progesterone-treated diabetic and control, nondiabetic female rats. Some of the animals received ICV saline, the rest received ICV insulin. General activity (ambulation, rearing and corner sniffing) was not affected by any of the treatments. Streptozotocin-induced diabetes resulted in a significantly decreased lordosis quotient, and ICV insulin was able to completely prevent this reduction. Furthermore, ICV insulin was able to cause a modest increase in the lordosis quotient among nondiabetic rats as well. Moreover, ICV insulin also increased the quality of lordosis among diabetic rats. Our results support a central role of insulin in the control of reproductive functions, beyond maintaining the homeostatic and metabolic balance.