[Mechanism of inhibition of hypothalamic pituitary-ovarian function in streptozotocin-diabetic mature female rats].

In order to clarify the mechanism of the failure of reproductive function in diabetic rats, the hypothalamic pituitary-ovarian function in streptozotocin-induced diabetic mature female rats was investigated. Estrous cycle patterns were disturbed in diabetic rats and these rats showed constant diestrus. In diabetic rats no preovulatory LH or FSH-surge were observed on presumed proestrus, and the number of ovulated ova and the weights of ovary and uterus were significantly less than those seen in control rats on presumed estrus. The response of the pituitary gland to LH-RH in diabetic rats and diabetic castrated rats was not significantly different from that in control rats on diestrous day and castrated control rats, respectively. However, the response of the hypothalamic-pituitary axis to steroidal feedback in diabetic castrated rats was significantly less than that in castrated control rats. The number of ovulated ova and ovarian growth induced by hCG in diabetic rats were also significantly lower than those in control rats. These results indicate that the impaired site in streptozotocin diabetic rats is not the pituitary gland, but the ovary and hypothalamic-pituitary function.