Etiology of anovulation in the immature alloxan-diabetic rat treated with pregnant mare's serum gonadotropin: absence of the preovulatory luteinizing hormone surge.

The effects of alloxan-induced diabetes on ovulation and other ovarian responses were investigated in immature rats injected with PMS gonadotropin (PMSG, 15 IU/100 g) on day 30 of age. Rats were killed on day 32 (presumed proestrus) or on day 33, at which time the oviducts were examined for ova. Ovarian weight gain was similar in control and diabetic rats and Graafian follicles were present in both groups on day 32. None of the diabetic rats ovulated while 96% of the control rats ovulated. Anovulation in diabetic rats could not be attributed to a drug side-effect of alloxan or to a lack of ovarian responsiveness, as 90% of the animals ovulated after treatment with insulin or with hCG (5 IU). Measurements of serum estradiol and LH on the morning of presumed proestrus revealed that concentrations of these hormones were not different in control and diabetic rats. However, measurements of LH in blood samples taken in the afternoon from control rats showed an LH surge, whereas no LH surge was found in diabetic rats. Thus, anovulation in immature diabetic rats treated with PMSG is not caused by an attenuation of ovarian responsiveness or by decreased secretion of estradiol, but rather is due to the loss of the LH surge.