EFFECT OF DIABETES-MELLITUS DURING THE LUTEAL-PHASE OF THE ESTROUS-CYCLE ON PREOVULATORY FOLLICULAR FUNCTION, OVULATION AND GONADOTROPINS IN GILTS

Development of preovulatory follicles was studied during the oestrous cycle in two experiments designed to examine the effects of short-term lack of insulin on preovulatory follicular function and (Expt 2 only) ovulation. In Expt 1, on day 12 of the third postpubertal oestrous cy cle, insulin treatment was discontinued in streptozocin-induced diabet ic gilts (n = 4), and on day 18, ovaries were removed from the diabeti c gilts and from four normal untreated gilts. Diabetic gilts had a hig her percentage of macroscopically atretic follicles (29.4 versus 6.8%; SEM = 5.9, P < 0.05) than did normal gilts. Binding of I-125-labelled hCG by freshly collected granulosa cells from non-atretic follicles w as similar in diabetic and normal gilts. Diabetic gilts had more LH pe aks in 3 h on days 12-17 of the oestrous cycle than did normal gilts ( 2.3 versus 1.6; SEM = 0.12; P < 0.01). Serum oestradiol and progestero ne concentrations were not affected by treatment, but serum testostero ne was increased (P < 0.01) in diabetic gilts. In Expt 2, insulin trea tment was withdrawn from nine diabetic gilts on day 12 of the oestrous cycle and ten normal gilts sewed as controls. On day 18, ovaries were removed from six diabetic and six normal gilts; four normal and three diabetic gilts were ovariectomized 25 days after oestrus. Follicular diameter of diabetic gilts tended to be smaller than that of control ( control: 3.95 versus diabetic: 3.01 mm; SEM = 0.4, P < 0.08) and the p roportion of follicles with histologic evidence of atresia was higher in diabetic gilts (control: 29 versus diabetic: 47%; SEM = 5; P < 0.05 ) on day 18. In both experiments, the insulin-like growth factor I (IG F-I) and oestradiol concentrations of follicular fluid of diabetic gil ts untreated with insulin from day 12 to day 18 was lower than in nond iabetic gilts. After day 18 in Expt 2, normal gilts exhibited oestrus (duration of cycle was 20 +/- 0.5 days) accompanied by preovulatory su rges in oestradiol and LH, whereas diabetic gilts did not exhibit oest rus or ovulate. In diabetic gilts, oestradiol concentrations were lowe r compared with those of normal gilts, and LH patterns were characteri zed by two (two gilts) or three (one gilt) increases of more than 2 ng ml(-1) between day 18 and day 25. Thus, impaired follicular function in diabetic gilts is not explained by decreased function of the hypoth alamo-pituitary axis, since LH was not decreased. We conclude that the decreased oestradiol production by diabetic gilts indicates either di srupted steroidogenesis due to the acute absence of insulin or lowered IGF-I, or both.