DEPLETION OF INSULIN IN STREPTOZOCIN-INDUCED-DIABETIC PIGS ALTERS ESTRADIOL, INSULIN-LIKE GROWTH-FACTOR (IGF)-I, AND IGF BINDING-PROTEINS IN CULTURED OVARIAN FOLLICLES

The objectives were to investigate whether insulin-dependent diabetes mellitus disrupts production of estradiol and activity of the insulin- like growth factor (IGF)-I system in individual ovarian follicles duri ng the preovulatory period of the estrous cycle. Diabetes mellitus was induced with streptozocin (150 mg/kg) in seven cyclic gilts at 180 +/ - 5 days of age. On Day 12 of the estrous cycle, insulin replacement t herapy was withdrawn from three gilts and continued in four; four gilt s served as normal controls. After ovary removal on Day 18, all follic les greater than or equal to 3 mm diameter were dissected free and cul tured for 6 h in the presence of 280 ng testosterone for assessment of estradiol and IGF-I production and binding protein activity. Treatmen ts did not affect corpora lutea number (15.4 +/- 0.8) or serum estradi ol (5.8 +/- 0.8 pg/ml) on Day 18. There were no differences for any me asure of follicular development between normal and insulin-treated dia betic gilts. Untreated diabetic gilts, compared to normal and insulin- treated diabetic gilts, had fewer total visible follicles (22.7 vs. 61 .3 and 63.3; SEM = 8; p < 0.01) and reduced follicular diameter (3.4 v s. 4.4 and 4.2 mm; SFM = 0.3; p < 0.0001), respectively. Untreated dia betic gilts had a greater percentage of macroscopically atretic follic les than normal and insulin-treated diabetic gilts (75% vs. 47% and 36 %; SFM = 10; p < 0.05). Untreated diabetes mellitus lowered estradiol (p < 0.01); however, effects of treatment on estradiol production were not significant when diameter was part of statistical models. When co ntents of IGF-I in follicular fluid and conditioned medium were summed after 6 h of culture, untreated diabetic pigs had lower IGF-I at all follicle diameters than pigs in the other treatments (p < 0.05). IGF b inding protein (BP) activity was affected by diabetes mellitus, with u ntreated diabetic pigs having greater IGFBP-1 activity in medium and w ith both diabetic groups having greater IGFBP-2 activity in follicular fluid (p < 0.05). Activity of IGFBP-1 predominated in conditioned med ium, and IGFBP-2 activity predominated in follicular fluid. IGFBP-3 wa s decreased in follicular fluid of atretic follicles and in medium of atretic follicles in all except the insulin-treated diabetic gilts; in these gilts it was increased in atretic follicles (treatment by atres ia interaction; p < 0.05). In conclusion, estradiol was most related t o size of the follicle; however, lowering of IGF-I regardless of folli cle diameter and alterations in IGFBP activity suggest that diabetes a ffects IGF-I and its binding proteins differently from estradiol produ ction. These alterations may explain reduced follicular growth and inc reased follicular atresia in diabetic pigs.