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 during 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 On Day 12 of the estrous cycle, insulin replacement therapy was withdrawn from three gilts and continued in four; four gilts served as normal controls. After ovary removal on Day 18, all follicles > or = 3 mm diameter were dissected free and cultured for 6 h in the presence of 280 ng testosterone for assessment of estradiol and IGF-I production and binding protein activity. Treatments did not affect corpora lutea number (15.4 +/- 0.8) or serum estradiol (5.8 +/- 0.8 pg/ml) on Day 18. There were no differences for any measure of follicular development between normal and insulin-treated diabetic 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 vs. 4.4 and 4.2 mm; SEM = 0.3; p < 0.0001), respectively. Untreated diabetic gilts had a greater percentage of macroscopically atretic follicles than normal and insulin-treated diabetic gilts (75% vs. 47% and 36%; SEM = 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 contents 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 binding protein (BP) activity was affected by diabetes mellitus, with untreated diabetic pigs having greater IGFBP-1 activity in medium and with both diabetic groups having greater IGFBP-2 activity in follicular fluid (p < 0.05). Activity of IGFBP-1 predominated in conditioned medium, and IGFBP-2 activity predominated in follicular fluid. IGFBP-3 was 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 atresia interaction; p < 0.05). In conclusion, estradiol was most related to size of the follicle; however, lowering of IGF-I regardless of follicle diameter and alterations in IGFBP activity suggest that diabetes affects IGF-I and its binding proteins differently from estradiol production. These alterations may explain reduced follicular growth and increased follicular atresia in diabetic pigs.
Edwards
J L
JL
Department of Animal and Dairy Sciences, Mississippi State University, Mississippi 39762, USA.
Hughey
T C
TC
Moore
A B
AB
Cox
N M
NM
D000818:Animals; D001345:Autoradiography; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D004958:Estradiol / Q000032:analysis* / Q000378:metabolism; D005260:Female; D015571:Follicular Fluid / Q000737:chemistry; D007328:Insulin / Q000172:deficiency* / Q000378:metabolism; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000032:analysis / Q000378:metabolism; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000032:analysis; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000032:analysis / Q000378:metabolism; D018969:Insulin-Like Growth Factor Binding Proteins / Q000032:analysis* / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000032:analysis* / Q000378:metabolism; D009924:Organ Culture Techniques; D006080:Ovarian Follicle / Q000166:cytology / Q000378:metabolism*; D013311:Streptozocin; D013552:Swine
D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2; D018972:Insulin-Like Growth Factor Binding Protein 3; D018969:Insulin-Like Growth Factor Binding Proteins; D004958:Estradiol; D013311:Streptozocin; D007334:Insulin-Like Growth Factor I