Effects of exogenous insulin and body condition on metabolic hormones and gonadotropin-induced follicular development in prepuberal gilts

To determine influences of insulin and body condition on follicular growth, prepuberal gilts (n = 16) treated with pregnant mare's serum gonadotropin (PMSG) were used in a 2 X 2 factorial experiment with main effects of insulin (0 or.4 IU/kg every 12 h beginning at 1800 on the day before PMSG) and backfat depth (moderate, 25 +/-.8; high, 32 +/-.7 mm; P .0001). Body weights were similar. Blood sampling was at 6-h intervals for analyses of LH, FSH, growth hormone (GH), glucagon, cortisol, insulin, insulin-like growth factor-I (IGF-I), plasma urea nitrogen (PUN), nonesterified fatty acids (NEFA), testosterone, estradiol-17 beta, and progesterone. Ovaries were removed 75 h after PMSG treatment, and visible small (less than or equal to 3mm), medium (4 to 6 mm), large (greater than or equal to 7 mm), and macroscopically atretic follicles were counted. Administration of insulin increased IGF-I in fluid of medium follicles (108.8 vs 60.7 ng/ml; SEM