OVARIAN AND HEPATIC INSULIN-LIKE GROWTH FACTOR-I GENE-EXPRESSION AND ASSOCIATED METABOLIC RESPONSES IN PREPUBERTAL GILTS SUBJECTED TO FEED RESTRICTION AND REFEEDING

The effects of feed restriction and refeeding on ovarian and hepatic i nsulin-like growth factor-I (IGF-I) gene expression, systemic and ovar ian IGF-I concentrations and on associated metabolic changes were meas ured in prepubertal gilts. Eleven pairs of littermate gilts (70.7 +/- 4.7 kg) were placed on a maintenance level of feeding for 7 days (days 1-7). On day 8, littermates were either fed at a maintenance level of energy or fed to appetite for a further 6 days. Blood samples were ta ken on day 13 (07.00-16.00 h) to determine plasma insulin and IGF-I, a nd on day 14 (02.00-06.00 h) to determine plasma GH levels. Following daughter on day 14, one ovary from each animal was retained to measure follicular fluid IGF-I and oestradiol concentrations. The remaining o vary and a sample of liver were retained for IGF-I mRNA analysis using a ribonuclease protection assay. Six days of refeeding significantly increased plasma IGF-I (P<0.005) and basal insulin (P<0.05) but there was no effect on plasma GH. Ovarian follicular volume and diameter wer e significantly larger after refeeding (P<0.05), with no effect on fol licular fluid oestradiol concentrations. Mean follicular fluid IGF-I c oncentrations were unaffected by treatment. However, the relationships between individual follicular IGF-I concentrations, absolute follicul ar fluid IGF-I contents and follicle volume were affected by feeding l evel (P<0.05). Regression analysis of the same data also revealed that at this stage of maturity, small follicles had greater follicular flu id concentrations of IGF-I than larger follicles. Refeeding increased the amount of IGF-I mRNA in hepatic but not ovarian tissue. We conclud e that there is differential regulation of the IGF-I gene in porcine h epatic and ovarian tissues, and that ovarian factors other than, or as well as, IGF-I are involved in the regulation of ovarian responses to refeeding.