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 insulin-like growth factor-I (IGF-I) gene expression, systemic and ovarian IGF-I concentrations and on associated metabolic changes were measured 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 taken on day 13 (07.00-16.00 h) to determine plasma insulin and IGF-I, and on day 14 (02.00-06.00 h) to determine plasma GH levels. Following slaughter on day 14, one ovary from each animal was retained to measure follicular fluid IGF-I and oestradiol concentrations. The remaining ovary 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 were significantly larger after refeeding (P < 0.05), with no effect on follicular fluid oestradiol concentrations. Mean follicular fluid IGF-I concentrations were unaffected by treatment. However, the relationships between individual follicular IGF-I concentrations, absolute follicular fluid IGF-I contents and follicle volume were affected by feeding level (P < 0.05). Regression analysis of the same data also revealed that at this stage of maturity, small follicles had greater follicular fluid concentrations of IGF-I than larger follicles. Refeeding increased the amount of IGF-I mRNA in hepatic but not ovarian tissue. We conclude that there is differential regulation of the IGF-I gene in porcine hepatic 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.
Charlton
S T
ST
Department of Animal Science, University of Alberta, Edmonton, Canada.
Cosgrove
J R
JR
Glimm
D R
DR
Foxcroft
G R
GR
D000818:Animals; D005260:Female; D015571:Follicular Fluid / Q000378:metabolism; D005508:Food Deprivation / Q000502:physiology*; D015870:Gene Expression / Q000502:physiology; D005821:Genetic Techniques; D013006:Growth Hormone / Q000097:blood; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000235:genetics* / Q000378:metabolism; D008099:Liver / Q000378:metabolism / Q000502:physiology*; D006080:Ovarian Follicle / Q000033:anatomy & histology; D010053:Ovary / Q000378:metabolism / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D011863:Radioimmunoassay; D012741:Sexual Maturation / Q000502:physiology; D013552:Swine / Q000502:physiology*
D007328:Insulin; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone