Regulation of the growth hormone receptor, insulin-like growth factor (IGF) I and IGF binding protein 2 in reproductive tissues of dairy cattle during lactation and associated effects on fertility

The components of the growth hormone (GH)/insulin-like growth factor (IGF) system play critical reproductive and metabolic roles in dairy cattle. In liver, GH receptor (GHR) and IGF-I are dynamically regulated by lactation and energy balance. Less is known about the regulation of GHR and IGF-I mRNA in reproductive tissues. The objective of these studies was to measure the expression of total GHR (tGHR), IGF-I and IGF binding protein (IGFBP) 2 mRNA in reproductive tissues during several stages of lactation and around the time of artificial insemination. Changes in gene expression were then evaluated for potential effects on fertility.; The expression of tGHR, IGF-I and IGFBP-2 was measured in uterine, luteal, follicular and hepatic tissue three times during the early postpartum period. Expression of tGHR and IGFBP-2 mRNA in the reproductive tissues did not change during early lactation. Luteal and follicular expression of IGF-I changed in an inverse manner from the second sample collection to the third (luteal expression decreased and follicular expression increased). Further research is needed to elucidate the implications these changes have for fertility in dairy cattle.; The expression of tGHR, IGF-I and IGFBP-2 was also measured in uterine and hepatic tissue at several stages of lactation around the time of insemination. Uterine tGHR mRNA, uterine IGF-I mRNA and plasma IGF-I concentrations increased at estrus. The timing of these changes suggests that uterine IGF-I does not directly affect early embryonic development, but may enhance the uterine environment for early embryonic development. The cows that became pregnant had higher liver tGHR and IGFBP-2 mRNA concentrations. The cows that became pregnant may have been metabolically distinct from the cows that did not become pregnant, resulting in different levels of hepatic gene expression and providing a reproductive advantage.