RESUMO
The oviduct provides the environment to support gamete maturation, fertilisation and early embryo development. As there is a high incidence of early embryonic death in lactating dairy cows, this study compared expression of IGF family members in the oviduct between lactating Holstein-Friesian dairy cows (n=16, 81±2.4 days in milk) and nulliparous heifers (n=16, age 1.6±0.07 years) at three stages of the oestrous cycle: A) newly selected dominant follicle in the luteal phase, B) follicular phase before the LH surge and C) pre-ovulatory phase after the LH surge. Expression of IGF1, IGF2, IGF binding protein 2 (IGFBP2), IGFBP3 and IGFBP6 mRNA was determined in the ampulla of the oviduct. Oviduct side (ipsilateral or contralateral) with respect to the dominant follicle did not affect gene expression. Expression of IGF1 and all three IGFBPs increased significantly between the luteal and the pre-ovulatory phases, with no further significant alteration post-LH surge. Concentrations of circulating IGF1 were higher in heifers than in cows, as was the mRNA expression of IGF1, IGFBP3 and IGFBP6. The pre-LH surge rise in IGFBP2 mRNA was only observed in heifers. IGF2 expression was not influenced by either age or stage of cycle. These three IGFBPs are generally considered to inhibit IGF action. These results indicate tight regulation of IGF bioavailability in the oviductal environment around oestrus, with pronounced differences between cows and heifers, which are likely to influence early embryonic development. Further studies are required to assess the implications for embryo survival.
