A Novel Role of Luteinizing Hormone in the Embryo Development in Cocultures1

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Abstract
Bovine oviductal epithelium contains LH receptors, which function in the increase of synthesis of oviductal glycoprotein (OGP). As with cocultures of embryos with oviductal epithelial cells, OGP is thought to promote early embryonic growth and development. These findings led us to test the hypothesis that LH treatment of cocultures further increases embryo development through OGP mediation. Coculture of ≥10 two-cell bovine embryos with bovine oviductal epithelial cells increased the development of the embryos into blastocysts. Treatment of these cocultures with hCG, used as a surrogate for LH because of its stability and purity, further increased embryo development. The hCG effect is dose dependent and hormone specific and requires the dimer conformation and the presence of LH receptors in oviductal epithelial cells. The inhibition of OGP synthesis and prevention of protein kinase A activation blocked the hCG effect in cocultures. Reverse transcription polymerase chain reaction and indirect immunofluorescence with laser scanning confocal microscopy demonstrated the presence of LH receptors in bovine oocytes, embryos, and blastocysts. However, embryo LH receptors may not have played any role in the beneficial hCG effects in cocultures. These findings suggest that elevated periovulatory LH levels may promote preimplantation embryo development in oviducts. These results have important implications for assisted reproductive technologies in which cocultures are used to improve pregnancy rates.

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