Expression of epidermal growth factor (EGF) and its receptor in bovine endometrium throughout the luteal phase: effects of EGF on prostaglandin production in endometrial cells

Epidermal growth factor (EGF) is produced in bovine endometrium throughout the estrous cycle. However, little is known about the expression of the EGF receptor (EGFR) and the roles of EGF in bovine endometrium. To clarify whether EGF is involved in local regulation of bovine endometrial function, first we determined the EGF protein and the expression of EGFR mRNA in endometrial tissues throughout the luteal stages. EGF protein concentration was higher (P < 0.05) in the mid (days 8-12) luteal stage than in the other luteal stages. EGFR mRNA expression was higher (P < 0.05) in the mid and late (days 15-17) luteal stages than in the other luteal stages. To investigate the protein concentrations of EGF and EGFR mRNA expression in cultured bovine endometrial cells, epithelial and stromal cells were isolated between day 0 and day 4 postovulation from 22 uteri. Both EGF protein concentration and EGFR mRNA expression were higher (P < 0.05) in epithelial cells than in stromal cells. Then, to examine the possible role of EGF in the regulation of prostaglandin F2α (PGF2α) and prostaglandin E2 (PGE2), cultured endometrial epithelial and stromal cells were exposed to EGF (0, 1, 10 and 100 nm) for 24 h. In epithelial cells, EGF (10 and/or 100 nm) increased (P < 0.05) PGF2α and PGE2 secretion, but in stromal cells EGF (100 nm) increased (P < 0.05) PGF2α, but not PGE2 secretion. These results indicate that 1) the highest amount of EGF is produced by bovine endometrium at the mid-luteal stage, 2) endometrial EGFR mRNA expressions are higher at mid and lateluteal stages than other stages, 3) EGF is expressed mainly by uterine epithelial cells and 4) EGF has the ability to increase PGE2 and PGF2α production in both epithelial and stromal cells and therefore may play a role in local regulation of uterine function.