Aromatase activity and oestrogen concentrations in bovine cotyledons and caruncles during gestation and parturition.

Two peaks of aromatase activities were detected in bovine cotyledons, 2.76 +/- 0.96 pmol min-1 mg-1 protein at month five of gestation and 3.62 +/- 0.78 pmol min-1 mg-1 protein immediately after parturition, but aromatase activity in caruncles was very low throughout gestation. Oestrone concentrations in the cotyledons and caruncles were 0.93 +/- 0.50 and 1.51 +/- 0.69 ng mg-1 protein at month five of gestation, but 4.31 +/- 1.66 and 3.36 +/- 0.98 ng mg-1 protein immediately after parturition, indicating a biphasic pattern. Our findings suggest that oestrogen synthesis in the bovine placenta increased to a maximum at least twice during the period from gestation to parturition; at month five of gestation and at parturition the changes in aromatase activity may only be partially explained by changes in oestrogen production.