Plasma steroids , prolactin and placental lactogen

Progesterone, total oestrogens (mainly conjugated and unconjugated oestrone), prolactin and placental lactogen have been determined during late pregnancy in the peripheral plasma of intact or hypophysectomized ewes after destruction of the foetal pituitary. During the prolongation of gestation due to the removal of the foetal hypophysis, progesterone and placental lactogen remained at a high level, while total oestrogens and prolactin maintained a low concentration. When the foetus was perfused for 2 days with dexamethasone, the induced lambing was preceded by a fall in progesterone concentrations followed by a decrease in placental lactogen ; at the same time, an abrupt increase in oestrogens and prolactin was observed.