Steroid and Prostaglandin Concentrations in the Plasma of Pregnant Ewes During Infusion of Adrenocorticotrophin or Dexamethasone to Intact or Hypophysectomized Foetuses

Abstract

Catheters were implanted into 16 ewes and their foetuses between days 110 and 124 of gestation. Hypophysectomy was attempted in eight of these foetuses. Continuous infusion of synthetic ACTH (10 microgram/h) or dexamethasone (1mg/24 h) into the foetus, starting between days 124 and 129, induced premature parturition. The concentration of progesterone in the maternal peripheral plasma decreased before parturition in all animals while the level of oestradiol increased in ewes with intact foetuses or in those in which hypophysectomy was incomplete. When hypophysectomy was complete, no increase in the maternal level of oestradiol occurred before delivery. The concentration of 13,14-dihydro-15-oxo-prostaglandin F2alpha increased in the peripheral plasma of ewes with intact or hypophysectomized foetuses infused with ACTH. It is suggested that an intact foetal pituitary gland is required for the rise in the level of oestrogen prepartum, but that this rise is not essential for increased prostaglandin production of parturition.

Plasma steroids, prolactin and placental lactogen in intact or hypophysectomized pregnant ewes with an hypophysectomized foetus. Effect of foetal perfusion of dexamethasone

“…These data agree with earlier reports (Flint et al, 1975 ;Kendall et al, 1977) and with infusion experiments using adrenocorticotropin (Kendall, et al, 1977 …”

“…This latter procedure momentarily inhibits cortisol secretion by the foetal adrenals and then stimulates it (Bosc and Fèvre, 1974). If the foetus has been hypophysectomized however, administration of cortisol to the mother does not induce delivery (Bosc, 1972) while perfusion into the foetus results in the birth of the lamb (Kendall et al, 1977 (Bosc, 1972 ; Bosc and Fèvre, 1975 Hormone assays : The steroids were assayed by radioimmunoassay. Progesterone was determined according to Palmer and Jousset (1975) with the following steps : plasma extraction (0,5 ml) with hexane (5 ml) ; after evaporation, addition of a phosphate-buffered solution containing tritiated progesterone and a specific antiserum (Yenikoye, 1977) fig.…”

“…2). (Bosc and Fèvre, 1975) and in cestrone or total oestrogens (Kendall et at., 1977) which remained at the levels observed during the pre-partum time. The results also show that a dexamethasone perfusion over 2 days into a hypophysectomized foetus resulted in delivery of the lamb which was preceded by a fall in plasma progesterone and a large increase in oestrogens ; these hormonal changes were similar to that occurring before natural lambing which has often been described (Bedford et al, 1972 ;Thorburn et al, 1972 ;Liggins et al, 1973).…”

The effect of passive immunization against oestrogens on the onset of parturition in the ewe

“…However, although the endocrine changes at parturition induced by the infusion of glucocorticoids and adrenocorticotrophin to the intact fetal lamb are similar to those at term , it has been suggested that the pre-partum rise in oestrogen level is not essential for parturition. This premise was based on the apparent absence of an increase in maternal plasma concentrations of oestrogen when parturition was induced by adrenocorticotrophin treatment of the hypophy¬ sectomized ovine fetus (Kendall et al, 1977).…”

Editorial: The Fetal Adrenal and the Maturation of the Growth Hormone and Prolactin Axes

“…Nevertheless, a role for GH in glucocorticoid action in the fetus is uncertain because the late gestational induction of PRLR expression coincides with a fall in fetal plasma GH levels in humans as well as sheep (24). Interestingly, the administration of dexamethasone to fetal sheep near term increases the levels of 17-␤ estradiol in fetal blood (31), suggesting that estrogens may mediate some of the biological effects of glucocorticoids in the fetus. The aforementioned studies of the induction of GH and PRL receptors in the ovine fetus (5,6,19) did not examine the effects of adrenalectomy or cortisol administration on fetal estrogen levels.…”