Induction of Premature Parturition in Sheep: Adrenocorticotrophin and Corticosteroid Changes During Infusion of Synacthen Into the Foetus

Abstract

Synacthen (10 \g=m\g/h) infused into foetal sheep at about day 125 of gestation caused premature delivery within 4 days. During the first 24 h of the infusion the secretion of adrenocorticotrophin was depressed and the assayable hormone concentration was within 500\p=n-\1000 pg/ml. Subsequently, large fluctuations occurred in the adrenocorticotrophin concentration in the pasma of foetal sheep which were consistent with the stimulation of adrenocorticotrophin secretion. No transfer of Synacthen to non-infused twin foetuses was observed. The plasma corticosteroid concentration in the infused foetus also showed a small rise during the first 24 h of the infusion followed by large fluctuations in concentrations that coincided with the changes in adrenocorticotrophin. No consistent changes in the plasma corticosteroid concentration in the non-infused twin foetus were observed. These results are discussed in relation to the hormone changes occurring during normal delivery.The need for an intact pituitary and adrenal for the induction of normal par¬ turition in the sheep is now well established (Liggins et al. 1973). There is an increased output of cortisol from the foetal sheep adrenal several days be-0 Present address:

Adrenocorticotrophin and Corticosteroid Changes During Dexamethasone Infusion to Intact and Synacthen Infusion to Hypophysectomized Foetuses

“…Synacthen infusion into hypophysectomized foetal sheep produces ACTH con¬ centrations comparable to those seen during the first 24 h of infusion into foetuses with an intact pituitary (Jones et al 1978). The absence of the later high and fluctuating ACTH concentrations seen in the foetal sheep with an intact pituitary indicates that these were neither caused by the infusion system nor can be explained by an initial period of saturation of the foetal tissue with hormone.…”

“…After implanting catheters the foe¬ tuses were left for at least 4 days after which foetal arterial samples were collected every 8 h for at least 3 days. Then the hypophysectomized foetuses were given a jugular vein infusion of Synacthen (ACTH1-24, Ciba Laboratories Ltd.) at 10 ,«g/h until delivery, as described by Jones et al (1978). The 4 foetuses with intact pituitaries were given jugular vein infusions of dexamethasone sodium phosphate (Merck, Sharp & Dohme, 1 mg/24 h) until delivery.…”

“…These results suggested that during Synacthen infusion ACTH secretion is first suppressed and then stimulated (Jones et al 1978). This possibility has been further investigated by infusing Synacthen into hypophysectomized foetuses.…”

Heterogeneity of adrenocorticotrophin in the pituitary gland and plasma during the perinatal period

“…No transplacental passage of ACTH was observed when labelled hormone was given to the mother or the fetus in several species including sheep (Jones et al, 1975), rabbits (Genazzani et al, 1975) and rats . The perfusion of ACTH to rhesus monkey fetuses was unable to induce a rise in the maternal plasma ACTH level (Walsh et al, 1979 (Jones et al, 1978 ;Jones and Roebuck, 1979) and in that of rat between 17 and 21 days (Chatelain and Cheong, 1985a, b) of pregnancy. In the latter species, these forms are similar to those observed in the fetal pituitary (Chatelain and Dupouy, 1985b).…”

Absence of Transplacental Passage of ACTH in the Rat: Direct Experimental Proof

“…According to Jones et al (1977), adrenocorticotrophin con centrations were higher in the arterial plasma of the fetuses than in the mothers in the latter half of pregnancy and during labour. No changes in maternal plasma ACTH were detected during Synacthen infusion into the fetal sheep (Jones et al, 1978). In comparison to the levels of ACTH in sows, the concentrations in fetal and newborn piglets were much higher (Brenner et al, 1978).…”