Adrenal corticosteroids and immunoreactive ACTH in chronically cannulated ovine foetuses with bilateral adrenalectomy.

Abstract

Abstract. The adrenal fails to develop in the hypophysectomised ovine foetus but adrenal growth, maturation and increased cortisol secretion occur in the intact foetus whilst plasma immunoreactive ACTH remains at a constant value. The presence of a feedback relationship between foetal adrenal and pituitary was examined in 8 ovine foetuses which were bilaterally adrenalectomised (adrx.) at the time of implantation of catheters in the carotid artery and jugular vein (90–127 days of gestation). Ten chronically cannulated foetuses served as controls. Gestation length in these sheep was 147 ± 5 days. Plasma immunoreactive (IR) ACTH (IR.ACTH) was measured with a Sorin Biomedica kit. The antibody cross-reacts with ACTH1–39, and ACTH1–24, but not with ACTH1–13, ACTH18–39, β-LPH or β-endorphin. Cortisol (F) and corticosterone (B) were measured by a double isotope dilution derivative assay. In intact foetuses the IR.ACTH was 69.6 ± 7.1 pg/ml (mean ± sem, n = 37) until the day before parturition when values increased to 326 ± 60 pg/ml (n = 6). In adrx. foetuses of 91–121. 122–135 and > 136 days gestation the IR.ACTH values were 50.3 ± 4 (n = 14), 444 ± 46 (n = 26) and 1155 ± 175 (n = 6) pg/ml, respectively. The foetal F and B concentrations were 0.12 ± 0.027 μg/100 ml and 40 ± 6 ng/100 ml (n = 14), respectively, in adrx. foetuses. These values are not significantly different from those in intact foetuses younger than 135 days. The mean F and B concentrations in adrx. foetuses were 22 ± 4.3% (n = 14) and 49 ± 5.4% (n = 14) of the respective maternal values. In summary prior to 120 days the IR.ACTH, F and B concentrations are similar in intact and adrx. foetuses. After 122 days the IR.ACTH secretion by the foetal pituitary first begins to exhibit a feedback relationship with some adrenal secretion (?not F or B) and after 130–135 days some subtle change in pituitary sensitivity to F and/or B may operate. It is suggested that about 120 days a significant alteration in the foetal pituitary capacity for ACTH synthesis occurs.