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

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Abstract
The adrenal fails to develop in the hypophysectomized ovine fetus, but adrenal growth, maturation and increased cortisol secretion occur in the intact fetus while plasma immunoreactive ACTH remains at a constant value. The presence of a feedback relationship between fetal adrenal and pituitary was examined in 8 ovine fetuses which were bilaterally adrenalectomized (adrx.) at the time of implantation of catheters in the carotid artery and jugular vein (90-127 days of gestation). Ten chronically cannulated fetuses served as controls. Gestation length in these sheep was 147 .+-. 5 days. Plasma immunoreactive (IR) ACTH (IR.cntdot.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, .beta.-lipotropin or .beta.-endorphin. Cortisol (F) and corticosteron (B) were measured by a double isotope dilution derivative assay. In intact fetuses, the IR.cntdot.ACTH was 69.6 .+-. 7.1 pg/ml (mean .+-. SEM [standard error of the mean], n = 37) until the day before parturition when values increased to 326 .+-. 60 pg/ml (n = 6). In adrx. fetuses of 91-121, 122-135 and > 136 days gestation the IR.cntdot.ACTH values were 50.3 .+-. 4 (n = 14), 444 .+-. 46 (n = 26) and 1155 .+-. 175 (n = 6) pg/ml, respectively. The fetal F and B concentrations were 0.12 .+-. 0.027 .mu.g/100 ml and 40 .+-. 6 ng/100 ml (n = 14), respectively, in adrx. fetuses. These values are not significantly different from those in intact fetuses younger than 135 days. The mean F and B concentrations in adrx. fetuses were 22 .+-. 4.3% (n = 14) and 49 .+-. 5.4% (n = 14) of the respective maternal values. Prior to 120 days, the IR.cntdot.ACTH, F and B concentrations are similar in intact and adrx. fetuses. After 122 days, the IR.cntdot.ACTH secretion by the fetal 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 after about 120 days, a significant alteration in the fetal pituitary capacity for ACTH synthesis occurs.

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