Adrenal secretion of glucocorticoids during hypoxemia in fetal sheep

Abstract

This work was undertaken to investigate the fetal adrenal corticoid secretory response to hypoxic stress in late gestation. Experiments were performed in two groups of fetal sheep of different gestational ages, group 1,129–132 (mean, 130) days and group II, 135–139 (mean, 136) days. Fetuses were prepared with chronic adrenal cannulas as well as peripheral arterial and venous catheters. With the fetus at rest and after 7, 9,11 and, in some instances, 30 and 60 min of hypoxia (maternal FIO210%), precisely timed (2 min) samples of adrenal effluent were collected for determination of cortisol (F) and corticosterone (B) secretion rates. Peripheral samples were obtained intermittently for blood gas and lactate determinations. Resting corticoid secretory rates were highly variable, suggesting an episodic secretory pattern. Corticoid secretory responses to hypoxemia were significantly elevated at 7–11 min, peaked at 30 min, and remained stable at 60 min. Specifically, in group I, F secretion increased from a baseline value of 37 ± 19 ng/min to a peak hypoxemic response of 376 ± 80 ng/min; B secretion increased from 6 ± 4 to 170 ± 32 ng/min. In group II, F secretion increased from 99 ± 20 to 653 ± 107 ng/min; B secretion increased from 12 ± 5 to 200 ± 28 ng/min. When related to adrenal gland weight, there was no difference between F secretory responses in groups I and II, whereas relative B secretory responses were lower in group II than in group I at 9 and 11 min of hypoxemia. We conclude that the 129–139 day sheep fetal adrenal cortex is highly sensitive to hypoxic stress with the effect presumably mediated by elevated levels of endogenous ACTH. The B stress response decreases as gestational age advances from the 129–132 day range to 135–139 days. © 1989 by The Endocrine Society.