AJP - Regulatory, Integrative and Comparative Physiology, Vol 263, Issue 4 936-R944, Copyright © 1992 by American Physiological Society
Adrenal corticosteroid secretion in fetal sheep: pulsatile pattern at rest
B. T. Jackson, A. F. Lee, S. H. Morrison, R. M. Baker, H. E. Cohn and G. J. Piasecki
Department of Surgery, Brown University, Providence, Rhode Island.
This study was undertaken to define the resting pattern of fetal
pituitary-adrenocortical function. Experiments were performed at 127-145
days gestation in fetal sheep with chronic peripheral and adrenal cannulas
inserted under halothane anesthesia. With the fetus in a baseline state,
over 6 h, at 30-min intervals, maternal and fetal peripheral samples were
collected for blood gases and cortisol (F), corticosterone (B), and
adrenocorticotropic hormone (ACTH) concentrations, and three successive,
2-min adrenal samples were collected for determination of F and B secretion
rates. We observed high-frequency, episodic bursts of F secretion. A lower
frequency oscillation of F secretion, with a period of approximately 90
min, was defined by cosinor analysis. The mean amplitude of the oscillation
increased from 45 to 507 ng/min with advancing gestation. The pattern of B
secretion was similar to that for F but was quantitatively lower. An
oscillatory period of approximately 90 min for plasma F was present in a
majority of experiments. Pulsatile rhythms for ACTH were defined in 10 of
14 experiments, with periods ranging from 1.64 h in the least mature group
to 2.37 h in the oldest fetus. Mean data revealed exponential increases in
both F secretion and plasma ACTH from 129 to 145 days gestation.
