Cortisol infusion depresses the ratio of bioactive to
immunoreactive acth in adrenalectomized sheep fetuses.
Zehnder, Timothy J., Nancy K. Valego, Jeffrey Schwartz, Jennifer
Green, and James C. Rose.
Departments of Physiology and Pharmacology and Obstetrics and
Gynecology and Perinatal Research Laboratories, Bowman Gray School of
Medicine of Wake Forest University, Winston-Salem, NC 27157-1066
APStracts 4:0254E, 1997.
We examined the effects of exogenous cortisol on plasma immunoreactive
ACTH (iACTH) bioactive ACTH (bACTH) and ACTH-(1-39) in 9
adrenalectomized fetuses at 126-130 and 136-140 days of gestation.
Fetuses received 4 hr cortisol (2 [mu]g/kg/min) or saline infusions
on consecutive days. Blood was obtained before and at intervals
during infusions. Arterial blood gases and hematocrits were normal
and did not change with age. Plasma cortisol did not change during
saline infusions, but increased significantly (range=30-70 ng/ml)
during cortisol infusions. Basal plasma iACTH, bACTH and ACTH-(1-39),
and the ratios bACTH/iACTH and ACTH-(1-39)/iACTH were significantly
higher in the older fetuses. Cortisol infusions decreased plasma
iACTH, bACTH, and ACTH-(1-39) in both groups, and the suppression as
a percent of the baseline was similar. The ratio bACTH/iACTH declined
to the same level at 126-130 (0.201+/-0.040 to 0.051+/-0.002) and
136-140 (0.389+/-0.088 to 0.046+/-0.002) days of gestation. These
data suggest that physiologic concentrations of cortisol selectively
inhibit bACTH secretion and the ACTH response to cortisol inhibition
is not different between 126 and 140 days of gestation in
adrenalectomized sheep fetuses.
Received 30 July 1997; accepted in final form 17 October 1997.
APS Manuscript Number E357-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997