AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 3 403-R410, Copyright © 1986 by American Physiological Society
Absence of fast negative feedback control of ACTH and renin in fetal and adult sheep
C. E. Wood
Fetal adrenocorticotropin (ACTH) and renin secretion are increased by a
variety of stimuli and decreased by cortisol negative feedback inhibition.
However, the time courses of these interactions are unknown. The present
studies were designed to test for rapid feedback negative suppression of
ACTH and renin secretion in fetal and adult sheep. In chronically
catheterized fetal sheep, ACTH and renin secretion were stimulated by
intravenous infusion of sodium nitroprusside, a vasodilator drug. Vehicle
or cortisol, infused at rates of 1, 2, or 4 micrograms/min for 2 min before
and during the infusion of nitroprusside did not significantly alter the
fetal ACTH or renin responses to nitroprusside. In five nonpregnant ewes,
chronically prepared with skin loops containing the carotid arteries,
nitroprusside (20 micrograms X kg-1 X min-1) was infused beginning 2 min
after infusion of vehicle or cortisol (3.5 or 7 micrograms X kg-1 X min-1).
Cortisol infusion produced a rising plasma cortisol concentration similar
to that after stress but did not alter the magnitude of the ACTH response
to nitroprusside. The results indicate that cortisol-induced suppression of
ACTH secretion does not occur rapidly in the fetal or adult sheep and that
the cortisol-induced suppression of fetal plasma renin activity is a slow
process.
