AJP - Endocrinology and Metabolism, Vol 242, Issue 2 102-E108, Copyright © 1982 by American Physiological Society
Comparison of canine corticosteroid responses to mean and phasic increases in ACTH
C. E. Wood, J. Shinsako and M. F. Dallman
To determine the dynamics and magnitudes of adrenal corticosteroid
responses to ACTH, we measured arterial plasma ACTH and corticosteroid
concentrations in conscious dogs during infusions of ACTH or saline.
Synthetic alpha 1-24-ACTH was infused at rates of 300,900, or 4,500 ng/30
min either as constant infusions or as three equal short infusions at
10-min intervals. In dogs infused with saline, plasma ACTH fluctuated,
whereas corticosteroids did not, suggesting that ACTH is secreted
episodically in dogs as in man. The magnitudes of the plasma corticosteroid
responses to ACTH infusions were linearly related to the logarithm of the
total amount of ACTH infused in 30 min and not to the pattern of
administration. In all ACTH infusion experiments, the lag between an
increase in arterial ACTH and corticosteroids was not less than 3 min. Mean
ACTH half-disappearance time, metabolic clearance rate, and volume of
distribution estimated from the different experiments ranged between 1.8
and 2.1 min, 24 and 38 ml . kg-1 . min-1, and 95 and 114 ml/kg,
respectively. Collectively, these results explain the apparent paradox that
corticosteroid responses to ACTH-releasing stimuli can be initiated before
a detectable increase in ACTH above the highest control value (Wood et al.
Apparent dissociation of ACTH and corticosteroid responses to ml/kg
hemorrhage in conscious dogs. Endocrinology In press).
