AJP - Regulatory, Integrative and Comparative Physiology, Vol 232, Issue 1 5-R9, Copyright © 1977 by American Physiological Society
Physiological inhibition and facilitation of adrenocortical response to hemorrhage
D. S. Gann, G. L. Cryer and J. C. Pirkle Jr
In a search for physiological feedback inhibition, secretion rates of
cortisol were measured in intact dogs before and after sequential
hemorrhages. The sucond of two sequential hemorrhages of 10 ml/kg separated
by 90 min evoked significantly less increase of secretion rate of cortisol
than did the first. This result was not explained by differential
hemodynamic effects. Exhaustion of pituitary or adrenal capacities was
excluded, since dogs responded normally to a second, larger hemorrhage.
However, no attenuation response to a second 10 ml/kg hemorrhage was seen
after a larger, 20 ml/kg, first hemorrhage. This led in turn to a search
for a physiological facilitatory mechanism which might offset the feedback
effect. The second of two rapid sequential hemorrhages to isovolemia
following preexpansion of plasma volume evoked significantly greater
increase of secretion rate of cortisol than did the first. This result also
was not explained by differential hemodynamic effects. The results support
the hypothesis that hemorrhage elicits both physiological feedback and
facilitatory effects which interact and which are (different) functions of
the intensity of stimulus.
