AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 2 343-R348, Copyright © 1995 by American Physiological Society
Fetal responses to carotid occlusion: immaturity of buffering systems
C. E. Wood
Department of Physiology, University of Florida College of Medicine, Gainesville 32610.
In postnatal animals, carotid occlusion does not stimulate reflex hormonal
responses, because decreases in carotid arterial baroreceptor activity are
balanced by reflex-mediated increases in vagal afferent traffic from aortic
and cardiac receptors. The present experiments were designed to test the
hypothesis that hormonal responses to carotid occlusion in fetal animals
are not inhibited by vagal afferents. In thirteen chronically catheterized
fetal sheep (125-146 days), bilateral carotid occlusion (n = 11) increased
arterial blood pressure from 44.0 +/- 2.4 to 55.2 +/- 3.3 mmHg, decreased
heart rate from 189 +/- 5 to 165 +/- 12 beats/min, increased plasma
adrenocorticotropin from 71 +/- 15 to 248 +/- 79 pg/ml and vasopressin from
3.0 +/- 1.0 to 7.4 +/- 2.6 pg/ml but did not significantly alter renin.
Plasma hormone concentrations were not significantly altered in control (n
= 7) experiments or in response to unilateral carotid occlusion (n = 4).
The results of these experiments demonstrate the functional immaturity of
the vagal afferent buffering systems in the late-gestation fetus compared
with the postnatal animal.
