AJP - Regulatory, Integrative and Comparative Physiology, Vol 256, Issue 5 1063-R1068, Copyright © 1989 by American Physiological Society
Role of endogenous opioids in the cardiovascular responses to asphyxia in fetal sheep
M. Espinoza, R. Riquelme, A. M. Germain, J. Tevah, J. T. Parer and A. J. Llanos
Departamento de Preclinicas, Facultad de Medicina, Universidad de Chile, Santiago.
Intravenous administration of the opioid receptor antagonist naloxone to
asphyxiated fetal sheep increases the arterial blood pressure. We examined
the hypothesis that endogenous opioids modify the cardiac output
distribution during asphyxia due to changes in the vascular resistance of
some fetal organs. Thirteen fetal sheep (0.8-0.9 of gestation) were
chronically catheterized. Fetal asphyxia was induced by reducing the
uterine blood flow with an inflatable occluder around the common internal
iliac artery to approximately 50% of control for 40 min. Naloxone solution
or the solvent alone was added for the last 20 min. Asphyxia caused
hypertension, and the fetal arterial blood pressure further increased when
asphyxiated fetuses received naloxone. Heart, brain, and adrenal blood
flows increased due to the increase in blood pressure, with no changes in
their vascular resistances. In contrast, kidney and carcass blood flows
decreased, and their vascular resistances increased. We conclude that
endogenous opioids inhibit the vasoconstriction of these vascular beds
during fetal asphyxia.
