Journal of Applied Physiology, Vol 40, Issue 4 549-558, Copyright © 1976 by American Physiological Society
Circulatory effects of prolonged hypoxia before and during antihistamine
J. E. Levasseur, H. A. Kontos, D. W. Richardson and J. L. Patterson Jr
Five chronically instrumented healthy dogs were exposed to a 5-day period
of breathing 10% oxygen in a chamber. The response to hypoxia was found to
be time dependent. During the first 24 h of hypoxia the circulatory
response was characterized by increases in cardiac output, heart rate,
pulmonary and systemic arterial blood pressures, and pulmonary vascular
resistance. Systemic vascular resistance increased; left atrial pressure
decreased. During the early part of hypoxia the animals became hypocapnic;
the arterial blood pH rose significantly. During the rest of the hypoxic
period cardiac output, heart rate, and arterial blood pH returned to the
control values; pulmonary and systemic arterial pressures and pulmonary
vascular resistance remained significantly elevated. Systemic vascular
resistance rose; left atrial pressure remained below control. This response
to hypoxia was not substantially modified when the experiment was repeated
during the administration of the antihistamine promethazine, an H1-receptor
blocking agent, in a dose which blocked the pulmonary vasoconstrictor
response to small doses of exogenous histamine. The circulatory response to
acute hypoxia in five anesthetized dogs was not modified by intravenous
administration of metiamide, an H2-receptor blocking agent.
