AJP - Heart and Circulatory Physiology, Vol 254, Issue 6 1194-H1199, Copyright © 1988 by American Physiological Society
Effects of intermittent hypoxia on structural vascular adaptation in chick embryos
T. H. Adair, J. P. Montani and A. C. Guyton
Department of Physiology and Biophysics, University of Mississippi Medical Center, Jackson 39216-4505.
We explored whether the blood vascular system of the chick embryo adapts
its structure to meet the maximum or average oxygen needs of the tissue
cells. Chick embryos were grown in continuous 12% oxygen, continuous 16%
oxygen, and intermittent 12% oxygen in which the embryos were exposed to
12% oxygen for 4 h each day. Control groups were grown in room air.
Measurements of structural vascular resistance (SVR), i.e., the resistance
of the maximally dilated vasculature, were used to estimate the whole body
vascularity of the 14- or 15-day-old embryos. Continuous exposure to 12%
oxygen decreased SVR by 63.1 +/- 1.2 (SE) %, and intermittent exposure to
12% oxygen decreased SVR by 55.6 +/- 0.5% when compared with a 15-day-old
normoxic control group. Based on studies with continuous exposure to
different levels of low oxygen, it was predicted that exposure to 19.5%
oxygen, the average concentration for the intermittent hypoxia group, would
decrease SVR by 15.0 +/- 0.3%. These results indicate that intermittent
hypoxia at 12% oxygen was approximately 90% as effective as continuous
hypoxia at the same level in decreasing SVR and about four times more
effective than 19.5% continuous oxygen. Therefore, the results support the
hypothesis that the blood vascular system adapts its structure to meet
almost entirely the maximum oxygen needs of the tissue cells.
