Key result
Exposure to high-altitude hypoxia for 109 days did not induce morphological adaptation in the myocardial capillarity of the ovine fetus compared to low-altitude controls.
Why the study?
Does chronic high-altitude hypoxia increase myocardial capillarity in the ovine fetal heart?
Does chronic high-altitude hypoxia increase myocardial capillarity in the ovine fetal heart?
Contrary to the hypothesis, chronic high-altitude hypoxia does not induce morphological adaptation to increase capillarity in the ovine fetal myocardium.
To determine the effect of chronic hypoxia on myocardial capillarity, we exposed pregnant ewes to an altitude of 3,820 m from day 30 to day 139 of gestation and compared the fetus to low-altitude (approximately 300 m) controls. We hypothesized that capillarity would increase in the hypoxic myocardium to optimize oxygen and metabolite flux to hypoxic tissues. Fetal hearts were fixed by retrograde aortic perfusion and processed for microscopy and stereological evaluation. Fiber cross-sectional area and capillary density were measured and standardized to sarcomere length. Capillary volume density and capillary diameter were measured, capillary-to-fiber ratio and capillary length density were calculated, and the capillary anisotropy coefficient was obtained from a table of known values. Capillary-to-fiber ratio, capillary volume density, and the capillary anisotropy coefficient were not different between hypoxia and control groups. Capillary diameter was significantly larger in the right compared with the left ventricle of hypoxic but not control hearts; fiber cross-sectional area tended to be larger in the right ventricle of both groups, but this was not significant. As a result of larger fiber size, capillary density and capillary length density were significantly smaller in the right ventricle of hypoxic but not control fetal hearts. Contrary to our hypothesis, the ovine fetus does not show morphological adaptation in the myocardium after approximately 109 days of high-altitude hypoxic stress.
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Lewis et al. (1999) studied Chronic hypoxia. High-altitude hypoxia (3,820 m) vs. Low-altitude (approximately 300 m) controls was evaluated on Myocardial capillarity (capillary-to-fiber ratio, capillary volume density, capillary anisotropy coefficient). Exposure to high-altitude hypoxia for 109 days did not induce morphological adaptation in the myocardial capillarity of the ovine fetus compared to low-altitude controls.
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