Abstract
After 15-18 months of experimental coarctation of the aorta, the weight of the rat left ventricle increased by 94%. Papillary muscle strips developed 46% less tension than strips of the same thickness from control hearts. The average rate of tension development was 53% below controls. Strips from hypertrophied hearts featured three characteristics probably associated with impairment of excitation-contraction coupling, namely a decreasing ability to respond to high-stimulation frequency, a decrease in the degree of potentiation by paired pulse stimulation, and an increase in the extent of incomplete relaxation at high-contraction rate as compared to controls. After 6-7 weeks of adaptation to high-altitude hypoxia, the rat papillary muscle strips taken from non-hypertrophied left ventricle developed 30% more tension than strips of the same thickness from control hearts. These strips showed a higher contraction amplitude at high-stimulation rates, and an increase in the degree of potentiation by paired pulse stimulation.
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