Abstract
To test the hypothesis that acclimation to simulated high altitude (SHA) may occur in the tissues as well as in the systemic regulatory apparatus of an organism, atria isolated from young rats acclimated to SHA of 6,000 m and from control rats were observed under normoxic conditions. SHA atria have slower spontaneous heart rates than atria isolated from controls (209 +/- 4 vs. 228 +/- 3, P less than 0.001). SHA atria are more sensitive to pentobarbital sodium (P less than 0.001) and ethanol (P less than 0.06): spontaneous mechanical activity stops at a lower drug concentration in SHA than in control atria. SHA atria are less sensitive to norepinephrine in the concentration range of 7.9 X 10(-9) to 3.1 X 10(-6) M and respond to increased bath concentrations (3.8, 5.8 and 7.8 mM) of calcium with a significantly (P less than 0.04) smaller chronotropic response and a greater inotropic response than atria from control animals. These data support the above-mentioned hypothesis.
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