Effects of hypoxia and Freon 12 on mechanics of cardiac contraction.

Data are presented which indicate that the mechanism of tension depression and subsequent recovery from dichlorodifluoromethane (Freon 12), an aerosol gas recently described as a potent cardiac depressant agent, differs from that of hypoxia. To analyze these differences, 22 rat papillary muscles, contracting isometrically in a myograph, were studied during and subsequent to 15-min interventions of of hypoxia. Freon 12 with adequate oxygenation, or Freon 12 combined with hypoxia. During each of the three interventions the developed force (F) was markedly depressed, while peak shortening velocity (Vpm) was selectively more depressed by Freon and Freon combined with hypoxia than by hypoxia alone. While hypoxia shortened the time to peak force (TTP) and one-half relaxation time (RT1/2) markedly, Freon 12 with adequate oxygenation slightly shortened RT1/2 (P is less than 0.001) but failed to shorten TTP significantly. In contrast, Freon 12 administered during hypoxia shortened TTP and RT1/2 significantly (P is less than 0.001), more than did hypoxia or Freon 12 alone. Posthypoxic prolongation of TTP and RT1/2 was not seen during recovery from Freon 12. This prolongation was depressed during recovery from Freon 12 given either during hypoxia or during recovery from hypoxia. The results indicate that Freon 12 and hypoxia act synergically, although the mechanisms through which they mediate their actions on myocardial tissue are not identical.