PROTECTIVE EFFECT OF A MILD ACIDOSIS ON HYPOXIC HEART-MUSCLE

Isolated spontaneously beating and electrically-paced rabbit hearts were perfused aerobically and then with hypoxic buffer (PO < 25 mmHg) at pH 7.4, 6.9 and 6.6, the required pH being established by varying the CO2 content of the gas mixture bubbled through the perfusion buffer. After the required period of hypoxic perfusion the hearts were either reoxygenated with buffer solution at pH 7.4 or they were assayed for ATP and creatine phosphate or their mitochondria were harvested and assayed for QO, respiratory control index and Ca2+-accumulating activity. Resting and peak developed tension were monitored continuously. Hearts made hypoxic at pH 7.4 exhibited reduced ATP and creatine phosphate content. The respiratory activity of their mitochondria was low and their Ca2+-accumulating activity high relative to that obtained for hearts made hypoxic at pH 6.9. There was a greater recovery of tension development during reoxygenation of hearts made hypoxic at pH 6.8, relative to recovery obtained for the pH 7.4 hypoxic hearts. Perfusion of pH 6.9 also resulted in a relatively smaller rise in resting tension relative to that found during hypoxic perfusion at 7.4. These results have been interpreted to mean that a mild respiratory acidosis has a protective effect on hypoxic heart muscle. This protective effect was not evident if the pH of the hypoxic buffer was decreased further, to 6.6. © 1979.