Effect of nisoldipine on the oxymyoglobin level of myocardial cells in hypoxic, perfused rat hearts.

The effect of nisoldipine on the oxygen balance in the hypoxic myocardial cells was studied. The isolated rat heart, driven at 300 beats/min, was perfused with Krebs-Henseleit solution equilibrated with a gas mixture containing 95% O2 + 5% CO2 (normoxic perfusion solution) at a constant flow rate (9 ml/min) according to the Langendorff's technique. The myocardial oxygenation level of myoglobin (reflecting intracellular oxygen tension) of the cells locating on the ventricular surface was continuously determined by means of an optical technique. Hypoxic perfusion (perfused with Krebs-Henseleit solution equilibrated with a gas mixture containing 30% O2 + 5% CO2 + 65% N2) decreased the oxymyoglobin level (MbO2), left ventricular pressure (LVP), and perfusion pressure (PP). Nisoldipine was infused into the aortic cannula for 10 min during the hypoxic perfusion. Larger doses of nisoldipine (282.9 and 141.5 nM expressed in terms of the final concentration in the perfusion solution) increased the MbO2 level and decreased LVP, without affecting PP. Smaller doses (70.7 and 35.4 nM) did not have a marked effect on these parameters. These results suggest that nisoldipine, in larger doses, improves the oxygen balance of the hypoxic myocardial cells, probably because of decrease in LVP hence oxygen demand, and that nisoldipine does not dilate further coronary vessels that have been dilated by hypoxia.