Oxygen consumption in rabbit Langendorff hearts perfused with a saline medium

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Abstract
Isolated rabbit hearts were perfused according to Langendorff at 38.degree. C and a pressure of 5.9 kPa [kilopascal] with gassed Tyrode solution. Gas mixtures containing 5% CO2 and 15, 20, 30, 60 or 95% O2 in N2 were used to saturate the perfusion medium. In some cases lactate (50 or 500 .mu.M) was present in the medium perfusing the heart. Coronary flow (CF), O2 pressure in the perfusion medium and in the cardiac effluent and lactate in the effluent were analyzed in all experiments. The O2 uptake in the hearts perfused with a medium equilibrated at atmospheric pressure with 95% O2 and 5% CO2 (O2 pressure .apprx. 87 kPa, O2 content 19 ml .times. l-1), averaged 3 ml .times. 100 g w.w.-1 [wet weight] .times. min-1. Reduction of the O2 pressure in the perfusion medium resulted in an increase in CF and in the fractional extraction of O2 from the medium, making it possible to maintain the heart''s O2 uptake (.ovrhdot.VO2) down to an O2 pressure in the perfusion medium of .apprx. 24 kPa (O2 content .apprx. 5 ml .times. l-1, the perfusion medium equilibrated with 20% O2 and 5% CO2 in N2). Myocardial lactate production was low during perfusion at pO2 .apprx. 87 kPa but increased rapidly when the O2 pressure was lowered. The addition of lactate (500 .mu.M) to the perfusion medium at pO2 .apprx. 87 kPa induced a fractional uptake of .apprx. 20%. Apparently the .ovrhdot.VO2 observed during perfusion at pO2 .apprx. 87 kPa mainly reflects aerobic myocardial metabolism in this preparation. This assumption is based on the facts that coronary flow and fractional O2 extraction are submaximal and that a considerable uptake of lactate occurs concurrently with a very limited production. Even moderate reduction of the O2 pressure in the perfusion medium (to .apprx. 61 kPa) is followed by a significant increase in lactate production, indicating that myocardial oxygenation is inefficient.

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