Myocardium-blood gradients of lactate and pyruvate in the dog.

Abstract

Myocardium – coronary sinus blood gradients (M/CS) of lactate and pyruvate were determined in 24 open-chest dogs under conditions of normoxia, hyperoxia, and hypoxia, in the presence and absence of carbon dioxide. Four groups of experiments were carried out according to the gas mixture used during a control and an experimental period: group Co, 20% O2 in nitrogen; group H1, 20% O2 in nitrogen and 6% O2 in nitrogen; group H2, 20% O2 plus 5% CO2 and 6% O2 plus 5% CO2; and group H3, 95% O2 plus 5% CO2 and 6% O2 plus 5% CO2. Normal myocardial lactate extraction and high M/CS ratios for lactate were present during ventilation with 20% O2 (group Co and control period of group H1). When 5% CO2 was added to the inspired gas (control period of group H2), much higher M/CS ratios were observed due to elevation of myocardial concentrations of lactate although blood levels and myocardial extraction remained unchanged. Ventilation with 95% O2 plus 5% CO2 (control period of group H3) was associated only with decreased lactate blood levels, and consequently higher M/CS ratios than in group Co. Acute hypoxia (group H1) caused a marked increase in blood and myocardial lactate levels with a fall in extraction and M/CS ratios (group H1). In the presence of 5% CO2 (group H2), hypoxia was associated with a smaller rise in blood lactate levels than that seen in group H1, myocardial lactate concentration failed to rise above the high prehypoxic control levels, and the M/CS ratio fell although a significant gradient persisted during hypoxia. Group H3, ventilated with 95% O2 plus 5% CO2 during the control period and exposed to 5% CO2 during hypoxia, showed moderate increase in blood and myocardial lactate levels and abolition of the M/CS gradient during O2 lack. The changes in blood and myocardial pyruvate observed in this study were similar to the described changes for lactate. These results show (1) that myocardium – coronary sinus blood gradients of lactate and pyruvate are present in the dog heart under these experimental conditions; (2) that these gradients may be influenced by ventilation with gas mixtures containing 5% CO2, by hyperoxia and hypoxia; and (3) that an active transport mechanism in the myocardium may be responsible for the uptake of these compounds against a concentration gradient.