Uptake of lactate by the liver: effect of red blood cell carriage

Multiple-indicator dilution experiments with labeled lactate were performed in the livers of anesthetized dogs. A mixture of Cr-51-labeled erythrocytes, [H-3]sucrose, and L-[1-C-14]lactate or a mixture of 51Cr-labeled erythrocytes, [C-14]sucrose, and L-[2-H-3]lactate was injected into the portal vein, and samples were obtained from the hepatic vein. Data were evaluated using a model comprising flow along sinusoids, exchange of lactate between plasma and erythrocytes and between plasma and hepatocytes, and, in the case of L- [1-C-14]lactate, metabolism to H[C-14]O-3(-) within hepatocytes. The coefficient for lactate efflux from erythrocytes was 0.62 +/- 0.24 s(-1), and those for influx into and efflux from hepatocytes were 0.44 +/- 0.13 and 0.14 +/- 0.07 s(-1), respectively. The influx permeability-surface area product of the hepatocyte membrane for lactate (PinS, in ml . s(-1) . g(-1)) varied with total flow rate (F, in mi s(-1) . g(-1)) according to PinS = (3.1 +/- 0.5)F + (0.021 +/- 0.014). Lactate in plasma, erythrocytes, and hepatocytes was close to equilibrium, whereas lactate metabolism was rate limiting.