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 erythrocyte s, [H-3]sucrose, and L-[1-C-14]lactate or a mixture of 51Cr-labeled erythro cytes, [C-14]sucrose, and L-[2-H-3]lactate was injected into the portal vei n, and samples were obtained from the hepatic vein. Data were evaluated usi ng a model comprising flow along sinusoids, exchange of lactate between pla sma and erythrocytes and between plasma and hepatocytes, and, in the case o f L- [1-C-14]lactate, metabolism to H[C-14]O-3(-) within hepatocytes. The c oefficient for lactate efflux from erythrocytes was 0.62 +/- 0.24 s(-1), an d 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 pro duct of the hepatocyte membrane for lactate (PinS, in ml . s(-1) . g(-1)) v aried 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 hepat ocytes was close to equilibrium, whereas lactate metabolism was rate limiti ng.