MEASUREMENT OF PYRUVATE AND LACTATE KINETICS ACROSS THE HINDLIMB AND GUT OF ANESTHETIZED DOGS

We have developed a new model to quantify regional pyruvate and lactat e transmembrane transport, shunting, exchange, production, and oxidati on in vivo. The method is based on the systemic continuous infusion of pyruvate or lactate stable isotopic carbon tracers and the measuremen t of pyruvate and lactate enrichment and concentration in the artery a nd vein of that region (e.g., leg or gut), the pyruvate and lactate en richment of intracellular free water in the tissue as measured by biop sy, and the rate of blood flow through the tissue. The purpose of the experiment was to measure the pyruvate and lactate kinetics in leg mus cle and gut in anesthetized dogs (n = 6). The transmembrane transport and degree of shunting of pyruvate and lactate were comparable in musc le and gut. When modified for substrate inflow, interconversion betwee n pyruvate and lactate took place at a rate twice as fast in muscle as in the gut, and production and oxidation of pyruvate was similar to 5 0% greater in muscle than in the gut. Thus our new model enables quant itation of many aspects of lactate and pyruvate kinetics. We conclude that in anesthetized animals the muscle is the tissue most responsible for whole body peripheral pyruvate and lactate kinetics.