Transpulmonary Lactate and Pyruvate Kinetics By Matthew Lawrence Johnson A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy

Transpulmonary Lactate and Pyruvate Kinetics by Matthew Lawrence Johnson Doctor of Philosophy in Integrative Biology University of California, Berkeley Professor George A. Brooks, Chair Shuttling of intermediary metabolites such as lactate and pyruvate contribute to the dynamic energy needs of tissues. Tracer kinetic studies offer a powerful method to measure the metabolism of substrates like lactate and pyruvate that are simultaneously taken up from and released into the circulation by organs. We examined the transpulmonary lactate and pyruvate kinetics in an anesthetized rat model during a control (Con), lactate load (LL) and epinephrine infusion (Epi) using a primedcontinuous infusion of [U-C]lactate and pyruvate. Compared to Con and Epi stimulation, LL significantly increased mixed central venous ([ v ]) and arterial ([a]) pyruvate and lactate concentrations (P < 0.05). Transpulmonary net lactate and pyruvate balances were positive during all three conditions indicating net metabolite uptake. Net balance was significantly greater during epinephrine stimulation compared to the control for both lactate and pyruvate (P < 0.05). Tracer measured lactate fractional extractions were similar for control and lactate load conditions, but negative during Epi stimulation when a transpulmonary production of lactate from venous pyruvate occurred. Tracer measured pyruvate fractional extraction averaged 42.8 ± 5.8% for all three conditions, and was significantly higher during epinephrine stimulation (P < 0.05) than during either Con or LL conditions, which did not significantly differ from each other. Lactate total release (= tracer measured uptake net release) increased due to a lactate load (i.e., LL) and decreased (i.e., negative) from epinephrine stimulation because of the transpulmonary pyruvate  lactate conversion. Pyruvate total release was significantly higher during epinephrine stimulation (400 ± 100 μg/min) vs. Con (30 ± 20 μg/min) (P < 0.05). For lactate, we conclude that transpulmonary concentration difference measurements across the lungs provide an incomplete – and perhaps misleading – picture of parenchymal lactate metabolism, especially during epinephrine stimulation. Regarding pyruvate, significant extraction occurs during circulatory transport across the lungs. The extent of pulmonary parenchymal pyruvate extraction predicts high expression of monocarboxylate (lactate/pyruvate) transporters (MCTs) in the tissue and western blot analysis of whole lung homogenates detected three isoforms: MCT1, MCT2, and MCT4. We conclude that a critical site of circulating pyruvate extraction resides in the lungs. Furthermore, during times of elevated circulating pyruvate or epinephrine stimulation, pyruvate extraction increases.