REPORT NUMBER 652 BIOCHEMISTRY OF SUBMARINE AND DIVING STRESS I. Lactate-Pyruvate and Redox State Responses of Blood and Tissue in Chronic Hypercapnia

Lactate and pyruvate concentrations were measured in blood and various tissues of guinea pigs exposed to 15% C02 in 21% O«. balance N2, for varying periods of time up to one week. Acute exposure resulted in reduction of lactate/pyruvate ratios (L/P) of blood, heart, and muscle but not liver. Blood L/P further~decreased after one day of exposure and slowly increased during the chronic phase of respiratory acidosis. Heart L/P returned to control values by six hours, while muscle L/P remained depressed for the duration of hypercapnia. Since L/P reflect the redox state of the free cytoplasmic nicotinamide-adenine dinucleotide couplet, the redox state, NAD/NADH was calculated from the L/P and pH of blood for the various periods of hypercapnia. During acute hypercapnia NAD/NADH increased in blood markedly indicating the existence of a more oxidized state during this period. Chronie hypercapnia returned blood NAD"*"/NADH toward initial values suggesting a normalization of glycolytic metabolism. The observed differences in L/P in the various tissues are apparently related to the different CO2 buffering capacities of tissues.