Concentrations of lactate and pyruvate and temperature effects on lactate dehydrogenase activity in the tissues of the big brown bat (Eptesicus fuscus) during arousal from hibernation.

1. The rectal temperatures, steady state concentrations of lactate and pyruvate, and the LDH isoenzyme composition in the heart, liver, and pectoral muscle of hibernating and arousing Eptesicus fuscus were measured. 2. Bat rectal temperature increased from 8.86 to 33.1 degrees C during arousal. 3. During arousal, steady state concentrations of pyruvate and lactate increased significantly in the tissues, however they remained generally below the level necessary to saturate LDH at the respective temperature. 4. The activities of the two LDH isoenzymes, M4, the predominant form in bat liver, and H4, the main form in bat heart and pectoral muscle, show substrate-dependent temperature effects described by the equation, mu = (E beta S + E alpha K t)/(K t + S). 5. Temperature effects (mu) on bat LDH activity increased during arousal but remained significantly lower than mu determined at saturating concentrations of substrate (E beta). 6. The parameters E beta-E alpha, E alpha and K tau are particularly important in describing the temperature dependence of LDH activity in tissues of the arousing bat.

Biochemical and morphometric studies of heart, liver and skeletal muscle from the hibernating, arousing and aroused big brown bat, Eptesicus fuscus.

Heart, liver, pectoralis major, and plasma of hibernating, arousing and aroused bats were studied. The activities of four mitochondrial enzymes and three morphometric parameters of mitochondria did not change in the heart. Mitochondrial enzyme activities in the liver and pectoralis major did not change. Lactate dehydrogenase activity and isoenzyme content in heart, liver and pectoralis major did not change. Heart lipid content determined morphometrically decreased transiently after 30 min arousal from hibernation. Plasma free fatty acid concentration increased significantly by 7.5 min and peaked at 15 min after arousal from hibernation. Concentrations of heart free fatty acids, triglycerides, glycerol, and cholesterol and liver triglycerides did not change.

Perturbation of mitochondrial composition in muscle by iron deficiency. Implications regarding regulation of mitochondrial assembly.

It has been reported that the mitochondrial cytochromes and citrate cycle enzymes occur in constant proportions to each other and increase or decrease roughly in parallel in response to various stimuli. The purpose of this study was to determine whether this proportionality is an obligatory consequence of the way in which mitochondria are assembled. Severe iron deficiency was used to bring about decreases of the iron-containing constituents of the mitochondrial respiratory chain in skeletal muscle. Cytochrome c concentration and cytochrome oxidase activity were decreased approximately 50%, while succinate dehydrogenase and NADH dehydrogenase activities were decreased by 78% in iron-deficient muscle. On electron microscopic examination, mitochondria in iron-deficient muscles had relatively sparse numbers of cristae. The iron deficiency had little or no effect on the levels of a range of mitochondrial matrix enzymes, including citrate synthase, isocitrate dehydrogenase, fumarase, aspartate aminotransferase, 3-hydroxyacyl-CoA dehydrogenase, 3-ketoacid-CoA transferase, and acetoacetyl-CoA thiolase. These results show that the usual constant proportions between the constituents of the mitochondrial respiratory chain and matrix enzymes are not obligatory; they provide evidence that mitochondrial matrix enzymes and respiratory chain constituents can be incorporated into mitochondria independently and that the ratios between them can vary within wide limits.

Effect of training on blood lactate levels during submaximal exercise.

Eight men were studied before and after a 12-wk exercise program to determine the effect of training on blood lactate levels during submaximal exercise. The training elicited a 26% increase in maximum O2 uptake (VO2max). Lactate concentrations at the same relative exercise intensities in the 55-75% of VO2max range were significantly lower after training. A significantly higher relative exercise intensity was needed to elicit a given lactate level in the 1.5- to 3.0-mM range after training. O2 uptake at the work rate required to raise blood lactate to 2.5 mM was 39% higher after training. A blood lactate of 2.5 mM was attained at 68 +/- 4% VO2max before and 75 +/- 3% of VO2max after training. Eight competitive runners required an even higher relative work rate (83 +/- 2% of VO2max) to attain a blood lactate of 2.5 mM. These data provide evidence that the adaptations to training that result in an increase in VO2max are, to some degree, independent of those responsible for the lower blood lactate levels during submaximal exercise.