Stainsby W N, Brechue W F, O'Drobinak D M
Department of Physiology, College of Medicine, University of Florida, Gainesville 32610.
Med Sci Sports Exerc. 1991 Aug;23(8):907-11.
It is not possible to make accurate measurements of muscle lactic acid net exchange during exercise by application of the Fick relationship. To make accurate measurements of lactic acid net exchange, preparations with isolated circulations have been used. Since such preparations utilize relatively small muscles or groups of muscles, the data apply to muscle contractions, not exercise. In exercise, external influences may affect lactate exchange. The net lactic acid exchange (L) of the isolated dog gastrocnemius-plantaris muscle group has been quantified for repetitive twitch and tetanic contractions, progressive contractions, and four repetitions of 30-s intense contractions with 3.5 min of recovery between each. Epinephrine has been infused during repetitive and progressive contractions; modest ischemia and hypoxic hypoxia, and the oxidation-reduction state of mitochondrial cytochrome a-a3 have been investigated. After the initiation of repetitive contractions, L rises transiently to a peak at 3-5 min and then declines to net uptake after 30 min of contractions. The peak L is roughly proportional to VO2. L rises progressively during progressive contractions to levels lower than the peak in repetitive contractions. Epinephrine increases L transiently during repetitive contractions and increases L during progressive contractions. L rises to levels similar to the repetitive peak during the four repeated 30-s bouts. Cytochrome a-a3 was more oxidized during contractions than when at rest. Ischemia has little or no effect on L. Hypoxic hypoxia sufficient to produce hypoxidosis increased L sharply, but transiently. Muscle L reflects the balance between the production of the products of glycolysis and their removal into the mitochondria.(ABSTRACT TRUNCATED AT 250 WORDS)
