Lactic acid formation in the working gastrocnemius of the dog

Summary In isolated, supramaximally stimulated, isotonically working gastrocnemii of dogs O₂ consumption and lactic acid (LA) output or uptake were measured according to the Fick principle. Simultaneously LA concentration of the muscle tissue was determined at rest and at different times during work. Within 1.6 min after the onset of work LA concentration of muscle tissue rose from 3.5 at rest to 17.2 (oles per gram wet weight and started to decline slowly at 3.6 min after the onset of work. Resting values were reached after about 30 min of exercise. Maximal LA output amounted to about 1.5 moles per gram per minute during the first minutes of work and decreased slowly until about the 18th minute. LA formation which was calculated from the changes of the LA concentration in muscle tissue and the LA output was 9.3 moles per gram per minute during the first 1.6 min and then declined rapidly reaching zero between the 3rd and the 4th minute. Concentration gradients of LA between muscle tissue and venous blood up to 30 moles per millilitre H₂O were observed, although blood flow was high. It is concluded that LA cannot permeate rapidly out of muscle tissue and that muscle cell membrane is the barrier to the diffusion. Since LA is formed only during the phase of O₂ deficit at the onset of work, there is no evidence for an aerobic glycolysis in skeletal muscle. LA accumulation in muscle cells possibly prevents the organism from metabolic acidosis at the beginning of heavy exercise.This investigation was supported by the Deutsche Forschungsgemeinschaft. 1 [1, 3, 7, 13, 15–17, 28, 29, 35, lit. in 32].