THE LACTIC ACID CONTENT OF RESTING MAMMALIAN MUSCLE

Abstract

The amount of lactic acid which can be present normally in living mammalian muscle varies between such wide limits that a characteristic value can be obtained only within uniformly well defined experimental conditions.The amount usually found is larger than that actually present in the tissue at the time of killing the animal, on account of the rapid formation during death struggles.Some of the lowest values previously observed for the lactic acid content of mammalian muscle include one of 11 mg.per 100 gm. of tissue' made by Kuhn and Baur (8) on a rabbit which had been allowed to die following fasting, and several of 10 to 14 mg.by Wacker (12).The former obtained 23 mg.as a minimum value after death from insulin overdosage, the latter 38 mg.Similar amounts, 23 and 36 mg., were observed by Hoet and Marks (7) during the immediate rigor following the death of rabbits which had been subjected to excessive thyroid feeding.They obtained 54 mg. in the muscles of an animal which had died from insulin overdosage.Many of the values found in the literature are considerably higher.The resting values for muscles of rats, which had been kept on a high fat diet and subjected to exercise, are given by Meyerhof (9) as varying from 70 to 140 mg.Embden, Schmitz, and Meincke (2) have found 57 to 79 in phlorhizinized dogs and amounts varying from 46 to 295 in rabbits.Cori (1) observed 83 to 120 in fasted mice, some of which were controls, others insulin-treated, and a third group epinephrine-treated.The very low values have been associated with depletion of the carbohydrate stores, and represented almost all of the lactic acid which could be formed by the muscle.Incubation (2 to 4 hours) of the muscle whose carbohydrate was depleted was followed by no gain or a very small gain in the lactic acid content found at death (7,8,12).This indicates either that the ' Ethyl chloride manufactured by Stratford-Cookson Co., Philadelphia.