The Lactic Acid Content of Resting Mammalian Muscle.

Abstract

The amount of lactic acid present in resting, atonic mammalian muscle is very low—10 to 20 mg. per 100 gm. of tissue. We have obtained values from 10.5 to 50 mg. by freezing in situ the gastrocnemius of guinea pigs with CO₂ snow. The animals were anesthetized with amytal and the muscles dissected as free from surrounding structures as possible without disturbing the nerve and blood supply. Packing CO₂ snow around the muscle, starting at the insertion and proceeding to the origin, has given the lowest values for lactic acid.

Fletcher 1 found 59 mg. per cent in rabbit muscle, but excised the muscle before freezing it in liquid air. We have obtained similar results from animals which died (from the anesthetic) during the dissection, even though the muscles were frozen in situ immediately and without stimulation. It seems likely that mammalian muscle forms lactic acid with such rapidity when oxygenation is stopped that it is possible to obtain a value approximating the normal only when it is frozen with the circulation still intact.

We have used ice cold trichloracetic acid (5% aqueous solution) as a protein precipitant. After freezing, the muscles were excised and the unfrozen portion at the origin discarded. They were then sliced, while frozen, into sections oi about 0.1 mm. thickness and immediately dropped into the trichloracetic acict. Lactic acid was determined by the Frietlemann, Cotonio and Shaffet-2 procedure adapted to quantities, between 0.02 and 0.2 mg.