Accumulation of a Precursor of Lactic Acid in Muscle After Epinephrine Injections.

Abstract

It has been found recently 1 that the glycogen content of the rat gastrocnemius diminishes on an average by 101 mg. % 30 minutes after an epinephrine injection, while the lactic acid content of the muscle increases by only 29 mg. %. Part of the lactic acid formed in muscle diffuses into the blood but even if one allows for this on the basis of the increase in blood lactic acid (which amounted to 21 mg. %), one arrives at a total of only 40 mg. % lactic acid. Hence, 61 mg. % of the muscle glycogen which disappears remains to be accounted for.

Three hours after an epinephrine injection, when the blood lactic acid has returned to the original level, a much larger portion of the disappearing muscle glycogen can be accounted for. 2 The liver glycogen formed from blood lactic acid including that part which is mobilized again, makes up for 83% of the glycogen lost from the muscles. The rest is such a small amount that it might have been oxidized without appreciably affecting the R.Q. which was 0.715 for the 3 hour period after the injection. Since most of the muscle glycogen which remains unaccounted for 30 minutes after the injection eventually (within 3 hours) yields liver glycogen by way of blood lactic acid, it seemed desirable to look for a substance, intermediary between glycogen and lactic acid, which might have accumulated in muscle owing to the fact that the conversion of glycogen into the precursor proceeds more rapidly than the conversion of the latter into lactic acid.

It seems fairly well established that the lactic acid precursor in muscle is a hexose-phosphoric acid ester.