The Meyerhof quotient and the synthesis of glycogen from lactate in frog and rabbit muscle. A reinvestigation

Abstract

1. The conversion of lactate into glycogen was demonstrated in frog sartorius muscle in oxygen. The rates and amounts are highest when lactate is added to the bathing medium and are dependent on lactate and CO(2) concentration, as well as pH. The glycogen content of a resting muscle can be doubled in 4h at 24 degrees C. 2. Sartorius muscle, recovering aerobically in liquid paraffin from a period of anoxia, converts preformed lactate into glycogen at a lower rate and in smaller amounts than when lactate is added in an aqueous medium. The lower rates are similar to those Meyerhof found under the same conditions, after correction for temperature; they can be attributed partly to low muscle pH and partly to the limited amounts of lactate present. 3. Rabbit psoas muscle also shows the ability to convert added lactate into glycogen under aerobic conditions. The rates are low and similar to those in frog sartorius muscle recovering from anoxia. 4. The present experiments yield a Meyerhof quotient of 6.2, compared with Meyerhof's value of 4-5. However, these values are not significantly different from one another. 5. It is suggested that the glycogen coefficient, i.e. mol of glycogen formed/mol of lactate disappearing, is a more reliable way of assessing the resynthetic mechanism than the original quotient, i.e. mol of lactate disappearing/mol of lactate oxidized. The found coefficient is 0.419+/-0.024.

Substrates for muscle glycogen synthesis in recovery from intense exercise in man.

“…However, the oxidation occurs in the first 10 min when there is the greatest potential to form pyruvate from lactate due to the high concentration of the latter, which suggests that lactate is the major source of the pyruvate oxidized in the mitochondria. This notion is supported by the findings of Bendall & Taylor (1970) that the glycogen synthesis equalled the lactate available for gluconeogenesis, when the latter was calculated based on the assumption that only lactate was the substrate for carbohydrate oxidation. Thus, the contribution of lactate to gluconeogenesis was probably closer to the 13 % than the 27 % of the lactate accumulated at the end of exercise.…”

“…Furthermore, the rates measured in this study are the average for all muscle fibres, and it is known that glyconeogenesis is faster in fast-twitch than slowtwitch fibres (McLane & Holloszy, 1979;Bonen et al 1990). The high muscle lactate and CO2 concentrations at the end of exercise favour a large glyconeogenesis rate, but a fast decrease in these variables during early recovery (femoral venous Pco2: 95,85 and 48 mmHg at 0, 2 and 3 min of recovery, respectively) lowers the rate, and so the mean value for the first 10 min of recovery (Bendall & Taylor, 1970;Bonen et al 1990). The reports of the effect of low pH on the synthesis of glycogen from lactate are conflicting.…”

“…However, Opie & Newsholme (1967) discovered sufficient quantities of the necessary enzymes in frog muscle. Later Bendall & Taylor (1970) demonstrated that glycogen can be formed in large amounts from lactate, added to isolated frog sartorius muscles. It seems also to occur in human skeletal muscle.…”

Aspects of anuran metabolism : effects of chronic hypoxia on maximal oxygen uptake rates and the fate of lactic acid

“…Previous studies of mammalian systems have indicated that a large percentage of endogenous lactate is converted to glycogen (Hermansen and Vaage, 1977;McLane and Holloszy, 1979 , 1942) to 80-90\ expired in rabbits (Drury and Wick, 1956). Bendall and Taylor (1970) There has been very little data concerning the fate of lactate, especially in amphibians. It has generally been assumed on energetic grounds, that the majority of the lactate accumulated after activity was oxidized (Preslar and Hutchison, 1979;Withers and Hillman, 1981).…”

“…What little has been published is mainly on isolated frog muscle (Bendall and Taylor, 1970) or fish (Hochachka, 1961). Cushman!.…”