Metabolic differentiation of fast, slow and cardiac muscles of chick during development

1. 1. The activity patterns of certain key enzymes in energy-supplying metabolism and in vitro glycogen synthesis were studied in fast (posterior latissimus dorsi, PLD), slow (anterior latissimus dorsi, ALD) and cardiac (H) muscle of the chick during prenatal development. 2. 2. The studies on the effects of insulin and epinephrine on the in vitro synthesis of glycogen in these muscle types revealed that insulin favours the synthesis and epinephrine depresses the sensitivity towards glycogen synthesis and the rate of synthesis or depression varies with muscle type and developmental stage. 3. 3. The anaerobic breakdown of glycogen is reduced in all the three types of muscles with advance in development. This is correlated with the measurements of oxygen consumption, P/O ratios and SDH cytochrome- c-oxidase activity. 4. 4. The changes in endogenous levels of pyruvate and lactate provided further insight in understanding the metabolic differentiation of the muscles. LDH, hexokinase and glycogen phosphorylase activities illustrated clearly that PLD becomes more anaerobic whereas ALD and H become aerobic with development.