Effects of electrical stimulation in vivo of M. pectoralis on carbohydrate metabolism with reference to certain liver and blood values in the pigeon.

The pectoralis muscles of two groups of anaesthetized pigeons were exercised in vivo by electrical stimulation for periods of 1 h and 5 h respectively. There was no significant change from controls in the level of blood glucose in both groups. Blood lactate level was significantly higher in the exercised groups but was relatively lower in the 5-h control group in comparison with its 1-h counter part. Blood lactate dehydrogenase (LDH) activity was significantly higher in the 1-h stimulated pigeons as was also the case with liver LDH in the same group but markedly lower in the 5-h ones. No significant change was seen in liver glycogen content in the stimulated pigeons. Liver phosphorylase activity was markedly low in the 5-h stimulated pigeons as was also the case with liver LDH activity. Circulating level of corticosterone was significantly higher in both the stimulated groups. Blood thyroxine (T4) as well as triiodothyronine (T3) levels were considerably reduced in both stimulated groups. The T3/T4 ratio was higher in the 5-h stimulated pigeons. It was concluded that, while initially carbohydrate was used as fuel for exercise, in prolonged exercise, lipid became the chief fuel as was shown in earlier studies. While fat continued to be used as the main fuel, carbohydrate was spared and also gluconeogenesis was enhanced. It was also concluded that the rôle of the thyroid hormones in promoting oxidative metabolism was enhanced by markedly increasing peripheral deiodination of T4 to T3 in prolonged exercise.