Effects of electrical stimulationin vivoofM. pectoralison carbohydrate metabolism with to certain liver and blood values in the pigeon

Abstract

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.

Flight Effects on Plasma Glucose, Lactate, Catecholamines and Corticosterone in Homing Pigeons

“…Earlier biochemical and histochemical studies on pigeons had shown that during forced flight or electrical stimulation of the pectoralis muscle, carbohydrates were initially used as fuel and then fat as the major source of energy for prolonged muscular activity (George and Berger 1966;Vallyathan, Grinyer and George 1970;John and George 1973;McKeown, John and George 1974;Parker and George 1974;l975;Pilo et al 1984). A similar conclusion was arrived at by Butler, West and Jones (1977) from their study of the respiratory exchange ratio in pigeons flying in a wind tunnel.…”

“…However, the magnitude of the increase in lactate levels obtained by Butler, West and Jones (1977) in pigeons at the end of a 6 min flight in the wind tunnel, was much higher than the 60-80 min flight increase observed in the present study. In experiments with electrical stimulation of the pectoralis muscle in pigeons, blood lactate level was significantly high after 1 h stimulation but was much reduced after 5 h stimulation (Pilo et al 1984). These observations suggest that in prolonged muscular activity lactate produc- tion is considerably reduced because the muscle would be metabolizing mainly fatty acids.…”

“…Earlier studies with prolonged electrical stimulation in vivo of the pectoralis muscle in the pigeon showed a decrease in plasma glucose when blood was drawn from the brachial vein (John and George 1973;McKeown, John and George 1974). In the more recent study (Pilo et al 1984) no change in plasma glucose level was observed when blood was drawn from the ventricle by cardiac puncture. The lack of a reduction in blood glucose in this study was attributed to the fact that the blood obtained from the heart would have contained blood from the liver which carried liver glucose released into circulation.…”

“…This increased stimulation of adrenocortical function may be attributed to increased adrenocorticotropin (ACTH) release since it has been shown that administration of exogenous ACTH increased circulating levels of corticosterone in ducks (Rees, Harvey and Phillips 1983). Increased adrenocortical secretion could also account for the increase in plasma corticosterone level observed in anaesthetized pigeons subjected to electrical stimulation in vivo of the pectoralis muscle (Pilo et al 1984). However, ducks that had previously received a 28 day training to walk on a treadmill, when exercised, were found to show significantly reduced corticosterone response which has been attributed to decreased endogenous ACTH release rather than to reduced ACTH sensitivity in the adrenal (Rees, Harvey and Phillips 1983).…”

“…Even though such experimental models could be used effectively to study muscle metabolism during exercise, there are physiological limitations in using such models especially for the study of hormonal changes in the blood due to flight. For example, it was observed that, with electrical stimulation in vivo, of the pectoralis muscle of anaesthetized feral pigeons, there was a significant increase in the levels of plasma corticosterone and lactate but no change in blood glucose concentration which in birds, unlike in mammals is high (Pilo et al 1984). It is also known that birds in general, unlike mammals, are resistant to high lethal doses of insulin (Chen, Anderson and Maze 1945).…”