Adrenergic influence on hormonal and hepatic metabolic response to exercise in rats

The adrenergic control of the hormonal and hepatic metabolic response to exercise was studied in untrained fed male rats. Rats were injected intraperitoneally with either saline, the alpha-adrenergic antagonist phentolamine, or the beta-adrenergic antagonist propranolol 30 min before exercise. The rats swam for 50 min in 34-35 degrees C water with a tail weight (5% of body wt). Exercise resulted in a suppression of plasma insulin in all treatment groups; however, plasma glucagon increased only in the propranolol group. The liver glycogen content was decreased with exercise only in the saline and propranolol groups. Likewise, phosphorylating respiration of liver mitochondria isolated after exercise was higher only in the saline and propranolol groups. Thus phentolamine pretreatment blocked the liver glycogen depletion and the increased liver mitochondrial phosphorylating respiration observed after exercise in fed rats. The results suggest that alpha-adrenergic mechanisms are operant with exercise and stimulate liver glycogenolysis and mitochondrial phosphorylating respiration.