Effect of fasting on liver and muscle glycogen in rats and guinea pigs.

The effect of a 48 hr fasting period on liver and muscle glycogen was studied in rats and guinea pigs. Total content of glycogen in the liver was similar in both species of fed animals and was totally exhausted after the fasting period. Muscle glycogen was twice as high in fed guinea pigs as in fed rats. The loss during fasting in guinea pigs was also twice that in rats. The differences in glycogen stores may explain the different metabolic response to fasting previously observed in the two species : hypoglycemia and decreased glucose production in fasted rats and constancy of these parameters in fasted guinea pigs.