Glycogen Formation in Liver and Muscle from Glucose and Fructose after Extreme Muscular Exhaustion

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Abstract
Rats, fasted and fatigued by swimming were fed glucose or fructose solutions by stomach tube. After 1-, 2- and 3-hour absorption periods the animals were anaesthetized with amytal, liver and muscle samples obtained, and the unabsorbed residues in the gastrointestinal tract were collected. The amount of sugar absorbed, and the increases in liver and muscle glycogen above the pre-formed control level were determined. Fructose was found to be absorbed at a some-what slower rate than glucose by the fatigued rat, but both sugars showed a falling off in absorption rate as the time was prolonged. To allow for the inequalities in rate of absorption, the new glycogen formation in liver and muscle from glucose and fructose was compared on the basis of the “index of glycogen formation,” which takes into account both absorption rates and glycogenesis rates, as well as on the basis of percentage of the total amount of sugar absorbed that is deposited in the total liver and muscle glycogen stores. Glucose was found to be superior to fructose in rebuilding the liver glycogen stores during the early stages, i.e., the first hour, of recovery after exhausting fatigue, the difference being statistically significant. Fructose approaches glucose in activity in the liver in the second hour, and in the third hour is much more effective than glucose. In muscle the average results for new glycogen formation indicate a greater effectiveness for glucose, especially in the first 2 hours, but the difference between the two sugars is not statistically significant at any time.

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