Effect of acute fasting on diaphragm strength and endurance

The effects of short periods of fasting on diaphragm contractile function remain unclear. The purpose of the present study was (1) to examine the relationship between duration of acute fasting and diaphragm contractile performance, and (2) to assess the effects of fasting on diaphragm glycogen stores and the relationship between changes in diaphragm function and alterations in muscle glycogen stores. Studies were performed on four groups of Syrian hamsters (nine animals in each group). One group served as a control and was allowed to feed normally, whereas the other three groups were fasted for either 1, 2, or 3 days. Diaphragm strips from animals were studied in vitro by measuring tension during electrically induced contractions. Two strips from each animal were studied; one strip was examined with a bath glucose equal to the prevailing blood glucose, and the second was preincubated in a high glucose solution (170 mg/dl) for 20 min. Fasting resulted in reductions in body weight, blood glucose concentrations, diaphragm strength, and diaphragm endurance in strips tested at the prevailing blood glucose levels. These effects were pronounced in animals fasted for 3 days, with little or no change in diaphragm contractility observed in animals fasted for shorter periods. Diaphragm weight, thickness, and glycogen content were unchanged in the fasted animals, as was the weight of the soleus muscle. Preincubation of strips from 3-day-fasted animals in a high glucose medium resulted in a significant increase in diaphragm strip strength and endurance. These data suggest that (1) fasting of sufficient duration to produce hypoglycemia may elicit reductions in diaphragm contractility, (2) these reductions in diaphragm function are not related to fasting-induced changes in diaphragm glycogen content, and (3) these decrements in contractility may be reversible by correcting the hypoglycemia.