Effects of starvation and refeeding on adult male rat diaphragm contractility, fatigue, and fiber types.

The effects of 4.5 days of acute starvation, either alone or followed by refeeding (ad libitum), on diaphragm contractility, fatigue, and fiber types were studied in male rats. Contractility and fatigue resistance indexes were measured in an in vitro costal diaphragm strip preparation with direct stimulation at 37 degrees C. Compared with controls, starvation produced a 28 +/- 1% (P < 0.001) reduction in body weight and an 18 +/- 4% (P < 0.001) reduction in costal diaphragm weight. Twitch and tetanic tensions (normalized for weight or cross-sectional area) were not reduced by starvation. Starvation produced significant increases in fatigue resistance indexes after a 5-Hz stimulation paradigm but not after a 100-Hz paradigm, supporting the hypothesis that fatigue resistance is dependent on the energy demand of a given paradigm. The proportions of type I and type II fibers were similar between diaphragms of starved and control rats, but the cross-sectional area of type II fibers decreased significantly by 18 +/- 7% (P < 0.01). Thus, despite the significant decrease in diaphragm weight after starvation, contractility was preserved and fatigue resistance was increased (low-output paradigm). This is consistent with the decrease in type II fiber area. Refeeding restored all parameters so that there were no longer significant differences in body or diaphragm weight, contractility, fatigue, or fiber types.