EFFECT OF LONG-TERM UNDERNUTRITION ON MALE AND FEMALE RAT DIAPHRAGM CONTRACTILITY, FATIGUE, AND FIBER TYPES

The effects of long-term undernutrition (10 wk) on diaphragm contracti lity, fatigue, and fiber type proportions were studied in male and fem ale rats. Contractility and fatigue resistance indexes were measured i n an in vitro diaphragm costal strip preparation by using direct stimu lation at 37 degrees C. Undernutrition allowed for continued growth in males and females but with substantial reductions in weight gain. Rel ative to control rats of the same sex, final weights were significantl y lower in undernourished males (74 +/- 3%) than females (90 +/- 5%), but weight gain was not significantly different between undernourished males (58 +/- 5%) and females (60 +/- 3%). Only in males did undernut rition significantly reduce costal diaphragm weight (to 77 +/- 5% of c ontrol). Diaphragm forces, normalized for cross-sectional area, were n ot significantly different from male or female control values. Fatigue resistance indexes (fatigue/baseline force) were increased at all sti mulation frequencies in undernourished males but not in undernourished females. Costal diaphragm atrophy, involving types I and II fibers, o ccurred in undernourished males but not in undernourished females. In conclusion, despite longterm undernutrition reducing weight gain to si milar levels in males and females (relative to control), there was exc ellent preservation of diaphragm weight, function, and structure in fe males but, although diaphragm atrophy occurred, there was preserved co ntractility and increased fatigue resistance in males.