Lack of recovery of fatigued rat diaphragm with refeeding after chronic undernutrition

This study investigated the effects of refeeding (RF) after chronic undernutrition (UN), to determine whether RF would reverse UN-induced changes in diaphragm force capacity (Ameredes BT, Am J Respir Crit Care Med 1995;151:A156). RF, as re-establishment of ad lib feeding after UN [30 wk. restricted caloric intake, ∼50% body weight difference from ad lib-fed controls (C)], restored body weight to that of C. Specific force (Fs) development was monitored before, at the end, and one hr. after, repetitive isometric-contraction trials (15°C, 560 ms trains, 20 Hz, 40% duty cycle, 5 min. trial); force-frequency (F-f) relationships were produced before fatigue, and with recovery. Initial force (Fs,) was not different across groups (mean=6.6 N/cm²). Post-fatigue RF diaphragm Fs was similar to UN (31 % and 33%of Fs,), both being significantly higher than post-fatigue C values (23% of Fs_i, p<0.05). Recovery of Fs, and the F-f relationship, one hr. after fatigue, was complete in UN diaphragms, but remained depressed in RF diaphragms (75% of Fs_i, p<0.05). Pre-fatigue (358ms) and recovery (356ms) relaxation rates (1/2RT) remained prolonged in UN diaphragms as compared to C (235ms, p<0.05), and were not significantly altered by RF (273 and 251ms, respectively). These results indicate that RF does not reverse chronic UN-induced changes in force-capacity of the rat diaphragm in vilro.