Alcohol protects the diaphragm during dietary restriction

We recently reported that alcoholic rat diaphragm develops greater contractile force than diaphragm of pair-fed control animals. The present experiment examines whether alcohol or dietary restriction is the more likely cause of this surprising finding. We conditioned 10 rats using a liquid diet containing ethanol as 36% of calories. Ten pair-fed control animals received an equal amount of isocaloric, ethanol-free liquid diet. Ten ad libitum control animals had unrestricted access to lab chow and water. Rats were killed after 30 weeks. Left costal diaphragm strips were studied in vitro at optimal length using direct stimulation at supramaximal voltage. Isometric force was measured and divided by muscle cross-section to compute stress. Maximal tetanic stresses developed by muscle from pair-fed controls were systematically less than alcoholic and ad libitum control values (p less than 0.0001); this did not depend on temperature (25 degrees vs. 37 degrees; p greater than 0.50). Pair-feeding increased twitch half-relaxation times (p less than 0.03) and shifted the tetanic stress-stimulation frequency relationship leftward by 10 Hz (p less than 0.01). Diaphragm of pair-fed rats continued to generate lower stresses during the fatigue caused by repeated contractions (p less than 0.01). We conclude that dietary restriction associated with pair-feeding compromises diaphragm performance in rats. Chronic alcohol consumption prevents or reverses these changes, since diaphragm function of alcoholic and ad libitum control animals was not different.