I explained nitro balance about a week ago, if you can find the thread
To add to sc's list...pyschologic stress can influence catabolism, as can lack of sleep, alcohol or a long list of drugs. I believe dehydration will also cause (or favor) catabolism. Hormones are very influencial, test, IGF-1, GH etc are anabolic, cortisol is the major catabolic hormone, but leukotrines, cytokines and a variety of other hormones can effect muscle catabolism.