Humoral Factors
Endogenous chemical factors produced in response to the disease condition are involved in wasting and cachexia [1, 3, 8, 18-21]. Two key aspects relate to: (1) factors that can be produced by the pathological process per se, e.g. chemicals released by tumours such as cytokines, bombesin (e.g. produced by small cell lung carcinoma) and serotonin (e.g. produced by bronchial and gastrointestinal carcinoid tumours), or by normal cells responding to an insult (e.g. cytokines produced by the immune system); and (2) the fact that various of these factors can act on the brain or peripheral target organs that signal to the brain to induce a behavioural, endocrine, autonomic, or other relevant CNS response.
Thus, based on the pleiotropic pathophysiolo-gy that occurs during wasting and cachexia, brain mechanisms may involve those: (a) activated within the brain, (b) generated in peripheral tissues/organs that can signal to and act on the brain, and (c) resulting from the combination of (a) and (b). Examples may encompass different classes of neurotransmitters, neuropeptides and cytokines.
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