15.1. Drugs that affect appetite
Appetite is regulated by complex neurohumoral systems. These include both central and peripheral mechanisms. Taste, smell, sight sensations, signals coming from the gastrointestinal tract and peripheral tissue metabolism are conventionally referred to as peripheral mechanisms. In the
CNS appetite is controlled by «the hunger center» (lateral nuclei of the hypothalamus) and «the satiety center» (ventromedial nuclei of the hypothalamus). Appetite greatly depends on the functional condition of the limbic system and the cerebral cortex (especially the frontal lobes). Appetite is mainly regulated by noradrenergic, dopaminergic and serotoninergic systems and by corresponding receptors (β1- and β2-adrenoceptors, αa1-adrenoceptors, dopamine D1-receptors, serotonin 5-HT1B- and 5-HT2C-receptors). There are substances in the organism that control appetite and energy balance. Some of these substances increase appetite (orexigenic activity), for example neuropeptide Y, A and B orexines (peptides), grelin1, a hormone that stimulates growth hormone release, GABA and others. Other endogenous substances suppress appetite (anorexigenic2 activity), for example leptine3, insulin, α-melanocyte-stimulating hormone, hormones stimulating the release of thyrotropic and corticotropic hormones, neurotensin, serotonin, glucagon-like peptides, cholecystokinin, and others.
If the appetite is abnormally low, appetite stimulants can be prescribed. These include bitter solutions such as wormwood tincture obtained from common wormwood (Artemisia absinthium). Wormwood tincture contains absintine, essential oil of terpens and absentole (an isomer of camphor). Their mechanism of action involves excitation of the receptors of the oral mucous membrane and reflex stimulation of the hunger center. Subsequent meal intake increases the first phase of gastric secretion.
Certain psychotropic agents (chlorpromazine, amitriptyline and lithium carbonate), neurotropic hypotensive agents (clonidine) and anabolic steroids can stimulate appetite.
Another group of agents include appetite suppressants (anorexigenic agents). They are used for the treatment of alimentary4 obesity, a condition that complicates the course of many diseases and leads to metabolic and cardiovascular disturbances. The most reasonable way to treat obesity is to limit the quantity and caloric content of the food, however this is not easy due to a strong sensation of hunger. In order to eliminate this sensation appetite suppressants are sometimes used (see Chapter 23).