Opioid involvement in feeding behaviour and the pathogenesis of certain eating disorders.

Incidental findings from animal experiments involving administration of exogenous opioid agonists indicate that there are close links between the endogenous opioid system and feeding behaviour. Subsequent investigations aimed at elucidating the nature of the opioid-feeding relationship led to a wide variety of findings, some of them apparently contradictory. This paper examines the effects of opioid agonists and antagonists on feeding behaviour, and considers the evidence relating levels of endogenous opioids to feeding states, with particular reference to certain eating disorders, including anorexia nervosa, bulimia nervosa, Prader-Willi syndrome, and eating-induced obesity. The receptors which may be involved in opioid-feeding relationships are discussed. Relationships between the endogenous opioid system and other systems, such as the dopaminergic, noradrenergic and hormonal systems, are considered insofar as they may have bearing on the modulation of feeding behaviour. Finally, three theories are briefly outlined which attempt to link the endogenous opioid system with feeding modulation and the pathogenesis of certain eating disorders. The suggestion is put forward that anorexia nervosa may represent a pathological consequence of the triggering of a primitive mechanism for coping with unforeseen food shortages which may have short-term advantages, e.g., for masking or temporarily alleviating a depressed state.