title: Opiate receptors: enkephalins and endorphins.
abstract: Opiate receptors in the central nervous system may be classified according to pharmacological, behavioural, or binding studies. Classical mu-receptors probably have beta-endorphin as an endogenous ligand, and seem to be involved in the modulation of pain perception, low-frequency acupuncture analgesia, and the stimulation of prolactin, growth hormone and thyroid-stimulating hormone release. Met-enkephalin is likely to be an endogenous ligand for the delta-receptors, which predominate in the basal ganglia and limbic systems; such receptors may tonically inhibit the release of corticotrophin-releasing factor. It has been suggested that the newly-described kappa-receptors may inhibit the release of vasopressin and gonadotrophin-releasing factor; dynorphin may be their endogenous ligand. Endogenous opiates controlling cardiovascular and respiratory reflexes are likely to activate mu-receptors, while high-frequency acupuncture may alleviate the symptoms of opiate withdrawal by allowing an increase in Met-enkephalin to activate delta-receptors. In the periphery, beta-endorphin is concentrated in the corticotrophs of the anterior pituitary, and is cosecreted with ACTH and related peptides. Circulating Met-enkephalin originates in the gut, sympathetic nervous system and adrenal medulla. Met-enkephalin may also be extracted from carcinoid tumours and phaeochromocytomas. Elevations in circulating Met-enkephalin may occur in certain disease states with cardiovascular and psychiatric manifestations. However, manipulation of endogenous or exogenous opiates has as yet no certain place in any clinical situation.
mesh_terms: D015670:Acupuncture Therapy; D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D001927:Brain Diseases / Q000378:metabolism; D002320:Cardiovascular Physiological Phenomena; D004723:Endorphins / Q000032:analysis* / Q000096:biosynthesis / Q000502:physiology; D004745:Enkephalins / Q000032:analysis / Q000096:biosynthesis; D013006:Growth Hormone / Q000378:metabolism; D006801:Humans; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects; D001523:Mental Disorders / Q000378:metabolism; D009369:Neoplasms / Q000032:analysis; D010146:Pain / Q000503:physiopathology; D011388:Prolactin / Q000378:metabolism; D011957:Receptors, Opioid / Q000032:analysis*; D012119:Respiration; D013972:Thyrotropin / Q000378:metabolism
chemical_list: D004723:Endorphins; D004745:Enkephalins; D011957:Receptors, Opioid; D000324:Adrenocorticotropic Hormone; D011388:Prolactin; D013972:Thyrotropin; D013006:Growth Hormone