d-ala(2)-mephe(4)-met(0)-ol-enkephalin and Pain

Topics: Animals; Blood Circulation; Body Temperature Regulation; Brain Chemistry; Cats; D-Ala(2),MePhe(4),Met(0)-ol-enkephalin; Emotions; Endorphins; Enkephalins; Guinea Pigs; Humans; Male; Mice; Motor Activity; Pain; Pituitary Gland; Rats; Receptors, Opioid; Respiration; Schizophrenia

The tail pinch (t-p) method added to a basal restraint stress produced inhibition of the stress-induced hyperglycemia, an effect that was neutralized with intrathecal anesthesia but not with intracerebroventricular (i.c.v.) naloxone (50, 100, 1000 ng/100 g) or with intraperitoneal naloxone injections (0.1-0.3 mg/100 g). A similar negative result was obtained with i.c.v. administration of 500 and 1000 ng/100 g of beta-endorphin. In contrast, a single i.c.v. injection of 1000 ng/100 g of Met-enkephalin reproduced the t-p inhibitory effect. The latter was not elicited by i.c.v. FK 33824, an enkephalin analogue, a result that supports the specific participation of the delta-opioid receptors. The results obtained with central alpha-adrenoceptor antagonists and central noradrenergic chemical destruction, or central alpha-adrenoceptor agonists, support the production of a reinforcement of the alpha-adrenoceptor stress stimulation by the t-p procedure, probably through noradrenaline and enkephalin mediation.

Topics: Animals; D-Ala(2),MePhe(4),Met(0)-ol-enkephalin; Enkephalin, Methionine; Hyperglycemia; Injections, Intraventricular; Insulin; Male; Naloxone; Pain; Rats; Rats, Inbred Strains; Restraint, Physical; Tail

Endogenous opioid peptides rose to prominence with the discovery of the enkephalins in 1975. Since then, a vast amount of research has been directed toward understanding their role in normal and pathophysiological situations. Although the place of endogenous opioids in psychiatry remains uncertain, there is good evidence that a variety of tumors may secrete endorphins or enkephalins, and these may contribute to the non-metastatic complications of malignant disease. In addition, changes in cerebrospinal fluid met-enkephalin and beta-endorphin after acupuncture may be involved in the effectiveness of this therapy in the treatment of heroin withdrawal and severe pain. The hormonal effects of opiate agonists and antagonists are now well characterized; exercise-induced changes in circulating catecholamines are markedly enhanced by the opiate antagonist naloxone. It is possible that the opiate inhibition of catecholamine release during exercise is a reflection of endogenous opioid modulation of effort perception.

Topics: Acupuncture Therapy; Adrenocorticotropic Hormone; beta-Endorphin; Catecholamines; D-Ala(2),MePhe(4),Met(0)-ol-enkephalin; Endorphins; Enkephalin, Methionine; Growth Hormone; Humans; Luteinizing Hormone; Naloxone; Pain; Physical Exertion; Receptors, Opioid; Sensory Thresholds; Stress, Physiological