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

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