Central and Peripheral Involvement of Endogenous Opioid Peptides in Gastric Protection in Stressed Rats

Abstract

The effects of intraperitoneal and intracerebroventricular administration of the inhibitor of endopeptidase EC 24.11 (enkephalinase), thiorphan, and the synthetic enkephalin analogue [D-Ala²-Met⁵]enkephalinamide (DALA) were investigated in cold-restraint-stressed rats. Drugs were administered alone or after pretreatment with naloxone or naloxone methiodide given 20 min prior to the drugs. Thiorphan and DALA, administered centrally (4 µg i.c.v./rat) or peripherally (400 µg/kg), induced a significant gastric protection. Prior treatment with naloxone s.c. (1 mg/kg) inhibited the effect induced by i.e.v. or i.p. injections of thiorphan or DALA. In contrast, s.c. administration of naloxone methiodide (1 mg/ kg) did not affect the response induced by central administration of thiorphan or DALA, but was able to prevent that of thiorphan or DALA when they were administered i.p. These data strongly support the hypothesis of a central and peripheral involvement of endogenous opioid peptides in gastric protection in stressed rats.

Involvement of central opioid systems in human interferon‐α induced immobility in the mouse forced swimming test

“…The other opioid antagonists were administered subcutaneously 30 min prior to testing. These pre‐treatment time and doses of antagonists were selected in accordance with the previous reports, in which these antagonists were adequately effective ( Carr et al ., 1993 ; Kamei et al ., 1995 ; Paul et al ., 1989 ; Scoto & Parenti, 1996 ). Animals of the control group received 0.9% physiological saline through injection sites identical to the experimental animals.…”