Antinociceptive Effect and Enzymatic Degradation of Endomorphin-1 in Newborn Rat Spinal Cord

• Published in: Japanese journal of pharmacology 1999, Vol.81(3), pp.264-270
• Main Authors: Sugimoto-Watanabe, Azusa, Kubota, Kazufumi, Fujibayashi, Kenji, Saito, Koji
• Format: Article
• Language: English
• Subjects: Endomorphin-1 and -2; Enkephalin; Enzymatic degradation; Slow ventral root potential; Spinal cord
• ISSN: 0021-5198; 1347-3506
• DOI: 10.1254/jjp.81.264

Recently discovered endomorphin-1 and -2 are the first endogenous agonists selective for the μ-opioid receptor. We examined the antinociceptive effect and enzymatic degradation of endomorphin-1 in the newborn rat spinal cord. Endomorphin-1 inhibited the binding of [3H][D-Ala2, N-Me-Phe4, Gly-ol5] enkephalin (DAMGO) to the membrane fraction of the newborn rat spinal cord as potently as DAMGO and morphine. Endomorphin-1 at 1 - 1, 000 nM reduced the slow ventral root potential, which reflects noxious transmission in the isolated newborn rat spinal cord, concentration-dependently via the μ-opioid receptor. A similar effect was observed with endomorphin-2. The newborn rat spinal cord homogenate degraded endomorphin-1 in a 120-min incubation procedure, while it degraded [Leu5]enkephalin even in a 30-min incubation procedure. The degradation of endomorphin-1 was inhibited by actinonin but not by thiorphan. These results showed that in the newborn rat spinal cord, endomorphins had high affinity for the μ-opioid receptor and exerted μ-opioid-receptor - mediated inhibitory effects on noxious responses. Endomorphin-1 was degraded by peptidases, but slowly compared with [Leu5]enkephalin degradation, and the degrading enzymes were actinonin-sensitive peptidases.