Investigation of possible interaction between the noradrenergic system and enkephalinergic system in experimental acute pain model in pain modulation

Investigation of Possible Interaction Between The Noradrenergic System and Enkephalinergic System In Experimental Acute Pain Model in Pain Modulation Endogenous enkephalins and antinociceptive noradrenergic pathways are the parts of the analgesia systems. Neutral endopeptidase (NEP) and aminopeptidase N (APN) enzymes cause short-term analgesic effect by catabolizing endogenous enkephalins. Opiorphin, isolated from human saliva, by inhibiting NEP and APN enzymes through protection of enkephalins bioactivity reinforces analgesic potential. The aim of this study is to investigate the possible interaction between the noradrenergic and the enkephalinergic systems by using opiorphin, noradrenaline (NA), ?1-, ?2- antagonist (prazosin, yohimbine) and ?1-agonist (phenylephrine) and a combination of these. After intraperitoneal administration of all agents to BALB-C male mice, thermally induced acute pain latencies were measured at 15, 30, 60 and 90 minutes in the thermal plantar analgesy test. Consecutive measurement times tested were compared with basal values which are measured before injection. Statistical analysis were performed, by use of Analysis of Variance (One-Way ANOVA) test was followed by Duncan?s post hoc tests for normally distributed data, while Kruskal Wallis test was used for data non-normally distributed which was followed by Mann-Whitney U test. P<0.05 value was accepted statistically significant. According to the results obtained, the significant analgesic effect and the pain sensation were obtained 0.1 mg/kg and 0.3 mg/kg opiorphin doses, respectively (P<0.05). Besides, the combinations of opiorphin (1 and 0.3 mg/kg) and NA (0.1 mg/kg) and the combinations of opiorphin (0.1 and 0.3 mg/kg) and phenylephrine (10 mg/kg) produced the significant analgesic effect (P<0.05). As a result, results from this study indicates that there is some level of interaction between the noradrenergic and the enkephalinergic systems in nociceptive processing and pain. Anahtar Sözcükler: Acute pain, analgesia, noradrenaline, opiorphin, phenylephrine, prazosin, thermal plantar analgesymeter test, yohimbine