α 2-Adrenoceptor Antagonist SL84.0418 Involvement in the Development of Opioid Withdrawal

The effects exerted by a novel α2-adrenoceptor antagonist SL84.0418 on the acute opiate withdrawal induced by morphine (μ and κ opioid receptor agonist), DAMGO (highly selective μ opioid receptor agonist) and U-50488H (highly selective k opioid receptor agonist) was investigated in vitro. Furthermore, a comparative study was performed with yohimbine, a well known α2-adrenoceptor antagonist. Following a 4 min in vitro exposure to the opioid agonist, the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone (80% of contraction vs acetylcholine control) whereas per se the addition of SL84.0418 and yohimbine before naloxone did not induce contracture. The addition of SL84.0418 (1x10-6-5x10-6-1x10-5 M) 10 min before each opioid agonist produced a concentrationdependent increase of the opioid withdrawal and its efficacy was comparable to yohimbine (1x10-6-5x10-6-1x10-5 M). The results of our experiments indicate that SL84.0418 is able to influence opiate withdrawal in vitro thus confirming an important functional interaction between the noradrenergic system and opioid withdrawal.