Gintzler A R, Pasternak G W
Neurosci Lett. 1983 Aug 19;39(1):51-6. doi: 10.1016/0304-3940(83)90164-7.
The ability of morphine to inhibit the electrically induced contractions of the guinea pig ileum is mediated through the mu class of opioid receptors. However, recent studies have implied the existence of two subtypes of mu receptors in the brain (mu1 and mu2), which differ both biochemically and pharmacologically. The antagonist naloxonazine and the agonist oxymorphonazine selectively and irreversibly bind mu1 sites. Treatment of both rat and guinea pig brain homogenates with naloxonazine in vitro to selectively inhibit mu1 binding significantly decreased [3H]dihydromorphine binding, whereas binding in similarly treated guinea pig ileum longitudinal muscle-myenteric plexus was virtually unaffected (P less than 0.0005). Similarly, the actions of both drugs in the guinea pig ileum contraction assay were reversible. The findings imply that morphine's actions on the guinea pig ileum were mediated through the mu2 subtype of opioid receptor.
吗啡抑制豚鼠回肠电诱导收缩的能力是通过阿片受体的μ类介导的。然而，最近的研究表明大脑中存在两种μ受体亚型（μ1和μ2），它们在生化和药理学方面都有所不同。拮抗剂纳洛酮嗪和激动剂羟吗啡酮嗪选择性且不可逆地结合μ1位点。在体外用纳洛酮嗪处理大鼠和豚鼠脑匀浆以选择性抑制μ1结合，显著降低了[3H]二氢吗啡的结合，而在类似处理的豚鼠回肠纵行肌-肌间神经丛中的结合几乎未受影响（P<0.0005）。同样，这两种药物在豚鼠回肠收缩试验中的作用是可逆的。这些发现表明吗啡对豚鼠回肠的作用是通过阿片受体的μ2亚型介导的。
