Mode Of Action Of Opiatesopioids

It is interesting to note that all commonly used opioids have a similar structure in regard to their terminal morphine ring and the distance between the ring and the N-substitution. Such common traits suggests that opioids must have a common structure in order to interact with a specific receptor site (Figure II-7).

Thus, central analgesics mediate their action by means of an interaction with specific opioid receptor sites located within specific areas of the central nervous system, which are engaged in the transmission of nociceptive afferences and the identification of pain. There, opioids act as agonists at highly definite receptor sites,

Opioids Similar Chemical Structure
Figure 11-7. A similar molecular structure of most opioids implies a structural prerequisite in order to interact with the opioid receptor site
Table II-1. The different population of opioid receptors, their main effects and the ligands that demonstrate a preference of binding

Opioid receptor

Clinical effects

Preference of binding

|| (mu)

Interaction with this type of receptor results primarily in central depression

Analgesia Resp. depression Bradycardia Hypothermia Miosis Constipation Euphoria

Morphine Fentanyl Alfentanil Sufentanil Remifentanil Lofentanil Endorphin

k (kappa)

Interaction with this type of receptor results primarily in sedation

Sedation Analgesia Low abuse potential Marginal resp. depression





(EKC) Bremazocine


8 (delta)

Interaction with this type of receptor results primarily in analgesia

Regulation of analgesia Feeling Behavior & Endocrine function

Leu-Enkephalin Met-Enkephalin

and there is general agreement on the existence of at least three types of opioid receptor sites (Table II-1).

1. The morphine mu receptor at which the prototype morphine binds,

2. The kappa receptor (k) at which the prototype agonist is ketocyclazocine, and

3. The delta receptor (8) at which the prototype endogenous opioid ligand enkephalin binds.

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