Korean J Anesthesiol.  2013 Mar;64(3):257-261. 10.4097/kjae.2013.64.3.257.

Functional activity of the cannabinoid 1 receptor is not affected by opioid antagonists in the rat brain

• Lee H

• KMID: 1767337
• DOI: http://doi.org/10.4097/kjae.2013.64.3.257

Abstract

BACKGROUND
WIN55212-2 is a synthetic cannabinoid agonist and selective to cannabinoid 1 (CB1) receptors, which are distributed mainly in the central nervous system. Opioid receptors and CB1 receptors have several similarities in terms of their intracellular signal transduction mechanisms, distributions, and pharmacological action. Several studies have therefore sought to describe the functional interactions between opioids and cannabinoids at the cellular and behavioral levels. The present study investigated agonist-stimulated [35S]GTPgammaS binding by WIN55212-2 in rat brain membranes and determined the antagonism by selective opioid antagonists at the level of receptor-ligand interaction and intracellular signal transduction.
METHODS
Sprague-Dawley rats (male, n = 20) were euthanized for the preparation of brain membranes. In agonist-stimulated [35S]GTPgammaS binding by WIN55212-2, the values of EC50 and maximum stimulation (% over basal) were determined in the absence or presence of the micro, kappa and delta opioid receptor antagonists naloxone (20 nM), norbinaltorphimine (3 nM), and naltrindole (3 nM), respectively. Ke values for opioid antagonist inhibition in the absence or presence of each opioid receptor antagonist were calculated using the following equation: [nanomolar antagonist] / (dose ratio of EC50 - 1).
RESULTS
In WIN55212-2-stimulated [35S]GTPgammaS binding in the rat brain membranes, the values of EC50 and maximum stimulation (% over basal) were 154 +/- 39.5 nM and 27.6 +/- 5.3% over basal, respectively. Addition of selective opioid antagonists did not produce a significant rightward shift in the WIN55212-2 concentration-response curve, and Ke values were not applicable.
CONCLUSIONS
Our results suggest that the functional activity of WIN55212-2-stimulated [35S]GTPgammaS binding was not affected by opioid antagonists in the rat brain membranes. Although the exact mechanism remains unclear, our results may partially elucidate their actions.

Keyword

GTP binding; Opioid antagonist; Rat brain; WIN55212-2

MeSH Terms

Analgesics, Opioid
Animals
Benzoxazines
Brain
Cannabinoids
Central Nervous System
Membranes
Morpholines
Naloxone
Naltrexone
Naphthalenes
Narcotic Antagonists
Rats
Rats, Sprague-Dawley
Receptor, Cannabinoid, CB1
Receptors, Opioid
Receptors, Opioid, delta
Signal Transduction
Analgesics, Opioid
Benzoxazines
Cannabinoids
Morpholines
Naloxone
Naltrexone
Naphthalenes
Narcotic Antagonists
Receptor, Cannabinoid, CB1
Receptors, Opioid
Receptors, Opioid, delta