Effect of inhalational anesthetics on the opioid receptors in the rat brain.

Effects of inhalational anesthetics, methoxyflurane and halothane, on the binding of various opioid ligands were studied. The binding affinity of 3H-methionine enkephalin (delta) was reduced by both anesthetics in the same manner, but the receptor density was not significantly affected. Methoxyflurane decreased the binding affinity but increased the receptor density of 3H-dihydromorphine (mu), while halothane had little effects on both affinity and density. Methoxyflurane also decreased binding affinities of 3H-ethylketocyclazocine (kappa) and 3H-SKF-10047 (sigma), but halothane did not decrease significantly. These effects of the anesthetics were completely disappeared by unsealing and ventilation.