Characterization of leucine and methionine enkephalin and their interaction with morphine on the guinea pig ileal longitudinal muscle
Vaught, J.L.; Takemori, A.E.
Research Communications in Chemical Pathology and Pharmacology 21(3): 391-407
1978
ISSN/ISBN: 0034-5164 PMID: 705020 Document Number: 129062
Using naloxone as the antagonist, a comparison of pA2 of morphine and sensitized the ileal strip to naloxone. This was evidenced by an increase in the morphine-naloxone pA2 value. Met-enkephalin or morphine pretreatment had no effect on subsequent morphine IC50 determinations but similarly increased the morphine-naloxone pA2 value. Although both leu- and met-enkephalin may be classified as pure narcotic agonists, their interaction with morphine on the ileal strip was markedly different. Leu-enkephalin may be an important physiological modulator of narcotic efficacy.