Oct 1, 1976

Loperamide binding to opiate receptor sites of brain and myenteric plexus

The Journal of Pharmacology and Experimental Therapeutics
C R MackererE Z Dajani


Loperamide, a new antidiarrheal agent, was tested to determine whether its biological activity involves binding to opiate receptor sites. Loperamide and morphine competitively inhibited 3H-naloxone binding to homogenates a guinea-pig brain and myenteric plexus. The Kp values obtain in the presence of Na+ were: morphine, 9.60-10(-9) M (brain), 1.66-10(-7) M (myenteric plexus); loperamide, 7.20-10(-9) M (brain), 1.33-10(-7) M (myenteric plexus); naloxone, 4.78-10(-10) M (brain), 1.27-10(-9) M (myenteric plexus. In the absence of Na+, binding a loperamide and morphine to brain homogenate was enhanced while the binding of naloxone was reduced. Morphine (IC50 = 7.5-10(-8) M) and loperamide (IC50 = 6.9-10(-9) M) inhibited the electrically induced contractions of longitudinal muscle from guinea-pig ileum, and naloxone competitively antagonized these effects. The Kd value calculated for the interaction of naloxone with binding sites associated with the contracting muscle was between 0.98-10(-9) M and 1.85-10(-9) M. In the mouse hot plate test, subcutaneous administration of morphine (minimal effective dose = 6.6 mugmol/kg) and loperamide (minimal effective dose = 78 mugmol/kg) delayed the response to heat stimuli and this effect was co...Continue Reading

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Mentioned in this Paper

Response to Heat
Entire Auerbach's Plexus
Reaction Time
Morphine Measurement
Contraction (Finding)

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