Prostaglandins reverse Inhibition of Electrically-induced Contractions of Guinea Pig Ileum by Morphine, Indomethacin and Acetylsalicylic Acid

Abstract

MORPHINE and other narcotic analgesics have long been known to block electrically induced contractions of the isolated guinea pig ileum by inhibiting the release of acetylcholine (ACh) from postganglionic parasympathetic nerve terminals1–3. Reversal of this effect by naloxone and other narcotic antagonists has been well documented4,5, the mechanism generally proposed being the displacement of the narcotic from its receptor. In this report, we show that certain prostaglandins, in particular PGE1 and E2, also reverse this action of morphine and other narcotics. Reversal is specific for narcotic drugs and occurs at very low concentrations of prostaglandin. It is suggested that the effect of narcotics on transmission is mediated through a prostaglandin receptor which is involved with the mechanism by which ACh is released upon electrical stimulation. Confirmation of the concept of such a role for prostaglandins was provided by studies involving the effects of indomethacin and acetylsalicylic acid (aspirin) on electrical stimulation.