Effect of metoclopramide in guinea-pig ileum longitudinal muscle: evidence against dopamine-mediation.
The investigation examines the hypothesis that metoclopramide-induced potentiation of gastrointestinal motility is mediated through dopamine receptors. In vitro studies on the longitudinal muscle of the guinea-pig ileum were performed. Metoclopramide, in concentrations comparable with those seen in plasma after therapeutic doses in man, selectively potentiated the cholinergic response Dopamine (1-100 microM) inhibited cholinergic transmission by inhibiting neuronal acetylcholine release. The inhibitory action of dopamine was antagonised by phentolamine, and alpha-adrenoceptor antagonist, but not by the dopamine receptor antagonists metoclopramide or primozide. Bromocriptine inhibited cholinergic responses by a postsynaptic mechanism which was not antagonised by metoclopramide, primozide, or phentolamine. The results are consistent with the view that metoclopramide-induced potentiation of gastrointestinal motility does not involve local dopamine receptors.
D000818:Animals; D002799:Cholinergic Fibers / Q000187:drug effects; D004298:Dopamine / Q000494:pharmacology; D018492:Dopamine Antagonists; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects*; D008297:Male; D008787:Metoclopramide / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009431:Neural Conduction / Q000187:drug effects; D011954:Receptors, Dopamine / Q000378:metabolism
D018492:Dopamine Antagonists; D011954:Receptors, Dopamine; D008787:Metoclopramide; D004298:Dopamine