title: Further evidence to support the alpha 2-adrenergic nature of amitraz-induced decrease in intestinal motility.
abstract: The effect of amitraz, a formamidine insecticide, on in vitro intestinal contractions was studied in teh transmurally-stimulated guinea-pig ileum. An electrical stimulation (with 80 V/0.5 msec/0.1 Hz shown on the dial of the stimulator) caused the ileum to contract presumably via the release of acetylcholine. Amitraz (10(-7) to 10(-6) M) produced a dose-dependent inhibition of these transmurally-stimulated contractions. This effect of amitraz was blocked and reversed by idazoxan (10(-6) M), an alpha 2-adrenoceptor antagonist, but was not prevented by prazosin (10(-6) M), an alpha 1-adrenoceptor antagonist. These results suggest that alpha 2-adrenoceptors mediate the effects of amitraz on the transmurally-stimulated guinea-pig ileum. The results also suggest that amitraz decreases intestinal contraction by activating the alpha 2-adrenoceptors in the myenteric (Auerbach's) plexus, thus inhibiting parasympathetic tone.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000502:physiology; D000818:Animals; D003864:Depression, Chemical; D004146:Dioxanes / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005769:Gastrointestinal Motility / Q000187:drug effects*; D006168:Guinea Pigs; D019329:Idazoxan; D007082:Ileum / Q000187:drug effects* / Q000502:physiology; D007306:Insecticides / Q000494:pharmacology*; D011224:Prazosin / Q000494:pharmacology; D014052:Toluidines / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000494:pharmacology*
chemical_list: D000316:Adrenergic alpha-Agonists; D004146:Dioxanes; D007306:Insecticides; D014052:Toluidines; C014983:amitraz; D011224:Prazosin; D019329:Idazoxan