Amitraz depresses cardiovascular responses to bilateral carotid occlusion

The ectoparasiticide amitraz stimulates alpha 2-adrenoceptors to produce side-effects such as bradycardia and hypotension. The actions of amitraz on baroreceptor reflex responses were evaluated in mongrel dogs by occlusion of both carotid arteries for 30-s periods. Incremental doses of amitraz given intravenously showed that doses of 60 micrograms/kg and above significantly depressed pressor responses to carotid occlusion. By comparison, 2 micrograms/kg amitraz given by intracisterna magna (i.c.m.) injection significantly depressed both blood pressure and heart rate responses. Pretreatment of dogs with i.c.m. yohimbine (30 micrograms/kg) prevented the depressant effects of amitraz on the reflex, but prazosin (20 micrograms/kg), in separate experiments, had no effect.