The effects of xylazine and alpha-adrenoreceptor antagonists on bovine uterine contractility in vitro

Abstract

The effects of alpha-adrenoreceptor antagonists prazosin (alpha-1), yohimbine (alpha-2), and idazoxan (alpha-2) on xylazine-induced bovine uterine contractility were tested in vitro. Uterine strips from proestrous/estrous and diestrous cows were mounted in tissue baths containing Tyrode's solution. Changes in uterine contractility were measured by strain gauge. The following results were observed: 1) Xylazine increased uterine contractility in a dose dependent manner (cumulative concentrations: 10 −8, 3×10 −8, 10 −7, 3×10 −7 and 10 −6M). 2) Idazoxan (10 −8, 10 −7 and 10 −6M) and yohimbine (10 −6, 10 −5 and 10 −4M) antagonized uterine contractility induced by xylazine in a dose-dependent manner. Idazoxan was approximately 50 to 100 times more potent than yohimbine. 3) Prazosin (10 −5M) did not alter the effect of xylazine on uterine contractility. These results suggested that xylazine-induced uterine contractility in the cyclic cow is directly mediated by myometrial alpha-2 adrenoreceptors.