Shin D H, Hsu W H
Department of Veterinary Physiology and Pharmacology, Iowa State University, Ames 50011.
Toxicol Appl Pharmacol. 1994 Sep;128(1):45-9. doi: 10.1006/taap.1994.1178.
Isolated uterine strips were used to study the effects of amitraz and its metabolites on porcine myometrial contractility during the luteal phase of the estrous cycle. Amitraz and its active metabolite BTS27271 (10(-8)-10(-5) M) caused a dose-dependent increase in myometrial contractility in the luteal phase strips, and BTS27271 was more efficacious than amitraz in this aspect. The other metabolites of amitraz at < or = 10(-4) M did not affect porcine myometrial contractility. The alpha 2-adrenoceptor antagonist, yohimbine (10(-8) -3 x 10(-7) M), but not the alpha 1-adrenoceptor antagonist, prazosin (10(-6) M), blocked the effect of amitraz and BTS27271 in a dose-dependent manner. When uterine strips were pretreated with the Ca(2+)-free Tyrode's solution or the voltage-dependent Ca2+ channel blocker verapamil (3 x 10(-5) M), the contractile effects of amitraz and BTS27271 were completely abolished, whereas those of carbachol were reduced. The results suggested that the amitraz- and BTS27271-induced myometrial contractions are mediated by alpha 2-adrenoceptors and this effect is mediated by an increase in extracellular Ca2+ influx through voltage-dependent Ca2+ channels.
采用离体子宫条研究了双甲脒及其代谢产物对发情周期黄体期猪子宫肌层收缩性的影响。双甲脒及其活性代谢产物BTS27271（10^-8 - 10^-5 M）可使黄体期子宫条的子宫肌层收缩性呈剂量依赖性增加，且在这方面BTS27271比双甲脒更有效。双甲脒的其他代谢产物在≤10^-4 M时不影响猪子宫肌层的收缩性。α2肾上腺素能受体拮抗剂育亨宾（10^-8 - 3×10^-7 M）可剂量依赖性地阻断双甲脒和BTS27271的作用，而α1肾上腺素能受体拮抗剂哌唑嗪（10^-6 M）则无此作用。当子宫条用无钙台氏液或电压依赖性Ca2+通道阻滞剂维拉帕米（3×10^-5 M）预处理后，双甲脒和BTS27271的收缩作用完全消失，而卡巴胆碱的收缩作用则减弱。结果表明，双甲脒和BTS27271诱导的子宫肌层收缩是由α2肾上腺素能受体介导的，且这种作用是通过电压依赖性Ca2+通道增加细胞外Ca2+内流介导的。
