EVIDENCE FOR ALPHA(2)-ADRENOCEPTOR AGONIST ACTIVITY OF MINOXIDIL

The present investigation was undertaken to study the mechanism of act ion of minoxidil using various smooth muscle preparations. Minoxidil ( 4.7 x 10(-6) M to 4.7 x 10(-4) M) produced a concentration-dependent i nhibition of field stimulation-evoked responses in rat anococcygeus mu scle and vas deferens. The inhibition produced by minoxidil was antago nized by yohimbine (2.5 x 10(-7) M). Minoxidil (1.4 x 10(-5) M to 4.7 x 10(-4) M) also produced a concentration-dependent relaxation in oest rogen-primed potassium chloride-depolarized rat uterus. These response s were blocked not only by yohimbine but also by glibenclamide (2.02 x 10(-8) M). Our results suggest that minoxidil possesses alpha(2)-adre noceptor agonist activity in addition to potassium-channel-opening act ivity.