Xylazine enhances porcine myometrial contractility in vitro: possible involvement of alpha 2-adrenoceptors and Ca2+ channels.
The effects of xylazine on porcine myometrial contractility were studied in vitro using uterine strips to determine the alpha 2-adrenergic influences during the diestrous stage of the estrous cycle. Xylazine (10(-8)-10(-5) M) caused a dose-dependent increase in the amplitude of myometrial contractility. The alpha 2-adrenoceptor antagonists idazoxan and yohimbine (10(-8)-10(-6) M) blocked the effects of xylazine in a dose-dependent manner. Yohimbine was approximately 10 times more potent than idazoxan in this regard. In contrast, an alpha 1-adrenoceptor antagonist prazosin (10(-7) and 10(-6) M) did not block the xylazine-induced increase in myometrial contractility, but a higher dose of prazosin (10(-5) M) did reduce the effects of xylazine. When the porcine uterine strips were pretreated with Ca2(+)-free Tyrod's solution or verapamil, a Ca2+ channel blocker, the effects of xylazine on myometrial contractility were completely abolished, whereas those of carbachol were only moderately reduced. The results suggest that the xylazine-induced myometrial contractility is mediated by alpha 2-adrenoceptors and that this effect is mediated, at least in part, by Ca2+ channels, whereas the effect of carbachol is attributed to an increase in both Ca2+ entry and release of Ca2+ from intracellular pools.
Ko
J C
JC
College of Veterinary Medicine, Iowa State University, Ames 50011.
Smith
B E
BE
Hsu
W H
WH
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D004146:Dioxanes / Q000494:pharmacology; D005260:Female; D019329:Idazoxan; D009215:Myometrium / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D011224:Prazosin / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology; D013552:Swine / Q000502:physiology*; D014590:Uterine Contraction / Q000187:drug effects* / Q000502:physiology; D014700:Verapamil / Q000494:pharmacology; D014991:Xylazine / Q000494:pharmacology*; D015016:Yohimbine / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D015220:Calcium Channels; D004146:Dioxanes; D011942:Receptors, Adrenergic, alpha; D014991:Xylazine; D015016:Yohimbine; D002217:Carbachol; D014700:Verapamil; D011224:Prazosin; D019329:Idazoxan