PROBABLE POSTSYNAPTIC ALPHA(2)-ADRENERGIC MEDIATED EFFECT OF XYLAZINEON GOAT UTERINE MOTILITY

Xylazine has been characterized as a selective alpha2-adrenoceptor ago nist, which has explained its central nervous system depressant and ot her pharmacological effects. In order to characterize the effect of xy lazine on uterine motility during the oestrus cycle in goats, intraute rine pressure changes were recorded in cycling goats using balloon-tip ped catheters placed in the uterine horns and connected to pressure tr ansducers and a recorder. The effect of xylazine on myometrial activit y was studied by giving increasing doses of the drug (1.0, 10.0, 100.0 or 500.0 mug/kg) intravenously (i.v.) to animals either in the follic ular or the luteal phase of the cycle. To establish the subtype of alp ha adrenergic receptor mediating the action of xylazine. goats were pr etreated with either prazosin (1.0 mg/kg, i.v.) or yohimbine (1.0 mug/ kg, i.v.). To establish whether the effect of xylazine was pre- or pos t-synaptic, xylazine (100 mg/kg, i.v.) was administered to goats pretr eated with reserpine (0.8 mg/kg, i.p.) to deplete presynaptic catechol amine stores. Xylazine induced a significant and dose-dependent increa se on uterine motility in cycling goats, apparently mediated by post-s ynaptic alpha2-adrenoceptors.