Clonidine and a ?-agonists induce hyperthermia in rats at high ambient temperature

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Abstract
The effects of theα-agonist clonidine and theβ-agonist clenbuterol on body temperature of rats kept at high ambient temperature (28°C) were studied. Both drugs induced a dose-dependent significant increase in temperature. The clonidine-induced hyperthermia was blocked by various a2-antagonists, yohimbine, rauwolscine and RX 781094 and theα1-antagonists, prazosin and corynanthine but not by l-propranolol, spiperone, metergoline. The hyperthermic effect of clonidine was potentiated in rats after a lesion of the central noradrenergic terminals by DSP-4. The clenbuterol-induced hyperthermia was counteracted by 1-propranolol, yohimbine and rauwolscine but not by atenolol, prazosin, spiperone, metergoline. These observations indicate that clonidine and clenbuterol-induced hyperthermia is mediated byα2-(postsynaptic) andβ-adrenoceptors, respectively. Moreover, in the latter effectα2-adrenoceptors are involved. The simple temperature measurement can thus be used as a preliminary indicator of centralα2 orβ-agonistic properties of the screened drug.