1. 1. Ergotamine (3-10 μg/kg) inhibited the electrical stimulation-induced pressor and cardiac responses without modifying pressor responses of noradrenaline and tyramine in the pithed rat. 2. 2. Yohimbine (0.3 mg/kg) partially prevented the ergotamine cardiac and vascular inhibitory effects but sulpiride (0.3 mg/kg) only prevented it at vascular level. Both antagonists together abolished the ergotamine inhibition of electrical stimulation-induced pressor responses. 3. 3. The cumulative dose-response curve of ergotamine (1-100 μg/kg) vasoconstrictor effects was partially inhibited to the same extent by prazosin (1 mg/kg) and yohimbine (0.3 mg/kg). A greater inhibition was observed with both antagonists administered together. 4. 4. Ergotamine (30 μg/kg), in presence of yohimbine, inhibited the pressor responses of methoxamine, without any effect on xylazine pressor responses. 5. 5. These data indicate that ergotamine acts as an agonist of both the presynaptic dopamine receptors and α2-adrenoceptors, of α1 and α2-postsynaptic adrenoceptors, and also as an antagonist of the postsynaptic α1-adrenoceptors. © 1988.
|Publication status||Published - 1 Jan 1988|