Central alpha-adrenoceptor influence over the cardiovascular reflexes activated by veratrine

Intravenous veratrine induced alterations in cardiovascular parameters in cats were used as a tool for assessing the influence of central alpha-adrenoceptors over reflex adjustments in the heart rate and blood pressure. Blockade of central alpha 2-adrenoceptors with idazoxan or yohimbine, inhibited, while their activation by clonidine, as also blockade of alpha 1-adrenoceptors, with prazosin, potentiated the veratrine induced bradycardia. The hypotensive effect was relatively unaltered by these treatments. Low doses of clonidine potentiated the veratrine-induced bradycardia. It appears that alpha 2-adrenoceptor mechanisms exert greater control over the reflex regulation of heart rate than over reflex control of blood pressure.