Baroreflex sensitivity alteration following transient hemispheric ischaemia in rats: protective effect of...

The reflex tachycardia to arterial vasodilation was analysed in anaesthetized and ventilated Long Evans rats. Nicardipine was given by slow intravenous injection. The decrease in blood pressure was accompanied by a sympathetically mediated reflex tachycardia. The slope of the mean blood pressure-pulse period relationship was considered as an index of baroreflex sensitivity. Two injections of nicardipine were given during a single experiment. For studying the suprapontine control of the baroreflex arc, rats were subjected to transient (10 min) bilateral hemispheric ischaemia. These rats exhibited a blood pressure drop following recirculation and baroreflex sensitivity was impaired. Pretreatment with alpha-methyldopa, guanfacine and enalapril lowered mean blood pressure to a similar extent. In those rats pretreated with alpha-methyldopa and guanfacine transient hemispheric ischaemia did not alter baroreflex sensitivity while enalapril pretreated rats exhibited an impaired baroreflex. The protective effect of alpha-methyldopa and guanfacine against the cardiovascular consequence of hemispheric ischaemia may depend on reduced monoamine turnover resulting from central alpha-adrenoceptor stimulation.