Evidence for a central sympathoinhibitory action of prazosin and indoramin

The effect of 1 h infusion of prazosin or indoramin was investigated on thoracic preganglionic sympathetic nerve activity in vagotomized and carotid sinus nerve activity in nonvagotomised anaesthetised, paralysed cats. Recordings were also made of blood pressure, heart rate and femoral arterial conductance. Prazosin and indoramin caused decreases in preganglionic sympathetic and carotid sinus nerve activity along with blood pressure and an increase in femoral arterial conductance. In the vagotomised cats there was only a small but non-significant fall in heart rate. These results indicate that the sympathoinhibitory action of prazosin and indoramin is not due to stimulation of baroreceptor afferents but is due to a central action.