Cardiovascular and sympathetic responses reflexly elicited through the excitation with bradykinin of sympathetic and vagal cardiac sensory endings in the cat

The intracoronary administration of bradykinin (30 ng·kg−1) was used to study the reflex responses to the excitation of sympathetic and vagal cardiac sensory endings in anaesthetised cats. The left main coronary artery was perfused with a constant flow pump to administer the drug without concomitant manipulations of the heart. The reflex effects were assessed by recording simultaneously target haemodynamic functions and the impulse activity of sympathetic preganglionic fibres, isolated from an outflow largely directed to the heart. In eight out of 13 cats with intact cardiovascular innervation the intracoronary injection of bradykinin produced a consistent and significant increase in systemic mean arterial pressure (MAP), left ventricular pressure (LVP) and LVdP/dtmax along with a significant increase in the sympathetic efferent impulse activity. In the remaining five animals, bradykinin caused a significant haemodynamic depressor response concomitant with a slight increase in sympathetic impulse activity. In eight additional cats with sinoaortic denervation, excitatory or inhibitory haemodynamic reflex responses were also observed, the types of response being consistent in each individual animal. However, in the case of inhibitory responses the sympathetic impulse activity was simultaneously decreased. After vagotomy, bradykinin induced a significant increase in MAP, LVP, LVdP/dtmax and in cardiac sympathetic efferent activity in all 21 cats. These excitatory responses were abolished after the interruption of a large part of the cardiac sympathetic afferents. Thus the intracoronary administration of bradykinin induced haemodynamic and sympathetic reflex responses that were dependent upon the interaction of opposite influences mediated by the simultaneous activation of cardiac vagal and sympathetic afferents.