Mechanism of reflex control of cardiac contractility by carotid sinus baroreceptors.

Effects of the carotid sinus baroreflex (CSR) on left ventricular dP/dt, mean arterial pressure (MAP), and heart rate (HR) were examined by changing the pressure in the vascularly isolated carotid sinus in anesthetized cats. When the carotid sinus pressure (CSP) was lowered, a significant increase was observed in dP/dt and MAP. These reflex changes were significantly increased after vagotomy. In vagotomized cats, cardiac sympathectomy attenuated but did not abolish the dP/dt and HR responses to CSR. The MAP response was little affected. The remaining response of dP/dt and HR were virtually abolished by subsequent adrenalectomy or beta-adrenergic blockade. Adrenalectomy reduced the MAP response by 39%. The effect of cardiac sympathectomy or adrenalectomy on the dP/dt response was greater when either procedure was performed in combination with the other. These results indicate that 1) the vagi interact with CSR and 2) both cardiac sympathetic nerves and adrenal secretion of catecholamines contribute to the reflex control of cardiac contractility by CSR in anesthetized cats. However, the relative contribution of either reflex system appears to vary depending on whether the other system in intact.