Similarity between carotid and coronary artery responses to sympathetic stimulation and the role of alpha-1 receptors in humans

Abstract

Background. Carotid artery (CCA) dilation occurs in healthy subjects during cold pressor test (CPT), whilst the magnitude of dilation relates to cardiovascular risk. To further explore this phenomena and mechanism, we examined carotid artery responses to different sympathetic tests, with and without α1-receptor blockade, and assessed similarity to these responses between carotid and coronary arteries. Methods. In randomised order, 10 healthy participants (25{plus minus}3yrs) underwent sympathetic stimulation using CPT (3-minutes left hand immersion in ice-slush) and lower-body negative pressure (LBNP). Before and during sympathetic tests, CCA diameter and velocity (Doppler ultrasound) and left anterior descending (LAD) coronary artery velocity (echocardiography) were recorded across 3-min. Measures were repeated 90-min following selective α1-receptor blockade via oral Prazosin (0.05mg-per-kg bodyweight). Results. CPT significantly increased CCA diameter, LAD maximal velocity and velocity-time integral area-under-the-curve (all P<0.05). In contrast, LBNP resulted in a decrease in CCA diameter, LAD maximal velocity and velocity time integral (VTI, all P<0.05). Following α1-receptor blockade, CCA and LAD velocity responses to CPT were diminished. In contrast, during LBNP (-30mmHg), α1-receptor blockade did not alter CCA or LAD responses. Finally, changes in CCA diameter and LAD VTI-responses to sympathetic stimulation were positively correlated (r=0.66, P<0.01). Conclusion. We found distinct carotid artery responses to different tests of sympathetic stimulation, where α1-receptors partly contribute to CPT-induced responses. Finally, we found agreement between carotid and coronary artery responses. These data indicate similarity between carotid and coronary responses to sympathetic tests and the role of α1-receptors that is dependent on the nature of the sympathetic challenge