Similarity between carotid and coronary artery responses to sympathetic stimulation and the role of α1-receptors in humans

Abstract

Carotid artery (CCA) dilation occurs in healthy subjects during cold pressor test (CPT), while the magnitude of dilation relates to cardiovascular risk. To further explore this phenomenon 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. In randomized order, 10 healthy participants (25 ± 3 yr) underwent sympathetic stimulation using the CPT (3-min 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 (0.05 mg/kg body wt). 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 (-30 mmHg), 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). 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. NEW & NOTEWORTHY We showed distinct carotid artery responses to cold pressor test (CPT; i.e., dilation) and lower-body negative pressure (LBNP; i.e., constriction). Blockade of α₁-receptors significantly attenuated dilator responses in carotid and coronary arteries during CPT, while no changes were found during LBNP. Our findings indicate strong similarity between carotid and coronary artery responses to distinct sympathetic stimuli, and for the role of α-receptors.

Keywords: cardiovascular disease; carotid artery; coronary artery endothelial function; sympathetic nervous system; α1-adrenoceptors.

Fig. 1.

Responses of the carotid artery (n = 9) and the lower anterior descending (LAD) coronary artery (n = 6) to CPT. A: diameter change of the carotid artery over time. B: percentage change in carotid diameter at baseline and during the cold pressor test (CPT; area under the curve, AUC). C: velocity time integral (VTI) change of the LAD coronary artery over time. D: percentage change in LAD coronary artery (VTI) at baseline and during CPT (area under the curve, AUC). Data are presented as means ± SE. Open bars represent baseline measurements, whereas solid bars represent peak values.

Fig. 2.

Responses of the carotid artery (n = 9) and the lower anterior descending (LAD) coronary artery (n = 5) to lower-body negative pressure (LBNP). A: diameter change of the carotid artery over time. B: percentage change in carotid diameter at baseline and during LBNP. C: velocity time integral (VTI) change of the LAD coronary artery over time. D: percentage change in LAD coronary artery VTI at baseline and during LBNP. Data are presented as means ± SE. Open bars represent baseline measurements, whereas solid bars represent peak values.

Fig. 3.

Responses of the carotid artery (n = 9) and the lower anterior descending (LAD) coronary artery (n = 6) to cold pressor test (CPT), Control vs. Prazosin condition. A: diameter change of the carotid artery over time. B: percentage change in diameter. C: velocity time integral (VTI) change of the LAD coronary artery over time. D: percentage change in LAD coronary artery VTI at baseline and during the CPT. Data are expressed as means ± SE. Open bars represent the control condition, whereas solid bars represent the prazosin condition.

Fig. 4.

Responses of the carotid artery (n = 9) and the lower anterior descending (LAD) coronary artery (n = 5) to lower-body negative pressure (LBNP), Control vs. Prazosin condition. A: diameter change of the carotid artery over time. B: percentage change in carotid diameter at baseline and during the LBNP. C: velocity time integral (VTI) change of the LAD coronary artery over time. D: percentage change in LAD coronary artery VTI at baseline and during the LBNP. Data are expressed as means ± SE. Open bars represent the control condition, whereas solid bars represent the prazosin condition.

Fig. 5.

Correlation between the carotid artery diameter response (CAR%) and coronary LAD response [change in the velocity time integral (VTI in cm)] pooled for the cold pressor test and lower-body negative pressure test (n = 16).

Fig. 6.

Mean coronary velocity expressed versus the rate pressure product (RPP). A: responses of mean coronary velocity vs. RPP during the cold pressor test (CPT). B: responses of mean coronary velocity vs. RPP during CPT with prazosin. C: responses of mean coronary velocity versus RPP during lower-body negative pressure (LBNP). D: responses of mean coronary velocity vs. RPP during LBNP with prazosin. Light gray arrows indicate individual responses, while the black arrows indicate the mean response.