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Sex differences in the coronary vascular response to combined chemoreflex and metaboreflex stimulation in healthy
Lindsey M Boulet1, Taylor L Atwater1, Courtney V Brown1
1Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada.
Insights
Coronary blood flow control differs between sexes. While both males and females increase coronary blood velocity during hypoxia, males experience a constraint from adrenergic stimulation, unlike females.
Area of Science:
- Cardiovascular Physiology
- Human Physiology
- Exercise Physiology
Background:
- Coronary hyperaemia involves metabolic and adrenergic signalling.
- Previous research indicates potential sex differences in cardiovascular regulation.
Purpose of the Study:
- To investigate sex-based differences in coronary vascular responses to adrenergic stressors.
- To examine how hypoxia and adrenergic activation interact in regulating coronary blood flow between males and females.
Main Methods:
- Healthy young males and females (n=32) underwent randomized trials involving isometric handgrip exercise and post-exercise circulatory occlusion (PECO).
- Transthoracic Doppler echocardiography measured mean left anterior descending coronary artery velocity (LADVmean).
- Participants were exposed to normoxia, sustained hypoxia, or hypoxia during PECO.
Main Results:
- Acute hypoxia increased baseline LADVmean more in males than females.
- Adrenergic activation during hypoxia paradoxically reduced coronary blood velocity in males, but not females.
- Sex differences were observed in coronary vasodilation during hypoxia and metaboreflex activation.
Conclusions:
- Coronary blood flow control mechanisms exhibit sex-specific differences.
- Adrenergic stimulation constrains the hypoxic coronary vasodilatory response in males, but not females.
- These findings highlight the importance of considering sex in cardiovascular research and clinical practice.
New Findings:
What is the central question of this study? Coronary blood flow in healthy humans is controlled by both local metabolic signalling and adrenergic activity: does the integration of these signals during acute hypoxia and adrenergic activation differ between sexes? What are the main findings and its importance? Both males and females exhibit an increase in coronary blood velocity in response to acute hypoxia, a response that is constrained by adrenergic stimulation in males but not females. These findings suggest that coronary blood flow control differs between males and females.
Abstract:
Coronary hyperaemia is mediated through multiple signalling pathways, including local metabolic messengers and adrenergic stimulation. This study aimed to determine whether the coronary vascular response to adrenergic stressors is different between sexes in normoxia and hypoxia. Young, healthy participants (n = 32; 16F) underwent three randomized trials of isometric handgrip exercise followed by post-exercise circulatory occlusion (PECO) to activate the muscle metaboreflex. End-tidal was controlled at (1) normoxic levels throughout the trial, (2) 50 mmHg for the duration of the trial (hypoxia trial), or (3) 50 mmHg only during PECO (mixed trial). Mean left anterior descending coronary artery velocity (LADVmean ; transthoracic Doppler echocardiography), heart rate and blood pressure were assessed at baseline and during PECO. In normoxia, there was no change in LADVmean or cardiac workload induced by PECO in males and females. Acute hypoxia increased baseline LADVmean to a greater extent in males compared with females (P < 0.05), despite a similar increase in cardiac workload. The change in LADVmean induced by PECO was similar between sexes in normoxia (P = 0.31), greater in males during the mixed trial (male: 12.8 (7.7) cm/s vs. female: 8.1 (6.3) cm/s; P = 0.02) and reduced in males but not females in acute hypoxia (male: -4.8 (4.5) cm/s vs. female: 0.8 (6.2) cm/s; P = 0.006). In summary, sex differences in the coronary vasodilatory response to hypoxia were observed, and metaboreflex activation during hypoxia caused a paradoxical reduction in coronary blood velocity in males but not females.
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