Adaptation to exercise-induced stress is not dependent on cardiomyocyte α 1A -adrenergic receptors

• Published in: Journal of molecular and cellular cardiology Vol. 155; p. 78
• Main Authors: Kaidonis, Xenia, Niu, Wenxing, Chan, Andrea Y, Kesteven, Scott, Wu, Jianxin, Iismaa, Siiri E, Vatner, Stephen, Feneley, Michael, Graham, Robert M
• Format: Journal Article
• Language: English
• Published: England 01.06.2021
• Subjects: Adaptation, Physiological; Animals; Biomarkers; Cardiac Output; Cardiomegaly - diagnosis; Cardiomegaly - etiology; Cardiomegaly - metabolism; Echocardiography, Stress; Genotype; Hemodynamics; Mice; Mice, Knockout; Mice, Transgenic; Models, Animal; Models, Biological; Myocardial Contraction; Myocytes, Cardiac - metabolism; Physical Conditioning, Animal; Receptors, Adrenergic, alpha-1 - genetics; Receptors, Adrenergic, alpha-1 - metabolism; Stress, Physiological; α(1A)-adrenergic receptor; Exercise; Cardiac hypertrophy
• ISSN: 1095-8584

The 'fight or flight' response to physiological stress involves sympathetic nervous system activation, catecholamine release and adrenergic receptor stimulation. In the heart, this induces positive inotropy, previously attributed to the β -adrenergic receptor subtype. However, the role of the α -adrenergic receptor, which has been suggested to be protective in cardiac pathology, has not been investigated in the setting of physiological stress. To explore this, we developed a tamoxifen-inducible, cardiomyocyte-specific α -adrenergic receptor knock-down mouse model, challenged mice to four weeks of endurance swim training and assessed cardiac outcomes. With 4-OH tamoxifen treatment, expression of the α -adrenergic receptor was knocked down by 80-89%, without any compensatory changes in the expression of other adrenergic receptors, or changes to baseline cardiac structure and function. Swim training caused eccentric hypertrophy, regardless of genotype, demonstrated by an increase in heart weight/tibia length ratio (30% and 22% in vehicle- and tamoxifen-treated animals, respectively) and an increase in left ventricular end diastolic volume (30% and 24% in vehicle- and tamoxifen-treated animals, respectively) without any change in the wall thickness/chamber radius ratio. Consistent with physiological hypertrophy, there was no increase in fetal gene program (Myh7, Nppa, Nppb or Acta1) expression. In response to exercise-induced volume overload, stroke volume (39% and 30% in vehicle- and tamoxifen-treated animals, respectively), cardiac output/tibia length ratio (41% in vehicle-treated animals) and stroke work (61% and 33% in vehicle- and tamoxifen-treated animals, respectively) increased, regardless of genotype. These findings demonstrate that cardiomyocyte α -adrenergic receptors are not necessary for cardiac adaptation to endurance exercise stress and their acute ablation is not deleterious.