Acute exercise increases the ventricular arrhythmia threshold via the intrinsic adenosine receptor system in conscious hypertensive rats

Abstract

Collins, Heidi L., and Stephen E. DiCarlo. Acute exercise increases the ventricular arrhythmia threshold via the intrinsic adenosine receptor system in conscious hypertensive rats. Am J Physiol Heart Circ Physiol 289: H1020 -H1026, 2005. First published May 6, 2005; doi:10.1152/ajpheart.00156.2005.-Coronary artery occlusioninduced tachyarrhythmias that culminate in ventricular fibrillation are the leading cause of death in developed countries. The intrinsic adenosine receptor system protects the heart from an ischemic insult. Thus the increased functional demands made on the heart during exercise may produce protective adaptations mediated by endogenous adenosine. Therefore, we tested the hypothesis that a single bout of dynamic exercise increases the ventricular arrhythmia threshold (VAT) induced by coronary artery occlusion in conscious hypertensive rats via the intrinsic adenosine receptor system. To test this hypothesis, we recorded the VAT before and on an alternate day after a single bout of dynamic treadmill exercise (12 m/min, 10% grade for 40 min). A single bout of dynamic exercise significantly reduced postexercise arterial pressure (⌬Ϫ24 Ϯ 4 mmHg) and increased VAT (⌬ϩ1.95 Ϯ 0.31 min). Adenosine receptor blockade with the nonselective adenosine receptor antagonists theophylline or aminophylline (10 mg/kg) attenuated the cardioprotective effects of a single bout of dynamic exercise. Results suggest that strategies that increase myocardial ATP requirements leading to adenosine production provide protection against coronary artery occlusion. coronary artery occlusion; cardioprotective strategies THE CARDIOVASCULAR RESPONSE to dynamic, whole body exercise places profound demands on the heart. For example, cardiac output can increase four-to fivefold. The increase in cardiac output is primarily mediated by an increase in heart rate (HR) and to a lesser extent by an increase in stroke volume. The increase in stroke volume is primarily mediated by an increase in end-diastolic volume (Frank-Starling mechanism) and, in part, to a reduction in end-systolic volume (increased contractility mediated by adrenergic stimulation). These cardiovascular responses markedly increase myocardial oxygen consumption and accordingly, coronary blood flow can increase four-to fivefold (46). There is a tight relationship between myocardial oxygen consumption and coronary blood flow that suggests that products of metabolism mediate local control of coronary blood flow. Adenosine, a breakdown product of ATP, has been proposed as the major mediator of local coronary blood flow (3). Specifically, adenosine is the vasodilatory metabolite that links coronary blood flow to myocardial metabolism (3).Adenosine also has an important role as an endogenous determinant of ischemic tolerance by modulating several components of cardiac function (6, 41). For example, adenosine has potent cardiac electrophysiological effects, including a negative chronotropic action on the sinus node and a predominant negative dromotropic action on the atriovent...

Electroacupuncture decreases the susceptibility to ventricular tachycardia in conscious rats by reducing cardiac metabolic demand

“…The heart was trimmed again, leaving only the ischemic region. The weight of the ischemic zone was expressed as a percentage of total ventricular weight (7,8,10,27,47).…”

“…The correct positioning of the electrodes at the acupoints was confirmed by observing slight repetitive paw twitches during stimulation, indicating stimulation of motor fibers in the median nerve (5,25,26). In six animals, Teflon-coated wires were sutured over the Pianli-Wenliu [large intestine (LI) [6][7] acupoints in the forelimb because they are near P 5-6 yet are located along another meridian (large intestine).…”

“…A coronary artery occluder, made from 5.0-gauge atraumatic prolene suture (8720H, Ethicon), which passed through a polyethylene-50 guide tubing (Clay Adams), was passed around the left main coronary artery 2 to 3 mm from the origin by inserting the needle into the left ventricular wall under the overhanging left atrial appendage and by bringing it out high on the pulmonary conus (7,8,22,27). The guide tubing with the other end of the occluder was then exteriorized at the back of the neck.…”

Sex differences to myocardial ischemia and β-adrenergic receptor blockade in conscious rats

“…The heart was trimmed again, leaving only the ischemic region. The weight of the ischemic zone was expressed as the percentage of total ventricular weight (8).…”

“…A coronary artery occluder was made from 5.0-gauge atraumatic prolene suture (8720H, Ethicon), which passed through a polyethylene-50 guide tubing (Clay Adams). The suture was positioned around the left main coronary artery 2 to 3 mm from the origin by inserting the needle into the left ventricular wall under the overhanging left atrial appendage and by bringing it out high on the pulmonary conus (8,9,27,29,30,31). The guide tubing with the other end of the occluder was then exteriorized at the back of the neck.…”