Repeated episodes of ischemia followed by reperfusion, commonly referred to as ischemic preconditioning (IPC), represent an endogenous protective mechanism that delays cell injury. IPC also increases blood Xow and improves endothelial function. We hypothesize that IPC will improve physical exercise performance and maximal oxygen consumption. The purpose of the study was to examine the eVect of ischemic preconditioning in leg skeletal muscles on cycling exercise performance in healthy individuals. Fifteen healthy, well-trained subjects performed two incremental maximal exercise tests on a bicycle ergometer. Power output, oxygen consumption, ventilation, respiratory quotient, and heart rate were measured continuously. Blood pressure and blood lactate were measured before and after the test. One exercise test was performed after the application of ischemic preconditioning, using a protocol of three series of 5-min ischemia at both legs with resting periods of 5 min in between. The other maximal cycling test served as a control. Tests were conducted in counterbalanced order, at least 1 week apart, at the same time of the day. The repeated ischemic periods signiWcantly increased maximal oxygen consumption from 56.8 to 58.4 ml/min per kg (P = 0.003). Maximal power output increased signiWcantly from 366 to 372 W (P = 0.05). Ischemic preconditioning had no eVect on ventilation, respiratory quotient, maximal heart rate, blood pressure or on blood lactate. Repeated short-term leg ischemia prior to an incremental bicycle exercise test improves maximal oxygen consumption by 3% and power output by 1.6%. This protocol, which is suggested to mimic the eVects of ischemic preconditioning, may have important implications for exercise performance.
Objective-Endothelin-1 (ET-1) contributes to the increased peripheral resistance in heart failure and hypertension.Physical inactivity is associated with cardiovascular disease and characterized by increased vascular tone. In this study, we assess the contribution of ET-1 to the increased vascular tone in the extremely deconditioned legs of spinal cord-injured (SCI) individuals before and after exercise training. Methods and Results-In 8 controls and 8 SCI individuals, bilateral thigh blood flow was measured by plethysmography before and during the administration of an ET A /ET B -receptor blocker into the femoral artery. In SCI, this procedure was repeated after 6 weeks of electro-stimulated training. In a subset of SCI (nϭ4), selective ET A -receptor blockade was performed to determine the role of the ET A -receptors. In controls, dual ET-receptor blockade increased leg blood flow at the infused side (10%, PϽ0.05), indicating a small contribution of ET-1 to leg vascular tone. In SCI, baseline blood flow was lower compared with controls (Pϭ0.05). In SCI, dual ET-receptor blockade increased blood flow (41%, PϽ0.001). This vasodilator response was significantly larger in SCI compared with controls (PϽ0.001). The response to selective ET A -receptor blockade was similar to the effect of dual blockade. Electro-stimulated training normalized baseline blood flow in SCI and reduced the response to dual ET-receptor blockade in the infused leg (29%, Pϭ0.04). Key Words: endothelin receptor Ⅲ endothelium Ⅲ exercise Ⅲ cardiovascular disease Ⅲ paraplegia T he endothelium plays an important role in the regulation of vascular tone via the release of vasodilator and vasoconstrictor substances. Endothelin-1 (ET-1) 1 is one of the most potent endothelium-derived constricting factors, and contributes to the regulation of peripheral vascular tone 2,3 by interacting with ET A -4 and ET B -receptors 5 on smooth muscle and endothelial cells. 6,7 In several pathological conditions, such as pulmonary 8 and systemic essential hypertension, 9 heart failure, 10,11 atherosclerosis, and obesity, 12 ET-1 plasma levels are elevated and contribute to the increased vascular tone observed in these disease states. In models of skeletal muscle deconditioning, such as unilateral limb suspension 13 and bed rest, 14 vascular tone is also increased. In the present study, we hypothesize that the elevated vascular tone in deconditioned muscles can be explained by an augmented contribution of ET-1. Conclusion-ET-1 mediates the increased vascular tone of extremely inactive legs of SCI individuals by increased activation of ETIndividuals with a spinal cord injury offer a unique model of nature to assess peripheral vascular adaptations to inactivity because the skeletal muscles below the level of the lesion are paralyzed and, therefore, extremely inactive. Previous research demonstrated that extensive vascular adaptations, such as an increased leg vascular tone, occur in the inactive and paralyzed legs of spinal cord-injured individuals. 15 These adaptation...
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