Interaction of Neural and Local Mechanisms in the Control of Skeletal Muscle Blood Flow
Wray, David Walter
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Wray, David Walter, Interaction of Neural and Local Mechanisms in the Control of Skeletal Muscle Blood Flow. Doctor of Philosophy (Biomedical Science), December, 2003, 181 pp., 1 table, 19 illustrations, references, 139 titles. The current project sought to characterize the interaction of neural and local mechanisms of skeletal muscle blood flow control through exogenous and endogenous α-andrenoreceptor activation. We hypothesized that α1- and α2-adrenoreceptors in the human leg would exhibit differential distribution and responsiveness, and that unilateral knee-extensor exercise would attenuate α-adrenoreceptor-mediated vasoconstriction in an intensity-dependent manner. We also hypothesized that carotid baroreflex (CBR)-mediated sympathoexcitation would provoke less vasoconstriction during exercise than at rest. Intra-arterial infusion of phenylephrine (PE, α1-agonist) or BHT-933 (α2-agonist) reduced femoral blood flow (FBF) by approximately 60% at rest, but during exercise (27W) the degree of vasoconstriction evoked by PE and BHT was significantly reduced. During ramped (7W-37W) exercise, BHT did not reduce FBF at any intensity, while some degree of PE-induced vasoconstriction was evident at all but the highest exercise intensity. Using sinusoidal neck pressure, CBR-mediated changes in heart rate (HR), arterial blood pressure (ABP) muscle sympathetic nerve activity (MSNA), FBF, and tissue oxygenation (TOm) were seen at rest. During 7w exercise, CBR-mediated control of ABP, FBF, and Tom was attenuated. We conclude that exercise attenuates α-adrenergic responsiveness to exogenous and endogenous activation to ensure sufficient muscle blood flow while maintaining systemic ABP homeostasis.