Sympathetic control of the collateral circulation: effects of time post-occlusion and exercise training
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] These studies evaluated the role of alpha-adrenergic receptors ([alpha]AR) and NPYergic receptors in the collateral circulation following acute and chronic femoral artery occlusion with and without exercise training. Following acute occlusion inhibition of [alpha]AR increased collateral circuit and ischemic muscle conductances. Also, following acute occlusion Neuropeptide Y Y1 receptor (NPY Y1R) inhibition increased ischemic muscle conductance. Our findings imply that in the presence of excessive sympathetic activation as can occur with occlusion, an exaggerated vasoconstriction of the existing collateral circuit and active muscle will occur. Further studies of the collateral circuit following chronic occlusion revealed that conductance through the collateral circuit increases with time, without intervention. With NPY Y1R inhibition the conductances through the collateral circuit and to ischemic muscles further increases. With the imposition of exercise training collateral circuit blood flow increases above sedentary levels. The addition of NPY Y1R inhibition further increased ischemic muscle conductance. These findings imply that with time the collateral circuit adapts to the stress of occlusion and that exercise training furthers this adaptation. Also, inhibition of sympathetic receptors coupled with exercise training can significantly increase collateral circuit conductance; this implies that mobility and the ease of performing daily living activities could be improved in patients through exercise training and pharmacological intervention.
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