Is tonic sympathetic vasoconstriction increased in the skeletal muscle vasculature of aged canines?

Abstract

.2010.-We tested the hypothesis that tonic adrenergic and nonadrenergic receptor-mediated sympathetic vasoconstriction would increase at rest and during exercise with advancing age. Young (n ϭ 6; 22 Ϯ 1 mo; means Ϯ SE) and old (n ϭ 6; 118 Ϯ 9 mo) beagles were studied. Selective antagonists for alpha-1, alpha-2, neuropeptide Y (NPY), and purinergic (P2x) receptors were infused at rest and during treadmill running at 2.5 mph and 4 mph with 2.5% grade. Prazosin produced similar increases in vascular conductance in young and old beagles at rest (Young: 158 Ϯ 34%; Old: 98 Ϯ 19%) and during exercise at 2.5 mph (Young: 80 Ϯ 10%; Old: 58 Ϯ 12%) and 4 mph and 2.5% grade (Young: 57 Ϯ 5%; Old: 26 Ϯ 4%). Rauwolscine caused similar (P Ͼ 0.05) increases in vascular conductance in old compared with young dogs at rest (Young: 119 Ϯ 25%; Old: 64 Ϯ 22%) and at 2.5 mph (Young: 86 Ϯ 13%; Old: 60 Ϯ 7%) and 4 mph with 2.5% grade (Young: 61 Ϯ 5%; Old: 43 Ϯ 7%). N2-(diphenylacetyl)-N-[4-hydroxyphenyl)methyl]-D-arginine amide (BIBP) caused a smaller increase (P Ͻ 0.05) in vascular conductance in old compared with young dogs at rest (Young: 179 Ϯ 44%; Old: 91 Ϯ 22%), whereas similar increases (P Ͼ 0.05) of experimental limb vascular conductance in young and old dogs occurred following BIBP during exercise at 2.5 mph (Young: 56 Ϯ 16%; Old: 50 Ϯ 12%) and 4 mph and 2.5% grade (Young: 45 Ϯ 10%; Old: 25 Ϯ 7%). Pyridoxal-phosphate-6-azophenyl-2=-4=-disulfonic acid infusion produced a larger increase in vascular conductance in old compared with young beagles at rest (Young: 88 Ϯ 14%; Old: 191 Ϯ 58%), whereas similar increases were observed at 2.5 mph (Young: 47 Ϯ 18%; Old: 31 Ϯ 11%) and 4 mph with 2.5% grade (Young: 26 Ϯ 13%; Old: Ϫ18 Ϯ 8%). At rest, NPY receptor-mediated restraint of skeletal muscle blood flow was reduced with advancing age, whereas P2x receptor-mediated restraint of skeletal muscle blood flow was increased. During exercise, the magnitude of adrenergic and nonadrenergic sympathetic vasoconstriction was not different between young and old dogs. Overall, these data demonstrate that adrenergic receptor-mediated vasoconstriction was not elevated at rest, but nonadrenergic sympathetic vasoconstriction was altered under basal conditions in aged beagles.aging; sympathetic vasoconstriction; skeletal muscle; exercise AGING IS ASSOCIATED WITH A decline in aerobic capacity (12)(13)(14). An inability to augment cardiac output during exercise has been functionally linked to the reduced exercise tolerance with aging (1, 23, 36, 53). A blunted skeletal muscle blood flow response to dynamic exercise has also been reported in older humans and animals (1,33,37,47,48,50). However, other studies have documented preserved skeletal muscle blood flow during exercise in aged humans (38,40,44,49). Thus, the effect of aging on the control of skeletal muscle blood flow appears to be an unresolved issue in the scientific literature.The observation of elevated efferent muscle sympathetic nerve activity in older adults at rest (16, 43) has led to the notio...

Effect of extraluminal ATP application on vascular tone and blood flow in skeletal muscle: implications for exercise hyperemia

“…There is growing evidence that P 2x receptors on vascular smooth muscle play an important role in vasoconstriction at rest and during exercise (7,8,15). This effect of ATP on hemodynamics is in congruence with the current finding that ATP evoked vasoconstriction at the lowest concentration of 10 nM.…”

Exercise training and α1 -adrenoreceptor-mediated sympathetic vasoconstriction in resting and contracting skeletal muscle

“…, ; DeLorey et al. , ). Recent evidence also suggests that NPY and P2X receptors regulate vasoconstriction on distal arterioles and activation of these receptors with selective agonists demonstrated that they are capable of producing substantial changes in vascular resistance (Al‐Khazraji et al.…”

“…2004b, ; DeLorey et al. , ). Acidosis and elevated temperature have been shown to reduce the responsiveness of purinergic receptors in vitro (Kluess et al.…”

High Intensity Aerobic Exercise Training Improves Deficits of Cardiovascular Autonomic Function in a Rat Model of Type 1 Diabetes Mellitus with Moderate Hyperglycemia

“…Another interesting outcome of the current study was the alteration of sympathetic vasomotor control in the D group, which was also modified by concurrent exercise training. In this study, prazosin treatment resulted in a drop in MAP that was approximately twofold greater in the D group compared to the C and DX groups, which is indicative of a much greater sympathetic contribution to the maintenance of baseline vascular resistance [ 75 , 76 ]. Similarly, Martinez-Nieves and Dunbar (1999) reported that male T1DM rats had a greater decrease in MAP after a bolus injection of prazosin compared to their control cohorts [ 77 ].…”