Aging-induced adaptations of microvascular reactivity.

Control of blood flow to skeletal muscle depends on the vasomotor tone present in the resistance vasculature. Although muscle blood flow has been shown to decline with advancing age, our knowledge of how alterations of reactivity of the resistance vasculature contribute to reduced delivery or altered distribution of blood in the aged is limited. Recent work has demonstrated that age alters the reactivity of resistance arteries and arterioles from skeletal muscle, and that impairment of both vasodilator and vasoconstrictor responses occurs with advancing age. The alterations in cellular mechanisms that contribute to age-related impairment of vasoreactive responses encompass both the vascular endothelium and smooth muscle, and differ in muscles of varying function and fiber type. Current research suggests that some degree of age-induced endothelial dysfunction occurs in resistance arteries and arterioles from most skeletal muscle; however, the severity of endothelial impairment appears greater in resistance arteries and arterioles from highly oxidative locomotory muscles. Age-related impairment of vasoconstrictor responses to metabolites and endogenous constrictor agents has also been documented. These age-related reductions in vasoreactivity that occur in the skeletal muscle resistance vasculature may contribute to inadequate delivery or distribution of blood flow during exercise and ultimately be a factor in loss of exercise capacity that occurs with advancing age.