Effects of aging and exercise training on the dynamics of vasoconstriction in skeletal muscle resistance vessels

It is unknown whether aging or exercise training affect the dynamics of arteriolar vasoconstriction. We hypothesized that old age will slow, and exercise training will speed, the dynamics of skeletal muscle arteriolar vasoconstriction in resistance vessels of aged rats. Young (6 month old) and aged (24 month old) male Fischer-344 rats were assigned to sedentary (Sed: n = 6/age group) or exercise-trained (ET: n = 5 aged and 6 young; via treadmill running for 10-12 weeks) groups. After completion of training, arterioles from the red portion of the gastrocnemius muscle were removed, cannulated, and exposed to 10(-4) M norepinephrine (NE) or 20 mM caffeine. Changes in luminal diameter were recorded for analysis of constrictor dynamics. Old age blunted all kinetic parameters (i.e., time delay, time constant) resulting in vasoconstriction taking similar to 3 times as long to reach a steady state (SS) versus younger counterparts for NE (aged-sed: 15.6 +/- 6.0 versus young-sed: 4.6 +/- 0.5 s; P < 0.05) with a similar time course to caffeine. Exercise training resulted in a similar time to SS between age groups for NE (aged-ET: 6.8 +/- 1.6 versus young-ET: 7.0 +/- 0.6 s) and caffeine (aged-ET: 7.8 +/- 0.6 versus young-ET: 8.6 +/- 1.0 s). The results of this study demonstrate that aging blunts the rate of vasoconstriction in skeletal muscle resistance vessels to the sympathetic neurotransmitter NE due, in part, to an attenuated rate of contraction from intracellular calcium release. Further, exercise training speeds the dynamics of constriction to both NE and caffeine with old age.