Exercise training enhances flow-induced vasodilation in skeletal muscle resistance arteries of aged rats:: role of PGI2 and nitric oxide

Flow-induced vasodilation is attenuated with old age in rat skeletal Muscle arterioles. The purpose of this study was to determine whether diminished cyclooxygenase (COX) signaling contributes to the age-induced attenuation of flow-induced vasodilation in gastrocnemius muscle arterioles and to determine whether, and through which mechanism(s). exercise training restores this deficit in old rats. Fischer 344 rats (3 and 22 mo old) were assigned to a sedentary or exercise-trained group. First-order arterioles were isolated from the gastrocnemius muscles. cannulated, and pres urized to 70 cmH(2)O. Diameter changes were determined in response to graded increases in intraluminal flow in the presence and absence of nitric oxide synthase (NOS) inhibition [10(-5) M N-G-nitro-L-arginine niethyl ester (L-NAME)]. COX inhibition ( 10(-5) 10 indomethacin, or combination NOS (10(-5) M L-NAME) Plus COX (10(-5) M indomethacin) inhibition. Aging reduced flow-induced va vasodilation in gastrocnemius muscle arterioles. Exercise training restored responsiveness to flow in arterioles of aged rats and enhanced flow-induced vasodilation in arterioles from Voting rats. L-NAME inhibition of flow-induced vasodilation was greater in arterioles front old rats compared with those from y,oung rats and was increased after exercise training in arterioles from both voting and old rats. Although the indomethacin-sensitive portion of flow-induced dilation was not altered by age or training, both COX-1 mRNA expression and PGI, production increased with training in arterioles from old rats. These data demonstrate that exercise training restores flow-induced vasodilation in gastrocnemius muscle arterioles from old rats and enhances flow-induced vasodilation in gastrocnemius muscle arterioles from young rats. III arterioles from both old and Young rats. the exercise training-induced enhancement of flow-induced dilation occurs primarily through a NOS mechanism.