TIME-DEPENDENT AND ORDER-DEPENDENT CHANGES IN FUNCTIONAL AND NO-MEDIATED DILATION DURING EXERCISE TRAINING

Arterial vessel responses to sodium nitro-prusside (SNP) and acetylcho line (ACh) were measured in the spinotrapezius muscle of sedentary (Se d) and treadmill-trained (Tr) rats to determine whether these endothel ium-dependent (ACh) and -independent (SNP) mechanisms contribute to th e training-induced increase in functional vasodilation previously obse rved. Control and maximal vessel diameters were similar between Sed an d Tr. After 8 wk of training, functional dilation (2-, 4-, and 8-Hz co ntractions) was enhanced in all orders of vessels studied [terminal fe ed artery (FA), largest arterioles (1A) and intermediate-sized arterio les (2A)], but responses to SNP were increased only in FA. Responses t o ACh were not significantly increased in any vessel order. After 16 w k of training, functional dilation had regressed in Tr such that only the FA response to 4 Hz was significantly elevated relative to Sed. Ho wever, the FA and 1A responses to SNP were significantly greater in Tr than in Sed, as were the 1A and 2A responses to ACh. These results sh ow a dissociation of functional dilation and SNP- or ACh-mediated resp onses, as well as age-dependent interactions, a time-dependent progres sion, and vessel order specificity in the adaptations to training.