CLINICS 2011;66(9):1523-1529 Prehypertension and stress reactivity Medeiros RF et al. Figure 2 - Percent change of hemodynamic responses to mental stress, adjusted for gender, before and after an exercise bout in subjects with prehypertension or normotension. NG-monomethyl-L-arginine was administered to healthy subjects to inhibit NO production, the increase in forearm vascular conductance during mental stress was blunted by approximately 45%5 to 65%.4 In this context, it was shown that subjects with HT have impaired NO-dependent vasodilation during mental stress. Considering that there is evidence that subjects with PHT also present a certain degree of endothelial dysfunction,31 it is conceivable that impaired endothelial-dependent vasodilation might also be involved in the blunted vasodilation during mental stress in subjects with PHT. The present study showed that the enhanced pressor response to mental stress in subjects with PHT was attenuated after a bout of exercise, which is consistent with similar findings from a meta-analysis that evaluated 15 randomized controlled studies that investigated the acute effects of aerobic exercise on blood pressure responses to mental stress in subjects with NT and HT.13 Boone et al.8 and the present study found that the HR response to mental stress was not affected by an acute exercise bout in subjects with PHT. No study has yet evaluated stroke volume and cardiac output responses to mental stress in this population 1527