12.6 THE ROLE OF NEURONAL NITRIC OXIDE SYNTHASE IN YOUNG ADULTS

Abstract

Background: Early elevation in blood pressure are characterised by a hyperkinetic circulation, with an elevated cardiac index (CI) being the dominant feature. Neuronal NOS is a key regulator of vascular tone during mental stress and is attenuated in patients with established hypertension. However, the role of nNOS has not yet been examined in young adults with a hyperactive response to stress. Methods: 20 subjects (M:11, 28±6 years) were dichotomised into high and low CI. Forearm blood flow (FBF) was measured using strain gauge plethysmography at rest and during a word interference test (Stroop); before and after the infusion of the nNOS-specific inhibitor, S-methyl-l-citrulline (SMTC). Results: Cardiac index was 2.88±0.7 versus 4.32±0.9 L/min/m2 in the low and high groups, respectively. Mental stress induced a marked increase in FBF in subjects with high CI versus low CI, which was signficantly blunted after infusion of SMTC (P<0.05 for Two-way repeated measures ANOVA). Figure 1:FBF response to mental stress during saline or SMTC in subjects with low versus high CI Conclusions: The vasodilatory response to mental stress is enhanced in individuals with elevated cardiac index and nNOS appears to play a key role in this response. This may be a protective response in individuals in whom sympathetic activity may be high.