Objective: Nitric oxide (NO) contributes to smooth muscle tone relaxation, however, in humans the role of smooth muscle tone and NO in regulating aortic stiffness is controversial. We hypothesised that the nitric oxide donor GTN would reduce aortic PWV in vivo, but this effect would be partly attenuated by reflex activation of the sympathetic nervous system. The aim of this study was to investigate whether the autonomic nervous system (ANS) masked any effect of NO on aortic stiffness.

Methods: 10 healthy subjects; mean age, 28 ± 6 years were studied on two visits, in a double-blinded, placebo controlled 2-way crossover design. On both visits, subjects were randomly selected to have either a bolus administration of pentolinium (ganglion blocker) or placebo followed by an infusion of GTN or placebo. The opposite arm was of the study was then carried out following a 60 minute break.

Heart rate variability, blood pressure, cardiac haemodynamics, brachial and aortic pulse wave velocity (PWV) were measured at regular intervals throughout the study.

Results: The main findings from this study were that incremental doses of GTN led to a significant 9% fall in brachial PWV (P<0.0001), with no effect on aortic PWV. Despite blockade of the ANS, aPWV remained unaffected by incremental doses of GTN.

Conclusions: The major findings were that despite blockade of the both the parasympathetic and sympathetic nervous system, subsequent systemic infusion of GTN had null effect on aortic pulse wave velocity suggesting that there are other mechanisms involved in the regulation of aortic stiffness.