Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC207
Inverse relationship between blood-borne and expired nitric oxide during exercise: an interpretative dilemma?
K. Evans1, D. M. Bailey1
1. University of Glamorgan, Pontypridd, United Kingdom.
Vascular nitric oxide (NO) is a critical molecule involved in the regulation of vascular function. However, its measurement is complex due to its short half-life and high reactivity. Given that blood is in contact with the vascular endothelium, blood-borne NO should be considered the “gold standard” measurement for its quantification. The reliance on the more distal measurement of exhaled NO may therefore be misrepresentative of NO bioavailability. To examine if any association exists between these two sites of measurement (blood vs. exhaled) the current study aimed to simultaneously measure exhaled and venous nitrite (NO2-) in response to an acute exercise challenge. Exhaled NO and venous NO2- was quantified before and after a maximal exercise challenge in seven apparently healthy males 35 (mean) ± 7 (SD) yrs. Venous blood was collected from an indwelling catheter placed in an antecubital vein and was immediately centrifuged (2500rpm; 4oC). Plasma was flash frozen and stored at -80oC before later analysis. Both exhaled NO and plasma NO2- concentrations were measured using established ozone-chemiluminescence techniques (Sievers NOA 280i). Acute exercise elicited no change in either exhaled NO (Pre: 19 ± 7 vs. Post: 19 ± 6 ppm; P > 0.05) or plasma NO2- (Pre: 309 ± 45 vs. Post: 376 ± 121 nmol; P > 0.05). No statistical relationship was observed between delta changes (exercise minus rest) in exhaled NO and plasma NO2-, however, there was a week inverse relationship between the two (r = -0.732, P = 0.06) (Figure 1). NO biochemistry is a very complicated field and many physiological parameters affect its availability and physiological function. Exhaled NO has become a popular way of assessing its bioavailability, however, the use of this technique must warrant caution. Current data tentatively suggests that exhaled NO may not reflect vascular NO bioavailability and therefore be an un-reliable marker of no activity.
Where applicable, experiments conform with Society ethical requirements