Plasma adenosine during investigation of hypoxic ventilatory response

Adenosine, an endogenous nucleoside, is released by hypoxic tissue, causes vasodilation, and influences ventilation. Its effects are mediated by P1-purinoceptors. We examined to what extent the plasma adenosine concentration in the peripheral venous blood correlates with hypoxic ventilatory response (HVR) and ventilatory drive P0.1 to find out whether endogenously formed adenosine has an influence on the individual ventilatory drive under hypoxic conditions. While investigating the HVR of 14 healthy subjects, the ventilatory drive P0.1 was measured with the shutter of a spirometer. Determination of the ventilatory drive P0.1(RA) started under room air conditions (21% O (2)) and then inspiratory gas was changed to a hypoxic mixture of 10% O (2) in N (2) to determine P0.1(Hyp). At the time of the P0.1 measurements, two blood samples were taken to determine the adenosine concentrations. After removal of cellular components and proteins, samples were analyzed by high-pressure liquid chromatography (HPLC). Both adenosine concentrations in plasma under room air (r = 0.59, p < 0.05) and adenosine concentrations under hypoxia (r = 0.75, p < 0.01) correlated significantly with the ventilatory drive P0.1. In addition, plasma adenosine concentrations during hypoxic conditions showed a significant correlation with HVR on the 0.01 level (r = 0.71, p < 0.01). The results indicate a possible role of endogenous adenosine in the regulation of breathing in humans. We assume that endogenous adenosine influences the HVR and the ventilatory drive, probably by modulating the carotid body chemoreceptor response to hypoxia.