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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.

Low-dose, slow-release theophylline reduces symptoms of AMS in association with alleviation of events of periodic breathing and oxygen desaturations.

Ubiquitin-activating enzyme was purified from the yeast Smd~arorrt_vces cererisirte by covalent affinity chromatography on ubiquitin-Sepharose followed by HPLC anion-exchange chromatography. Enzyme activity was monitored by the ubiquitin-dependent ATP: "PPi exchange assay. The purified enzyme has a specific activity of I.5 Nnroi "PPi incorporated into ATP*min-'*mg-' at 37'C and pH 7.0 under standard conditions for substrate concentrations as described by Ciechanovcr et al. (1982) J. Biol. Chem. 257. 2537-2542. The catalytic activity showed a maximum at p1-I 7.0. Its molecular weight both in non-denaturing and in SDS-gel electrophoresis was estimated to be 115 kDa. suggesting a monomeric form. The isoelectric point determined by gel electrofocusing was approximately 4.7. Two protein bands differing slightly in electrophoretic mobility could bc distinguished when SDS gels were loaded with very small amounts of purified El and immunoblottcd. the one with higher molecular weight being clearly predominant. The same two bands were also found in anti-El immunoblots of crude yeast lysates prepared under broad protease inhibition.

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