Adenosine, theophylline, and perfusate pH in the isolated, perfused guinea pig heart.

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Abstract
In isolated, perfused, spontaneously beating guinea pig hearts the influence of perfusate pH on the coronary vasodilation produced by exogenous adenosine and on the inhibition of adenosine vasodilation by theophylline was investigated. Perfusate pH 7.20 and 6.89, produced by increasing PCO2 [particle CO2 pressure], reduced the concentration at which adenosine produced a response. The flow increment in response to higher adenosine concentrations was greater at pH 6.89 and less at pH 7.69 than at pH 7.42. The flow responses to alterations in pH was greater in the presence of adenosine (5 .times. 10-7 M) than in its absence. Theophylline, in amounts which by themselves were without effect on coronary flow, partially inhibited coronary vasodilation caused by adenosine at pH 7.43 and 7.20. The coronary vasodilation produced by adenosine is apparently pH sensitive, but attenuation of this dilation by theophylline is not, at the values of pH tested. Theophylline''s inability to regularly attenuate reactive hyperemia might be related to enhanced adenosine dilation caused by increased tissue H ion activity. The H ion might participate in coronary flow regulation in part via this interaction with adenosine.