Inhibitory effects of selected purine derivatives on guinea pig pulmonary tissues

The inhibitory (relaxation) effects of five purine derivatives (ATP, ADP, AMP, Adenosine and Guanosine) on guinea pig tracheal and lung parenchymal smooth muscle were investigated. The tracheal spirals and parenchymal strips were bisected longitudinally and all twins submaximally precontracted with histamine. Isoproterenol was applied to one set of tracheal and parenchymal strips, and one of the purine derivatives to the other to produce cumulative concentration-effect relationships. For tracheal tissues, the isoproterenol curves did not differ significantly and could be pooled for comparison. Analysis of the EC50 values by Tukey's Studentized (HSD) test of mean isoproterenol and purine curves from tracheal tissue showed that isoproterenol values differed significantly from those of all the purines; there were no significant differences between the purine values. In parenchymal strips, isoproterenol values could not be pooled. Comparison of EC50 values for each purine derivative with its' isoproterenol group showed that ATP and adenosine did not cause significantly different values from isoproterenol, AMP did cause significant differences, and that ADP and guanosine could not be compared for failure to cause 50% relaxation. ATP responses were not significantly different from those of beta, gamma-methylene ATP, which only slowly degrades, suggesting that ATP has specific receptors in the airways of guinea pigs. In this study purines produced better relaxation in trachea than in parenchyma. A difference in purine receptor distribution between trachea and parenchyma is suggested.