Beta-adrenoceptor Stimulation and Cyclic AMP Levels in Bovine Tracheal Muscle of Old and Young Animals

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Abstract
The relationship between cyclic[c]AMP levels and mechanical activity after exposure to isoprenaline was studied in tracheal smooth muscle. The basal cAMP content decreased with age. The relaxing effects of isoprenaline, theophylline and papaverine were tested on muscles contracted by histamine, acetylcholine or carbacholine. Isoprenaline completely releaxed histamine contracted tracheas, but not those contracted by acetylcholine or carbacholine. Theophylline and papaverine completely relaxed the tracheas irrespective of whether the contracting agent was histamine, acetylcholine or carbacholine. Isoprenaline increased the cAMP content of bovine trachea; this effect was stronger in muscles with spontaneous tension than in histamine-contracted muscles. In muscles contracted by carbachol, isoprenaline increased the cAMP level after 5 min. The correlations between the changes in the cAMP levels and the tension in tracheal smooth muscle support the hypothesis that this nucleotide plays a role in the relaxation process.