cAMP-phosphodiesterase inhibitors and tracheal smooth muscle relaxation

A series of compounds drawn from a wide variety of chemical and pharmacologic classes were tested for their ability to act as inhibitors of a guinea pig tracheal cAMP-phosphodiesterase. Active compounds, defined as equal to or more potent than 1,3-dimethylxanthine (theophylline), were subsequently tested for guinea pig tracheal smooth muscle relaxant activity in vitro. A strong correlation ( r = 0.988 with 95 per cent confidence limits of 0.933 to 0.988) was found between the two activities, suggesting that, under these conditions, smooth muscle relaxation was due to elevation of tracheal cAMP levels.