Actions of 5'-methylthioadenosine in isolated guinea pig tracheal rings.

The effects of 5'-methylthioadenosine (MTA) on smooth muscle were investigated using isolated guinea pig tracheal rings. MTA, at high concentrations caused the relaxation of isolated guinea pig tracheal rings in a concentration-dependent manner. These actions were pronounced in the tracheal rings contracted by histamine or leukotriene D4. The tracheal contractions induced by varying doses of histamine or leukotriene D4 were also suppressed by pretreatment of relatively low doses of MTA in a dose-dependent manner. Pretreatment of the tracheal rings with propranolol, tetrodotoxin, indomethacin and dipyridamole did not block the actions of MTA. In contrast, theophylline blocked the effects of MTA. These results suggested that MTA action on tracheal smooth muscle cells may be mediated by direct action on adenosine receptors.