[Adenosine-3',5'-monophosphate content and muscle tension in isolated coronary arteries under the effect of lanthanum ions].

According to experimental conditions lanthanum ions exert either relaxing or contracting actions on isolated bovine coronary arteries. Both the relaxing and the contracting effect were accompanied by an increase of the cAMP content. The enhancement of the cAMP level could be abolished by diisopropylfluorophosphate (DFP), an inhibitor of adenylate cyclase. The lanthanum-induced relaxation, however, was not influenced neither by DFP nor by the PDE-inhibitor methylisobutylxanthine. It is concluded that cAMP is not involved in the mechanism of La3+-induced relaxation. On La3+-contracted vessels isoprenaline, theophylline, papaverine and trapidil have a spasmolytic action that seems not to be mediated by cAMP.