The influence of the calcium antagonist fendiline on tone and motility of the guinea pig gut smooth muscle and the cAMP and cGMP concentrations of the isolated terminal ileum.

In various parts of the guinea pig gastrointestinal tract the calcium antagonist N-(2-benzhydryl-ethyl)-N-(1-phenyl-ethyl)-amine hydrochloride (fendiline, Sensit) decreases the smooth muscle tone elevated by K+-induced depolarisation. This effect is antagonized by addition of extra-Ca++. The muscle relaxation is dos-dependent and amounts to 45-90% after 1-5 microng/ml fendiline. Proportionally to this effect the tissue concentration in cGMP is decreased whereas cAMP remains unchanged. After 54 micron/ml theophylline the cAMP level in the terminal ileum is increased significantly whereas cGMP does not change. Theophylline has no influence on the relaxing effect of 1 microng/ml fendiline. By contrast, the increase in cAMP after theophylline is prevented by fendiline. These findings are explained by the antagonistic effect of fendiline to Ca++, which activates the guanylate cyclase and inhibits the adenylate cyclase. Furthermore, fendiline seems to prevent the binding of theophylline to guinea pig ileal phosphodiesterase. It is discussed that cGMP plays a physiological role in controlling the intestinal smolth muscle tone and motility.