Intracellular cyclic AMP level and intestinal smooth muscle relaxation

The intracellular level of cyclic AMP in the taenia from the guinea pig caecum was significantly increased by isoprenaline in a dose-dependent manner. Papaverine also increased the intracellular cyclic AMP level, but a synthetic antispasmodic agent, Aspaminol (1,1-diphenyl-3-piperidinobutanol hydrochloride) did not modify it. The results suggest that there are two mechanisms for the so-called papaverine-like actions. The increase in the intracellular cyclic AMP concentration produced by isoprenaline was prevented by propranolol. In taenia depolarized by KCl, papaverine caused relaxation but isoprenaline did not. This difference can be explained by the observation that the intracellular cyclic AMP level in the KCl-depolarized taenia is increased by papaverine but not by isoprenaline.