Antispasmodic Activity of Benzylisoquinoline Alkaloids Analogous to Papaverine

Abstract

In vitro, reticuline, norarmepavine, coclaurine, and papaverine competitively antagonize the uterine muscular contractions induced by acetylcholine and calcium. The antagonism is more efficient for the alkaloid coclaurine which is even stronger than papaverine. The pA₂ values obtained with each of the four alkaloids for both agents, acetylcholine and calcium, respectively, were as follows: reticuline (5.35 and 4.81), norarmepavine (5.55 and 4.09), coclaurine (7.42 and 6.91), papaverine (5.32 and 6.23).

The two components, phasic and tonic, of the response of the vas deferens to potassium are reduced by the four alkaloids. The reduction is greater for the tonic phase, with the following IC₅₀ values: reticuline 474 µM, norarmepavine 101 µM, coclaurine 68.9 µM, and papaverine 14.3 µM.

The antispasmodic activity of the three alkaloids, similar to papaverine, is related to an inhibiting effect of extracellular calcium, an intracellular effect, or both.

Key words

Papaverine - reticuline - norarmepavine - coclaurine - benzylisoquinoline alkaloids - antispasmodic activity