Spasmolytic effect of lidamidine on uterine smooth muscle.

1-(2,6-Dimethylphenyl)-3-methylamidinourea hydrochloride (lidamidine hydrochloride) has previously been reported to inhibit intestinal smooth muscle contractile activity in vivo and in vitro. This study showed lidamidine also inhibited contractile activity in the isolated gravid rat uterus preparation and antagonized, the spasmogenic effects of acetylcholine, serotonin, oxytocin, and PGF2 alpha and BaCl2. Increasing Ca2+ concentrations in the bathing medium from 0.9 mmol/l to 7.2 mmol/l effectively antagonized the lidamidine inhibition of responses to BaCl2 and acetylcholine in the gravid rat uterus preparation. These results suggest that the spasmolytic effect of lidamidine may be due to its interference with the availability of Ca2+ necessary for excitation-contraction coupling in smooth muscle.