Isolated ileal strips of mouse were included in this study to investigate the effect of different concentrations of Pyrimethamine on the contraction of the smooth muscles. The results showed that ileal smooth muscles of mouse exhibits regular autorhythmic contractions. This normal contraction mainly depended on the extracellular calcium in their tension and maintenance .
Pyrimethamine caused a concentration dependent relaxation, and a high concentration (8-14 mM) of it rapidly caused relaxation for a normal contraction. Free calcium solution reduced smooth muscles response to pyrimethamine, The low and moderate concentrations (0.2 and 8) mM led to a partial inhibition of the rhythmic contractions and inhibition of tonic phase of acetylcholine induced contraction.