Spasmolytic action of the methanol extract and isojuripidine from Solanum asterophorum Mart. (Solanaceae) leaves in guinea-pig ileum

Solanum asterophorum Mart. (Solanaceae) is a shrub popularly known as "jurubeba-defogo" in the northeast of Brazil. In the present work, the methanol extract (SA-MeOH, 3750 microg/mL) and isojuripidine (10(-7) - 3 x 10(-4) M), a steroidal alkaloid obtained from S. asterophorum Mart. leaves, inhibited phasic contractions induced by both 1 microM histamine IC50 = (225.8 +/- 47.4), g/mL and (3.5 +/- 0.8) x 10(-5) M] or 1 microm acetylcholine IC50 = (112.5 +/- 20.6) microg/mL and (2.3 +/- 0.4) x 10(-5) M] in guinea-pig ileum, respectively. The extract and isojuripidine also relaxed the ileum (SA-MeOH, 1-750 microg/mL, and isojuripidine, 10(-9) - 3 x 10(-4) M) pre-contracted with 1 M histamine EC50 = (101.1 +/- 17.4) microg/mL and (1.2 +/- 0.3) x 10(-6) M] or 1 microM acetylcholine EC50 = (136.8 +/- 21.1) microg/mL and (1.9 +/- 0.4) x 10(-6) M] or 40 mm KCl EC50 = (149.4 +/- 19.5) microg/mL and (1.8 +/- 0.7) x 10(-6) M], respectively, in an equipotent and concentration-dependent manner. This effect is probably due to inhibition of calcium influx through voltage-operated calcium (Ca(v)) channels. To confirm this hypothesis, we evaluated their effect on cumulative CaCl2 curves in depolarizing medium nominally without Ca2+. SA-MeOH (27, 243, 500, and 750 microg/mL) and isojuripidine (3 x 10(-8), 10(-6), 3 x 10(-5), and 3 x 10(-4) M) inhibited the contractions induced by CaCl2, in a concentration-dependent manner. The concentration-response curves to CaCl2, in the presence of SA-MeOH and isojuripidine, were shifted downward in relation to a control curve in a non-parallel manner resulting in reduction of the maximum effect E(max) = (71.2 +/- 9.2); (57.4 +/- 9.2); (43.8 +/- 3.4); (41.5 +/- 2.4) and (90.6 +/- 4.8); (74.7 +/- 8.7); (66.4 +/- 3.9); (31.3 +/- 4.1)%, respectively]. SA-MeOH and isojuripidine present spasmolytic action in guinea-pig ileum due to a partially blockade of calcium influx through Ca(v) channels.