No abstract

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, 3-750 μg/mL) and isojuripidine (10-7 - 3 x 10-4 ᴍ), a steroidal alkaloid obtained from S. asterophorum Mart. leaves, inhibited phasic contractions induced by both 1 μᴍ histamine [IC50 = (225.8 ± 47.4) μg/mL and (3.5 ± 0.8) x 10-5 ᴍ] or 1μᴍ acetylcholine [IC50 = (112.5 ± 20.6) μg/mL and (2.3 ± 0.4) \ 10-5 ᴍ] in guinea-pig ileum, respectively. The extract and isojuripidine also relaxed the ileum (SA-MeOH, 1-750 μg/mL, and isojuripidine, 10-9 - 3 x 10-4 ᴍ) pre-contracted with 1 μᴍ histamine [EC50 = (101.1 ± 17.4) μg/mL and (1.2 ± 0.3) x 10-6 ᴍ] or 1 μm acetylcholine [EC50 = (136.8 ± 21.1) μg/mL and (1.9 ± 0.4) x 10-6 ᴍ] or 40 mᴍ KCl [EC50 = (149.4 d 19.5) μg/mL and (1.8 ± 0.7) x 10-6 ᴍ], respectively, in an equipotent and concentration-dependent manner. This effect is probably due to inhibition of calcium influx through voltage-operated calcium (Cav) 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 μg/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 concentrationdependent manner. The concentration-response curves to CaCl2, in the presence of SAMeOH and isojuripidine, were shifted downward in relation to a control curve in a nonparallel manner resulting in reduction of the maximum effect [Emax = (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 Cav channels.