Effects of hispidulin, a flavone isolated from Inula viscosa, on isolated guinea-pig smooth muscle.
1. In small concentrations (10(-7)-3 X 10(-6) M), hispidulin caused concentration-dependent contraction of isolated guinea-pig ileum and only mild relaxation of guinea-pig tracheal rings. 2. Larger concentrations (up to 3 X 10(-4) M) caused concentration-dependent relaxation of the ileum and the trachea. All the effects on the ileum and the trachea are reversible upon removal of the compound. 3. In concentrations from 10(-7) to 3 X 10(-4) M, hispidulin had no effect on the tone of the epinephrine-contracted rings of the guinea-pig main pulmonary artery. 4. Hispidulin caused a shift to the right of the acetylcholine concentration-effect curves on ileum and trachea and significantly inhibited the maximum contractions induced by acetylcholine. 5. In Ca2+-free, depolarizing solution, hispidulin caused both a shift to the right, and an inhibition of the maximum contractions, of the CaCl2 concentration-effect curves on ileum, trachea and pulmonary artery. 6. In Ca2+-free, EGTA-containing solution, hispidulin caused concentration-dependent inhibition of the contractions induced in the pulmonary artery by epinephrine and in the ileum by histamine. 7. These observations suggest that hispidulin may interfere with Ca2+ binding to the Ca2+-receptor protein(s) in the smooth muscle cell and/or with the agonist-induced Ca2+-release from intracellular stores. Less likely, hispidulin may interfere with Ca2+ influx through smooth muscle cell membrane.
Abdalla
S
S
Department of Biological Sciences, Faculty of Science, University of Jordan, Amman.
Abu-Zarga
M
M
Afifi
F
F
Al-Khalil
S
S
Sabri
S
S
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002122:Calcium Chloride / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D047309:Flavones; D005419:Flavonoids / Q000494:pharmacology*; D006168:Guinea Pigs; D038143:Inula; D007444:Inulin / Q000032:analysis*; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D010936:Plant Extracts / Q000032:analysis*
D047309:Flavones; D005419:Flavonoids; D010936:Plant Extracts; D007444:Inulin; D002122:Calcium Chloride; C055957:hispidulin; D002118:Calcium