Effects of cirsiliol, a flavone isolated from Achillea fragrantissima, on rat isolated ileum.

1. In concentrations from 10(-8) M to 3 x 10(-4) M, cirsiliol caused concentration-dependent relaxation of rat isolated ileum. 2. Phentolamine (10(-6) M) or phentolamine and propranolol (10(-6) M) had no significant effects on the concentration-effect curves or on the EC50 of cirsiliol on the ileum. 3. Cirsiliol shifted to the right the acetylcholine (Ach) concentration-effect curves on ileum and significantly inhibited the maximum contractions induced by Ach. 4. In Ca(2+)-free, depolarizing solution, cirsiliol shifted to the right the CaCl2 concentration-effect curves and inhibited the maximum contractions induced by CaCl2 on ileum. 5. Large concentrations (10(-4) M, 3 x 10(-4) M) of cirsiliol induced relaxation followed by contraction of the ileal segments incubated in Ca(2+)-free solution. 6. In Ca(2+)-free solution, cirsiliol (10(-4) M, 3 x 10(-4) M) caused concentration-dependent potentiation of the ileal contractions induced by 3 x 10(-3) M Ach when the latter was added 2-3 min after cirsiliol. When Ach was added 15-20 min after cirsiliol, the latter compound inhibited the Ach-induced contractions. 7. These observations suggest that cirsiliol inhibits Ca2+ influx but stimulates Ca2+ release from intracellular stores. Furthermore, they suggest that cirsiliol utilizes the same Ca2+ source used by acetylcholine in Ca(2+)-free solution.