Effects of rhubarb on isolated gastric muscle strips of guinea pigs.

Aim: To study the effects of rhubarb (dried root of Rheum officinale Baill.) on contractile activity of isolated gastric muscle strips of guinea pigs and its possible mechanism.

Methods: A total of 48 guinea pigs were killed to remove the whole stomach. Then, the stomach was opened and the mucosal layer was removed. Parallel to the circular fibers, muscle strips were cut from the body. Each isolated gastric muscle strip was suspended in a tissue chamber containing 5 mL Krebs solution, constantly warmed by water jacket at 37 degrees and bubbled continuously with a mixed gas of 950 mL/L O2 and 50 mL/L CO2. After being incubated for 1 h with 1 g tension, rhubarb of varied concentrations (1%, 2%, 7%, 20% and 70%) was added cumulatively into the tissue chamber at intervals of 2 min. Atropine (10(-6) mol/L) or isoptin (5 x 10(-8) mol/L) or hexamethonium (10(-5) mol/L) was given 2 min before the administration of rhubarb. The isometrical response was measured with an ink-writing recorder.

Results: Rhubarb dose dependently increased the resting tension of gastric body circular muscle (CM) (r = 0.726, P<0.05). Atropine (r = 0.829, P<0.05), isoptin (r = 0.764, P<0.05) and hexamethonium (r = 0.797, P<0.05) did not affect its action in a dose-related manner. Atropine apparently reduced the increasing action of 1%, 3%, 10%, 30% and 100% rhubarb on the resting tension of gastric body CM. Isoptin inhibited the effect of 10%, 30% and 100% rhubarb on the resting tension of gastric body CM. Hexamethonium reduced the increasing action of 1%, 10%, 30% and 100% rhubarb on the resting tension of gastric body CM. Rhubarb increased the contractile frequency of CM of body. While atropine, isoptin and hexamethonium did not inhibit the contractile frequency of gastric body CM in comparison with rhubarb at the same concentration, rhubarb at the highest concentration (100%) decreased the mean contractile amplitude of gastric body CM. Atropine, isoptin and hexamethonium did not affect the mean contractile amplitude of gastric body CM compared to rhubarb at the same concentration.

Conclusion: Rhubarb has exciting actions on isolated gastric smooth muscle strips of guinea pig. The exciting action of rhubarb is partly mediated via cholinergic M receptor, cholinergic N receptor and L-type calcium channel.