Pharmacological reactivity of isolated guinea pig ileum to ethanol leaf extracts of Amaranthus caudatus and Solanum melongena.

The pharmacological reactivity of guinea pig ileum to ethanol leaf extract of Amaranthus caudatus and Solanum melongena were determined in vitro. Parameters evaluated include the threshold value and the concentration ratio (CR). The potency of the plant extracts as expressed by EC50, the Emax (maximum response) and its corresponding concentration were determined from the concentration response curve in the absence or presence of 2X10-7 M atropine or 2X10-7 M mepyramine. The study showed that the extract of Amaranthus caudatus or Solanum melongena produced a dose-dependent contraction of the smooth muscle of the guinea pig ileum with threshold values at 80 or 100mg/ml respectively. 2X10-7 M atropine or 2X10-7 M mepyramine individually caused a right shift on the cumulative concentration-response curve for each plant extract. The potencies of the plant extracts were significantly decreased, and the concentration producing Emax was significantly increased in the presence of the antagonists. The ileal contraction produced by A. caudatus was more sensitive to mepyramine antagonism. The EC50 (373.80±51.56mg/ml) and the concentration producing Emax (855.00±75.00mg/ml) for A. caudatus extract increased significantly to 849.00±29.16 mg/ml and 875.00±25 respectively in the presence of atropine, indicating that the extract interacted with muscarinic receptors. The mean EC50 and the concentration eliciting the Emax for S. melongena extract increased significantly from 288.91±32.46mg/ml and 600.00±22.00mg/ml to 385.21±19.20mg/ml and 800±0.00 mg/ml respectively in the presence of mepyramine thus indicating stimulation of the histaminergic H1 receptors of the gastrointestinal tract. Taken together, this study demonstrated that A. caudatus predominantly stimulates muscarinic receptors to produce contraction of the gastrointestinal smooth muscle, while S. melongena predominantly stimulates histaminergic H1 receptors.