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 EC
50, the E
max (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 (p<0.05) decreased, and the concentration producing E
max was significantly (p<0.05) increased in the presence of the antagonists. The ileal contraction produced by
A. caudatus was more sensitive to mepyramine antagonism. The EC
50 (373.80±51.56mg/ml) and the concentration producing E
max (855.00±75.00mg/ml) for
A. caudatus extract increased significantly (p<0.05) 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 EC
50 and the concentration eliciting the E
max for
S. melongena extract increased significantly (p<0.05) 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 H
1 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 H
1 receptors.
