Inhibition of gastric emptying by triterpene saponin, momordin Ic, in mice: Roles of blood glucose, capsaicin-sensitive sensory nerves, and central nervous system

The roles of capsaicin-sensitive sensory nerves and the central nervous sys tem in the inhibitory effect of momordin Ic, a principal saponin constituen t in various Chinese and Japanese herbal medicines, such as the fruit of Ko chia scoparia (L) SCHRAD., on gastric emptying were investigated in nonnutr ient meal- or nutrient meal-loaded mice. Momordin Ic (12.5-50 mg/kg) signif icantly inhibited gastric emptying in 1.5% carboxymethyl cellulose sodium s alt test meal-loaded mice by 8.4%-60.6%, 40% glucose test meal-loaded mice by 42.8% (50 mg/kg), milk test meal-loaded mice by 36.4% (50 mg/kg), and 60 % ethanol test meal-loaded mice by 37.2% (50 mg/kg). The inhibitory effect on the gastric emptying in 1.5% carboxymethyl cellulose sodium salt test me al-loaded mice was potentiated by glucose (2 g/kg, i.v. or 5 g/kg, i.p.), b ut markedly attenuated by pretreatment with alloxan (50 mg/kg, i.v.) and st reptozotocin (100 mg/kg, i.v.), in which the activity of sympathetic nervou s system was decreased, or by insulin (1 or 3 U/kg, s.c.). The effect of in sulin (1 U/kg) was markedly reduced by glucose (2 g/kg, i.v.), which can di rectly nourish the brain, but not by fructose (2 g/kg, i.v.), which cannot be used by the brain. The effect of momordin Ic was also attenuated by pret reatment with capsaicin (75 mg/kg in total, s.c.). These results suggest th at the inhibition of gastric emptying by momordin Ic is relative to serum g lucose and, at least in part, mediated by capsaicin-sensitive sensory nerve s and the central nervous system.