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 system in the inhibitory effect of momordin Ic, a principal saponin constituent in various Chinese and Japanese herbal medicines, such as the fruit of Kochia scoparia (L.) SCHRAD., on gastric emptying were investigated in nonnutrient meal- or nutrient meal-loaded mice. Momordin Ic (12.5-50 mg/kg) significantly inhibited gastric emptying in 1.5% carboxymethyl cellulose sodium salt 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 meal-loaded mice was potentiated by glucose (2 g/kg, i.v. or 5 g/kg, i.p.), but markedly attenuated by pretreatment with alloxan (50 mg/kg, i.v.) and streptozotocin (100 mg/kg, i.v.), in which the activity of sympathetic nervous system was decreased, or by insulin (1 or 3 U/kg, s.c.). The effect of insulin (1 U/kg) was markedly reduced by glucose (2 g/kg, i.v.), which can directly 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 pretreatment with capsaicin (75 mg/kg in total, s.c.). These results suggest that the inhibition of gastric emptying by momordin Ic is relative to serum glucose and, at least in part, mediated by capsaicin-sensitive sensory nerves and the central nervous system.