Effects of milk-derived β-casomorphins on glucose absorption of the small intestine and serum glucose concentration in rats.

To investigate the effects of β-casomorphins(β-CMs),one of the primarily milk-derived bioactive peptides,on glucose absorption of the small intestine and serum glucose concentration in rats,in vitro and in vivo experiments were conducted in this study.In the in vitro experiment,the effects of β-CM7 and β-CM5 at concentrations of 0(control group),7.5×10-5(high-dose group),7.5×10-6(medium-dose group) and 7.5×10-7 mol/L(low-dose group) on intestinal absorption of glucose were studied by using reversed small intestine sac.At the same time,the combination of naloxone(special blocker of opioid receptor) and β-CM7(2∶1,molar ratio) was used to investigate the opioid mechanism of β-CM7 on intestinal absorption of glucose.In the in vivo experiment,twenty-one healthy adult Sprague-Dawley(SD) rats were randomly divided into control group(intragastric physiological saline infusion),β-CM7 group(intragastric 7.5×10-6 mol/L β-CM7 infusion) and β-CM5 group(intragastric 7.5×10-6 mol/L β-CM5 infusion).After 30-day experiment,the rats were killed by breaking off the neck,and the blood,liver and muscle were sampled for testing serum glucose and insulin levels,and the contents of hepatic glycogen and muscle glycogen.The results of in vitro experiment showed that,β-CM7 and β-CM5 at all different concentrations(7.5×10-7 to 7.5×10-5 mol/L) could inhibit the intestinal absorption of glucose in vitro in a dose-dependent manner,and naloxone addition did not reverse the inhibition of β-CM7 on the in vitro absorption of glucose in small intestine.The results of in vivo experiment showed that,in later period of the experiment,the concentration of serum glucose and the content of muscle glycogen in β-CM7 and β-CM5 groups were lower than those of the control group(P0.01),and the content of hepatic glycogen in β-CM5 group was lower than that of the control group(P0.01) while the content of serum insulin showed little disparity in comparison with that of the control group(P0.05).In conclusion,β-CM7 and β-CM5 have the assistant effect of lowering serum glucose,and this effect has some relationships with the consumption of muscle glycogen and the inhibition of β-CMs on glucose absorption of the small intestine via non-opioid way.