A tryptic hydrolysate from bovine milk αs1-casein enhances pentobarbital-induced sleep in mice via the GABAA receptor

Abstract Studies have shown that enzymatic hydrolysis of casein, the primary protein component of cow’s milk, produces peptides with various biological activities, and some of these peptides may have sleep-promoting effects. In the present study, we evaluated the sedative and sleep-promoting effects of bovine α S1 -casein tryptic hydrolysate (CH), containing a decapeptide α S1 -casein known as alpha-casozepine. CH was orally administered to ICR mice at various concentrations (75, 150, 300, or 500 mg/kg). An hour after administration, assessment of its sedative (open-field and rota-rod tests) and sleep-potentiating effects (pentobarbital-induced sleeping test and EEG monitoring) were conducted. Although a trend can be observed, CH treatment did not significantly alter the spontaneous locomotor activity and motor function of mice in the open-field and rota-rod tests. On the other hand, CH (150 mg/kg, respectively) enhanced the sleep induced by pentobarbital sodium in mice. It also promoted slow-wave (delta) EEG activity in rats; a pattern indicative of sleep or relaxation. These behavioral results indicate that CH has sleep-promoting effects, but no or has minimal sedative effects. To elucidate the probable mechanism behind the effects of CH, we examined its action on intracellular chloride ion influx in cultured human neuroblastoma cells. CH dose-dependently increased chloride ion influx, which was blocked by co-administration of bicuculline, a competitive GABA A receptor antagonist. Taken together, the results of the present study suggest that CH has sleep-promoting properties which are probably mediated through the GABA A receptor–chloride ion channel complex.