Tryptic hydrolysate from bovine milk alpha-s1 casein reduces physiological and behavioural responses to an acute stress exposure in Wistar male rat

A tryptic hydrolysate from bovine milk alpha-s1 casein (CTH) has been found to display an anxiolytic activity in rats, and to be a potent anti-stress product in humans. The present study aimed to confirm the anti-stress activity of CTH in rats submitted to an acute stress exposure. In a first experiment, the animals were stressed for 1h using the restraint stress model. During that, the arterial blood pressure (ABP) and the colonic temperature (CT) were measured at different times. After the stress session, rats were tested for their anxiety-related behaviour in the elevated plus-maze (EPM). CTH was suspended in 0.3% methyl cellulose (MC) and administrated p. o. at a dose of 15 mg/kg 1h before the stress session whereas the control animals received the same volume of MC. In control rats, the restraint stress exposure induced significant increases of the ABP and CT from the fifth minute to the end of the experimental session whereas in CTH-treated animals, these two physiological parameters progressively returned to baseline values after 15 min of stress. In the EPM, no difference was observed between the two groups probably related to the inability of the restraint stress to induce an increase of the anxiety level of animals. In a second experiment, the effects of CTH on the stress-induced anxiety responses were investigated by using the forced swim stress as an alternative model. Forced swim stress (2 min in water at 21°C) induced in controls a complete avoidance of the open space in the maze associated with a significant decrease of the total number of arm entries (median=2). Then, CTH was able to reduce the stress-induced anxiety as reflected by significant increases of the percentage of open arm entries (median=26%) and the total number of arm entries (median=4) compared to MC-treated rats. These results confirm the anti-stress properties of CTH, possibly supported by the biological activity of a peptide that corresponds to the 91-100 fragment of alpha-s1 casein.