In rats, a low dose (40 µg/kg) of delta sleep‑inducing peptide (DSIP) boosted liver antioxidant enzymes (catalase and SOD) during short‑term stress, but higher doses didn’t help. Under long‑term stress, the same low dose actually lowered those enzymes, while a mid dose (120 µg/kg) reduced a liver damage marker (AST) and raised total protein. The highest dose (360 µg/kg) had no effect.

We studied the effect of delta sleep-inducing peptide (40, 120, and 360 μg/kg intraperitoneally, 1 h before the experiment) on free radical oxidation in the liver, aminotransferase activity, and total serum protein content in male Wistar rats during restraint stress. Treatment with the peptide in a dose of 40 μg/kg increased catalase and superoxide dismutase (SOD) activities and malonic dialdehyde (MDA) concentration in the liver homogenate of animals subjected to acute stress. No significant changes were found after administration of this peptide in other doses. Under conditions of chronic stress, the peptide in a dose of 40 μg/kg caused the most pronounced effect. Catalase and SOD activities and MDA concentration decreased, while aminotransferase activity and protein content remained unchanged under these conditions. Administration of the peptide in a dose of 120 μg/kg was accompanied by a decrease in SOD activity and MDA concentration, increase in total protein content, and reduction of AST activity. Increasing the peptide dose to 360 μg/kg abolished its effects.