Effects of Northwest Russia’s Photoperiodic Conditions and Exogenous Melatonin on Physiological and Biochemical Parameters in Syrian Hamsters (Mesocricetus auratus)

Abstract

The effects of the photoperiodic conditions in northwestn Russia (Republic of Karelia, Petrozavodsk) and exogenous melatonin on the body weight and the physiological and biochemical parameters of blood serum in males and females of the Syrian hamster (Mesocricetus auratus) were studied. The animals were divided into two groups: control (LD: 12 h light/12 h darkness) and experimental (NL: decrease in the duration of the daylight phase from 19:36/4:24 to 12/12, which was typical for the Republic of Karelia from June 25, 2018, to September 25, 2018). Each group was divided into two subgroups: hamsters of the first subgroup received drinking water without melatonin (LD, NL), the second group received melatonin (100 μg/animal) at night (LD + mel, NL + mel). Males were found to be the most sensitive to the change in the photoperiod: the NL conditions led to an increase in feed intake, and body weight in the middle of the experiment, and total cholesterol and urea levels by the end of the experiment, while the activities of amylase, lactate dehydrogenase, and aspartate aminotransferase in the blood were lower than in LD. The melatonin effect on the studied parameters depended on the conditions and sex of the animals. Melatonin treatment of the NL-females caused enhancement in the effect of the light regime and increase in most of the biochemical parameters of blood serum compared to the control as well as an increase in body weight for the entire study period. The use of melatonin in the LD conditions had a negative effect on the Syrian hamsters, causing intensification of metabolic processes and, as a result, a significant decrease in body weight in both males and females. In our opinion, the revealed differences between the experimental groups are primarily associated with a change in the synthesis of melatonin by the pineal gland in various light conditions.