Endocrine Abstracts

Introduction: Reproductive processes are regulated with the participation of the kisspeptinergic neurotransmitter system and the hormonal axis hypothalamus – adenohypophysis – gonads. The action of all regulators of reproductive processes can be disturbed by the development of inflammation and the action of pro-inflammatory cytokines. In this case, cognitive dysfunctions may occur, since sex hormones are involved in the regulation of brain functions. The study analyzed the effect of melatonin on the course of the estrous cycle and cognitive functions of adult female rats under conditions of an experimental model of chronic inflammation (the effect of LPS – lipopolysaccharide Salmonella typhi).

Methods: To create chronic inflammation, group A rats received LPS (i.p., 50 µg/kg) daily for 10 days. Group B rats received LPS with melatonin (oral, 0.5 mg/kg) for 10 days. Rats in the control group received sterile water. The phases of the estrous cycle were determined by the ratio of different cell types on stained vaginal smears by light microscopy. The behavior of rats in all experimental groups was tested under the following experimental conditions: open field, elevated plus maze, Barnes’ maze, extrapolation escape.

Results: Exposure to LPS in group A led to disruption of the estrous cycle. The duration of diestrus increased by 28% (P< 0.05). In vaginal smears, the number of epithelial cells with destruction of organelles significantly decreased, the karyopicnic index decreased by 24% (P< 0.05). The action of melatonin reduced the pathological effect of inflammation on the estrous cycle. Group A rats showed a low level of exploratory activity in the open field. In the Barnes maze, group A rats spent more time searching for a safe haven and showed more erroneous responses. In the extrapolation escape test, group A showed an increase in the time to escape from a stressful situation. Rats treated with melatonin maintained higher levels of cognitive ability on various tests.

Conclusions: Melatonin reduces the pathological influence of the used inflammation model on the neuroendocrine mechanisms of regulation of the estrous cycle and cognitive functions. It is likely that the established effects of melatonin may be related to its immunomodulatory and neurotropic properties.