The impact of chronic restraint stress on the estrous cycle in NMRI female mice

Abstract

Introduction: Stress represents a set of reactions in the organism activated by external factors. In order to maintain homeostasis and protect the organism, numerous mechanisms for adaptation to stress evolved. Stressors that act in short-term period cause acute stress reaction with generally positive effect on organism. When the stressor persists, and the organism fails to respond to the challenge, chronic stress develops, leading to pathological conditions, such as women's menstrual cycle disorders. Aim: To examine the impact of chronic restraint stress on the estrous cycle in NMRI female mice. Material and methods: A number of 12 mature female NMRI mice were randomly divided into control (n = 6) and experimental (n = 6) group. The induction of stress was performed for the experimental group by using restrain chambers 2 hours daily in 14 days. From the beginning of the experiment, vaginal lavages were taken from all mice for making smears that were analyzed to determine estrous cycle stages. For analysis of chronic stress effect, the frequency of estrus stages alternation observed in experimental group compared to control was examined. Results: The estrous cycle was observed and divided into proestrus, estrus, metestrus and diestrus. During the adaptation period, prolonged diestrus was dominantly present in both groups. When stress was induced, in the experimental group animals the absence of diestrus stage and oscillation to other stages was obseved, in contrast to the control group, where the diestus stage was frequently observed. Frequency of diestrus stage deviation in stressed animals was shown to be statistically significant (p < 0.01) when compared to control. Conclusion: The induction of chronic restraint stress in female NMRI mice leads to the alternation of the estrous cycle. Considering the fact that NMRI female mice share the similar hormonal regulation of the estrous cycle with women's menstrual cycle, they could present a solid model for studying women's reproductive disorders.