RESUMO
BACKGROUND: Stress has been considered as one of the causes of decreased reproductive function in women. However, direct evidence of the effect of chronic stress on oocytes depending on estrous cycle phases is limited. OBJECTIVE: The present study aimed to evaluate the impact of chronic stress on the viability, integrity, and maturation of rat oocytes depending on estrous cycle phases, specifically proestrus, estrus, and diestrus. METHODS: For this purpose, adult female rats were stressed daily by cold water immersion (15 °C) for 30 consecutive days. RESULTS: In chronically stressed female rats, irregular estrous cyclicity, increased corticosterone levels, decreased oocyte viability, and an increased percentage of abnormal oocytes were obtained in all the estrous cycle phases, resulting in reduced oocyte maturation during proestrus. CONCLUSION: Oocyte maturation disturbed by chronic stress is a crucial factor by which chronic stress disrupts female reproduction.
RESUMO
Infertility is a growing worldwide public health problem, and stress is a main factor exerting detrimental effects on female reproduction. However, knowledge regarding the neuroendocrine changes caused by chronic stress in females is limited. Therefore, this study assessed the effects of stress on hormones that control female reproduction during the proestrus and diestrus stages of the estrous cycle, as well as its effects on fertility. Adult females were assigned to either a control or a stress group. Stress consisted of exposure, for 15 min, to cold-water immersion daily for 30 days. Estrous cyclicity, female sexual behavior, as well as hypothalamic kisspeptin, gonadotropin releasing hormone (GnRH) content, serum luteinizing hormone (LH), estradiol (E2), progesterone (P4), corticosterone (CORT) and fertility were assessed after chronic stress. The results show that chronically stressed females exhibited disrupted estrous cyclicity, decreased receptivity, low pregnancy rates and lower numbers of fetuses. The content of Kisspeptin and GnRH in the Anteroventral Periventricular/medial Preoptic Area decreased during proestrus, while Kisspeptin increased in the Arcuate nucleus in proestrus and diestrus. Serum LH decreased only during proestrus, whereas E2 and P4 concentrations decreased during proestrus and diestrus, with a concomitant increase in CORT levels in both stages. As a whole, these results indicate that chronic stress decreases Kisspeptin content in AVPV nucleus and GnRH in POA in females, and might induce disruption of the LH surge, consequently disrupting estrous cyclicity and fertility, leading to lower rates of pregnancy and number of fetuses.