A RELATION BETWEEN ESTRADIOL AND PROLACTIN AND VAGINAL MICROBIOTA COMPOSITION IN THE ONE-YEAR ISOLATION EXPERIMENT “SIRIUS-23”

As part of the 365-day isolation experiment "SIRIUS 23," a relationship between hormone concentrations (estradiol and prolactin) and vaginal microbiota composition in four female participants was assessed. Vaginal swabs were collected 10–14 days before the start of isolation, on days 36, 64, 102, 123, 186, 256, and 339 of isolation study, and 10 days after its cessation. Blood estradiol and prolactin concentrations were measured using an enzyme-linked immunosorbent assay, while microbiological analysis included microbial culture on selective media and identification using MALDI-TOF MS, followed by statistical data processing using factorial and regression analysis, and nonparametric tests (Friedman, Mann-Whitney). The study revealed that estradiol concentrations decreased after the onset of isolation, reaching a minimum level on day 123 (p=0.05), while prolactin demonstrated an upward trend on day 36, followed by a statistically significant decline on day 64. Factor analysis identified three main factors influencing the "hormone-bacteria" system: i) combined opportunistic microorganisms (OM) and prolactin; ii) included estradiol concentration and its antagonistic relation with some OM number; iii) mirrored competitive interplay between microorganisms. Estradiol concentration correlated positively with protective lactobacilli count (L. vaginalis, L. jensenii, L. crispatus) and negatively with OM count, while prolactin concentration was more often positively associated with OM count (S. hominis, S. anginosus, C. amycolatum) and negatively with lactobacilli count. Regression analysis confirmed direct and inverse relationships, such as a positive association between prolactin concentration and E. coli count on day 64 and an inverse association between estradiol concentration and S. anginosus count. Stress factors (resource limitation, psychoemotional stress) exacerbated microbiota imbalance through decreased estradiol and increased prolactin level, which was particularly evident on day 102 of isolation, when OM count peaked in parallel with decreased lactobacilli count. The results highlight the key role for estradiol in maintaining vaginal microbiota balance and the opposite effect of prolactin associated with OM, which justifies a need to monitor hormonal levels and microbiota in women under extreme conditions (e.g., during space flights) and development of personalized probiotic strategies to minimize dysbiosis risks.