Colon Histophysiological Features and Gut Microbiome in Tolerant and Susceptible to Oxygen Deficiency Wistar Rats After the Prolonged Intermittent Hypoxic Exposure.

Systemic hypoxia influences the state of the intestinal epithelial barrier and the microbiome; however, the role of the initial tolerance of the organism to oxygen deficiency in the development of these changes remains poorly studied. The aim of the study was to evaluate the colon histophysiological features and the gut microbiome in rats that were tolerant and susceptible to hypoxia under intermittent hypoxic exposure of varying severity. In male Wistar rats, tolerance to oxygen deficiency was determined according to the Hif1a, Epas1, and Hif3a expression levels in peripheral blood leukocytes, after which they were subjected to intermittent hypoxic exposure at an "altitude" of 5000 m or 7000 m for 1 h daily for 21 days. Subsequently, the state of the intestinal epithelial barrier was assessed using histological, histochemical, and immunohistochemical methods, and the microbiota composition was analyzed by PCR. Under normoxic conditions, in comparison with rats that are tolerant to hypoxia, susceptible animals demonstrated a greater volume fraction of goblet cells and a low abundance of Parabacteroides spp. Intermittent hypoxic exposure induced multidirectional changes depending on the initial tolerance and the severity of the regimen. In tolerant-to-hypoxia animals, an increase in the goblet cells volume fraction was detected after the exposure at the 5000 m "altitude", while at an "altitude" of 7000 m, a decrease in the number of cells in the lamina propria of the mucosa and Clostridium perfringens gr. abundance, as well as a reduction in the Firmicutes/Bacteroidetes ratio, was observed. In susceptible-to-hypoxia animals, a higher abundance of Clostridium perfringens gr. in comparison with tolerant rats was revealed after the exposure at an "altitude" of 7000 m, with no structural changes in the intestinal wall. Thus, intermittent hypoxic exposure led to a rearrangement of the gut microbiome and the morphofunctional characteristics of the intestinal barrier, and the severity of these changes depended on the initial tolerance of the organism to oxygen deficiency and the severity of the hypoxic regime, which should be taken into account when conducting biomedical research.