[Biorhythm of oxygen tension in uterine and fetal tissues]

Hypoxic cycles with a two fold reduction in PO2 levels (down to 51.7, 43.9 and 53.4%), the frequency of 0.63 +/- 0.07, 1.47 +/- 0.14, 1.98 +/- 0.3 per minute, and the duration of 45.4 +/ 2.9, 28.4 +/- 2.3 and 19.8 +/- 1.9 sec., respectively, were recorded during the measurement of oxygen content in the uterine tissue of pregnant (3-5 days) and non-pregnant rats, as well as in tissues of 13-14-day-old rat fetuses. The oxygen content remained unchanged throughout the whole experiment (30 min) in the peristaltic intestinal wall. The hypoxic cycles were assessed as a mechanism of rhythmic periodic stimulation of metabolic reactions directed towards not only the increased resistance to hypoxia but also towards non-specific resistance of uterine fetal tissues and female body in and out of pregnancy.