Intrauterine Oxygen Tension During the Estrous Cycle in the Rat: Its Relation to Uterine Respiration and Vascular Activity

Intrauterine oxygen tension, measured in vivo in the adult virgin rat, varied during the course of the estrous cycle. Average pO2 was maximal during diestrus-1 (47.6 mm Hg) and minimal during estrus (25.7 mm Hg). Metestrous, diestrous-2 and proestrous values were intermediate to these extremes. The frequency of alteration in intraluminal oxygen tension, a measure of vascular contractility, increased uniformly from 15.7 peaks/hr during diestrus-2 to 70.3 peaks/hr during metestrus. Only slight changes in pO2 amplitude were noted. The timing of pO2 changes during the cycle, and of the vasodynamic activity which affects these changes, apparently preceded the gross morphologic and metabolic alterations in the uterus by about 12–24 hr. The primary regulation of the level of intrauterine pO2 during the cycle appeared to be through steroid hormone control of vasodynamic and metabolic activity, with myometrial contractile activity being only of secondary influence. (Endocrinology83: 701, 1968)