Intrauterine oxygen tension during the estrous cycle in the guinea pig: its relation to uterine blood volume and plasma estrogen and progesterone levels.

Abstract

This study was undertaken to determine: 1) the oxygen tension (p02) within the lumen of the guinea pig uterus throughout the estrous cycle and during the preimplantation period; 2) the relationships between intrauterine p02, uterine blood volume (UBV) and endogenous plasma estradiol-1 7� (E) and progesterone (P) levels; and 3) the effects of exogenous ovarian steroid hormones on uterine blood volume and intraluminal p02. Mean arterial and venous p02 remained constant throughout the cycle. Mean intrauterine oxygen tension did not differ significantly from venous p02 except at the times of ovulation and uterine capacity for implantation. Intrauterine p02 increased rapidly to a peak during Day 0 (proestrus-estrus) and returned to venous levels by Day 1. A second dramatic increase in p02 began on Day 4, reached a peak on Day 6 and declined to venous levels by Day 8. Similarly, uterine blood volume remained at basal levels throughout the cycle except for dramatic increases at approximately the times of ovulation and uterine receptivity to the blastocyst. Also temporally correlated with the increases in intrauterine p02 and UBV were elevations in plasma E concentration. Estrogen was low throughout the cycle except on Days 0 and 6. Plasma progesterone peaked on Day 0, returned to basal levels on Day 1 and was elevated on Days 2-7. Intrauterine p02 increased following ovariectomy; exogenous estrogen administered to ovariectomized animals markedly elevated pO2; progesterone suppressed the postovariectomy increase in intraluminal p02, maintaining oxygen tension at venous levels; E + P briefly increased p02. Ovarian steroid treatments in ovariectomized animals resulted in changes in intrauterine p02 concomitant with those of UBV. Synchronous changes in plasma ovarian steroid levels, uterine blood volume and intrauterine oxygen tension suggest that intraluminal oxygen concentration is regulated in part by estrogen and progesterone via alterations in uterine hemodynamics. Furthermore, intrauterine p02 is low until the anticipated time of conceptus entry, but increases rapidly thereafter to maximum levels at the time of uterine receptivity to the ovum. The coincidence of peaks in p02 with ovulation and implantation suggests that increased intrauterine oxygen tension may play a role in sperm viability, conceptus development and implantation.