Unexpected low oxygen tension of intravaginal culture

The goal of this study was to assess whether the metabolic activity of gametes or the local environment had a greater influence on the pH, pO2 and pCO2 of the culture medium in the intravaginal culture (IVC) technique. The pH, pO2 and pCO2 of the culture medium in four groups of intravaginal cryotubes with or without spermatozoa and oocytes, together with the pO2 and pCO2 of vaginal epithelium, were measured before and 48 h after IVC. Hermetically closed cryotubes sealed in a cryoflex envelope were used throughout. Similar results were obtained from all four groups. The pH and pCO2 were unchanged but pO2 significantly decreased during IVC, presumably because of equilibration with the low pO2 (5 mmHg) and pCO2 (49 mmHg) present in the vaginal epithelium. A second series of experiments was then performed with standard culture conditions using culture medium with or without motile spermatozoa in cryotubes covered with cryoflex maintained in air supplemented with 5% CO2. The pH, pO2 and pCO2 were all unchanged in all samples. When the samples were maintained in air only, the pH increased, pO2 remained unchanged and pCO2 decreased, presumably because of equilibration with the low pCO2 (0. 3 mmHg) present in the air. However, when the samples were cultured under venous blood, the pH and pO2 decreased and pCO2 increased, presumably because of the high pCO2 and low pH of venous blood. Thus the pO2 and pCO2 of the culture medium were able to equilibrate with the local environmental gas milieu owing to the permeability of O2 and CO2 through the plastic material. IVC results in a constant pH due to an identical pCO2 in the vaginal epithelium but in a reduced pO2 concentration due to the lower pO2 in the vaginal epithelium.