Oxygen tension in follicular fluid falls with follicle maturation

The increase in follicular diameter during maturation is accompanied by an increase in vascular supply. The oxygen tension (PO2) in the follicular fluid of the growing follicle should therefore give an insight whether the oxygen delivery during this pertinent process is sufficient. Follicular fluid of 20 patients subjected to in vitro fertilization and embryo transfer were sampled in heparinized glass capillaries which were placed between the puncturing needle and the collecting reservoir. All patients were treated with human menopausal gonadotropin (HMG) and follicle-stimulating hormone (FSH). The PO2, PCO2 and pH of the follicular fluid were measured with an automatic gas analyser (Ciba Corning). Simultaneously, the same parameters were estimated in maternal capillary blood taken from the arterialized well perfused earlobe. Follicular size was measured by ultrasound. With growing follicular size (FS), the oxygen partial pressure (PO2) fell from 80 to 50-60 mmHg (PO2 = 114.4-3.3.FS; r = 0.79) while the carbondioxide partial pressure (PCO2) in the follicle increased from 35 to 50 mmHg (PCO2 = 15.1 +/- 1.9.FS; r = 0.71). In correlation to these results, the pH in follicular fluid fell from 7.40 to 7.30 (pH = 7.6-0.019.FS; r = 0.62). The correlation between the PCO2 and the pH demonstrates a deviation from the regression line if no metabolic alterations take place (delta log PCO2/delta pH = -0.69). The increase in ovarian blood flow during follicular maturation is obviously not sufficient to bridge the growing diffusion distance between the capillary network surrounding the follicle and its center.(ABSTRACT TRUNCATED AT 250 WORDS)