Purine levels and metabolism in human follicular fluid.
Adenosine (ADO) in low micromolar levels and hypoxanthine (HYP) in millimolar levels have been shown to inhibit maturation of cumulus-enclosed oocytes. To determine the effect of ovarian stimulation with gonadotrophins on follicular purine metabolism, we measured ADO, HYP, inosine (INO), adenine (ADE) and cyclic AMP (cAMP) levels in follicular fluid (FF) from natural (n = 7) or human menopausal gonadotrophin/human chorionic gonadotrophin (HMG/HCG)-stimulated (n = 35) cycles. Purines were extracted immediately (natural cycles) or within 30 min of recovery (HMG/HCG cycles) and analysed by high pressure liquid chromatography (HPLC). The concentration of all ADE purines in FF was in the low micromolar range (1-20 microM); cAMP levels were markedly increased (greater than 100 microM) in FF of HMG/HCG-treated patients. While ADO levels were within the range effective for inhibition of oocyte maturation, those of HYP were not. No correlation was found between purine levels in FF and ovum maturation. Purine levels in FF of natural cycles were uniformly lower than those of stimulated cycles. Significant conversion of 5'-AMP into ADO, ADO into INO and INO into HYP occurred within 1 h when FF was incubated at 25 but not at 4 degrees C. These purine levels in human FF confirm our previous findings with bovine FF and suggest a possible role of ADO, but not of HYP, in the inhibition of oocyte maturation in the human.