Investigation of oocyte maturation inhibitory proteins from urine of pregnant women.

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In mammals, the germinal vesicle of follicle-enclosed oocytes remains arrested at the dictyate stage of meiosis until the occurrence of a gonadotropin surge. Upon releasing the oocytes from the follicles in vitro, the meiotic process resumes, leading to a spontaneous germinal breakdown(GVBD)followed by the first polar body formation(PBF)of the oocytes, suggesting that oocyte maturation inhibitor(s)sustain the meiotic arrest of oocytes. In normal pregnancy, although hormonal levels of chorionic gonadotropin and estrogen are high, significant maturation of the oocytes and follicles do not occur for a long period, suggesting the possibility of a considerable increase in concentration of oocyte maturation inhibitor(s)in urine during pregnancy. The purpose of this study was to determine protein inhibitor(s)using denuded mouse oocytes in culture, if such inhibitor(s)are present in urine of pregnant women.The results obtained from this study are as follows :1. A protein inhibitor of PBF was purified from a uine of pregnant women by Sephadex G-100 and reversed-phase chromatographies. It was revealed that this protein possessed an ribonuclease activity and amino terminal sequence analysis showed that this protein is a product of a peculiar processing of a nonsecretory ribonuclease precursor. This protein was detected only in urine of pregnant women but not of normal men and women.2. A fraction with molecular mass of less than 2, 000 daltons containing peptide inhibitor(s)of GVBD was prepared by gel filtration from pregnancy urine. The inhibitory activity of this fraction was partially reversed in the presence of naloxon, a potent opioid antagonist. Activity of this fraction obtained from pregnancy urine was significantly potent than same fractions obtained from normal women and men.