Serum progesterone (P4) levels greater than 2.86 nmol/L (0.9 ng/mL) on the day of hCG administration are reportedly associated with decreased pregnancy rates in in vitro fertilization/embryo transfer (IVF/ET) cycles. To further assess this phenomenon we measured serial serum P4, LH, and estradiol levels in 115 consecutive patients undergoing stimulation for IVF/ET with midluteal leuprolide acetate and human menopausal gonadotropins. IVF/ET cycle outcome was retrospectively correlated with P4 levels on the day of hCG administration. Two critical breakpoints were identified, 1.27 nmol/L (0.4 ng/mL) and 286 nmol/L (0.9 ng/mL). Clinical pregnancies occurred in 9 of 18 patients in group I (P4, less than 1.27 nmol/L) compared to 11 of 81 patients in group II (1.27 less than P4 less than 2.86 nmol/L; P = 0.001) and 0 of 14 patients in group III (P4, less than or equal to 2.86 nmol/L) (P = 0.001). Eleven patients in group III had cryopreservation of embryos during that cycle. Six subsequently underwent frozen embryo transfer, and clinical pregnancies occurred in 2, both of whom have delivered. These findings demonstrate that even modest increases in serum P4 levels (greater than 1.27 nmol/L) are associated with reduced pregnancy rates in IVF/ET cycles. In addition, it appears that the mechanism may not exclusively involve poor oocyte quality.

A monoclonal antibody to a fungal protein has been used to demonstrate the presence of the nonhormone binding component of molybdate-stabilized steroid receptors in a variety of vertebrate tissues. We recently identified a steroid receptor in the aquatic fungus Achlya ambisexualis where sexual morphogenesis of the male is directed by the steroid antheridiol. This receptor resembles receptors of higher organisms in exhibiting an 8S, molybdate-stabilized form. In the chick oviduct, a 90 000 molecular weight protein has previously been shown to be associated with the molybdate-stabilized complex of the progesterone receptor. We have isolated a similar protein of molecular weight about 88 000 from A. ambisexualis and have obtained a hybridomal-derived monoclonal antibody directed against it. This mouse anti-Achlya immunoglobulin G1 (IgG1) cross-reacts with the 90 000 molecular weight protein in chick oviduct cytosol and was used to detect analogous 90 000 molecular weight proteins in mammalian tissues. Tissue cytosols were incubated with antibody, and the complexes were isolated onto protein A-Sepharose. The resin-bound proteins were then analyzed by gel electrophoresis. This procedure revealed the presence of 90 000 molecular weight proteins in several mammalian tissues including rat liver, mouse liver and uterus, pig ovarian granulosa cells, human endometrium, and HeLa cells. These results demonstrate that the 90 000 molecular weight protein is not peculiar to the chick oviduct but is present in several different tissues from a variety of animals. This antibody should be a useful probe for further studies on the biological role of these proteins.

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Previous studies have shown that the molybdate-stabilized progesterone receptor from the chick oviduct contains a nonhormone binding component with a molecular weight of 90 000. This protein has also been shown to be associated with some other molybdate-stabilized steroid receptors of the oviduct. In order to access this larger pool of the receptor binding protein, we have developed an isolation procedure based on the observation that the protein is selectively shed from proteins adsorbed to heparin-agarose when molybdate is removed. The protein obtained by this procedure is shown to be the same as that isolated from affinity-purified progesterone receptor as compared by protease digestion and one-dimensional peptide mapping. Four immunoglobulin G secreting hybridoma cell lines were generated against the 90 000-dalton antigen. All of the antibodies recognize the 90 000-dalton protein obtained by electrophoretic transfer from sodium dodecyl sulfate-polyacrylamide gels. In addition, two of the antibodies complex the molybdate-stabilized progesterone receptor as demonstrated by sedimentation analysis on sucrose gradients. One of these antibodies was used to show the presence of the 90 000-dalton component in molybdate-stabilized glucocorticoid and androgen receptors and also to show its presence in brain, liver, and skeletal muscle, but not in serum.

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