Abstract
Summary
No significant differences in progesterone concentrations in serum were observed between pregnant and pseudopregnant rabbits at any time prior to implantation. There is a factor present in blastoceolic fluid which reduces the binding of 125I-hCG to receptor sites on luteal membranes, but this factor is also present in uterine flushings obtained from pregnant and pseudopregnant rabbits and has an estimated molecular weight of greater than 150,000. When rabbit blastocysts collected 120 hr after insemination are incubated in vitro for 24 hr with 3H-amino acids, no large molecular weight proteins can be detected in blastoceolic fluid or incubation medium. These data suggest that the preimplantation rabbit blastocyst does not secrete a gonadotropic factor similar to hCG or LH.
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