Identification and partial characterization of a prolactin-like hormone produced by rat decidual tissue.

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Abstract
Rat decidual tissue produces a prolactin-like hormone, decidual luteotropin, which markedly affects luteal cell function. Extracts of decidual tissue do not cross-react with antisera to either rat or ovine prolactin (PRL). Whether the decidual tissue contains a substance that binds to PRL receptors in rat luteal membranes and was determined. This molecule was identified, quantitated and characterized with the use of an ovarian radioreceptor assay. Decidual tissue was induced in day 5 pseudopregnant rats by scratching the antimesometrial wall of the uterus; it was collected on day 9 and homogenized and extracted. Decidual tissue extracts bound specifically to ovarian PRL receptors. Graded dilutions of the extracts yielded curves that were parallel to the ovine PRL standard, indicating that decidual luteotropin competes for the same receptors sites on rat luteal membranes. To determine the levels of decidual luteotropin throughout pseudopregnancy, decidual tissue was obtained on each day between days 6-12. The PRL-like activity was detectable in decidual tissue as early as day 6, reached a maximum on day 9 and declined thereafter. The elution profile obtained from gel filtration of a day 9 decidual tissue extract displayed a major component of decidual luteotropin eluting at a Ve/Vo ratio of .apprxeq. 2.0. Column chromatography indicated that decidual luteotropin corresponds to a protein with a MW of 23,500. The hormone was heat labile, digestible by trypsin and appears to contain disulfide linkages. The identification, quantitation and partial characterization of a PRL-like hormone produced by the decidual tissue of the rat is reported.