Studies of the luteotropic and mammotropic factor found in trophoblast and maternal peripheral blood of the rat at mid‐pregnancy

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Abstract
Bioassay data demonstrate that trophoblastic elements of the midpregnancy rat placenta contain a substance or substances possessing luteotropic and mammotropic properties. This material is also present in high potency in maternal serum but only at midpregnancy. The standard bioassay animal preparation utilized in demonstrating these properties was the immature, PMSG‐stimulated, hypophysectomized female Long‐Evans rat. The end point for detection of luteotropic activity was the deciduoma reaction and that for detection of mammogenic activity was proliferation of locally treated mammary parenchyma. The local injection of one day 12 placental equivalent daily for seven days consistently induced deciduoma formation and mammary parenchymal proliferation. Similar responses were observed in animals injected with 0.1 ml serum from peripheral blood of the day 12 pregnant rat.These biological extracts also possessed lactogenic activity, which was demonstrated by mammary secretory response to trophoblastic extracts and midpregnancy serum containing prednisolone acetate in suspension. Assay animals used in detecting this activity had been hypophysectomized, ovariectomized, and adrenalectomized.The pigeon crop sac responded weakly and tibial epiphyseal cartilage failed to respond to large doses of the biological extracts. No target organs other than the corpus luteum and mammary gland were found. It is proposed that an appropriate designation for this hormone would be Rat Chorionic Mammotropin (RCM).

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