The prolongation of pseudopregnancy in the rat as a result of hysterectomy (Melampy, Anderson & Kragt, 1964) or massive deciduoma (Velardo, Olsen, Hisaw & Dawson, 1953; Melampy et al., 1964) suggests that a luteolyticprinciple is produced by the uterine endometrium. There is evidence that the proposed luteolysin acts locally: pseudopregnancy is extended in rats following excision of one uterine horn and of the contralateral ovary, while no extension results when the ovary adjacent to the excised horn is removed (Anderson, Melampy & Chen, 1966; Barley, Butcher & Inskeep, 1966). Pseudopregnancy is also prolonged by spatial separation of the uterine horns from their related ovaries (Anderson, Melampy & Chen, 1966; Barley et al., 1966). We have been able to confirm these observations.
A local luteolytic action has been observed in the unilaterally pregnant gilt (Du Mesnil du Buisson, 1961) and the Canadian porcupine (Erethizon dorsatum)(Mossman 8c Judas, 1949). Although unilateral pregnancy has been described in the intact rat (Deanesly & Parkes, 1931), the possibility of a local luteolytic action has not been investigated and this is the subject of the present study.
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