Abstract
Earlier investigators have studied the hormone content of the placenta by the reactions of the mammary glands 1 and uterus 2 , 3 , 4 to injected extracts. It has been difficult to use such test reactions quantitatively. In collaboration with Dr. Doisy and others the writer 5 , 6 , 7 has shown that lipoid extracts of placenta will induce full oestrous growth in the vagina of the spayed rat and mouse, as will certain ovarian extracts. This reaction offers the following distinct advantages: (1) it affords several observations upon the living animal at definite intervals instead of a single one at autopsy for the determination of results; (2) it substitutes a maximum reaction which may be obtained in a shorter time interval (two days) for the partial reaction used in some of the earlier work; and (3) its clear cut end-point makes possible the quantitative utilization of this test for the biologic standardization of extracts in rat or mouse units.
Most of the extracts of placenta used in earlier work have been made from human material. Recently it was demonstrated that extracts of human placenta were as effective as follicular hormone from pig ovaries in inducing experimental menstruation in ovariectomized monkeys. 8 Why the placenta should contain a substance similar to the essential hormone of the ovaries and to what extent these endocrine functions are related are fascinating problems. In the case of the opossum, from the nature of the embryonic membranes, such a hormone is probably not necessary to the mechanism of the pregnant cycle. The great diversity among mammals of structural modifications of the tissues making contact between mother and embryo would lead one to look for wide variation in this endocrine function. It is reasonable to suppose that some of the mammals might reproduce without it.
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