Decidualization: The Decidua and the Deciduoma

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DECIDUALIZATION: THE DECIDUA AND THE DECIDUOMA M. C. SHELESNYAK* One ofthe recurring episodes in the normally functioning primate female genital tract is menstruation. The extensive endometrial growth and proliferation which goes on before and after ovulation readies the lining ofthe womb for the arrival and nesting ofthe fertilized ovum, the blastocyst . When none appears, rapid regression ofthe highly specialized endometrial tissue results in shedding ofthe degenerated tissue and consequently produces the menses. Though this dramatic event is limited to certain primates, non-menstruating mammals also experience the periodic endometrial growth and differentiation in preparation for the blastocyst. Regression ofthe endometrial tissue is, however, "silent." But when fertilization ofthe ovum is successfully achieved, an alternate process occurs, a highly integrated complex ofbiodynamic activities. The stroma and endometrium in the uterus undergo a sequence of dramatic changes. In the course ofthese physiological and structural developments, the mucosa ofthe uterus becomes transformed into tissue which is capable ofreceiving the fertilized ovum. This transformed uterus is a system with characteristics which make it very different from the ordinary non-gravid —or, more correctly, pre-gravid—uterus. This transformation of endometrium results in decidua, and the process is called decidualization. Decidualization ofthe progestational uterine mucosa produces first the decidual cells; they form an essential share ofthe mucosa ofthe pregnant uterus, which has been designated the decidua. Amoroso (i) has described the anatomy and physiology ofplacentation (attachment ofthe fertilized ovum to the maternal anchorage) in great detail with clarity and precision . He notes that the term decidua was derived from the fact that at * Professor of Endocrine and Reproduction Physiology; Head, Department of Biodynamics; Weizmann Institute of Science, Rehovoth, Israel. 503 the end of gestation a thin layer forms (in many rodents and in man) through which the separation and shedding, or deciduation, is accomplished . But he warns that "one should guard againstthe common error of supposing that the formation ofdecidual cells is directly determined by the presence ofdeciduating maternal tissues." Decidual cells defy rigid categorization. They vary greatly from species to species and within species; they vary with regard to cells oforigin (not entirely clear); in structure (some large basophilic, some small round); in function (some have glycogen, some lipids), etc. Thus, although decidual cells are products ofdecidualization, neither the process nor the products can be defined critically in terms ofcomponents or sequences. Their importance to natural progestation and gestation is, however, established; and they are an essential feature ofmost mammalian pregnancies. What is the deciduoma? Somewhat more than halfa century ago, in 1907, Leo Loeb (2, 3), one of America's outstanding medical biologists, described briefly some observations on the reaction of the non-pregnant uterus ofthe guinea pig to mechanical injury. He reported that, following injury to the uterus during a specific phase ofthe estrus cycle, the endometrium developed a massive growth of decidual cells. This artificially induced decidual tissue bore striking similarity in form and function to the maternal component ofthe placenta, the decidua. It has been named deciduoma . It has also been called placentoma but, though neither name can bejustified on the current bases ofnomenclature oftumors (the deciduoma was considered such at the time), deciduoma is preferred. The French literature uses the word déciduome to denote the decidual tissue irrespective ofhow it is provoked—artificially or associated with natural implantation ofthe blastocyst. The term déciduome is useful. The deciduoma is an extremely useful tissue for investigation ofmany physiological phenomena associated with processes of reproduction and endocrine relationships within the complex of the pituitary-thyroidadrenal -gonad system. Study ofthe blastocyst-uterus relation during progestation has also benefited greatly from use of the deciduoma as a tool and a model system. We have been employing deciduoma and decidualization as a model system for studying the mechanism of nidation during the past several years (4). Wehave beenled to the conviction that decidualization is essen504 M. C. Shelesnyak · Decidualization Perspectives in Biology and Medicine · Summer 1962 tial and prerequisite to successful pregnancy: no decidualization, no nidation and no gestation. A second conclusion, based on observations from many experiments on decidualization and nidation, is that the process of decidualization is an organogenetic process and thatthe decidua is essentially a newly developed organ, with specific...

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