Studies on the physiology of the maternal placenta in the rat

Abstract

[Plates 1-6]Although a great many investigators have made adequate studies on the maternal placenta from the morphogenetic point of view, little attention has so far been given to the humoral conditions which make the formation of the placenta materna possible. Experimental investigations of the problems of placental physiology have as yet been few, and leave unanswered many important questions. Which are the factors deter mining the life span of the placenta, and what is responsible for its ageing ? In what way are the pregnancy changes influenced by the three structures -maternal placenta, foetal placenta, and embryo-present during gesta tion, and what is the role of each ?Recent advances in the physiology of reproduction have made it possible to attempt the elucidation of these problems under unusually favourable conditions. Of great importance was the observation of Leo Loeb that the maternal placenta could be produced experimentally in the rodent. Furthermore, we have reported experiments which showed that the embryos could be removed from the pregnant rat and mouse without interfering with the development of either the foetal or the maternal placenta. These facts, together with the important progress of the past few years in the physiology of the female sex hormones in general, have formed the basis for our present studies, and have enabled us to elucidate some of the problems indicated above.Many of the observations on the physiology of the maternal placenta have been presented in the literature as incidental findings, rather than as the product of a direct investigation. It is obviously of importance that these findings should be correlated, and since no attempt has pre viously been made to do this, we have thought it worth while to review the literature as completely as possible.

Migratory trophoblast cells express a newly identified member of the prolactin gene family

“…Metrial glands were obtained via dissection of mesometrial uterine tissue immediately adjacent to the conceptus. The metrial gland is a heterogeneous tissue comprised of blood vessels, immune cells, trophoblast cells and fibroblasts (Selye & McKeown 1935, Pijnenborg et al 1981, Peel 1989. All tissues were snap-frozen in liquid nitrogen for northern blot analysis.…”

The demonstration of immunoglobulin in the metrial gland cells of the rat placenta

“…They have been shown to contain glycogen (Bridgman, 1948), and their cytoplasmic granules are characterized by a diastase-fast periodic acid-Schiff reaction (Wislocki, Weiss, Burgos & Ellis, 1957) and a high content ofacid hydrolases (Bulmer, 1968). A variety of functions has been attributed to them, including the provision of nutrient to the developing embryo (Selye & McKeown, 1935), the liberation of a holocrine secretion facilitating disruption of the muscle coat during the expansion of the uterine wall (Bloch, 1964), and the production of relaxin (Velardo, Dawson, Olsen & Hisaw, 1953;Dallenbach-Hellweg, Battista & Dallenbach, 1965); none of these, however, has been proven or considered generally acceptable.…”

Decidualization in the post-partum uterus of the mouse

“…Oil injected into the lumen is broken up into droplets some of which become located in the antimesometrial extremity of the lumen, as do blastocysts (Hinchliffe & El-Shershaby, 1975;Martin, 1979). The post-partum nodule interrupts the continuity of the circular muscle layer in the rodent uterus (Selye & McKeown, 1935;Deno, 1937) and it is possible that the presence of post-partum nodules could affect the circular muscle contraction which is associated with the antimesometrial placement of oil droplets or blastocysts (Martin, 1979). However, the presence of post-partum nodules could alter local uterine responses in other ways such as by the influence of the many biologically active factors secreted by the macrophages reported to be present in nodules (Deno, 1937).…”

“…Each nodule overlies a site of placental detachment at parturition, or the site of the résorption of a feto-placental unit or decidualized implantation site (Conaway, 1955). These nodules are often called 'placental scars' and may persist for many months post partum, perhaps even the lifespan of a rodent (Selye & McKeown, 1935;Davis & Emlen, 1948). The colour of the nodules derives from the presence of haemosiderin-laden cells, probably macro¬ phages, which may persist after the disappearance of any overt swelling (Deno, 1937).…”

“…Gross examination of the post-parturient uterus of many rodents, including the common laboratory species, will reveal the presence of discrete pigmented nodules along the uterine-mesometrial bound¬ ary (Selye & McKeown, 1935;Deno, 1937). Each nodule overlies a site of placental detachment at parturition, or the site of the résorption of a feto-placental unit or decidualized implantation site (Conaway, 1955).…”