I. Cyclical alterations of the endometrium of the rat during the normal cycle, pseudopregnancy, and pregnancy. II. Production of deciduomata during pregnancy

Studies on the physiology of the maternal placenta in the rat

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 determining 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 gestation, 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.

Ia antigen expression in the rat uterus

Using indirect immunofluorescence and monoclonal antibodies, we have determined the distribution of Ia+ cells in the non-pregnant rat uterus. In cycling animals, Ia+ cells, most of dendritic shape and non-specific esterase negative, were abundant in the connective tissue of the myometrium and throughout the endometrium, especially adjacent to the luminal and glandular epithelia. In contrast, the number of T lymphocytes was very much less and few of these cells expressed Ia antigen. Stromal Ia+ cells were more numerous during estrus than in any other phase of the cycle. Only a few Ia+ cells were seen in neonatal uterine samples, but the numbers increased to approximately adult levels by 32 days of age. Prepubertal glands were consistently negative, but epithelial expression of Ia antigens in adult uteri showed interesting variations. The luminal epithelium was always negative, whereas the glandular epithelial cells often were positive. Glandular staining was quite heterogeneous in individual samples, but most gland profiles were negative or weakly positive during proestrus and estrus and positive during diestrus. Ovariectomized females given different steroid supplements revealed significant hormonal effects. Estrogen alone dramatically increased the numbers of Ia+ stromal cells compared with control samples, but progesterone alone had no effect. However, progesterone given with estrogen abrogated the estrogenic influence. Progesterone alone caused decreased expression of Ia antigens by the glandular epithelium. If the highly-Ia/ cells in the stroma are capable of antigen presentation, these results indicate a significant potential for local antigen processing with the uterine endometrium.