W.R. Allen

Placentation in the African elephant (Loxodonta africana): II morphological changes in the uterus and placenta throughout gestation.

The gross and microscopic development of the zonary endotheliochorial placenta in the African elephant was studied in 22 gravid uteri that ranged in gestational stage from 0.5 to 20.6 months. The conceptus only ever occupies one horn of the uterus and is associated with 2-5 large corpora lutea that persist in the ipsilateral ovary throughout gestation. Initially, the trophoblast in the equatorial region of the conceptus completely replaces the lumenal epithelium of the endometrium to which it is apposed. Blunt upgrowths of endometrial stroma then develop, each closely invested by trophoblast, and containing the capillaries that will vascularize this maternal component of the resulting placental band. With advancing gestation the lamellate stromal upgrowths increase markedly in length and become much thinner, thereby bringing the trophoblast into intimate contact with the endothelium of the maternal capillaries. They also become folded or pleated to increase the total area of intimate feto-maternal contact. At the lateral edges of the placental band the lamellae bend over towards the endometrium to form a blind cleft. Leakage of blood into this area creates haemophagous zones in which phenotypically specialized trophoblast cells phagocytose the blood components. The presence of large resorbing blood clots and circumferential scars in the uteri of three post parturient animals initiated the hypothesis that, when the standing elephant gives birth at term, the passage of the 120 kg fetus through the vagina may wrench the placenta off the endometrium by severing its very narrow maternal placental hilus. The resulting intrauterine haemorrhage may then play a role in preventing further conception for around 2 years.

Horse Conceptuses Secrete Insulin-Like Growth Factor-Binding Protein 3

Abstract Insulin-like growth factor-I (IGF-I) promotes early embryonic development in several species. In the rabbit, IGF-I binds to the embryonic coats from Day 3 of development onward by a 38-kDa protein that is probably insulin-like growth factor-binding protein 3 (IGFBP3). In the present study, ligand, Western, and Northern blot analyses were used to demonstrate the presence of IGF-I-binding activity, several immunoreactive IGFBP3 proteins, and IGFBP3 mRNA in horse conceptuses with particularly large amounts of immunoreactive IGFBP3 in the conceptus capsule. In addition, immunoprecipitation of radiolabeled proteins showed that cultured horse conceptuses secreted IGFBP3 into the culture medium. Endometrial samples from mares also contained IGFBP3 mRNA and protein; but there was no evidence of secretion of IGFBP3 into the uterine lumen by ligand blot analysis, and there was evidence of only very small amounts by Western blot analysis. These results indicate that the horse conceptus secretes significant quantities of IGFBP3 toward the conceptus capsule from as early as Day 10 after ovulation. Thus, most of the IGFBP3 contained within the capsule, which binds IGF-I to this special extracellular matrix of the preimplantation horse conceptus, is likely to be embryonic in origin. IGFBP3 in the horse conceptus capsule may enhance or modulate the action of IGFs on the developing conceptus.

Immunohistochemical Localization of Oestrogen Receptors α and β, Progesterone Receptor and Aromatase in the Equine Placenta

The functions of placental oestrogens during equine pregnancy are still unclear. Yet, they may act predominantly as local regulators of growth and differentiation in the microplacentomes. Thus, expression patterns of oestrogen receptors (ERs) alpha and beta were investigated in the microcotyledonary placenta from pregnant mares at 110, 121, 179, 199 and 309 days of gestation by immunohistochemistry. In microplacentomes, both the ER isoforms were detected in trophoblast (T) cells, chorionic villous stroma (FS), microcaruncular epithelium (ME) and microcaruncular stroma (MS). Proportions of positive cells were 38-91% (T), 11-41% (FS), 55-89% (ME), 17-51% (MS) for ERalpha and 66-76% (T), 21-37% (FS), 41-68% (ME) and 24-55% (MS) for ERbeta. Between days 110 and 199, proportions of cells positive for progesterone receptor (PR) varied between 19% and 62% (T), 3% and 50% (CS), 15% and 46% (ME), and 4% and 33% (MS). At day 309, PR was virtually absent in T, CS and ME (percentages < 0.1), whereas in MS 14.3% of cells were still positive. The expression of ERs and PR in equine microplacentomes gives evidence for a role of placental steroids as regulators of placental growth, differentiation and function. The detection of ERalpha, ERbeta and PR in foetal and maternal vascular tissue suggests that placental steroids are also involved in the control of placental angiogenesis and /or vascular functions. The co-localization of ERs with aromatase in T suggests auto- or intracrine functions of oestrogens in this cell type.