Immunohistochemical localization of oestrogen receptors alpha and beta, 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.

Microvascular architecture of the near-term uterine caruncles in water buffaloes (Bubalus bubalis).

The present investigation was carried out on five near-term pregnant water buffaloes for studying the microvascular architecture of the uterine caruncles. The vascular casts were obtained by injection of 4:1 mixture of mercox and methylmethacrylate through the branches of the uterine arteries. After complete polymerization of the plastic, corrosion was conducted in 20% potassium hydroxide, then the vessel casts were immersed in distilled water, cut into small pieces, sputter coated with gold, and examined by using a scanning electron microscope. The buffalo uterine caruncle is highly vascularized through two slightly convoluted arteries and a single less tortuous vein. The arteries branch into several stem arteries at the base of the uterine caruncle, which follow nearly straight course in the primary septa towards the fetal side. During the courses of these stem arteries arterioles of variable diameters arise. The arterioles run in the secondary and tertiary septae and at this location arterioles and venules are connected through a voluminous capillary complex. The latter consists of capillaries of greatly variable diameters with vigorous coiling and sinusoidally dilated zones. From the capillary complexes the blood is driven through postcapillary venules back to the tertiary, secondary and primary septa, respectively, and then converge into stem veins which leave the caruncles through the branches of the uterine vein.

Structural and haemovascular aspects of placental growth throughout gestation in young and aged mares.

This investigation was carried out to study the equine placenta from early gestation to near term, with special reference to morphological changes associated with the development of the vasculature of the fetal component of the microcotyledons. Pregnant uteri were removed post mortem from five Thoroughbred mares between 110 and 309 days of gestation, two of which were aged, multiparous animals suffering age-related degenerative changes in their endometrium (endometrosis), while the other three were young, and had primigravid normal healthy uteri. Pieces of endometrium with placenta attached were fixed for light microscopy and fetal vascular casts were made by injecting the placental arteries with a mixture of Mercox and methylmethacrylate. The casts were examined under the scanning electron microscope. In an aged, endometrotic mare at 110 days of gestation, most of the microplacentomes were irregular in shape with a mean+/-sem diameter of 399+/-30.53 microm. Capillaries with variable diameters made up widely meshed network villi with pointed ends (Type 1 terminal villi), and narrow-meshed networks with finger-like ends (Type 2 terminal villi). In the "paired" young healthy mare at day 121 of gestation, most of the microplacentomes were globular in shape and appeared smaller in diameter than those in the 110-day "pair". The narrow-meshed capillary networks formed villi with stems that consisted of both intermediate and terminal parts, the latter of which represented more the Type 2 than the Type 1 terminal villus. In another aged endometrotic mare at 179 days of gestation, the microplacentomes were typically globular in shape and they showed a mean diameter of 534+/-36.07 microm. The villi were short and thick and they were distinctly differentiated into stem, intermediate and terminal parts. The density of the fetal capillaries had now greatly increased so that, three dimensionally, they constituted bulb-like capillary networks at the base of the stem of each villus. At 199 days in the young healthy "pair", the microplacentomes were again smaller in diameter (402+/-16.24 microm) than in the old mare at 179 days and the interhaemal distance had now reduced to 14.28+/-0.42 microm. The vascular density was lower than in the day 179 aged mare and the fetal villi were much longer and thinner. In the single late stage, healthy young mare at 309 days of gestation (term=336 days), the microplacentomes, each of around 2 mm diameter, exhibited maximal length villi. The capillaries were arranged simply, mostly in straight lines along the axis of the villus, and with communications visible at irregular intervals. Simple and slightly more complicated side capillary loops could be seen along the whole length of the villi and at the top of the terminal villi. Most of the capillaries were characterized by zones containing dilated sinusoids, which increased the surface area for materno-fetal exchange. Thus, the morphological development of the microplacentomes on the surface of the horse placenta during gestation was studied, with special reference to the growth and organisation of the fetal and maternal capillary beds within each microplacentome. The study also reinforced previous work showing the disadvantageous influence of age-related endometrial degenerative changes on microplacentome development and on both the extent and intimacy of physical and haematological contact at the fetomaternal interface, and hence upon fetal growth.

Development of the areola in the early placenta of the one-humped camel (Camelus dromedarius): a light, scanning and transmission electron microscopical study.

This study aimed to elucidate development of the areola in the early dromedary placenta in comparison with that of the pig and mare. Placental tissues from 25 pregnant camels were obtained from Cairo abattoir and prepared for light, scanning and transmission electron microscopy by routine methods. Vascular casts were made by injection of 4 : 1 liquid plastic mixture of mercox and methylmethacrylate. Areolar formation was first observed at 4.5 cm curved-crown-rump CVR length, while by 5-9 cm CVR length, the endometrial surface was uneven and studded with numerous uterine gland openings, where corresponding foetal areolae were barely detectable and the foetal areolar cells were of variable appearance and covered with long microvilli. At 10-13 cm CVR length the uterine gland openings developed irregular folds and the maternal areolar cells showed numerous apical blebs. At 14-29 cm CVR length the foetal areolae showed a great increase in height at the expense of their width. At 30-34 cm (CVR) length the maternal areolae appeared discoid and sharply demarcated from the surrounding inter-areolar tissues and the foetal areolae were rounded to irregular in shape with well-developed areolar rims. The vascular casts showed a widely meshed capillary network on the maternal areola, connecting with the pre- and post-capillary vessels, whereas the foetal side showed a relatively dense capillary meshwork. These studies indicate that the areola in the placenta of the one-humped camel is of the regular type like in the pig, and is poorly vascularized.