Ultrastructural studies of the rabbit placenta in the last third of gestation.

Placental attachment and the ultrastructure of the decidua and placental labyrinth have been studied in rabbits during the final third of gestation. The placenta became progressively easier to separate from the uterine wall as gestation proceeded. This ease of separation was associated with degenerative changes in the decidual tissue, but disruption of the placental labyrinth was not observed until the last 24 hr of pregnancy. Two types of decidual cells were observed; smaller uninucleate glycogen-containing cells and larger multinucleate cells with lipid inclusions. The ageing placentae exhibited increasing decidual degeneration associated with deposition of extracellular fibrous materials. Glycogen became less widely distributed over the period of study and changed from the beta- to the alpha-configuration. In contrast to the observed disruption of the decidual tissue, the placental labyrinth maintained its integrity until the final stages of pregnancy. A dramatic increase in subcellular activity was observed in the syncytiotrophoblast after 28 days of gestation.     

Ultrastructural changes in the placenta of the ewe following foetal infusion of cortisol.

The placental changes which followed continuous infusion of cortisol into the sheep foetus in the later stages of gestation were, like the hormonal changes, broadly similar to those of spontaneous parturition. There was, however, a premature separation of foetal and maternal tissues in certain areas of the placental cotyledons, and this separation appeared to protect the foetal epithelium from the degenerative changes which normally take place in the short space of time between the birth of the lamb and the delivery of the foetal membranes. The results suggest that an experimental model in which premature labour is induced by the administration of cortisol to the foetus is probably incomplete, and that additional factors almost certainly contribute to the cascade phenomenon of spontaneous parturition.     

Incidence of retained placenta following induction of parturition with corticoids or prostaglandins

Three trials involving 214 cows were conducted to 1) compare the timing of events during normal parturition with parturition induced with a corticoid or a prostaglandin; 2) determine if synchrony could be improved by injection of steroids either concurrently or after injection of a corticoid or a prostaglandin; 3) determine if the incidence of retained placenta could be reduced; and 4) explore methods of treating retained placenta. The timing of events following induction of parturition was compared with that following a normal parturition in 76 heifers. The time from onset of labor to appearance of the placenta, abdominal press, appearance of feet and expulsion of the fetus did not differ between normal and induced parturition. The time from onset of labor to calf standing was increased from 2.3 +/- 2.0 hours in normal parturition to 5.8 +/- 5.5 hours in cows receiving 10 mg of flumethazone (P<0.05). The interval from onset of labor to calf nursing also tended to be longer (P>0.05<0.01). All control cows expelled fetal membranes by 48 hours after onset of labor, but the proportion expelled by the treatment groups varied from 24 to 76%. None of the treatments used in this study significantly increased placental expulsion over that noted when flumethazone or prostaglandins were used alone. No difference in placental expulsion time was noted in cows douched with nolvasan or injected with 30 cc oxytetracycline. None of the treatments used in the three trials reported in this study improved synchrony of parturition over that noted in the cows receiving only an injection of flumethazone or prostaglandins.     

Macrophage trafficking in the uterus and cervix precedes parturition in the mouse.

Immune activation is implicated in the etiology of preterm labor, but little is known about macrophage number or distribution in the uterus or cervix at term. This study tested the hypothesis that macrophages migrate into the reproductive tract before the onset of parturition. Paraffin-embedded sections from the mid-uterine horn and cervix of C3/HeN mice on Days 15 and 18 of pregnancy, the day of birth (Day 19), and 1 day postpartum were stained with a pan-macrophage marker to analyze cell numbers and distribution. During pregnancy, uterine macrophages were dispersed in endometrium, usually associated with vasculature and subluminal epithelium. In myometrium, macrophages were clustered in stromal connective tissue; near term and postpartum, cells appeared to surround the muscle bundles. Total macrophage numbers were increased on Day 15 relative to those in nonpregnant controls, declined before birth, and increased postpartum. In the cervix, macrophages congregated in subepithelium, often perivascular or near ganglia. Macrophage numbers in the cervix peaked on Day 18, then declined to nonpregnant levels by the day after birth. Thus, macrophage numbers in the uterus were inversely related to those in the cervix. These findings raise the possibility that macrophages and their products may be involved in uterine contractility and cervical remodeling during the processes of parturition.     

Sperm-induced leukocytosis in the equine uterus

The objective of this study was to investigate the inflammatory reaction induced in the equine uterus by insemination with fresh and frozen semen. Eleven groups (6 to 8 mares per group) were studied during 2 breeding seasons. The mares were inseminated using raw semen, frozen semen, extended fresh and frozen semen, concentrated fresh semen, seminal plasma and seminal extenders only. One group was bred naturally. Six hours after insemination, the uteri were flushed with 50 ml of phosphate-buffered saline (PBS). Seventeen out of 104 samples (16%) exhibited slight bacterial growth. Neutrophil concentrations were significantly (P < 0.05) higher in all treated mares than in the controls. Mares infused with PBS, seminal extenders or the supernatant from centrifuged frozen-thawed semen exhibited only a mild neutrophil response. Insemination with frozen semen resulted in higher neutrophil concentrations than insemination with extended fresh semen (means of 59 vs 5 million neutrophils/ml; P < 0.05). Highest neutrophil counts were found after insemination with frozen semen or concentrated fresh semen. Bacterial contamination of uteri was insignificant 6 hours after breeding. Neutrophilia seems to be induced by spermatozoa rather than bacteria. The intensity of the neutrophil reaction seems to depend on concentration and/or volume of inseminate.     

Ultrasonic anatomy and pathology of the equine uterus

The morphological and pathological status of the uterus in mares was evaluated using a linear-array ultrasound scanner, and the ultrasonic properties of the uterus were characterized. The uterus was examined each day in 16 mares, beginning at mid-diestrus. The uterus was recorded as having an ultrasonic morphology characteristic of diestrus (endometrial folds not distinguishable), estrus (prominent endometrial folds) or an intermediate stage (folds only moderately distinguishable). The number of mares with an intermediate or estrous image increased gradually between day -7 (2 14 mares; ovulation = day 0) and days -3 (11 16 ) and -2 (10 16 ) and then declined between days -2 and +1 (0 12 ). In another study, a large nonechogenic area (ejaculate) was visible in the uterine lumen immediately after mating in all of six mares. During the course of pregnancy diagnoses and hand-breeding, several pathological conditions of the uterus were first observed by ultrasound examination and confirmed by digital exploration of the uterus or at slaughter. Cysts contained nonechogenic material (fluid) and were usually compartmentalized. The purulent material associated with pyometria was relatively nonechogenic but contained echogenic spots. Mummified fetuses and remnants of fetal bones showed echogenic properties consistent with high tissue density. The results demonstrated that ultrasound technology provides a noninvasive form of visual access to the uterus to evaluate normal, morphological changes and to detect and study certain pathological processes.     

Ultrastructural and kinetic studies on uteroglobin secretion in the uterus and oviduct of the pseudopregnant rabbit

The intracellular localization of uteroglobin, a progesterone-induced protein, was studied in uterus and oviduct by means of immunoelectron microscopy with the protein A-gold technique. In the uterus, uteroglobin was synthesized in the columnar epithelium of the endometrium where most of the cells were immunoreactive. The protein was localized mainly in small secretory granules which were seen in the process of release into the uterine lumen. The luminal microvilli were also heavily stained. In the oviduct, the secretory cells contained large immunoreactive granules at the apical zone, some of which were observed while discharging into the lumen. Within these secretory granules, uteroglobin accumulated particularly in lens-shaped patches at the periphery of the granules. In vitro kinetic studies on the secretion of newly synthesized uteroglobin indicated that the ability to store uteroglobin is greater in the oviduct than in the uterus; however, the rate of uteroglobin secretion is greater in the uterus than in the oviduct. Thus, there appears to be a good correlation between the microscopic and the functional observations.     

Studies on the equine placenta II. Ultrastructure of the placental barrier.

In early pregnancy the equine placenta consists of a simple apposition of fetal and maternal epithelia, but it becomes more complex with the formation of microcotyledons between 75 and 100 days of gestation. Although the placental barrier maintains an epitheliochorial arrangement throughout the course of pregnancy, a thinning of the maternal epithelium and a progressive indentation of the chorionic epithelium by fetal capillaries shortens the length of the diffusion pathway and reduces the amount of placental tissue between fetal and maternal bloodstreams. These structural modifications may reflect the changing requirements of the fetus for O2 and other metabolites as gestation proceeds. During the first 200 days of pregnancy there is evidence of intense pinocytotic activity by the cells of the trophoblast. From the 100th day of pregnancy there is a pronounced development of smooth endoplasmic reticulum, while rough endoplasmic reticulum and irregular, dense, membrane-bound bodies are a prominent feature of the paranuclear cytoplasm from Day 200. These changes suggest that the cells of the trophoblast become more highly involved in synthetic processes with increasing gestational age.     

Ultrastructural aspects of feeding and secretion-excretion by the equine parasite Strongylus vulgaris.

Light, scanning, and transmission electron microscopy were employed to provide further data on the putative origins of the immunogenic secretory-excretory product (ESP) of Strongylus vulgaris (Looss 1900). The sharply delineated but superficial attachment to the equine caecum by the mouth leaves behind an oval area devoid of epithelial cells. Attachment does not extend deeply enough to reach the muscularis mucosa layer of the equine intestine. The progressive digestion of the ingested plug of tissue (epithelial cells, blood cells and mucous) was visualized. The coelomocytes, floating cells and membranous structures located in the pseudocoelom and intimately associated with the digestive, excretory and reproductive systems, and with the somatic muscles are described. The secretory-excretory system comprises two, ventrally-located, secretory-excretory glands connected to tubular elements. These glands synthesize granules of various sizes and densities that are delineated.     

Acetylesterase isoenzymes in rat uterus and placenta

The occurrence of acetylesterase activity in the uterus and placenta of the rat has been investigated using a general histochemical simultaneous coupling technique after separation on polyacrylamide gradient gels. apart from a complex band associated with serum esterases which was demonstrated in all the tissues studied, several other isoenzyme bands were demonstrable in differing degrees in the yolk sac and the virgin uterus. Two of these bands were evident in metrial gland up to day 16 of pregnancy, and a third became present by day 17. Unlike the other two bands, this new band did not seem to be associated with the large granules of the granulated metrial gland cells. None of these bands were detected in trophoblast. The metrial gland isoenzymes reacted as well at acid pH as at neutral pH. The yolk sac isoenzymes reacted either as well or slightly better at acid pH, and one extra band was demonstrable under acid conditions.     

Progesterone receptors in the human uterus and their possible role in parturition

An overview is given on the role of progesterone in parturition in the human. Progesterone withdrawal is considered to be a major event for the beginning of parturition. However, in the human, no evidence exists in favour of a decline in placental progesterone production prior to labour. Progesterone actions are mediated by two functionally different but structurally highly related intranuclear proteins, progesterone receptor (PR) A and PRB. In the human, functional progesterone withdrawal is thought to play a role. This may be mediated by a change in the expression of the two isoforms of the PR, with an increase in the PRA:PRB ratio, and this is accompanied by an increase in the expression of the estrogen receptor. These mechanisms are considered to be critical for the endocrine control of parturition.     

Studies on the equine placenta. III. Ultrastructure of the uterine glands and the overlying trophoblast

Ultrastructural studies of the uterine glands at intervals during pregnancy in the mare show that secretory activity continues after formation of the placental exchange units. The nature of the glandular secretion appeared initially to be proteinaceous, but cellular debris was also present during the last third of gestation. These secretions were absorbed by the trophoblast overlying the mouths of the glands. The fate secretions and their significance for the fetus and placenta are unknown.     

Cell proliferation patterns during development of the equine placenta

Placentation involves considerable growth and reorganization of both maternal and fetal tissues. In this investigation, immunohistochemical localization of the proliferation marker Ki-67 antigen was used to monitor cell division during placentation in mares. Endometrial biopsies were obtained from eight mares between day 14 and day 26 of pregnancy and from eight anoestrous mares that had been treated with various combinations of progesterone and oestrogen. Samples of endometrium and fetal membranes were obtained from 19 mares carrying normal horse conceptuses between day 30 and day 250 of gestation and from three failing extraspecific donkey-in-horse pregnancies. Proliferation in the superficial strata of the endometrium was increased by day 18 of gestation and this effect could be mimicked by supplementing with oestradiol benzoate during the last 6 days of a prolonged period (18-36 days) of progesterone administration. Fetal chorionic girdle cells were proliferating vigorously at days 30-32 of gestation, but stopped dividing after they invaded the endometrium, while the trophoblast cells of the allantochorion showed an increase in mitotic activity after day 38. The luminal epithelium of the endometrium started to proliferate only after the primary villi of the true epitheliochorial placenta had been formed, and during days 58-70 this effect was seen only in the pregnant horn in which placentation was further advanced. During the second half of gestation, most of the mitotic activity was confined to the periphery of the microcotyledons which were still growing. In the donkey-in-horse pregnancies, proliferation rates of the maternal and fetal epithelial at day 70 of gestation were markedly reduced in areas of heavy endometrial lymphocyte infiltration and poor placentation. These results provide a basis for further studies on factors that influence invasive and non-invasive placentation.