Ultrastructural localization of uteroglobin immunoreactivity in rabbit lung and endometrium,and rat ventral prostate

Summary Recent biochemical studies have demonstrated amino acid sequence homologies between uteroglobin from rabbit endometrium and prostatic binding protein from rat ventral prostate. We have studied the ultrastructural distribution of uteroglobin-immunoreactive material in rabbit lung and endometrium and rat ventral prostate using an uteroglobin antibody raised in guinea pigs. Secretory granules of bronchiolar Clara cells, endometrial non-ciliated cells and rat prostate secretory cells gave a positive immunoreaction when this antibody was used. The results indicate a close relationship of immunoreactive epitopes of proteins present in those secretory cells. The functional properties of these proteins (glycoproteins, steroid binding, androgen-dependent secretion) suggest a close functional relationship, for instance a surface action such as coating, capping, masking or lubrication.Supported by grants Au 48/7-8 and Ki 154/9-3 from the Deutsche Forschungsgemeinschaft     

Fate of hamster oviductin in the oviduct and uterus during early gestation

Oviductins are a family of glycoproteins which are synthesized and secreted by oviductal secretory cells and which, upon their secretion in the lumen of the oviduct, become associated with postovulatory oocytes and developing embryos. Recently, we showed that hamster oviductin is maximally secreted in the oviduct at the time of ovulation and is later associated with a certain population of uterine epithelial cells, where it is subsequently endocytosed and degraded. In light of these results, this study was conducted to follow the fate of hamster oviductin in the oviduct and uterus during early gestation. Using a monoclonal antibody against hamster oviductin, immunofluorescence and immunogold labeling revealed that during early gestation, immunoreactivity to oviductin in the uterus gradually diminished to an almost total disappearance at time of implantation. However, the strong labeling intensity remained unchanged in the oviduct. Biochemical analyses demonstrated that a degradation of oviductin occurs in the uterus, and a loss of immunoreactivity was also observed as gestation progressed, so that by the time of implantation, immunoreactivity to oviductin was barely detectable. The decrease of oviductin along the uterine epithelium at the time of blastocyst attachment and its final disappearance at implantation suggest that this glycoprotein could be a potential modulator of uterine receptivity. Mol. Reprod. Dev. 46:306–317, 1997. © 1997 Wiley-Liss, Inc.     

Intracellular pathway and kinetics of protein secretion in the coagulating gland of the mouse

The coagulating gland of male rodents is part of the prostatic complex. Various mechanisms of secretion have been postulated, in part because organelles commonly involved in the secretory process possess unusual features, such as extreme distension of the rough endoplasmic reticulum. In the present study, the pathway, kinetics, and mode of secretion in the coagulating gland of the mouse were studied by electron microscope autoradiography at intervals between 5 min and 8 h after administration of 3H-threonine. The percentage of grains associated with the rough endoplasmic reticulum was initially high and generally decreased throughout the experiment, while a pronounced rise in the proportion of grains associated with the Golgi apparatus and secretory granules was observed 6 h after injection of precursor. In addition, there was a smaller elevation in the percentage of grains over the Golgi apparatus and secretory granules between 1 and 4 h, and radioactive material first reached the lumen of the gland 4 h after injection of the precursor. Although the general pathway of intracellular transport of secretory protein resembles that in other cells, the results indicate that there are several unusual aspects to the secretory process in the coagulating gland. First, the rate of transport was markedly slower than in most other exocrine gland cells, since the bulk of the labeled protein did not reach the Golgi apparatus and secretory granules until 6 h after administration of precursor. This reflected prolonged retention of secretory products in the endoplasmic reticulum. Second, in addition to the major bolus of labeled material that traversed the cells at about 6 h, a smaller wave of radioactivity appeared to pass through the Golgi apparatus and secretory granules and reach the lumen earlier, within the first few hours after the injection. Finally, the primary mode of secretion in the coagulating gland appears to be merocrine because the secretory granules contained much labeled protein.     

Oviductal morphology in relation to hormonal levels in the snapping turtle, Chelydra serpentina

Microscopic and in situ visual observations were used to relate circulating hormone levels to morphological changes in the oviduct of the snapping turtle Chelydra serpentina throughout the ovarian cycle. Increase in levels of progesterone (P), estradiol (E2) and testosterone (T) levels coincide with an increase in number and growth of endometrial glands, luminal epithelial cells and secretory droplets throughout the oviduct. Testosterone and estradiol levels rose significantly (P < 0.05) after the May-June period and remained high throughout the rest of the summer. Progesterone levels remained stable throughout the summer, with a brief decline in July due to luteolysis. Hormonal values declined significantly (P < 0.001) at the end of the ovarian cycle in the fall. In situ visual observation of fresh oviducts at different stages of gravidity in recently ovulated turtles revealed that proteinaceous like components from the endometrial glands were released into the lumen to form fibers. The morphological features of the oviduct remained active throughout the summer months even though the snapping turtle is a monoclutch species which deposits all the eggs in late-May to mid-June. The high steroid levels correlate with and may be responsible for the secretory activity present throughout the summer and their decline correlates with change to low secretory activity in the fall. Calcium deposition accompanied by morphological changes in luminal cells are suggestive of secretory activity. In the egg-bearing turtles, uterine Ca2+ concentrations measured by flame atomic absorption spectrophotometry revealed significantly higher Ca2+ concentrations (P < 0.001) in eggs with soft shell than eggs without shell. There was a significant increase in calcium granules and proteinaceous fibers in luminal surface of the uterus during the period of eggshelling. This supports the fact that in the snapping turtle like in other reptiles, eggshelling process occurs in the uterus.     

Light- and electron-microscopic radioautographic study of glycoprotein secretion in the granular duct of the submandibular gland of the male mouse

Summary L-³H-fucose was injected intravenously into adult male mice, after which, at different time intervals, the submandibular glands were removed and processed for light-and electron-microscopic radioautography. This radio active hexose was taken up by newly synthesized glycoproteins in the cells lining the granular ducts which were maximally labeled at 4 h after injection. Between 4 and 72 h the amount of labeled glycoproteins decreased moderately indicating that these macromolecules undergo a slow renewal. The main subcellular site of incorporation of 3 H-fucose into glycoproteins was the Golgi apparatus. From this organelle labeled glycoproteins were transferred to small secretory granules (diameter up to 1.0 m) located not only near the Golgi region but also throughout the apical cytoplasm. At 1 h after injection the concentration of label reached a maximum in the small secretory granules and labeling of medium (diameter between 1.1 and 2.0 m) and large (diameter over 2.0 m) granules was very low. At this postinjection interval the secretion product inside the lumen of the duct was already labeled. Between 1 and 72 h after injection the concentration of radioactivity in the small secretory granules decreased intensely while increasing in the medium and in the large ones. The concentration of fucose label reached a maximum in the medium secretory granules at 24 h and in the large ones at 72 h after injection. Additional experiments using mice previously injected with 4 intraperitoneal doses of ³H-fucose given 3 h apart demonstrated that the large granules undergo a very slow renewal. Some were found to be labeled as long as 28 days after administration of ³H-fucose. Recorded in this latter series of experiments was the labeling pattern of dense bodies that were regularly visualized in the cells lining the granular ducts. Their significance in the secretory process is discussed. In conclusion, newly synthesized glycoproteins are transferred from the Golgi apparatus to small secretory granules which carry a readily releasible pool of these macromolecules to the lumen of the duct. The small secretory granules also transfer newly synthesized glycoproteins to medium and large secretion granules which store a pool that is released very slowly. This characterizes the large secretory granules as the intracellular sites of storage of secretion products. The results of this investigation were correlated with the knowledge about the chemical composition of the different macromolecules that are known to be synthesized by the secretory cells of the granular ducts of the submandibular gland of the mouse.     

Maturation of secretory granules in the endosalpinx one to four days post coitum in sheep

Summary The ultrastructure of granules in the secretory cells of the endosalpinx of 20 Merino ewes was examined on days 1, 2, 3, and 4 post coitum. Based on the different frequency of granules of different size and structure on days one to four post coitum, one can assume that the ovoid, membrane bounded secretory granules mature in five successive stages. In stage I small, electron-lucent vesicles with a finely granulated and filamentous content become apparent, initially in the neighbourhood of the Golgi complex. In stage II the granules become larger and progressively more eletron-dense by an increase of the granulated material. In stage III, the primarily granulated content forms membranes, that lie in characteristic stacks at different angles to one another, separated by electron-dense areas. This structure fragments when the granule comes to lie beneath the surface of the cell (stage IV) and opens into the lumen of the oviduct, where its content is discharged in membrane fragments or vesicles (stage V). This discharge is mainly observed shortly before the egg is transported into the uterus.     

Fine structural observations on magnum mucosa in quail and hen oviducts

Summary Previous investigators have reported that albuminous material in the albumin-secreting (tubular gland) cells of the magnum of hen oviduct accumulates in the ergastoplasmic cisternae and is released directly into the glandular lumen without being first concentrated into secretory granules in the Golgi region (Zeigel and Dalton, 1962). Present fine structural studies on the tubular gland cells in oviducts from actively laying wild-type Japanese quail and in an oviduct from an actively laying hen indicate that the Golgi apparatus is directly involved in the formation of secretory granules. At least three types of granules can be observed in the tubular gland cells at various times, and all types seem to be associated initially with the Golgi apparatus.In actively laying quail, the distribution of electron opaque, intermediate, and light granules within the superficial and deep regions of the glandular epithelium varies, depending on the presence of an egg in a particular region of the oviduct. Secretion of the product is merocrine, involving fusion of granule membranes with the plasmalemma of the cell surface.Granules first appear in the tubular gland cells of quail oviducts at about 4 1/2 weeks of age. The granules are of the electron opaque type and probably represent secretion in concentrated storage form. At this age, a few of the tubular gland cells exhibit distended ergastoplasmic cisternae containing material of low electron density. The appearance of these light cells, which occur with greater frequency in oviducts from older quail, probably reflects an increased level of secretory activity initiated by changes in hormonal levels. From 5 weeks of age on, intermediate and light (less concentrated) granules, as well as dark granules, are present.Supported by the National and Medical Research Councils of Canada.     

Development of female accessory glands of Chrysomya putoria (Wiedemann) (Diptera: Calliphoridae) during oogenesis

Females of Chrysomya putoria (Diptera: Calliphoridae) have two sexual accessory glands, which are tubular and more dilated at the distal extremity. The glands open independently into the common oviduct. Two morpho-physiological regions were distinguished in the longitudinal semi-thin sections of the glands. The secretory region is constituted by three layers: a cuticular intima, lining the lumen, followed by a layer of small cells, and then a layer of very large secretory cells. The ductal region of the gland presents only two layers: the cuticular intima and a cellular layer. In both regions a basement membrane is present. Each secretory cell has in its apical region a reservoir, which enlarges throughout oogenesis; in its basal region there is a large nucleus. The ductal cells are cylindrical and smaller than the secretory cells. The glandular secretion is synthesized in the cytoplasm of the secretory cells, stored and/or modified in the reservoir, then drained to the lumen through an end apparatus seen in the apical region of the secretory cell. Histochemical tests indicate that this secretion is a glycoprotein. Measurements of the glands from females at different physiological conditions and fed on different diets correlate with the results obtained for changes in the ovary during oogenesis. Cell number averaged 561.2 ± 77.54 per gland. There was no increase in cell number during oogenesis.     

Morphometric and ultrastructural features of the mare oviduct epithelium during oestrus

Morphometric, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations have displayed regional differences in the mare oviductal epithelium. The entire mucosa of the oviduct was lined with a pseudostratified epithelium, which consisted of two distinct cell types, ciliated and non-ciliated. Ciliated cells were predominant in the three different segments of the oviduct and their percentage increased from fimbriae to ampulla and significantly decreased in the isthmus. SEM revealed in the infundibulum finger-like mucosal folds, some of them interconnected, in the ampulla numerous and elaborated branched folds of the mucosa, whereas the isthmus displayed a narrow lumen, short and non-branched mucosal folds. In the ampulla and isthmus the majority of non-ciliated cells showed apical blebs provided or not of short microvilli. TEM displayed different ultrastructural features of ciliated and non-ciliated cells along the oviduct. Isthmus ciliated cells presented a more electron-dense cytoplasm than in infundibulum and ampulla cells and its cilia were enclosed in an amorphous matrix. The non-ciliated cells of infundibulum did not contain secretory granules but some apical endocytic vesicles and microvilli coated by a well developed glycocalyx. Non-ciliated cells of ampulla and isthmus contained secretory granules. Apical protrusions of ampulla displayed two types of secretory granules as well as occasional electron-lucent vesicles. Isthmus non-ciliated cells showed either electron-lucent or electron-dense cytoplasm and not all contained apical protrusions. The electron-dense non-ciliated cells displayed microvilli coated with a well developed glycocalyx. Three types of granules were observed in the isthmus non-ciliated cells. The regional differences observed along the epithelium lining the mare oviduct suggest that the epithelium of the each segment is involved in the production of a distinctive microenvironment with a unique biochemical milieu related to its functional role.     

Ultrastructural immunocytochemistry and lectin histochemistry of the subcommissural organ in the snake Natrix maura with particular emphasis on its vascular and leptomeningeal projections

The ependymal cells of the subcommissural organ (SCO) of the snake Natrix maura display long basal processes which terminate either on blood vessels or on the leptomeninges. The cell body and the basal processes contain a secretory material detectable immunocytochemically at the light-microscopic level using an antibody raised against bovine Reissner's fiber. The present investigation deals with the ultrastructural location in these cells of the (i) immunoreactive material; (ii) concanavalin A (Con A)- and wheat-germ agglutinin (WGA)-binding sites. In the subnuclear region the immunoreactive material was located within dilated cisternae of the rough endoplasmic reticulum and had affinity for Con A but not for WGA. In the supranuclear region the secretory material was exclusively located within numerous granules. Since all these granules showed affinity for WGA, they can be regarded as "post-Golgi" elements. Thus, at variance with the situation in the mammalian SCO, in the ophidian SCO most of the secretion is stored in secretory granules rather than in dilated cisternae of the rough endoplasmic reticulum. In the perivascular and leptomeningeal endings the immunoreactive material was located within granules which, because of their affinity for WGA, should also be regarded as true secretory granules derived from the Golgi apparatus. It is concluded that these granules are transported along the basal processes and accumulated in the perivascular and leptomeningeal endfeet. This observation favours the view of a local release of the content of these granules, since there is no evidence for a reverse transport of these granules all the way back from the distal termination to the apical pole, to be finally released into the ventricle.     

Secretion of proteins by cultured bovine oviducts collected from estrus through early diestrus

To characterize in vitro protein secretion by the oviduct throughout early stages of the estrous cycle, 16 cows received a luteolytic dose of PGF2 alpha and were randomly assigned to be killed on day (D) 0, 2, 5, or 8 after subsequent estrus. Explant cultures of oviducts (ampulla and isthmus) were incubated for 24 h at 39 degrees C in a modified Eagle's minimal essential medium supplemented with 50 microCi L-[4,5-3H]leucine. Oviductal secretion of de novo synthesized protein measured by incorporation of [3H]leucine into nondialyzable radioactivity in culture supernatants was greatest at D 0 and declined thereafter. Incorporation of [3H]leucine into TCA-precipitable macromolecules in tissue homogenates was also greatest at D 0. Analysis of culture supernatants by one-dimensional polyacrylamide gel electrophoresis revealed four major bands of radiolabeled proteins at greater than 97 kDa, 85-97 kDa, 55 kDa, and 30 kDa. Analysis of individual polypeptides resolved by two-dimensional polyacrylamide gel electrophoresis indicated that five of 32 individual polypeptides examined were secreted at significantly greater rates at estrus than at other times examined. One of these five polypeptides, a 97-kDa peptide with an apparent pI of 5.0, was the major secretory product at estrus and accounted for 18% of total radioactivity recovered from two-dimensional gels. Two of 32 polypeptides examined were secreted at significantly greater rates by explants of the oviduct contralateral to the side of ovulation. In summary, estrus is associated with an elevation in total protein secretion by the bovine oviduct. This increase is due to selective amplification of secretion of several but not all secretory proteins.     

Secretion of old versus new exportable protein in rat parotid slics. Control by neurotransmitters

The possibility that old and new secretory granules do not mix and that older exportable protein can be secreted preferentially was tested on parotid gland in vitro. Slices from fasted animals were pulse labeled for 3 min with L-[3H]leucine. Subcellular fractionstion showed that after 1 90-min chase period, the formation of new labeled secretory granules was mostly completed. The ratio of label in secretory granules to label in microsomes increased 250-fold during the period 5--90 min postpulse. After the 90-min chase, a submaximal rate of secretion was initiated by adding a low concentration of isoproterenol to the slices. Preferential secretion of old unlabeled exportable protein was evident from the finding that the percent of total amylase secreted was 3.5-fold greater than the percent of labeled protein secreted. Preferential secretion of old unlabeled exportable amylase was undiminished even when the chase period before addition of isoproterenol was extended to 240 min. Such long chase incubations were still meaningful due to the fact that the spontaneous rat of amylase release and radioactive protein release from the slices was negligibly low. A high isoproterenol concentration added to the slices after a 90-min chase produced the following results. An initial phase of preferential secretion of old unlabeled protein was soon replaced by secretion of a random mixture of new and old exportable protein. Electron micrographs indicated that high rates of secretion involved sequential fusion of secretory granules so that the lumen extended deep into the cell where the new labeled granules were presumably located. At low rates of secretion, the lumen showed no such deep extensions. Experiments were also conducted on slices from glands which had been largely depleted of old granules by prior injection of isoproterenol into the animals. Secretion of labeled protein from such slices stopped with the export of 80% of the labeled protein. This finding indicates that about 20% of the radioactive protein is cellular nonexportable protein and that the slices are capable of exporting the entire amount of secretory protein which was symthesized in vitrol. In addition to the beta-adrenergic receptor which mediates protein secretion, the parotid acinar cell also possesses an alpha-adrenergic and a cholinergic receptor both of which cause K+ release, vacuole formation, and water secretion. Activation of either of the latter two receptors in conjunction with the beta-adrenergic receptor increased randomization of the protein secreted. It is concluded that in the rat parotid acinar cell there is little spontaneous mixing between old granules near the luminal cell membrane and new granules coming up behind from the Golgi complex. The neurotransmitters which induce secretion produce the observed randomization.     

Calnuc,an EF-hand Ca(2+)-binding protein,is stored and processed in the Golgi and secreted by the constitutive-like pathway in AtT20 cells

Calnuc is an ubiquitous, EF-hand Ca(2+) binding protein found in the cytoplasm where it binds to Galphai3, in the Golgi lumen where it constitutes a Ca(2+) storage pool, and secreted outside the cell. Here we investigated the pathway of secretion of calnuc in AtT20 cells. We found by pulse-chase experiments that calnuc is synthesized in the endoplasmic reticulum, transported to the Golgi where it remains greater than 12 h and undergoes posttranslational modification (O-glycosylation and sulfation) followed by secretion into the culture medium. We examined if calnuc is secreted by the constitutive or regulated secretory pathway in AtT20 cells. By immunofluorescence and immunogold labeling, endogenous calnuc is found in immature secretion granules (ISG) but not mature regulated secretory granules (RSG), whereas overexpressed calnuc-green fluorescent protein (GFP) is found in both ISG and RSG, where it colocalizes with ACTH. Neither calnuc nor calnuc-GFP are released by the regulated secretory pathway, suggesting that endogenous calnuc and calnuc-GFP are progressively removed from ISG and RSG during granule maturation. We conclude that calnuc is secreted via the constitutive-like pathway and represents a useful endogenous marker for this pathway in AtT20 cells. Together, these observations indicate that calnuc has a unique itinerary as it is retained in the Golgi and is then constitutively secreted extracellularly where it may influence cell behavior via its Ca(2+)-binding properties.     

Cytochemical and ultrastructural characteristics of the lining epithelium of the distal part of the epididymis in hamsters (Mesocricetus auratus)

In the terminal segment of the hamster epididymidis there was some evidence of micro-merocrine protein secretion a the level of the principal cells and clear evidence of granular secretion in the light cells, presumable of glycoproteins. The PAS and protein cytochemistry reactivities observed in both these cells, of the ductus epithelial lining, but especially in the light cells, are suggestive of mucopolysaccharides and protein complexes synthesis and secretion. This secretion is carried out to the epididymal epithelium from the lumen and luminal content. A complex of small vacuoles and vesicles appeared to form from the Golgi complex is showed in the principal cells. It was suggested that this complex may represented merocrine secretory vacuoles and vesicles in these cells. Dense granules, at the TEM level, are observed in all the cytoplasm of the light cells, with correspondence to similar PAS-positive granules observed in these cells, at the light microscope level. These granules, at the TEM level, are actually secreted to the epididymal duct lumen, by the apical cytoplasms of the light cells. Signs of absorption were suggested to the principal and light columnar cells through the ultrastructural observations of micropinocytosis, apical multivesicular bodies or great membrane-bounded vacuoles in the adluminal cytoplasms.     

Reduction of the disulfide bond of chromogranin B (secretogranin I) in the trans-Golgi network causes its missorting to the constitutive secretory pathways.

The role of the single, highly conserved disulfide bond in chromogranin B (secretogranin I) on the sorting of this regulated secretory protein to secretory granules was investigated in the neuroendocrine cell line PC12. Treatment of PC12 cells with dithiothreitol (DTT), a membrane permeable thiol reducing agent known to prevent disulfide bond formation in intact cells, resulted in the secretion of newly synthesized chromogranin B, but only slightly decreased the intracellular storage of newly synthesized secretogranin II, a regulated secretory protein devoid of cysteines. The secretion of newly synthesized chromogranin B in the presence of DTT occurred with similar kinetics to those of a heparan sulfate proteoglycan, a known marker of the constitutive secretory pathway in PC12 cells. Analysis of the various secretory vesicles derived from the trans-Golgi network (TGN) indicated that DTT treatment diverted newly synthesized chromogranin B to constitutive secretory vesicles, whereas the packaging of secretogranin II into immature secretory granules was unaffected by the reducing agent. The chromogranin B molecules diverted to constitutive secretory vesicles, in contrast to those stored in secretory granules, were found to contain free sulfhydryl residues. The effect of DTT on chromogranin B occurred in the TGN rather than in the endoplasmic reticulum. We conclude that the sorting of CgB in the TGN to secretory granules is dependent upon the integrity of its single disulfide bond.     

Three-dimensional imaging of the mucus secretory process in the cryofixed frog respiratory epithelium.

Using the frog palate as a representative model of human mucociliary epithelium, we analyzed, after quick freezing fixation, the three-dimensional (3-D) respiratory mucus secretory release with high voltage (200-300 kV) transmission electron microscopy (TEM). The 3-D vision of the mucus release from the secretory cells was obtained as stereo-pairs and "bas-relief" images after analysis of stereo-pairs using an image analyzer. After standard glutaraldehyde fixation, the secretory cells showed a typical goblet shape with secretory granules heterogeneous in size and electron-density which often fuse together. On the other hand, quick-frozen secretory cells exhibited a columnar shape and their membrane-bound secretory granules contained a homogeneously dark matrix. The expanded gel mucus layer was preserved and its depth never exceeded 2 microns. When the epithelium was immersed in culture medium in presence of cholinergic agonist, a marked discharge of mucus was observed and the granules swelled at the apex of the secretory cell before being discharged in the lumen. In native cryofixed epithelium, the secretory granules exhibited a marked deformability during the process of their extrusion from the secretory cell. Clusters of secretory granules surrounded by cytoplasmic material were observed in the extracellular lumen, suggesting an apocrine-type secretion. These observations indicate that rapid cryofixation and 3-D stereoscopic imaging enable a unique opportunity to analyze, without artifact, the mucous secretory process. We speculate that, apart from the classical merocrine-type secretion mechanism, the respiratory mucus may be released, at least partly by an apocrine-type secretion.     

Ultrastructural changes in the oviductal mucosa throughout the sexual cycle in Bufo arenarum

In Bufo arenarum the oviduct exhibits conspicuous changes throughout the sexual cycle. In the present study, we analyzed the optical and ultrastructural characteristics of the oviductal pars convoluta mucosa, the portion responsible for jelly secretion, during both the preovulatory and postovulatory periods. Secretory epithelial cells, ciliated cells, basal cells, and glandular cells are described. Secretory epithelial cells are characterized by the presence of secretory granules, the size, shape and electron density of which vary markedly. Their contents are mainly released by exocytosis into the oviductal lumen. Moreover, in the preovulatory period, apocrine, and holocrine secretion processes frequently occur. During the postovulatory period, these cells exhibit a marked diminution of secretory granules. Ciliated cells show a typical ultrastructural organization. Basal cells are distinguished in the lower part of the epithelium by their heterochromatic nuclei and electron‐lucent cytoplasm. These cells, to the best of our knowledge, are reported for the first time in Amphibia. Glandular cells exhibit oval, round, or polyhedric granules, most of them with one or more cores. Our results indicate that the contents of epithelial and glandular secretory cells are partially secreted during the preovulatory period. Additional secretion occurs during the transit of the oocytes. J. Morphol. 239:61–73, 1999. © 1999 Wiley‐Liss, Inc.     

Immunolocalisation of the uterine secretory proteins uterocalin, uteroferrin and uteroglobin in the mare's uterus and placenta throughout pregnancy

Previous studies have shown that the equine uterus produces many progesterone-dependent proteins throughout gestation. In particular, uterocalin and uteroferrin are detectable using electrophoresis or blot analyses but information regarding the immunohistochemical placental distribution of these two proteins is rare and information regarding uteroglobin is still lacking. The aim of the present study was to co-immunolocalise these three secretory proteins in the mare's uterus throughout gestation in an effort to understand their functional role in the maintenance of pregnancy. Therefore, endometrial biopsy samples were obtained from 20 pregnant mares between 16 and 309 days of gestation and labelled immunohistochemically for uteroglobin, uteroferrin and uterocalin. Uteroferrin remained detectable in almost every endometrial gland at all stages but with an increase in staining intensity as gestation advanced. The most progesterone-dependent protein, uterocalin, showed variable staining throughout gestation with the most intense labelling in early pregnancy and during the period of endometrial cup reaction. Uteroglobin secretion was only detectable in traces and only in individual glands throughout gestation. The results indicate that uterocalin and uteroferrin, but not uteroglobin, may play important roles in supplying nutrients for the conceptus, thereby contributing to the maintenance of pregnancy. However, further investigations are necessary to understand the role of uteroglobin during gestation.