Immunocytochemical localization of oviduct-specific glycoproteins in the oviductal epithelium from cows at follicular and luteal phases

A Comparative View on the Oviductal Environment during the Periconception Period

The oviduct plays important roles in reproductive events: sperm reservoir formation, final gamete maturation, fertilization and early embryo development. It is well known that the oviductal environment affects gametes and embryos and, ultimately, the health of offspring, so that in vivo embryos are better in terms of morphology, cryotolerance, pregnancy rates or epigenetic profile than those obtained in vitro. The deciphering of embryo-maternal interaction in the oviduct may provide a better understanding of the embryo needs during the periconception period to improve reproductive efficiency. Here, we perform a comparative analysis among species of oviductal gene expression related to embryonic development during its journey through the oviduct, as described to date. Cross-talk communication between the oviduct environment and embryo will be studied by analyses of the secreted or exosomal proteins of the oviduct and the presence of receptors in the membrane of the embryo blastomeres. Finally, we review the data that are available to date on the expression and characterization of the most abundant protein in the oviduct, oviductin (OVGP1), highlighting its fundamental role in fertilization and embryonic development.

Extra-oviductal expression of oviductal glycoprotein 1 in mouse: Detection in testis, epididymis and ovary

Oviductal glycoprotein 1 (OVGP1), also called oviductin, is an oviduct-specific protein and is suggested to play a role in fertilization. Traditionally, Ovgp1 has been shown to be exclusively expressed by the oviduct; however, recent studies have demonstrated its expression in some cancers. This observation led us to hypothesize that Ovgp1 might have some extra-oviductal expression. In the current study, we evaluated the mRNA and protein expression of Ovgp1 in normal reproductive tissues of male and female mice. For the first time, we demonstrate that beyond the oviduct, Ovgp1 mRNA is expressed in the testis, epididymis and ovary, but not in the uterus, cervix, vagina, breast, seminal vesicles and prostate gland. In the testis, Ovgp1 mRNA was localized in the cells at the base of seminiferous tubules (most likely, Sertoli cells), while the protein was detected in the round and elongating spermatids. In the epididymis, Ovgp1 transcripts were localized in epididymal epithelium of the caput but not the corpus and cauda; OVGP1 protein was, however, not detected in any of the segments but was present in the epididymal sperm. In the ovary, Ovgp1 transcripts and protein were detected in the surface epithelium, granulosa cells of the preantral and the antral follicles and corpus luteum. In both, the ovary and oviduct, the expression of Ovgp1 was found to be higher at estrus stage than at diestrus stage. To the best of our knowledge, this is the first study demonstrating the extra-oviductal expression of Ovgp1. Our data suggests that, beyond fertilization, Ovgp1 might have specific roles in gonadal physiology. [Laheri S, Modi D and Bhatt P 2017 Extra-oviductal expression of oviductal.

Bovine oviductal epithelial cells: their cell culture and applications in studies for reproductive biology

Epithelial cells of the mammalian oviduct play an important role in reproductive and developmental events that occur there. Oviductal epithelial cells from several mammalian species can be isolated and cultured in serum or serum-free medium in vitro and cell culture of bovine oviductal epithelial cells (BOEC) has been described by many investigators. Cultured BOEC show a wide variety of secretory activities and these secretory factors may influence early embryonic development or sperm function. Monolayer cultures of BOEC have been widely used for in vitro co-culture of bovine preimplantation embryos. The use of BOEC co-culture systems has improved embryonic development in nearly all the studies conducted. In addition, interaction of bovine spermatozoa with BOEC, in a similar manner to that observed for spermatozoa in vivo, induced specific changes in sperm capacitation and consequently improved the fertilizing capacity of bovine spermatozoa in vitro. Thus co-culture systems with BOEC may not only offer an excellent model for studying the mechanisms of capacitation and acrosome reaction of bovine spermatozoa but also provide a useful tool for the improvement of embryo development in vitro.

Sperm binding properties and secretory activity of the bovine oviduct immediately before and after ovulation

The possibility that differences in hormonal regimes between the two oviducts in the cow around ovulation affects secretory activity of the oviduct epithelial cells and/or sperm-oviduct binding was studied. Oviducts were collected immediately after slaughter at 6 hr before to 5 hr after timed ovulation of 14 normally cyclic cows that had been inseminated (n = 6) or not (n = 8) and material obtained from the same cows was processed in three ways. First, in vivo, after artificial insemination of the cows, low numbers of sperm cells (approx. 15 per oviduct) were found within the entire oviducts as observed by scanning electron microscopy (SEM). Almost all sperm were located in the isthmus and then only on ciliated cells and showed without exception fully matured, intact morphology. Secretory activity of noninseminated oviduct epithelia was induced after ovulation which was most predominant in the pockets of the ipsi-lateral ampulla compared to the contra-lateral ampulla (P < 0.01). Second, ex vivo, explants dissected from oviducts of the noniseminated cows were incubated with sperm. In all cases, the sperm bound to the explants in a similar pattern as observed in vivo and this binding was strictly fucose-dependent. The main difference with in vivo experiments was the high numbers of sperm bound at any site of the oviduct ( approximately 3,000 cells per mm(2)) indicating the high sperm binding capacity of the oviduct epithelia. Ovulation induced a striking drop in sperm binding capacity in the oviducts and was most pronounced in the isthmus ( approximately 1,300 cells per mm(2); P < 0.001) and to a lesser extent in the ampulla ( approximately 2,000 cells per mm(2), P < 0.01). Third, in vitro, pieces of tissue dissected from oviducts of the noninseminated cows were cultured to mono-layers. Culturing epithelial cells resulted in loss of their normal morphological appearance. In all cases, the sperm binding capacity in monolayers was very low (<50 cells per mm(2)) when compared to corresponding explants (P < 0.0001). Sperm binding to monolayers originating from the isthmus (<25 cells per mm(2)) was lower than in those from the ampulla (40-50 cells per mm(2); P < 0.01) and remained similar after ovulation. In all three approaches, no significant differences were found in sperm-oviduct binding characteristics and sperm-distribution in the ipsi- versus contra-lateral oviducts. This indicates, that systemic endocrine changes around ovulation rather than specific oviduct changes at the ipsi-lateral oviduct induce secretion in oviduct epithelial cells, and thus induce sperm release.

Cyclic Related and Pathological Changes in the Lectin-binding Sites on the Swine Oviduct

This study was carried out to compare the lectin-binding pattern in the normal and pathological oviduct of sows during the ovarian cycle. Lectin-binding patterns showed differences between segments, phases of ovarian cycle and presence of morphologic lesions. In the infundibulum, it was observed that the cysts, in the follicular phase, reduced Ricinus communis-I (RCA-I) and Ulex europaeus-I (UEA-I) binding. Furthermore, in the pathological oviducts of the luteal-phase group, there is a reduction of Concanavalia ensiformis (Con-A) reactivity in this segment of the tube having wall cysts, adenomyosis and diverticulus. The Arachis hypogaea (PNA) binding in the infundibulum, during the luteal phase, decreased in the tube having adenomyosis. In animals with wall cysts, the Con-A, Triticum vulgaris (WGA) and RCA-I reactivity was minor in the glycocalyx of the isthmus epithelium during follicular phase. Con-A and Dolichos biflorus (DBA) binding pattern was minor in the luteal-phase isthmus of the tube having wall cysts, adenomyosis and diverticulus. In the ampulla, the wall cysts impaired the Con-A reaction only in the basal region of the epithelium, in the follicular phase. Binding with Con-A was decreased in the ampulla of animals in the luteal phase in the tube lesions with cysts and diverticulus. In addition, the diverticulus observed in the ampulla, during the luteal phase, reduced the PNA tubaric binding. The results of this study showed that the morphologic alterations modify the sugar pattern in the oviduct of sows. These modifications in glycoconjugates may be one of the reasons for the failure of fertility in sows.

Ultrastructural features of goat oviductal secretory cells at follicular and luteal phases of the oestrous cycle

The aim of the present study was to investigate the ultrastructure of secretory cells in the various regions of the goat oviduct during the follicular and luteal phases of the oestrous cycle. During the follicular phase in the fimbriae, the secretory cells contained small secretory granules with electron-dense matrices. In the luteal phase, the secretory granules disappeared and cytoplasmic protrusions, extending beyond the luminal border of the ciliated cells and often containing the nucleus, were predominant. During the follicular phase in ampullary secretory cells, numerous secretory granules with moderately electron-dense matrices were present in the supranuclear cytoplasm and exocytosis of secretory granules was observed. The number of secretory granules was dramatically reduced in the ampullary secretory cells at the luteal phase. Conspicuous cytoplasmic protrusions of secretory cells were observed similar to those of the fimbrial epithelium. Isthmic cells were almost free of secretory granules and lysosome-like bodies were found both at the follicular and luteal phases. In conclusion, our ultrastructural observations of goat oviduct revealed marked cyclic changes in the ultrastructural features of secretory cells and the ultrastructural features and the numbers of secretory granules were distinctive for each particular segment.

Ultrastructural and ultracytochemical features of secretory granules in the ampullary epithelium of the hamster oviduct

The epithelium of mammalian oviducts consists mainly of ciliated and non-ciliated secretory cells. In some mammals, secretory products originating from oviductal secretory cells have been shown to bind to the surface of, or accumulate within, ovulated eggs and/or developing embryos. These findings suggest that the secretions of the oviductal epithelial cells may play an important role in reproductive and developmental events that occur in the oviduct. In the present study, ultrastructural and cytochemical features of secretory cells in the hamster ampullary epithelium were shown by routine electron microscopy, lectin-gold cytochemistry and both conventional freeze-fracture and rapid-freezing techniques with special reference to the organizational aspects of their secretory granules. The use of ferrocyanide-reduced osmium tetroxide as a post-fixative in the Epon embedment of ampullary tissue samples also proved to be advantageous especially in revealing the carbohydrate contents of certain cellular compartments. The most conspicuous characteristic of the secretory cells, based on their staining property, was the presence of two types of secretory granules: those with a homogeneous electron-dense matrix and those with an electron-lucent matrix. Under favorable conditions, distinct features of the organizational arrangement of a crystalline lattice inside the secretory granules were also revealed. This well organized crystalline lattice shown in sections of Epon-embedded oviductal tissue was confirmed by examination of replicas of freeze-fractured oviducts prepared by the rapid-freezing technique. We also demonstrated with high resolution lectin-gold cytochemistry the intracellular distribution of lectin-binding glycoconjugates in the secretory cells of the hamster oviductal ampulla often in a linear array following the crystalline lattice. The results obtained in this study, taken together, provide insight into a possible link of the internal topographical features of oviductal secretory granules along with the cytochemical properties of their contents to the anticipated regulatory mechanism underlying their process of secretions.

Morphological features of epithelial cells in the sheep isthmus oviduct during early pregnancy

BACKGROUND

The objective of the present study was to define the morphological changes that occur in the epithelium of the isthmus oviduct of the sheep during the first few weeks of pregnancy.

MATERIALS

Isthmus oviducts were obtained from ovariectomized, estrous (day O) and pregnant (day 2, 3, 4, 6, and 16) ewes and analyzed using light and electron microscopy.

RESULTS

The epithelium was low cuboidal in the isthmus from ovariectomized sheep, significantly increased in height at estrus, underwent an additional increase at day 3, and was significantly reduced by day 4 of pregnancy. Ciliated and nonciliated epithelial cells were present at all reproductive stages. Ciliated cells were always the predominant cell type. The percentage of ciliated and nonciliated cells did not significantly change at any stage examined. In addition, a third cell type, located adjacent to the basement membrane, was present. These "basal" cells were rounded in appearance and more frequently observed in the epithelial lining of ovariectomized ewes and after day 3 of pregnancy. The secretory organelles of nonciliated epithelial cells obtained from ovariectomized ewes were poorly developed. In estrous ewes, the Golgi apparatus in nonciliated cells consisted of stacked cisternae that atrophied later in pregnancy. The most striking alterations in the secretory apparatus occurred in ciliated cells. Two populations of ciliated cells were observed at estrus-one with abundant, membrane bound supranuclear granules and one without granules. The granules in ciliated cells were rare after day 3 of pregnancy and no evidence of secretion was ever observed. Large lipid droplets were present in the cytoplasm of ciliated cells at estrus. Lysosomes were abundant in nonciliated cells by day 16 of pregnancy. Regularly arranged microvilli were present in nonciliated cells obtained from ovariectomized, estrous, and pregnant ewes. No appreciable change in nuclear shape or chromatin content was observed at any reproductive stage examined. The ultrastructural characteristics and relative abundance of other cytoplasmic organelles such as the RER, SER, mitochondria, and glycogen varied slightly during pregnancy in ciliated and nonciliated cells.

CONCLUSIONS

These data show that the epithelial lining of the isthmus oviduct in the sheep undergoes subtle, yet distinctive, structural changes during the first few weeks of pregnancy.

S-100 protein subunits in bovine oviduct epithelium: in situ distribution and changes during primary cell culture

Cultures of bovine oviduct epithelial cells are widely used in co-culture systems to improve the results of in vitro fertilization. The aim of the present study was to evaluate the suitability of S-100 protein as a differentiation marker for bovine oviduct epithelial cells in vitro. The distribution of S-100 alpha and S-100 beta was examined immunohistochemically in bovine oviduct epithelium in situ and in primary cell cultures derived from it. Three segments of the Fallopian tube (isthmus, ampulla and fimbriae) were compared and analysed during different stages of the oestrus cycle (luteal phase and follicular phase). Ciliated and non-ciliated cells of the epithelium reacted with anti-S-100 alpha, S-100a (alpha beta) and S-100 beta antibodies, except for isthmic non-ciliated cells, which did not bind anti-S-100 beta or anti-S-100a (alpha beta). In addition, basal cells never showed immunoreactivity for S-100. In confluent monolayers of cultured oviduct epithelial cells, disappearance of reactivity for S-100 paralleled morphological signs of dedifferentiation (loss of cilia, cytoplasmic vacuolization). Free-floating oviduct epithelial cells, in contrast, retained morphological differentiation and still expressed S-100 antigen even after seven days in vitro. The immunohistochemical findings were confirmed by polyacrylamide gel electrophoresis and Western blotting. The results indicate that the presence of S-100 is closely connected to morphological differentiation and to the specific functional condition of bovine oviduct epithelial cells.

Effect of steroids and oviductal cells, from the different parts of the oviduct, on the incidence of monospermy in porcine in vitro fertilization

A high incidence of polyspermy occurs in porcine in vitro fertilization. It is also known that in vivo, the oviductal cells and their secretions play an important role in fertilization and early development. Vesicles from oviductal cells from different parts of the oviduct (isthmus or ampulla) pretreated with estradiol or progesterone or ethanol were used to assess their role in the fertilization process. Oviductal cells were co-cultured with 0.5 million motile sperm/ml for 30 min. A 10-microl sample (spermatozoa bound with the cells) was added to 40-microl droplets of fertilization medium containing 5 oocytes. After 15 to 18 h, oocytes were examined for penetration and monospermy. The results show a lower penetration rate with oviductal cells than that of the control. The use of oviductal cells from the isthmus treated with estradiol significantly decreased the percentage of polyspermy compared with that of ampulla treated with the estradiol or with the control. When the isthmus cells were treated with progesterone, an increase in the incidence of polyspermy was observed. Therefore, it is possible to use oviductal cells to increase the incidence of monospermy in porcine in vitro fertilization; moreover, estradiol increases the proportion of monospermy when added to isthmus-derived oviductal cells.

Regional differences in uteroglobin biosynthesis along the rabbit oviduct: immunohistochemical and biochemical studies

The biosynthesis of uteroglobin in three regions of the rabbit oviduct was assessed by means of immunocytochemical studies, radioimmunoassay measurements of the protein, and quantitative determinations of its mRNA. Immunocytochemical observations suggested that the number of immunopositive cells and the intensity of their immunolabelling were similar in the distal (infundibular) and the middle regions. In contrast, the isthmic portion appeared to contain less positive cells and weaker immunolabelling. In agreement with these findings, biochemical studies demonstrated that the tissue contents of uteroglobin and its mRNA were similar in the distal and the middle regions whereas the concentrations of both were about three-to four-fold lower in the isthmic portion. The results are discussed in relation to a possible role for uteroglobin in maintaining appropriate environmental conditions for the gametes and the early embryo.

Capacitation in vitro of bovine spermatozoa by oviduct epithelial cell monolayer conditioned medium

The effect of the active capacitating factor secreted from oviduct epithelial cell monolayers (OECM) in different environments on in vitro fertilization was evaluated. Capacitation was determined as the ability of sperm to fertilize bovine oocytes in vitro. When the mTALP was supplemented with glucose during conditioning, the sperm penetration rate was significantly reduced (P < 0.05) compared to the control (7% +/- 1 vs. 30% +/- 4). The percentages of sperm penetrated oocytes were higher following insemination in the OECM-conditioned medium derived from the early stage (48% +/- 7) of the estrous cycle than in the OECM-conditioned medium derived from either mid (35% +/- 2) or late stages (28% +/- 3) of the estrous cycle. When the medium was supplemented with 0.1 or 0.5 microgram/ml estradiol-17 beta during medium conditioning, sperm penetration rates increased (P < 0.05) compared to the control group (55% +/- 4 vs. 40% +/- 3 and 54% +/- 2 vs. 41% +/- 3, respectively). In addition, the percentages of penetrated oocytes significantly decreased (P < 0.05) following insemination when the OECM-conditioned medium was added to 0.01%, 0.05%, and 0.1% ethanol compared to the control (25% +/- 4, 19% +/- 2, 18% +/- 3, and 45% +/- 3, respectively). Sperm penetration rates significantly (P < 0.01) decreased when the OECM-conditioned medium was heated to 100 degrees C for 5 min (10% +/- 1 vs. 40% +/- 3). These results suggest that the active capacitating factor was secreted by the OECM and that this capacitating factor in the OECM-conditioned medium was inhibited by the presence of glucose. This factor was found to be heat-sensitive and its action was affected by ethanol. The OECM derived from the three phases of the estrous cycle as well as the presence of estradiol-17 beta influenced the capacity of the OECM to secrete this capacitating factor in vitro.

Bovine oviduct-specific glycoprotein: a potent factor for maintenance of viability and motility of bovine spermatozoa in vitro

In the cow, a specific glycoprotein--bovine oviduct-specific glycoprotein (BOGP)--is secreted by the epithelial cells of the oviduct at the follicular stage of the estrous cycle. In this study, we examined the effects of purified BOGP on the viability and motility of bovine spermatozoa in culture in vitro. Frozen-thawed bovine spermatozoa were incubated in modified Tyrode's solution (TALP) that contained purified BOGP (TALP-BOGP). In TALP-BOGP, both the viability and motility of bovine spermatozoa were more effectively maintained than in the control medium without any added protein. The increases in both the viability and motility of spermatozoa were dose-dependent. Spermatozoa were also incubated in TALP medium supplemented with bovine serum albumin, egg albumin, lactalbumin, or gastric mucin, and their viability and motility in these media were compared with that in TALP-BOGP. Both the viability and motility of spermatozoa were more effectively maintained in TALP-BOGP throughout a 12-hr incubation than in other media tested. An immunolabeling study demonstrated that a monoclonal antibody specific for BOGP reacted with the posterior region of the head, the middle portion, and the tail of spermatozoa that had been incubated with TALP-BOGP, suggesting that BOGP becomes specifically associated with particular regions of the spermatozoon. These results suggest that BOGP is a potent factor for maintenance of the viability and motility of sperm. On the basis of the present results, we also propose that BOGP may play an important role in sperm functions during the reproductive process.

Oviductins possess chitinase- and mucin-like domains: a lead in the search for the biological function of these oviduct-specific ZP-associating glycoproteins

Over the last 10 years considerable progress has been made in the immunological and biochemical characterization of oviduct-specific glycoproteins. It is now well established that a subclass of these secretory products, designated as oviductins, associate with the zona pellucida of the ovulated oocyte and with the early embryo. Recent reports on the cloning of cDNAs of oviductins from various species, including that of golden hamster (Mesocricetus auratus) oviductin by our laboratory, allowed us to compare their deduced amino acid sequences with those of other proteins. Optimal alignment analysis showed that oviductins contain regions of significant similarity with catalytically inactive mammalian members of the bacterial and microfilarial chitinase protein family. Most importantly, a close examination of the hamster and human deduced amino acid sequences revealed that both glycoproteins possess contiguous Ser/Thr rich repeated units, clustered in their carboxy-terminal portions. These mucin-type motifs are similar in the hamster and human glycoprotein, although hamster oviductin contains more of these complete units. This striking feature might indicate that these molecules play a similar role to mucin-type glycoproteins, e.g., in protecting the oocyte and early embryo against attacks from their environment. We propose a model whereby oviductins are targeted to the oocyte via the interaction of their chitinase-like domains with specific oligosaccharide moieties of the zona pellucida. Once localized to this structure, oviductin molecules would act as a protective shield around the oocyte and early embryo by virtue of their densely glycosylated mucin-type domains.

Immunological detection and characterization of an estrus-associated antigen in the goat oviduct

The present study was designed to investigate the possibility that the goat oviduct produces specific substance(s) similar to the oviductal glycoprotein (BOGP) of the bovine oviduct. Oviductal flushings obtained from goats at the follicular and luteal phases of the estrous cycle were examined by immunoblotting for the presence of material that cross-reacted with monoclonal antibodies (MAbs) specific for BOGP. The MAbs immunoreacted with a broad band with a molecular mass of protein of about 97 kDa in the flushings of goat oviducts after fractionation of proteins by electrophoresis under reducing conditions. The antigen was present in flushings obtained from the ampullar segments of oviducts from goats at the follicular stage, but this antigen could hardly be detected in the flushings from the ampulla at the luteal phase and or the flushings from the isthmus at either the follicular or the luteal phase. This antigen was not detected in uterine flushings, follicular fluid, or serum. An immunohistochemical study demonstrated that the MAbs reacted specifically with the epithelial cells of the goat oviduct. Intense labeling was observed in the ampullar and fimbrial epithelia of goat oviducts at the follicular phase, but the immunohistochemical reaction was very weak at the luteal phase. In the isthmus, the reaction was faint during both the follicular and the luteal phase. No specific immunohistochemical reactivity with the MAbs was observed with other tissues from the reproductive tract or with nonreproductive tissues. Immunofluorescent staining showed that the antigen was associated with the zona pellucida of goat ovarian eggs that had been incubated with ampullar flushings from goats at the follicular stage.(ABSTRACT TRUNCATED AT 250 WORDS)

Secretory products of bovine oviductal epithelial cells support the viability and motility of bovine spermatozoa in culture in vitro

The ability of secretions from the bovine oviduct to maintain the viability and motility of bovine spermatozoa was investigated by incubating frozen-thawed spermatozoa with oviductal flushings, uterine flushings, or the medium from cultures of oviductal epithelial cells and endothelial cells. The flushings obtained from both oviducts and uteri were effective for the maintenance of the viability and motility of spermatozoa, irrespective of the stage of the estrous cycle at which they had been collected. The flushings obtained from the ampullar region of oviducts at the follicular phase of the estrous cycle were most effective for the maintenance of viability and motile activity, for example, the forward motion of spermatozoa. Sperm viability and motility were also maintained by the medium from 6-hour culture of epithelial cells obtained from oviducts at the follicular phase of the estrous cycle. In contrast, the medium derived from bovine fetal artery endothelial cells had no significant effect on sperm viability and motility. These results suggest that the fluids of the female reproductive tract, in particular, the oviductal fluids at the follicular stage, provide a suitable environment for the maintenance of the viability and motility of bovine spermatozoa. It is also suggested that secretory product(s) of oviductal epithelial cells may play an important role in sustaining both the viability and motility of spermatozoa.

Biochemical characterization of a bovine oviduct-specific sialo-glycoprotein that sustains sperm viability in vitro

A bovine oviduct-specific glycoprotein (BOGP) that sustained the viability of bovine spermatozoa in vitro was purified from an extract of bovine oviducts. The amino-terminal amino acid sequence of BOGP was found to be a homologous with that of oviductin, a protein from hamster that was recently characterized by Mallete and Bleau (1993: Biochem. J. 295, 437-445). Purified BOGP was characterized as a sialo-glycoprotein containing N-linked and O-linked sialo-oligosaccharides side chains with galactose, mannose, N-acetyl-D-galactosamine, N-acetyl-D-glucosamine, fucose and sialic acids in its core protein (57 kDa). Intact BOGP has a wide range of isoelectric points (pIs) from 6.5 to 3.0 but a narrow range of molecular masses around 95 kDa. On isoelectric focusing of neuraminidase-treated BOGP (AS-BOGP), a narrow band with a pI of 9.3 was observed, and the ability of AS-BOGP to maintain sperm viability was negligible. We propose that BOGP is a mucin-type sialo-glycoprotein with a molecular mass of 72 kDa that contains one N-linked and approx. 15 O-linked sialo-oligosaccharide chains. These side chains appear to be important for the maintenance of sperm viability.

Regional variations in the ultrastructural features of secretory cells in the rat oviductal epithelium

BACKGROUND

In mammals, the oviductal secretory cells and their secretions play important roles in reproductive and developmental events. Therefore, many electron microscopic studies of mammalian oviductal epithelial cells have been performed.

METHODS

The secretory cells in various regions of the rat oviduct during the estrous cycle were examined by transmission electron microscopy.

RESULTS

In the fimbriae, the secretory cells contained small secretory granules with moderately electron-dense matrices and many large bodies that resembled lipid droplets. In the ampullar cells, small secretory granules with moderately electron-dense matrices were observed in the apical cytoplasm. In the isthmus, the secretory cells contained numerous secretory granules with moderately electron-dense matrices. Electron-dense areas were frequently observed in many of the granules of the isthmic cells. Vesicles, partially filled with a dense substance, frequently were observed in the isthmic cells and occasionally in the ampullar cells. Very long stereocilia projected from the surfaces of the isthmic secretory cells into the lumen. Exocytosis of the secretory granules was observed. In addition, there was evidence to suggest the release of the bodies that resembled lipid droplet occurred. Cysts and ciliated vacuoles that appeared to be intraepithelial were frequently observed in the fimbrial and ampullar epithelia. No dramatic changes in the relative numbers of ciliated and secretory cells in any oviductal segment were observed during the estrous cycle.

CONCLUSIONS

Our ultrastructural observations of the rat oviduct revealed marked regional variations in the morphological features of secretory cells. These results may provide insight into regional and cellular differences in the function of the rat oviduct.