Regulation of anion secretion by cyclo-oxygenase and prostanoids in cultured epididymal epithelia from the rat

Effects of Heparan sulfate acetyl-CoA: Alpha-glucosaminide N-acetyltransferase (HGSNAT) inactivation on the structure and function of epithelial and immune cells of the testis and epididymis and sperm parameters in adult mice

Heparan sulfate (HS), an abundant component of the apical cell surface and basement membrane, belongs to the glycosaminoglycan family of carbohydrates covalently linked to proteins called heparan sulfate proteoglycans. After endocytosis, HS is degraded in the lysosome by several enzymes, including heparan-alpha-glucosaminide N-acetyltransferase (HGSNAT), and in its absence causes Mucopolysaccharidosis III type C (Sanfilippo type C). Since endocytosis occurs in epithelial cells of the testis and epididymis, we examined the morphological effects of Hgsnat inactivation in these organs. In the testis, Hgsnat knockout (Hgsnat-Geo) mice revealed statistically significant decrease in tubule and epithelial profile area of seminiferous tubules. Electron microscopy (EM) analysis revealed cross-sectional tubule profiles with normal and moderately to severely altered appearances. Abnormalities in Sertoli cells and blood-testis barrier and the absence of germ cells in some tubules were noted along with altered morphology of sperm, sperm motility parameters and a reduction in fertilization rates in vitro. Along with quantitatively increased epithelial and tubular profile areas in the epididymis, EM demonstrated significant accumulations of electrolucent lysosomes in the caput-cauda regions that were reactive for cathepsin D and prosaposin antibodies. Lysosomes with similar storage materials were also found in basal, clear and myoid cells. In the mid/basal region of the epithelium of caput-cauda regions of KO mice, large vacuolated cells, unreactive for cytokeratin 5, a basal cell marker, were identified morphologically as epididymal mononuclear phagocytes (eMPs). The cytoplasm of the eMPs was occupied by a gigantic lysosome suggesting an active role of these cells in removing debris from the epithelium. Some eMPs were found in proximity to T-lymphocytes, a feature of dendritic cells. Taken together, our results reveal that upon Hgsnat inactivation, morphological alterations occur to the testis affecting sperm morphology and motility parameters and abnormal lysosomes in epididymal epithelial cells, indicative of a lysosomal storage disease.

Epididymal epithelial degeneration and lipid metabolism impairment account for male infertility in occludin knockout mice

Occludin (OCLN) is a tight junction protein and Ocln deletion mutation causes male infertility in mice. However, the role of OCLN in male reproductive system remains unknown. In this study, we used an interdisciplinary approach to elucidate the underlying mechanism of male infertility in related to OCLN function, including Ocln knockout mice as well as a combined omics analysis and immunofluorescent labelling. Our results showed that the epididymis of Ocln-null mice displayed a phenomenon resembling epididymal sperm granuloma, which occurred especially in the junctional region between caput and corpus epididymidis. Sperm motility and fertilisation capacity were also impaired in these Ocln-null mice, accompanied by enlarged tubules in the proximal regions and degeneration in the distal regions of epididymis. Cellular localization analysis showed that OCLN immunofluorescence was enriched only in the apical junction of epithelial principal cells in the proximal regions of epididymis. Integrative omics analysis revealed the downregulation of gene clusters enriched in acid secretion and fatty acid metabolism in the Ocln-null epididymis, especially the enzymes related to the unsaturated arachidonic acid pathway. The number of proton-pump V-ATPase-expression clear cells, a key player of luminal acidification in the epididymis, declined drastically from prepubertal age before sperm arrival but not in the early postnatal age. This was accompanied by programmed cell death of clear cells and increased pH in the epididymal fluid of OCLN-deficient mice. The lipidomics results showed significantly increased levels of specific DAGs conjugated to unsaturated fatty acids in the Ocln-mutant. Immunofluorescent labelling showed that the arachidonic acid converting enzyme PTGDS and phospholipase PLA2g12a were prominently altered in the principal cells and luminal contents of the Ocln-mutant epididymis. Whereas the carboxylate ester lipase CES1, originally enriched in the WT basal cells, was found upregulated in the Ocln-mutant principal cells. Overall, this study demonstrates that OCLN is essential for maintaining caput-to-corpus epithelial integrity, survival of acid-secreting clear cells, and unsaturated fatty acid catabolism in the mouse epididymis, thereby ensuring sperm maturation and male fertility.

Contribution of epididymal epithelial cell functions to sperm epigenetic changes and the health of progeny

BACKGROUND

Spermatozoa acquire their motility and fertilizing abilities during their maturation through the epididymis. This process is controlled by epididymal epithelial cells that possess features adapted to sense and respond to their surrounding environment and to communicate with spermatozoa. During the past decade, new intercellular communication processes have been discovered, including the secretion and transport of molecules from the epithelium to spermatozoa via extracellular vesicles (EVs), as well as sensing of the intraluminal milieu by cellular extensions.

OBJECTIVE AND RATIONALE

This review addresses recent findings regarding epididymal epithelial cell features and interactions between spermatozoa and the epididymal epithelium as well as epigenetic modifications undergone by spermatozoa during transit through the epididymal microenvironment.

SEARCH METHODS

A systematic search was conducted in Pubmed with the keyword 'epididymis'. Results were filtered on original research articles published from 2009 to 2021 and written in the English language. One hundred fifteen original articles presenting recent advancements on the epididymis contribution to sperm maturation were selected. Some additional papers cited in the primary reference were also included. A special focus was given to higher mammalian species, particularly rodents, bovines and humans, that are the most studied in this field.

OUTCOMES

This review provides novel insights into the contribution of epididymal epithelium and EVs to post-testicular sperm maturation. First, new immune cell populations have been described in the epididymis, where they are proposed to play a role in protecting the environment surrounding sperm against infections or autoimmune responses. Second, novel epididymal cell extensions, including dendrites, axopodia and primary cilia, have been identified as sensors of the environment surrounding sperm. Third, new functions have been outlined for epididymal EVs, which modify the sperm epigenetic profile and participate in transgenerational epigenetic inheritance of paternal traits.

WIDER IMPLICATIONS

Although the majority of these findings result from studies in rodents, this fundamental research will ultimately improve our knowledge of human reproductive physiopathologies. Recent discoveries linking sperm epigenetic modifications with paternal environmental exposure and progeny outcome further stress the importance of advancing fundamental research on the epididymis. From this, new therapeutic options for infertile couples and better counseling strategies may arise to increase positive health outcomes in children conceived either naturally or with ART.

Effects of dipyrone and acetylsalicylic acid on contractions of distal cauda epididymis duct, serum testosterone and sperm count in rats

The effects of dipyrone and acetylsalicylic acid (ASA) on male fertility are still not fully understood, mainly considering the epididymis as a putative target for their anti-fertility effects. Therefore, this study aimed to investigate the effects of dipyrone and ASA on the contractions of distal cauda epididymis duct, serum testosterone levels and sperm parameters in rats. Firstly, we checked the in vitro effects of dipyrone and ASA (10-1000 μM) on the contractions of distal cauda epididymis duct by pharmacological experiments. We also evaluated the effects of in vivo treatment with dipyrone and ASA 100 mg/kg (p.o.) for 15 days on epididymal duct contractions, serum testosterone levels and sperm parameters. In vitro dipyrone or ASA decreased the epididymal duct contractions induced by phenylephrine or carbachol. We observed that in vivo treatment with both drugs decreased the daily sperm production, serum testosterone levels and sperm count through epididymis without altering the epididymal duct contractions and sperm transit time through epididymis. In conclusion, in vitro dipyrone and ASA were able to diminish the contractions of epididymal duct, whilst in vivo administration decreased the sperm count throughout epididymis as a consequence of a low sperm production caused by reduced testosterone levels.

Spatio-temporal landscape of mouse epididymal cells and specific mitochondria-rich segments defined by large-scale single-cell RNA-seq

Spermatozoa acquire their fertilizing ability and forward motility during epididymal transit, suggesting the importance of the epididymis. Although the cell atlas of the epididymis was reported recently, the heterogeneity of the cells and the gene expression profile in the epididymal tube are still largely unknown. Considering single-cell RNA sequencing results, we thoroughly studied the cell composition, spatio-temporal differences in differentially expressed genes (DEGs) in epididymal segments and mitochondria throughout the epididymis with sufficient cell numbers. In total, 40,623 cells were detected and further clustered into 8 identified cell populations. Focused analyses revealed the subpopulations of principal cells, basal cells, clear/narrow cells, and halo/T cells. Notably, two subtypes of principal cells, the Prc7 and Prc8 subpopulations were enriched as stereocilia-like cells according to GO analysis. Further analysis demonstrated the spatially specific pattern of the DEGs in each cell cluster. Unexpectedly, the abundance of mitochondria and mitochondrial transcription (MT) was found to be higher in the corpus and cauda epididymis than in the caput epididymis by scRNA-seq, immunostaining, and qPCR validation. In addition, the spatio-temporal profile of the DEGs from the P42 and P56 epididymis, including transiting spermatozoa, was depicted. Overall, our study presented the single-cell transcriptome atlas of the mouse epididymis and revealed the novel distribution pattern of mitochondria and key genes that may be linked to sperm functionalities in the first wave and subsequent wave of sperm, providing a roadmap to be emulated in efforts to achieve sperm maturation regulation in the epididymis.

Cellular mechanism underlying oxytocin-stimulated Cl- secretion in rat cauda epididymal epithelium

The neurohypophyseal hormone oxytocin (OT) plays critical roles in lactation and parturition, while its function in male reproduction system is largely unknown. This study aims to investigate the effect of OT on regulating transepithelial ion transport in rat cauda epididymal epithelium. With the use of RT-PCR, Western blot, and immunohistochemical analysis, we found that OT receptor (OTR) was expressed and localized at the basal membrane of rat cauda epididymal epithelium. The short-circuit current (I_sc) measurement showed that basolateral application of OT to the primary cultured rat cauda epididymal epithelial cells elicited an increase in I_sc, which was abrogated by pretreating the epithelial cells with CFTR_inh-172, a blocker of cystic fibrosis transmembrane conductance regulator (CFTR). Pretreatment with the prostaglandin H synthase inhibitors indomethacin and piroxicam, or the nonselective antagonists of prostaglandin E2 (PGE₂) receptor EP2 or EP4, AH-6809, and AH-23848, significantly attenuated OT-stimulated I_sc response. Furthermore, the generation of PGE₂ was measured using enzyme-linked immunosorbent assay, demonstrating that OT induced a substantial increase in PGE₂ release from primary cultured rat cauda epididymal epithelial cells. In conclusion, activation of OTR by OT triggered PGE₂ release, resulting in CFTR-dependent Cl^- secretion through paracrine/autocrine pathways in rat cauda epididymal epithelium.

Effects of prostaglandin E2 on gap junction protein alpha 1 in the rat epididymis

Gap junctions are responsible for intercellular communication. In the adult mammalian epididymis, gap junction protein alpha 1 (GJA1) is localized between basal and either principal or clear cells. GJA1 levels and localization change during the differentiation of basal cells. The present objective was to determine the role of basal cells and prostaglandin E2 (PGE2) on GJA1 in the rat epididymis. Prior to basal cell differentiation, GJA1 is colocalized with TJP1 at the apical lateral margins between adjacent epithelial cells. When basal cells are present, GJA1 becomes associated between basal and principal cells, where it is primarily immunolocalized until adulthood. Basal cells express TP63, differentiate from epithelial cells, and produce prostaglandin-endoperoxide synthase 1 by 21 days of age. Prior to day 21, GJA1and TP63 are not strongly associated at the apical region. However, by day 28, TP63-positive basal cells migrate to the base of the epithelium, and also express GJA1. To assess effects of PGE2 on GJA1, rat caput epididymal (RCE) cells were exposed to PGE2 (50 μM) for 3 h. PGE2 increased levels of Gja1 mRNA in RCE cells, while levels of Gjb1, Gjb2, Gjb4, and GjB5 were unaltered. Furthermore, PGE2 increased protein levels of GJA1, phospho-GJA1, phospho-AKT, CTNNB1, and phospho-CTNNB1. Total AKT and the tight junction protein claudin1 were also not altered by PGE2. Data suggest that development of the epididymal epithelium and differentiation of epididymal basal cells regulate the targeting of GJA1, and that this appears to be mediated by PGE2.

Epithelial dynamics in the epididymis: role in the maturation, protection, and storage of spermatozoa

Epithelial cells line the lumen of tubular organs and are key players in their respective functions. They establish a unique luminal environment by providing a protective barrier and by performing vectorial transport of ions, nutrients, solutes, proteins, and water. Complex intercellular communication networks, specific for each organ, ensure their interaction with adjacent epithelial and non-epithelial cells, allowing them to respond to and modulate their immediate environment. In the epididymis, several epithelial cell types work in a concerted manner to establish a luminal acidic milieu that is essential for the post-testicular maturation and storage of spermatozoa. The epididymis also prevents autoimmune responses against auto-antigenic spermatozoa, while ensuring protection against ascending and blood pathogens. This is achieved by a network of immune cells that are in close contact and interact with epithelial cells. This review highlights the coordinated interactions between spermatozoa, basal cells, principal cells, narrow cells, clear cells, and immune cells that contribute to the maturation, protection, selection, and storage of spermatozoa in the lumen of the epididymis.

Isolated Rat Epididymal Basal Cells Share Common Properties with Adult Stem Cells

There is little information on the function of epididymal basal cells. These cells secrete prostaglandins, can metabolize radical oxygen species, and have apical projections that are components of the blood-epididymis barrier. The objective of this study was to develop a reproducible protocol to isolate rat epididymal basal cells and to characterize their function by gene expression profiling. Integrin-alpha6 was used to isolate a highly purified population of basal cells. Microarray analysis indicated that expression levels of 552 genes were enriched in basal cells relative to other cell types. Among these genes, 45 were expressed at levels of 5-fold or greater. These highly expressed genes coded for proteins implicated in cell adhesion, cytoskeletal function, ion transport, cellular signaling, and epidermal function, and included proteases and antiproteases, signal transduction, and transcription factors. Several highly expressed genes have been reported in adult stem cells, suggesting that basal cells may represent an epididymal stem cell population. A basal cell culture was established that showed that these basal cells can differentiate in vitro from keratin (KRT) 5-positive cells to cells that express KRT8 and connexin 26, a marker of columnar cells. These data provide novel information on epididymal basal cell gene expression and suggest that these cells can act as adult stem cells.

Histopathological, biochemical and molecular changes of reproductive function after malathion exposure of prepubertal male mice

We aimed in the present work to evaluate the implication of oxidative stress in the toxicological effects of subchronic malathion exposure on reproductive function in mice.

The blood-epididymis barrier and inflammation

The blood-epididymis barrier (BEB) is a critical structure for male fertility. It enables the development of a specific luminal environment that allows spermatozoa to acquire both the ability to swim and fertilize an ovum. The presence of tight junctions and specific cellular transporters can regulate the composition of the epididymal lumen to favor proper sperm maturation. The BEB is also at the interface between the immune system and sperm. Not only does the BEB protect maturing spermatozoa from the immune system, it is also influenced by cytokines released during inflammation, which can result in the loss of barrier function. Such a loss is associated with an immune response, decreased sperm functions, and appears to be a contributing factor to post-testicular male infertility. Alterations in the BEB may be responsible for the formation of inflammatory conditions such as sperm granulomas. The present review summarizes current knowledge on the morphological, physiological and pathological components associated with the BEB, the role of immune function on the regulation of the BEB, and how disturbance of these factors can result in inflammatory lesions of the epididymis.

Connexins and pannexins: Coordinating cellular communication in the testis and epididymis

Gap junctions and connexins are critical for coordinating cellular functions in complex epithelia. In recent years there has been increased interest in understanding the regulation and function of gap junctions in both the testis and epididymis. Studies in transgenic mice in which connexin 43 (Cx43) is mutated or is knocked down only in Sertoli cells have demonstrated the essential role of Cx43 in spermatogenesis and differentiation of Sertoli cells. In the epididymis developmental studies have shown a role for numerous connexins in the differentiation of epithelial cells and communication between the basal cells and both principal and clear cells. In both tissues several factors, such thyroid hormones and androgens, are important in regulating expression and function of connexins. Pannexins, which form cellular channels but are structurally similar to gap junction proteins, have been identified in both testis and epididymis and, in the epididymis, are regulated by androgens. The objective of this review is to summarize the advances that have been made on the role and regulation of connexins and pannexins in the testis and epididymis and their implication in spermatogenesis and sperm maturation.

Tyrosine phosphorylation modulates store-operated calcium entry in cultured rat epididymal basal cells

Store-operated calcium entry (SOCE) is essential for many cellular processes. In this study, we investigated modulation of SOCE by tyrosine phosphorylation in rat epididymal basal cells. The intracellular Ca(2+) ([Ca(2+)]i) measurement showed that SOCE occurred in rat epididymal basal cells by pretreating the cells with thapsigargin (Tg), the inhibitor of sarco-endoplasmic reticulum Ca(2+)-ATPase. To identify the role of Ca(2+) channels in this response, we examined the effects of transient receptor potential canonical channel blockers 2-aminoethoxydiphenyl borate (2-APB), 1-[β-[3-(4-methoxyphenyl)pro-poxy]-4-methoxyphenethyl]-1H-imidazole hydrochloride(SKF96365), Gd(3+), and non-selective cation channel blocker Ni(2+) respectively on SOCE and found that these blockers could inhibit the Ca(2+) influx to different extent. Furthermore, we studied the regulation of SOCE by tyrosine kinase pathway. The inhibitor of tyrosine kinase genistein remarkably suppressed the SOCE response, whereas sodium orthovanadate, the inhibitor of tyrosine phosphatase, greatly enhanced it. The results suggest that tyrosine kinase pathway plays a significant role in the initiation of SOCE and positively modulates SOCE in epididymal basal cells.

Testosterone upregulates anion secretion across porcine vas deferens epithelia in vitro

Testosterone induces and maintains prostaglandin endoperoxide synthase 2 (PTGS2, also known as cyclooxygenase 2) expression in vas deferens epithelial cells, but it remains unknown whether this has a physiological role in the context of male reproductive biology. Prostaglandins induce concentration-dependent increases in anion secretion in porcine vas deferens epithelial cell (1 degrees PVD) monolayers, where bicarbonate contributes to cAMP-stimulated anion secretion. Moreover, bradykinin induces anion secretion across 1 degrees PVD monolayers that is indomethacin sensitive, and both PTGS2 and PTGS1 are expressed in this model system. Therefore, it was hypothesized that testosterone modulates anion secretion across vas deferens epithelia via PTGS-dependent pathways and prostaglandin synthesis. Porcine vas deferens epithelial cells were isolated and cultured as monolayers on permeable supports until assayed in modified Ussing chambers. RNA and protein were isolated concurrently for semiquantitative expression analysis. Testosterone upregulated basal and bradykinin-induced short-circuit current across 1 degrees PVD monolayers, indicative of anion secretion. Testosterone also induced greater transepithelial electrical resistance. Increases in anion secretion were associated with preferential upregulation of PTGS2 at the mRNA and protein levels. In addition, testosterone induced greater basal and bradykinin-induced anion secretion across vas deferens epithelial cells isolated from the distal segment of the duct. Taken together, these results suggest that testosterone upregulates epithelial responsiveness to acute modulations of anion secretion (likely bicarbonate secretion), which ultimately modifies the environment to which sperm are exposed.

Regulation of smooth muscle contractility by the epithelium in rat vas deferens: role of ATP-induced release of PGE2

Recent studies suggest that the epithelium might modulate the contractility of smooth muscle. However, the mechanisms underlying this regulation are unknown. The present study investigated the regulation of smooth muscle contraction by the epithelium in rat vas deferens and the possible factor(s) involved. Exogenously applied ATP inhibited electrical field stimulation (EFS)-evoked smooth muscle contraction in an epithelium-dependent manner. As the effects of ATP on smooth muscle contractility were abrogated by inhibitors of prostaglandin synthesis, but not by those of nitric oxide synthesis, prostaglandins might mediate the effects of ATP. Consistent with this idea, PGE(2) inhibited EFS-evoked smooth muscle contraction independent of the epithelium, while ATP and UTP induced the release of PGE(2) from cultured rat vas deferens epithelial cells, but not smooth muscle cells. The ATP-induced PGE(2) release from vas deferens epithelial cells was abolished by U73122, an inhibitor of phospholipase C (PLC) and BAPTA AM, a Ca(2+) chelator. ATP also transiently increased [Ca(2+)](i) in vas deferens epithelial cells. This effect of ATP on [Ca(2+)](i) was independent of extracellular Ca(2+), but abolished by the P2 receptor antagonist RB2 and U73122. In membrane potential measurements using a voltage-sensitive dye, PGE(2), but not ATP, hyperpolarized vas deferens smooth muscle cells and this effect of PGE(2) was blocked by MDL12330A, an adenylate cyclase inhibitor, and the chromanol 293B, a blocker of cAMP-dependent K(+) channels. Taken together, our results suggest that ATP inhibition of vas deferens smooth muscle contraction is epithelium dependent. The data also suggest that ATP activates P2Y receptor-coupled Ca(2+) mobilization leading to the release of PGE(2) from epithelial cells, which in turn activates cAMP-dependent K(+) channels in smooth muscle cells leading to the hyperpolarization of membrane voltage and the inhibition of vas deferens contraction. Thus, the present findings suggest a novel regulatory mechanism by which the epithelium regulates the contractility of smooth muscle.

Bradykinin-stimulated cyclooxygenase activity stimulates vas deferens epithelial anion secretion in vitro in swine and humans

Epithelia lining the male reproductive duct modulate fertility by altering the luminal environment to which sperm are exposed. Although vas deferens epithelial cells reportedly express high levels of cyclooxygenases (Ptgs), and activation of bradykinin (BK) receptors can lead to upregulation of PTGS activity in epididymal epithelia, it remains unknown whether BKs and/or PTGSs have any role in modulating epithelial ion transport across vas deferens epithelia. Porcine and human vas deferens epithelial cell primary cultures and the PVD9902 cell line responded to lysylbradykinin with an increase in short circuit current (I SC; indicating net anion secretion), an effect that was 60%-93% reduced by indomethacin. The BK effect was inhibited by the B2 receptor subtype (BDKRB2) antagonist HOE140, whereas the B1 receptor subtype agonist des-Arg9-BK had no effect. BDKRB2 immunoreactivity was documented in most epithelial cells composing the native epithelium and on Western blots derived from cultured cells. Gene expression analysis revealed that the PTGS2 transcript is 20 times more abundant than its PTGS1 counterpart in cultured porcine vas deferens epithelia and that BDKRB2 mRNA is likewise highly expressed. Subsequent experiments revealed that prostaglandin E2, 1-OH prostaglandin E1 (prostaglandin E receptor 4 [PTGER4] agonist) and butaprost (PTGER2 agonist) increase I SC in a concentration-dependent manner, whereas sulprostone (mixed PTGER1 and PTGER3 agonist) produced no change in I SC. These results demonstrate that autacoids can affect epithelial cells to acutely modulate the luminal environment to which sperm are exposed in the vas deferens by enhancing PTGS activity, leading to the production of prostaglandins that act at PTGER4 and/or PTGER2 to induce or enhance anion secretion.

Differential modulation of bovine epididymal activity by oxytocin and noradrenaline

Passage of spermatozoa through the epididymis and emission of sperm during ejaculation are based on spontaneous and induced contractions of epididymal peritubular muscle layers. This study deals with the ejaculation-relevant factors noradrenaline (NA) and oxytocin (OT) and their contractile effects in the course of the bovine epididymal duct. Muscle tension recording revealed excitatory effects of NA in all duct regions. A peculiarity was found in a duct section between the mid-cauda and ductus deferens, where the responsiveness to NA was particularly faint in comparison with the adjacent regions. NA-induced contraction was primarily mediated by postjunctional alpha(2)-adrenoceptors (ADRA) in the caput and corpus regions, and by alpha(1)-ADRA in the cauda region. Contrary to NA, OT exerted regionally varying effects. The peptide induced contraction in intact and epithelium-denuded caput as well as in epithelium-denuded corpus segments but had a relaxant net effect in intact corpus and proximal cauda segments. Within the mid-cauda, OT evoked strong contraction, which progressively decreased distally. Receptor specificity of the epididymal OT effects was verified using the selective OT receptor (OTR) agonist [Thr(4),Gly(7)]OT and vasopressin. OTR immunoreactivity was detected in the epididymal peritubular muscle wall and epithelial principal cells. RT-PCR analysis confirmed the presence of OTR in all duct regions. In summary, different contractile responses to OT and NA occur in the course of the epididymal duct, possibly preventing excessive sperm transport through the corpus and serving orthograde emission of sperm during ejaculation.

Mechanisms Regulating Spontaneous Contractions in the Bovine Epididymal Duct1

Muscular autorhythmicity provides propulsion of spermatozoa through the epididymal duct, thereby ensuring sperm maturation. In the present study, the mechanisms underlying the bovine epididymal spontaneous phasic contractions (SCs) were analyzed by using muscle-tension recording and patch-clamp techniques. SCs were recorded from the caput, the corpus, and the proximal cauda region and found to be predominantly myogenic in origin. Removal of the luminal fluid induced a burstlike contraction pattern, and removal of the epithelium, a complete loss of SCs. Application of nifedipine, but not heparin and cyclopiazonic acid, suppressed SCs, indicating that influx of Ca2+ through L-type Ca2+ channels, but not Ca2+ release from intracellular stores, was crucial for maintaining SCs. The prostaglandin-endoperoxide synthase 2 (PTGS2) inhibitor NS-398 caused a region-dependent decrease in SCs and tone. These effects were mimicked by the mitogen-activated protein kinase (MAPK) kinase inhibitor PD-98059. Similarly, the prostaglandin F(2alpha) (PGF(2alpha))-receptor antagonist AL-8810 reduced SC generation, whereas PGF(2alpha) induced SC-like activity in epithelium-denuded segments. Cell-isolation experiments revealed the existence of three morphologically different types of contractile cells, which also showed distinct biophysical properties: typical smooth muscle cells in the cauda, myofibroblast-like cells all along the duct, and atypical muscle cells (ATMs) with filament-like spurs in all regions with SCs. These data suggest that the bovine epididymal autorhythmicity is based on an epithelial PTGS2-dependent release of (an) excitatory prostaglandin(s) and a MAPK-dependent activation of L-type Ca2+ channels in the contractile cells. ATM cells may provide electrical coupling between myofibroblasts, which is essential for the generation of regular myogenic activity.

ROLE OF CYCLOOXYGENASE-2 IN THE DEVELOPMENT OF BLADDER OVERACTIVITY AFTER CEREBRAL INFARCTION IN THE RAT

PURPOSE

We investigated the role of cyclooxygenase (COX) isoforms in bladder overactivity induced by cerebral infarction (CI) in rats.

MATERIALS AND METHODS

CI was induced by left middle cerebral artery occlusion (MCAO) in female Sprague-Dawley rats. Bladder activity was monitored with continuous infusion cystometrography of conscious rats. Specimens were obtained from the pontine tegmental area (PTA) 1, 3, 5, 12 and 24 hours after CI or sham operation (SO). The effects of MK-801 (0.1 mg/kg intravenously), an NMDA (N-methyl-D-aspartate) glutamatergic receptor antagonist, on bladder activity, and on COX-1 and 2 mRNA expression following MCAO were examined. Real-time quantitative reverse transcriptase-polymerase chain reaction was performed to evaluate the effects of CI on gene expression in the PTA. The effects of the COX-2 inhibitor NS398 (0.01 to 10 mg/kg intravenously) on bladder activity were examined.

RESULTS

The bladder capacity of CI rats was significantly decreased 1 to 24 hours after MCAO compared with that of SO rats (p <0.05 or 0.01). One and 3 hours after MCAO mean COX-2 mRNA expression +/- SE had increased significantly to 22.4 +/- 3.5 in terms of its expression relative to the outer control in a sample obtained immediately after MCAO, in contrast to that in SO rats (p <0.01). The expression level returned to the control level within 12 hours after MCAO. COX-1 expression was not influenced by MCAO. Pretreatment with MK-801 inhibited the development of bladder overactivity and significantly decreased the expression of COX-2 mRNA in the PTA (p <0.01). Treatment with NS398 before MCAO prevented the development of bladder overactivity in a dose dependent manner and did not influence infarct volume.

CONCLUSIONS

These results indicate that the development of bladder overactivity following MCAO is accompanied by an increase in COX-2 mRNA expression in the PTA and is mediated by NMDA receptor activity. COX-2 in the brain may be a new target for the treatment of neurogenic voiding dysfunction after cerebral infarction.

Functional characterization of a conditionally immortalized mouse epididymis caput epithelial cell line MEPC5 using temperature-sensitive simian virus 40 large T-antigen

A conditionally immortalized epididymis caput cell line, MEPC5, was established by infecting primary cultured mouse epididymis caput cells with a temperature-sensitive simian virus 40 large T-antigen. At a permissive temperature of 33 degrees C, the large T-antigen was expressed and the cells grew continuously. However, the downregulation of T-antigen at a nonpermissive temperature of 39 degrees C and the upregulation of cell density at 33 degrees C were associated with growth arrest and the increased protein expression of p21(waf1), a cell cycle inhibitor. The cells expressed epididymal caput-expressed genes such as phosphatidylethanolamine binding protein, polyoma enhancer activator 3, ME1, sulfated glycoprotein-2 (SGP-2), androgen receptor, and retinoic acid receptor alpha. Interestingly, the expression levels of ME1 and SGP-2 were significantly elevated under the cell growth-restricted conditions. The established mouse epididymis caput epithelial cell line MEPC5 retains some characteristics of differentiated epididymis epithelial cells, and should prove an excellent model for studies of gene expression and the physiological functions of epididymis caput epithelial cells.

Cell-cell interaction underlies formation of fluid in the male reproductive tract of the rat

The epithelia lining the epididymides of many species consists of several cell types. We have provided evidence that the basal cells are essential to the integrated functions of the epithelium. Basal cells, but not principal cells, and other cells in the epididymis express TRPC3 and COX-1. We have isolated basal cells from intact rat epididymis using antibody-coated Dynabeads and subjected them to whole-cell patch-clamp measurement of nonselective cation channel activity, a feature of TRPC3 protein, and Fluo-3 fluorescence measurement of intracellular Ca2+ concentration. The results show that a nonselective cation current blockable by La3+ (0.1 mM), Gd3+ (0.1 mM), or SKF96365 (20 microM) could be activated by lysylbradykinin (200 nM). In cells loaded with Fluo-3, addition of lysylbradykinin (100 nM) caused a sustained increase of intracellular Ca2+. This effect was blocked by Gd3+ (0.1 mM) or SKF96365 (20 microM) and was not observed in Fluo-3-loaded principal cells. Stimulation of basal cell/principal cell cocultures with lysylbradykinin (200 nM) evoked in principal cells a current with CFTR-Cl- channel characteristics. Isolated principal cells in the absence of basal cells did not respond to lysylbradykinin but responded to PGE2 (100 nM) with activation of a CFTR-like current. Basal cells, but not principal cells, released prostaglandin E2 when stimulated with lysylbradykinin (100 nM). The release was blocked by SKF96365 (20 microM) and BAPTA-AM (0.05 or 0.1 mM). Confluent cell monolayers harvested from a mixture of disaggregated principal cells and basal cells responded to lysylbradykinin (100 nM) and PGE2 (500 nM) with an increase in electrogenic anion secretion. The former response was dependent on prostaglandin synthesis as piroxicam blocked the response. However, cell cultures obtained from principal cells alone responded to PGE2 but not to bradykinin. These results support the notion that basal cells regulate principal cells through a Ca2+ and COX signaling pathway.

Immunolocalization and regulation of cystic fibrosis transmembrane conductance regulator in the adult rat epididymis

Cystic fibrosis is the most common serious autosomal recessive condition in whites, and more than 95% of men with cystic fibrosis are infertile. The cystic fibrosis transmembrane conductance regulator (CFTR), a cyclic adenosine monophosphate (cAMP)-regulated chloride channel, has been localized in the efferent ducts; however, to our knowledge, its expression and regulation in the epididymis by testicular factors have not been examined. In the present study, these parameters were examined immunocytochemically by the light microscope with an anti-CFTR antibody in Bouin-fixed, paraffin-embedded control adult rat epididymides and both orchidectomized adult rats with or without testosterone supplementation and efferent duct-ligated rats sacrificed at different time points. In control animals, a thick dense band of immunoperoxidase reaction product was visualized over the apical plasma membrane of the principal cells but not their microvilli. The apical band was prominent only in the corpus and cauda regions. While there was no CFTR expression in basal cells, clear cells of the corpus and cauda regions showed a weak-to-moderate band of apical plasma membrane staining. An examination of orchidectomized, orchidectomized and testosterone, and efferent duct-ligated rats revealed that CFTR was no longer expressed as an intense band on the apical plasma membrane of the principal cells of the corpus and cauda regions. However, under these conditions, an intense apical/supranuclear reaction was noted in the form of small vesicular structures. Clear cells were unaffected by the different experimental treatments. Together, these data indicate that CFTR is expressed in a cell- and region-specific manner and that, while its synthesis in principal cells is not under the control of testicular factors, targeting to the apical plasma membrane is regulated by a testicular luminal factor.

PGE2 stimulates Cl- secretion in murine M-1 cortical collecting duct cells in an autocrine manner

Prostaglandin E2 (PGE2) is thought to be an important modulator of renal ion and water transport, but its effects remain complex and incompletely understood. Here we examined the effects of PGE2 on transepithelial ion transport of M-1 mouse cortical collecting duct cells using short-circuit current (ISC) measurements. Basolateral addition of PGE2 (1 microM) produced a transient peak increase in ISC of 6.3+/-0.8 microA cm(-2) (n=11), followed by a sustained plateau. The PGE2-evoked response was preserved in the presence of 100 micro M apical amiloride with an average peak increase of 10.6+/-1.0 microA cm(-2) (n=23). However, it was greatly diminished in both the presence of apical diphenylamine-2-carboxylic acid (DPC, 1 mM) and the absence of extracellular Cl-, indicating that Cl- secretion had been stimulated. Basolateral PGE2 induced a concentration dependent response, with an EC50 of about 8 nM. Apical addition of PGE2 elicited an ISC response similar to that observed with basolateral PGE2. Furthermore, apical exposure to arachidonic acid (AA) produced a similar increase in ISC, which could be prevented by the cyclooxygenase inhibitor indomethacin, while AA failed to exert an additional effect in the presence of PGE2. Using RT-PCR, we confirmed the expression of the PGE2 (EP) receptor subtypes EP1, EP3 and EP4 but not of EP2 in cultured M-1 CCD cells. We conclude that M-1 cells express functional cyclooxygenase activity and can generate PGE2 which acts in an autocrine manner, causing Cl- secretion.

Regulation of epididymal principal cell functions by basal cells: role of transient receptor potential (Trp) proteins and cyclooxygenase-1 (COX-1)

The epithelia lining the epididymides of many species including the human are known to consist of several cell types. Among them, the principal cells are the most abundant and their functions most extensively studied. There are other cell types such as the narrow cells, clear cells, halo cells and basal cells which are scattered along the duct in lesser number. Although these minority cell types have not been studied to the same extent as the principal cells, it is conceivable that their presence are essential to the integrated functions of the epididymis. In the intact epididymis, basal cells can be seen adhering to the basement membrane forming close contact with the principal cells above them. Work in our laboratory has provided evidence that through local formation of prostaglandins, basal cells may regulate electrolyte and water transport by the principal cells. This regulatory process involves two proteins which are exclusively expressed by the basal cells. They are the transient receptor potential (Trp) proteins, which serve as transmembrane pathways for Ca(2+) influx, and cyclooxygenase 1 (COX-1), a key enzyme in the formation of prostaglandins. The role of the two proteins in the integrated functions of the basal cells as humoral regulators of principal cells is discussed.

Immortalization of epididymal epithelium in transgenic mice expressing simian virus 40 T antigen: characterization of cell lines and regulation of the polyoma enhancer activator 3

In the present study epididymal epithelium was immortalized in transgenic mice by expressing simian virus 40 T antigen under a 5.0-kb mouse glutathione peroxidase 5 promoter (GPX5-Tag1). Epididymal tumorigenesis was associated with an increase in c-Myc expression, and a marked decrease in B-Myc expression, with a 500-fold lower level in the GPX5-Tag1 caput epididymis compared with wild-type caput. Furthermore, B-Myc was undetectable in the immortalized corpus and cauda epididymis. Hence, it is possible that the normally high B-Myc expression in the epididymis is one of the factors contributing to the highly resistant nature of epididymis toward immortalization. Morphologically different epithelial cell lines were generated from the immortalized epididymides, and the cells expressed several genes typical for epididymal epithelium, such as mouse epididymal 1, mouse epididymal protein 9, androgen and estrogen receptors, anion exchangers 2 and 4, retinoic acid receptor alpha, and polyoma enhancer activator 3 (PEA3). This indicated the differentiated status of the cells and their usefulness for analyzing epididymal gene expression in vitro. As PEA3 is considered to be one of the transcription factors responsible for epididymal gene expression, we further studied its regulation in epididymal cells in vitro. The data showed that PEA3 mRNA expression is regulated in the epididymis via protein kinase A and ERK signaling cascades. Inhibiting protein kinase A resulted in up-regulation and inhibiting ERK resulted in down-regulation of PEA3 mRNA, whereas no significant effect on PEA3 expression was found by modulating the protein kinase C, stress-activated p38, phosphoinositol 3-kinase and p70 S6 kinase cascades.

Activation of proteinase-activated receptor 1 stimulates epithelial chloride secretion through a unique MAP kinase- and cyclo-oxygenase-dependent pathway

Proteinase-activated receptor 1 (PAR-1) is activated by thrombin and induces chloride secretion by intestinal epithelial cells. To elucidate further the mechanisms whereby PAR-1 stimulates secretion, monolayers of SCBN intestinal epithelial cells were studied in modified Ussing chambers. Short circuit current responses were determined after basolateral application of thrombin and the PAR-1-activating peptide, Ala-parafluoro-Phe-Arg-cyclohexyl-Ala-Citrulline-Tyr (Cit-NH2) in the presence or absence of a variety of signal transduction and cyclo-oxygenase (COX) pathway inhibitors. Increased kinase activity was monitored by immunoprecipitation and Western blot analysis of target phosphoproteins. The PAR-1-induced chloride secretory response was significantly attenuated by inhibitors of the EGF receptor tyrosine kinase, Src-kinase, MEK1/2, as well as by inhibitors of cytosolic phospholipase (cPL) A2, COX-1 and COX-2. PAR-1-induced activation of cPLA2, as shown by Western blot of phosphoserine residues, was blocked in cells treated with the MEK inhibitor U0126, indicating that the MEK-ERK1/2 MAP kinase pathway mediated PAR-1-induced cPLA2 phosphorylation. Our data show that PAR-1-induced chloride secretion in SCBN cells involves Src, EGF receptor trans-activation, activation of a MAPK pathway, phosphorylation of cPLA2, COX activity, but not PGF2alpha or PGE2. These findings may be of clinical importance in inflammatory diseases of the intestine where secretory dysfunction is evident and thrombin levels are elevated.

COX-dependent and -independent pathways in bradykinin-induced anion secretion in rat epididymis

Lysylbradykinin (LBK) added to the apical or basolateral side of cultured rat epididymal monolayers stimulated a rise in short-circuit current (Isc) due to anion secretion. The concentration-response relationships for the apical and basolateral applications have EC50 value of 0.001 microM. The responses to apical or basolateral application of LBK were blocked by WIN64338, a specific B2 receptor antagonist, but not by Des-Arg9,[Leu8]-BK, a specific B1 receptor antagonist, indicating that the LBK effects were mediated through B2 bradykinin receptors. Experiments to desensitize the B2 receptors by repeated stimulation have demonstrated that the responses to apical or basolateral LBK were due to discrete receptors on the apical or basolateral surface. In epithelia clamped in the Ussing chambers, addition of LBK to the apical or basolateral surface evoked release of PGE2 into the apical and basolateral bathing solutions over the first 10 min following hormone addition. LBK added to the basolateral side elicited a greater release than it was added to the apical side. Pretreatment of the epithelia with piroxicam (5 microM) abolished PGE2 release elicited by apical or basolateral LBK and abrogated the Isc induced by basolateral LBK. However, the rise in Isc induced by apical LBK was reduced by 31.3% only. The anion secretion response to apical LBK was not affected by MDL-12330A, an adenylate cyclase inhibitor, but greatly attenuated by thapsigargin, an inhibitor of intracellular Ca2+ release. However, the reverse effects were seen for basolateral LBK. It is concluded that distinct pathways are involved in the stimulation of anion secretion by apical or basolateral LBK. The response to basolateral LBK was COX-dependent, mediated by PGE2 and involves cAMP as second messenger. In contrast, the response to apical LBK is largely COX-independent, not mediated by PCE2 and involves Ca2+ as intracellular messenger.

Mammalian lipocalin-type prostaglandin D2 synthase in the fluids of the male genital tract: putative biochemical and physiological functions

Prostaglandin D2 synthase (PGDS) is a major epididymal secretory protein in several species. We quantified PGDS in ram and bull semen using a specific antiserum. Strong variations in PGDS concentration existed between animals. In the bull, the highest concentrations were found preferentially in animals with normal or high fertility, as was previously suggested. However, low concentrations were found in males with all ranges of fertility, suggesting that the function of PGDS either is not necessary for male fertility or can be assumed by other proteins when its concentration is low. In the ram and stallion, cDNA and deduced protein sequences of PGDS were obtained by reverse transcription-polymerase chain reaction and showed that PGDS possessed the sequences involved in the three-dimensional folding characteristic of the lipocalin family and a cysteine at position 65 that is involved in the enzymatic activity. The enzymatic activity of PGDS was estimated in the ram by in vitro incubation of epididymal-isolated tubules with radioactive arachidonic acid. Prostaglandin (PG) D2 represented approximately 10% of the PGs produced in the lumen, irrespective of the presence or absence of luminal PGDS, suggesting that this protein is not involved in PGD2 biosynthesis. These results were corroborated by the absence of conversion of PGH2 to PGD2 when epididymal fluids were incubated with PGH2. In the rat, inhibition of PG biosynthesis in vivo by nonsteroidal anti-inflammatory drugs for 60 days did not change spermatozoa mobility or male fertility. It is likely that PGDS, which has a structure similar to that of lipocalin, functions as a lipophilic carrier protein, because we have shown that epididymal PGDS binds retinoic acid and testosterone in vitro.

Cyclooxygenase-2 regulates apoptosis in rat epididymis through prostaglandin D2

In previous studies, cyclooxygenase (COX)-1 and COX-2 isozymes have been detected in the rat epididymis. COX-1 mediates electrolyte and fluid secretion induced by a number of peptide hormones, including bradykinin, angiotensin, and endothelin, via local formation of prostaglandin (PG) E2; however, the physiological role of COX-2 remains largely unknown. Marked apoptotic cell death in the rat epididymis following androgen depletion has been reported. Because expression of both COX isozymes is dependent on androgen, we investigated whether these isozymes control apoptosis in the epididymis. Apoptosis was detected in rat epididymal epithelial cells by in situ staining using the TUNEL method and by the presence of internucleosomal DNA fragmentation using capillary electrophoresis with laser-induced fluorescence detection. Specific COX inhibitors were used to delineate the roles of the 2 isozymes. There was no significant apoptotic cell death in normal and specific COX-1 inhibitor (SC-560)-treated epididymal cells. However, application of a specific COX-2 inhibitor (NS-398) induced apoptosis in a dose- and time-dependent manner. A similar apoptotic effect of COX-2 inhibitor was seen in the in vivo study. The drastic DNA fragmentation induced by COX-2 inhibitor could be reversed completely by PGD2 and partially by PGE2. In addition, the protective effect of PGD2 against COX-2 inhibition was significantly blocked by a PGDP-receptor antagonist, BWA868C. These results indicate that the COX-2 products PGD2 and, to a lesser extent, PGE2 control apoptosis in cultured rat epididymal cells in vitro.

Cocaine- and amphetamine-regulated transcript peptide in the rat epididymis: an immunohistochemical and electrophysiological study

Cocaine- and amphetamine-regulated transcript (CART) is a novel family of peptides, of which CART peptide fragments 55-102 and 62-102 are reported to be the endogenous, physiologically active peptides. Immunohistochemical studies with an antiserum directed against the CART peptide fragment 55-102 revealed CART-like immunoreactive (CART-LI) nerve fibers in the rat epididymis. The number was highest in the cauda epididymis and became progressively fewer toward the caput epididymis; the vas deferens exhibited an abundance of CART-LI fibers. Injection of the retrograde tracer Fluorogold (Fluorochrome, Inc., Englewood, CO) to the junction between the vas deferens and cauda epididymis labeled a large number of neurons in the major pelvic ganglion, some of which were CART-positive. Double-labeling the ganglion sections with tyrosine hydroxylase (TH) and CART antisera revealed that CART-LI and TH-LI were expressed in two distinct populations of ganglion cells. Some of the TH-LI cells in the ganglia, however, were covered with web-like CART-LI endings. The effects of CART peptide 55-102, referred to herein as CART, on anion secretion in the form of short circuit currents (Isc) were assessed in cultured epithelia. The CART (1 to 5 microM) applied to the basolateral or apical side of the cultured epithelia caused no significant responses on Isc, whereas lys-bradykinin (1 microM) produced a large Isc response in the same preparations. Our results show that CART-LI is present in a population of rat pelvic ganglion cells, which may give rise to CART-LI nerve fibers as observed in the vas deferens and the epididymis. The biological function of CART in the rat epididymis is not known, but it apparently is not involved in ion secretion across the epithelium.

Lonidamine and analogue AF2785 block the cyclic adenosine 3', 5'-monophosphate-activated chloride current and chloride secretion in the rat epididymis

The cystic fibrosis transmembrane conductance regulator (CFTR) or the small conductance cAMP-activated chloride channel encoded by the CFTR gene has been shown to play an important role in the formation of the epididymal fluid microenvironment. Mutation of the gene has led to widespread effects on male reproduction. Like other ion channels, CFTR is amenable to pharmacological intervention. Blocking CFTR in the epididymis could in principle lead to disruption of the epididymal fluid environment. We report for the first time two indazole compounds: lonidamine and 1-(2, 4-dichlorobenzyl)-indazole-3-acrylic acid (AF2785) are potent blockers of CFTR in the epididymis. When added to the external solution under whole-cell patch clamp conditions, AF2785 and lonidamine inhibited the cAMP-activated chloride current in rat epididymal cells with apparent IC(50) values of 170.6 and 631.5 microM, respectively; by comparison the IC(50) value for diphenylamine-2-carboxylate, a well-known chloride channel blocker was 1294 microM. In cultured rat epididymal epithelia mounted in a Ussing chamber, AF2785 and lonidamine inhibited the cAMP-stimulated short-circuit current (a measure of chloride secretion) when added to the apical bathing solution with potency greater than any known chloride channel studied. It is proposed that in view of the important role CFTR plays in male reproduction, further study with these and other new indazole compounds for their CFTR blocking actions can provide a new avenue of research into the development of novel male contraceptives.

Androgen control of cyclooxygenase expression in the rat epididymis

Bradykinin and a number of peptide hormones such as angiotensin, endothelin, and vasopressin stimulate anion secretion in rat epididymis via local formation of PGE(2). These effects are mediated by cyclooxygenase (COX)-1 isozyme. The present study was undertaken to assess the androgen control of COX expression in the epididymis. Adult male Sprague-Dawley rats were bilaterally castrated through a scrotal route. Reverse transcription-polymerase chain reaction was used to measure COX-1 and COX-2 mRNAs in the epididymis in normal and castrated rats. Anion secretion in epithelia grown from the epididymides of these rats was studied by the short-circuit current technique. In normal rats, COX-1 and COX-2 mRNAs were detected in the intact epididymis. Elimination of spermatozoa by the technique of efferent duct ligation or flushing out spermatozoa did not affect the expression of either enzyme in the epididymis, indicating that the epithelium, but not spermatozoa, expressed the enzymes. Castration caused a time-dependent decrease in expression of COX-1 and COX-2 mRNAs, which were partially restored upon testosterone replacement. In epithelia cultured from castrated rats, there was a complete loss of bradykinin-induced anion secretion. This effect was reversible upon testosterone replacement. Although epithelia from castrated rats did not respond to bradykinin, they could respond to cAMP, forskolin, and PGE(2) with only 20% loss of response magnitude when compared with epithelia from normal rats. These results suggest that the expression of COX-1 and COX-2 are dependent on androgen. The loss of COX-1 expression after castration correlates with the specific loss of anion secretion induced by bradykinin and possibly other hormones.

Serotonin via 5-HT1B and 5-HT2B receptors stimulates anion secretion in the rat epididymal epithelium

1. The short-circuit current (Isc) technique was used to study the role of 5-hydroxytryptamine (5-HT) in the regulation of anion secretion in cultured rat cauda epididymal epithelia. 2. 5-HT, the 5-HT1B-selective agonist 5-nonyloxytryptamine (5-NOT) and the 5-HT2B-selective agonist alpha-methyl-5-hydroxytryptamine (alpha-methyl-5-HT) added basolaterally stimulated Isc in a dose-dependent manner with EC50 values of 0.4, 20 and 0.3 microM, respectively. No other agonists for 5-HT receptors had any effect. 3. The pattern of responses to 5-HT was biphasic. Pretreating the tissues with the 5-HT1B-selective antagonist isamoltane (200 microM) and the 5-HT2B-selective antagonist rauwolscine (200 microM) inhibited the rapid transient phase by 55 and 45 %, whereas the sustained phase could only be blocked by rauwolscine. 4. Removal of chloride or bicarbonate or both from the normal Krebs-Henseleit solution reduced the responses to 5-HT, 5-NOT and alpha-methyl-5-HT to varying degrees. The results suggest that 5-HT1B- and 5-HT2B-mediated responses were mainly due to chloride and bicarbonate secretion, respectively. 5. Manipulation of the cAMP and Ca2+ signal transduction pathways with chemical agents provided evidence that the responses to 5-HT were mediated through cAMP. 6. Piroxicam pretreatment abolished the Isc response to alpha-methyl-5-HT but not to 5-NOT, indicating that the 5-HT2B-mediated response, but not the 5-HT1B-mediated response, is dependent on prostaglandin synthesis. 7. Immunohistochemical studies showed that 5-HT-like immunoreactivity was detected in nerve fibres and in small granular cells surrounding the epididymal tubules. 8. It is suggested that the 5-HT released from serotonergic nerve endings and/or from mast cells regulates electrolyte and fluid secretion in the epididymis.