The concentration of carnitine in the luminal fluid of the testis and epididymis of the rat and some other mammals.

Luminal fluid was collected by micropuncture techniques from the testis and epididymis of the rat, hamster, rabbit, boar and ram and the concentration of free L-carnitine in the fluid was estimated using enzymic methods. Carnitine was present in the testicular fluid of the rat in concentrations less than 1 mM but increased down the epididymis to reach 53 mM in luminal fluid from the cauda epididymidis, approximately 2000 times higher than in blood plasma. A high concentration was first found in the luminal fluid from the distal caput epididymidis, at about the point where the spermatozoa become motile. Carnitine was also present in the epididymal luminal fluid of the other species studied; the amounts were not as high as those in the rat but were still higher than those in blood plasma.     

An epididymal form of cauxin, a carboxylesterase-like enzyme, is present and active in mammalian male reproductive fluids

Mass spectrometric analysis of a prion protein (PrP)-containing complex isolated from ram cauda epididymal fluid revealed a protein that showed homology to a carboxylesterase-like protein previously identified in cat urine (cauxin). Using anti-cauxin antibodies, immunoreactive bands were detected in corpus and cauda epididymal fluid from all mammals tested (ram, boar, mouse, and cat). In the ram, the protein was also present in seminal fluid but not found to be associated with sperm. The bands reacting with the anti-cauxin antibody coincided with those having esterase activity in a zymographic assay and its levels paralleled the esterase activity of native epididymal fluids. A partial nucleotide sequence of 1143 bp, corresponding to 380 amino acids, was obtained by RT-PCR amplification from total RNA from the corpus epididymis (zone 6). The deduced protein sequence shows a high degree of homology (up to 90%) with the different cauxin proteins found in databases but only up to 60% with other known carboxylesterases. By PCR, strong mRNA expression was found in the corpus and cauda epididymis, while the testis, kidney, and caput epididymis had low expression. No mRNA was detected in the lung, heart, or liver. These data demonstrate that an epididymal form of the cauxin enzyme is secreted into mammalian epididymal fluid. In the ram, it is associated with a high molecular-weight PrP-associated complex and may be responsible for the majority of the esterase activity in the cauda epididymal fluid of this species.     

A 105- to 94-kilodalton protein in the epididymal fluids of domestic mammals is angiotensin I-converting enzyme (ACE); evidence that sperm are the source of this ACE

SDS-PAGE analysis of luminal fluid from the ram testis and epididymis revealed a protein of about 105 kDa in the fluid in the caput epididymal region. The molecular mass of this fluid protein shifted from 105 kDa to 94 kDa in the distal caput epididymidis and remained at 94 kDa in the lower regions of the epididymis. The possible sperm origin of this protein was suggested by the decrease in intensity of a 105-kDa compound on the sperm plasma membrane extract and by its total disappearance from the fluid of animals with impaired sperm production caused by scrotal heating. The 94-kDa protein was purified from ram cauda epididymal fluid, and a rabbit polyclonal antiserum was obtained. This antiserum showed that membranes of testicular sperm and sperm from the initial caput were positive for the presence of an immunologically related antigen. The protein was immunolocalized mainly on the flagellar intermediate piece, whereas in some corpus and caudal sperm, only the apical ridge of the acrosomal vesicle was labeled. The purified protein was microsequenced: its N-terminal was not found in the sequence database, but its tryptic fragments matched the sequence of the angiotensin I-converting enzyme (ACE). Indeed, the purified 94-kDa protein exhibited a carboxypeptidase activity inhibited by specific blockers of ACE. All the soluble seminal plasma ACE activity in the ram was attributable to the 94-kDa epididymal fluid ACE. The polyclonal antiserum also showed that a soluble form of ACE appeared specifically in the caput epididymal fluid of the boar, stallion, and bull. This soluble form was responsible for all the ACE activity observed in the fluid from the distal caput to the cauda epididymidis in these species. Our results strongly suggest that the epididymal fluid ACE derives from the germinal form of ACE that is liberated from the testicular sperm in a specific epididymal area.     

Evidence for the presence of oxytocin in the ovine epididymis

The testes of several species contain oxytocin and/or neurophysin, but the content or localization of oxytocin in epididymal tissue has not been studied. The present study was undertaken to localize oxytocin and neurophysin in epididymal tissue of the ram, and to quantify oxytocin in the ductus epididymidis and fluids entering and leaving the ductus epididymidis. Neurophysin was not detected in the epididymis; thus, synthesis of oxytocin by the epididymis is unlikely. Immunohistochemical localization of oxytocin was confined to the epithelium and capillaries. Oxytocin immunostaining was most intense for epithelium of the caput and declined in corpus and cauda regions. However, based on radioimmunoassay, no difference in oxytocin concentration was detected among regions of the epididymis. Since rete testis fluid entering and cauda epididymal fluid leaving the epididymis contained at least fourfold more oxytocin than testicular venous plasma, it was concluded that regional differences in epithelial concentration of oxytocin may have been masked by oxytocin contained in the luminal fluid. It was concluded further that the epididymis of the ram does not synthesize oxytocin, but about 22 ng/day enters the epididymis in rete testis fluid. Most of this luminal oxytocin apparently is absorbed by the epithelium of the caput epididymidis, with additional adsorption in the corpus and cauda. Although a role for oxytocin in ductal contractility cannot be excluded, it is more likely that the luminal oxytocin influences epithelial or sperm function.     

ATP-induced reactivation of ram testicular, cauda epididymal, and ejaculated spermatozoa extracted with Triton X-100

It was possible to demembrante and reactivate not only freshly collected testicular, cauda epididymal, and ejaculated ram sperm but also sperm that had been stored for several days at 0 degrees C and for several months at -196 degrees C in rete testis fluid or egg yolk citrate media. Sperm were usually washed free of seminal plasma before demembranation, but this was not essential for reactivation. Bovine serum albumin (1.0%) in the wash medium increased the survival of sperm, but more than 0.25% in the extraction medium decreased reactivation. A macro-molecular component of cauda epididymal fluid also inhibited the reactivation of testicular sperm. Triton X-100 concentrations between 0.01% and 1.00% in the extraction medium were satisfactory for demembranating the sperm. Rapid cooling (i.e., cold shock) mimicked the effect of detergent in making the sperm responsive to added ATP and demonstrated that damage to ram sperm in cold shock does not involve the axoneme. Ejaculated and cauda sperm were reactivated immediately on addition of ATP and activity persisted for up to 10 min. Testicular sperm, on the other hand, required about 4 min to become fully reactivated. The optimal ATP concentration for activation of sperm was 0.1-1.0 mM. Magnesium ions (0.1-1.0 mM) were important for reactivation, and testicular sperm required a higher magnesium concentration than did cauda or ejaculated sperm. Manganese ions were almost as effective as magnesium for reactivating cauda epididymal and ejaculated sperm. Cobalt and cadmium ions were much less active for cauda and ejaculated sperm and none of these ions were effective for testicular sperm. Fluoride (25-50 mM) inhibited reactivation. The presence of 50 microM cAMP in the extraction medium or preincubation of testicular sperm with theophylline or caffeine increased low levels of activation, but this was not evident with ejaculated or cauda sperm. We conclude that the motor apparatus is already functionally assembled in spermatozoa on leaving the testis, but some fine adjustment must take place during maturation in the epididymis.     

Identification of the bull sperm p80 protein as a PH-20 ortholog and its modification during the epididymal transit

We have identified an 80 kDa protein in ejaculated bull spermatozoa (p80) which is found in acrosomal and post-acrosomal areas of the head. It has a hyaluronidase activity and shares homologies with PH-20, a sperm surface glycoprotein involved in sperm-egg interaction. The aim of the present study was to characterize bull sperm p80 protein at the nucleic and amino acid levels to determine whether it is the bovine PH-20 ortholog. The complete nucleotide sequence determined by RT-PCR, 3' and 5' RACE show that bull p80, displays identity with the PH-20 nucleotide and amino acid sequences. Messenger RNA and protein expressions determined by Northern blot and immunohistochemistry revealed that the protein is testicular (expressed in spermatocytes and spermatids). The localization of p80 on spermatozoa, determined by indirect immunofluorescence using a monoclonal antibody, shows the protein in acrosomal and post acrosomal areas of the head with an increase in the signal intensity as sperm progress through the epididymis. Post-translational modifications of the protein were investigated during the epididymal maturation by Western blot on protein extracts from sperm collected in the caput, corpus and cauda portions of bull epididymis. Glycolysation status of sperm p80 protein on proteins from ejaculated and epididymidal sperm was investigated. Result show that the glycosylation status is modified as spermatozoa migrate through the epididymis. Hyaluronidase activity evaluated in protein extracts from spermatozoa of the three different epididymal sections revealed that the activity is higher at pH 7 than 4 and is not affected by epididymal maturation. These data strongly suggest that p80 is the bovine PH-20.     

Glycoproteins: a variable factor in surface transformation of ram spermatozoa during epididymal transit

To determine sequential surface glycoprotein changes in ram spermatozoa during epididymal maturation, labeling procedures were used that were specific for galactosyl, galactosaminyl, and sialyl residues. Spermatozoa and fluids were collected from the rete testis through surgically inserted catheters or flushed from the lumen of selected regions of the epididymis: i.e., caput, proximal and distal corpus, and cauda epididymidis. Ejaculated spermatozoa were collected by electrical stimulation. Electrophorectic analysis of galactose (GAO)-sodium boro[3H]hydride (NaB3H4)-treated spermatozoa revealed a sharp overall decrease in carbohydrate residue labeling during sperm transport through the efferent ducts and caput epididymidis, whereas several high molecular weight components in the 600K to 250K zone persisted throughout epididymal transit. Preincubation of spermatozoa with neuraminidase (NEUA) exposed galactose residues that had not been labeled with GAO alone (i.e., 97K, 43K, 24K) in both cauda epididymal and ejaculated spermatozoa. Treatment with sodium metaperiodate-NaB3H4 labeled many of the surface components displayed by NEUA-GAO-treated spermatozoa and revealed an overall shift in sialyl residue labeling from high molecular weight components in immature testicular spermatozoa to low molecular weight components in mature cells. The labeling procedures applied allowed only a qualitative interpretation of the results and they presumably represent the minimum possible changes. Nonetheless, our results demonstrate that glycoproteins are a major factor in surface transformations of ram spermatozoa in the epididymis, especially during the initial stages of maturation.     

Capacity of rete testicular and cauda epididymal boar spermatozoa to undergo the acrosome reaction and subsequent fusion with egg plasma membrane

The capacity to undergo the acrosome reaction and subsequent fusion with egg plasma membrane was examined in rete testicular and cauda epididymal spermatozoa from boars. Sperm penetration assay using zona-free hamster eggs demonstrated that the penetration rates for rete testicular spermatozoa preincubated for induction of the acrosome reaction for 2 and 3 h were 55% and 97%, respectively. However, most of the eggs (93%) were penetrated with polyspermy by cauda epididymal cells preincubated for 2 h. Results obtained by the triple-stain technique revealed the percentages of acrosome-reacted spermatozoa in the rete testicular and cauda epididymal samples preincubated for 3 h to be 61% and 74%, respectively. These results indicate that many rete testicular spermatozoa possess the capacity to undergo the acrosome reaction and subsequent fusion with egg plasma membrane in vitro, which appears to be completely established only after sperm transit through at least the proximal part of the epididymis. © 1993 Wiley-Liss, Inc.     

Amino acids in ram testicular fluid and semen and their metabolism by spermatozoa

1. The testis of the ram secretes considerable amounts of amino acids (200μmoles/day) into the fluid collected from the efferent ducts. The principal amino acid in this testicular fluid is glutamate, which is present in concentrations about eight times those in testicular lymph or in blood from the internal spermatic vein. 2. The concentration of glutamate in seminal plasma from the tail of the epididymis is about ten times that in testicular fluid, and, though glutamate is the major amino acid in ejaculated seminal plasma, its concentration is less than in epididymal plasma. 3. After the intravenous infusion of [U-¹⁴C]glucose, labelled glutamate was found in the testicular fluid. Radioactivity was also detected in alanine, glycine, serine plus glutamine and aspartate. Alanine had the highest specific activity, about 50% of the specific activity of blood glucose. 4. When [U-¹⁴C]glutamate was infused, the specific activity of glutamate in testicular fluid was only about 2% that in the blood plasma. 5. Testicular and ejaculated ram spermatozoa oxidized both [U-¹⁴C]glutamate and [U-¹⁴C]leucine to a small extent, but neither substrate altered the respiration from endogenous levels. 6. No radioactivity was detected in testicular spermatozoal protein after incubation with [U-¹⁴C]glutamate or [U-¹⁴C]leucine. Small amounts of radioactivity were detected in protein from ejaculated ram spermatozoa after incubation with [U-¹⁴C]glutamate. 7. The carbon of [U-¹⁴C]glucose was incorporated into amino acids by testicular spermatozoa; most of the radioactivity occurred in glutamate.     

In vivo secretion and association of clusterin (SGP-2) in luminal fluid with spermatozoa in the rat testis and epididymis.

Clusterin (sulfated glycoprotein-2) is a heterodimeric glycoprotein synthesized and secreted by rat Sertoli cells. An antigenically similar form is synthesized and secreted by the epididymis. The goal of this study was to define the epididymal regions in which clusterin is present and the regions in which clusterin is secreted and interacts with developing spermatozoa. Seminiferous tubule (STF), caput, corpus, and cauda fluids were collected by micropuncture and/or microperfusion and two-dimensional Western blot analysis was performed with a polyclonal antibody directed against Sertoli cell clusterin. Clusterin was found in both STF and epididymal fluid. STF contained predominantly the clusterin heavy chain (45 kd); however, a 70 Kd heterodimer was present under nonreducing conditions. Two subunits of clusterin with lower molecular weights (41 kd, heavy chain; 32 kd, light chain) and higher isoelectric points were present in the luminal fluid of all epididymal regions. The intraluminal levels of the heavy and light chains decreased from caput to cauda. Analysis by two-dimensional gel electrophoresis of proteins secreted directly into the epididymal luminal fluid revealed that clusterin was secreted by caput epithelium and not by the corpus and cauda epithelium. Western blots of membrane extracts from testicular, caput, and cauda spermatozoa revealed that testicular clusterin was associated with testicular sperm and epididymal clusterin with predominantly caput sperm. Our findings suggest that clusterin is secreted into the caput epididymal lumen, where it binds to sperm and then dissociates from sperm to be endocytosed by cells of the distal epididymal epithelium.     

Germinal angiotensin I-converting enzyme is totally shed from the rodent sperm membrane during epididymal maturation

Acquisition of sperm fertilizing ability is due, in part, to the reorganization of plasma membrane proteins that occurs during epididymal sperm transit. Using polyclonal antibodies against angiotensin I-converting enzyme (ACE), we showed that this enzyme is immunolocalized mainly on the middle piece of rat and mouse testicular sperm and with less intensity along the initial part of the principal piece of the flagellum. In both species, only some sperm from the caput epididymis were still reactive, whereas no labeling was observed on cauda epididymal sperm. The 105- to 110-kDa germinal ACE was absent from the rat testicular fluid but appeared in the fluid of the anterior epididymis. Thereafter, its molecular weight shifted to 94 kDa in the corpus epididymal fluid and remained at this weight in the caudal region. The 105- to 110-kDa immunoreactive protein was present in testicular rat sperm extract but was completely absent from epididymal sperm extracts. Western blot analysis of testicular and epididymal tissue extracts from the rat and mouse also confirmed that the germinal enzyme was absent from the epididymal sperm cell. Our results demonstrated that the rodent germinal ACE is released from the testicular sperm membrane when sperm enter the epididymis, a process similar to that observed in domestic mammals. This result is discussed in view of the suggested role for this enzyme in sperm fertility.     

Changes in the protein composition of rat spermatozoa during maturation in the epididymis

Spermatozoa from the testis and cauda epididymidis were solubilized by detergent treatment and electrophoresis on SDS polyacrylamide gels revealed that the relative amounts of 13 detergent-extractable proteins decreased during passage of spermatozoa through the epididymis, 6 increased, whilst the remainder showed little or no change. Lactoperoxidase-catalysed iodination of plasma membrane proteins showed that the components carrying most of the label in testicular spermatozoa had Mr values of 110 000, 94 000, 84 000, 55 000 and 42 000 whereas on cauda epididymal spermatozoa the Mr values were 47 000, 24 000, 17 000, 14 500 and 13 500. Substantial differences were also noted in the protein composition of rete testis fluid and cauda epididymal plasma. The results support the concept that there is a considerable reorganization of the molecular architecture of the plasma membrane of spermatozoa during maturation in the epididymis.     

Identification of a major secretory glycoprotein from rat epididymis: interaction with spermatozoa

A polypeptide with molecular mass of 17 kDa has been partially purified and identified as a major secretory glycoprotein in the rat epididymis. It is phosphorylated and contains high mannose-type oligosaccharides with 5 and 6 mannose units predominantly. These sugar residues are sufficiently exposed in the molecule to be released by endo-beta-N-acetylglucosaminidase H without prior denaturation or protease digestion. Specific binding of the glycoprotein to testicular spermatozoa was demonstrated with Ka 0.2 x 10(9) M-1 and 17,200 sites per cell, while no binding to epididymal spermatozoa was detectable. Direct labeling of surface proteins on cauda epididymis spermatozoa revealed the presence of a major band of 16.2 kDa, which may be equivalent to GP17. The interaction of the epididymal secretory protein with sperm suggests a possible role in the maturation process.     

Glutathione-independent prostaglandin D2 synthase in ram and stallion epididymal fluids: origin and regulation

Microsequencing after two-dimensional electrophoresis revealed a major protein, glutathione-independent prostaglandin D2 synthase (PGDS) in the anterior epididymal region fluid of the ram and stallion. In this epididymal region, PGDS was a polymorphic compound with a molecular mass around 30 kDa and a range of pI from 4 to 7. PGDS represented 15% and 8% of the total luminal proteins present in this region in the ram and stallion, respectively. The secretion of the protein as judged by in vitro biosynthesis, and the presence of its mRNA as studied by Northern blot analysis, were limited to the proximal caput epididymidis. Using a specific polyclonal antibody raised against a synthetic peptide, PGDS was found throughout the epididymis, decreasing in concentration toward the cauda region. PGDS was also detected in the testicular fluid and seminal plasma by Western blotting. Castration and efferent duct ligation in the ram led to a decrease in PGDS mRNA and secretion. PGDS mRNA was not detected in the stallion 1 mo after castration, and it was restored by testosterone supplementation. This study showed that PGDS is present in the environment of spermatozoa throughout the male genital tract. Its function in the maturation and/or protection of spermatozoa is unknown.     

The phospholipid-binding protein of the reproductive tract of the bull — Effect on the removal of spermatozoal cytoplasm droplets in other species and influence of antibodies on its reactivity

The phospholipid-binding protein (PBP) isolated from bull seminal vesicle fluid removed cytoplasm droplets not only from bull, but also from ram, boar and rabbit epididymal spermatozoa. However, the presence of a protein cross-reacting with anti-PBP antisera was demonstrated by immunofluorescent staining in ram seminal vesicles and ampullae. In contrast to PBP from bull, the ram PBP-like protein did not lyse bull or ram erythrocytes. Rabbit antiserum against PBP only negligibly reduced the ability of PBP to remove cytoplasm droplets from bull epididymal spermatozoa, but it inhibited the haemolytic effect of the protein.     

Novel molecular species of sphingomyelin containing 2-hydroxylated polyenoic very-long-chain fatty acids in mammalian testes and spermatozoa.

Polyenoic very-long-chain fatty acids (VLCFA) have been shown to be localized in unusual molecular species of sphingomyelin in the testes and spermatozoa of the ram, bull, rat, and boar and in the spermatozoa of man. The composition of polyenoic VLCFA-sphingomyelin was comparable in the testes and spermatozoa of each mammalian species; however, the sphingolipid was more concentrated in spermatozoa. The composition of testicular and spermatozoan polyenoic VLCFA-sphingomyelin differed considerably between animal types. Human spermatozoa mainly contained n-6 polyenoic VLCFA with two to four double bonds and even-carbon chain lengths up to 32. In ram and bull testes and spermatozoa, n-3 and n-6, tetra-, penta-, and hexaenoic VLCFA with even-carbon chain lengths up to 34 predominated. In rat and boar testes and spermatozoa, the polyenoic VLCFA were mainly n-6 derivatives with three to five double bonds and even- and odd-carbon chain lengths up to 34. The testes and spermatozoa of the latter two animal species contained 2-hydroxylated, in addition to non-hydroxylated, polyenoic VLCFA in sphingomyelin. This is the first time that 2-hydroxylated polyenoic VLCFA have been recognized in biological systems. Non-hydroxylated polyenoic VLCFA were initially observed in the sphingomyelin of rat testes 25 days after birth, followed by 2-hydroxylated derivatives at 30 days. The total amount of polyenoic VLCFA associated with rat testicular sphingomyelin increased dramatically from 25 to 40 days of postnatal life and then remained constant to 60 days (sexual maturity). The ratio of 2-hydroxylated to non-hydroxylated polyenoic VLCFA increased during this period. Polyenoic VLCFA-sphingomyelin seems to occur exclusively in the testes and spermatozoa of mammals, and it is postulated that this lipid plays a role in reproduction.     

Lipid diffusion in the plasma membrane of ram and boar spermatozoa during maturation in the epididymis measured by fluorescence recovery after photobleaching

Maturation of spermatozoa in the epididymis involves remodelling of many protein and lipid components of the plasma membrane. In this investigation we have examined whether (a) diffusion of lipid molecules in the surface membrane changes during epididymal maturation; (b) diffusion is spatially restricted; and (c) differences in lipid diffusion can be related to known changes in membrane composition. For this purpose we have used the technique of fluorescence recovery after photobleaching (FRAP) to measure diffusion of the lipid reporter probe ODAF (5‐(octa‐decanoyl)aminofluorescein) in spermatozoa from two species: ram, where substantial changes in membrane lipids occur during passage through the epididymis, and boar, where there are relatively few changes. Results on ram spermatozoa show that between the testis and cauda epididymidis, diffusion coefficients values (D) for ODAF increase significantly in all the surface domains. Percentage recovery values (%R) remain constant irrespective of maturational status. In boar spermatozoa, however, D and %R values do not change significantly between epididymal regions. Cholesterol, which has widespread effects on the behaviour of lipid molecules in cell membranes, was visualized by binding of filipin. In both species filipin was concentrated over the acrosomal domain and cytoplasmic droplet of testicular spermatozoa, but in the epididymis it had a heterogenous distribution over the whole head and tail. These results are discussed in relation to the establishment and maintenance of lipid domains in spermatozoa and their influence on development of fertilizing capacity. Mol. Reprod. Dev. 52:207–215, 1999. © 1999 Wiley‐Liss, Inc.     

Secreted epididymal glycoprotein 2D6 that binds to the sperm's plasma membrane is a member of the beta-defensin superfamily of pore-forming glycopeptides

The plasma membrane of spermatozoa undergoes substantial remodeling during passage through the epididymal duct, principally because of changes in phospholipid composition, exchange of glycoproteins with epididymal fluid, and processing of existing membrane proteins. Here, we describe the interaction of an epididymal glycoprotein recognized by monoclonal antibody 2D6 with the plasma membrane of rat spermatozoa. Our goals have been to understand more about the mechanism of secretion of epididymal glycoproteins, how they interact with the sperm's plasma membrane, and their disposition within it. Reactivity to 2D6 monoclonal antibody was first detectable in principal cells in the distal caput epididymidis and as a soluble high-molecular-weight complex in the secreted fluid. It was not associated with membranous vesicles in the duct lumen. On cauda spermatozoa 2D6 monoclonal antibody recognized a 24-kDa glycoprotein (the subunit of a disulfide cross-linked homodimer of 48 kDa) that was present on the plasma membrane overlying the sperm tail. Binding of 2D6 to immature spermatozoa in vitro was cell-type specific but not species specific, and the antigen could only be extracted from cauda spermatozoa with detergents. Sequencing studies revealed that the 24-kDa glycoprotein was a member of the beta-defensin superfamily of small pore-forming glycopeptides of which several others (ESP13.2, Bin1b, E-2, EP2, HE2) are found in the epididymis. This evidence suggests that some epididymal glycoproteins are secreted into the luminal fluid in a soluble form and bind to specific regions of the sperm's surface via hydrophobic interactions. Given the antimicrobial function of beta-defensins, they have a putative role in protecting spermatozoa and the epididymis from bacterial infections.     

gamma-glutamyl transpeptidase and related enzyme activities inthe reproductive system of the male rat.

The γ-glutamyl transpeptidase activity of the epididymis is much higher than that of the several other organs of the reproductive system of the male rat. The epididymal caput has much more activity than the epididymal cauda. Relatively low activity was found in spermatozoa. The enzyme is present in the epididymal fluid in a particulate form suggesting that it originates from membranes of epididymal epithelial cells. The epididymal caput exhibits high γ-glutamylcysteine synthetase activity indicating an active γ-glutamyl ycle in this tissue, which plays an important role in transport phenomena.     

Cauda epididymal sperm motility: a comparison among five species

Rat spermatozoa are immotile in the cauda epididymidis and are kept quiescent by a protein which increases viscoelasticity of cauda luminal fluid. How species-specific this phenomenon is, is unknown. In the present study, the motility of cauda epididymal spermatozoa of rats, hamsters, guinea pigs, rabbits and humans have been investigated. Sperm motility was observed in undiluted cauda sperm samples and in samples diluted with physiological diluents with or without Ca++, among others. Hamster sperm were studied in further detail to determine if the motility inhibiting factor in hamster cauda lumen fluid had characteristics similar to those previously described in the rat. Cauda fluid protein concentrations and apparent viscoelasticity were also determined and related to cauda sperm motility in all species. The results demonstrated that all species studied except rabbits have immotile sperm in their native cauda fluid and that additional Ca++ is not a factor in the initiation of motility. Cauda sperm immotility is not always related to fluid viscosity, however, so other as yet unknown mechanisms must be called upon in some species. The vigorous motility of rabbit spermatozoa in their native fluid implies that a fundamental difference exists in the relationship between epididymis and spermatozoa in rabbits from that observed in other species.