Passage Of Spermatozoa Research Articles

Structural features of the abalone egg extracellular matrix and its role in gamete interaction during fertilization.

Abalone eggs are surrounded by a complex extracellular coat that contains three distinct elements: the jelly layer, the vitelline envelope, and the egg surface coat. In this study we used light and electron microscopy to describe these three elements in the red abalone (Haliotis rufescens) and ascribe function to each based on their interactions with sperm. The jelly coat is a spongy matrix that lies at the outermost margin of the egg and consists of variably sized fibers. Sperm pass through this layer with their acrosomes intact and then go on to bind to the vitelline envelope. The vitelline envelope is a multilamellar fibrous layer that appears to trigger the acrosome reaction after the sperm binding. Next, sperm release lysin from their acrosomal granules, a nonenzymatic protein that dissolves a hole in the vitelline envelope through which the sperm swims. Sperm then contact the egg surface coat, a network of uniformly sized filaments lying directly above the egg plasma membrane. This layer mediates attachment of sperm, via their acrosomal process, to the egg surface.

Sperm migration through the female genital tract of the New World monkey Cebus apella.

This study was designed to characterize sperm migration in the female genital tract of Cebus apella. Forty-eight cycles of eighteen females mated during the periovulatory period were studied. Eggs were searched for and spermatozoa were counted in segmental flushings of the genital tract performed in situ 1-7 h, 19-31 h, or 45-56 h after coitus. Of 14 eggs recovered, 8 were fertilized, thus assuring a reasonable normality of prefertilization phenomena in both males and females. A downward gradient of several orders of magnitude in sperm numbers was recognized from cervix to ampulla, particularly over the first interval. The population in the cervix and uterus decreased progressively between the first and last interval. Spermatozoa were recovered from the ampulla as early as 1 h after mating. Different trends were observed in the isthmus and ampulla. From the first to the last interval, sperm numbers decreased in the ampulla, but not in the isthmus. The number of spermatozoa recovered from the ampulla of the ovulatory side 1-31 h postcoitum was higher in postovulatory than in preovulatory monkeys, while in the nonovulatory side, recovery was similar in the two conditions. This findings suggests that the passage of spermatozoa up to the site of fertilization is under local control and is synchronized with ovulation. The pattern of sperm migration that emerges from these data bears similarities to the pattern in nonprimate species as well as distinctive features. A unique feature in common with the pattern in human is the early establishment of a fairly abundant and persistent sperm population in the ampulla.

Sperm drinking by female catfishes: a novel mode of insemination

We report on unique reproductive behaviour and a new mode of egg insemination in a small catfish Corydoras aeneus (Callichthyidae). A male courts a female by presenting his abdomen to her. Before releasing eggs, the female attaches her mouth to the male's genital opening and directly drinks his sperm. The sperm pass through her intestine and are discharged together with eggs into the ‘pouch’ formed by her pelvic fins. Thus, eggs are mixed with fresh non-dispersed sperm in an enclosed space, ensuring effective insemination. This mode of insemination is novel to fishes, but is likely not restricted to catfishes of the genus Corydoras.

Follicular oocyte maturation and sperm penetration in vitro in the silver fox ( Vulpes vulpes)

Of the 950 follicular oocytes recovered, a high percentage (12%) were found to be degenerate and 7% had undergone germinal vesicle breakdown. Incubation of the remaining cumulus oocyte complexes in TCM 199 medium supplemented with 10% fetal calf serum, with or without human chorionic gonadotropin (HCG), in a 5% CO 2 in air atmosphere at 38.5°C resulted in expansion of the cumulus in 45% of the HCG supplemented group and in 22% of the non-supplemented group. Cumulus expansion was accompanied by germinal vesicle breakdown in almost all instances. Nineteen per cent of oocytes reached Metaphase I or II by 48 h of culture in the HCG supplemented group. Following insemination in vitro, decondensing sperm nuclei were found in the vitellus of 11% of the oocytes that had not been cultured and in the vitellus of 18% of those that had been cultured for 48 h. The results presented indicate that: (1) silver fox follicular oocytes can be matured in vitro, (2) HCG can promote development of the cumulus oocyte complexes, (3) maturation of the oocytes is not required for sperm passage through the zona pellucida, (4) the spermatozoa required capacitation which took approximately 5–8 h in vitro.

Fertilization of the lamprey (Lampetra japonica) eggs: Implication of the presence of fast and permanent blocks against polyspermy

AbstractWe have carried out a morphological examination to analyze the mechanism of monospermic fertilization in the lamprey, Lampetra japonica. Upon insemination, many sperm passed through a “tuft” of jelly that is found only on the animal pole area of the egg and underwent the acrosome reaction after they came into contact with the outer surface of the two‐layered vitelline envelope. The acrosomal filaments were admitted into the envelope and their tips touched the ooplasmic surface. The Hoechst dye transfer method revealed that a single sperm showed intense fluorescence before its nucleus penetrated the vitelline envelope; this indicated the actual fusion of the gametes. No other sperm with acrosomal filaments fluoresced, however. These findings indicate that a fast block against polyspermy is established at the plasma membrane level and prevents additional sperm‐egg fusion.The separation of the ooplasmic surface from the vitelline envelope (perivitelline space formation) was initiated beneath the margin of the animal pole region and progressed toward the animal and vegetal poles of the egg. At this stage, the head of a fertilizing sperm passed through the thickness of the vitelline envelope. The nuclei of supernumerary sperm were unable to enter the inner layer of the vitelline envelope. During the early phase of the perivitelline space formation at the animal pole region, many thin threads and one, or a small number, of the thick projection(s) of the ooplasm connected the envelope with the vitellus. A fertilizing sperm invariably moved along one of the thin threads and was embedded in the ooplasm at the animal pole region. Cytochalasin B inhibited sperm from passing through the inner layer of the vitelline envelope. When ionophore‐activated eggs were inseminated, the tips of the acrosomal filaments were prevented from touching the ooplasmic surface by the intervening presence of the perivitelline space. None of these sperm passed through the vitelline envelope. These findings suggest that the fusion of the acrosomal filament with the egg plasma membrane is a prerequisite for the passage of sperm through the inner layer of the vitelline envelope. Furthermore, actin‐mediated ooplasmic activity is probably involved in the passage. We conclude that the formation of the perivitelline space at the animal pole region contributes to the establishment of a permanent block against polyspermy in the lamprey egg. © 1994 Wiley‐Liss, Inc.

Chromatin condensation in hamster sperm: A flow cytometric investigation

In this study we have used acridine orange staining, as described by Evenson (1990), to follow changes in DNA packaging as they occur in hamster spermatozoa which have left the testis and are undergoing maturation in the epididymis. Measurement of the green and red fluorescent intensities of hamster sperm nuclei by flow cytometry demonstrated a decrease in acridine orange binding to DNA as sperm made their way from proximal corpus epididymis to the vas deferens. Using sperm from the cauda epididymis of the mature hamster as the standard, a method was developed for estimating the % of cells in a given sample that have matured with regard to DNA packaging. Staining with bromobimane was used to determine the extent of sulfhydryl oxidation in the nuclei. It was seen that sulfhydryl oxidation occurred mainly in the cauda epididymis whereas another process in chromatin condensation occurred earlier, during sperm passage through the caput epididymis. This earlier process could be mimicked by incubating sperm nuclei with alkaline phosphatase, suggesting that it consists of removal of phosphate in protamine.

An ultrastructural study of epithelium differentiation in the human fetal fallopian tube.

The epithelial structure of the developing human fetal Fallopian tube has been studied systematically by parallel light, transmission and scanning electron microscopy. The specimens for this study were collected from spontaneous abortions at the 14th, 18th, 20th and 22nd weeks and from cases of intrauterine fetal death at the 24th and 31st weeks (hydrocephalus). The epithelium lining the wall of the female genital ducts was pseudostratified in a columnar fashion. It consisted of differentiating ciliated and microvillous cells and some degenerating elements. Microvillous cells-by far the most abundant in the early phases of tubal development-often showed a solitary cilium. Ciliated elements, though always less numerous than microvillous cells, were more densely concentrated on the developing fimbriae and at the uterotubal junction than in the ampulla. On the mucosal surface of the same regions, rounded intercellular holes delimited many crypts, from which ciliated elements sometimes sprouted. Notable aspects of cell proliferation and ciliogenesis were commonly observed and are likely to be related to circulating estrogens. These ultrastructural data indicate that the typical pattern of the adult oviduct is already sketched in fetal life. Furthermore, a strategic gathering of cilia was noted primarily at the sites of the developing oviduct, which will serve to mediate the passage of sperm and/or ova and promote fertilization in adult life.

Roles of pH and cyclic adenosine monophosphate in the acquisition of potential for sperm motility during migration from the sea to the river in chum salmon.

In the natural process of the migration of chum salmon from the sea to the river, spermatozoa moved from the testis to the sperm duct, and the pH value of seminal plasma, concentration of cyclic adenosine monophosphate (AMP) in the sperm cells, and potential for sperm motility increased. Cyclic AMP levels and the potential for motility gradually increased when testis spermatozoa with no capacity for movement were incubated in the artificial seminal plasma of which the pH was much the same as, or higher than, the pH of natural seminal plasma from the sperm duct. Such correlation in motility, pH, and cyclic AMP suggests that the increases in seminal pH and intracellular cyclic AMP level during passage of spermatozoa from the testis to the sperm duct cause the acquisition of potential for motility. Motility of testicular spermatozoa demembranated with Triton X-100 was very low in fish caught in the sea, while motility of spermatozoa from the posterior portion of the sperm duct was much higher in fish caught in the river. Furthermore, nondemembranated, intact spermatozoa showed a lag in the timing of the acquisition of potential for motility vs. demembranated spermatozoa: The demembranated sperm exhibited the potential earlier than the nondemembranated sperm. These data suggest that increase in activity of the motile apparatus, the axoneme, is a prerequisite, in part, for the acquisition of sperm motility, whereas the development of some function of the plasma membrane also contributes to this phenomenon.

Sex preselection through albumin separation of sperm

To determine if passage of sperm through columns of liquid albumin before their use in artificial insemination could affect the sex ratio at birth. Sperm were isolated by layering over columns of liquid albumin. The isolated fractions were inseminated into the uterus on the presumptive day of ovulation. Patients were treated in 65 clinical practices (Sperm Centers) located both in this country (57) and abroad (8). Individuals were self-selected by their desire to have a child of a specified sex. The sex of offspring resulting from the insemination of isolated sperm. Insemination with sperm isolated to enhance male sex preselection produced 71% and 76% males depending on the technique. Use of isolated sperm in women who were taking clomiphene citrate was associated with a 69% birth of females. Separation of sperm on columns of liquid albumin can affect the sex ratio at birth.

Plasma membrane alterations of maturing goat (Capra indicus) spermatozoa: lectin-binding and freeze-fracture study.

A qualitative and quantitative analysis of lectin-binding sites has been undertaken on spermatozoa recovered from different regions of the epididymis of the goat (Capra indicus) using fluorescein isothiocyanate-linked lectins (Bauhinia purpurea BPA, Concanavalin A Con A, Dolichos biflorus DBA, Maclura pomifera MPA, Arachis hypogaea or peanut agglutinin PNA, Glycine max or soyabean agglutinin SBA, Ulex europaeus UEA, and Triticum vulgaris or wheat-germ agglutinin WGA), in conjunction with scanning and transmission electron microscopy, and freeze-fracture techniques. Flow cytometric analysis has also been used to quantitize binding affinity. Spermatozoa from caput to cauda epididymidis show no significant variation in lectin-binding ability, but the samples removed from the corpus epididymidis contain a greater number of binding sites. The passage of spermatozoa through the epididymidis is accompanied by a redistribution of the plasma membrane lectin-receptors covering the sperm head and tail. Receptors for BPA, DBA, PNA and SBA are specifically restricted to the anterior region of the acrosome in caudal spermatozoa. Freeze-fracture replicas, examined to study changes in organisation of intramembranous particles of the plasma membrane during sperm maturation, reveal distinct changes in their distribution in the acrosome, post-acrosome and spermatozoon tail, especially in the corpus and cauda epididymidis.

Autotransposition of vas in a 2-stage procedure. An experimental study in the rat.

The patency rate of vasovasostomy in autotransposed vas has been studied using a technique set up in a rat model. In a two-stage procedure, 1 cm of the vas deferens was transposed to the opposite side. The anastomoses were performed with a simplified microsurgical suturing technique. On final examination, 9 of 15 rats operated upon showed good sperm passage over the transposed vas segment. Sperm granulomas were recorded in four of fifteen cases. Sperm antibodies were demonstrated in eight of fifteen cases.

Movement characteristics and hyperactivation of human sperm on different epithelial cell monolayers

Studies of sperm movement characteristics concern mainly sperm swimming between two glass surfaces (as in the Makler chamber). Using automated videomicrography, (CellSoft, Cryo Resources, New York, USA), we have analysed the movements of human sperm swimming on monolayers of different origins: monkey kidney (Vero) cells, bovine oviduct cells, and human endometrial cells. About 10(5) sperm were deposited upon preparations consisting of monocellular layers adhering to a coverglass, and placed in a deep slide-coverglass system. Experiments were first performed at room temperature then at 37 degrees C. At room temperature, motion characteristics on Vero cell layers (six samples) were not different from those measured in either the conditioned or corresponding non-conditioned media, except for the amplitude of lateral head displacement (ALH) which was significantly lower. Comparison of the three different cell monolayers showed no difference between them for the corresponding motion parameters. The data were dramatically different at 37 degrees C: sperm swimming on cell monolayers of genital origin (oviduct or endometrium) exhibited high rates of hyperactivation (HA: 36.7% and 38.6% respectively), which was significantly more than on either Vero cells (10.9%) or in a control medium (12.6%). Moreover, HA rates were significantly higher on genital cell monolayers than in the corresponding conditioned medium. Hyperactivated sperm exhibited lasting 'star-spin' trajectories rather than 'transitional phases'. It is concluded that passage of sperm on either oviduct or endometrial epithelial cell monolayers can induce sperm hyperactivation and improve their fertilizing capacity.

Thiol status in human sperm

The passage of spermatozoa along the epididymis is characterized by a gradual stabilization of intracellular organelles mainly through the oxidation of thiol groups. In this study, we examined the relationship between the thiol-disulfide status of human spermatozoa (using a specific fluorescent probe, monobromobimane) and routine semen analysis parameters. Fluorescence intensity was measured by spectrofluorimeter and its frequency distribution within samples, using a fluorescence-activated cell sorter. The mean proportion of reactive thiols SH/(SS + SH) in 29 semen samples was 29.8% +/- 2.5%. When comparing thiol labeling patterns, oligozoospermic samples differed from normozoospermic ones (P less than 0.05). However, within the normozoospermic group, no correlation was found between thiol-labeling patterns and routine sperm parameters or fertilizing capacity in vitro. No difference in thiol labeling patterns was found between "swim-up" and "whole semen" preparations.

The interaction of boar sperm proacrosin with its natural substrate, the zona pellucida, and with polysulfated polysaccharides

Boar sperm acrosin is an acrosomal protease with trypsin-like specificity, and it functions in fertilization by assisting sperm passage through the zona pellucida by limited hydrolysis of this extracellular matrix. In addition to a proteolytic active site domain, acrosin binds the zona pellucida at a separate binding domain that is lost during proacrosin autolysis. In this study, we quantitate the binding of proacrosin to the physiological substrate for acrosin, the zona pellucida, and to a non-substrate, the polysulfated polysaccharide fucoidan. Binding was analogous to sea urchin sperm bindin that binds egg jelly fucan and the vitelline envelope of sea urchin eggs. Proacrosin was found to bind to fucoidan and to the zona pellucida with binding affinities similar to bindin interaction with egg jelly fucan. These interactions were competitively inhibited by similar relative molecular mass polysulfated polymers. Since bindin and proacrosin have distinctly different amino acid sequences, their interaction with acidic sulfate esters demonstrates an example of convergent evolution wherein different macromolecules localized in analogous sperm compartments have the same biological function. From cDNA sequence analysis of proacrosin, this binding may be mediated through a consensus sequence for binding sulfated glycoconjugates. Proacrosin binding to the zona pellucida may serve as both a recognition or primary sperm receptor, as well as maintaining the sperm on the zona pellucida once the acrosome reaction has occurred.

SPERM COMPETITION AND THE EVOLUTION OF NONFERTILIZING SPERM IN MAMMALS.

Nonfertilizing sperm with special morphologies have long been known to exist in invertebrates. Until recently, abnormal sperm in mammals were considered errors in production. Now, however, Baker and Bellis (1988, 1989) have proposed that mammalian sperm, like some invertebrate sperm, are polymorphic and adapted to a variety of nonfertilizing roles in sperm competition, including prevention of passage of sperm inseminated by another male. More specifically, their "kamikaze" sperm hypothesis proposes that deformed mammalian sperm are adapted to facilitate the formation and functioning of copulatory plugs (Baker and Bellis, 1988). Here I argue that most, maybe all, mammals are unlikely to produce nonfertilizing sperm. First, mammals might not be able to afford to evolve nonfertilizing sperm, given that a) fertilization is often unlikely despite the huge numbers of sperm produced; b) production of larger numbers of sperm is constrained, presumably because of metabolic costs, evidence for which includes the fact that in species in which sperm morphology and anatomy of the female reproductive tract increase the probability of fertilization, the numbers of sperm produced is lower than in others; and c) selection appears to act against the production of deformed sperm. Second, some of the evidence advanced for the existence of nonfertilizing sperm does not in fact support the idea. Third, accessory gland secretions are sufficient on their own to coagulate semen and produce fully functioning plugs; thus the male that used accessory gland secretions would be at a clear advantage over the male that diluted his fertilizing sperm with "kamikaze" sperm; and indeed, current evidence indicates selection on accessory glands, not sperm morphology, to enhance coagulation of semen. Fourth, predictions made on the basis of the "kamikaze" sperm hypothesis are not supported by quantitative comparisons of data from polyandrous and monandrous primates (i.e., those in which several males mate with a fertile female, and therefore in which sperm competition should be operating, and those in which only one male mates). Although sperm competition is almost certainly more intense in polyandrous genera than in monandrous genera (as indicated by, e.g., more frequent copulations and the production of more sperm per ejaculate from larger spermatogenic organs), polyandrous genera do not produce a greater proportion of deformed (i.e., nonfertilizing) sperm than do monandrous genera, or even necessarily a greater number of deformed sperm; nor a greater variety of sperm sizes-indeed they might produce fewer; nor fewer motile sperm (as might be expected if sperm are selected to stay behind and compete with sperm from subsequent males); and nor larger sperm (as might be expected if sperm are produced for functions other than to reach the egg). In sum, currently available evidence suggests that the function of all mammalian sperm is to fertilize, and that sperm competition in mammals occurs through scramble competition, not contest competition.

Fine structure and morphogenesis of the micropylar apparatus in the medfly Ceratitis capitata (Wiedemann) (Diptera : Tephritidae)

The micropylar apparatus (MA) in Ceratitis capitata (Diptera : Tephritidae) is a cone-like protrusion, 18 μm long, at the anterior pole of the egg, and exhibits about 40 follicle cell imprints externally. It consists of chorionic and vitelline membrane parts. The first contains at least a 3 μm wide micropylar canal; the tip of the MA is covered by a “tuft” and includes the micropyle, i.e. the entrance of the micropylar canal. The canal leads to the vitelline membrane part, where it forms a pocket. The sperm enters the oocyte by passing through the micropyle-micropylar canal-pocket route. At least 40 follicle cells participate in the formation of the micropylar apparatus. Two of these form 2 projections, which are tightly connected, and serve as a template for the formation of the canal and the pocket. Throughout their length, both projections have microtubules in parallel arrangement. During oogenesis, the remaining micropylar cells secrete the successive eggshell layers, i.e. the vitelline membrane, the wax layer, the innermost chorionic layer, the endochorion, and the exochorion. Towards the end of oogenesis, the 2 projections degenerate, and the canal becomes available for sperm passage.

Sperm passage through the zona pellucida

Sperm passage through the zona pellucida requires the occurrence of the acrosome reaction. This latter reaction, in turn, is supposedly needed to release the acrosomal enzymes, particularly acrosin which has been involved in the sperm binding to and penetration through the zona pellucida. The application of the immunogold technique using the monoclonal antiacrosin antibody ACR-C2E5 allowed us to identify acrosin in hamster, human and guinea-pig spermatozoa at the optic and scanning electron microscope, in which the immunogold labelling was silver enhanced. At the transmition electron microscope the monoclonal antibody was indirectly labelled with 10nm gold particles. In hamster spermatozoa there were three patterns of labelling: a) either no labelling, or an intense one over acrosomal region of apparently acrosome intact spermatozoa (Figures la,b, 2a & 3a); b) an intense labelling over the inner acrosomal surface and on the acrosomal cap of acrosome reacted spermatozoa (Figures lc,d, 2b & 3b); and c) either a slight labelling over the equatorial region or no labelling on acrosome reacted spermatozoa (Figure le,f,2c).

Decreased Spermatozoal Survivability Associated with Aberrant Morphology of the Ductuli Efferentes Proximales of the Chicken (Gallus Domesticus)1

The objective of this research were twofold: 1) to determine if decreased spermatozoal longevity, a previously reported heritable trait in chickens, was attributable to spermatozoal passage through the excurrent ducts, and 2) to document the morphology of the testicular excurrent ducts from affected roosters. Though spermatozoa were viable at ejaculation, as evidenced by their exclusion of ethidium bromide, fertility after intravaginal insemination of spermatozoa from affected roosters was less (p less than 0.001) than that observed with spermatozoa from nonaffected controls, 37 +/- 2.3 versus 58 +/- 1.5%, respectively, over a 21-day egg-collection interval. In contrast, fertility after intramagnal insemination of testicular spermatozoa from affected roosters was equivalent (p greater than 0.05) to that of nonaffected controls, 47 +/- 2.2 versus 41 +/- 3.6%, respectively. After intravaginal insemination, neither type of testicular spermatozoa fertilized oocytes. The ductuli efferentes proximales from affected roosters were characterized by a greater luminal cross-sectional area as well as a diminished height and number of longitudinal epithelial folds (p less than 0.005). It was concluded that heritable decreased spermatozoal longevity in the chicken is not attributable to an inherent spermatozoal defect. Rather, the defect is acquired during passage of spermatozoa through the extragonadal ducts of the rooster.

Ascidian sperm penetration and the translocation of a cell surface glycosidase.

Sperm bind to vitelline coat (VC) glycosides of ascidian eggs by means of a sperm surface glycosidase (Hoshi et al.: Zool Sci 2:65, 1985). In the genus Ascidia, N-acetylglucosamine (NAG) is the VC ligand. After initial binding by the tip of the head, sperm pass through the VC and perivitelline space leaving the single mitochondrion outside. This process can also be followed in vitro on a coverslip. Analysis of recorded video images shows that the sperm moves away from the anchored mitochondrion. Our model for sperm penetration suggests that mitochondrial translocation is responsible for driving the sperm into the egg. In the work presented here, we have demonstrated that ascidian sperm have N-acetyl-beta-D-glucosaminidase (NAGase) activity with an acidic pH optimum. This enzyme, which can be removed from the sperm with Triton X-100, binds to concanavalin A, demonstrating that it is glycosylated. Histochemical methods disclose that the enzyme is originally located at the tip of the head but subsequently remains with the surface overlying the mitochondrion during translocation. Fluorescent Con A was used as a second label for localization of the enzyme on the cell surface during translocation. Colocalization of both probes of the enzyme support a crucial facet of our model; the sperm surface VC binding site remains over the mitochondrion during translocation. This would couple mitochondrial translocation with sperm penetration and drive the sperm into the egg.

Two-dimensional gel electrophoretic analysis of rat sperm membrane interaction with cauda epididymal fluid.

Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) was used to analyze the polypeptide composition of rat cauda epididymal fluid, blood serum and membrane-enriched fractions of caput, corpus, and cauda epididymal spermatozoa. Several polypeptides were found in both cauda fluid and blood serum, and in both cauda fluid and epididymal spermatozoa. Prominent cauda epididymal fluid polypeptides that were associated with caput, corpus, and cauda sperm membranes were 32 and 33 kDa. Passage of spermatozoa from the caput to the cauda epididymidis was characterized by the loss of three glycopolypeptides of 32, 30 and 29 kDa, and by the addition of a 37-kDa glycopolypeptide. Incubation of intact caput, corpus and cauda spermatozoa with cauda epididymal fluid revealed major changes in the polypeptide maps of the incubation fluid and the membrane-enriched fractions of caput and corpus, but not cauda spermatozoa. The incubation of cauda fluid with caput and corpus sperm cells was characterized by a loss of several polypeptides and the addition of a 24-kDa glycopolypeptide. The most striking change in spermatozoa incubated with cauda epididymal fluid was the addition of two glycopolypeptides of 32 and 33 kDa to the polypeptide maps of caput sperm cells. These data demonstrate that rat spermatozoa undergo surface modifications during epididymal maturation and that these modifications can be influenced by epididymal fluid.