Spontaneous Acrosome Reaction Research Articles

Plasma membrane and acrosomal integrity in bovine spermatozoa with the knobbed acrosome defect

Previous studies have shown that bovine spermatozoa with the knobbed acrosome defect have a reduced ability to bind to and penetrate the bovine zona pellucida. Cryopreserved spermatozoa from a normal control bull (N) and two bulls with the knobbed acrosome defect (K1 and K2) were subjected to a hypoosmotic swelling test (HOST) to evaluate the functional integrity of the plasma membrane. A capacitation assay and a calcium ionophore challenge test was used to determine the ability of spermatozoa to undergo capacitation and acrosome reaction (AR), respectively. The mean percentage of spermatozoa responding to the HOST was significantly higher for Bull N (68.8±2.4) than for Bulls K1 (36.1±4.6) and K2 (40.2±4.7). The mean percentage of capacitated spermatozoa (54.0±1.8) was significantly higher for the treatment group (incubation in capacitating medium) for Bull N than that of the negative control group (29.5±1.8). However, there was no difference between the treatment and the negative control groups of the bulls with the knobbed spermatozoa (36.5±1.4 and 27.1±3.0 for Bull K1 and 47.5±3.8 and 35.2±6.6 for Bull K2, respectively). Although the mean percentage of acrosome-reacted spermatozoa (60.7±1.3) was higher for the treatment group (receiving calcium ionophore) for Bull N than that of the negative control (29.5±1.3), there was no difference between the treatment and the negative control groups for the bulls with the knobbed spermatozoa (47.8±3.3 and 49.3±5.0 for Bull K1 and 58.8±10 and 59.5±9.7 for Bull K2, respectively). A positive correlation existed between the proportion of spermatozoa that did not respond to the HOST and that undergoing a spontaneous AR. Results suggest that spermatozoa with the knobbed acrosome defect have impaired plasma membrane function which predisposes them to premature capacitation and spontaneous AR on incubation after thawing.

Effect of Methyl-.BETA.-Cyclodextrin and Fertilization Promoting Peptide on Capacitation of Boar Spermatozoa in a Protein-Free Medium.

The present study was undertaken to examine the effect of methyl-β-cyclodextrin (MBCD) and fertilization promoting peptide (FPP; pGlu-Glu-ProNH2) on the capacitation and acrosome reaction of boar spermatozoa in a protein-free medium. After washing with a protein-free medium, ejaculated spermatozoa (resuspended at 1 × 106 cells/ml) were cultured in 2 ml of modified Medium-199 containing polyvinylalcohol (mM199-PVA) supplemented or not supplemented with MBCD and/or FPP for 2 h in an atmosphere of 5% CO2 in air at 39 C. Effects of MBCD and FPP on boar spermatozoa were determined by chlortetracycline fluorescence assessment. When spermatozoa were cultured in various MBCD concentrations, capacitation was induced in a concentration-dependent manner, but spontaneous acrosome reaction was not affected. When the effect of FPP in mM199-PVA was determined, sperm capacitation was induced and spontaneous acrosome reaction was inhibited in 100 nM FPP, regardless of the absence or presence of BSA. In the last experiment, spermatozoa were cultured in mM199-PVA supplemented with various concentrations of MBCD and/or FPP. An accelerative effect of MBCD on sperm capacitation was observed in a concentration-dependent manner even in the presence of FPP, whereas 1-2 mM of MBCD neutralized the stimulatory effect of FPP on capacitation. Furthermore, FPP inhibited spontaneous acrosome reaction even in the presence of MBCD. These results demonstrate that MBCD and PFF can induce capacitation of boar spermatozoa in a protein-free medium and that FPP alone also inhibits spontaneous acrosome reaction.

Acrosome reaction in fertile and subfertile boar sperm.

The main purpose of sperm evaluation is to predict its fertilizing ability. However, basic sperm test results show a low correlation with fertilizing ability. The purpose of this study was to determine whether there is an association between acrosome reaction (AR) and the incidence of subfertility of normal sperm boar. The production records of 22 farms were analyzed to identify boars with low fertility and/or prolificity, classified as subfertile. Twenty-two subfertile boar semen samples were analyzed and compared with 51 samples of fertile boars. Sperm were capacitated during 4 h at 39 degrees C. viability was determined by bisbenzimide (Hoechst-33258) staining. Acrosome reaction was assessed with fluorescein isothiocyanate conjugated Pisum sativum agglutinin. The percentage of spontaneous acrosome reaction (SAR) was not significantly different in fertile (4.5%) and subfertile boars (4.75%) (p > .05). Nevertheless, the percentage of progesterone-induced acrosome reaction (IAR) was significantly lower in subfertile boars (5.75%) as compared with fertile boars (10%) (p < .01). These results suggest that assessment of IAR in vitro may be a useful parameter to identify subfertility in boars.

Exposure of sperm head equatorin after acrosome reaction and its fate after fertilization in mice.

Equatorin is a sperm head equatorial protein, possibly involved in sperm-oocyte fusion (Toshimori et al., Biol Reprod 1998; 59:22-29). In the present work, we have shown that equatorin contained in the posterior acrosome is detectable only after spontaneous or induced acrosome reactions following fixation and permeabilization, but not in intact spermatozoa. The presence of protease inhibitors during sonication or ionophore treatments does not inhibit the exposure of the antigenic epitope. The zona-penetrated spermatozoa lying in the perivitelline space display equatorin, similar to those of the acrosome-reacted ones. After sperm-egg fusion during in vitro fertilization (IVF), the equatorin dissociates from the sperm head equatorial region and remains at the vicinity of the decondensing male pronuclei. During pronuclear apposition stage, it is pushed away from the pronuclei, possibly by the perinuclear microtubules. After first cleavage, equatorin is inherited by one of the proembryonic cells. The residual equatorin disappears after the second cleavage. Microinjected whole spermatozoa or sperm heads into the MII stage oocytes display equatorin similar to those of the perivitelline sperm. After activation, it dissociates from the sperm nuclei in a similar manner as during IVF. The mode of equatorin degeneration during fertilization is similar to those of the sperm tail components or mitochondria, but different from those of the membrane associated proteins.

Evidence that human epididymal protein ARP plays a role in gamete fusion through complementary sites on the surface of the human egg.

Human epididymal sperm protein ARP, a member of the cysteine-rich secretory proteins (CRISP) family, exhibits significant homology with rat epididymal protein DE, a candidate molecule for mediating sperm-egg fusion in rodents. The aim of this study was to investigate the involvement of ARP in human gamete fusion. Sequential extraction of proteins from ejaculated human sperm revealed the existence of a population of ARP that is tightly associated with the sperm surface and thus, potentially capable of participating in gamete interaction. Exposure of capacitated human sperm to a polyclonal antibody against recombinant ARP (anti-ARP) produced a significant and concentration-dependent inhibition in the ability of human sperm to penetrate zona-free hamster eggs. This inhibition was not due to a deleterious effect on the gametes because anti-ARP affected neither sperm viability or motility, nor egg penetrability. The antibody did not inhibit the occurrence of spontaneous or Ca(2+) ionophore-induced acrosome reaction, nor did it inhibit the ability of sperm to bind to the oolema, supporting a specific inhibition of the antibody at the sperm-egg fusion level. As a relevant evidence for a role of ARP in gamete fusion, the existence of complementary sites for this protein on the surface of human eggs was investigated. Experiments in which zona-free human oocytes discarded from in vitro fertilization programs were exposed to ARP, fixed, and subjected to indirect immunofluorescence revealed the presence of specific ARP-binding sites on the entire surface of the human egg, in agreement with the fusogenic properties of the human oolema. Together, these results strongly support the participation of ARP in the sperm-egg fusion process, suggesting that this protein would be the functional homologue of DE in humans.

Alkalinization of Acrosome Measured by GFP as a pH Indicator and Its Relation to Sperm Capacitation

We previously targeted EGFP (a mutant of green fluorescent protein) to the lumen of the mouse sperm acrosome and reported the time course of EGFP release during the acrosome reaction. In the study reported here, we estimated the pH within the mouse sperm acrosome utilizing the pH-dependent nature of EGFP fluorescence. The average intra-acrosomal pH was estimated to be 5.3 ± 0.1 immediately after sperm preparation, gradually increasing to 6.2 ± 0.3 during 120 min of incubation in TYH media suitable for capacitation. Spontaneous acrosome reactions were noted to increase concomitantly with acrosomal alkalinization during incubation. We also demonstrated that acrosomal antigens detected by monoclonal antibodies MN7 and MC41 did not dissolve following the acrosome reaction in pH 5.3 media, but dissolved at pH 6.2. These data suggest that acrosomal alkalinization during incubation conducive for sperm capacitation may function to alter acrosomal contents and prepare them for release during the acrosome reaction.

Fertilizing characteristics of bovine sperm with flattened or indented acrosomes

Frozen semen from a control bull (C: 89% morphologically normal sperm) and two bulls with acrosomal defects (K1: 92% flattened acrosomes; K2: 82% indented acrosomes) were used to investigate the fertilizing ability of bull sperm with flattened or indented acrosomes. In experiment 1, frozen-thawed sperm were evaluated for acrosomal integrity with fluorescent microscopy. In experiment 2, proteolytic activity of the acrosomal contents of sperm was evaluated through a gelatin digestion assay. In experiment 3, an IVF test system was used to determine the ability of sperm with flattened or indented acrosomes to bind to bovine oocytes and penetrate the zona pellucida. In experiment 4, IVM zona-free bovine oocytes (ZFO) were fertilized and examined to evaluate sperm chromatin decondensation. In experiment 1, bulls K1 and K2 had a lower proportion of sperm with intact acrosomes (0 and 13.6±4.5%, respectively) than bull C (30.2±5.6%) after 2 h of incubation. In experiment 2, the proportion of sperm with proteolytic activity, as indicated by gelatin digestion around sperm heads, did not differ among bulls (C: 55%, n=410; K1: 43%, n=426; K2: 48%, n=324). In experiment 3, a lower proportion of sperm with flattened (K1) or indented acrosomes (K2) bound to oocytes than sperm from the control bull, C. The percentage of zona penetrated (55%, n=20; 13%, n=23; 4%, n=25) and the mean (±S.E.M.) number of sperm penetrating these zona pellucida (19.7±2.5; 6.9±1.0; and 2.6±0.5) was higher ( P<0.05) for bull C than for bulls K1 or K2, respectively. In experiment 4, the percentage of ZFO penetrated (95%, n=20; 52%, n=30; 30%, n=33) and the mean (±S.E.M.) number of sperm with chromatin decondensation (7.8±1.6; 0.8±0.2; and 0.3±0.1) were also higher ( P<0.05) for the control bull, C than for bulls K1 or K2, respectively. Results suggest that although sperm with the flattened or indented acrosomes had a tendency to undergo spontaneous acrosome reaction on incubation after thawing, the proteolytic activity of the acrosomal contents appeared to be normal. Sperm with the flattened or indented acrosomes also appeared to have a reduced ability to fuse with oolemma as demonstrated by confocal microscopy. This would impair the ability to penetrate ooplasm and undergo sperm chromatin decondensation.

Influence of antisperm antibodies on the acrosome reaction as determined by flow cytometry

Objective: To evaluate the influence of antisperm antibodies on the acrosome reaction (AR).Design: Clinical study.Setting: University of Marburg, Department of Andrology, Clinical Training Center of the European Academy of Andrology.Patient(s): Spermatozoa from a pool of healthy donors were incubated with 30 seminal plasma samples from infertile men containing antisperm antibodies; they were compared to a control group of 10 samples without antisperm antibodies and five samples with buffer only.Intervention(s): The spontaneous acrosome reaction (SAR) and the induced acrosome reaction (IAR) by calcium ionophore A23187 were observed and determined by means of a flow cytometer. Flow cytometric double-staining estimates of acrosomal integrity were determined by using a monoclonal antibody (TÜS 19), marked with a secondary fluorescein isothiocyanate–labeled antibody. Cell viability was determined by counterstaining with propidium iodide (PI).Main Outcome Measure(s): Number of acrosome reacted spermatozoa.Result(s): The spermatozoa treated with antisperm antibodies showed significantly higher SAR and IAR responses than the control group.Conclusion(s): Some of the antisperm antibodies from individual patients are able to enhance the acrosome reaction in donor sperm, but none of them appeared to inhibit acrosome reaction.

Effects of the purified IGF-I complex on the capacitation and acrosome reaction of rabbit spermatozoa.

A protein complex containing IGF-I, purified from rabbit seminal plasma, was used to investigate its effects on the capacitation and acrosome reaction of rabbit spermatozoa. Uncapacitated sperm (Pattern F), capacitated sperm (Pattern B), and acrosome-reacted sperm (Pattern AR) were determined by CTC staining, and the results were validated by PSA-staining. The addition of the IGF-I complex to the capacitative medium directed the spermatozoa to spontaneous acrosome reaction. On the other hand, IGF-I complex, added to capacitated spermatozoa, acted as inducer of the acrosome reaction. Results of IVF experiments showed high rates of fertilization with capacitated spermatozoa, acrosome-reacted by either A23187 or IGF I complex, whereas significantly lower rates were obtained with spermatozoa capacitated in the presence of IGF-I complex.

The role of glucose in supporting motility and capacitation in human spermatozoa.

Glucose has been reported to be beneficial to human sperm for optimal capacitation and fertilization, although it is unclear whether glucose is required for providing extra metabolic energy through glycolysis, or for generating some other metabolic product. In this study, the effects of sugars on human sperm capacitation, motility, and energy production were investigated. The glucose concentration that supported the greatest number of acrosome reactions was 5.56 mmol L(-1). Compared with incubations with no added sugar, this concentration of glucose, fructose, mannose, or galactose appeared to slightly increase the number of acrosome reactions occurring after 18 hours of capacitation, or following induction by 2 micromol A23187 + 3.6 mmol pentoxifylline L 1, but only glucose had a statistically significant effect. Glucose supported increased penetration of zona-free hamster oocytes, but its advantage was not statistically significant. The addition of 5.56 mmol glucose or fructose L(-1) to sugar-free medium immediately increased the adenosine triphosphate (ATP) concentration and motility of sperm. These parameters were then stable for 3 hours, but declined markedly after 18 hours. In the absence of a glycolysable sugar, motility began to decline in the first hour and only 2% or 3% of sperm remained motile after 18 hours. Glucose or fructose was required to support hyperactivated motility. 2-Deoxyglucose was detrimental to the ATP concentration and motility of sperm, and supported fewer spontaneous or progesterone-stimulated acrosome reactions than were observed in the absence of a sugar. We conclude that glycolytic ATP production is required for vigorous motility and hyperactivation in human sperm. Other products of glucose metabolism are not essential to support capacitation, but they may have a small, enhancing effect.

Effects of estrogenic compounds on human spermatozoa: evidence for interaction with a nongenomic receptor for estrogen on human sperm membrane

Estrogens play an important role in the development and regulation of the male reproductive system. We have earlier shown that a nongenomic receptor for estradiol present on sperm plasma membrane mediates the effects exerted by this hormone on sperm intracellular calcium concentrations ([Ca 2+] i ), as well as on the biological response to progesterone (P). In particular, 17 β-estradiol (17βE 2) shows an inhibitory effect on P-mediated calcium influx and acrosome reaction (AR). In the present study, the effects of different anti-estrogens and xenoestrogens on [Ca 2+] i and AR stimulated by P have been investigated in human spermatozoa in order to better define the pharmacological characteristics of the sperm membrane estrogen receptor. The anti-estrogens tamoxifen (Tx) and ICI 164 384 (ICI) induce only a slight increase of [Ca 2+] i , which, however, as in the case of 17βE 2, results in a reduction of P-stimulated calcium influx. Moreover, both the compounds reduce the calcium response to 17βE 2 without affecting 17βE 2-inhibition of calcium response to P. Concerning AR, Tx alone does not alter either spontaneous or P-stimulated AR but partially revert the inhibitory effect of 17βE 2. These results indicate that the two estrogens act as pharmacological agonists of the membrane estrogen receptors of human spermatozoa. On the other hand, the xenoestrogens bisphenol A (BPA) and octyiphenol polyethoxilate (OP) do not exert any direct effect on calcium fluxes and AR in human spermatozoa either in basal conditions or in response to P challenge. Moreover, although these environmental estrogens have been suggested to mimic estrogen effects in the other cell types, probably acting through genomic receptors, in human spermatozoa they do not interfere with 17βE 2 binding to its membrane receptor and with the short-term effects exerted by this steroid. In conclusion, our data indicate that the membrane receptor for estradiol in human spermatozoa shows both biochemical and pharmacological differences respect to the genomic receptor.

Stimulation by n6-cyclopentyladenosine of A1 adenosine receptors, coupled to galphai2 protein subunit, has a capacitative effect on human spermatozoa.

The effects of selective A(1) receptor agonist on human spermatozoa were examined to verify physiological responses and to investigate the signal transduction pathway. N6-Cyclopentyladenosine on uncapacitated spermatozoa did not induce spontaneous acrosome reaction after 5 h capacitation, whereas the number of capacitated spermatozoa, assessed by lysophosphatidylcholine-induced acrosome reaction with Pisum sativum agglutinin staining, was significantly increased. N6-Cyclopentyladenosine was also added to capacitated human spermatozoa to find out whether the agonist could induce the acrosome reaction. Results, although statistically significant, could not be considered biologically significant. A1-Mediated capacitation was followed by the increase of tyrosine phosphorylation of a protein subset ranging between M(r) = 200 000 and 30 000. Stimulation of A1 receptor with the selective agonist elicited an agonist-induced inositol phospholipid hydrolysis leading to a transient rise of inositol triphosphate (IP3). This increase was not induced by A(1) receptor antagonist and was blocked by phospholipase C inhibitor. Coimmunoprecipitation experiments showed that the A(1) receptor is coupled to Galphai2 subunit suggesting that the activation of phospholipase C is mediated by betagamma subunits. In conclusion, the A(1) adenosine receptor in human spermatozoa is coupled to Galphai2, signals via IP3, and affects the capacitative status of ejaculated spermatozoa.

Capacitation and acrosome reaction in buffalo bull spermatozoa assessed by chlortetracycline and [formula omitted] agglutinin fluorescence assay

Studies on buffalo sperm capacitation have been limited because of the non-availability of a direct assay system. We describe two methods for detecting the acrosomal status of buffalo spermatozoa, namely chlortetracycline (CTC) fluorescence assay and Pisum sativum agglutinin (FITC-PSA) stain. We also test them under various treatment regimens and simultaneously standardize and calibrate them with transmission electron microscopy. An initial comparison of three physiological media, such as Krebs-Ringer bicarbonate buffer, Tyrode solution and Brackett & Oliphant medium (having different calcium concentrations and osmolality) used for studying the capacitation of buffalo spermatozoa and assessed by CTC, FITC-PSA, Giemsa stain and TEM, revealed Brackett & Oliphant medium to be marginally better than the other two media. When stained with chlortetracycline, three distinct fluorescent patterns were visible in buffalo spermatozoa under capacitating conditions. These were ‘F’ with fluorescence in the post acrosomal region characteristic of uncapacitated acrosome-intact cells; ‘B’ with fluorescence on the anterior portion of the sperm head and a dark band in the post-acrosomal region, characteristic of capacitated, acrosome intact cells and ‘AR’ with a fluorescent band on the posterior portion of the head, characteristic of acrosome-reacted cells. The FITC-PSA intensely labels the acrosomal region of acrosome intact buffalo sperm. Acrosome reacted sperms had diminished acrosomal labelling by both the probes used. Buffalo spermatozoa was not capacitated when calcium was either omitted from the medium or chelated with EGTA. In the presence of Ca 2+ ionophore, A23187, 68% at 4 h and 85% at 8 h completed the acrosome reaction. Time course studies revealed a 4 h incubation period at 1.71 mM Ca 2+ concentration to be necessary before transformation of ‘F’ to ‘B’ cells could take place. Spontaneous acrosome reaction induced at 6 and 8 h incubation of buffalo spermatozoa in KRB medium resulted in conversion of ‘B’ cells to ‘AR’ while ‘F’ cells remained unchaged. A simultaneous evaluation of acrosome intact and acrosome-reacted cells using FITC-PSA, Giemsa and TEM gave results similar to examination by CTC stain. Both the assays are rapid, reproducible, reliable and they detect an increase in physiological acrosome reactions. They thus can be used to study effects of calcium and prove to be good monitoring systems to identify buffalo sperm capacitation and acrosome reaction in individual buffalo bulls for fertility studies.

Clinical importance of a micro-assay for the evaluation of sperm acrosome reaction using homologous zona pellucida.

This study aimed to develop an acrosome reaction assay using microvolumes of solubilized human zonae pellucidae among 35 couples attending an in vitro fertilization programme. The sperm morphology of the men was classified as g-pattern (5-14% normal forms) and/or normal pattern (> 14% normal forms). All the couples had a history of repeated poor or failed in vitro fertilization rates from previous attempts. A zona-induced acrosome reaction test was performed using homologous 0.25 zona pellucida microl-1 incubated with spermatozoa to induce the acrosome reaction. Acrosome reactions were measured with FITC-PSA staining, and expressed as the difference between zona-induced and spontaneous acrosome reaction spermatozoa. The results indicated that microvolumes of solubilized human zona pellucida could successfully be used to determine the acrosome reaction status of spermatozoa. The results were compared with in vitro fertilization rates of metaphase II oocytes, and analysed with the receiver operating characteristics curve. Receiver operating characteristics analyses divided the patients into two groups: i.e. zona-induced acrosome reaction < 15% and > 15%. The sensitivity and specificity for zona-induced acrosome reaction results versus fertilization were 93% and 100%, respectively. The correlation coefficient between zona-induced acrosome reaction and in vitro fertilization was r = 0.94 (P < 0.0001). Zona-induced acrosome reaction data can be used as an indicator for fertilization failure, thus helping clinicians to refine the therapeutic approach for infertile couples prior to the onset of the treatment.

Effects of Genistein Isoflavone (4',5',7-Trihydroxyisoflavone) and Dexamethasone on Functional Characteristics of Spermatozoa.

Caudal epididymal spermatozoa were used to study the influence of genistein isoflavone and dexamethasone (dxm) on the functional characteristics of spermatozoa. The effects of genistein alone and in combination with dxm on sperm motility, sperm morphology, spontaneous acrosome reaction (AcR), and ionophore A23187-induced AcR were investigated. The FITC-PSA/Hoechst 33258 staining procedure was used to assess sperm cell viability and AcR status and thus to differentiate between true AcR and acrosome degeneration. The overall results indicated that (1) lower doses of genistein alone, or in combination with dxm, did not significantly influence sperm motility or sperm morphology; (2) ionophore A23187 induced AcR in rat spermatozoa; (3) there appeared to be no direct correlation between sperm motility and AcR, (4) higher doses of genistein, alone or in combination with dxm, significantly interfered with percentage sperm motility and caused significant detachment of sperm heads but did not cause morphological defects; and (5) higher doses of genistein caused significant decrease in sperm acrosome reactivity with long duration of exposure. In view of the fact that sperm capacitation and AcR are physiological prerequisites for successful fertilization of oocytes, the findings suggest that chronic exposure of spermatozoa to high doses of genistein could be associated with infertility problems through suppression/inhibition of AcR and sperm motility. Dexamethasone did not appear to influence the effect of genistein on the functionality of postspermatogenic spermatozoa.

Calcitonin, angiotensin II and FPP significantly modulate mouse sperm function.

Fertilization-promoting peptide (FPP) regulates the adenylyl cyclase (AC)/cAMP pathway to elicit capacitation-dependent responses, stimulating capacitation in uncapacitated spermatozoa and then arresting it in capacitated cells, thereby inhibiting spontaneous acrosome reactions. Like FPP, calcitonin and angiotensin II are found in seminal plasma and so might affect sperm function; this study investigated responses in uncapacitated and capacitated mouse spermatozoa to these three peptides. Both calcitonin (5 ng/ml) and angiotensin II (1 and 10nmol/l), like FPP (100nmol/l), significantly stimulated capacitation, assessed using chlortetracycline (CTC) fluorescence and fertilization in vitro analyses. Combinations of two or three peptides, at high and low, non-stimulatory concentrations, were more stimulatory than the individual peptides, suggesting that they may act on the same signalling pathway, plausibly AC/cAMP; preliminary data indicate that calcitonin does stimulate cAMP production. In capacitated cells, FPP and calcitonin elicited pertussis toxin-sensitive inhibition of spontaneous acrosome loss, suggesting involvement of inhibitory G proteins; angiotensin II had no detectable effect. When all three peptides were used, angiotensin II did not interfere with inhibitory responses to FPP/calcitonin. These results suggest that angiotensin II, calcitonin and FPP may somehow modulate the AC/cAMP signal transduction pathway, but the precise mechanisms involved have yet to be elucidated.

Morphological and functional changes of stallion spermatozoa after cryopreservation during breeding and non-breeding season

The study compared quality and freezability of stallion semen during breeding and non-breeding seasons. Ejaculates were collected twice per week from four stallions during May ( n=24) and December ( n=24). The semen was mixed with skim milk extender, centrifuged and resuspended in fresh extender. Aliquots of this sperm suspension were separated from extender and diluted in TALP medium for sperm evaluation or with cryoextender (type “Gent” or a combination of Triladyl ® and skim milk). Samples of 0.5 ml were cryopreserved in straws using a programmed freezer. Parameters of sperm quality were evaluated before and after freezing/thawing. These included percentages of motile spermatozoa and of morphological intact sperm. Typical injuries were demonstrated by scanning electron microscopy (S.E.M.). The acrosomal status was visualised using FITC-conjugated peanut agglutinin, and the acrosome reaction was induced by calcium ionophore A 23187. The chromatin stability was estimated by acridine orange test. In winter, the average percentages of motile and morphologically normal sperm (67 and 74.3%, respectively) were higher than during the breeding season in May (59 and 65.9%; P<0.05). After freezing/thawing the proportions of vital and intact sperm decreased significantly. The number of motile sperm declined to 15 and 18% in May and December (range 5–40%), and of morphologically intact sperm to 51% in both seasons. Results of S.E.M. showed typical membrane ruptures in the acrosomal region and some sperm with abnormal necks. The proportion of frozen sperm with spontaneous acrosome reaction was higher during winter (86.5 versus 77.0%), suggesting a higher degree of membrane reactivity. Percentages of spermatozoa with denaturated chromatin were minimal and showed minimal differences between fresh and frozen state, stallions or seasons. An additional decondensation treatment with papain and DTE revealed a slightly enhanced number of spermatozoa with denaturable DNA after cryopreservation, especially in December (5.4±1.3%). The influence of cryoextenders was not significant for most sperm parameters, but there was a high variability between the stallions. Altogether, the influence of factors on the quality of spermatozoa has the following rank order: cryopreservation>stallion>season. Different cellular structures seem to have different susceptibilities to physicochemical stress. The cryopreservation of sperm during December results in survival rates similar to those measured during the breeding season, even more important for successful preservation is the selection of suitable semen donors.

Acrosome reaction: methods for detection and clinical significance.

The present article reviews the methods for detection and the clinical significance of the acrosome reaction. The best method for the detection of the acrosome reaction is electron microscopy, but it is expensive and labour-intensive and therefore cannot be used routinely. The most widely used methods utilize optical microscopy where spermatozoa are stained for the visualization of their acrosomal status. Different dyes are used for this purpose as well as lectins and antibodies labelled with fluorescence. The acrosome reaction following ionophore challenge (ARIC) can separate spermatozoa that undergo spontaneous acrosome reaction from those that are induced, making the result of the inducible acrosome reaction more meaningful. Many different stimuli have been used for the induction of the acrosome reaction with different results. The ARIC test can provide information on the fertilizing capability of a sample. The ARIC test was also used to evaluate patients undergoing in vitro fertilization since a low percentage of induced acrosome reaction was found to be associated with lower rates of fertilization. The cut-off value that could be used to identify infertile patients is under debate. Therapeutic decisions can also be made on the basis of the value of the ARIC test.

Elevated Seminal (SP) Plasma Lead (Pb2+) Levels Result in Significant Impairment of Human Sperm Function and Reduced Artificial Insemination (AI) Cycle Fecundity Rates ( f)

Objectives: Under an IRB approved protocol, 2-3 blood plasma (BP) and 2-9 SP specimens were collected over a six month period from AI semen donors (n=14) and from an unselected population (n=13) answering an advertisement for research participation. The Pb2+ levels in these specimens had low (<9.5%) intra-male variation but varied between men over a wide range (e.g., <10 μg/L to ∼1200 μg/L). Pb2+ in BP and SP were positively correlated (Spearman correlation [SC], r=0.9, p<0.0001). Comparable BP/SP Pb2+ levels were previously seen in IVF patients, whose increased Pb2+ levels: [1] were negatively correlated with conventional insemination fertilization rates (SC, n=89, r=−0.6, P<0.0001), and [2] were unrelated to serum FSH, LH or testosterone levels. Preliminary findings also suggested that Pb2+ levels and f were negatively related (n=3, SP Pb2+ <250 μg/L, f >16% vs. n=2, SP Pb2+ >700 μg/L, f <6%; t-test, P<0.004). Therefore, the purpose of this study was to determine if increased Pb2+ levels were related to levels of other toxic metals, to decreased expression of sperm biomarkers for high IVF fertilization rates, and to f. Design: A double-blind study of cadmium (Cd2+) levels, sperm function and f (in 341 AI attempts) in specimens previously examined for Pb2+ content. Metal ion effects were modeled in vitro by exposure of fertile donor sperm (n=24) under capacitating conditions to increasing doses of exogenous Pb2+ (0–5180 μg/L). Materials and Methods: Cd2+ in BP and SP was assayed by graphite furnace atomic absorption spectroscopy. WHO (1992) semen parameters were recorded for fresh semen. Motile sperm populations were obtained from frozen/thawed semen by Percoll density gradient centrifugation and were examined for surface expression of mannose (Man) receptors (MR) and non-nuclear progesterone (P) receptors (NNPR), spontaneous and agonist (free Man and P)-stimulated acrosome reactions (AR). Results were compared using SC and repeated measures analysis of variance (RMANOVA) models. Results: BP and SP Cd2+ levels were more tightly clustered than Pb2+ (range, 0.081 μg/L to 0.161 μg/L). Pb2+ and Cd2+ in BP and SP were positively correlated (SC, respectively, n=11, r=0.7, P<0.01 and n=13, r=0.7, P<0.007). SP Pb2+ levels and sperm count, motility, percentage normal morphology and NNPR were not related. In contrast, significant inverse relationships existed between SP Pb2+ levels and MR (SC, n=12, r=−0.5, P<0.007), Man AR (SC, n=15, r=−0.5, P<0.04) and P AR (SC, n=26, r=−0.4, P<0.03). SP Pb2+ and spontaneous AR were positively correlated (SC, n=16, r=0.6, P<0.01). SP Pb2+ levels and f showed a strong inverse relationship (SC, n=24, r=−0.6, P<0.02). In vitro exposure of fertile donor sperm to exogenous Pb2+ resulted in a dose-dependent decrease in MR (RMANOVA, P<0.01), Man AR (RMANOVA, P<0.0008) and a dose-dependent increase in spontaneous AR (RMANOVA, P<0.0007). Conclusions: SP Pb2+ in subjects studied are representative of the general population. Within the AI group, selected for normal WHO semen parameters, donors with high SP Pb2+ had significantly lower fertility. The correlation between Cd2+ and Pb2+ suggests other metal toxicants may play a role. But in vitro modeling shows Pb2+ alone is sufficient to induce the same characteristics (increased spontaneous AR, decreased MR, decreased agonist-induced AR) in fertile sperm as seen in vivo in subjects with high SP Pb2+. We suggest that potential donors be screened for Pb2+ levels and sperm biomarker expression prior to acceptance into an AI program. These methods may also prove useful in directing ART patients to conventional IVF or to ICSI. (Support: NIH Grant No. ES 06100 to S.B.)

The Effect of Cryopreservation on the Spontaneous Acrosome Reaction of Human Spermatozoa

Objectives: Cryopreserved spermatozoa are widely used in assisted reproduction programs. While processing and incubation increase the rate of spontaneous acrosome reaction in human spermatozoa, little is known about the effect of cryopreservation. This study was conducted to assess the effect of cryopreservation on the spontaneous acrosome reaction of human spermatozoa. To the best of our knowledge, this is the first study to include a period of incubation before assessing the rate of acrosome reaction.