Use of spin labels to evaluate effects of cold shock and osmolality on sperm

Kinetic vitrification: concepts and perspectives in animal sperm cryopreservation

Sperm cryopreservation is an important tool for genetic diversity management programs and the conservation of endangered breeds and species. The most widely used method of sperm conservation is slow freezing, however, during the process, sperm cells suffer from cryoinjury, which reduces their viability and fertility rates. One of the alternatives to slow freezing is vitrification, that consist on rapid freezing, in which viable cells undergo glass-like solidification. This technology requires large concentrations of permeable cryoprotectants (P- CPA's) which increase the viscosity of the medium to prevent intracellular ice formation during cooling and warming, obtaining successful results in vitrification of oocytes and embryos. Unfortunately, this technology failed when applied to vitrification of sperm due to its higher sensitivity to increasing concentrations of P-CPAs. Alternatively, a technique termed 'kinetic sperm vitrification' has been used and consists in a technique of permeant cryoprotectant-free cryopreservation by direct plunging of a sperm suspension into liquid nitrogen. Some of the advantages of kinetic vitrification are the speed of execution and no rate-controlled equipment required. This technique has been used successfully and with better results for motility in human (50-70% motility recovery), dog (42%), fish (82%) and donkey (21.7%). However, more studies are required to improve sperm viability after devitrification, especially when it comes to motility recovery. The objective of this review is to present the principles of kinetic vitrification, the main findings in the literature, and the perspectives for the utilization of this technique as a cryopreservation method.

The necessity of antioxidant inclusion in caprine and ovine semen extenders: A systematic review complemented with computational insight

The inclusion of antioxidants (AOXs) has been proposed in various protocols to conserve the normal physiology of spermatozoa during (cryo) preservation. The main aim of this review was to understand the necessity of AOXs inclusion in semen extenders of caprine and ovine semen samples and to decipher physico-chemical space of AOXs used in semen extenders till now. A total 27 full-text relevant articles were finally discussed here. This systematic review showed that the inclusion of AOXs may improve the success of semen cryopreservation although at least three studies could not support this finding. AOXs have been not added after assaying total antioxidant capacity of the sample of interest, and this is principal measurement bias of all papers. Furthermore, no rational dose-response curve and precise posology have been considered in comparable studies. Furthermore, new methodologies are requested to detect the oxidative status of semen specimens before AXOs fortification and new methodologies like imaging are also needed to detect various injuries of sperms during semen (cryo)preservation. Defining computational chemical and physical spaces of AOXs which used in semen (cryo)preservation would be an interdisciplinary effort to hasten deciphering epoch-making compounds. In conclusion, more in-depth analytical, toxicological and pharmacological methodologies should be pursued in supplementation or addition of AOXs during caprine and ovine semen (cryo)preservation after determining the oxidative status of semen samples.

Investigation of in vitro measurable sperm attributes and their influence on electroejaculated bull semen with a fixed-time artificial insemination protocol in Australian Bos indicus cattle

Increasing use of fixed-time artificial insemination (FTAI) in beef cattle production has presented an opportunity for the use of fresh or chilled semen as an alternative to standard cryopreserved semen. The objective of this study was to examine in vitro sperm function and pregnancy rate of electroejaculated semen, chilled and stored for 48 hr, compared to conventionally cryopreserved semen with an optimized FTAI protocol in Brahman cattle. Semen from three Brahman bulls was collected, and aliquots were extended in either chilled (at 5°C) or frozen (LN₂ ) in a Tris-egg yolk extender base with 2.4% or 7.0% glycerol, respectively. Semen samples were assessed 48 hr after collection or post-thaw and warming, for sperm motility, in vitro sperm function and fertilizing ability, and used in a FTAI programme. The overall pregnancy rates was significantly different (p < .01) after FTAI with frozen (n = 173; 53.2%) and chilled semen (n = 174; 31.6%). In contrast, the in vitro sperm assessment showed that the chilled semen had significantly faster motility (p < .05), a higher proportion of progressively motile spermatozoa (p < .05), with significantly higher proportions of acrosome intact, viable spermatozoa (p < .01). This study showed that reasonable pregnancy rates in Brahman cattle can be achieved using FTAI with chilled semen collected using electroejaculation and stored for up to 48 hr. However, improvements in semen extenders are required in consideration of semen collection method to improve the longevity of sperm fertilizing ability to significantly increase FTAI output using chilled storage of bull semen.

The physiological role of ADP and Mg2+ in maintaining a stable beat cycle in bull sperm

Sperm flagella derive their motive power from the motor protein dynein. In this study, we show that maintenance of the flagellar beat cycle in detergent-extracted bull sperm models is highly dependent on the ratio of Mg(2+) to adenosine triphosphate (ATP). An excess of either ATP un-complexed with Mg(2+) , or an excess of Mg(2+) without an equivalent concentration of ATP, results in the loss of beat amplitude and a reduced curvature development in the beat cycle. In addition, we find that adenosine diphosphate (ADP) can stabilize the beat cycle and permit rhythmic beating across a broader range of ATP and Mg(2+) concentrations. We provide evidence that suggests that when ATP is un-complexed with Mg(2+) , it disrupts the beat cycle by reducing dynein adhesion and thereby, reduces the transmission of dynein-generated force between the doublets. Excess Mg(2+) does not act by the same mechanism and induces a condition where the flagellum is more resistant to bending. This is consistent with the idea that high Mg(2+) stabilizes rigor bridges, and ATP reduces the microtubule binding affinity of dynein. Our results may explain how intact sperm are able to sustain coordinated flagellar beating under a wide range of metabolic conditions, as intact sperm produce ADP in direct proportion to their consumption of ATP.

Comparison of the permeability properties and post-thaw motility of ejaculated and epididymal bovine spermatozoa

There are very few experimental reports on the comparative water transport (membrane permeability) characteristics of ejaculated and epididymal mammalian spermatozoa during freezing. In the present study, we report the effects of cooling ejaculated and epididymal bovine sperm from the same males with and without the presence of a cryoprotective agent, glycerol. Water transport data during freezing of ejaculated and epididymal bovine sperm suspensions were obtained at a cooling rate of 20 degrees C/min under two different conditions: (1) in the absence of any cryoprotective agents, CPAs and, (2) in the presence of 0.7 M glycerol. Using values published in the literature, we modeled the spermatozoa as a cylinder of length 39.8 microm and a radius of 0.4 microm with an osmotically inactive cell volume, V(b), of 0.61 V(o), where V(o) is the isotonic cell volume. The subzero water transport response is analyzed to determine the variables governing the rate of water loss during cooling of bovine spermatozoa, i.e. the membrane permeability parameters (reference membrane permeability, L(pg) and activation energy, E(Lp)). The predicted best-fit permeability parameters ranged from, L(pg)=0.021-0.038 microm/min-atm and E(Lp)=27.8-41.1 kcal/mol. The subzero water transport response and consequently the subzero water transport parameters are not significantly different between the ejaculated and epididymal bovine spermatozoa under corresponding cooling conditions. If this observation is found to be more generally valid for other mammalian species as well, then in the future the sperm extracted from the testes of a postmortem male could be optimally cryopreserved using procedures similar to those derived for ejaculated sperm.

Cryopreservation of the Mediterranean mussel (Mytilus galloprovincialis) spermatozoa

The effects of cryoprotectants, cooling rate and freezing on the mussel Mytilus galloprovincialis sperm were evaluated. At the end of each step of the experimental protocol, motility and fertilization ability of sperm were analyzed, compared to fresh semen. Five cryoprotectants were tested in their toxicity level: dimethylsulfoxide, ethylene glycol, 1-2 propylene glycol at 5%, 7%, 10%, 15% and 20% concentration; glycerol and methanol at concentration of 5%, 7% and 10%. The incubation times were 10, 20 and 30 min at 20+/-1 degrees C. Only dimethylsulfoxide, ethylene glycol and 1-2 propylene glycol at 5%, 7% and 10% were chosen for the following pre-freezing step. Five adaptation/chilling rates were analyzed: 10 min at 20+/-1, -2, -1, -0.5 and -0.25 degrees C/min and the last one was used for testing the best freezing procedure among seven gradients. Particularly, two rapid rates, three slow rates and two double step rates were conducted. Thawing results showed that M. galloprovincialis sperm are very sensitive to rapid pre-freezing and freezing protocols and only a slow procedure assured good motility and fertilization percentages.

Effect of glycerol and cholesterol-loaded cyclodextrin on freezing-induced water loss in bovine spermatozoa

Recent experimental data show that incubating bovine sperm with cholesterol-loaded cyclodextrin (CLC) before cryopreservation increases the percentages of motile and viable cells recovered after freezing and thawing, compared with control sperm. In the present study, we report the effect of incubating bovine sperm with CLC on the subzero water transport response and the membrane permeability parameters (reference membrane permeability (Lpg) and activation energy (ELp)). Water transport data during freezing of bovine sperm cell suspensions were obtained at a cooling rate of 20 °C/min under three different conditions: 1. in the absence of cryoprotective agents (CPAs); 2. in the presence of 0.7 M glycerol; and 3. in the presence of 1.5 mg/ml CLC and 0.7 M glycerol. With previously published values, the bovine sperm cell was modeled as a cylinder of length 39.8 μm and radius 0.4 μm, with osmotically inactive cell volume (Vb) of 0.61Vo, whereVois the isotonic cell volume. By fitting a model of water transport to the experimentally obtained data, the best-fit water transport parameters (LpgandELp) were determined. The predicted best-fit permeability parameters ranged fromLpg= 0.02 to 0.036 μm/min-atm andELp= 26.4 to 42.1 kcal/mol. These subzero water transport parameters are significantly different from the suprazero membrane permeability values (obtained in the absence of extracellular ice) reported in the literature. Calculations made of the theoretical response of bovine spermatozoa at subzero temperatures suggest that the optimal cooling rate to cryopreserve bovine spermatozoa is 45–60 °C/min, agreeing quite closely with experimentally determined rates of freezing bovine spermatozoa.

Effect of different thawing temperatures on the viability, in vitro fertilizing capacity and chromatin condensation of frozen boar semen packaged in 5 ml straws

The effect of two different thawing temperatures on frozen boar semen viability, in vitro fertilizing capacity and chromatin condensation and stability was studied. Freeze-thaw motility, normal apical ridge (NAR), in vitro fertilizing (IVF) capacity and chromatin condensation and stability were evaluated after thawing at 42 degrees C, 40s and 50 degrees C, 40s. Chromatin condensation degree was determined by flow cytometry, using propidium iodide as fluorochrome intercalating agent, and chromatin stability was evaluated by the same procedure after inducing sperm chromatin decondensation with ethylene diamine tetraacetic acid (EDTA) and sodium dodecyl sulfate (SDS). The results showed that thawing straws at 42 degrees C, 40s significantly reduced motility compared to straws thawed at 50 degrees C, 40s. NAR, penetration, monospermy and polyspermy were not different between the two groups of samples thawed at different temperatures. Chromatin was significantly more compact when thawing was performed at 50 degrees C, but its stability did not show any difference relative to thawing at 42 degrees C. It is suggested that the interactions involved in chromatin overcondensation had a non-covalent nature.

Protection of boar spermatozoa from cold shock damage by 2-hydroxypropyl-beta-cyclodextrin

This study examined whether 2-hydroxypropyl-beta-cyclodextrin (HBCD) could play a role in protecting spermatozoa from cold shock, as judged by motility parameters, intact acrosomes, and membrane integrity. Motility parameters were assessed by a computer-assisted sperm motility analysis (CASA) system, and the acrosome and membrane integrity were evaluated by fluorescent staining with FlTC-labeled peanut agglutinin and SYBR-14 plus Propidium Iodide, respectively. The addition of HBCD to the BF5 extender significantly increased the percentages of spermatozoa with intact acrosomes and increased membrane integrity after cold shock. The motility, progressive motility, and progressive velocity of the cold-shocked spermatozoa in the presence of HBCD were significantly higher than in the absence of HBCD. In contrast, further supplement of HBCD with cholesterol-3-sulfate (a cholesterol analogue) resulted in a decrease in all the aforementioned criteria, suggesting that the ability of HBCD to protect spermatozoa from cold shock injury is blocked by saturating the cholesterol binding sites of HBCD. It is therefore concluded that HBCD protects spermatozoa against cold shock injury, possibly due to its ability to remove membrane cholesterol.

Storage of ram semen

Storage of ram semen in liquid and frozen state, the diluents used for both methods, processing, cooling, freezing and thawing of semen are reviewed. Factors influencing the fertility of stored semen and methods used for improvement are discussed, and fertility results of long-term frozen stored ram semen are also given.

Basic aspects of frozen storage of semen

Basic concepts of cryopreservation and the causes of cryoinjury are reviewed. The possible roles of cryoprotectants and additives are considered in the context of their putative interactions with the sperm plasma membrane. Modern approaches to the laboratory assessment of spermatozoa after freeze-thawing are also briefly discussed.

Electron paramagnetic resonance spectroscopy for the investigation of the fluidity of human spermatozoa plasma membranes: a feasibility study

Spermatozoal membrane perturbations may play a role in abnormal sperm functions. The objective of this investigation was to study the feasibility of measuring membrane fluidity of isolated human sperm by electron paramagnetic resonance (EPR) spectroscopy and to compare the order parameter of spectra obtained from the sperm plasma membranes of living sperm of fertile men with that of infertile men. Ejaculates of infertile and fertile men were washed and the spermatozoa labelled with 5-doxylstearic acid (5-DSA) and 16-doxylstearic-acid (16-DSA) (10 nmol per 4 x 10(7) sperm). The reporter group of 5-DSA partitions into the outer, hydrophilic part of the sperm plasma membrane, whereas that of 16-DSA is distributed in the inner hydrophobic part. The following results were obtained: (i) the lowest measurable cell count was 3.6 to 7 x 10(6) sperm and the interassay variance of the order-parameter s was < 1%; (ii) swim-up experiments revealed a higher fluidity of sperm with a higher percentage of motility; (iii) sperm membranes of infertile patients exhibited a decreased fluidity of their plasma membranes in the polar interface region of 5-DSA compared with volunteer semen donors and fertile men (P=0.002). No difference of membrane fluidity was found between the different groups using 16-DSA. It is concluded that EPR spectroscopy can be used to study the fluidity of sperm plasma membranes in fertile and infertile men.

Water distribution and permeability of zebrafish embryos, Brachydanio rerio

Teleost embryos have not been successfully cryopreserved. To formulate successful cryopreservation protocols, the distribution and cellular permeability to water must be understood. In this paper, the zebrafish (Brachydanio rerio) was used as a model for basic studies of the distribution to permeability to water. These embryos are a complex multi-compartmental system composed of two membrane-limited compartments, a large yolk (surrounded by the yolk syncytial layer) and differentiating blastoderm cells (each surrounded by a plasma membrane). Due to the complexity of this system, a variety of techniques, including magnetic resonance microscopy and electron spin resonance, was used to measure the water in these compartments. Cellular water was distributed unequally in each compartment. At the 6-somite stage, the percent water (V/V) was distributed as follows: total in embryo = 74%, total in yolk = 42%, and total in blastoderm = 82%. A one-compartment model was used to analyze kinetic, osmotic shrinkage data and determine a phenomenological water permeability parameter, Lp, assuming intracellular isosmotic compartments of either 40 or 300 mosm. This analysis revealed that the membrane permeability changed (P < 0.05) during development. During the 75% epiboly to 3-somite stage, the mean membrane permeability remained constant (Lp = 0.022 +/- 0.002 micron x min-1atm-1 [mean +/- S.E.M.] assuming isosmotic is 40 mosm or Lp = 0.049 +/- 0.008 micron x min-1atm-1 assuming isosmotic is 300 mosm). However, at the 6-somite stage, Lp increased twofold (Lp = 0.040 +/- 0.004 micron x min-1atm-1 assuming isosmotic is 40 mosm or Lp = 0.100 +/- 0.017 micron x min-1atm-1 assuming isosmotic is 300 mosm). Therefore, the low permeability of the zebrafish embryo coupled with its large size (and consequent low area to volume ratio) led to a very slow osmotic response that should be considered before formulating cryopreservation protocols.

New approaches for studying the permeability of fish embryos: toward successful cryopreservation

This paper describes some new approaches for understanding the permeability of teleost embryos. The dechorionated zebrafish (Brachydanio rerio) was used as a model for basic studies of water and cryoprotectant permeability. These embryos are composed of two compartments, a large yolk (surrounded by the yolk syncytial layer) and differentiating blastoderm cells. Cellular water was distributed unequally in each compartment. Measurements indicated that the total water in the embryo was 74%, while the total water in the yolk was 42%, and total water in the blastoderm was 82%. The internal isosmotic value for the zebrafish embryo is unknown. However, for one-compartment modeling studies of membrane permeability, the mean Lp (+/- SEM) values were 0.022 +/- 0.002 to 0.049 +/- 0.008 microns x min-1 atm-1 at 40 mOsm (assuming this was one possible internal isosmotic value for the entire embryo) and 0.040 +/- 0.004 to 0.1 +/- 0.017 microns x min-1 atm-1 at 300 mOsm (assuming this was another possible internal isosmotic value for the entire embryo). When three- and six-somite embryos were placed in 1.5 and 2.0 M cryoprotectants (dimethyl sulfoxide and propylene glycol), osmometric measurements of volume changes indicated no cryoprotectant permeation. However, similar measurements with methanol revealed a small volume decrease (ca. 8%) and recovery (ca. 5%) for six-somite embryos in a 2.0 M solution. Magnetic resonance (MR) images of the spatial distribution of three cryoprotectants (dimethyl sulfoxide, propylene glycol, and methanol) demonstrated that only methanol permeated the entire embryo within 15 min. The other cryoprotectants exhibited little or no permeation into the yolk over 2.5 h. The results from MR spectroscopy and cryoprotectant microinjections into the yolk suggested that the yolk syncytial layer plays the critical limiting role for cryoprotectant permeation throughout the embryo.

Adenosine triphosphate catabolism in bovine spermatozoa

Adenosine triphosphate metabolism in caudal epididymis bovine spermatozoa was studied. Measurements by HPLC at appropriate time intervals of the spermatozoa content of ATP and its derivatives were carried out under different experimental conditions. In the presence of 2-D-glucose, cellular ATP was transformed almost quantitatively into ADP and AMP at a rate of 2.3 nmol/min per 10(8) cells. At the same time, ADP and AMP accumulated at a rate of 1.52 and 0.58 nmol/min per 10(8) cells, respectively. In the first 4 min, about 50% of total ATP was degraded, the AEC of the cells dropped to non-physiological values while the content of other nucleosides did not vary significantly. Inorganic P(i) content also remained unchanged. Under non-induced conditions up to 240 min, no variations of the adenylic content and of the EC value was observed. Under induced and non-induced conditions, IMP and adenosine were not detected within the spermatozoa. The lack of IMP might be ascribed either to the absence of AMP deaminase, whose activity has never been found in the spermatozoa or to the intracellular environment which down regulates the activity of the enzyme. In order to explain low levels and absence of variations of adenosine, several enzymic investigations were carried out. Adenosine kinase activity was not determined, therefore the transformation of adenosine into AMP had to be excluded. Nevertheless, enzymic activities potentially able to dephosphorylate the formed AMP are present in the spermatozoa. Our findings are indicative of the existence in the spermatozoa of acid and alkaline phosphatase and of 5'-nucleotidase membrane-derived.(ABSTRACT TRUNCATED AT 250 WORDS)

Human spermatozoa glycerol permeability and activation energy determined by electron paramagnetic resonance

The permeability of human spermatozoa to glycerol and its activation energy were determined using electron paramagnetic resonance (EPR) techniques. EPR was used to monitor the aqueous cell volume change vs. time during the glycerol permeation process using the aqueous spin label 15N-tempone and the membrane impermeable broadening agent potassium trioxalatochromiate (chromium oxalate). The permeation process was completed in tens of seconds, requiring the use of a stopped-flow methodology. The glycerol permeability coefficient (Pg) was determined by fitting a simple theoretical model to the experimental data. The permeabilities of human spermatozoa in 1 molar and 2 molar glycerol at 20 degrees C are (10.3 +/- 0.3).10(-4) cm/min (mean +/- S.D.) and (6.0 +/- 1.4).10(-4) cm/min, respectively. The permeabilities of human spermatozoa in 2 molar glycerol at 30, 20, 10, and 0 degrees C are (8.3 +/- 1.3).10(-4) cm/min, (6.0 +/- 1.4).10(-4) cm/min, (2.1 +/- 0.4).10(-4) cm/min, and (1.1 +/- 0.3).10(-4) cm/min, respectively. The activation energy (Ea) for glycerol permeation between 30 degrees C and 0 degrees C was found to be 11.6 kcal/mol.

Determination of boar spermatozoa water volume and osmotic response

Boar spermatozoa water volume and osmotic response were determined by a shapeindependent method for measuring cellular volume, electron paramagnetic resonance (EPR), employing the spin label, tempone, and the broadening agent, potassium chromium oxalate (CrOx). A water volume of 18.4 +/- 1.6 mum(3) (X +/- SD) was obtained for individual boar spermatozoa at 290 milliosmolar (mOsm) which, after correction for the presence of cytoplasmic droplets, yields a boar sperm water volume of 13.0 to 15.0 mum(3). Assuming 59% of the total cell volume is water, the total cell volume of boar spermatozoa is 22.0 to 25.4 mum(3). In addition, the experiment indicated that the relative water volume versus the reciprocal of the external osmolality (Boyle van't Hoff plot) was linear over the range of 210 to 1500 mOsm of sodium chloride (r(2) = 0.996), supporting the hypothesis that boar spermatozoa act as ideal osmometers. A non-zero y axis intercept of 0.23 from the Boyle van't Hoff plot indicated a 23% spin label accessible, but osmotically inactive water component.

Maturation, capacitation, and metabolism of goat spermatozoa using magnetic resonance methods

The ability of intact cells to reduce spin labels has been utilized to characterize the activity of spermatozoa of goat. The kinetics of reduction of TEMPO has been found to be sensitive to the quantity, quality and state of epididymal maturation of the spermatozoa. Presence of alcohol caused activation and Gossypol acetic acid left sperm activity unaltered. Electron spin resonance (ESR) and 31P Nuclear magnetic resonance (NMR) indicate that the period of in vitro capacitation requires optimization. 31P NMR spectra indicate a good correlation with the progressive maturation of the cells.

Effects of cryopreservation procedures on sperm membranes

Empirical approaches to semen cryopreservation have resulted in the production of young in a broad range of species. However, acceptable levels of fertility in most domestic animal species has not been achieved. In this review, an attempt has been made to describe the complexity of the sperm plasma membrane and the many steps in a cryopreservation procedure where membrane perturbations can occur. Improvement in sperm cryopreservation procedures will require a careful consideration of the complexity of the sperm plasma membrane, the interaction of its components and the influence of cooling, freezing and thawing on these interactions.

Cryopreservation of boar semen. III: Ultrastructure of boar spermatozoa frozen ultra-rapidly at various stages of conventional freezing and thawing

Ejaculated boar spermatozoa subjected to a conventional freezing and thawing process, were ultra-rapidly fixed, freeze-substituted and examined by electron microscopy to monitor the presence of real or potential intracellular ice and the degree of cell protection attained with the different extenders used during the process. Numerous ice crystal marks representing the degree of hydration of the cells were located in the perinuclear space of those spermatozoa not in proper contact with the extender containing glycerol (i.e. prior to freezing). The spermatozoa which were in proper contact with the extenders presented a high degree of preservation of the acrosomes, plasma membranes as well as the nuclear envelopes. No ice marks were detected in acrosomes before thawing, indicating that the conventional assayed cryopreservation method provided a good protection against cryoinjury. The presence of acrosomal changes (internal vesiculization, hydration and swelling) in thawed samples however, raises serious questions about the thawing procedure employed.

Cryopreservation of poultry sperm: the enigma of glycerol

This review summarizes recent data for cryopreservation of poultry sperm and data establishing the contraceptive effect of glycerol. Successful cryopreservation protocols for bovine sperm are compared to the requirements for rooster sperm, with emphasis on glycerol-induced alterations in avian reproductive systems. It has been shown that molar concentrations of glycerol can affect (a) physical features of the cytoplasm (cytoplasmic organization and viscosity), (b) permeability and stability of the membrane bilayer(s), and (c) noncovalent attachment of proteins to the sperm surface. Perturbing effects of glycerol on sperm metabolism and the essentiality of maintaining bioenergetic balance during the temperature changes associated with any cryopreservation protocol are discussed. Emphasis is placed on the processes in avian reproduction that may be altered by interactions with glycerol. Finally, we discuss the potential value of using available genetic models (lines of roosters differing in the capacity of their sperm to survive a freeze-thaw cycle) to clarify and overcome damage to poultry sperm induced by cryopreservation.

Predictive water loss curves for ram spermatozoa during cryopreservation: comparison with experimental observations

Calculated curves predicting intracellular water loss during cryopreservation at different cooling rates were calculated from published equations. To compute these curves, basic cell parameters specific to ram spermatozoa were measured, i.e., the total surface area (139 microns2), the hydraulic conductivity (0.222 micron3/micron2.atm-1.min-1), and its temperature dependence (0.045/degree C). Cell surface area was derived from measurements of physical dimensions. Hydraulic conductivity was calculated from measurements of the critical medium hypotonicity on exposure of sperm to various hypotonic solutions and the time taken for membrane rupture in sperm exposed to distilled water (spermolysis time). The temperature dependence of the water permeability was derived from measurements of spermolysis time at various temperatures above zero. Several discrepancies were noted between the resulting calculated curves and experimental observations made on the effects of cooling rate on sperm cell survival. These could be due to errors in the estimates of the basic parameters, or to false assumptions in the basic equations used to compute the curves, e.g., the validity of the Boyle-van't Hoff relationship. Nevertheless, this study represents a first attempt to predict intracellular water loss from ram sperm during cooling and may provide a novel approach for the interpretation of the many empirical studies carried out to investigate optimal conditions for the cryopreservation of sperm.

Differential effects of butylated hydroxytoluene analogs on bull sperm subjected to cold-induced membrane stress

Previous reports established that butylated hydroxy toluene (BHT) minimized cold-induced membrane rupture in sperm from several species. No data regarding the specificity of its effect is available. In this study 25 BHT analogs were tested for their effect on bovine sperm membrane stability. Fourteen were membrane lytic at 25 degrees C and 6 were neither membrane lytic nor membrane stabilizing. The remaining 5 compounds, a family of 2,6-tert-butyl phenols with substitutions at position 4 of hydrogen, methyl (BHT), ethyl, butyl, hexyl, or octyl, afforded effective membrane protection to cold shock. Since membrane protection is a function of both the ability of a compound to partition into the membrane and a molecule's effectiveness once there, an analysis of each analog's membrane partitioning, assessed by measuring the cellular analog/cholesterol ratio, showed the following extents of transfer for the analogs: ethyl = butyl greater than methyl = hydrogen greater than hexyl greater than octyl. Thus, an optimum chain length exists for partitioning from micellar donors into cells. A separate experiment established that all analogs, when incorporated in equivalent amounts, protect equally plasma and mitochondrial membranes from cold shock. No effect on acrosomal membrane stability was noted. BHT, but not the other analogs, reduced sperm motility. Addition of egg yolk to extender containing BHT analog protected sperm motility from cold shock but had little effect on membrane stabilization. Analysis of sperm membrane compartments revealed that little to no analog was partitioned into the outer acrosomal membrane or the plasma membrane overlying the acrosome, but rather was localized in other portions of the sperm. We conclude that (a) the effective BHT analogs, if partitioned into the membrane, are indistinguishable with regard to their capacity to eliminate cold-induced membrane lysis; (b) membrane-linked events (e.g., motility) are uniquely disrupted by a subset of this analog family; and (c) when concentrations of egg yolk and BHT analogs are carefully controlled, unique synergistic effects are noted.

Superoxide radical level and superoxide dismutase activity changes in maturing mammalian spermatozoa

Mammalian spermatozoa, which like other living cells are susceptible to oxygen toxicity, generate increasing quantities of superoxide radical as epididymal maturation proceeds. This is associated with a concomitant reduction in the activity of superoxide dismutase. A possible involvement of superoxide radicals in bringing about some of the reported oxidative changes occurring during epididymal maturation of mammalian spermatozoa is discussed. It is suggested that superoxide radical may be involved in regulating membrane changes accompanying sperm maturation.

Activation of iodine into a free-radical intermediate by superoxide: a physiologically significant step in the iodination of tyrosine

A pivotal biochemical event in the thyroid physiology is identified unravelling a superoxide anion radical-mediated activation of iodine into an active I.- form, which could be the intermediate that is incorporated onto tyrosine. This active iodine species gives fairly stable spin-adducts with PBN that could be characterized using EPR spectroscopy. Thus, a long-lasting puzzle regarding the iodine intermediate formed before iodination of tyrosine seems to be solved.

Discovery of a novel and alternate hydrogen peroxide generation machinery in the mammalian thyroid gland that modulates iodination of tyrosine

The hydrogen peroxide-dependent and peroxidase-mediated iodination of tyrosine, a pivotal step in the thyroxine biosynthesis in thyroid glands of mammals, has always been thought to be dependent on a glucose-glucose oxidase system to meet its demand for hydrogen peroxide. This report documents a novel and probably kinetically faster hydrogen peroxide-generating system operating in the thyroid gland cells involving the superoxide dismutase and superoxide anion radical. In the female cycling mice, the superoxide radical and superoxide dismutase activity are shown to be at persistently high levels, quite likely acting as a potent hydrogen peroxide synthesizer in the mammalian thyroid gland. The significance of this discovery in relation to the thyroid physiology is discussed.

A possible role of superoxide anion radical in the process of blastocyst implantation in Mus musculus

Superoxide anion radical and superoxide dismutase, the enzyme responsible for dismutating it, are both present in the ovary and uterus of Mus musculus during early pregnancy. The detectable, stable levels of superoxide radical and the constant high levels of superoxide dismutase in the ovary during early pregnancy suggests that these may be involved in the regulation of extended luteal steroidogenesis for the maintenance of pregnancy. An inverse correlation between the levels of superoxide anion radical and superoxide dismutase in the uterus is shown. The high levels of superoxide anion radical in the uterus on the early morning of Day 5 of pregnancy point towards a probable role for this radical in the act of implantation and in mediating the increased vascular permeability at the initiation of implantation.

Evaluation of butylated hydroxytoluene as a cryopreservative added to whole or skim milk diluent for bull semen

Effect of five concentrations of butylated hydroxytoluene on the percent motility and percent intact acrosomes was evaluated for bull sperm frozen and thawed in whole and skim milk diluents. Twelve ejaculates were frozen in .5-ml straws in moving nitrogen vapor after each ejaculate was split among the five butylated hydroxytoluene treatments within the two diluents. Prefreeze and postthaw percent motility and postthaw percent intact acrosomes were evaluated at 0 and 4 h. Before freezing, sperm motilities were similar in whole or skim milk diluents with and without butylated hydroxytoluene. Upon thawing, sperm motility was 10 percentage points higher in whole milk diluent containing .5 and .75 mM butylated hydroxytoluene than in samples without it. After 4 h, percentage motile sperm was similar among all whole milk treatments. Sperm motility was similar among all skim milk treatments at both 0 and 4 h. Percent intact acrosomes were similar among all treatments for each diluent. Oxidation in whole milk diluent stored at 4 degrees C for 1 wk was reduced in the presence of 1.0, 2.0, and 4.0 mM butylated hydroxytoluene.

Changes in the levels of superoxide anion radical and superoxide dismutase during the estrous cycle of Rattus norvegicus and induction of superoxide dismutase in rat ovary by lutropin

Superoxide dismutase, which has been shown to be present in a number of tissues, exhibits cyclic changes during the reproductive cycle of rats. An inverse correlation is seen between the levels of superoxide dismutase and superoxide radical. In immature, pseudopregnant rats, primed with human Chorionic Gonadotropin, lutropin seemed to induce ovarian superoxide dismutase, which could be blocked significantly by the introduction of anti-LH serum. These results point out the specific induction of superoxide dismutase by lutropin. It is reasonable to postulate that during luteal functioning, luteinizing hormone induces superoxide dismutase which in turn seems to play a central role generating hydrogen peroxide from superoxide anion radicals. Hydrogen peroxide, thus formed, drives the peroxidase-ascorbate system, responsible for production of progesterone.

Isolation and characterization of the plasma membrane of rat cauda epididymal spermatozoa

Cauda epididymal rat spermatozoa were isolated by flushing the excised epididymis and the plasma membrane was detached by a nitrogen cavitation treatment (500 psi, 10 minutes equilibration at 4 C). Membrane vesicles were recovered after sucrose gradient centrifugation. Portions of the sperm surface releasing the plasma membrane were assessed by light microscopy of fluoroscein isothiocyanate-succinylated concanavalin A-treated spermatozoa and by transmission electron microscopy. Plasma membrane was detached from the region overlying the acrosome from most spermatozoa and from the middle-piece overlying the mitochondria from some cells. Thus, the fraction analyzed was derived from at least two portions of the sperm surface. The fractions from the sucrose density gradient were analyzed for gross chemical composition (phospholipid, protein and sterol) and the protein components were detected after electrophoresis under denaturing conditions; the peak fractions (at density approximately 1.13 g/ml) were judged homogeneous. Replicate analyses of such preparations established mass ratios of protein to phospholipid of 0.63, total sterol to phospholipid of 0.18, and demosterol to cholesterol of 0.32. The molecular composition of the phospholipid fraction was determined to be 10% phosphatidylserine (mole percent), 3% phosphatidylinosital, 3% sphingomyelin, 31% phosphatidylethanolamine, 27% phosphatidylcholine, 10% diphosphatidylglycerol and 5% of an unknown component. Fatty acyl analyses of the phospholipid fraction revealed that approximately 70% of the residues consisted of palmitoyl (16:0) and stearoyl (18:0) acyl groups, with the balance distributed among various unsaturated acyl groups (18:1, 22:3, 22:4 and 22:5); about 40% of the recovered phospholipids represented ether acyl phosphatides. Differences in the lipid composition of rat vesicles described here and similar vesicles isolated from ram and boar spermatozoa (described previously) are discussed. The partitioning of the nitroxyl spin label 3-doxylheptane into vesicles isolated from rat and ram spermatozoa was assessed by electron paramagnetic resonance spectroscopy at temperatures between 4 C and 26 C; no difference in the response of the spin label in the two vesicle preparations was detected.

Flagellar movement of intact and demembranated, reactivated ram spermatozoa

The flagellar movement of intact ejaculated ram sperm, and of demembranated models reactivated with ATP, has been studied using high-speed, high-resolution video microscopy. Intact sperm attached to the coverslip by their heads had an average beat frequency of 20.9 Hz and an average wave amplitude of 20.2 micron. There was little difference in the beat frequency or waveform of these sperm and sperm swimming freely near the coverslip or captured by their heads with a micropipette and held far from the coverslip, indicating that the flagellar waveform of ram sperm is relatively resistant to distortion as a result of immobilization of the head or proximity to a surface. The beat envelope was nearly planar as determined by observations of free-swimming sperm and sperm captured by their head and oriented so they were beating either parallel or perpendicular to the plane of focus. The effect of various conditions for demembranation and reactivation of the sperm were examined. Treatment of sperm with 0.2% Triton X-100 removed most of their plasma membrane. Under optimal conditions, nearly 100% of the demembranated sperm reactivated at MgATP2- concentrations ranging from approximately 4 microM to approximately 20 mM. From approximately 1 mM to approximately 10 mM MgATP2-, their beat pattern closely resembled that of intact sperm; beat frequency depended on MgATP2- concentration. Percent motility was maximal between pH 7.5 and 8.0 and decreased sharply below pH 7.0 and above pH 8.5. The addition of 50 microM cAMP to the reactivation medium had no effect on percent motility or the beat pattern and did not accelerate the initiation of movement.

The effect of buffer osmolality on the survival of cat () spermatozoa at 5°C

Cat semen was diluted at 37 degrees C in Tes-Tris buffer (TesT), pH 7.5, at osmolalities ranging from 195 to 390 m0sm/kg, cooled to 5 degrees C over 90 minutes and stored for 24 hours at that temperature. Motility and percentage of spermatozoa staining with a supravital stain were estimated before cooling, after cooling and after storage for 24 hours. The osmolality of undiluted pooled ejaculates from five animals was measured, and also that of different diluents (citrate with phosphate buffer, lactose and TesT-egg yolk) used for cat semen. The osmolality measurements of cat semen suggested an osmolality of less than 320 m0sm/kg at ejaculation, increasing with time after ejaculation. Varying the egg yolk concentrations (2% to 20%) did not affect the osmolality of TesT diluent. Diluent osmolalities of less than 292 m0sm/kg were found to reduce sperm motility significantly (P <0.001 ) although there was no significant increase in the percentage of cells staining with a supravital stain, while those greater than 325 m0sm/kg increased the variation of response among animals. Cooling and storage significantly reduced motility (P <0.01 to P <0.001 ) and increased the number of stained cells (P <0.001 ). There were significant differences between ejaculates (P <0.01 ) and significant interactions between osmolality and cooling/storage (P <0.05 to P <0.001 ). The best overall results were seen with a TesT diluent of 292 to 325 m0sm/kg which supported good motility for at least 24 hours.

Synthetic antioxidants: biochemical actions and interference with radiation, toxic compounds, chemical mutagens and chemical carcinogens

Biological actions of 4 commonly used synthetic antioxidants--butylated hydroxyanisole, butylated hydroxytoluene, ethoxyquin and propyl gallate--on the molecular, cellular and organ level are complied. Such actions may be divided into modulation of growth, macromolecule synthesis and differentiation, modulation of immune response, interference with oxygen activation and miscellaneous. Moreover, an overview of beneficial and adverse interactions of these antioxidants with exogenous noxae is given. Beneficial interactions include radioprotection, protection against acute toxicity of chemicals, antimutagenic activity and antitumorigenic action. Possible mechanisms of the antitumorigenic action of antioxidants are discussed. This discussion is centered around antioxidant properties which may contribute to a modulation of initiation-related events, especially their ability to interfere with carcinogen metabolism. The beneficial interactions of antioxidants with physical and chemical noxae are contrasted to those leading to unfavorable effects. These include radiosensitization, increased toxicity of other chemicals, increased mutagen activity and increased tumor yield from chemical carcinogens. At present, the latter one can most adequately be characterized as tumor promotion at least in the case of butylated hydroxytoluene. It is concluded that current information is insufficient to promote expectations as to the use of antioxidants in the prevention of human cancer.

Review: putative mutagens and carcinogens in foods. III. Butylated hydroxytoluene (BHT)

Although the average American's daily consumption of BHT can be measured in milligrams, there are numerous reports that BHT causes organ damage in laboratory animals. Only a few genotoxic effects of BHT have been reported, however, including mutagenicity in the abnormal sperm assay and ambiguous results regarding its teratogenicity. More dramatic are the modulatory effects of BHT on the actions of established mutagens and carcinogens. BHT can either enhance or inhibit mutagenic potency, depending on the substance tested. For example, in the Ames test, BHT is antimutagenic towards benzo(a)pyrene, but increases the number of Salmonella revertants induced by aflatoxin B1. BHT is one of the few compounds to have both tumor prophylactic and tumor promoting capacities. It is the temporal sequence in which BHT and carcinogens are administered to test animals which determines how BHT affects the response to these carcinogens. In common with other antioxidants, BHT inhibits the ability of carcinogens to induce tumors in various rodent organs when the animal is given BHT prior to carcinogen treatment. Unlike other antioxidants, however, the number of tumors increase when BHT is administered after carcinogen exposure. The comutagenic and cocarcinogenic properties of BHT have been demonstrated in tests ranging from the Ames test to cell transformation procedures to in vivo assays. These effects are probably mediated by metabolites of BHT, rather than by BHT itself.