Effects of heat stress on mouse testicular cells and sperm chromatin structure

Scrotal regions of mice were exposed to a 38.0, 40.0, or 42.0 degrees C (+/-0.1) H2O bath for 60 minutes to determine the effects of elevated temperatures on testicular cells and sperm chromatin structure. Mice were killed on various days after exposure, and ratios of acridine orange-stained testicular cell populations were determined by flow cytometry. Testicular weights of mice exposed to 42.0 degrees C decreased significantly day 1 (P < 0.01) through 35 (P < 0.001). Also, a significant relative decrease in testicular haploid cells was seen on days 3-35 (P < 0.001) with a corresponding increase in the diploid population (P < 0.001). Testicular analyses of mice exposed to 38.0 degrees C were not significantly different from control values. Testis weights of mice exposed to 40.0 degrees C were not affected, but a relative decrease in percent haploid cells occurred on days 11 and 14 (P < 0.001). The sperm chromatin structure assay (SCSA) was used to measure the susceptibility of cauda epididymal sperm DNA to in situ denaturation at low pH. Caudal epididymides of mice exposed to 42.0 degrees C had no sperm. Caudal epididymal sperm from mice exposed to 40.0 degrees C were most susceptible to acid-induced DNA denaturation on days 3 (P < 0.05), 7, 11, and 14 (all P < 0.001). The 38.0 degrees C exposed mice showed some minor sperm chromatin abnormalities at later time points (days 11-35). When compared to sperm head morphology measurements, SCSA parameters were more sensitive indicators of heat-induced sperm abnormalities. These results show that mouse spermatogenesis is disrupted by scrotal exposure to environmental temperatures several degrees over normal physiological temperature and, of more biological interest, that some thermal ranges above normal allowed production of sperm with compromised nuclear chromatin structure.

Bull sperm head morphometry related to abnormal chromatin structure and fertility

This study investigated the relationship between morphologically abnormal sperm, sperm chromatin structure, and fertility. Semen samples were obtained from 13 bulls. The sperm chromatin structure assay (SCSA), a sensitive measure of denaturability of sperm nuclear DNA in situ following acid treatment, was performed on each sample to quantitate abnormal chromatin structure. Feulgenstained sperm head morphology was measured by computerized image analysis (ONCOR-Image): Sixteen parameters were measured for each of 200 nuclei per sample. Fertility estimates were available for nine of the bulls. The SCSA variable SD alpha t was correlated with fertility ranking (r = 0.617, P < 0.01). No correlations were seen between means of the imaging variables and SCSA variables % COMP alpha t or SD alpha t. Significant correlations (P < 0.05) were seen between SD alpha t and the variation of imaging variables eccentricity, width, and light blobs. Significant correlations (P < 0.05) were seen between % COMP alpha t and the variation of imaging variables area, perimeter, p2a, bending energy, nmac, sphericity, eccentricity, length, and width. A regression model for fertility rankings incorporating the standard deviation of the imaging variables area, bending energy, nmac, eccentricity, condensity, light blobs, and dark blobs was highly significant (r2 = 0.999, P < 0.05). These results indicate that variation of morphometry measurements is likely a sensitive biomarker related to fertility potential and abnormal chromatin structure.

Mammalian sperm DNA susceptibility to in situ denaturation associated with the presence of DNA strand breaks as measured by the terminal deoxynucleotidyl transferase assay

Sperm from four mammalian species were analyzed by the sperm chromatin structure assay (SCSA) and the terminal deoxynucleotidyl transferase assay (TdTA) using flow cytometry. The SCSA quantitates the susceptibility of sperm nuclear DNA to in situ acid denaturation, while the TdTA quantitates the presence of endogenous DNA strand breaks in sperm nuclear chromatin. Correlations were seen between the percentage of sperm cells showing susceptibility to in situ acid denaturation and the percentage of cells showing the presence of DNA strand breaks for humans (r = 0.56, P = 0.004), rams (r = 0.84, P < 0.001), bulls (r = 0.78, P < 0.001), and stallions (r = 0.65, P < 0.001). No significant differences were seen when using fresh or frozen samples for either assay. These results suggest that sperm cells that are more susceptible to in situ DNA denaturation may have a greater number of accessible endogenous DNA strand breaks. We hypothesize that the DNA strand breaks produced in the normal transition from a somatic cell histone complex to a protamine complex are not ligated properly, resulting in residual DNA strand breaks and altered chromatin structure. Alternatively, altered chromatin structure could lead to the accessibility of the endogenous DNA strand breaks.

Effects of X-irradiation on mouse testicular cells and sperm chromatin structure

The testicular regions of male mice were exposed to x-ray doses ranging from 0 to 400 rads. Forty days after exposure the mice were killed and the testes and cauda epididymal sperm removed surgically. Flow cytometric measurements of acridine orange stained testicular samples indicated a repopulation of testicular cell types following x-ray killing of stem cells. Cauda epididymal sperm were analyzed by the sperm chromatin structure assay (SCSA), a flow cytometric measurement of the susceptibility of the sperm nuclear DNA to in situ acid denaturation. The SCSA detected increased susceptibility to DNA denaturation in situ after 12.5 rads of x-ray exposure, with significant increases following 25 rads. Abnormal sperm head morphology was not significantly increased until the testes were exposed to 60 rads of x-rays. These data suggest that the SCSA is currently the most sensitive, non-invasive method of detecting x-ray damage to testicular stem spermatogonia.

Effects of acetaminophen and hydroxyurea on spermatogenesis and sperm chromatin structure in laboratory mice

High doses of acetaminophen (400 mg/kg) or hydroxyurea (200 mg/kg) given intraperitoneally daily for 5 d caused reduction in relative testicular weight in mice (B6C3/F1/BOM M). Testicular atrophy of several tubules was seen in the hydroxyurea-treated mice 5 d after the last exposure, whereas acetaminophen did not lead to such changes. Exposure to acetaminophen caused neither a depletion of glutathione in the testis nor a marked increase in covalent binding. In contrast, significant decreases in the incorporation of thymidine into the testis were observed during the first 3 h following a single treatment with acetaminophen (100 to 400 mg/kg) or hydroxyurea (100 to 200 mg/kg). In mice treated with acetaminophen (400 mg/kg) or hydroxyurea (200 mg/kg) daily for 5 d, flow cytometric analysis revealed large reductions in one of the tetraploid populations of testicular cells (mostly early pachytene spermatocytes) on days 5 and 10. Changes in the populations of the various spermatid stages occurred later; thus, both compounds appeared to cause a delay in spermiogenesis. Indications of abnormal chromatin structure were seen in an increased frequency of vas deferens sperm on days 27 and 33 after the last exposure, when measured as increased susceptibility towards DNA denaturation in situ. In conclusion, high doses of acetaminophen or hydroxyurea inhibit DNA synthesis in the testis. The present data indicate that this leads to reduced testicular weight, a reduction in the number of early pachytene spermatocytes, changes in the proportions of the various spermatid stages, and an apparent alteration in sperm chromatin structure.

Expression of an avian protamine in transgenic mice disrupts chromatin structure in spermatozoa

The objective of this study was to determine the consequences of disrupting spermatozoal chromatin condensation on spermatozoal development and function. The avian protamine, galline, was targeted to spermatids of transgenic mice using the mouse protamine 1 gene promoter. Three transgenic mouse lines were established that expressed galline mRNA at 65%, 120%, and 185% of the level found in rooster testis. Galline mRNA accumulated in round spermatids to levels similar to that of mouse protamine and, as with the mammalian counterpart, translation was delayed until the elongating spermatid stage. Protein gels revealed that galline accumulated in mature spermatozoa whereas mouse protamines were reduced, suggesting that galline competes with protamines for binding to spermatozoal DNA. Acridine orange binding analysis indicated that DNA of the transgenic spermatozoa was not as tightly packed as that of controls. This was corroborated by electron microscopy, which revealed disruption of the normal dense chromatin structure of spermatozoal heads. Despite these perturbations of chromatin condensation, the transgenic spermatozoa were functionally normal, as the majority of transgenic mice had normal fertility. However, in mice that expressed excessive galline, there was a gradual destruction of seminiferous tubules leading to infertility. Our findings suggest that very precise packaging of DNA in germ cells may not be essential for subsequent unpackaging in the pronucleus of fertilized eggs and for subsequent normal development of the embryo.

Glutathione depletion potentiates ethyl methanesulfonate-induced damage to sperm chromatin structure

Male rats were treated with phorone at dosages previously shown to reduce glutathione in rodent reproductive tracts, followed by a single challenge with ethyl methanesulfonate, a known mutagenic and clastogenic agent. Epididymal sperm collected 8 and 15 days after exposure from phorone pretreated animals had a significantly greater alteration of sperm chromatin structure, defined as an increased susceptibility to DNA denaturation in situ, relative to sperm obtained from animals injected with saline alone or saline+EMS (50, 100, 150, or 200 mg/kg bw). These data support the hypothesis that ethyl methanesulfonate-induced alkylation of developing sperm chromatin protamines causes a significant stress on chromatin structure leading to increased DNA damage. This is the first report showing that glutathione depletion potentiates EMS-induced chromatin structural alterations that are likely related to dominant lethal mutations.

Studies on sperm chromatin structure alterations and cytogenetic damage of mouse sperm following in vitro incubation. Studies on in vitro-incubated mouse sperm

Mouse epididymal sperm incubated in Tyrode's T6 fertilization media were analyzed over time for chromosome damage by two methods. First, cytogenetic analysis was done on paternal pronuclei metaphase chromosomes. After 6 hours incubation 11% of the cells demonstrated chromosome structural abnormalities. Secondly, sperm nuclei were measured by the sperm chromatin structure assay, which is a measure of the susceptibility of sperm DNA to the nuclei demonstrated an increased susceptibility to DNA denaturation, reaching near 100% by 48 hours. Changes in chromatin structure at the molecular level may lead to chromosome breaks seen in pronuclear chromosomes.

Zinc-silicon interactions influencing sperm chromatin integrity and testicular cell development in the rat as measured by flow cytometry

Flow-cytometric procedures were used to determine effects of dietary Zn and Si variations on rat testicular cell development, including integrity of caudal epididymal sperm chromatin structure defined as the susceptibility of DNA to denaturation in situ. Concentrations of 4 (deficient), 12 (adequate), and 500 (excessive) mg of Zn/kg of diet were used with Si concentrations of 0 (low), 540 (medium), and 2,700 (high) mg/kg of diet in a 3 x 3 factorial arrangement. Three-week-old Sprague-Dawley male rats were fed the experimental diets for 8 wk. Rats fed the Zn-deficient/Si-low diet demonstrated significant deviations in the ratio of testicular cell types present, including a reduction of S phase and total haploid cells. Furthermore, approximately 50% of epididymal sperm had a significant decrease in resistance to DNA denaturation in situ. In the Zn-deficient/Si-medium treatment, the effects of Si on animal and testicular growth, distribution of testicular cell types, and sperm chromatin structure integrity were quite similar to the effects of the Zn-adequate diets. A toxic effect of Zn on sperm chromatin structure integrity observed in the Zn-excess/Si-medium treatment seemed to be counteracted by Si in the Zn-excess/Si-high treatment. Silicon at medium and high levels seems to affect Zn metabolism through potentiation and antagonistic reactions, respectively. Zinc deficiency likely disrupts the normal sperm chromatin quaternary structure in which Zn plays a role by providing stability and resistance to DNA denaturation in situ.

Hydroxyurea exposure alters mouse testicular kinetics and sperm chromatin structure

The effects of hydroxyurea (HU) on testicular cell kinetics and sperm chromatin differentiation were investigated in mice. Whole testis, minced testicular cell suspensions and caudal epididymal sperm cells were obtained at 8 and 29 days after i.p. injections containing 0, 25, 50, 100, 200, 400 and 500 mg/kg HU x 5 days. Testis weights were unaffected by 25 mg/kg HU while 500 mg/kg caused up to a 50% loss of testicular weight by 29 days. Flow cytometrically measured acridine-orange (AO) stained testicular cells revealed altered population ratios at the highest dosages at 8 days and for all dosages except 25 mg/kg HU at 29 days. At 8 days, 400-500 mg/kg HU caused a near depletion of tetraploid cells. Flow cytometry of AO stained sperm, previously treated with acid to potentially induce DNA denaturation, was used to follow the shift from normal chromatin structure to an abnormal form with increased sensitivity to DNA denaturation in situ. The extent of DNA denaturation was quantitated for each cell by the computer-derived value alpha t, alpha t = [red/(red+green) fluorescence]. The flow cytometry measures, standard deviation of alpha t (SD alpha t), mean of alpha t (X alpha t) and cells outside the main peak of alpha t (COMP alpha t), gave similar dose response curves to the sperm head morphology assay. SD alpha t was more sensitive than the X alpha t as a measure of HU-induced alteration of chromatin structure. The major conclusions reached are that HU inhibits DNA synthesis, probably by inhibiting ribonucleotide reductase, causing maturation depletion of pachytene spermatocytes and, subsequently, depletion of meiotic daughter cells and differentiated cell types leading to mature sperm. This inhibition of DNA synthesis is related to an alteration of sperm chromatin structure and abnormal sperm head morphology.

Rapid determination of sperm cell concentration in bovine semen by flow cytometry

A flow cytometric technique is described for determining sperm concentration in fresh or extended semen with improved accuracy, precision, repeatability, ease of conduct, and rapidity. The technique is designed to measure the ratio of a known number of fluorescent beads admixed with sperm stained with either acridine orange or propidium iodide. A significant advantage of the technique is the distinct resolution between sperm and other particles (e.g., somatic cells, fat droplets, and bacteria in the semen or extender) that interfere in other counting protocols. Field testing of this protocol over the past 3 yr has demonstrated its superiority over the Coulter counter, hemacytometer, and spectrophotometer for accuracy in counting sperm in extended semen and the accuracy of counting sperm in straws based on preextension spectrophotometric determination of sperm concentration. Sperm chromatin quality can be determined simultaneously with this sperm counting procedure. This approach to counting sperm provides an excellent procedure for quality control of sperm numbers in processed semen.

Flow cytometric analysis for reproductive biology

Flow cytometric studies of spermatogenesis have been advanced by the need for: i) rapid, sensitive, objective and multiparameter measurements of reproductive effects due to environmental, occupational, and therapeutic exposure to toxicants; and ii) assessment of fertility potential of human and animal sperm. As a consequence, various flow cytometric techniques are already available to identify germ cell subpopulations undergoing both proliferative and maturative processes in normal and perturbed conditions. Significant improvements have been introduced in order to investigate the spermatogenic complex differentiation pathway and the apparent uniformity of mature sperm. Flow cytometry (FCM) has been applied to the measurement of both testis and sperm cells in a variety of species, including man. End points considered in toxicology studies are: altered testicular germ cell ratios, DNA and RNA content, increase of the coefficient of variation, induction of diploid elongated spermatids and diploid sperm, altered nuclear morphology, sperm cell viability, mitochondrial function and sperm chromatin structure. Precise DNA content measurements allow accurate analysis to determine the proportion of X- and Y-chromosome bearing sperm and sorting of these subpopulations for gender preselection. FCM technology has reached a maturation level that allows its inclusion in the list of available and routine methods for reproductive studies in human and animal populations.

Effects of methyl methanesulfonate on mouse sperm chromatin structure and testicular cell kinetics

Effects of methyl methanesulfonate (MMS) on mouse testicular cell kinetics and sperm chromatin structure were determined flow cytometrically. Mice were exposed to a single ip injection of saline containing 0 or 150 mg/kg MMS. Relative ratios of 1N, 2N and 4N testicular cells were not affected until 22 days postexposure. Ratios of 1N cell types were altered from 13 to 22 days and were near normal by 25 days. This study revealed an MMS induced alteration of chromatin structure in testicular, elongated spermatids by the sperm chromatin structure assay (SCSA), a flow cytometric measure of the susceptibility of acridine orange stained sperm DNA to denaturation in situ. The SCSA also detected alterations in cauda sperm chromatin structure at 3 days, which was 8 days prior to alterations in sperm head morphology, indicating the increased sensitivity of the SCSA. SCSA data were practically similar whether measuring either fresh or frozen/thawed sperm, or whether measured by two different types of flow cytometers: a) laser driven, orthogonal optical axis; or b) low cost mercury arc lamp system with epiillumination. The data support the model of Sega and Owens [Mutat Res 111:227-244:1983] that MMS alkylates cysteine-SH groups in sperm protamines, thereby destabilizing sperm chromatin structure and leading to broken chromosomes and mutations.

Effects of egg yolk-citrate and milk extenders on chromatin structure and viability of cryopreserved bull sperm

Semen from four Holstein bulls was evaluated to compare effects of four extender treatments on postthaw semen quality. Extender fractions A and B, either heated whole milk or 20% egg yolk-citrate, were combined to yield the extender treatments 1) milk and milk, 2) milk and egg yolk-citrate, 3) egg yolk-citrate and milk, and 4) egg yolk-citrate and egg yolk-citrate. Semen was evaluated at thawing and after 30, 60, 120, and 180 min of incubation at 38.5 degrees C. Flow cytometry showed that acridine orange-stained sperm were most susceptible to in situ DNA denaturation when fraction A was milk. For sperm stained with rhodamine 123, flow cytometry showed that the proportion with intact mitochondrial membrane potential was lowest of all treatments at thawing but greatest at 180-min incubation with milk and milk extender. Flow cytometry of propidium iodine-stained sperm showed greatest proportion of cell membrane intact sperm when fraction A was egg yolk-citrate. Light microscopy showed the lowest proportion of cell membrane intact sperm with milk and milk extender after eosin-aniline blue vital staining. Postthaw motility scores tended to be reduced when both extender fractions were egg yolk-citrate. Results demonstrate differential extender effects on postthaw semen quality and indicate that altering extender composition or sequence of adding extender components may improve postthaw quality of cryopreserved sperm.

Individuality of DNA denaturation patterns in human sperm as measured by the sperm chromatin structure assay

Eight monthly semen samples from 45 men not known to be exposed to industrial toxicants were measured by the flow cytometric sperm chromatin structure assay (SCSA). This assay determines susceptibility of sperm DNA to in situ, acid-induced denaturation and is quantitated by the metachromatic shift of acridine orange fluorescence from green (native DNA) to red (denatured DNA). The observed green versus red fluorescence scattergram (cytogram) patterns were generally unique between donors and homogeneous within a donor over time. Within a donor, the cytogram patterns were the same whether intact sperm cells or detached nuclei were measured. For some individuals the cytogram patterns differed for some months and then returned to the original pattern. Intraclass correlations for mean and standard deviation of alpha t [alpha t = red/(red + green) fluorescence] were higher (.67 to .90) than any classically measured semen variables, suggesting that SCSA results within an individual were more consistent than other measures. Furthermore, average within-donor CV of alpha t parameters expressed as a percent of any given individual's means was around 10%, which is significantly lower than those derived from common semen measures. The SCSA is an objective, technically sound, biologically stable, sensitive, and feasible measure of semen quality.

Comparison of semen quality in young and mature Holstein bulls measured by light microscopy and flow cytometry

Random samples of cryopreserved, milk-extended semen, collected from 20 Holstein bulls at about 14 mo of age (young) and again at about 4 yr of age (mature), were evaluated at thawing and during 3-h incubation to compare semen quality of young versus mature bulls. Evaluation by differential interference contrast microscopy showed greater proportions of cytoplasmic droplets in semen from young versus mature bulls. Mature bulls exhibited greater proportions of intact acrosomes in freshly thawed semen than did young bulls. Evaluation of sperm chromatin structure by flow cytometry after staining with acridine orange showed lower values for mature versus young bulls, indicating resistance of DNA in nuclear chromatin to acid denaturation increased with age. Correlations between ages for most sperm morphology, acrosome integrity, and flow cytometry variables were high and positive. Nonreturn rate for young bulls was positively related to morphologically normal sperm and acrosomal integrity and negatively related to flow cytometry traits. Results suggest semen quality of young bulls was related to subsequent quality as mature bulls. With flow cytometry, differences were detected between semen samples that were not evident with light microscopy.

Effect of 1,3-dinitrobenzene on prepubertal, pubertal, and adult mouse spermatogenesis

Exposure of prepubertal, pubertal, and adult mice to 0, 8, 16, 32, 40, or 48 mg 1,3-dinitrobenzene (m-DNB)/kg body weight and measuring responses 1-25 d posttreatment (dpt) demonstrated significant effects on testicular function only at 48 mg/kg dosage. m-DNB had no effect on body or testis weights with the exception of reduced adult mouse testis weights at 22 dpt with 48 mg/kg (p less than .05). None of the exposures resulted in detectable levels of germinal epithelial cells in the ductus epididymis. Exposure of prepubertal and pubertal mice to m-DNB caused only minimal nonsignificant changes in the relative percent of testicular cell types present up to 25 dpt. The adult mice testicular cell type ratios, in particular the round and elongating spermatid populations, changed significantly at doses of 48 mg/kg. Also, a reduction in the percent tetraploid cells occurred at d 1, suggesting these cells may be a primary target of m-DNB action. Caput and caudal sperm from mice exposed to m-DNB prior to puberty did not demonstrate an increased susceptibility to DNA denaturation when analyzed by the sperm chromatin structure assay. However, in pubertal mice, m-DNB exposure further exaggerated the abnormal chromatin structure that normally characterizes sperm during the onset of sperm production. In adult mice, 48 mg/kg resulted in increased susceptibility to DNA denaturation of caput sperm chromatin at 11 dpt (p less than .05) and in caudal sperm at 22 dpt (p less than .01). The abnormal chromatin structure of cauda sperm from adult mice was highly correlated with sperm head morphology abnormalities (ABN; 0.82 to 0.95, p less than .01, 11 and 22 dpt, respectively), but showed lower correlations with dose (0.60 to 0.79, p less than .01, 11 and 22 dpt, respectively). For pubertal mice, a positive relationship was also observed between the variation of sperm chromatin structure abnormalities and ABN. The effect of m-DNB on testicular function in prepubertal and pubertal mice appear to be less pronounced than in adult mice. Furthermore, following exposure to the same dosage, the effect of m-DNB is less severe in adult mice than that observed for adult rats as reported in the companion paper.

Flow cytometric analysis of effects of 1,3-dinitrobenzene on rat spermatogenesis

Exposure of 100-d old rats to 1,3-dinitrobenzene (m-DNB) at dosages up to 48 mg/kg resulted in disruption of spermatogenesis as measured by flow cytometry (FCM) of acridine orange-stained sperm and testis cells. One day (d 1) after a single exposure to 48 mg/kg m-DNB, FCM measurements of caput epididymal fluid cells demonstrated the presence of testicular germinal epithelial cells apparently sloughed off into the epididymis. Also, at d 1 after the same exposure, a decrease in pachytene spermatocytes was observed. By d 16 after exposure to 32 or 48 mg/kg, testicular damage was evidenced by an alteration of cell type ratios in FCM-analyzed populations of testicular cells. Extensive recovery of cell type ratios occurred by d 32. At d 16, dosages of 32 and 48 mg/kg caused alterations of sperm chromatin structure as determined by the flow cytometric sperm chromatin structure assay (SCSA); 48 mg/kg caused alterations at both d 16 and d 32. Exposure to m-DNB caused a dose response increase in percent sperm head morphology abnormalities (%ABN) assessed in cauda epididymal and vas sperm. A slightly higher correlation existed between dose and SCSA alpha t values (d 16, .78; p less than .01) than between dose and %ABN (d 16, .70; p less than .01). Also, a higher correlation existed between standard deviation of alpha t (SD alpha t) values and %ABN (.97; p less than .01) than between dose and %ABN (.70; p less than .01). This study demonstrated rapid and unique FCM procedures originally derived for reproductive toxicology studies in mice to be equally useful for studies in rats.

Flow cytometric analysis of rodent epididymal spermatozoal chromatin condensation and loss of free sulfhydryl groups

Flow cytometric measurements were made on acridine orange (AO) and 7-diethylamino-3-(4'-maleimidylphenyl)-4-methyl-coumarin (CPM)-stained epididymal- and vas deferens-derived spermatozoal nuclei to follow the course of chromatin condensation and oxidation of free sulfhydryl groups, respectively, during passage through mouse and rat posttesticular reproductive tracts. Alterations of mouse and rat spermatozoal chromatin during transition from a testicular elongated spermatids to epididymal caput spermatozoa resulted in a threefold loss of DNA stainability with AO. Passage of spermatozoa from the caput to corpus epididymis was accompanied by an approximate 15% loss of DNA stainability, which was maintained at that level throughout passage into the vas deferens. AO stainability of epididymal spermatozoal nuclei was generally independent of -SH group stainability. CPM stainability of rat spermatozoal nuclei free -SH groups was 83%, 18%, and 11% of caput spermatozoal values for corpus, cauda epididymis, and vas deferens, respectively. Comparable values for mice were 69%, 20%, and 18%. CPM stainability was relatively homogeneous for these mouse and rat reproductive tract regions, except mouse corpus epididymis spermatozoal nuclei stained very heterogeneously. Rat spermatozoa detained by ligature up to 7 days in the caput, corpus, and cauda epididymi had CPM staining values equal to or below those of normal vas spermatozoa, indicating that disulfide (S-S) bonding is intrinsic to the spermatozoa and is independent of the epididymal environment. These data suggest that chromatin condensation and loss of spermatozoal DNA stainability during passage from the testis to the vas deferens are independent of S-S bonding.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo and in vitro effects of hydralazine on cellular growth, differentiation, and chromatin structure

The effects of hydralazine (1-hydrazinophthalazine), an antihypertensive drug, on mammalian cell growth, viability, and differentiation were assessed using Friend leukemia cells, Chinese hamster ovary cells, human lymphocytes, and rat lymphocytes, testicular germ cells, and epididymal sperm. Cultured cells in exponential phase growth were more susceptible to hydralazine cytotoxicity than stationary phase (G0) cells. Growth inhibition was associated with a dose-related slowdown of cell progression through S phase and was observed prior to a decrease of cell viability. At high drug concentrations, progression in all phases of the cell cycle was partially or totally inhibited. Hydralazine did not have an effect on the proliferation and differentiation of testicular germ cells in spontaneously hypertensive rats receiving 0-90 mg/kg/day (up to 20 times the dose used in humans) of hydralazine for a 12-week period. Hydralazine-exposed, histone-containing somatic cells and protamine-containing sperm cells failed to show any alterations in stainability with a DNA-intercalating dye nor in the susceptibility of nuclear DNA to undergo acid-induced denaturation in situ. The data suggest that hydralazine causes a dose-related suppression of mammalian cell growth with S phase appearing to be the most susceptible to hydralazine cytotoxicity. Furthermore, the interaction of hydralazine with chromatin at concentrations leading to antigenicity did not inhibit DNA staining with the intercalating dye acridine orange, suggesting that the drug does not competitively intercalate at a detectable level. Association of hydralazine with chromatin did not cause a detectable level of stabilization or destabilization of the DNA to denaturation in situ.

The sperm chromatin structure assay. Relationship with alternate tests of semen quality and heterospermic performance of bulls

Data obtained by the sperm chromatin structure assay (SCSA) on spermatozoa from nine bulls were correlated with fertility, measured by heterospermic performance (-0.94, P less than 0.01) and by alternate tests of sperm quality, including motility, acrosome integrity, Sephadex filtration and morphology of spermatozoa (all significant at P less than 0.05 to P less than 0.01). The SCSA uses flow cytometry to determine the susceptibility of nuclear DNA to low pH-induced denaturation in situ as measured by the ratio of acridine orange binding to double- or single-stranded DNA. The error associated with multiple SCSA measurements was relatively low. The primary finding is that the assay of chromatin structure stability performed on killed spermatozoa was as highly correlated with the heterospermic performance of semen as the best of the classical tests for semen quality. The SCSA may therefore be a highly useful technique for evaluation of sperm quality.

Heterogeneity of sperm nuclear chromatin structure and its relationship to bull fertility

The relationship between sperm nuclear chromatin structure and fertility was evaluated in two groups of Holstein bulls: Group 1, 49 mature bulls, and Group 2, 18 young bulls. Fertility ratings had been estimated for Group 1 and nonreturn rates were known for Group 2. Semen samples were measured by the sperm chromatin structure assay (SCSA): sperm were treated to induce partial in situ DNA denaturation, stained with acridine orange, and evaluated by flow cytometry. Acridine orange intercalated into double-stranded DNA emits green fluorescence upon excitation with 488 nm light, and red fluorescence when associated with single-stranded DNA. An index of DNA denaturation per cell is provided by alpha-t [alpha t = red/(red + green) fluorescence]. The standard deviation (SD alpha t), coefficient of variation (CV alpha t) and proportion of cells outside the main population (COMP alpha t) of the alpha t distribution quantify the extent of denaturation for a sample. Intraclass correlations of the alpha t values were high (greater than or equal to 0.70), based on four collections obtained over several years from Group 1 bulls. Negative correlations were obtained between fertility ratings and both SD alpha t (-0.58, p less than 0.01) and COMP alpha t (-0.40, p less than 0.01) in Group 1, and between nonreturn rates and both SD alpha t (-0.65, p less than 0.01) and COMP alpha t (-0.53, p less than 0.05) in Group 2. These data suggest that the SCSA will be of value for identification of low fertility sires and poor quality semen samples.

Effects of the fungicide methyl-benzimidazol-2-yl carbamate (MBC) on mouse germ cells as determined by flow cytometry

Dual-parameter (DNA, RNA) flow cytometry (FCM) measurements were made on testicular and epididymal sperm cells isolated from mice exposed by oral gavage to 0, 250, 500, or 1000 mg/kg X 5 d of the fungicide methylbenzimidazol-2-yl carbamate (MBC), which is known to bind with tubulin subunits and inhibit polymerization and microtubule formation. Effects of exposure to MBC were measured at 7, 24, and 39 d posttreatment. MBC had no effect on body weights, but testis weights and sperm parameters were altered, with few exceptions, only at the highest exposure level. Testis weights were reduced by about 25% at 7 and 24 d after exposure; recovery was observed by 39 d after treatment. FCM measurements of testicular cells showed relative percentages of certain testicular populations (round, elongating, and elongated spermatids) were different from the control pattern 7 and 24 d after treatment. The mean percent of cauda epididymal sperm head morphology abnormalities and the susceptibility of the nuclear DNA to denaturation were both elevated at 7, 24, and 39 d after exposure to 1000 mg/kg. The level of denaturation was determined by FCM measurements of the metachromatic shift in acridine orange (AO) stained sperm nuclei from green (native DNA) to red (single-stranded DNA) fluorescence and quantitated by the expression alpha t[red/(red + green] fluorescence. These data demonstrate that spermatogenesis is sensitive to high-dose MBC exposure resulting in an altered ratio of testicular cell types present, abnormal sperm head morphology, and an altered sperm chromatin structure.

Semen cryopreservation and artificial insemination for Hodgkin's disease

Seventy-nine men with Hodgkin's disease were treated with chemotherapy protocols at Memorial Sloan-Kettering Cancer Center and had pretreatment semen analysis performed at the area semen bank. The patients were evaluated to determine: the quality of pretreatment semen, the effect of treatment on spermatogenesis, and the success rate of artificial insemination after semen cryopreservation. Pretreatment sperm concentration, fresh motility, fresh progression, postthaw motility and postthaw progression were all significantly decreased in men with Hodgkin's disease compared with normal controls. Posttreatment semen analysis in 44 men showed azoospermia in 80%, sperm concentration, less than or equal to 10 X 10(6)/mL in 11%, and sperm concentration greater than 10 X 10(6)/mL in 9%. Eleven couples attempted artificial insemination using cryopreserved semen, thus far resulting in three pregnancies. Semen cryopreservation and artificial insemination offer a partial solution to posttreatment azoospermia in this population, but further methods are needed to minimize gonadal toxicity without compromising therapy for Hodgkin's disease.