Seasonal variations in antioxidant enzyme activity in ram seminal plasma

Heat stress on reproductive function and fertility in mammals

In most mammalian species including cattle, heat stress has deleterious effects on nutritional, physiological and reproductive functions. Exposure of animals to a hot environment causes an increase in body temperature in mammals, including domestic animals. High ambient temperature also causes a decrease in the length and intensity of estrus by disturbing ovarian function as well as decreasing pregnancy rate after artificial insemination. Therefore, it is important to understand the effects of heat stress on reproductive function in order to improve the production of domestic animals. Heat stress decreases appetite, weight gain, and milk yield in dairy cattle. It also adversely affects the reproductive performance of both sexes. In males, it reduces spermatogenic activity, while in females it adversely impacts oogenesis, oocyte maturation, fertilization development and implantation rate. Detection and evaluation of the deteriorating effects of heat stress on reproductive organs and cells can help to design measures to prevent them and improve reproductive functions. In this review, we discuss the impacts of heat stress on reproductive functions.

Seasonal changes in antioxidant defence systems in seminal plasma and fluids of the boar reproductive tract

This study aimed to analyze seasonal variations in the antioxidant defence systems of the seminal plasma and fluids of the cauda epididymis and vesicular glands of the boar. The analyzed antioxidants included superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and total L-glutathione (GSH+GSSG). Seasonal changes in total protein content and total antioxidant status (TAS) of the seminal plasma and reproductive fluids were also analyzed. Compared with the spring-summer period, total protein content in the seminal plasma was significantly higher during the autumn-winter period. Among the antioxidants analyzed, only SOD activity showed marked seasonal variations, being significantly higher during the spring-summer period. Likewise, the fluid of the cauda epididymis exhibited greater SOD and CAT activity during the spring-summer period, whereas TAS levels were markedly higher during the autumn-winter period. Neither GPx activity nor total GSH+GSSG content in the cauda epididymal fluid was significantly affected by the seasonal periods. The vesicular gland fluid exhibited an approximately 4-fold greater level of SOD activity during the autumn-winter period, as compared with the spring-summer period. By contrast, greater CAT and GPx activity, and a higher level of total GSH+GSSG were observed in the vesicular gland fluid during the spring-summer period. In conclusion, the findings of this study indicate that seasonal variations could have varying effects on the antioxidant defence systems in the seminal plasma and fluids of the boar reproductive tract.

Antioxidant defence system of boar cauda epididymidal spermatozoa and reproductive tract fluids

Antioxidants secreted by the reproductive tract protect spermatozoa against the toxic effects of reactive oxygen species (ROS) after ejaculation. This study aimed at characterizing the level of antioxidant protection in boar cauda epididymidal spermatozoa and fluids of the cauda epididymidis, vesicular and prostate glands. Also, this study investigated the effect of a 5-h period of dialysis on the antioxidant capacity of boar seminal plasma. Superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione transferase (GST) and phospholipid hydroperoxide glutathione peroxidase (PHGPx) activities were monitored in the cauda epididymidal spermatozoa or reproductive tract fluids. Also, the concentrations of total glutathione (GSH + GSSG), L-ergothioneine (ERT) and l-ascorbate and the total antioxidant status (TAS) of the fluids were measured. It was found that the cauda epididymidal spermatozoa exhibited high SOD activity and relatively low activity of PHGPx. The relative amounts of GPx, GR and GST activities in the cauda epididymidal spermatozoa were negligible, whereas CAT activity was undetectable. Greater SOD activity was found in the fluids of the cauda epididymidis and prostate gland. Furthermore, the prostate gland fluid appeared to be the main source of CAT activity in the seminal plasma, whereas the highest level of GPx activity was derived from the cauda epididymidal fluid. The reproductive tract fluids exhibited negligible amounts of GR and GST activities. It seemed that the significant amounts of GSH + GSSG, ERT and L-ascorbate in the reproductive tract fluids could have an ameliorative effect on the level of TAS in the seminal plasma. Dialysis had a marked effect on the total antioxidant capacity of the seminal plasma, which was manifested in greater activity of SOD and GPx. The findings of this study confirmed that the scavenging potential of the seminal plasma is dependent on the contributions of different antioxidants, originating in various fluids of boar reproductive tract.

Seasonal variations of melatonin in ram seminal plasma are correlated to those of testosterone and antioxidant enzymes

BACKGROUND

Some breeds of sheep are highly seasonal in terms of reproductive capability, and these changes are regulated by photoperiod and melatonin secretion. These changes affect the reproductive performance of rams, impairing semen quality and modifying hormonal profiles. Also, the antioxidant defence systems seem to be modulated by melatonin secretion, and shows seasonal variations. The aim of this study was to investigate the presence of melatonin and testosterone in ram seminal plasma and their variations between the breeding and non-breeding seasons. In addition, we analyzed the possible correlations between these hormones and the antioxidant enzyme defence system activity.

METHODS

Seminal plasma from nine Rasa Aragonesa rams were collected for one year, and their levels of melatonin, testosterone, superoxide dismutase (SOD), glutathione reductase (GRD), glutathione peroxidase (GPX) and catalase (CAT) were measured.

RESULTS

All samples presented measurable quantities of hormones and antioxidant enzymes. Both hormones showed monthly variations, with a decrease after the winter solstice and a rise after the summer solstice that reached the maximum levels in October-November, and a marked seasonal variation (P < 0.01) with higher levels in the breeding season. The yearly pattern of GRD and catalase was close to that of melatonin, and GRD showed a significant seasonal variation (P < 0.01) with a higher activity during the breeding season. Linear regression analysis between the studied hormones and antioxidant enzymes showed a significant correlation between melatonin and testosterone, GRD, SOD and catalase.

CONCLUSIONS

These results show the presence of melatonin and testosterone in ram seminal plasma, and that both hormones have seasonal variations, and support the idea that seasonal variations of fertility in the ram involve interplay between melatonin and the antioxidant defence system.

Seasonal variation in the protective effect of seminal plasma on frozen-thawed ram spermatozoa

The response of ram spermatozoa to seminal plasma is highly variable, in part due to the presence of both stimulatory and inhibitory factors. The aim of this study was to assess variation in the protection of ram spermatozoa during freezing by seminal plasma. The seminal plasma variables studied were season of collection, fractionation and method of supplementation. Spermatozoa were supplemented before freezing with 4 mg of seminal plasma proteins (SPPs) per 10(8) cells, and their motility and viability were assessed during post-thaw incubation (37 degrees C). In Experiment 1, semen was (a) frozen with no supplementation (Control) (b) extended with a Tris-based diluent (C + TRIS), or (c) supplemented with seminal plasma collected throughout the year (in the Southern Hemisphere) and pooled for January-March, April-June, July-August and October-December, and either fractionated to produce a concentrated >10 kDa seminal plasma protein retentate (>10 kDa SPP), or kept as crude seminal plasma (CP). There was no effect of season or seminal plasma type (CP or >10 kDa SPP) on motility of spermatozoa. CP and >10 kDa SPP improved the viability of spermatozoa when collected from January-September compared to Control. Supplementation with >10 kDa SPP increased viability of spermatozoa, compared to CP, when collected from January to July. In Experiment 2, >10 kDa SPP were either added directly to the spermatozoa or included in the cryodiluent or >10 kDa SPP were not supplemented (Control). Both supplementation methods improved the motility and the proportion of viable, acrosome-intact spermatozoa but direct supplementation resulted in more viable, acrosome-intact spermatozoa compared with supplementation of the cryodiluent. These results show that supplementation of ram spermatozoa with CP, or its protein component (>10 kDa SPP), before freezing protects them from freeze-thaw damage. The protective effect is greatest when seminal plasma is collected during the breeding season, fractionated with >10 kDa filters and added directly to the spermatozoa.

Manganese provides antioxidant protection for sperm cryopreservation that may offer new consideration for clinical fertility

Reactive oxygen species (ROS) are generated by sperm metabolism. While, ROS are required for maturation, capacitation and acrosome reaction, they also modify many peroxidable cellular compounds. There is production of ROS during cryopreservation and frozen spermatozoa are highly sensitive to lipid peroxidation (LPO). Antioxidants exert a protective effect on the plasma membrane of frozen bovine sperm preserving both metabolic activity and cellular viability. Manganese (Mn(++)) is proved to be a chain breaking antioxidant in biological system. Therefore, we examined the role of (Mn(++)) during cryopreservation of cattle bull semen. Semen was divided into four parts and cryopreserved in egg-yolk-citrate extender + glycerol (EYC-G), EYC-G + 100 microM of Mn(++), EYC-G + 150 microM of Mn(++) and EYC-G + 200 microM of Mn(++). After four hours of cooling and 24 hrs of freezing, the spermatozoa were examined for percentage motility, Hypo-osmotic swelling (HOS), LPO and protein leakage. Addition of manganese to the semen during cryopreservation showed a protective effect and accounted for an increase in semen quality parameters [percentage motility, HOS percent and decrease in malondialdehyde (MDA) production and protein leakage]. The effect of manganese on motility and HOS was non-significant (p < 0.05) in cooled spermatozoa but significant with 150 microM of Mn(++) in frozen-thawed spermatozoa. MDA production and protein leakage decreased to a significant and maximum level (p < 0.05) on addition of 200 microM of manganese. The addition of manganese to EYC-G dilutor will improve the quality/fertility of semen, which will result in improvement of in vitro fertilization and artificial insemination success rate.

Undernutrition and exogenous melatonin can affect the in vitro developmental competence of ovine oocytes on a seasonal basis

This study evaluated the effects of exogenous melatonin and level of nutrition on oocyte competence, in vitro fertilization (IVF), and early embryonic development in sheep during seasonal anoestrus (SA) and the reproductive season (RS). Adult Rasa Aragonesa ewes were assigned randomly to one of four treatment groups in two experiments based on a 2 x 2 x 2 factorial design. Individuals were treated (+MEL) or not treated (-MEL) with a subcutaneous implant of melatonin for 42 days and then were fed 1.5 (Control, C) or 0.5 (Low, L) times the daily maintenance requirements for 20 days. Ewes were synchronized and mated at oestrus (Day = 0). On Day 5, ovaries were collected and oocytes were used for IVF. Season had a significant (p < 0.01) effect on the number of oocytes recovered (RS: 19.6 +/- 1.0; SA: 14.5 +/- 1.0) and the number of healthy oocytes (RS: 13.9 +/- 0.7; SA: 9.0 +/- 0.7). In the RS, neither nutrition nor melatonin had a significant effect on the evaluated oocytes quality parameters although melatonin implants appeared to reduce the number of unhealthy oocytes in the undernourished group (p < 0.05). During SA, in undernourished ewes exogenous melatonin tended to increase the number of healthy (L+MEL: 9.4 +/- 1.0, L-MEL: 7.6 +/- 1.4; p < 0.1), and significantly improved both cleaved oocytes (L+MEL: 7.0 +/- 0.7, L-MEL: 4.1 +/- 0.9; p < 0.05) and blastocyst rate (L+MEL: 37.2, L-MEL: 21.9%; p < 0.05). In conclusion, oocyte competence in ewes was affected by season, and melatonin implants appeared to improve developmental competence in the seasonal anoestrous period, particularly in experimentally undernourished ewes.

Effects of the seminal plasma zinc content and catalase activity on the semen quality of water buffalo (Bubalus bubalis) bulls

In order to determine zinc and catalase content of seminal plasma in the buffalo and to study their associations with the semen characteristics, 54 semen samples were collected from 10 buffalo bulls; semen volume and sperm concentration, gross and progressive motility and viability were evaluated, seminal plasma was then harvested by centrifugation and its zinc content was estimated by atomic absorption spectrophotometer and its catalase activity determined by using a commercial kit. The zinc content of the seminal plasma (Mean +/- SEM) was recorded as 154.40 +/- 1.74 mg L(-1), while, the mean catalase value was 32.00 +/- 0.42 U mL(-1). The mean zinc values was highly correlated with sperm progressive motility and viability and with catalase values (p = 0.000 for all) and also was associated with gross motility (p = 0.020) and negatively with abnormal morphology (p = 0.049). The catalase values were highly associated with sperm progressive motility, viability and zinc content (p = 0.000 for all) and was associated with sperm gross motility (p = 0.024). For further clarification of these correlations, the samples were categorized in three groups of excellent (Ex, >90% motile, n = 33), good (Go, 80-89% motile, n = 15) and moderate (Mo, <79% motile, n = 6) according to their percentage of sperm motility. The mean progressive motility in Ex group was 92.54 +/- 0.51%, in Go group was 81.66 +/- 0.62% and in Mo group was 71.66 +/- 1.05%. The mean zinc and catalase values were recorded as 161.07 +/- 1.63 mg L(-1) and 33.41 +/- 0.34 U mL(-1) in Ex, 146.70 +/- 1.91 mg L(-1) and 31.01 +/- 0.67 in Go and 136.42 +/- 4.97 mg L(-1) and 26.51 +/- 0.87 U mL(-1) in Mo groups. The mean zinc value in Ex group was highly associated with sperm motility, viability and catalase values, in Go group was associated with catalase values and highly associated with sperm abnormal morphology and in Mo group it was highly associations with catalase values only. The mean catalase value in Ex group, was highly associated with sperm motility and viability, in Go group was associated with zinc content and in Mo groups was highly associated with the zinc content. These results show that seminal plasma zinc and catalase content are correlated with semen characteristics and synergistically act to preserve motility and viability of the spermatozoa after ejaculation.

In vitro stimulatory effect of anti-apoptotic seminal vesicle protein 4 on purified peroxidase enzymes

The enzymatic activities of purified horseradish peroxidase, selenium-dependent glutathione peroxidase, thyroid peroxidase and myeloperoxidase, but not that of lactoperoxidase, were markedly enhanced when added into a reaction mixture containing 5 mum native seminal vesicle protein 4, a major protein secreted from rat seminal vesicle epithelium. A further increase of horseradish peroxidase activity was obtained using Ser58-phosphorylated or acetylated seminal vesicle protein 4. The activating effect of native seminal vesicle protein 4 was highest (about 60-fold) on horseradish peroxidase when 4-chloro-1-naphtol was used as the electron donor substrate. The main kinetics parameters of the stimulatory effect on horseradish peroxidase were evaluated and the enzyme-electron donor substrate interaction was investigated by HPLC and electrospray-MS. A native seminal vesicle protein 4/4-chloro-1-naphtol noncovalent adduct was detected when the protein and 4-chloro-1-naphtol were present in the appropriate molar ratio in the horseradish peroxidase-catalyzed reaction. By contrast, no adducts were formed between native seminal vesicle protein 4 and horseradish peroxidase. This native seminal vesicle protein 4/4-chloro-1-naphtol interaction might underlie the native seminal vesicle protein 4-induced horseradish peroxidase stimulation. Furthermore, native seminal vesicle protein 4 was shown by spectrophotometric and electrospray-MS analysis to interact with NADPH, an electron donor substrate of the selenium-dependent glutathione peroxidase/glutathione reductase redox system, with formation of an adduct between them. Although further investigation is required to elucidate the mechanism of adduct formation, this interaction, probably by promoting the release of the NADPH electrons required for glutathione disulphide reduction, could explain the stimulatory effect of seminal vesicle protein 4 on mammalian peroxidases possibly involved in its physiological function on the selenium-dependent glutathione peroxidase/glutathione reductase system. The biological significance of these properties of native seminal vesicle protein 4 might be related to its ability to downregulate reactive oxygen species and oxidative stress-induced apoptosis.