Identification and immunolocalisation of melatonin MT(1) and MT(2) receptors in Rasa Aragonesa ram spermatozoa

The reproductive seasonality of sheep suggests that melatonin receptors may be present in ram spermatozoa. The present study confirms the presence of melatonin MT(1) and MT(2) receptors. The MT(1) receptor was detected using immunocytochemistry, with four sperm subpopulations identified based on the following labelling patterns: (1) one small subpopulation with labelling over the entire head and tail; (2) one of two main subpopulations that exhibited reactivity at the equatorial, post-acrosomal, neck and tail regions; (3) another main subpopulation with equatorial and tail labelling only; and (4) a subpopulation in which staining was detected only in the tail. Immunocytochemistry revealed the presence of the melatonin MT(2) receptor, with intense staining on the acrosome, post-acrosomal region and neck and tail regions of all cells, but not in the equatorial region. Western blot identification of ram protein extracts revealed a 39-kDa band compatible with both MT(1) and MT(2) receptors, a 75-kDa band compatible with MT(1)/MT(2) heterodimerisation, a 32-kDa band compatible with MT(1) receptor activation and a double band of 45-55 kDa that is compatible with MT(2) receptor homodimerisation or heterodimerisation with other G-proteins. In conclusion, we provide evidence of the presence of MT(1) and MT(2) receptors in ram spermatozoa, although the biochemical pathway triggered by these receptors and their function in terms of fertility remains to be elucidated.

Use of laparoscopic intrauterine insemination associated with a simplified superovulation treatment for in vivo embryo production in sheep: a preliminary report

This study evaluated the reproductive performance of sheep that were subjected to superovulatory treatment and intrauterine insemination with two different doses of semen. The main objective was to determine whether intrauterine insemination is associated with higher rates of embryo recovery than existing procedures. In the first experiment 30 Ojalada de Soria ewes were used at the end of their productive life and nine younger ewes of the same breed were used in Experiment 2. Synchronisation of oestrus was conducted with intravaginal sponges and the superovulation treatment consisted of an intramuscular injection of 210 IU pFSH and 500 IU eCG administered 24 h before sponge removal. After 48 h of sponge withdrawal, ewes were inseminated by laparoscopy. They were divided into two groups: low dose group (LD, 25 × 106 sperm; n = 14 Expt 1 and n = 5 Expt 2) and high dose group (HD, 100 × 106 sperm; n = 14 Expt 1 and n = 4 Expt 2). Embryos were recovered 7 days after the onset of oestrus by laparotomy and uterine flushing. Two blood samples were collected in order to analyse cortisol, at sponge insertion and the day the embryos were recovered. The same protocol was repeated twice in Experiment 1, with an interval of 2 months between two consecutive treatments. Results show a significant effect of the number of recovery on ovulation rate (21.7 ± 2.2 v. 11.8 ± 1.1 corpora lutea for first and second recoveries, respectively), and number of structures recovered (11.4 ± 1.6 v. 5.2 ± 1.1, P < 0.01). Differences of embryo performance in the second recovery compared with the first one were more evident in the LD group compared with the HD group. In Experiment 2, results reflected a significant superiority of the HD group compared with the LD group, especially rate of fertilisation, which was 25% higher. Sheep producing non-fertilised embryos had higher cortisol levels at the time of flushing than those with embryos (P < 0.01). It is concluded that the use of simplified and consecutive superovulatory treatments associated with intrauterine insemination is a potential means of obtaining embryos, although the response seems to depend on donor sheep age. The use of a higher number of sperm cells per millilitre results in better outcomes in terms of embryos produced.

Repeated superovulation using a simplified FSH/eCG treatment for in vivo embryo production in sheep

This study investigated the efficacy of a simplified repeated superovulation treatment (eCG plus FSH in a single dose, rather than the usual protocol of six decreasing doses of FSH) in the in vivo embryo production in Ojalada donor ewes during the breeding season. In vitro viability after vitrification and warming of embryos recovered from both treatments was also assessed. In addition, the study examined the effects of the concentration of anti-eCG antibodies before each eCG/FSH treatment on in vivo embryo production. Thirty-eight females at the end of their reproductive lives were given the decreasing (n = 19) or simplified (n = 19) superovulatory treatment up to three times at intervals of ≥ 50 d. The onset of estrus was 5 h earlier (P < 0.05) among ewes that received the eCG/FSH protocol (25.2 ± 0.80 h) than it was among those that received the decreasing superovulatory treatment (30.1 ± 1.0 h), but the two treatments did not differ significantly in ovulation rates or the number and viability of embryos recovered. Both of the superovulatory protocols were significantly (P < 0.05 to P < 0.01) less effective after the first application. After three superovulatory treatments, the average number of viable embryos per ewe was 14.1 ± 2.3 and 13.7 ± 2.5 in the decreasing and simplified protocols, respectively. High anti-eCG antibody concentrations just before the superovulatory treatment with eCG/FSH were associated with a significant decrease (P < 0.05) in the rates of fertilization, viability, and freezability, especially in the second and third recoveries. Repeated superovulatory treatments with eCG/FSH can provide an efficient means of producing high quality embryos in the ewes of endangered breeds at the end of their reproductive lives, although further studies are needed to characterize the response associated with high concentrations of anti-eCG antibodies.

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.

Effects of exogenous melatonin on in vivo embryo viability and oocyte competence of undernourished ewes after weaning during the seasonal anestrus

This study investigated the effects of exogenous melatonin on embryo viability and oocyte competence in post-partum undernourished ewes during the seasonal anestrus. At parturition (mid-Feb), 36 adult Rasa Aragonesa ewes were assigned to one of two groups: treated (+MEL) or not treated (-MEL) with a subcutaneous implant of melatonin (Melovine(R), CEVA) on the day of lambing. After 45 d of suckling, lambs were weaned, ewes were synchronized using intravaginal pessaries, and fed to provide 1.5x (Control, C) or 0.5x (Low, L) times daily maintenance requirements. Thus, ewes were divided into four groups: C-MEL, C+MEL, L-MEL, and L+MEL. At estrus (Day=0), ewes were mated. At Day 5 after estrus, embryos were recovered by mid-ventral laparotomy and classified based on their developmental stage and morphology. After embryo collection, ovaries were recovered and oocytes were classified and selected for use in in vitro fertilization (IVF). Neither diet nor melatonin treatment had a significant effect on ovulation rate and on the number of ova recovered per ewe. Melatonin treatment significantly improved the number of fertilized embryos/corpus luteum (CL) (-MEL: 0.35 +/- 0.1, +MEL: 0.62 +/- 0.1; P = 0.08), number of viable embryos/CL (-MEL: 0.23 +/- 0.1, +MEL: 0.62 +/- 0.1; P < 0.01), viability rate (-MEL: 46.6%, +MEL: 83.9%; P < 0.05), and pregnancy rate (-MEL: 26.3%, +MEL: 76.5%; P < 0.05). In particular, exogenous melatonin improved embryo viability in undernourished ewes (L-MEL: 40%, L+MEL: 100%, P < 0.01). Neither nutrition nor exogenous melatonin treatments significantly influenced the competence of oocytes during IVF. Treatment groups did not differ significantly in the number of healthy oocytes used for IVF, number of cleaved embryos, or number of blastocysts and, consequently, the groups had similar cleavage and blastocyst rates. In conclusion, melatonin treatments improved ovine embryo viability during anestrus, particularly in undernourished post-partum ewes, although the effects of melatonin did not appear to be mediated at the oocyte competence level.

Melatonin prevents capacitation and apoptotic-like changes of ram spermatozoa and increases fertility rate

We recently demonstrated the presence of melatonin in ram seminal plasma and differences in its concentration in this fluid between the breeding and nonbreeding season. In this study, we investigate the hypothesis that in vitro treatment with melatonin affects ram sperm quality, and that this is reflected in the in vitro fertilization (IVF) results. Semen from nine rams was collected during the nonreproductive season and treated with 1 mum, 10 nm and 100 pm melatonin. Samples were incubated at 39 degrees C and 5% CO2, and motility, viability, capacitation status and phosphatidylserine (PS) translocation were assessed before and after melatonin addition, either 1 or 3 hr of incubation. Fertility rate of the melatonin-treated samples was determined by means of IVF. Although melatonin failed to affect both sperm kinematic parameters and viability, the exposure of ram spermatozoa to melatonin has a direct effect, decreasing capacitation and PS translocation at 1 mum, and increasing short-term capacitation at 100 pm, which caused an increased oocyte fertilization rate following IVF. Furthermore, cleavage rate of oocytes fertilized with 100 pm melatonin-treated spermatozoa was higher than that with 1 mum melatonin and control samples (P < 0.1). These results prove that melatonin has a direct effect on ram spermatozoa in the nonreproductive season, which can be explained, at least in part, by the melatonin capacity as a reactive oxygen species scavenger and antioxidant. These findings might help to select the optimal experimental conditions for IVF and to improve sperm preservation protocols.

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.

Changes in calmodulin immunocytochemical localization associated with capacitation and acrosomal exocytosis of ram spermatozoa

The aim of this study was to determine the localization of calmodulin (CaM) in ram sperm and the possible changes during in vitro capacitation (CA) and the ionophore-induced acrosome reaction (AR). Likewise, changes in intracellular calcium levels ([Ca(2+)](i)) were also analysed by using flow cytometry. CA was induced in vitro in a medium containing BSA, CaCl(2), NaHCO(3), and AR by the addition of the calcium ionophore A23187. The acrosomal status was assessed by the chlortetracycline-fluorescence (CTC) assay. Flow cytometry (FC) analyses were performed by loading samples with Fluo-3 AM, that emits fluorescence at a high [Ca(2+)](i), combined with propidium iodide (PI) that allowed us to discriminate sperm with/without an integral plasma membrane both with high/low [Ca(2+)](i). Immunocytochemistry localized CaM to the flagellum, and some sperm also contained CaM in the head (equatorial and post-acrosomal regions). CA and AR resulted in a slight increase in the post-acrosomal labelling. The treatment of sperm with increasing concentrations of two CaM antagonists, W7 and calmidazolium (CZ), accounted for an increase in capacitated and acrosome-reacted CTC-sperm patterns. CZ induced a significant reduction in the content of three protein tyrosine-phosphorylated bands of approximately of 30, 40 and 45kDa. However, W7 showed no significant effect at any of the studied concentrations. Neither of them significantly influenced protein serine and threonine phosphorylation. FC analysis revealed that the main subpopulation in the control samples contained 70% of the total sperm with integral plasma membrane and a medium [Ca(2+)](i). After CA, 67.1% of the sperm preserved an integral membrane with a higher [Ca(2+)](i). After AR, only 7.2% of the total sperm preserved intact membranes with a very high [Ca(2+)](i). These results imply that CaM appears to be involved in ram sperm capacitation, and both treatments increased its localization in the post-acrosomal region.

Effects of melatonin implants during non-breeding season on sperm motility and reproductive parameters in Rasa Aragonesa rams

The effect of melatonin implants administered during non-breeding season in Rasa Aragonesa rams on sperm motility parameters and other reproductive traits was assessed. In a first experiment, two Rasa Aragonesa rams were implanted (with melatonin group M), remaining other two males as control group (C). Semen of each group was collected from 1 May to 23 June, twice or three times a week, and motility parameters were assessed using a computer-assisted sperm analysis system. Melatonin increased the percentage of progressive motile spermatozoa, particularly during 46-75 days after melatonin implantation (p < 0.01). In experiment 2, M and C in vitro fertilization ability had been determined by zona-pellucida binding assays, using spermatozoa from experiment 1, obtained 60-70 days after melatonin was implanted. A significantly higher number of spermatozoa attached per oocyte was observed in frozen-thawed immature ovine oocytes incubated with sperm from M animals than in those incubated with sperm from the C group (p < 0.01). Finally, a field assay (experiment 3) was performed. In this case, five Rasa Aragonesa rams were implanted with melatonin and three remained as control group. Sperm doses from those animals were used for artificial insemination of 2608 Rasa Aragonesa ewes from 39 different farms at non-breeding season. Fertility, litter size and fecundity were studied. Semen from melatonin implanted rams seemed to increase both fertility and fecundity in ewes inseminated with spermatozoa obtained 46-60 days after implantation (p < 0.1). Thus, melatonin treatment in rams during non-breeding season modifies sperm motility parameters and seems to improve the fertilization parameters obtained.

Effects of ageing and exogenous melatonin on pituitary responsiveness to GnRH in ewes during anestrus and the reproductive season

The study examined the effect of melatonin implants on in vivo pituitary responsiveness to GnRH in control, fully productive (5.7+/-0.4 years old, n=17) and aged (10.7+/-0.3 years old, n=14) ovariectomized, estradiol-treated Rasa Aragonesa ewes. On 27 February, eight ewes in each age group received a single implant containing 18 mg melatonin. On 10 April, blood samples to be assayed for LH were collected at 10-min intervals over 4h (starting at 09:00 and 22:00 h). After samples 6 and 18 were collected, ewes received a single i.v. injection of GnRH (20 ng/kg liveweight). The pituitary response to GnRH was assessed using the difference between plasma LH concentrations before and after (highest value) each injection (DLH1, DLH2)), and the area under the LH response curve for 1h after each GnRH injection (AUC1, AUC2). On 23 September, the previously implanted ewes received a new melatonin implant and, on 17 November, all of the ewes were subjected to the same diurnal and nocturnal sampling protocols, again. Generally, non-implanted aged ewes exhibited a lower pituitary response to GnRH than did non-implanted control ewes, particularly in November and after the first injection (P<0.05 for DLH1 and AUC1 in both the diurnal and nocturnal tests). The response was significantly affected by the interaction of age and melatonin treatment, particularly in the diurnal tests (P<0.1 for DLH1 and AUC1, and P<0.05 for AUC2 in April; P<0.05 for DLH1, AUC1 and AUC2 in November), which indicated that exogenous melatonin increased LH levels after GnRH injections in aged ewes compared to non-implanted ewes, this effect being the opposite in control females. Thus, melatonin can restore in ewes the functionality of the neuroendocrine system, after it has been reduced by senescence.

The effect of melatonin implants during the seasonal anestrus on embryo production after superovulation in aged high-prolificacy Rasa Aragonesa ewes

The aim of this study was to assess the effect of melatonin implants administered in March on the ovarian cyclicity, ovulatory response and embryo production after repeated superovulation of selected high-prolificacy Rasa Aragonesa aged ewes. During the seasonal anestrus of two consecutive years, 113 superovulatory treatments have been performed. Ewes were treated (M) or not (C) with melatonin implants in March (day 0). All of them received intravaginal progestogen sponges on day 24 (recovery 1) and 80 (recovery 2) after melatonin implants insertion in year 1, and on day 28 and 77 in year 2. The intravaginal sponges were removed after 14 days. Superovulatory treatments consisted of eight doses in decreasing concentrations (2 mL x 2 and 1 mL x 6) of oFSH (Ovagen) administered twice daily starting 72 h before sponge removal. Seven days after the onset of estrus, embryos were recovered by laparotomy. Melatonin increased cyclicity only in recovery 2 year 2 (83% versus 42%; P < 0.05) but not in the other experimental periods. Among the 78% (88) ewes that ovulated and produced functional corpora lutea, melatonin implants tended to improve embryo viability in recovery 2 by increasing the number of blastocysts per superovulatory treatment (2.4 +/- 0.6 versus 1.1 +/- 0.4; P = 0.09), the rate of viability (67 +/- 9% versus 43 +/- 9%; P < 0.05), and freezability (55 +/- 9% versus 33 +/- 8%; P < 0.05). More specifically, melatonin induced a significant reduction of the number and rate of non-viable (degenerate and retarded) embryos in recovery 2 (0.4+/-0.1 embryos versus 1.3 +/- 0.3 embryos and 4 +/- 1% versus 22 +/- 6%, respectively; P < 0.05). Our results demonstrate that melatonin implants in March can improve at medium term (3 months after implantation) the viability of embryos collected from selected high-prolificacy Rasa Aragonesa aged ewes after superovulation.