Gonadotropin-releasing Hormone Agonist Implants Research Articles

Endocrine regulation of long-term enhancement of spermiation in meagre (Argyrosomus regius) with GnRHa controlled-delivery systems

Meagre (Argyrosomus regius) undergo spermatogenesis and spermiation when reared in captivity, but often produce low milt volumes, sometimes with reduced quality and for a limited time period. In the present study we a) compared the efficiency of gonadotropin releasing hormone agonist (GnRHa) implants versus injections on testicular stimulation and spermiation enhancement, b) investigated the effect of GnRHa on the endocrine spermiation regulation (sex steroid hormones), and c) evaluated a commercial induced spawning simulation scenario. Firstly, males (n = 5) were injected with 15.0 ± 0.2 μg GnRHa kg−1 (Injections) or implanted with 51.0 ± 5.1 μg GnRHa kg−1 (Implant) and compared their sperm production response. Secondly, the best hormonal treatment (Implant) was tested treating males (n = 8) with 57.5 ± 7.5 μg GnRHa kg−1 every 3 weeks for a period of 70 days. Milt production was improved by the GnRHa implants with only minor sperm quality alterations (improved sperm motility percentage). Elevated plasma testosterone (T) and 11-ketotestosterone (11-KT) levels were recorded in response to GnRHa implants, while no significant difference for 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) was observed. In the commercial induced spawning simulation, it was shown that meagre females are capable of on-demand induction of spawning at random intervals (5–21 days) using GnRHa injections, over a period of at least 2.5 months. During this period, spermiation enhancement was achieved with GnRHa implants every 3 weeks, producing sperm with stable, in general, quality and motility parameters. Percentage of motile cells, motility duration and density fluctuated significantly, but remained within levels that are considered appropriate for high fertilization success in this species.

Effect of GnRHa on plasma levels of Fsh and Lh in the female greater amberjack Seriola dumerili.

The effects of gonadotropin-releasing hormone agonist (GnRHa) on plasma levels of follicle-stimulating hormone (Fsh) and luteinising hormone (Lh) are reported for female greater amberjack Seriola dumerili with post-vitellogenic ovarian oocytes. Five females were implanted with pellets containing GnRHa (600 μg kg-1 body weight), while five other females were injected with saline. All females implanted with GnRHa-containing pellets ovulated 36-42 h post-implantation. The GnRHa implants elevated Lh, but not Fsh plasma levels within 42 h of GnRHa administration.

Spawning kinetics and egg/larval quality of greater amberjack (Seriola dumerili) in response to multiple GnRHa injections or implants

The greater amberjack (Seriola dumerili) is one of the most promising finfish species for aquaculture, due to its cosmopolitan distribution and acceptability, high growth rates and large size. However, lack of reproduction control has been one of the main bottlenecks for its commercialization. The study examined two endocrine methods for the induction of oocyte maturation/ovulation and spawning, which are based on the induction of endogenous Luteinizing Hormone (LH) release from the pituitary, through the use of Gonadotropin Releasing Hormone agonist (GnRHa) either in the form of sustained-release delivery systems (implants) or injections (acute release). The stock (n = 28) consisted of wild fish captured in 2011 and each GnRHa administration method was conducted in two replicates, with 6 and 8 fish per tank, respectively, at a 1:1 sex ratio. Fish were given a GnRHa injection once a week (three administrations), or a GnRHa implant every 2 weeks (two administrations). Mean daily relative fecundity was significantly higher (t1.3 = −5.24, P = 0.012) in the implanted fish (15,170 ± 2,738 eggs kg−1 female day−1) compared to the injected fish (6,119 ± 2,790 eggs kg−1 female day−1). Total relative fecundity was also significantly higher (t1.3 = −9.93, P = 0.003) in the implanted fish (102,402 ± 20,337 eggs kg−1 female) compared to the injected ones (26,517 ± 9,938 eggs kg−1 female), but there were no differences in the quality of eggs in terms of fertilization, 24-h embryo survival, hatching and 5-d larval survival. The number of females with fully vitellogenic oocytes eligible for induction of spawning decreased from the initial to the final sampling, from 7 to 6 females for the GnRHa implant treatment and from 7 to 3 females for the GnRHa injection treatment. In addition to apparently promoting the proper endocrine changes leading to multiple cycles of oocyte maturation, ovulation and spawning, and thus producing larger numbers of eggs; the use of GnRHa implants may be more appropriate in greater amberjack than multiple injections because (a) it also stimulates vitellogenesis and (b) involves less handling of the fish.

Spawning Induction of First-Generation (F1) Greater Amberjack Seriola dumerili in the Canary Islands, Spain Using GnRHa Delivery Systems

The development of a sustainable aquaculture industry requires the closing of the life-cycle of a potential species in captivity, and the establishment of breeding selection programs using hatchery-produced breeding stocks. The greater amberjack Seriola dumerili is a cosmopolitan pelagic species that has been considered as a good candidate for the species diversification of aquaculture production in the Mediterranean region. However, commercial production is still very limited due to bottlenecks in reproduction, larval rearing and management control during grow out. The aim of the present study was to examine the reproductive development of hatchery-produced greater amberjack and to develop a spawning induction protocol based on the use of gonadotropin releasing hormone agonist (GnRHa) in a controlled-release delivery system. The results showed that hatchery-produced greater amberjack undergo normal gametogenesis and can be induced to undergo maturation, ovulation and spawning after multiple administrations of GnRHa implants, over an extended spawning period lasting from May to September in the Canary Islands, Spain. The use of GnRHa-delivery systems resulted in multiple spawns of fertilized and viable eggs. Egg production was high and egg quality adequate for the implementation of larval rearing for commercial purposes. The handling required to administer the GnRHa implants during the prolonged spawning season did not result in any negative effect on the welfare and reproductive performance of the fish based on evaluation of several biochemical parameters. The developed reproduction control method shows great potential to advance the commercial production of greater amberjack, by enabling the use of hatchery-produced broodstocks for further breeding selection.

Reproduction of hatchery-produced meagre Argyrosomus regius in captivity III. Comparison between GnRHa implants and injections on spawning kinetics and egg/larval performance parameters

Hatchery-produced meagre (Argyrosomus regius) were induced to spawn using either controlled-release delivery systems (implants) loaded with gonadotropin-releasing hormone agonist (GnRHa) or GnRHa injections. Over two consecutive years, individual females were paired with single males after treatment with a GnRHa implant (40–104 μg kg− 1) or a GnRHa injection (15–25 μg kg− 1). Three consecutive GnRHa implants were given every 20–30 days, while five (in 2012) or seven (in 2013) consecutive GnRHa injections were given every 10 days. Fecundity and fertilization success was evaluated the day of spawning, and embryo/larval development was evaluated using 96-well microtiter plates. The first implantation with GnRHa produced up to 23 almost daily spawns, but most females failed to spawn repeatedly after the second implantation, even though their ovaries contained significant numbers of post-vitellogenic oocytes. Most of the eggs were produced in the first 3–4 spawns after GnRHa implantation, while the remaining batches were of low fecundity, which related directly to low fertilization. On the other hand, GnRHa injections produced consistently two spawns on days 2 and 3 after each treatment. Fecundity also decreased over time in response to the subsequent injections, but the response was more gradual and less dramatic than in GnRHa implanted females. Although both methods produced similar overall results in terms of total fecundity and egg/larval quality, multiple GnRHa injections resulted in more consistent spawning results and better egg production control, and this method may offer significant advantages over the use of controlled-release GnRHa implants. We present an efficient spawning induction method for meagre, which is the result of extensive experimentation both in previously published works, as well as in this one. The resulting method is proposed for its effectiveness and efficiency to the aquaculture industry.

Clinical use of deslorelin (GnRH agonist) in companion animals: a review.

Over the years, many contraceptive medications have been developed for companion animals, but many secondary adverse effects have limited their use. A major advancement was achieved with the use of gonadotropin-releasing hormone (GnRH) analogues, mainly GnRH agonists, which mimic the effects of native GnRH. The development of effective low-dose, slow-release implants with potent agonists such as deslorelin (Suprelorin®, Virbac) have allowed their use to become widespread in recent years, with many potential benefits in companion animals. While the major application of deslorelin was initially male contraception, due to its two differing actions, either the stimulation of oestrus or the sterilization of fertility, its use has been increasing in the bitch as well. The aim of this study is to review the applications of deslorelin GnRH agonist implants in companion animal, such as dogs, cats and some exotic pets.

Reproduction of hatchery-produced meagre Argyrosomus regius in captivity II. Hormonal induction of spawning and monitoring of spawning kinetics, egg production and egg quality

The present study aimed at the development of an effective and efficient hormonal spawning induction method for meagre Argyrosomus regius, using controlled-release delivery systems loaded with gonadotropin-releasing hormone agonist (GnRHa). Three sets of spawning induction experiments were undertaken in the course of three years. In experiment 1, group spawnings were performed at different times during the reproductive period, in order to determine the most appropriate time for hormonal induction of spawning. Experiment 2 described in more detail the spawning kinetics of individual females induced to spawn at different times during the season, in order to obtain important information on spawning kinetics, batch fecundity and total fecundity in response to the hormonal treatment. In experiment 3, two similar broodstocks were used to obtain further production characteristics and monitor variations in egg/larval quality over the spawning period. The effective GnRHa doses used were 55–84μgGnRHakg−1 body weight in males and 46–92μgGnRHakg−1 in females. In general, successful spawning induction was achieved between early May and early June. Implantation with GnRHa induced spawning 2–3d after treatment and produced an average (±SD) of 12±5 spawns per broodstock or female over 3weeks, most of them over consecutive days. Batch fecundity was extremely variable (mean of 6631 to 104,409eggskg−1), with the largest batches occurring 3–4d after treatment, and very low fecundity after 1week from GnRHa treatment. As a result, the first 4 spawns of all spawning induction experiments constituted a mean of 75±13% of the total relative fecundity. Overall mean total relative fecundity was variable at 380,780±167,577eggskg−1. Evaluation of the ovaries after the cessation of spawning, demonstrated that the females still contained large numbers of oocytes in full vitellogenesis, and it is hypothesized that these fish could spawn further in response to a second GnRHa implantation. Fertilization success was very high in all spawning induction experiments, with the overall mean being 89±5%. Similarly, the produced eggs were of very high quality, based on the survival of the eggs during embryogenesis (>95%), hatching success (>99%) and larval survival 5d after egg collection (>87%), resulting in an overall larva survival of 73% of the total number of eggs spawned. These studies demonstrate that the GnRHa implants are an effective and efficient method for the induction of spawning in meagre, leading to the production of eggs of high fecundity and quality.

Comparative effects of human chorionic gonadotropin (hCG) and gonadotropin-releasing hormone agonist (GnRHa) treatments on the stimulation of male Senegalese sole ( Solea senegalensis) reproduction

The aquaculture of Senegalese sole ( Solea senegalensis) is limited by the failure of cultured breeders (F1 generation) to produce fertilized spawning. Critical reproductive dysfunctions have been observed in both female and male Senegalese sole cultured breeders, including reduced fecundity and diminished sperm production. The present work aimed to study the effectiveness of different hormonal treatments on the stimulation of male reproduction. Male Senegalese sole cultured breeders were treated with 1) saline injections (controls), 2) gonadotropin-releasing hormone agonist (GnRHa) injections (25 μg kg −1), 3) GnRHa slow release implants (40 μg kg −1) or 4) human chorionic gonadotropin (hCG) injections (1000 IU kg −1). Each group of males was placed in separated spawning tanks together with females treated with GnRHa implants. All three hormonal treatments increased plasma testosterone (T) and 11-ketotestosterone (11-KT) levels and the gonadosomatic index (GSI), with highest effects exerted by the hCG treatment. Histological examination of the testes showed no effect of the GnRHa injection, but a clear stimulation of germ cell proliferation and testicular maturation by GnRHa implants and hCG injections. As expected, GnRHa implantation of females induced egg release in all experimental tanks and interestingly, female fecundity increased in tanks containing GnRHa- or hCG-treated males. A fertilized spawning was obtained only from the group containing hCG-treated males. In conclusion, hormonal treatments stimulated steroidogenesis and spermatogenesis in male Senegalese sole, with highest efficiency of the hCG multiple injection treatment. Female fecundity was affected by the hormonal treatment applied over the accompanying males, suggesting a pheromone communication between fish. However, none of the treatments seemed to be adequate in solving the problem of lack of fertilized spawning in cultured Senegalese sole broodstocks.

Spawning induction of pejerrey Odontesthes bonariensis in captivity using sustained-release gonadotropin releasing hormone agonist implants

The aim of this study was to induce and synchronize spawning of pejerrey Odontesthes bonariensis (Valenciennes, 1835), using gonadotropin releasing hormone agonist (GnRHa) implants. In the first experiment, the ovarian condition was assessed by ovarian biopsies and the measurement of the genital pore width (GPW). Females having the leading clutch of oocytes with a diameter of around 800–900 μm and a GPW between 4.5 and 5.5 mm were treated with GnRHa implants. Eighty per cent of females spawned between 2 and 9 days after treatment, 12 days earlier than 20% of the fish in the control group that presented signs of spawning activity. In order to avoid any possible ovarian injury and/or stress by the catheterization procedure, in a second experiment, females were selected only by visual inspection of the abdomen and GPW measurement. As in experiment 1, 80% of females spawned between 2 and 8 days after treatment, 8 days earlier than 30% of the fish that spawned in the control group. In both experiments, fertilization and hatching success were similar between control and GnRHa-treated groups. These results clearly demonstrated that GnRHa implantation can advance and synchronize ovulation and spawning in pejerrey without affecting egg quality.

Spawning performance and plasma levels of GnRHa and sex steroids in cultured female Senegalese sole ( Solea senegalensis) treated with different GnRHa-delivery systems

The aquaculture of Senegalese sole ( Solea senegalensis) is limited by the poor spawning performance of the F1 generation cultured broodstock. The present study compared the efficiency of two sustained-release delivery systems loaded with gonadotropin-releasing hormone agonist (GnRHa) and a single GnRHa injection on the stimulation of oocyte maturation (OM), sex steroid hormone secretion and spawning. Analysis with an ELISA showed that the administered GnRHa was no longer detectable in the plasma 3, 7 and 14 d after administration via a single injection, microspheres and an implant, respectively. All GnRHa treatments induced a transient elevation of testosterone (T) and 17β estradiol (E 2) plasma levels after 1–3 d. Only three spawns were obtained from controls on days 35, 41 and 42 of the study and ovarian biopsies showed abundant fully vitellogenic oocytes, but little OM. Fish given a GnRHa injection spawned sporadically with the first spawn at 20 days post-treatment (dpt). In contrast, GnRHa implants and microspheres stimulated OM and daily spawning starting at 4 and 5 dpt, respectively, and lasting for a period of 28 d. Total fecundity in the broodstock treated with GnRHa-delivery systems was 15–22 times greater than controls and 3–5 times greater than GnRHa-injected fish. Although egg quality appeared to be high, no fertilization was obtained. The results suggest that GnRHa-delivery systems are highly efficient on stimulating OM and spawning in Senegalese sole, presumably through the long-term elevation of pituitary luteinizing hormone release, which in turn stimulated the appropriate changes in ovarian steroidogenesis. However, the effectiveness of the treatment was negated by possible dysfunctions of the male breeders or of the reproductive behavior of the broodstock.

Treatment of GnRHa-implanted Senegalese sole (Solea senegalensis) with 11-ketoandrostenedione stimulates spermatogenesis and increases sperm motility

The effect of 11-ketoandrostenedione (OA) on plasma concentrations of sexual steroids and spermatogenesis of Senegalese sole (Solea senegalensis) implanted with gonadotropin-releasing hormone agonist (GnRHa) was investigated. Males were treated with saline (control) or with GnRHa implants (50 mug kg(-1)) in the presence or absence of OA (2 or 7 mg kg(-1)) during twenty eight days. Treatment with GnRHa alone slightly stimulated spermatogenesis and milt production with respect to controls, and this was associated with a transient elevation of plasma 11-ketotestosterone (11-KT) at day seven and an increase of 5beta-reduced metabolite(s) of 17,20beta-dihydroxy-pregn-4-en-3-one (17,20betaP) at day twenty eight. However, treatment with GnRHa+OA increased plasma concentrations of 11-KT and free+sulphated 5beta-reduced metabolites of 17,20betaP at days seven, fourteen and twenty one. After twenty eight days, the testis of GnRHa+OA-treated fish showed a lower number of spermatogonia B and spermatocytes I, and a higher number of spermatids, than fish treated with GnRHa alone. In addition, the motility of spermatozoa produced by GnRHa+OA males was enhanced by 2-fold with respect to controls or GnRHa males. These results suggest that treatment of Senegalese sole with GnRHa+OA stimulates spermatogenesis resulting in more motile sperm. Such effects could be mediated by an increased synthesis of 11-KT and/or 17,20betaP in the testis but further studies will be required to elucidate the specific mechanism involved.

Induction of spawning of cultured greater amberjack ( Seriola dumerili) using GnRHa implants

The objective of the current study was to examine the possibility of maturing Mediterranean greater amberjack ( Seriola dumerili) in culture at two different facilities in Greece and inducing spawning using gonadotropin releasing-hormone agonist (GnRHa) implants. Males in both stocks ( n=8) were in spermiating condition in mid June, though sperm motility was low ranging between 5% and 30%, while motility duration ranged between 2.1 and 2.5 min. Females of the first stock ( n=4) at the same time had ovaries with either primary oocytes or early vitellogenic oocytes at advanced stages of atresia, indicating a failure in oogenesis. On the contrary, the only female of the second stock contained oocytes at all stages of oogenesis, including early final oocyte maturation (FOM; oocyte diameter 650 μm). Implantation with a GnRHa implant induced the first spawn about 36 h later. In the absence of another spawn, a gonadal biopsy was taken 15 days later, indicating the existence of more oocytes at post vitellogenesis and some with almost complete lipid droplet coalescence. A second GnRHa implantation at this time resulted in consecutive egg releases after 36 h, 4 and 5 days, with fertilized eggs only at 36 h and 5 days. The study underlines the existence of important reproductive dysfunctions of greater amberjack in captivity, and demonstrates that GnRHa implants can be used for the induction of multiple spawns of viable eggs.

Sexual behavior after treatment with prostaglandin-F 2α in boars with suppressed concentrations of gonadal steroids

We tested the hypothesis that prostaglandin-F 2α (PGF 2α) enhances sexual behavior in boars with suppressed testosterone and estradiol secretion. After semen collection at week 0, boars received an s.c. implant containing a gonadotropin-releasing hormone agonist (GnRHa) or were sham-implanted. Beginning at week 1, GnRHa-implanted boars received i.m. treatment with 10 mg PGF 2α ( n = 5) or vehicle ( n = 5) upon entering the semen collection room. Sham-implanted boars ( n = 5) received i.m. vehicle. Blood was sampled and sexual behavior assessed at weeks 0 and 5. Compared to sham-implanted boars and GnRHa-implanted boars receiving PGF 2α, serum concentrations of testosterone and estradiol were lower in GnRHa-implanted boars receiving saline ( P < 0.05). The number of boars ejaculating, time from entering collection room to the first attempt to mount the artificial sow, time from entering to the start of ejaculation, and duration of ejaculation did not differ among treatments ( P > 0.05). The number of false mounts (mounting artificial sow but dismounting prior to semen collection) was increased ( P < 0.05) by GnRHa implants, an effect reversed ( P < 0.05) by PGF 2α. The data indicates that acutely suppressing concentrations of testosterone and estradiol will not abolish sexual behavior in boars, but leads to an increase in the number of unsuccessful mounts of an artificial sow. The number of false mounts can be decreased by treatment with PGF 2α.

Enhancement of spermiation in European sea bass (Dicentrarchus labrax) at the end of the reproductive season using GnRHa implants

Abstract Spermiating European sea bass ( Dicentrarchus labrax ) were treated at the end of the reproductive period (22 February 2002) with implants of gonadotropin-releasing hormone agonist (GnRHa), in order to examine their potential in enhancing expressible milt volume, sperm quality and in vitro fertilization success. The GnRHa implants at all doses (20, 40 and 80 μg GnRHa kg −1 body weight [bw]) stimulated a significantly higher production of milt compared to controls over a 27-day period, increasing total volume from 0.5 to 2.2 ml kg −1 sample time −1 . No differences in milt production were observed among the three GnRHa doses. Histological evaluation of the testes indicated that, by day 21, control fish had entered into gonadal regression, containing almost exclusively spermatogonia. At the same time, testes from GnRHa-implanted fish still contained large numbers of spermatozoa in the testes, indicating that spermiation was still underway. Sperm density varied between 7.4 and 14.4×10 10 spermatozoa ml −1 , but remained unchanged in response to GnRHa implantation. Sperm motility was high at the beginning of the experiment (92–100%) and decreased significantly by day 27 (32–55%), whereas motility duration was unchanged (0.9–1.2 min). Neither sperm motility nor motility duration was affected by the GnRHa treatment. Finally, fertilization success was high (40–80%) and not significantly different in response to GnRHa implantation. These results demonstrate that GnRHa implants are effective at increasing milt production at the end of the spermiation period, maintaining high sperm density and not affecting, either positively or negatively, sperm quality and fertilization capacity.

Spawning induction of individual European sea bass females ( Dicentrarchus labrax) using different GnRHa-delivery systems

The present study evaluated the effect of different delivery systems loaded with gonadotropin-releasing hormone agonist (GnRHa) on spawning induction, and egg and larval quality in female European sea bass ( Dicentrarchus labrax). Mature females (mean±S.E.M. oocyte diameter=905±10 μm) were treated with [ d-Ala 6, Pro 9 NEt]-mGnRHa using GnRHa-loaded microspheres, Mc (60 μg kg −1 body weight, bw) GnRHa-loaded implants, EVAc (50 μg kg −1 bw) or received a single injection of GnRHa in saline, IN (15 μg kg −1 bw). Controls (C) were injected with saline. Females were allocated individually in 2-m 3 tanks with two GnRHa-treated males and were allowed to spawn without further handling. All GnRHa treatments induced spawning 3 days after treatment (d.a.t.), whereas control fish did not spawn during the 21-day experimental period. GnRHa microspheres and implants induced up to four consecutive spawns in one female, whereas GnRHa-injected fish spawned only once. Egg quality seemed relatively lower in all GnRHa-treated groups compared to spontaneously spawning fish (natural spawns, NAT group) maintained in large populations (80 fish in 15-m 3 tanks), possibly due to both the isolation of individual females in separate tanks and the stress from handling. Mean egg quality of the first spawns was variable, but similar in all GnRHa treatments (6.6–18.2% buoyancy; 21.7–27.4% hatching). In subsequent spawns, the Mc-treated females produced eggs of higher buoyancy than the EVAc group (20.5±6.0% vs. 2.87±1.14%), and similar to the first spawn of the GnRHa-injected group. Our results indicate that, compared to a single GnRHa injection, GnRHa-loaded microspheres can induce multiple spawns in European sea bass, without a negative effect on egg quality.

Effects of chronic gonadotropin-releasing hormone agonist treatment on serum luteinizing hormone and testosterone concentrations in boars

Summary Mature boars were subjected to chronic treatment with a gonadotropin-releasing hormone (GnRH) agonist, goserelin (D-Ser[But]6, Azgly-NH210), and serum luteinizing hormone (lh) and testosterone concentrations were measured. Ten sexually mature boars were randomly assigned to treatment (n = 5) or control (n = 5) groups. On day 0, boars were implanted sc (day 0) with 2 GnRH agonist implants (1 mg of GnRH/implant) or sham implants. Blood samples were collected at 12-hour intervals on days – 2 and –1, at 6-hour intervals on days 0 through 4, and at 12-hour intervals on days 5 through 8. In addition, blood samples were collected at 15-minute intervals for 6 hours on days –1, 0, 4, and 8. Serum testosterone and (lh concentrations were determined by radioimmunoassay. Maximal (lh (7 ± 1 ng/ml) and testosterone (26 ± 3 ng/ml) concentrations were observed at 5 and 18 hours, respectively, after GnRH agonist treatment. Subsequently, (lh and testosterone concentrations decreased to pretreatment values (0.3 ± 0.1 ng/ml and 1.8 ± 0.4 ng/ml, respectively) by 24 and 48 hours, respectively, after GnRH agonist implantation. Few differences in the characteristics of pulsatile (lh release were observed between the groups. Testosterone and lh concentrations in samples collected at 6- and 12-hour intervals and pulsatile (lh release did not change after sham treatment of control boars. Whereas previous reports indicated that chronic GnRH administration suppressed serum lh and testosterone concentrations in rams, rats, and dogs, our results indicate that chronic GnRH agonist treatment induced transitory increases, without subsequent suppression, in lh and testosterone concentrations in mature boars.