Effects of GnRH Antagonists vs Agonists in Domestic Carnivores, a Review

Effect of a GnRH Antagonist on Anti-Müllerian Hormone and Follicular Population in Anestrous Bitches

The objective of this study was to describe the effect of the third-generation GnRH antagonist, acyline, on ovarian follicular population and serum anti-Müllerian hormone (AMH) concentrations in female dogs. Four late anestrous bitches were administered 330 μg/kg SC acyline every 10 days for 60 days and followed up for 45 days. Blood samples were drawn on days -1, 15, 30, 45, 60, 75, 90 and 105 for AMH determination. Then, the females were ovariectomized and the excised ovaries were gross and histologically evaluated. The total ovarian follicles were counted. None of the female dogs presented estrus during treatment. Only one bitch presented an ovulatory estrus 20 days after treatment. The total number of ovarian follicles in these bitches was 96,200.10 ± 26,125.12, with 84.13%, 11.36%, 7.8% and 0.01% corresponding to primordial, primary, secondary and antral structures, respectively. Pretreatment AMH concentrations were 0.62 ± 0.17 ng/mL. This hormone varied throughout the study period (p < 0.01), diminishing to nadir values during treatment to then rapidly recover after its effect (0.2 ± 0.05 vs. 0.67 ± 0.22 ng/mL; p < 0.01). Acyline rapidly and reversibly prevented the initiation of cycling without affecting follicle count but diminishing serum AMH concentrations.

Diagnostic tests in canine andrology - What do they really tell us about fertility?

Dog breeders often require breeding soundness evaluations which include andrological examinations of the genital organs, hormone measurements, and semen analyses. During the past decades, a considerable number of research results have been published, allowing diagnoses of specific andrological conditions and fertility assessment. For specific examinations, however, no standard procedures have been defined and for some parameters different reference ranges have been published. Therefore, examination results from different facilities are difficult to compare and profound conclusions regarding health and fertility of a male dog are not always possible. Conventional semen examination, however, is still useful in identifying deviations or no deviations from normality, especially if confounding factors are taken into account and if the exam is repeated in case of inconclusive findings. A standardization of examination procedures and reference ranges would help to harmonize the exchange of examination results and interpretation of the findings.

Testicular effects of a postnatal GnRH antagonist in domestic cats

The aim of this study was to describe the histological effects of two high postnatal doses of the potent third-generation GnRH antagonist, acyline in the domestic cat testicle. Secondly, the physical, endocrine, and steroidogenic findings of this pharmaceutical protocol are also reported. Twelve postnatal littermate male kittens were administered acyline in a dose of 2.2 mg/100 g SC weekly for 2 weeks (ACY; n = 6), or placebo (PL; n = 6). All the animals were followed up until puberty when they were castrated. Serial faecal samples were collected until the age of 10 weeks for testosterone (T) measurement. The kittens achieved puberty without either age (236.5 ± 19.7 vs. 221.7 ± 23.7 days) or body weight (3.05 ± 0.15 vs. 2.78 ± 0.28 kg, P > 0.05) differences between ACY and PL, respectively. Acyline suppressed faecal T concentrations for 3 weeks (P < 0.01). From the fourth week on, both groups had low concentrations up to the end of the follow-up period (P > 0.05). Histological assessment of the testes showed that ACY cats presented a reduced height of the epithelium (P < 0.01) due to the diminished number of germinal cells accompanied by an enlarged luminal area (P < 0.01) with cellular debris (P < 0.01). The immunostaining of P450c17 also appeared partially diminished in ACY testes.

Feline testicular ultrasonogram differentiates pre vs. postpubertal and normal vs. disrupted spermatogenesis

The aims of this study were: to ultrasonograhically describe and compare testicular parenchyma echogenicity and heterogeneity using digital image analysis in: I) prepubertal (PREP), peripubertal (PERI) and mature (MAT) cats; II) Normal and abnormal mature felids. Secondary, the relationships between histomorphological and ultrasonographic attributes of the testes were also determined. I) Fourteen, PREP, PERI and MAT male cats were ultrasonographically examined and then castrated. II) Seven adult cats were ultrasonographically examined before and after a GnRH antagonist administration and then castrated. All the testes were grossly and histomorphometrically assessed. In the frozen digital images of the longitudinal ultrasound sections, 3 regions of interest (ROI, 1 mm2) were selected. Within each ROI the echogenicity and the heterogeneity of the testicular parenchyma were digitally analyzed. In experiment I, testicular volume (0.15 ± 0.0 vs. 0.49 ± 0.1 vs. 1.65 ± 0.1; P < 0.01) and gonadosomatic index (0.04 ± 0.0 vs. 0.05 ± 0.0 vs. 0.08 ± 0.0; P < 0.01), echogenicity (56.54 ± 0.75 vs. 81.87 ± 5.88 vs.94.67 ± 3.62; P < 0.01) and heterogeneity (10.2420 ± 1.3740 vs.13.65 ± 0.65 vs. 14.67 ± 1.49; P < 0.01) augmented throughout PRE, PERI, and MAT. In experiment II, testicular volume (1.00 ± 0.09 vs. 0.85 ± 0.09; P < 0.05), echogenicity (87.74 ± 1.53 vs. 83.32 ± 1.54; P 0.01) but not heterogeneity (14.09 ± 0.26 vs. 14.19 ± 0.29; P > 0.05) decreased in the post GnRH antagonist abnormal testes. For both experiments, testicular volume, seminiferous tubular diameter, percentage of spermatids as the most mature cell type, and luminal/intertubular ratio were highly correlated (P < 0.01) with their echotextural attributes. Computer-assisted image analysis of B mode ultrasonogram appears as a good indicator of pubertal development and mild alterations of spermatogenesis in felids.

Effect of GnRH agonist deslorelin implant on spermatogenesis and testosterone concentration in Guinea pigs (Cavia aperea porcellus)

Guinea pigs are social animals that are often kept in groups regardless of their gender. Due to reproduction control and male aggressiveness prevention, surgical castration is commonly required. In the present study, we evaluated the effect of GnRH agonist implant (4.7 mg deslorelinum) on the serum testosterone concentration (T) and spermatogenesis in male guinea pigs. Twenty-four animals were divided into two groups. All animals in the first group were neutered (Group 1), animals in the second group (Group 2) were administered the implant subcutaneously and then neutered in one-month intervals. A histological examination was performed when cross sections of seminiferous tubules were assessed. Subsequently, these tubules were divided based on the most developed germ cell observed: spermatogonia, spermatocytes, round spermatids, elongating spermatids and elongated spermatids. The anticipated decrease in testosterone concentration and cessation of spermatogenesis was not achieved. Thus, the results obtained proved the inefficacy of the deslorelin implant in male guinea pigs so the alternative methods of contraception remain the methods of choice.

Quantitative bidimentional and Doppler ultrasound assessment of the effect of a GnRH antagonist on canine prostatic hyperplasia

The objectives of this article were: a) To describe the effect of a single administration of the third generation GnRH antagonist, acyline, on canine benign prostatic hyperplasia (BPH) b)To quantitatively compare parenchyma echogenicity, heterogeneity (SD echogenicity) and blood flow in hyperplastic and treated prostate glands. Seven mixed bred dogs, 11.14 ± 0.8 years of age, weighing 8.5 ± 1.4 (3.8-15.6) kg, with BPH were included in this study and administered acyline 330 mg/kg sc (day 0). Then the dogs were examined by B Mode and Doppler ultrasound on days 15, 30 and 60 after treatment. Parenchymal frozen images were digitally analyzed. On day -7, prostatic volume was 1.60-5.36 fold (volume ratio) enlarged in relation to the expected volume. Prostatic volume decreased up to a mean of -38.44% (P < 0.01; range -32.2 to -70.9%) on day 30 to gradually increase towards pretreatment values. A correlation between volume ratio and nadir treatment volume was also found (r = - 0.87; P < 0.05). Mean parenchyma echogenicity (P < 0.01) and heterogeneity (P < 0.01) diminished in all the post treatment evaluations. Pretreatment intraprostatic cysts disappeared at the time point of peak treatment effect. Prostatic arteries RI increased on day 30, being different from day -7 and also from day 60 values (P < 0.05). It was concluded that a single administration of a third generation GnRH antagonist safely decreased prostatic volume and parenchyma and blood flow abnormities associated with canine BPH during 30 days. Monthly administrations of this treatment could represent a rapid, efficient and safe therapeutic option for BPH.

Effects of Osteocalcin on Synthesis of Testosterone and INSL3 during Adult Leydig Cell Differentiation

Proliferation and differentiation of adult Leydig cells are mainly completed in puberty. In many studies, apart from normal postnatal development process, it is widely indicated that, through administrating EDS, Leydig cell population is eliminated and regenerated. It is believed that osteocalcin released from osteoblasts, which is responsible for modulating bone metabolism, induces testosterone production in Leydig cells, independent of the HPG axis. In addition, INSL3 produced by Leydig cells, such as testosterone, plays a critical role in bone metabolism and is known to reflect the development process and functional capacities of Leydig cells. This study is aimed at investigating OC-mediated testosterone regulation and INSL3 synthesis during differentiation of adult Leydig cells that are independent of LH. For this purpose, male rats were divided into 2 groups: prepubertal normal rats and adult EDS-injected rats. Each group was divided into 4 subgroups in which GnRH antagonist or OC was applied. After adult Leydig cells completed their development, testicular tissue samples obtained from the sacrificed rats were examined by light-electron microscopic, immunohistochemical, and biochemical methods. Slight upregulation in 3βHSD, INSL3, and GPRC6A expressions along with the increase in serum testosterone levels was observed in groups treated with osteocalcin against GnRH antagonist. In addition, biochemical and microscopic findings in osteocalcin treated groups were similar to those in control groups. While there was no significant difference in the number of Leydig cells reported, the presence of a significant upregulation in INSL3 and GPRC6A expressions and the increase in serum testosterone and ucOC levels were observed. After evaluation of findings altogether, it is put forward that, for the first time in this study, although osteocalcin treatment made no significant difference in the number of Leydig cells, it increased the level of testosterone through improving the function of existing adult Leydig cells during normal postnatal development process and post-EDS regeneration. This positive correlation between osteocalcin-testosterone and osteocalcin-INSL3 is concluded to be independent of LH at in vivo conditions.

Effects of long-acting GnRH antagonist, degarelix acetate, on plasma insulin-like peptide 3, testosterone and luteinizing hormone concentrations, and scrotal circumference in male goats

We recently reported that plasma insulin-like peptide 3 (INSL3) concentrations increased soon after endogenous and exogenous stimulations of LH in male goats and bulls. However, the effects of LH suppression on INSL3 secretion are unknown in domestic animals. Here, we examined the effects of a long-acting GnRH antagonist (degarelix acetate; 4 mg/kg) on the secretions of plasma INSL3 and testosterone in two phases, an immediate and a long-term phase in male goats (n = 6; aged, 13-16 months). During the immediate phase, blood was taken at 15-minute intervals for 8 hours on Days -5, 0, and 3. The GnRH antagonist was administered after 2-hour sampling of Day 0. Moreover, a daily blood sample was taken from Day 0 to Day 7, followed by twice a week until 9 weeks and finally at week 10. The scrotal circumference was recorded before treatment and continued biweekly until week 10. Concentrations of LH, INSL3, and testosterone in plasma were determined by EIA and the pulsatile nature of secretion analyzed using pulse XP software. The mean concentrations, pulse frequency (per hour), and pulse amplitude (peak-nadir) of plasma LH and testosterone reduced from pretreatment to posttreatment Day 0 and Day 3 (P < 0.05). A decline in mean concentrations, pulse frequency, and pulse amplitude of INSL3 was exhibited on posttreatment Day 3 compared with pretreatment (P < 0.01). During long-term sampling, a decline (P < 0.01) in plasma testosterone and INSL3 concentrations was observed 1 day after treatment and remained lower until 8.5 weeks after treatment, and thereafter returned to pretreatment levels. A reduction in scrotal circumference was recorded 4 weeks after treatment and remained lower until 10 weeks after treatment (P < 0.05). In conclusion, the acute regulation of INSL3 by LH was confirmed by reduction of plasma INSL3 levels within 3 days after GnRH antagonist treatment in male goats. Although the onset of suppression of testosterone was more rapid than that of INSL3, the low levels persisted for 8.5 weeks for both hormones, and subsequently the concentrations returned to pretreatment levels. A significant reduction in testicular size was also observed. The quick, long-lasting, and transient suppression of testosterone and INSL3 after a single injection implies a potential application of this antagonist in reversible long-term chemical castration in male goats.

Recent advancements in the hormonal stimulation of ovulation in swine

Induction of ovulation for controlled breeding is available for use around the world, and conditions for practical application appear promising. Many of the hormones available, such as human chorionic gonadotropin (hCG), gonadotropin-releasing hormone (GnRH) and its analogs, as well as porcine luteinizing hormone (pLH), have been shown to be effective for advancing or synchronizing ovulation in gilts and weaned sows. Each of the hormones has unique attributes with respect to the physiology of its actions, how it is administered, its efficacy, and approval for use. The timing for induction of ovulation during the follicle phase is critical as follicle maturity changes over time, and the success of the response is determined by the stage of follicle development. Female fertility is also a primary factor affecting the success of ovulation induction and fixed time insemination protocols. Approximately 80%-90% of female pigs will develop mature follicles following weaning in sows and synchronization of estrus in gilts. However, those gilts and sows with follicles that are less developed and mature, or those that develop with abnormalities, will not respond to an ovulatory surge of LH. To address this problem, some protocols induce follicle development in all females, which can improve the overall reliability of the ovulation response. Control of ovulation is practical for use with fixed time artificial insemination and should prove highly advantageous for low-dose and single-service artificial insemination and for use with frozen-thawed and sex-sorted sperm.

Treatment of canine pyometra with the gonadotropin-releasing hormone antagonist acyline: a case series

To describe the effect of the third-generation gonadotropin-releasing hormone antagonist acyline in the treatment of 4 diestrous bitches with the cystic endometrial hyperplasia-pyometra complex. The 4 bitches were treated with 330 μg/kg of subcutaneous acyline on day 0 and antibiotics, and followed up for 2 weeks. One closed-cervix case showed cervical dilatation 36 hours after treatment, and all the 4 animals showed resolution of clinical signs starting on day 3 posttreatment. Ultrasonographic uterine diameters and luminal contents decreased in the bitches having high progesterone serum concentrations before treatment but not in those with low levels. Serum progesterone importantly decreased from high to basal concentrations in the 3 "ultrasonographically cured" animals. No local or systemic side effects related to the treatment were observed. The gonadotropin-releasing hormone antagonist acyline may have a promising place for the medical treatment of cystic endometrial hyperplasia-pyometra complex in dogs.

Effect of azaline B on follicular development and functions in the hamster

The usefulness of azaline B, a GnRH antagonist, in suppressing gonadotropin secretion in the golden hamster was examined by examining follicular development, steroidogenesis and expression of steroidogenic enzymes. Serum levels of P and E declined significantly, while FSH or LH was undetectable in azaline B-treated hamsters. FSH significantly increased serum E levels, whereas LH upregulated serum P levels. The formation of antral follicles ceased in azaline-treated hamsters, but was reversed by FSH with or without LH supplement. FSH also activated the primordial follicle pool resulting in increased formation of primary and preantral follicles. Further, an increasing trend in the formation of preantral follicles in response to E or E + P, and the formation of antral follicles in response to E + P treatment was evident. The level of Cyp11a1 mRNA increased markedly in LH- or LH + FSH-treated hamsters, whereas FSH with or without LH upregulated Cyp17a1, Cyp19a1 and Fshr mRNA expression. E without or with P also upregulated ovarian Cyp19a1 mRNA expression. The expression of enzyme protein corroborated the mRNA data. In summary, azaline B is an efficient GnRH antagonist in the hamster, and will be useful in studying the selective effect of gonadotropins on ovarian functions without disrupting the physiological functions of other hormones in ovarian cells.

Molecular cloning, sequencing, and distribution of feline GnRH receptor (GnRHR) and resequencing of canine GnRHR

GnRH receptors play vital roles in mammalian reproduction via regulation of gonadotropin secretion, which is essential for gametogenesis and production of gonadal steroids. GnRH receptors for more than 20 mammalian species have been sequenced, including human, mouse, and dog. This study reports the molecular cloning and sequencing of GnRH receptor (GnRHR) cDNA from the pituitary gland of the domestic cat, an important species in biomedical research. Feline GnRHR cDNA is composed of 981 nucleotides and encodes a 327 amino acid protein. Unlike the majority of mammalian species sequenced so far, but similar to canine GnRHR, feline GnRHR protein lacks asparagine in position three of the extracellular domain of the protein. At the amino acid level, feline GnRHR exhibits 95.1% identity with canine, 93.8% with human, and 88.9% with mouse GnRHR. Comparative sequence analysis of GnRHRs for multiple mammalian species led to resequencing of canine GnRHR, which differed from that previously published by a single base change that translates to a different amino acid in position 193. This single base change was confirmed in dogs of multiple breeds. Reverse transcriptase PCR analysis of GnRHR messenger RNA in different tissues from four normal cats indicated the presence of amplicons of varying lengths, including full-length as well as shortened GnRHR amplicons, pointing to the existence of truncated GnRHR transcripts in the domestic cat. This study is the first insight into molecular composition and expression of feline GnRHR and promotes better understanding of receptor organization, and distribution in various tissues of this species.

Use of GnRH-agonists for medical management of reproductive disorders in birds

Pet birds suffer from a wide range of reproductive conditions and diseases. Chronic egg laying, egg binding, and excessive reproductive activities are common problems. Veterinarians may prescribe behavior modification, changes in captive care, and medical therapy to curb these behaviors. Surgical removal of the oviduct is effective at stopping egg production; however, it is a specialized surgery that carries surgical and anesthetic-related risks. The inability to surgically remove the ovary in birds may result in persistent ovarian activity and secondary complications. Therefore, hormone therapy as an adjunct or main therapeutic approach, using sustained-release GnRH agonists, shows promise in pet birds.