A role for GnRH in olfaction and cognition: Implications for veterinary medicine

Pulsatile secretion of gonadotropin-releasing hormone (GnRH) is essential for the activation and maintenance of the function of the hypothalamic-pituitary-gonadal (HPG) axis, which controls the onset of puberty and fertility. Two provocative recent studies suggest that, in addition to control reproduction, the neurons in the brain that produce GnRH are also involved in the control postnatal brain maturation, odour discrimination and adult cognition. Long-acting GnRH antagonists and agonists are commonly used to control fertility and behaviour in veterinary medicine, primarily in males. This review puts into perspective the potential risks of these androgen deprivation therapies and immunization on olfactory and cognitive performances and well-aging in domestic animals, including pets. We will also discuss the results reporting beneficial effects of pharmacological interventions restoring physiological GnRH levels on olfactory and cognitive alterations in preclinical models of Alzheimer's disease, which shares many pathophysiological and behavioural hallmarks with canine cognitive dysfunction. These novel findings raise the intriguing possibility that pulsatile GnRH therapy holds therapeutic potential for the management of this behavioural syndrome affecting older dogs.

The use of a 4.7 mg deslorelin slow release implant in male dogs in the field

OBJECTIVE

Slow-release GnRH agonist implants (SRI) are used for reversible medical downregulation of testicular function in male dogs as an alternative to surgery. The 4.7 mg deslorelin SRI should reduce testosterone after 6-8 weeks and induce castration-like effects for 6 months (mon). However, some individual variation is described in the field in regard to onset and duration of effect. For this reason, we aimed to study the effects of the 4.7 mg deslorelin SRI in a larger cohort.

MATERIAL AND METHODS

In total 50 intact, healthy male dogs (12-48 months, mon; 9-40 kg) were treated with a 4.7 mg deslorelin SRI into the umbilical area (TG, n=45) or served as untreated controls (CG, n=5). CG dogs were surgically castrated after measurement of testicular dimensions and blood sampling for testosterone. In TG, SRIs remained for 5 mon in place and subsequently 3-7 male dogs were surgically castrated at removal (week, W 0) or 1, 2, 3, 4, 5, 6, 7, 8 or 10 weeks later. Examination parameters were testicular dimensions (before treatment, at 4, 8, 12 W, 5 mon, weekly until castration), testosterone (before treatment, at 8 W, 5 mon, castration) and testicular histology (castration).

RESULTS

Whereas examination parameters did not differ between CG and TG before treatment, testicular volume and testosterone was significantly reduced at all time points during treatment. In all but 3 (8 W) and 2 male dogs (5 mon) testosterone was basal during treatment before removal, whereas the parameters were significantly reduced compared to pre-treatment in the respective dogs. After implant removal, testosterone and testicular volumes increased. However, different to earlier studies, the "restart" was more variable with individual basal testosterone until W7, but also physiological testosterone concentrations in W2. Similarly, histological testicular findings at castration were quite variable: besides an arrest on spermatogonia and spermatocytes, elongated spermatids with normal spermatogenesis were found in individual dogs.

CONCLUSION

Our study confirms the efficacy of the deslorelin SRI, but also individual variation especially regarding reversibility of effects on endocrine and germinative testicular function.

CLINICAL RELEVANCE

Deslorelin SRIs offer a suitable alternative to surgical castration with individual variation to be considered when used in clinical practice.

Reversible control of reproduction in tom cats: medical options for manipulating libido and fertility

BACKGROUND

There has been a growing interest in alternatives to surgery for controlling reproduction in tom cats, and the resultant medical options add to a practitioner's toolbox when handling these cases in clinical practice. It is important, however, that when suggesting these drugs, veterinarians have a good understanding of their mode of action, and their correct use and dosage.

CLINICAL RELEVANCE

Breeders increasingly wish to be able to switch on/off the reproductive ability of their tom cats in a controlled manner. In addition, in small animal medicine, there has been concern from some academics, and a growing number of pet cat owners, about potential long-term effects of surgical sterilisation. Further, for some cats surgical castration may not be possible due to health conditions that mean anaesthesia is unsafe. In all of these scenarios, medical alternatives to surgery can prove useful.

EQUIPMENT AND TECHNICAL SKILLS

No special equipment or technical skills are required. A good knowledge of the medical alternatives to surgical sterilisation for controlling reproduction in a tom, and making sure the patient is a suitable candidate, are, however, important for ensuring the cat's health during and after treatment and the owner's satisfaction.

AUDIENCE

This review is aimed principally (but not exclusively) at veterinary practitioners working with cat breeders who seek a temporary arrest in their tom cat's reproduction. It may also help practitioners with clients who would like an alternative to surgery or with cats where anaesthesia for surgical castration is not possible.

EVIDENCE BASE

Advances in reproductive feline medicine have resulted in improved knowledge of medical contraception. This review draws on scientific evidence-based papers that report on the mode of action, length of efficacy and potential side effects of different methods of medical contraception, as well as the authors' own clinical experience.

Chronic Use of Deslorelin in Dogs: Six Cases (2005-2022)

Deslorelin is currently registered for the induction of temporary infertility in male dogs, male cats, male ferrets, and also prepubertal female dogs, but research has shown its usefulness for other conditions requiring chronic treatment. This paper presents six cases of dogs chronically treated with deslorelin for indications such as benign prostatic hyperplasia, control of fertility, abnormal reproductive behavior and urinary incontinence. All animals were in good health during treatment. Treatment duration was 2-9 years. No short-term side effects were observed except for flare-up reactions, which were observed only in 1/4 intact males. Two dogs developed a neoplasia: a spayed bitch treated for urinary incontinence developed a pituitary carcinoma, and an intact male dog implanted for control of fertility developed a bladder carcinoma. While the pituitary carcinoma seems unlikely to be related to deslorelin, the bladder carcinoma could be due to the neutered condition of the dog (which was treated for 9 years) as urinary tract neoplasia is more common in dogs following gonadectomy. Chronic treatment with deslorelin is regarded as safe when an animal is being treated for life. The possibility that a pause in the treatment might be helpful for the animal should be investigated.

The function of the pituitary-testicular axis in dogs prior to and following surgical or chemical castration with the GnRH-agonist deslorelin

Chemical castration, that is the reduction of circulating testosterone concentrations to castrate levels by administration of a GnRH-agonist implant, is a popular alternative to surgical castration in male dogs. Detailed information concerning the pituitary-testicular axis following administration of a GnRH-agonist implant is still scarce. Therefore, GnRH-stimulation tests were performed in male dogs, prior to and after surgical and chemical castration. This approach also allowed us to determine plasma concentrations of testosterone and oestradiol in intact male dogs for future reference and to directly compare the effects of surgical and chemical castration on the pituitary-testicular axis. In intact male dogs (n = 42) of different breeds GnRH administration induced increased plasma LH, FSH, oestradiol and testosterone concentrations. After surgical castration basal and GnRH-induced plasma FSH and LH concentrations increased pronouncedly. Additionally, basal and GnRH-induced plasma oestradiol and testosterone concentrations decreased after surgical castration. After chemical castration, with a slow-release implant containing the GnRH-agonist deslorelin, plasma LH and FSH concentrations were lower than prior to castration and lower compared with the same interval after surgical castration. Consequently, plasma oestradiol and testosterone concentrations were lowered to values similar to those after surgical castration. GnRH administration to the chemically castrated male dogs induced a significant increase in the plasma concentrations of LH, but not of FSH. In conclusion, after administration of the deslorelin implant, the plasma concentrations of oestradiol and testosterone did not differ significantly from the surgically castrated animals. After GnRH-stimulation, none of the dogs went to pre-treatment testosterone levels. However, at the moment of assessment at 4,4 months (mean 133 days ± SEM 4 days), the pituitary gonadotrophs were responsive to GnRH in implanted dogs. The increase of LH, but not of FSH, following GnRH administration indicates a differential regulation of the release of these gonadotrophins, which needs to be considered when GnRH-stimulation tests are performed in implanted dogs.

Efficacy and Safety of 4.7 mg Deslorelin Acetate Implants in Suppressing Oestrus Cycle in Prepubertal Female Dogs

Our multicentric, masked, controlled and randomised study aimed to assess the efficacy and safety of Suprelorin® 4.7 mg (Virbac, Carros, France) regarding oestrus prevention in prepubertal intact bitches. Twelve- to eighteen-week-old females (n = 83) were allocated either a deslorelin implant (n = 62) or 0.9% sodium chloride (n = 21) group. Clinical assessment (heat signs), 17β oestradiol and progesterone assays, and vaginal cytology were performed at day (D)0, D7, D21, month (M)3 and M6 after product administration, and were then performed every other month until reaching puberty. Trained owners assessed heat signs between each veterinary visit. All bitches (n = 83) reached puberty before M30. Deslorelin significantly extended the median time to sexual maturity when compared to the control group (377 days versus 217 days after D0, p < 0.0001). Three females, implanted between 16 and 18 weeks of age, expressed an induced oestrus. Additional descriptive data, collected over a 24 month-period, showed functional reproductive abilities in both deslorelin (n = 52) and control (n = 21) groups once puberty was achieved. In conclusion, Suprelorin® 4.7 mg seems to be an effective and safe option for postponing the onset of oestrus when administered to prepubertal female dogs aged from 12 to 16 weeks.

Prepubertal Use of Long-Term GnRH Agonists in Dogs: Current Knowledge and Recommendations

The search for an alternative approach of estrus control (induction or suppression) in dogs is an important issue and the use of slow GnRH agonist-releasing implants has been the subject of frequent research in recent years. Studies to date demonstrate that the short- and long-term effects of deslorelin implants applicated at different time points of the prepubertal period are similar to those of adult dogs; however, there are important differences. The age of the prepubertal bitch and the dosage appear to be the main determinants of the response to deslorelin, as well as the individual metabolism of the bitch. Recent studies reported that the deslorelin-mediated long-term delay of puberty does not have negative carry-over effects on subsequent ovarian functionality, serum steroid hormone concentrations, uterine health, and fertility; however, more molecular studies are needed to determine the effects of application time of GnRH agonists on hormone concentrations and peripheral receptor expression. Furthermore, the long-term effects of delay of puberty with deslorelin on joint health, tumor development, the immune system, and social behavior deserve further investigations.

A Comparative Study of the Effects of Osaterone Acetate and Deslorelin Acetate on Sperm Kinematics and Morpho-Functional Parameters in Dogs

Simple Summary

Benign prostatic hyperplasia affects over 80% of old, non-castrated male dogs. In many cases, the severity of the symptoms means that treatment is required. The treatment of choice is surgical castration, which is unacceptable for the owners of stud dogs who are interested in therapy that does not exclude their animals from breeding. In those cases, treatment with deslorelin acetate or osaterone acetate offers an alternative to surgery. The aim of our study was to compare the changes in semen parameters over time. The deslorelin acetate implant gradually, during the course of its action, led to a full prevention the stud dogs from mating. However, in the first week following implant placement, in some individuals we observed an increase in sperm concentration (flare up effect), offering the possibility to obtain sperm in valuable dogs before the action of deslorelin acetate is completely established, precluding semen collection. On the other hand, osaterone acetate allowed for the continuous reproductive use of a stud dog, as it only affected some semen parameters, and mainly caused a temporary reduction in semen volume with the subsequent increase in semen concentration without altering the libido.

Abstract

Benign prostatic hyperplasia (BPH) is one of the most common problems in older male dogs that often has a huge impact on their health and welfare. This article presents a comparison between osaterone acetate (Ypozane^®; Virbac^®)(OA) and deslorelin acetate (Suprelorin^®; Virbac^®)(DA), medications that are the main therapeutic alternative to castration in dogs with BPH. Forty dogs were divided into four groups: I—negative control (five dogs without BPH); II—positive control (10 individuals diagnosed with BPH); III—15 dogs treated with DA, and IV—10 individuals treated with OA. Semen fractions were collected on days 0 (day of treatment), 7, 14, and 21, and weeks 8, 12, 16, and 20. Macroscopic, microscopic and CASA analyses were performed. Both DA and OA significantly affected the properties of the canine ejaculate. The DA lead to the lack of libido and had lesser effects to the sperm function before it caused azoospermia, whereas OA had no effect on libido and only temporary reduction in seminal plasma volume was observed, which resulted in temporary deterioration in the percentage of motile and progressive spermatozoa.

Double-Blind, Placebo-Controlled Trial of Cyproterone Acetate to Prevent Flare-Up Effect on Dogs Implanted With Deslorelin

Deslorelin slow-released implants are registered in Europe for the reversible suppression of fertility in male dogs. After administration, a time-limited increase in sex hormones concentration and related behavioral problems may be observed. The aim of this work was to assess whether cyproterone acetate, a synthetic progestogen, can prevent this flare-up effect. Eighteen privately-owned entire male dogs were enrolled in this double-blind, placebo-controlled, randomized clinical trial. All subjects received a 4.7 mg deslorelin implant by SC route and 1-3 capsules containing either cyproterone acetate 2 mg/kg (N = 9) or a placebo (N = 9), by oral route BID for 14 days, depending on the dog's weight. The dogs were followed for 28 days. An increase in the blood testosterone concentration was observed in respectively 9/9 and 7/9 dogs of the control and cyproterone groups (p = 0.47). However, a worsening of the sex hormone related problems (i.e., urinary marking, mounting, aggressiveness toward other dogs and/or escape) was only observed in the placebo group, in 56 or 66% of the dogs as measured by respectively the veterinarian and the owners. Our study suggests that cyproterone acetate is effective and safe to supress the deslorelin induced behavioral flare-up effect, but not the rise in testosterone.

Identification of Circular RNAs in the Anterior Pituitary in Rats Treated with GnRH

Simple Summary

The pituitary gland, an important endocrine organ, can secrete a variety of reproductive hormones under the action of hypothalamus-secreted gonadotropin-releasing hormone. Circular RNAs are a class of RNA molecules with stable covalently closed circular structures. In this study, we performed RNA sequencing of GnRH-treated rats to identify differentially expressed circRNAs in the anterior pituitary. The results revealed 1433 related circRNAs, 14 of which were differentially expressed. We predicted targeted relationships between the differentially expressed circRNAs and FSHb-LHb-associated miRNAs. In all, a total of 14 circRNAs were identified that may act on the secretion and regulation of reproductive hormones in GnRH-treated rats.

Abstract

The pituitary gland, an important endocrine organ, can secrete a variety of reproductive hormones under the action of hypothalamus-secreted gonadotropin-releasing hormone (GnRH) and plays important roles in animal reproduction. Circular RNAs (circRNAs) are a class of RNA molecules with stable covalently closed circular structures. CircRNAs are equipped with miRNA response elements (MREs), which can regulate the expression of target genes by competitively binding miRNAs. However, whether the expression levels of circRNAs in the pituitary gland change under the action of GnRH and whether such changes can further affect the secretion of reproductive hormones are still unclear. In this study, we performed RNA sequencing (RNA-Seq) of GnRH-treated rats to identify differentially expressed circRNAs. The results revealed 1433 related circRNAs, 14 of which were differentially expressed. In addition, we randomly selected five differentially expressed circRNAs and tested their relative expression levels by RT-qPCR, the results of which were consistent with the RNA sequencing results. Finally, we predicted targeted relationships between the differentially expressed circRNAs and FSHb-LHb-associated miRNAs. In all, a total of 14 circRNAs were identified that may act on the secretion and regulation of reproductive hormones in GnRH-treated rats. Our expression profiles of circRNAs in the anterior pituitaries of rats treated with GnRH can provide insights into the roles of circRNAs in mammalian development and reproduction.

Short-term effect of ovariohysterectomy on urine serotonin, cortisol, testosterone and progesterone in bitches

Objective

This study aimed to investigate the short-term effect of ovariohysterectomy on urine levels of serotonin and its relation to levels of cortisol, testosterone and progesterone in female dogs. Seven bitches were studied before surgical ovariohysterectomy and then once a week during 4 weeks. Spontaneously voided urine samples were collected and concentration ratios of hormone/creatinine in urine were analysed.

Results

The bitches had significantly lower levels of cortisol, testosterone, and progesterone 1 week after ovariohysterectomy compared with before and the levels stayed low throughout the study (P ≤ 0.05). Interestingly, serotonin levels tended to increase 4 weeks after surgery (P = 0.08). A positive correlation between cortisol and progesterone was found before and after surgery. After surgery, serotonin was positively correlated with cortisol and progesterone (P ≤ 0.05).

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-021-05680-y.

Deslorelin Slow-Release Implants Delay Ovulation and Increase Plasma AMH Concentration and Small Antral Follicles in Haflinger Mares

Simple Summary

In horses, oocyte collection followed by intra-cytoplasmatic sperm injection is increasingly used. The yield of oocytes is a limiting factor and depends on the number of follicles present on the ovary during oocyte collection. Therefore, the aim of this study was to analyze the effect of slow-release implants containing the GnRH analogue deslorelin on the number of follicles and on hormones regulating follicular development. Six mares received a deslorelin implant and six mares served as controls. The interval to the first spontaneous ovulation was prolonged in treated mares. The treatment changed the release pattern of the gonadotrophins LH and FSH. Changes in the number of follicles 10 to 15 mm in diameter were detected in deslorelin-treated mares. These changes were also reflected by increasing plasma anti-Muellerian hormone concentrations, a hormone produced by growing follicles. In conclusion, deslorelin implants induce changes in ovarian follicle subpopulations and could be a promising tool for the preparation of mares for assisted reproductive procedures.

Abstract

There is an increasing interest in the manipulation of ovarian follicular populations in large domestic animals because this could prove beneficial for assisted reproductive techniques such as ovum pick-up (OPU). The aim of the present study was to evaluate the effects of deslorelin slow-release implants (SRI) on the interovulatory interval, antral follicle count (AFC), number of follicles of different size ranges and plasma anti-Muellerian hormone (AMH) concentration in mares. To synchronize their estrous cycles, Haflinger mares (n = 12) were treated twice with a PGF_2α analogue. One day after the second injection (day 0), mares received a 9.4 mg deslorelin SRI (group DES, n = 6) or 1.25 mg deslorelin in a short-acting formulation (CON; n = 6), respectively. Regular transrectal ultrasonography of the genital tract was performed and blood samples were collected for the analysis of progesterone, AMH and gonadotrophins. The interval from implant insertion to the first spontaneous ovulation was 23.8 ± 10.5 days in group DES compared to 17.0 ± 3.9 days in group CON (p < 0.05). For the concentrations of LH, FSH and AMH, interactions between time and treatment were detected (p < 0.05). The AFC and the mean number of follicles with 5 to 10, 10 to 15 and 15 to 20 mm in diameter changed over time (p < 0.05). A time x treatment interaction was demonstrated for follicles of 10 to 15 mm in diameter (p < 0.05). The changes in this follicular subpopulation were reflected by increased plasma AMH concentration in group DES. In conclusion, 9.4 mg deslorelin implants show minor effects with regard to estrus suppression in mares, whereas the changes in the subpopulation of small ovarian follicles could be a promising tool for preparation of mares for OPU.

The past, present and future of hormonal contraceptive use in managed captive female tiger populations with a focus on the current use of deslorelin acetate

Tigers (Panthera tigris spp.) are endangered in the wild; ensuring sustainable insurance populations requires careful planning within zoological collections. In captive situations, contraceptives are often used to control breeding and ensure genetically viable populations that contain manageable numbers of animals; reversible contraceptives are ideal because they offer flexibility for breeding management. Historically, synthetic progestins, such as melengestrol acetate implants, were used in female tigers, but these are associated with an increased risk of reproductive pathology and subsequent infertility. Recent management advice to ex-situ collections has been to transition to the use of gonadotropin-releasing hormone agonists, such as deslorelin acetate implants, which do not appear to have a similar risk of reproductive pathology but are associated with highly variable reversal times in exotic felids. Using data from 917 contraceptive records in female tigers captured by the Association of Zoos and Aquariums Reproductive Management Center and the European Association of Zoos and Aquaria Reproductive Management Group's joint Contraception Database and from supplementary surveys, this study reviews the changing use of contraceptives in captive female tigers. The aim was to describe the historical and current use of contraceptives and provide a comprehensive assessment on the use of deslorelin implants, including data on product protocols, efficacy, pathology, and reversibility. This study determined that current dose, frequency, reversibility, and anatomical placement sites of deslorelin implants are highly variable, indicating that specific, readily available, unified, evidence-based recommendations on the use of deslorelin would be useful for future contraceptive use in managed tiger populations.

Determination of Efficacy of Single and Double 4.7 mg Deslorelin Acetate Implant on the Reproductive Activity of Female Pond Sliders (Trachemys scripta)

The use of long-acting gonadotropin-releasing hormone (GnRH) agonists to suppress fertility has been poorly investigated in reptiles, and the few available studies show inconsistent results. The efficacy of single and double intramuscular 4.7 mg deslorelin acetate implants in captive pond sliders (Trachemys scripta) was investigated, with 20 animals divided into three groups: a single-implant group (6 animals), a double-implant group (6 animals), and a control group (no implant). During one reproductive season (March to October), plasmatic concentration of sexual hormones (estradiol, progesterone, and testosterone) and ovarian morphometric activity via computed tomography were monitored about every 30 days. A significative decrease in the number of phase II ovarian follicles was detected in the double-implant group compared with the control group, but no significant difference was noted in the number of phase III and phase IV follicles, egg production, and plasmatic concentration of sexual hormones. Results show that neither a single nor a double deslorelin acetate implant can successfully inhibit reproduction in female pond sliders during the ongoing season, but the lower number of phase II follicles in the double-implant group can possibly be associated with reduced fertility in the following seasons.

GnRH-a-Induced Perimenopausal Rat Modeling and Black Cohosh Preparations' Effect on Rat's Reproductive Endocrine

BACKGROUND

Endometriosis (EMS) is an estrogen-dependent disease, which easily recurs after operation. Gonadotropin-releasing hormone agonist (GnRH-a), an estrogen-inhibiting drug, can effectively inhibit the secretion of gonadotropin by pituitary gland, so as to significantly decrease the ovarian hormone level and facilitate the atrophy of ectopic endometrium, playing a positive role in preventing postoperative recurrence. The application of GnRH-a can lead to the secondary low estrogen symptoms, namely the perimenopausal symptoms, and is a main reason for patients to give up further treatment. The add-back therapy based on sex hormones can well address the perimenopausal symptoms, but long-term use of hormones may cause the recurrence of EMS, as well as liver function damage, venous embolism, breast cancer and other risks, which has long been a heated topic in the industry. Therefore, it is necessary to find effective and safe anti-additive drugs soon. Studies at home and abroad show that, as a plant extract, isopropanolic extract of cimicifuga racemosa (ICR) can well relieve the perimenopausal symptoms caused by natural menopause. Some studies have preliminarily confirmed that black cohosh preparations can antagonize perimenopausal symptoms of EMS patients treated with GnRH-a after operation.

OBJECTIVE

To establish a rat model of perimenopausal symptoms induced by GnRH-a injection, for the purposes of laying a foundation for further research and preliminarily exploring the effect of black cohosh preparations on reproductive endocrine of the rat model.

METHOD

The rat model of perimenopausal symptoms was established by GnRH-a injection, and normal saline (NS injection) was used as the control. The rats were randomly divided into four groups according to different modeling methods and drug intervention schemes. GnRH-a injection + normal saline intervention group (GnRH-a + NS), normal saline injection control + normal saline intervention group (NS + NS), GnRH-a injection + estradiol intervention group (GnRH-a + E2), and GnRH-a injection + black cohosh preparations intervention group (GnRH-a + ICR). After modelling was assessed to be successful with the vaginal smear method, the corresponding drugs were given for intervention for 28d. In the process of rat modeling and drug intervention, the skin temperature and anus temperature of the rat tails were measured every other day, the body weights of the rats were measured every other day, and the dosage was adjusted according to the body weight. After the intervention was over, the serum sex hormone level, the uterine weight, the uterine index, and the endometrial histomorphology changes, as well as the ovarian weight, the ovarian index, and the morphological changes of ovarian tissues of each group were measured.

RESULTS

(1) The vaginal cell smears of the control group (NS + NS) showed estrous cycle changes, while other model rats had no estrous cycle of vaginal cells. (2) The body weight gains of the GnRH-a + NS, GnRH-a + E2 and GnRH-a + ICR groups were significantly higher than that of the NS + NS control group. The intervention with E2 and ICR could delay the weight gain trend of rats induced by GnRH-A. (3) After GnRH-a injection, the temperature of the tail and anus of rats showed an overall upward trend, and the intervention with E2 and ICR could effectively improve such temperature change. (4) The E2, FSH, and LH levels in the GnRH-a + NS, GnRH-a + E2, and GnRH-a + ICR groups were significantly lower than those in the NS + NS group (P < 0.01). The E2 level was significantly higher and the LH level was significantly lower in the GnRH-a + E2 group than those in the GnRH-a + NS and GnRH-a + ICR groups (P < 0.05). Compared with those of the GnRH-a + NS and GnRH-a + ICR groups, the FSH level of the GnRH-a + E2 group showed a slight downward trend, but the difference was not statistically significant (P > 0.05). There was no significant difference in the levels of sex hormones between the GnRH-a + NS group and GnRH-a + ICR group (P > 0.05). (5) Compared with those of the NS + NS group, the uterine weight and uterine index of the GnRH-a + NS, GnRH-a + E2 and GnRH-a + ICR groups significantly decreased (P < 0.01). In a comparison between the groups, the uterine weight and uterine index in the GnRH-a + NS and GnRH-a + ICR groups were significantly lower than those in the GnRH-a + E2 group (P < 0.01). There was a statistical difference in the uterine weight and uterine index between the GnRH-a + NS group and GnRH-a + ICR group (P > 0.05). (6) Compared with those of the NS + NS group, the ovarian weight and ovarian index of the GnRH-a + NS, GnRH-a + E2 and GnRH-a + ICR groups significantly decreased (P < 0.01). There was no statistical difference in the ovarian weight and ovarian index among the GnRH-a + E2, GnRH-a + NS and GnRH-a + ICR groups (P > 0.05). (7) Compared with those in the NS + NS group, the number of primordial follicles increased significantly, while the number of growing follicles and mature follicles decreased significantly in the GnRH-a + NS, GnRH-a + E2, and GnRH-a + ICR groups (P < 0.01), but there was a statistical difference in the total number of follicles among the four groups (P > 0.05).

CONCLUSIONS

The GnRH-a injection could achieve the desired effect. The animal model successfully achieved a significant decrease in the E2, FSH, and LH levels in rats, and could cause the rats to have rising body surface temperature similar to hot flashes in the perimenopausal period. The intervention with E2 and ICR could effectively relieve such "perimenopausal symptoms", and ICR had no obvious effect on the serum sex hormone level in rats.

Transient suppression of ovulatory ovarian function in pony mares after treatment with slow-release deslorelin implants

Behavior during the estrous cycle of mares can affect their performance and therefore inhibition of cyclical ovarian activity is indicated. We hypothesized that implants containing the GnRH analog deslorelin downregulate GnRH receptors and inhibit ovulation in mares. The estrous cycles of Shetland mares were synchronized with 2 injections of a PGF_2α analog. One day after the second injection (day 0), mares received 9.4 (group D1, n = 6) and 4.7 mg deslorelin (D2, n = 5) as slow-release implants or 1.25 mg short-acting deslorelin as a control (C, n = 5). Ultrasonography of the reproductive tract and ovaries and observation of estrous behavior and collection of blood samples for analysis of progesterone and LH concentrations were performed every second day until day 10 and thereafter at 5-d intervals. Stimulation tests with the GnRH-agonist buserelin were performed on days 10 and 45. Until day 50, there were less spontaneous ovulations in group D1 (P < 0.01) and estrous behavior was reduced in groups D1 and D2 compared with group C (P < 0.05). The time until first ovulation (D1 62.0 ± 8.6, D2 44.2 ± 14.1, C 22.2 ± 3.1 d, P < 0.05) and the number of days with estrous behavior (P < 0.05) differed among groups. On day 10 after treatment, a GnRH stimulation test revealed interactions between group and time (P < 0.001) in plasma LH concentration that were no longer detectable on day 45 after treatment. In conclusion, long-acting deslorelin implants result in a transient downregulation of pituitary GnRH receptors that is associated with inhibition of ovulation and estrous behavior in Shetland mares.

Effects of Lupron and surgical castration on fecal androgen metabolite concentrations and intermale aggression in capybaras (Hydrochoerus hydrochaeris)

To curb agonistic interactions in a bachelor group of three male capybaras (Hydrochoerus hydrochaeris), a single dose of leuprolide acetate (Lupron®) was used in an attempt to chemically sterilize the males. Concurrently, fecal androgen metabolite (FAM) concentrations were quantified via enzyme immunoassay to monitor changes in testosterone production after injection of the gonadotropin-releasing hormone agonist. When Lupron proved ineffective in suppressing intraspecific aggression, surgical castration was performed on two males, with continued noninvasive endocrine monitoring. In all three capybaras, FAM concentrations increased initially as a result of the luteinizing hormone surge, but then decreased significantly following chemical sterilization. Surgical castration resulted in further, persistent declines in FAM concentrations in two males, while the third, intact male demonstrated a rise in FAM to pre-Lupron concentrations at 8.5 and 9.5-month postadministration. Despite successful suppression of sperm and testosterone production, intermale aggression continued, ultimately necessitating separation of the animals and transfer to other holding institutions. Under this set of conditions, a single Lupron dose was inadequate for suppressing intraspecific aggression in a group of three males with a pre-established history of aggression.

Contraceptive implants used by cat breeders in France: a study of 140 purebred cats

OBJECTIVES

Deslorelin 4.7 mg and melatonin 18 mg subcutaneous implants were studied in purebred male and female cats, via questionnaires sent to French cat breeders, to assess breed, age, duration of the contraceptive effect, fertility after use, changes in behaviour and side effects.

METHODS

Reproductive data were collected in 57 tom cats and 41 queens implanted with deslorelin 4.7 mg, and 42 queens implanted with melatonin 18 mg, for a total of 140 purebred cats, from 38 different catteries, representing 18 breeds.

RESULTS

Using deslorelin (Suprelorin 4.7 mg; Virbac), sexual behaviour in males was inhibited for a mean ± SD of 13.4 ± 3.2 (range 8-21) months in 37/57 cats. Of these, 24/37 mated successfully and produced litters at a mean of 15.5 ± 3.6 (range 9-20) months. Inhibition lasted 11 ± 1.1 (range 9-12; n = 6), 13.2 ± 2.4 (range 12-18; n = 6) and 15 ± 3.5 (range 9-18; n = 6) months in Norwegian Forest Cat, Singapura and Ragdoll males, respectively. In 26/41 females implanted with deslorelin 4.7 mg, oestrus was inhibited for a mean of 16.0 ± 5.7 (8-38) months; 12/26 went on to produce a litter. Of the side effects specific to females: two presented persistent oestrus, leading to the removal of the implant; two developed lactation; one had fibroadenomatosis; and one was sterilised owing to cystic endometrial hyperplasia. Using melatonin (Melovine 18 mg; Ceva), 33/42 females had oestrus inhibited for a mean of 86 ± 50 (range 21-277) days after implantation with a peak return to oestrus in March, and 12/33 had a subsequent litter. No side effects were reported.

CONCLUSIONS AND RELEVANCE

This study is the first to collect a large amount of field data, in 140 purebred male and female cats where a deslorelin 4.7 mg or a melatonin 18 mg implant was used. These field results may allow for more accurate clinical advice and open up new avenues of research.

Interval between Removal of a 4.7 mg Deslorelin Implant after a 3-, 6-, and 9-Month Treatment and Restoration of Testicular Function in Tomcats

Deslorelin implants have been used to produce a reversible sterilization in several species. In cats, the prolonged duration (12-15 months in tomcats and 18-22 months in queen) is often too much for cat breeders who request early implant removal. The interval between implant removal and resumption of reproductive function in cats has never been investigated. Eighteen tomcats received a 4.7 mg deslorelin implant placed in the periumbilical area and surgically removed during all seasons of the year after 3, 6, or 9 months (n = 6, 6, and 6 cats, respectively). Following implant removal, all cats received a clinical exam every two weeks, including testicular ultrasonographic measurement, observation of penile spikes, and blood collection for serum testosterone assay. Restoration of serum testosterone secretion occurred after 23 ± 6, 23 ± 6, and 22 ± 7 days in the 3-, 6-, and 9-month groups, respectively. Restoration of testicular function was confirmed by histology in 13/15 cats undergoing orchiectomy at the end of the study while the owners of the remaining two cats opted to maintain their animals intact. Removal of a 4.7 mg deslorelin implant after 3, 6, or 9 months is followed by resumption of serum testosterone secretion after about 3 weeks independent of age or season.

Gonadotropin-Releasing Hormone (GnRH) Agonist Implants for Male Dog Fertility Suppression: A Review of Mode of Action, Efficacy, Safety, and Uses

At present, only surgical sterilization is available for veterinarians and pet owners seeking suppression of fertility in male dogs, in most countries. An alternative contraceptive alternative approach is GnRH releasing implants that desensitize the pituitary to the stimulatory effects of GnRH and thereby block testicular function (testosterone and sperm production). Two GnRH agonists (deslorelin and azagly-nafarelin) have been researched in controlled release formulations for this purpose. A deslorelin-releasing biodegradable implant, marketed under the name Suprelorin®, has been available in Australia and New Zealand since 2007, the European Union (EU) since 2008, and received regulatory approval in China and Mexico in late 2019. Two versions of the implant are available, one labeled for a minimum of 6 months of fertility suppression in male dogs, and the other for a minimum of 12 months in male dogs. Another GnRH agonist (azagly-nafarelin) was also included in a solid implant (Gonazon®). Research results showed it delivered 6-months to 1 year of suppressed fertility; however, it is not commercialized. This review paper summarizes research on the mechanism of action for these technologies and compiles and interprets the research on efficacy and safety. New findings on usage of the deslorelin releasing implant in countries where veterinarians and pet owners have this option is shared. Research on off-label use of the product in male dogs is also reviewed. This review aims to aid in the evaluation of the deslorelin releasing implant as an adjunct or alternative for surgical sterilization of male dogs.

Deslorelin acetate implant induces transient sterility and behavior changes in male olive baboon (Papio anubis): A case study

This case study evaluates the effects of a 4.7 mg deslorelin acetate implant on one male olive baboon (Papio anubis). Implantation induces transient azoospermia after which the subject was able to conceive again. Behavior was also impacted with a decrease in our proxies of aggressiveness and sexual arousal.

Desexing Dogs: A Review of the Current Literature

Background: Desexing dogs is promoted for population control, preventative healthcare, and behavior modification. Common methods are orchiectomy and ovariectomy/ovariohysterectomy. GnRH superagonist implants are available in some areas. Alternative methods like vasectomy and salpingectomy/hysterectomy are uncommon. The terminology used to describe desexing is inconsistent and contradictory, showing a need for the adaption of standardized terminology. Population Control: Surprisingly, empirical studies show no effects of desexing on population control in companion and shelter dogs despite desexing being consistently recommended in the literature. There is evidence for a population control effect in free-roaming dogs, where desexing also has benefits on zoonotic disease and bite risk. Population control in free-roaming dogs is mostly correlated with female, not male desexing. Health and Lifespan: Desexing affects numerous disease risks, but studies commonly neglect age at diagnosis and overall lifespan, age being by far the most important risk factor for most diseases. We argue that lifespan is a more important outcome than ultimate cause of death. A beneficial effect of desexing on lifespan is consistently demonstrated in females, while evidence for a beneficial effect in males is inconsistent. Studies are likely biased in desexing being a proxy for better care and desexed dogs having already lived to the age of desexing. Desexing reduces or eliminates common life-limiting diseases of the female reproductive system such as pyometra and mammary tumors, while no analogous effect exists in males. Disease risks increases across sexes and breeds include cruciate ligament rupture, various cancers, and obesity. Urinary incontinence risk is increased in females only. Various other disease risk changes show considerable variability between breeds and sexes. Behavioral Effects: Desexed males show reduced libido, roaming, conspecific mounting, and urinary marking frequency, as well as reduced male dog-directed aggression in a majority of males desexed for behavioral reasons. There is a detrimental effect on the risk and progression of age-related cognitive dysfunction. Desexed dogs may be less likely to cause bite injuries across sexes. The evidence for other effects such as human-directed aggression, human or object mounting, resource guarding, or shyness and anxiety is inconsistent and contradictory. There are few studies specific to females or individual breeds. Conclusions: The evidence for a beneficial effect of desexing is stronger in female than in male dogs; however, there is significant variation between breeds and sexes, and more research is needed to further elucidate these differences and to arrive at individualized evidence-based recommendations for clinical practice.

Gonadotrophin-Releasing Hormone Agonists and Other Contraceptive Medications in Exotic Companion Animals

The use of a gonadotrophin-releasing hormone agonist slow-release implant (GnRH A-SRI) has become increasingly popular as an alternative for surgical contraception in many species. Although these implants have proven to be very effective in some species (eg, ferrets, rats, chicken, psittacines, and iguanas), they have been found less effective in other species (eg, male guinea pigs and rabbits, veiled chameleons, slider turtles, and leopard geckos). This review provides an overview of the available literature on the effects of GnRH A-SRIs in companion exotic animals.

Evaluation of Canine Sperm and Management of Semen Disorders

Semen evaluation of the male dog is a critical step in any canine infertility work-up. Assessment of total sperm count, sperm viability, and sperm morphology are the mainstay of breeding soundness evaluation. Adjunct tests, such as ultrasonography and serum hormone levels, can aid in diagnosis. Pharmacologic treatments, dietary supplements, and management practices may help improve breeding success in subfertile dogs. This article discusses a clinically practical approach to assessing sperm abnormalities and fertility in male dogs.