EFFECT OF GnRH-AGONIST (DESLORELIN) IMPLANTATION ON REPRODUCTIVE PERFORMANCES IN EARLY PREPUBERTAL MALE AND FEMALE CATS

Abstract

The main objective of this study was to investigate the effect of GnRH-agonist (Deslorelin) implantation on the sexual behavior, reproductive function and gonadal Luteinizing hormone receptor (LHR) and Follicular stimulating hormone receptor (FSHR) expression in pre-pubertal male and female cats. The study had two main parts. In the first part of the study two experiments were performed. The 1st experiment was conducted to investigate the effect of GnRH-agonist implantation on sexual behavior, reproductive performance and expression of testicular LHR and FSHR in pre-pubertal tomcats, and in the 2nd experiment testicular characteristics, and LuteinLHR and FSHR expression were compared between pre-pubertal and adult tomcats (n = 6 / group). In Expt.1, 3 months-old tomcats (n=6/group) were either implanted with or left without 4.7 mg deslorelin implants for a period of 48 weeks. Semen collection and evaluation were performed just before castration after 48 weeks of treatment; removed testes were analyzed for mRNA and protein expression of LHR and FSHR. Body weight and testicular volume were compared between groups using Independent t-test. General linear model (GLM) was performed to compare the protein and mRNA expression of LHR and FSHR and the epididymal weight. Wilcoxon rank sum test was performed to compare the testicular weight, the mean diameter of seminiferous tubules and the grade of seminiferous tubules between groups. It was possible to collect semen from all the control cats, whereas semen could not be collected in implanted cats. Sexual behavior was absent in the deslorelin-implanted cats throughout the study period whereas it was present in the control cats from 28th week of the experiment onwards. Testicular volume started to decrease from 30th week of the implantation onwards compared to the controls (P < 0.05). Testicular tissue score, seminiferous tubule diameter and LHR protein expression were found to be significantly lower in the implanted cats (P < 0.05) but no differences were observed in mRNA expression of LHR and protein expression of FSHR between groups. The mRNA expression of FSHR was higher in the implanted (P < 0.05) compared to control cats. In Expt. 2, testes from pre-pubertal (n=6) and adult (n=6) male cats were collected after castration and analyzed for mRNA and protein expression of LHR and FSHR. No difference were observed in the protein expression of LHR and FSHR between the two groups, while mRNA expression of FSHR was higher in pre-pubertal cats (P < 0.05) compared to adult ones. Testicular and epididymal weight, diameter of seminiferous tubules and the testicular grade were higher in the adult compared to pre-pubertal cats (P < 0.05). The second part of the study was performed in prepubertal female cats; they were either implanted with 4.7 mg deslorelin (Group 1: n=6) or left without implants (Group 2: n =18; Group 3: n =6). Body weights, fecal estradiol and sexual behavior of cats in Groups 1 and 2 were monitored for 48 weeks followed by collection of their ovaries and uteri. Ovaries and uteri were collected from the control cats (Group 2) at their follicular, luteal and inter-estrus stage (n = 6/group) of the estrous cycle. Ovaries and uteri were collected from cats in Group 3 while they were still pre-pubertal. Both ovaries and uteri were analyzed for anatomical and histological characteristics. Ovaries were also analyzed for LHR and FSHR protein and mRNA expression. Data were statistically analyzed; body weights were compared between Groups 1 and 2 by Independent T-test and GLM was used to compare the ovarian weight, endometrial gland diameter, thickness of endometrium and myometrium, number of primordial, primary, secondary and antral follicles, and the mRNA and protein expression of LHR and FSHR among the experimental groups. The control cats had significantly higher (P < 0.05) body weight compared to implanted cats only during the 22nd to 26th week of the experimental period. Unlike the control cats, neither fecal estradiol peak nor estrus behavior was observed in the implanted cats. Deslorelin significantly (P < 0.05) reduced the ovarian weight and the number of antral follicles. Endometrial thickness and gland diameter were not affected by deslorelin. However, myometrial thickness of the implanted cats was significantly (P < 0.05) lower than the control cats at the follicular and luteal stage. Ovarian LHR mRNA expression was significantly (P < 0.05) lower in the implanted compared to the control cats at follicular stage of estrous cycle. FSHR mRNA and LHR protein expression did not differ among the 3 groups. FSHR protein expression was, however, significantly (P < 0.05) lower in pre-pubertal cats but was not affected by deslorelin-implantation. In summary GnRH-agonist implantation of pre-pubertal male and female cats suppressed their sexual behavior and reproductive function without any adverse effects for at least 48 weeks. In male cats, the GnRH-agonist implants suppressed the protein expression of LHR and enhanced mRNA expression of FSHR along with suppression of reproductive function. In conclusion, GnRH-agonist implantation can be effectively used in pre-pubertal male and female cats to suppress their reproductive function and delay puberty without any adverse effects for at least 48 weeks. In female cats the ovarian weight, follicle development, estradiol production and myometrial thickness were suppressed by GnRH-agonist implantation possibly through a change in the ovarian mRNA expression of LHR.