GnRH agonist active immunization influences ovarian development and GnRH receptor mRNA expression levels of pituitary in Japanese white rabbits (Oryctolagus cuniculus)

The present study was conducted to assess the effects of active immunization against the gonadotropin-releasing hormone agonist (GnRHa) on ovary development and GnRH receptor mRNA expression levels in pituitary in Japanese white rabbits (Oryctolagus cuniculus). Twenty-four three-month-old rabbits were randomly divided into four groups (n = 6). The animals were subcutaneously injected with 100 μg of GnRHa (alarelin) antigen in experimental group I (EG-I), 100 μg in experimental group II (EG-II) and 50 μg in experimental group III (EG-III) respectively. Alarelin antigens were re-injected in EG-II and EG-III with the same dosage on 20 days. CG was blank. The samples of ovaries and uteri were collected aseptically at the end of the experiment (70 days). Tissue slices were observed under light and electron microscopes. Serum anti-GnRH antibody titers and concentrations of FSH and LH were measured with ELISA. The anti-GnRH antibody titers reached the peak levels respectively at 30 days in EG-I (1:800), at 40–50 days in EG-II (1:1600) and at 40–50 days in EG-III (1:800). From 40 to 70 days, anti-GnRH antibody titers in EG-II were higher than that in EG-I and EG-III (p < 0.05). The highest FSH levels in EG-II and EG-III were detected on 40 days. FSH level in EG-II was higher than those in EG-I, CG (p < 0.01) and EG-III (p < 0.05) on 40 days. There was no significant difference in FSH levels between EG-I and CG. Serum LH concentrations in EG-II and EG-III reached the peak levels on 50 days and 40 days, LH level in EG-II exceeded other 3 groups on 50 days (p < 0.05). Real-time quantitative PCR analysis indicated that the levels of FSH-β mRNA and GnRH-R mRNA in pituitary significantly declined, while LH-β mRNA increased at 70 days following alarelin antigen treatment. The results also showed that alarelin antigen treatment improves the development of ovaries, follicles and uteri in Japanese white rabbits. Alarelin antigen treatment and re-injection with 100 μg dose had better effects than 50 μg treatment. This may have significance for the development of novel GnRH-based techniques in regulative functions in rabbits.