| Gonadotropin releasing hormone I (GnRH-I), a decapeptide is synthesized andsecreted by hypothalamus, which stimulates the produce and release of the gonadotropin，in combination with the specific receptor of gonadotropin secretory cells in the pituitarygland, thus regulates the reproductive activities. Active immunization against GnRH-I canproduce the GnRH-I antibody which neutralize the endogenic GnRH-I, which can inhibitthe reproductive function of animal. Many studies showed that active immunization againstGnRH-I could be used to restrain reproductive endocrine, reproductive organ developmentetc. So it can be used for immunocastration, contraception and termination of pregnancy inanimals. At present, scholars at home and abroad have carried on the extensive research onactive immunization against GnRH-I for the effect of the reproductive function andproduction performance in pig, cattle and sheep, but few reports are found in dogs.GnRH-I vaccine has been developed in our laboratory, which displays strongimmunogenicity in pig, rabbit and rat and so on. In this study, effect of activeimmunization against GnRH-I on the reproductive function in dogs was investigated,which provided the scientific theoretical basis for wide application and promotion ofGnRH-I vaccine in the future.Twelve healthy dogs (male and female are fifty-fifty) with the similar age (3monthsold) and about3.0?4.0Kg were used. The six male or female dogs were divided into twogroups in random, respectively. That is, control (n=3) and immunized (n=3). Dose of1.5mg maltose binding protein-gonadotropin releasing hormone I hexamer(MBP-GnRH-I6) were taked and dissolved into3mL saline, then were mixed with3mLAl(OH)3adjuvant. Dogs were approximately4-months-old at the beginning of theexperiment when the immunization treatment started. Immunized dogs were administered2mL MBP-GnRH-I6intramuscularly, in the neck. Dogs were boosted with the same doseand by the same route at6-week intervals. Control dogs were mock immunized with saline.During the experiment time, blood samples from all dogs were taken from the vein onceevery month. After blood collection, samples were centrifuged at200xg for20min at4°Cand serum obtained was stored at-20°C until assay. The testes and ovaries were surgicallyremoved at seven-months-old, and their weights and sizes were measured. Tissues fromtestes and ovaries were fixed in10%neutral buffered formalin and processed forhistological studies. Five-jam-thick sections of tissue were prepared with a microtome and stained with the hematoxylin and eosin (H&E)，and were observed under the opticalmicroscope.The results showed that, male dogs in immunized group had signiifcant difference(P<0.05) in the weight, diameter, transverse diameter, traverse perimeter and longitudinalperimeter of testes and the concentration of serum testosterone compared to the controlgroup. The weight, diameter, transverse diameter, traverse perimeter and longitudinalperimeter of ovary and the level of serum estradiol in the immunized group were lowerthan those of the control group (P<0.05). Tissue from dogs immunized againstMBP-GnRH-I6, showed a striking atrophy of interstitial cells and the lining epithelium ofthe seminiferous tubules, which were practically depleted of germ cells. Comparison,testicles of intact dogs had normal testicular tissue and active spermatogenesis, Stratiifedepithelium layers of the spermatogonium, primary spermatocytes, and spermatids werepresent. Many atretic follicles of the ovary were found in the immunized group, a lot ofprimordial follicles，primary follicles and secondary follicles were present in the ovary ofcontrol group.In conclusion this study that active immunization against MBP-GnRH-I6suppress thegrowth and development of testicular and ovary, and reduce the concentration oftestosterone and estradiol in the serum, and also restrain the spermatogenesis and folliculardevelopment, make the testes and ovary atrophy, which suggest that MBP-GnRH-I6is avery effect immunogen in dogs. |
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