Abstract: The purpose of this study was to obtain the sequence of the rabbit GnIH gene, detect its expression patterns in different tissues and different developmental stages in the hypothalamus, and investigate its effect on the secretion of reproductive hormones in young male rabbits. In this study, the 90-day-aged healthy male Minxinan black rabbits were used as experimental animals, the sequence of the GnIH gene was cloned by RACE (rapid-amplification of cDNA ends)and analyzed by bioinformatics methods; the relative expression levels of GnIH in different tissues of male rabbits aged 90 days (n=5) and in the hypothalamus aged 11, 30, 60, 90, 120 and 150 days (n=6) were determined by real-time quantitative PCR (qPCR); the male rabbits aged 80 days were chosen and intraperitoneally injected with 0, 0.5, 5 or 50 μg quail GnIH related peptides for 10 consecutive days, respectively (n=10). These rabbits were slaughtered and their testes were collected after ear vein blood sampling on the morning of the 11th day, and then, the concentrations of reproductive hormones (GnRH, FSH, LH, INHB, and T) in serums and the mRNA levels of testosterone synthesis related enzyme genes (StarR, 3β-HSD and p450scc) in testes were tested, respectively. A total length of 904 bp GnIH gene sequence was cloned successfully, including 41 bp of 5'UTR, 606 bp of CDS, and 227 bp of 3'UTR, encoding 201 amino acids. The GnIH gene expressed in most tissues and its mRNA level was higher in the hypothalamus than in other tissues (P<0.001); Aged from 11 to 150 days, its mRNA levels in hypothalamus reached the lowest point at 90 day-aged (P<0.01), and then significantly increased with increasing age(P<0.001). The young male rabbits were administrated at different doses of GnIH polypeptide. The results showed that the concentration of serum testosterone in group 50 μg was signicantly lower than those in control and 0.5 μg groups(P<0.001), the concentration of testosterone in group 5 μg was significantly lower than those both in control and 0.5 μg groups(P<0.05), and the concentration of LH in group 50 μg was significantly higher than that in control group (P<0.05); the mRNA level of p450scc gene in group 5 μg was significantly higher than those in the other groups(P<0.001), and there were no significant differences in the mRNA levels of other testosterone synthesis related enzyme genes among the GnIH administrating-groups and control group (P>0.05). These results indicated that the GnIH gene might be related to the synthesis and secretion of LH and testosterone, and participate in the regulation of reproductive development of male rabbits, chronic injection with a high dose of GnIH-related peptide leads to drug insensitivity of male rabbits, and the specific regulatory mechanism needs subsequent studies.

Key words: GnIH, Minxinan black rabbit, gene cloning, gene expression, reproductive hormone