Abstract:

To explore the effects of active immunization against GnRH on the hypothalamus GnRH biosynthesis and gonadal feedback regulation system in adult Sprague-Dawley (SD) rats. Thirty-six male adult SD rats at the age of 12 weeks were randomly allocated to three groups of 12 animals each. Briefly, 12 rats were immunized against GnRH with a booster vaccination 8 weeks later. 12 intact males and 12 castrated rats were not administrated and served as controls. The GnRH antibody titers and reproductive hormone levels in sera, and the content of GnRH in the median eminence were determined by radioimmunoassay (RIA). The mRNA expressions of reproduction-related genes in the hypothalamus were quantified by real-time fluorescence quantitative PCR technique. Active immunization against GnRH significantly increased serum GnRH antibody titers in eleven of twelve immunized rats, reduced serum LH, FSH and testosterone to around or undetectable levels (P<0.05), and resulted in a subcutaneously atrophy of testes in these rats (immunocastrates). Compared with intact controls, immunocastration of rats significantly reduced the content of GnRH in the median eminence and mRNA levels of androgen-receptor (AR), estrogen receptor alpha (ERα), kiss-1, GPR54 and GnRH in the hypothalamus (P<0.05). As to surgical rats, excepting the serum LH and FSH levels, and the hypothalamic ERα mRNA levels were significantly higher than those in intact rats, the remaining experimental parameters were similar to those of immunocastrates. These data firstly indicate that the feedback regulations of gonads on the hypothalamus and the synthesis capacity of GnRH in the hypothalamus are both suppressed by active immunization against GnRH.