Effects of GnRH immunization on the reproductive axis and thymulin

    1. Yunsheng Li
    1. College of Animal Sciences and Technology, Anhui Agricultural University, 130, Changjiang West Road, Hefei, Anhui 230036, People's Republic of China
      1College of Life Science, Fujian Agriculture and Forestry University, Fuzhou 350002, People's Republic of China
      2The Biotechnology Center of Anhui Agriculture University, Hefei, People's Republic of China
    1. Correspondence should be addressed to F Fang; Email: fgfang{at}ahau.edu.cn


    The bidirectional regulation of thymulin in the reproductive-endocrine function of the hypothalamic–pituitary–gonadal (HPG) axis of rats immunized against GnRH remains largely unclear. We explored the alterations in hormones in the HPG axis in immunized rats to dissect the repressive effect of immunization on thymulin, and to clarify the interrelation of reproductive hormones and thymulin in vivo. The results showed that, in the first 2 weeks of booster immunization, thymulin was repressed when reproductive hormones were severely reduced. The self-feedback regulation of thymulin was then stimulated in later immune stages: the rising circulating thymulin upregulated LH and FSH, including GnRH in the hypothalamus, although the levels of those hormones were still significantly lower than in the control groups. In astrocytes, thymulin produced a feedback effect in regulated GnRH neurons. However, in the arcuate nucleus (Arc) and the median eminence (ME), the mediator of astrocytes and other glial cells were also directly affected by reproductive hormones. Thus, in immunized rats, the expression of glial fibrillary acidic protein was distinctly stimulated in the Arc and ME. This study demonstrated that thymulin was downregulated by immunization against GnRH in early stage. Subsequently, the self-feedback regulation was provoked by low circulating thymulin. Thereafter, rising thymulin levels promoted pituitary gonadotropins levels, while acting directly on GnRH neurons, which was mediated by astrocytes in a region-dependent manner in the hypothalamus.

    • Received in final form 21 May 2015
    • Accepted 27 May 2015
    • Made available online as an Accepted Preprint 27 May 2015
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