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Submitted on May 27, 2003
Accepted on July 11, 2003
1 Clinical Research Center and Rehabilitation Center, International University of Health and Welfare, 2600-1 Kitakanemaru, Otawara, Tochigi 324-8501, Japan.
* To whom correspondence should be addressed. E-mail: watah{at}iuhw.ac.jp.
It is well established that endotoxemia disrupts reproductive capability, and several proinflammatory cytokines, especially interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-
in the brain, have been implicated in this endocrine aberration. However, no previous study has directly compared the effects of the three major proinflammatory cytokines (IL-1beta, IL-6, and TNF-) on the in vivo release of hypothalamic gonadotropin-releasing hormone (GnRH), a secretagogue of LH (LH) from the pituitary. Therefore, in this study we addressed this issue with two complementary approaches involving push-pull perfusion in freely-moving ovariectomized female rats. Firstly, we examined the effects of systemic lipopolysaccharide (LPS) treatment on the release of plasma LH, and of GnRH, IL-1beta, IL-6, and TNF- in the hypothalamic medial preoptic area (MPOA), where the majority of GnRH neuronal perikarya are located. LPS inhibited the secretion of both LH and GnRH, and concomitantly stimulated the release of all three cytokines. We next tested the effects of direct MPOA perfusion with the respective cytokines (at three different concentrations each) on the GnRH and LH secretion. IL-1beta and TNF-, at the concentrations that were observed in the MPOA after the LPS injection, were equipotent in inhibiting the GnRH-LH system, whereas IL-6 was ineffective even at a supraphysiological concentration. These results strongly suggest that IL-1beta and TNF- may represent the major proinflammatory cytokines mediating the LPS-induced suppression of GnRH and LH release, while the role of IL-6 seems to be insignificant.
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