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      Effect of Bacterial Endotoxin on in vivo Pulsatile Gonadotropin Secretion in Adult Male Rats

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          Immune system disorders are often accompanied by alterations in the reproductive axis. The bacterial endotoxin (lipopolysaccharide or LPS) has central inflammatory effects, and activates cytokine release (immune system mediatory factors) in the hypothalamus, where the luteinizing hormone-releasing hormone neurons are located. The present study was designed to investigate the effect of LPS on the pulsatile release of LH and FSH in adult male rats. With this aim, orchidectomized male rats were implanted with an atrial catheter and received, after two basal blood collections, LPS (250 µg/kg i.v.) or saline. Subsequently, blood samples were taken at regular intervals during 110 min. As expected, LH release was markedly reduced following exposure to LPS. In order to quantify these effects objectively, we subjected these data to PC-pulsar analysis. Pulsatile LH release was clearly disrupted in LPS-treated animals as compared to control rats: pulse frequency 1.3 ± 0.3 versus 0.43 ± 0.2/110 min, p < 0.05; pulse amplitude 17.18 ± 2.2 versus 8.33 ± 0.66 ng/ml, p < 0.05; overall mean release 15.2 ± 0.75 versus 7.08 ± 1.11 ng/ml, p < 0.001; maximum values 27.5 ± 3.08 versus 9.95 ± 2.16 ng/ml, p < 0.001; baseline levels 13.83 ± 0.77 versus 6.55 ± 0.74 ng/ml, p < 0.001. Regarding FSH secretion, LPS administration significantly lowered baseline levels (p < 0.05) and overall mean release (p < 0.01); FSH pulsatility parameters showed no significant differences. These observations indicate that LPS decreases LH and FSH mean release rates and baseline levels and inhibits several pulsatility parameters of LH release (frequency, amplitude and maximum values); FSH pulsatility parameters are not altered by LPS administration. We speculate that this effect is exerted principally at the hypothalamic level by modifying GnRH secretion.

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          Immunoreactive interleukin-1β localization in the rat forebrain

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            Interleukin-1 beta inhibits the endogenous expression of the early gene c-fos located within the nucleus of LH-RH neurons and interferes with hypothalamic LH-RH release during proestrus in the rat.

            The ability of central interleukin-1 beta (IL-1 beta) administration to modulate the hypothalamic LH-RH release as well as the endogenous expression of the c-fos protein located within the nucleus of LH-RH neurons was examined during the afternoon of proestrus in rats. In a first series of experiments, 50 or 100 ng IL-1 beta were infused into the lateral ventricle of the rat brain at either 08.30, 12.00, 14.30, or 17.00 h of proestrus. The animals were then perfused transcardially with a solution of 4% paraformaldehyde from 17.30 and 18.00 h. In a second series of experiments, the rats were equipped with an intracerebroventricular (i.c.v.) cannula in the lateral ventricle and a push-pull cannula into the median eminence (ME), and LH-RH secretion was measured during the afternoon of proestrus. The third experiment investigated the putative role of corticotropin-releasing factor (CRF) in modulating the inhibitory effect of IL-1 beta on LH secretion by infusing CRF antagonists before the i.c.v. administration of the cytokine to gonadectomized male and female rats. The central infusion of 50 or 100 ng IL-1 beta at 12.00 h completely blocked the spontaneous expression of c-fos protein which normally occurs in the nucleus of LH-RH neurons between 17.30 and 18.00 h on proestrus. In contrast, 50 ng IL-1 beta was less effective (P < 0.05) when administered at 08.30 h, and totally without effect when infused at 14.30 h. Infusion of 50 ng IL-1 beta also markedly suppressed the hypothalamic release of LH-RH in proestrus rats bearing a push-pull cannula into the ME, and significantly decreased plasma LH levels in both gonadectomized male and female rats. Finally, we observed that the central administration of CRF antagonists did not modify the inhibitory effects of the cytokine on the activity of the hypothalamic-pituitary-gonadal (HPG) axis. These results provide the first direct evidence that IL-1 beta is a potent inhibitor of LH-RH neuronal activity during the proestrus LH surge in intact cycling rats. As central administration of this cytokine completely inhibited the endogenous expression of c-fos protein within the nucleus of LH-RH neurons, our findings also suggest that IL-1 beta acts at the level of LH-RH perikarya.
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              Localization of type I interleukin-1 receptor mRNA in the rat brain


                Author and article information

                S. Karger AG
                March 1998
                11 April 1998
                : 67
                : 3
                : 275-281
                Department of Physiology, School of Medicine, University of Buenos Aires, Argentina
                54323 Neuroendocrinology 1998;67:275–281
                © 1998 S. Karger AG, Basel

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                Page count
                Figures: 4, Tables: 1, References: 35, Pages: 7
                Neuroimmune Interactions


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