Inhibition by lipopolysaccharide of naloxone-induced luteinising hormone secretion is accompanied by increases in corticotropin-releasing factor immunoreactivity in hypothalamic paraventricular neurones in female rats.
We have recently reported that lipopolysaccharide (LPS), a bacterial endotoxin, inhibits steroid-induced as well as naloxone-induced luteinising hormone (LH) secretion in ovariectomised oestrogen-primed rats. In the present study, we examined whether corticotropin-releasing factor (CRF) may be involved in the LPS-induced inhibition of LH secretion. Unanaesthetised rats were treated with an intravenous (i.v.) injection of LPS (10 microg) or saline, followed by an i.v. injection of naloxone (20 mg/kg). After sequential blood samples were collected for determination of serum LH concentrations, the brains were fixed and CRF-immunoreactivity was examined histochemically. In control rats receiving saline injections, only a small number of CRF-immunoreactive (ir) cells were found in the parvocellular portion of the hypothalamic paraventricular nucleus (PVN), and naloxone significantly increased serum LH concentrations within 10 min. By contrast, in LPS-treated rats, the number of CRF-ir cells was significantly greater than that in control rats, and the effect of naloxone was completely abolished. In a separate experiment, an intracerebroventricular injection of 5 microg CRF inhibited naloxone-induced LH release, mimicking the effect of LPS. These results suggest that LPS stimulates production of CRF in PVN neurones, which in turn inhibits LH secretion without opioidergic mediation.
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Department of Physiology, St Mariana University School of Medicine, Kawasaki, Japan.
Akema
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D000818:Animals; D000906:Antibodies; D003346:Corticotropin-Releasing Hormone / Q000276:immunology / Q000378:metabolism*; D004347:Drug Interactions; D005260:Female; D007150:Immunohistochemistry; D008070:Lipopolysaccharides / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000378:metabolism*; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010286:Paraventricular Hypothalamic Nucleus / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D000906:Antibodies; D008070:Lipopolysaccharides; D009292:Narcotic Antagonists; D009270:Naloxone; D007986:Luteinizing Hormone; D003346:Corticotropin-Releasing Hormone