title: Interleukin-1 inhibits the ovarian steroid-induced luteinizing hormone surge and release of hypothalamic luteinizing hormone-releasing hormone in rats.
abstract: Interleukin-1 (IL-1), a polypeptide cytokine secreted by activated macrophages, has been postulated as a chemical messenger between the immune and endocrine systems. IL-1-immunopositive neurons and fibers have been visualized in the human and rat hypothalamus, and IL-1 receptors are present in the rat brain. We have examined the effects of human recombinant IL-1 (alpha- and beta-subtypes) on LH release in vivo and hypothalamic LHRH release in vitro. Ovariectomized rats were primed with estradiol benzoate, and progesterone was injected 48 h later to elicit a LH surge in the afternoon. IL-1 alpha and IL-1 beta were injected either intracerebroventricularly (icv) via a preimplanted cannula in the third ventricle of the brain or iv. Systemic injection of IL-1 alpha or IL-1 beta (58.8 pmol at 1300 and 1500 h) failed to influence the afternoon LH surge seen in saline-injected control rats. However, IL-1 beta (1.76 pmol) administered icv at 1300 and 1500 h or a single icv injection at 1300 h blocked the progesterone-induced LH surge. Similar icv injections of IL-1 alpha also significantly suppressed the afternoon LH surge compared to that in saline-injected control rats. However, IL-1 alpha was relatively less effective than the beta-subtype, since the LH surge was detected in some rats. To ascertain whether suppression of the LH surge was due to inhibition of LHRH release, the medial basal hypothalamus-preoptic area of estradiol benzoate-progesterone-treated ovariectomized rats was incubated with and without IL-1. Both IL-1 alpha and IL-1 beta, at concentrations of 0.1 nM and higher, significantly suppressed LHRH release in vitro from the medial basal hypothalamus-preoptic area. In contrast, IL-1 (10 nM) was completely ineffective in suppressing LHRH release from the microdissected median eminence. These results demonstrated an overall inhibitory effect of icv IL-1 on the LHRH-LH axis and suggest that suppression of the steroid-induced LH surge by IL-1 may primarily be due to inhibition of LHRH release at hypothalamic sites located within the blood-brain barrier.
authors.affiliation: Department of Obstetrics and Gynecology, University of Florida College of Medicine, Gainesville 32610.
authors.forename: P S
authors.initials: PS
authors.lastname: Kalra
authors.forename: A
authors.initials: A
authors.lastname: Sahu
authors.forename: S P
authors.initials: SP
authors.lastname: Kalra
mesh_terms: D000818:Animals; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007031:Hypothalamus / Q000378:metabolism*; D007276:Injections, Intraventricular; D007375:Interleukin-1 / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000378:metabolism*; D011374:Progesterone / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D007375:Interleukin-1; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone