An interleukin-1-alpha-like neuronal system in the preoptic-hypothalamic region and its induction by bacterial lipopolysaccharide in concentrations which alter pituitary hormone release.
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We studied the effect of intravenous injection of lipopolysaccharide (LPS) (30-250 micrograms) on the release of several anterior pituitary hormones as indicated by changes in their concentrations in plasma. Within 30 min after intravenous injection of LPS there was a dose-related stimulation of ACTH release; prolactin (PRL) release was induced only by the highest LPS dose injected (250 micrograms). Even the lowest dose of LPS (30 micrograms) decreased plasma growth hormone (GH) by 60 min. Higher doses lowered plasma GH by 30 min, but thyroid-stimulating hormone release was only significantly inhibited by the highest dose of LPS. The action of LPS seems to be primarily exerted on the central nervous system, since incubation of hemipituitaries with LPS for 3 h in doses ranging from 0.001 to 10 micrograms/ml had no effect on ACTH release. LPS is thought to induce its effects on hormones either by release of cytokines from immune cells which subsequently induce the hormonal changes or possibly by direct action within the hypothalamus. In this report we demonstrate the immunocytochemical localization of a population of interleukin-1 alpha (IL-1 alpha)-like cells in a region extending from the basal forebrain at the level of the diagonal band of Broca, caudally and dorsally to the dorsolateral preoptic region and the hypothalamus at the level of the paraventricular nucleus. Further caudally, IL-1 alpha-like immunoreactive cells were located in the midportion of the amygdala. Two hours after injection of the 125-micrograms dose of LPS, the number of these immunoreactive cells was dramatically increased.(ABSTRACT TRUNCATED AT 250 WORDS)