Effects of continuous infusion of interleukin 1 beta on corticotropin-releasing hormone (CRH), CRH receptors, proopiomelanocortin gene expression and secretion of corticotropin, beta-endorphin and corticosterone.

Abstract

A number of recent studies suggest that interleukin 1 beta (IL-1 beta) is a major mediator of hypothalamo-pituitary-adrenal (HPA) responses following infectious aggression. We investigated whether IL-1 beta mediates long-term changes in HPA activity and studied the cellular regulation of the anterior pituitary. To mimic chronically elevated IL-1 beta production thought to occur during infectious diseases, osmotic pumps (Alzet type) were implanted in the peritoneal cavity of male rats and hIL-1 beta was infused continuously at rates of 1 or 3 micrograms/day. Effects of hIL-1 beta action on plasma ACTH, beta-endorphin (beta-EP) and corticosterone (CORT) secretion and on anterior pituitary (AP), ACTH and beta-EP content were followed. In addition, hypothalamic (HT) CRH mRNA and in AP, CRH receptor (CRH-Rc) mRNA, POMC nuclear primary transcript RNA, POMC nuclear intermediate processing RNA and POMC nuclear and cytoplasmic mRNA were quantified using a highly sensitive solution hybridization nuclease protection assay. Continuous infusion of hIL-1 beta stimulated the HPA axis at varying degrees. Increased HT CRH gene expression, AP POMC gene transcription, ACTH and beta-EP release occurred only during the first 3 days of the treatment. A long-lasting enhancement of ACTH and beta-EP synthesis and of POMC gene expression resulted from activated POMC gene transcription followed by an increased POMC mRNA stability and decreased POMC mRNA turnover. In the AP, stimulation of ACTH and beta-EP secretion and POMC gene transcription disappeared after continuous IL-1 beta treatment, possibly in part due to a refractory process mediated by decreased CRH-Rc gene expression in corticotropes.