The relative contribution of constitutive and inducible cyclooxygenase activity to lipopolysaccharide-induced prostaglandin production by primary cultures of rat hypothalamic astrocytes Giuseppa Pistritto a , Cesare Mancuso a , Giuseppe Tringali a , Mauro Perretti b , Paolo Preziosi a, *, Pierluigi Navarra a a Institute of Pharmacology, Catholic University Medical School, Largo Francesco Vito 1 -00168 Rome, Italy b Department of Biochemical Pharmacology, The William Harvey Research Institute, Charterhouse Square, London EC1M 6BQ, UK Received 11 September 1997; received in revised form 16 January 1998; accepted 6 March 1998 Abstract In this study, we have compared the time-course effects of lipopolysaccharide (LPS) and interleukin-1b on prostaglandin (PG) production by primary cultures of rat astrocytes. At variance with interleukin-1b, LPS produced significant increases in PGE2 release after only 1 h of incubation, an effect unlikely to depend on new protein synthesis; the involvement of constitutive cyclooxygenase (COX-1) was therefore investigated. Experiments with acetylsalicylic acid showed that 80% of PGE2 production after 1 h of treatment with LPS is accounted for by COX-1; this figure decreases to about 30% after a 24-h treatment. The increase in PGE2 production occurring after a 24-h challenge with the endotoxin seems to involve the activation of phospho- lipase A2. In fact, LPS-stimulated PGE2 release was significantly reduced by a peptide from the primary sequence of lipocortin- 1, peptide Ac2–26, which was previously shown to inhibit phospholipase A2 in several in vitro models.  1998 Elsevier Science Ireland Ltd. Keywords: Lipopolysaccharide; Prostaglandin E2; Cyclooxygenase; Phospholipase A2; Interleukin-1b; Lipocortin-1; Astrocytes Recently, renewed interest in cyclooxygenase (COX) activity within the central nervous system (CNS) was kindled by the observation that the COX endproducts, pros- taglandins (PG), appear to play a role in the pathogenesis of neurodegenerative disorders such as Alzheimer disease [1]. Although COX has been found predominantly associated to neurons [2], the in vitro activation of glial cells is currently considered a valuable experimental model to investigate the role of inflammatory mediators, including PG, in neurode- generation [5]. Therefore, several in vitro studies have been recently conducted to characterize COX regulation and PG production in primary cultures of glial cells, in particular microglia and astrocytes [7,9]. These studies showed that, unlike neurons, glial cells are broadly comparable to per- ipheral monocytes and tissue macrophages because they express an inducible COX isoform (COX-2) after activation by proinflammatory cytokines, phorbol esters or bacterial lipopolysaccharide (LPS). Hence, any COX-2-mediated increase in PG levels is associated with enhanced gene expression and new protein synthesis, which is a relatively time-consuming process, whereas increases in PG produc- tion caused by COX-1 can occur independently of protein synthesis and will presumably account for the early increase in PG production under immune-inflammatory challenges. Within this conceptual framework, it became of interest to investigate the time-course of PG production by glial cells in vitro. In the present study, we have compared the time-dependent effects of LPS and interleukin-1b (IL-1b) on PG production in primary cultures of rat hypothalamic astrocytes, and investigated the relative contribution of con- stitutive and inducible COX in the effects of the above Neuroscience Letters 246 (1998) 45–48 0304-3940/98/$19.00  1998 Elsevier Science Ireland Ltd. All rights reserved PII S0304-3940(98)00226-2 * Corresponding author. Tel.: +39 6 30154253; fax: +39 6 3050159.