Continuous i.v. infusion of norepinephrine in rats has been shown to induce early interleukin (IL)-6 mRNA expression in the left ventricle (LV) which was followed by hypertrophy and fibrosis. In this study, two approaches were used. In the first, NE (0.1 mg/kg per hour) was infused i.v. in rats for several time periods, and freshly obtained ventricular myocardium was dissociated into myocyte (MC) and non-myocyte (NMC) fractions. Second, isolated adult MCs and fibroblasts were treated with NE (10 microM). NE infusion (4 h, in vivo) caused an 11-fold increase in IL-6 mRNA in both cell populations. In vitro treatment of isolated adult MCs for 2 h and of fibroblasts for 1 h with NE induced a 3.5- and 23-fold maximum increase, respectively, in IL-6 mRNA. After in vivo NE treatment, the expression of the mRNA of the transcriptional factor of IL-6, C/EBP-beta, was elevated earlier (after 45 min of NE infusion) than IL-6 mRNA (after 4 h) and was seen in MCs and NMCs. The mRNAs of both receptors of IL-6, the soluble IL6R and gp130, were increased subsequently to IL-6 mRNA. Gp130 was elevated after 24 h and, like IL6R, predominantly in NMCs. In contrast, the IL6R protein and the downstream regulator STAT3 were increased only in MCs after 24 h of NE infusion. The mRNA of C/EBP-delta, which is regulated by STAT3, was elevated only in myocytes.