Stress hormones modulate lipopolysaccharide stimulation of head kidney interleukin-6 production in the catfish Heteropneustes fossilis: In vivo and in vitro studies

•Catfish head kidney is a useful model for studying endocrine-immune interaction.•Lipopolysaccharide (LPS) stimulated interleukin-6 (IL-6) in vivo and in vitro.•Dexamethasone inhibited basal and LPS-induced increase in IL-6 levels.•Catecholamines did not alter the basal level of IL-6 in vitro.•Epinephrine and Norepinephrine inhibited the LPS-induced IL-6 stimulation.•Dopamine may increase the LPS stimulation of IL-6 in a synergistic manner. Interleukin-6 (IL-6) is a pleiotropic cytokine secreted by immune tissues such as monocytes/macrophages and have pro-inflammatory/anti-inflammatory and neuroendocrine actions. In this study, we report the modulatory effects of stress hormones, the cortisol agonist dexamethasone and catecholamines on lipopolysaccharide (LPS) - induced stimulation of head kidney IL-6 in the catfish Heteropneustes fossilis. In the in vivo study, the intraperitoneal administration of LPS stimulated, and dexamethasone time-dependently inhibited IL-6 level. In the in vitro study, the incubation of macrophage cultures with LPS stimulated IL-6 level significantly in all incubation times. Dexamethasone did not alter the basal IL-6 level but inhibited time-dependently the LPS-induced stimulation. Likewise, catecholamines did not alter the basal level of IL-6. Both epinephrine and norepinephrine inhibited the LPS-induced stimulation of IL-6. Dopamine, on the other hand, was ineffective. The results indicate that IL-6 is a useful marker of head kidney macrophage activity for studying endocrine–immune interactions in the catfish.