Norepinephrine depresses the nitric oxide production in the ascidian hemocytes

► In invertebrates norepinephine (NE) may regulate the immune system. ► NE acts by reducing phagocytosis and burst capacity. ► Here we studied the effect of NE on the production of nitric oxide (NO) by hemocytes of an ascidian. ► NO was detected in the hemocytes using the fluorescent indicator DAF-FM. ► NE and α or β-adrenoreceptor agonist or antagonist down-regulates NO production.