Norepinephrine depresses the nitric oxide production in the ascidian hemocytes

Norepinephrine (NE) is a neuro-hormone released by vertebrates and invertebrates during acute stress, and can influence their immune function. We found that NE depressed the production of nitric oxide (NO) by the hemocytes of ascidians. Our results with a fluorescent indicator for NO in assays using both NE and either α or β-antagonist revealed that NE down-regulated NO production by the ascidian hemocytes. Our data suggest that NE may be acting via specific hemocyte receptors to induce a decrease in immune function.