In vivo treatment with progestogens causes immunosuppression of carp Cyprinus carpio leucocytes by affecting nitric oxide production and arginase activity

In this study, carp Cyprinus carpio were injected with various steroid compounds, including syntheticand natural progestogens and the glucocorticoid cortisol, to investigate effects on leucocytesisolated from their kidneys. Injection of cortisol led to an increased spleeno-somatic index (IS) onday 21 post-injection (pi) and immunosuppressive effects measured as decreased nitric oxide (NO)production and increased arginase activity in isolated leucocytes on days 14 and 21 pi, respectively.Moreover, reduced NO production was also observed after injection of the synthetic progestogens,levonorgestrel (LEV) and medroxyprogesterone acetate. In addition, LEV influenced arginase activityin head kidney cells on day 14 and day 21 pi. This study is the first demonstration in fishes thatthe application of these steroid compounds in vivo affects NO production and arginase activity ofisolated leucocytes.