In vitro activation of fish phagocytic cells by GH, prolactin and somatolactin

The activation of rainbow trout (Oncorhynchus mykiss) phagocytic cells by chum salmon GH, prolactin (PRL) and somatolactin (SL) was investigated in vitro. Rainbow trout kidney leucocytes were cultured in RPMI 1640 medium containing 1, 10, 50 or 100 ng of each hormone/ml and the production of superoxide anion was measured using reduction of nitroblue tetrazolium (NBT) and ferricytochrome C. Macrophages incubated with 10-100 ng GH or PRL/ml showed significantly enhanced production of superoxide anion in both the NET and ferricytochrome C tests compared with control macrophages (without hormone). SL did not induce enhanced production of superoxide anion in macrophages. The phagocytic cells treated with GH or PRL also showed increased phagocytic activity and phagocytic index. However, the cells treated with SL showed no enhancement of phagocytic activity or index. These results indicate that GH and PRL stimulate macrophages in vitro.