The immunoregulatory role of GH in sea bass (Dicentrarchus labrax), in relation to the intensity of infection by the myxosporean parasite Sphaerospora dicentrarchi, was investigated. The in vitro detection of superoxide anion (O2 -) in head kidney phagocytes was optimised using the nitroblue tetrazolium (NBT) assay. O2 - production was proportional to the quantity of total protein per well, and 15 and 30 min of PMA triggering gave the highest stimulation index. Cells adhered overnight produced more O2 - than cells adhered for 3h. Trifluoperazine abolished the reduction of NBT almost completely, whereas superoxide dismutase only caused 374% inhibition. Cells from fish parasitised by S. dicentrarchi, produced higher levels of O2 - compared with non-parasitised fish. Overnight priming with 5 nM recombinant rainbow trout growth hormone (rtGH) produced a significant increase in the respiratory burst of phagocytes from non-parasitised fish. Phagocytes from fish with medium intensity of infection attained the maximum response at 50 nM and 150 nM rtGH. LPS (20 μg ml-1) priming did not induce an increase in O2 - production, but it significantly increased cell adherence in non-parasitised fish.

This work was supported by a researchgrant from the Spanish CICYT no. AGF95-0058. J. A. Calduch-Giner was recipient of aresearch grant from the Generalitat Valenciana, and P. Muñoz received a grant fromthe Ministerio de Educación y Ciencia of Spain.