In vitro studies of eosinophilic granule cells of rainbow trout (Oncorhynchus mykiss) small intestine

In this study, an attempt was made to induce the degranulation of Eosinophilic granule cells (EGCs) from rainbow trout (Oncorhynchus mykiss) small intestine in vitro using the mast cell secretagogues compound 48/80 (100 $\mu$g/ml) and A23187 (10 $\mu$g/ml). Evaluation of EGC degranulation was done at both a histological and biochemical level.

Cell counting at the light microscope level was used to determine if exposure to compound 48/80 or A23187 would result in a significant decrease in the number of intact EGCs in the stratum compactum of the trout intestine. Tissues (n = 4) were exposed for 30 minutes to one of the above agents or its respective control. Evidence of a significant decrease in the number of intact EGCs in the treatment tissues was not observed (p $>$ 0.05). This was due in part to regions of explosive degranulation evident in both control and treatment tissues. This nonspecific degranulation may have masked any observable effects of in vitro exposure to compound 48/80 or A23187.

High performance liquid chromatography (HPLC) was used to determine if exposure to either compound 48/80 or A23187 could result in the release of the mast cell mediator serotonin. Tissue bath concentrations of serotonin were measured before and 30 minutes after exposure to both drugs (n = 12). Serotonin and its metabolite, 5-hydroxyindole acetic acid (5-HIAA), were quantified using reversed-phase (C18) HPLC with electrochemical detection. Results obtained indicate that baseline concentrations of serotonin and 5-HIAA did not increase significantly following exposure to either compound 48/80 or A23187 (p $>$ 0.05). (Abstract shortened by UMI.).