Inhibitory Effect of Cortisol on the Degranulation of Eosinophilic Granular Cells in Tilapia.

Abstract

We examined the effect of cortisol on the degranulation and number of eosinophilic granular cells (EGCs) in tilapia, Oreochromis niloticus. One hour after injection of stimulants (killed Escherichia coli or substance P, a neurotransmitter) into the swim bladder, the percent of the degranulated EGCs in the swim bladder membrane was determined. Peritoneal implantation of coconut oil containing cortisol (50 mg/kg body weight) 24 h before injection of stimulants significantly reduced the percent of the degranulated EGCs, compared with the control fish administered with coconut oil without Cortisol. Cortisol also suppressed the in vitro degranulation of EGCs stimulated with substance P or with tilapia normal sera containing zymosan. To investigate the effect of cortisol on the abundance of EGCs, the number of EGCs in the swim bladder membrane was counted. Density of EGCs was decreased after implantation of cortisol, compared with that of the control group. These results suggest that cortisol suppresses the degranulating activity of EGCs and decreases the density of EGCs in the tissue.