THE EFFECT OF GLYCYRRHIZIN ON RAINBOW-TROUT, ONCORHYNCHUS-MYKISS (WALBAUM), LEUKOCYTE RESPONSES

Treatment of rainbow trout macrophages with glycyrrhizin (GL), an aque ous extract of licorice, Glycyrrhiza glabra, enhanced their respirator y burst activity. Maximal effects were seen using concentrations of 10 -100 mu g ml(-1). GL also modulated trout lymphocytes, increasing prol iferation responses to the mitogen phytohaemagglutinin some two-fold o ver a range of GL concentrations. In addition, GL elicited the release of a macrophage activating factor (MAF) from head kidney leucocytes, as assessed by the ability of generated supernatants to increase respi ratory burst activity of target macrophages. MAF activity was most app arent using 100 mu g ml(-1) GL to induce MAF release and a 48-h incuba tion period with the target macrophages. Finally, GL was shown to enha nce the release of MAF in response to the mitogen concanavalin A. The possible use of GL as a stimulant of fish innate defences is discussed .