The liquorice root derivative glycyrrhetinic acid can ameliorate ionoregulatory disturbance in rainbow trout (Oncorhynchus mykiss) abruptly exposed to ion-poor water

To consider the idea that a dietary botanical supplement could act as an adaptogen in a teleost fish, the effect of a liquorice root derivative (18β-glycyrrhetinic acid, 18βGA) on rainbow trout following an acute ionoregulatory stressor was examined. Freshwater (FW) trout were fed a control or 18βGA supplemented diet (0, 5, or 50 μg 18βGA/g diet) for 2 weeks, then abruptly exposed to ion-poor water (IPW) for 24 h. Following IPW exposure, muscle moisture content and serum cortisol levels elevated and serum [Na+] and/or [Cl−] reduced in control and 50 μg/g 18βGA-fed fish. However, these endpoints were unaltered in 5 μg/g 18βGA-fed fish. Gill tissue was investigated for potential mechanisms of 18βGA action by examining mRNA abundance of genes encoding corticosteroid receptors (CRs), 11β-hydroxysteroid dehydrogenase 2 (11β-hsd2), and tight junction (TJ) proteins, as well as Na+-K+-ATPase and H+-ATPase activity, and mitochondrion-rich cell (MRC) morphometrics. Following IPW exposure, CR and 11β-hsd2 mRNA, MRC fractional surface, Na+-K+-ATPase and H+-ATPase activity were unaltered or decreased in 50 μg 18βGA fish, as was mRNA encoding select TJ proteins. In contrast, 5 μg 18βGA-fed fish exhibited elevated 11β-hsd2 and CR mRNA abundance versus 50 μg 18βGA-fed, and reduced MRC apical area as well as some differences in TJ protein mRNA abundance versus control fish. Data suggest that 18βGA, at low levels, may be adaptogenic in trout and might help to ameliorate ionoregulatory perturbation following IPW exposure. This seems to occur, in part, through 18βGA-induced alterations in the biochemistry and physiology of the gill.