Effect of the liquorice root derivatives on salt and water balance in a teleost fish, rainbow trout (Oncorhynchus mykiss)

The effect of liquorice root derivatives (LRDs) glycyrrhizic acid (GL) and glycyrrhetinic acid (18 beta GA) on salt and water balance and end points of gill ion transport in a freshwater teleost, (rainbow trout) was examined after feeding fish diets containing GL or 18 beta GA (0, 5, 50 or 500 mu g/g diet) for a two week period. Serum cortisol levels and gill 11 beta-hydroxysteroid dehydrogenase type 2 mRNA abundance decreased in fish fed GL but increased (at select doses) in fish fed 18 beta GA. At higher doses of GL, gill Na+-K+-ATPase and H+-ATPase activity increased, while cystic fibrosis transmembrane conductance regulator type II mRNA abundance significantly decreased at the lowest dose of GL End points of gill transcellular ion transport were not significantly altered in fish fed 18 beta GA, except for a reduction in Na+-K+-ATPase activity at a 50 mu g/g dose. In contrast, high doses of GL and 18 beta GA increased gill transcript abundance of the tight junction protein claudin-31 (cldn-31). Other end points of gill paracellular transport differed in fishes fed LRDs. Tricellulin mRNA abundance was increased by high dose GL and decreased by high dose 18 beta GA, and cldn-23a and cldn-276 mRNA abundance significantly decreased in response to GL irrespective of dose. Despite the above observations, systemic end points of salt and water balance (i.e. serum [Na+ and [Cl-1] as well as-muscle-moisture) were unaffected by LRDs. Therefore data suggest that LRDs can.alter end points of ion transport in fishes but that overall salt and water balance need not be perturbed. (C) 2014 Elsevier Inc All rights reserved.