Energy metabolism of hyperthyroid gilthead sea bream Sparus aurata L

Thyroid hormones, in particular 3,5,3 '-triiodothyronine or T-3, are involved in multiple physiological processes in mammals such as protein, fat and carbohydrate metabolism. However, the metabolic actions of T-3 in fish are still not fully elucidated. We therefore tested the effects of T3 on Sparus aurata energy metabolism and osmoregulatory system, a hyperthyroid-induced model that was chosen. Fish were implanted with coconut oil depots (containing 0, 2.5, 5.0 and 10.0 mu gT(3)/g body weight) and sampled at day 3 and 6 post-implantation. Plasma levels of free T-3 as well as glucose, lactate and triglyceride values increased with increasing doses of T-3 at days 3 and 6 post-implantation. Changes in plasma and organ metabolite levels (glucose, glycogen, triglycerides, lactate and total alpha amino acid) and enzyme activities related to carbohydrate, lactate, amino acid and lipid pathways were detected in organs involved in metabolism (liver) and osmoregulation (gills and kidney). Our data implicate that the liver uses amino acids as an energy source in response to the T-3 treatment, increasing protein catabolism and gluconeogenic pathways. The gills, the most important extruder of ammonia, are fuelled not only by amino acids, but also by lactate. The kidney differs significantly in its substrate preference from the gills, as it obtained metabolic energy from lactate but also from lipid oxidation processes. We conclude that in S. aurata lipid catabolism and protein turnover are increased as a consequence of experimentally induced hyperthyroidism, with secondary osmoregulatory effects. (c) 2015 Elsevier Inc. All rights reserved.