Glucosensing in liver and Brockmann bodies of rainbow trout through glucokinase-independent mechanisms

We hypothesize that glucosensor mechanisms other than that mediated by glucokinase (GK) are present in the liver and Brockmann bodies (BB) of rainbow trout, and are affected by stress. We evaluated in these tissues changes in parameters related to putative glucosensor mechanisms based on liver X receptor (LXR), mitochondrial activity, sweet taste receptor, and SGLT-1 6 h after intraperitoneal injection of saline solution alone (normoglycaemic treatment) or containing insulin (hypoglycaemic treatment), or d-glucose (hyperglycaemic treatment). Half of tanks were kept at normal stocking density (NSD; 10 kg fish mass·m− 3) whereas the remaining tanks were kept at high stocking density (HSD; 70 kg fish mass·m− 3). The results provide for the first time in fish evidence for the presence of putative glucosensor systems based on mitochondrial activity and sweet taste receptor in liver whereas in BB systems based on LXR, mitochondrial activity, sweet taste receptor, and SGLT-1 could be operative. We also obtained for the first time in fish evidence for the functioning of integrative metabolic sensors in response to changes in nutrient levels since changes in the mRNA abundance of sirtuin 1 (SIRT-1) were observed in response to increased glucose levels. The stress conditions elicited by HSD altered the response of the glucosensor systems based on mitochondrial activity, sweet taste receptor, and SGLT-1 in the liver, and LXR and SGLT-1 in the BB.