Glucosensing capacity in rainbow trout liver displays day-night variations possibly related to melatonin action.
To assess whether the glucosensing capacity in peripheral (liver and Brockmann bodies) and central (hypothalamus and hindbrain) locations of rainbow trout displays day-night variations in its response to changes in circulating glucose levels, we evaluated the response of parameters related to glucosensing [glucose, glycogen and glucose 6-phosphate levels, activities of glucokinase (GK), glycogen synthetase (GSase) and pyruvate kinase (PK), and mRNA abundance of GK, glucose transporter 2 (GLUT2), and K(ATP) channel subunits Kir6.x-like and sulfonylurea receptor (SUR)-like] in fish subjected to hyperglycemic treatment under night or day conditions. No day-night significant variations were noticed in the glucosensing capacity of the hypothalamus, hindbrain and Brockmann bodies. In contrast, a clear differential response was noticed in the liver, where glucose levels, GK activity (and mRNA levels) and GSase activity displayed increased values during the day in hyperglycemic fish compared with controls, and lower (GK mRNA levels) or non-existent (glucose, GK and GSase activities, and Kir6.x-like mRNA levels) values during the night. A similar decrease in parameters related to glucosensing in the liver was observed when fish under day conditions were treated with melatonin, suggesting a modulatory role of melatonin in day-night changes of the glucosensing response in the same tissue.
Laboratorio de Fisioloxía Animal, Departamento de Bioloxía Funcional e Ciencias da Saúde, Facultade de Bioloxía, Universidade de Vigo, E-36310 Vigo,  Spain.
Marta
M
Conde-Sieira
Marcos A López
MA
Patiño
Jesús M
JM
Míguez
José L
JL
Soengas
D000818:Animals; D001786:Blood Glucose / Q000187:drug effects / Q000378:metabolism; D002940:Circadian Rhythm / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D005941:Glucokinase / Q000235:genetics / Q000378:metabolism; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D051273:Glucose Transporter Type 2 / Q000235:genetics / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism; D007274:Injections, Intraperitoneal; D019344:Lactic Acid / Q000097:blood; D008099:Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008550:Melatonin / Q000097:blood / Q000378:metabolism*; D017686:Oncorhynchus mykiss / Q000097:blood / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism; D011770:Pyruvate Kinase / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012249:Rhombencephalon / Q000187:drug effects / Q000378:metabolism
C489478:BIK channel; D001786:Blood Glucose; D051273:Glucose Transporter Type 2; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger; D019344:Lactic Acid; D006003:Glycogen; D006006:Glycogen Synthase; D005941:Glucokinase; D011770:Pyruvate Kinase; D005947:Glucose; D008550:Melatonin