Effects of cortisol and thyroid hormone treatment on the glycogen metabolism of selected tissues of domesticated rainbow trout, Oncorhynchus mykiss

Abstract

Glycogen, glucose, protein and glycogen phosphorylase and glycogen synthetase activity in liver, white muscle and kidney were determined in domesticated rainbow trout ( Oncorhynchus mykiss) treated with 3,5,3′-triiodo-L-thyronine (T 3), thyroxine (T 4) and cortisol and combinations of all these hormones for 10 days. Plasma protein and glucose levels were also determined. Declines in liver glycogen and glucose were observed after cortisol treatment as compared to values obtained in controls (controls: 27.54 ± 1.73 mg glycogen/g and 16.81 ± 1.50 mg glucose/g) such as 15.94 ± 2.64 mg glycogen/g and 8.63 ± 1.22 mg glucose/g. T 4 treatment did not produce any effects on the measured parameters. T 3 plus T 4 treatment caused a fall in hepatic glycogen and glucose levels ( 11.97 ± 1.27 mg glycogen/g and 8.98 ± 2.06 mg/g, respectively). All cortisol and thyroid hormone combinations produced a fall in liver glycogen levels (range between 6.07 ± 1.19 and 16.38 ± 1.56 mg glycogen/g) as well as an increase (from 37 to 44%) in glycogen phosphorylase activity. No changes were observed in any of the measured parameters for the different hormone treatments assessed in white muscle and kidney. Under our experimental conditions, cortisol and probably T 3 are involved in liver glycogen mobilization and apparently do not elicit a response in white muscle and kidney.