14C-glucose injection in Atlantic cod, Gadus morhua, metabolic responses and excretion via the gill membrane

In the present study cod were separately placed in fish metabolic chambers. Ten individuals were injected with a dose of 1 μCi ¹⁴C-glucose, in addition to 1 g pure glucose per kg live weight, and 10 individuals were kept under the same conditions and sham injected with 9 g L^?1 (0.9%) sterile saline solution.
Of the injected ¹⁴C-glucose, 3% was recovered in plasma, 2.9% in liver, 1.7% in red muscle, 18.2% in white muscle, 0.2% in heart, 1.9% in gills and 12.1% in gill-surrounding water. Of the 12.1% in gill-surrounding water, 9.1% was found to be in the form of CO₂, leaving 3% to pure glucose and lactate. These results indicate a relatively high production of CO₂ from glucose showing a utilization for energy, and a possible route of excretion of excess glucose via the gill membrane.
Activity of ¹⁴C-glucose on a concentration basis showed in descending order the following organs to be metabolically active in glucose utilization: gills > plasma (as a transporter) > heart > red muscle > liver > white muscle.
Of the total amount of ¹⁴C-glucose injected, only 0.3% was recovered in the liver lipid fraction, and mainly as triacylglyceroles; minor ¹⁴C-activity was found in mono- and diacylglyceroles and free fatty acids. These results show very low activity of de novo syntheses of lipid from injected glucose in the cod.