魚類の炭水化物代謝-III.

コイのグルコース-U-¹⁴Cおよびグルタミン酸-U-¹⁴C代謝におよぼす飼料組成の影響

抄録

In order to examine the previous assumption that the primary energy source for carp is not carbohydrate (glucose) but protein (amino acids), incorporation of radioactivity from glucose-U-¹⁴C or glutamate-U-¹⁴C into hepatopancreatic lipid and glycogen, blood glucose, and its excretion as ¹⁴CO₂ in carp were measured. Carp used were bred for 45 days with two kinds of diet, HC (90% carbohydrate) and C (50% carbohydrate), which were composed of potato starch and casein.
Excretions of ¹⁴CO₂ from glutamate-U-¹⁴C of both diet groups were extraordinarily higher than those from glucose-U-¹⁴C. In both groups, glucose-U-¹⁴C was hardly incorporated into hepatopancreatic lipid but was incorporated into glycogen. In contrast, much more glutamate-U-¹⁴C was incorporated into lipid whereas little into glycogen. The blood glucose levels of both diet groups were unusually increased probably by injections of glutamate-U-¹⁴C with carrier glutamate, and the radioactivities in blood glucose 6 hours after the injections were 1/7 to 1/5 of the residual activities from glucose-U-¹⁴C.
From these results it was suggested that oxidation of amino acids by carp is superior to glucose oxidation and that depot lipid is principally synthesized from amino acids while only a little glucose is converted to glycogen. Therefore, amino acids appear to be a more excellent energy source than glucose in carp and the energy utilization resembles that in diabetic mammals.