Incorporation of orally administered glucose-U-14C and fructose-U-14C into the triglyceride of liver, plasma, and adipose tissue of rats

Male rats, fasted for 5–6 hr, were given glucose-U-¹⁴C or fructose-U-¹⁴C, with their respective carrier, by intragastric instillation. Sequential radioactivity in plasma carbohydrates and in the triglyceride of the liver, plasma, and adipose tissue and plasma immunoreactive insulin and free fatty acids were measured. The validity of taking the triglyceride labeling rate as the triglyceride synthesis rate was tested by measuring the metabolic activity of endogenous glucose. Two or three times greater radioactivity was found in the liver and plasma triglycerides after fructose than after glucose while the reverse was true for adipose tissue. The greater radioactivity in triglyceride of the liver and plasma after fructose was mainly due to triglyceride-glycerol radioactivity. The greater radioactivity in adipose tissue triglyceride was due to the radioactivity of both triglyceride-fatty acids and triglyceride-glycerol. Three hours after glucose, 92% of the total radioactivity in triglyceride was in adipose tissue and 8% was in the liver. However, 3 hr after fructose, 57% of the radioactivity was in adipose tissue and 42% was in the liver. Daily repetition of such a pattern of fructose handling may lead to abnormal metabolism of endogenous triglyceride.