Abstract
Estimates of the glucose pool, the glucose space, the turnover rate, and the recycling of glucose were made after the injection of [U-14C]glucose into (a) obese rats fed a high fat diet and (b) rats fed a carbohydrate diet. The specific activity--time curve consisted of two components. Physiological parameters were calculated by using a two-compartment model. The glucose pool and glucose space were the same in both groups of rats. The turnover rate was 1.96 mg. min-1 for the carbohydrate-fed rats and 1.55 mg. min-1 for the fat-fed rats. There was about 12 percent recycling in both groups. In the carbohydrate-fed group, another approach based on simultaneous use of [6-14C]glucose and [6-3H]glucose yielded nearly the same values for these parameters. Respiratory excretion of CO2 and the incorporation of labeled glucose into lipids of some tissues were also measured. The rate of excretion of labeled CO2 and the conversion of labeled glucose into fatty acids in fat-fed rats were lower than in the carbohydrate-fed rats by 50 percent and 80 percent, respectively. More glucose was diverted into glyceride glycerol in the fat-fed group. It is suggested on the basis of the results that glyceride glycerol can serve as a gluconeogenic substrate in these rats where the turnover rate of glucose is much higher than the daily intake of carbohydrates.
Highlights
- The turnover rate was 1.96 mg .min” for the carbohydrate-fed rats and 1.55 mg min-l for the fat-fed rats
It is well known that feeding rats a high fat, low carbohydrate diet produces a syndrome characterized by excess adiposity
Curiously,inthediaphragm, a high fat diet has little effect, if any, on the uptake of glucose, thoughoxidation of thissubstrateisstrongly depressed (2). These effects that differ from one tissue to anotherinvitro have raisedquestions concerning in vivo glucose utilization in rats fed a high fat, low carbohydrate diet.Thisstudywasundertakento provide quantitative informationon glucose utilizationandto investigate the following questions: ( a ) Istherate of glucose turnover modified by such a diet? (6) Is there a sparing effect on oxidation of glucose to COz ? (c) Does the in vivo effect of a fat diet on the incorporation of labeled glucose in tissues confirm the in vitro findings?
Summary
Rats of the Commentry France Wistar strain were purchased atweaningand fed adlib. one of the following diets for 4-6 wk. (7) Highcarbohydratediet (YO,w/w): casein, 12.1; DL-methionine, 0.4;lard, 1.1; wheatflour, 77.1; saltmixture,4.0;vitaminmixture, 2.2; bran, 3.0; water,0.2(proteins,18%;carbohydrates, 59%; fat, 3%). Carbon dioxide was determined on the following physiological parameters were calculated: 10-ml aliquots of the NaOH solution by titration with glucose pool size, glucose space, rate constant We chose high fat diet for 6 wk were injected intraperitoneally with this route of injection because it is much less stressful for 15PCi of [U- 'C] glucose (120-1 50 mCi/mmole) disthe animals thanintravenous injection. Seven blood samples of 20 pl each were obtained within from each group were decapitated at[45,105,165, 225], the first 5-30 min after the intraperitoneal injection, and and 300 min, and heart, liver, and perirenal and epididythey were placed in counting vials. The log of specific activity were counted in the toluene-ethanol scintillation fluid and (dpm/pg of glucose) was plotted against the time, and a the glycerol in Bray's solution (7). Student’s t test was used for statistical comparisons between twogroups of data.Calculationswerecarried out on an Olivetti electronic calculator, Pxogramma 101, with the help of the programs perfected by Lowy and Manchon (12)
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