Endogenous loss of leucine and methionine in adult male rats.
1. The fractional rate of loss of 14C and body-weight was measured in adult male rats after giving 14C-labelled methionine or leucine and maintaining rats for 30 d on a low-protein or a specific methionine+cystine-free diet: carcasses were then analysed for protein and fat 14C radioactivity. 2. The fractional loss of 14CO2 from [14C]methionine or [14C]leucine between day 20 and day 30 was always greater than the fractional loss of body-weight. 3. Carcass protein 14C radioactivity after giving [14C]leucine was higher than after giving [14C]methionine, but fat 14C radioactivity after either 14C-labelled amino acid was only a small proportion of the total body 14C radioactivity. 4. After correction of the fractional loss of 14CO2 for urinary 14C loss, but not body-weight loss, absolute amino acid loss was calculated using published values for methionine and leucine content of rats. 5. The best estimates of endogenous amino acid loss obtained using I-14C-labelled amino acids, expressed as mg/kg body-weight 0.75 per day were leucine 79, methionine 38.
D000818:Animals; D001823:Body Composition; D001835:Body Weight; D002245:Carbon Dioxide / Q000378:metabolism; D004032:Diet; D007930:Leucine / Q000378:metabolism*; D008297:Male; D008715:Methionine / Q000378:metabolism*; D009747:Nutritional Physiological Phenomena; D011506:Proteins / Q000378:metabolism; D051381:Rats; D013997:Time Factors
D011506:Proteins; D002245:Carbon Dioxide; D008715:Methionine; D007930:Leucine