Monosodium glutamate (MSG) administered by gastric tube to 10 infant monkeys at doses of 1-4 g/kg produced rapid increases in plasma glutamate (17- to 33-fold) and aspartate (50- to 90-fold) levels. The degree of elevation was proportional to the dose administered. Levels of other amino acids were unaffected. Two of the monkeys exhibited high fasting glutamate levels and abnormal glutamate tolerance curves. Despite this apparent decreased ability to metabolize glutamate, neither these animals nor any of the others for whom morphologic studies have been previously reported demonstrated neurotoxicity. Studies using 14-C-labeled glutamated indicated conversion of administered glutamate to two ninhydrin-negative compounds identified as glucose and lactate, as well as to asparate.
Saccharin has been used as a nonnutritive sweetenjlng agent for nearly a century. Studies conducted over 50 years ago indicated that it is completely, or nearly completely, absorbed from the gastrointestinal tract and rapidly excreted in the urine in unchanged form ( 1). Largely ignored since these early studies, several factors make a reassessment of saccharin )metabolism advisable: (i) evidence of increasing saccharin consumption, estimated at more than 5 million pounds in the United States in 1970, (ii) a heightened awareness of possible adverse effects of many food additives, and (iii) the paucity of metabolic data based on modern methods, of investigation.We report below a study of absorption, distribution, metabolism, and excretion of saccharin in rhesus monkeys.Methods. Eight adult female rhesus monkeys (Macaca mulntta) , weighing from 5.7 to 6.7 kg, were utilized in the study. After an overnight fast, the animals were tranquilized with phencyclidine hydrochloride (Sernylan, Parke Davis and Co., Detroit, Mich.) 1 mg/kg intramuscularly. With the animal in the recumbent position, an incision was made in the groin, exposing the femoral vessels. A polyethylene catheter was inserted through the femoral vein into the inferior vena cava for sequential blood sampling. The incisions were then sutured and the animal was restrained in the dorsal recumbent position without use of additional phencyclidine. An indwdimg catheter was placed in the urinary
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