Reduced, positive nitrogen balance and elevated plasma free fatty acid concentration in growing, glutamate-induced...

Glutamate-induced obesity of Wistar-rats is known to develop under normophagic and normoinsulinemic conditions, although hyperphagia and hyperinsulinemia are common to obese individuals. Rats of this obesity model show retarded growth, reduced mass of some organs, carcass and whole body as well as an extraordinary high fat content, whereas protein content is reduced. In this study, nitrogen (N) balance, urinary excretion of urea-N, ammonia-N, creatine-N and alpha-amino acid-N and plasma free fatty acid concentration of growing, glutamate-induced obese rats were determined. The main results were independent of frame of reference (mmol N/kg body mass; mmol N/kg0.75 metabolic body mass; N in % of nitrogen intake): Nitrogen intake, urinary excretion of alpha-amino acids and nitrogen excretion in faeces were equal between lean and obese rats. Nitrogen excretion in urine was elevated in obese rats, mainly resulting from increased amounts of urea and ammonia. Nitrogen balance was positive in both groups, but reduced in obese rats. These data point to normal digestion of food proteins, but an unusual high oxidative desamination rate of the absorbed amino acids in obese rats. Taking into account the various hormonal and nerval alterations in glutamate-induced obese rats, resulting e.g. in increased hepatic insulin concentration, the retained amino acid carbon should be channelled into hepatic fatty acid synthesis. Really, unfasted and overnight fasted obese rats showed elevated plasma free fatty acid concentrations. Channeling of amino acids into lipogenesis may explain the low muscle mass and striking fat accumulation--despite normophagia and peripheral normoinsulinemia--of growing, glutamate-induced obese Wistar-rats.