REDUCED, POSITIVE NITROGEN-BALANCE AND ELEVATED PLASMA-FREE FATTY-ACID CONCENTRATION IN GROWING, GLUTAMATE-INDUCED OBESE RATS

Glutamate-induced obesity of Wistar-rats is known to develop under nor mophagic and normoinsulinemic conditions, although hyperphagia and hyp erinsulinemia are common to obese individuals. Rats of this obesity mo del show retarded growth, reduced mass of some organs, carr-ass and wh ole body as well as an extraordinary high fat content, whereas protein content is reduced. In this study, nitrogen (N) balance, urinary excr etion of urea-N, ammonia-N, creatinine-N and alpha-amino acid-N and pl asma free fatty acid concentration of growing, glutamate-induced obese rats were determined. The main results were independent of frame of r eference (mmol N/kg body mass; mmol N/kg0,75 metabolic body mass; N in % of nitrogen intake): Nitrogen intake, urinary excretion of alpha-am ino acids and nitrogen excretion in faeces were equal between lean and obese rats. Nitrogen excretion in urine was elevated in obese rats, m ainly resulting from increased amounts of urea and ammonia. Nitrogen b alance was positive in both groups, but reduced in obese rats. These d ata point to normal digestion of food proteins, but an unusual high ox idative desamination rate of the absorbed amino acids in obese rats. T aking into account the various hormonal and nerval alterations in glut amate-induced obese rats, resulting e.g. in increased hepatic insulin concentration, the retained amino acid carbon should be channelled int o hepatic fatty acid synthesis. Really, unfasted and overnight fasted obese rats showed elevated plasma free fatty acid concentrations. Chan neling of amino acids into lipogenesis may explain the low muscle mass and striking fat accumulation - despite normophagia and peripheral no rmoinsulinemia - of growing, glutamate-induced obese Wista-rats.