Effects of tryptophan on the eating behavior of adult rats with neonatal malnutrition

Objective This study investigated the effects of tryptophan on the eating behavior of adult rats submitted or not to early malnutrition. Methods Sixty-four male Wistar rats were divided into nourished (n=32, casein=17%) and malnourished (n=32, casein=8%) according to the diet given to the dam during lactation. After weaning, all rats were fed a diet with a protein content of 23%. The rats were weighed on day 7, day 21 and day 70 after birth. On day 70 after birth, each nutritional group was divided into 4 subgroups: nourished-saline (n=16), nourished-tryptophan (n=16), malnourished-saline (n=16) and malnourished-tryptophan (n=16). The tryptophan groups were given 1.0mL/100g of tryptophan for 14 days, at a dosage of 50mg/kgw of body weight and the saline groups were given 1.0mL/100g of 0.9% NaCl, also for 14 days. The eating behavior parameters were assessed during this period. The mean relative food intake and mean relative weight gain were then determined. The statistical analyses were done by the Student's t-test and ANOVA, followed by the Tukey test, with p <= 0.05. Results During the first 70 days of life, pups from protein-malnourished damns remained lighter than pups from well-nourished damns (p <= 0.01). Well-nourished rats treated with tryptophan (M=6.88, SD=0.05) ate less than those given saline (M=7.27, SD=0.08) (p <= 0.01) but weight was unaffected. No difference was found for the malnourished rats. Conclusion In this study, neonatal protein restriction affected weight gain in rats. Furthermore, early malnutrition made adult rats resistant to the inhibitory effects of tryptophan on food intake.