Differential feeding patterns induced by tumor growth and by TPN

The effects of anorexia induced by early tumor, and anorexia induced by total parenteral nutrition (TPN) on food intake and the indexes of food intake, were investigated in rats infused with saline after jugular catheter placement and concomitant inoculation with methylcholanthrene (MCA)-induced tumor cells on day 0, and in rats without catheters receiving tumor only. Tumor became palpable around day 10 and increased to represent 6-8% of host body weight by day 26. On day 18, food intake started to decrease. Catheter-bearing rats were then randomized to saline controls (n = 9) for 11 d or to TPN-100 (n = 9) for 4 d providing 100% of daily caloric needs. Both then received saline until day 26. Food intake and feeding indexes were continuously measured using the Automated Computerized Rat Eater Meter (ACREM) and data was analyzed using ANOVA and regression analysis. In controls (both with and without catheter) the tumor induced a specific feeding pattern which consisted of a significant (P < 0.01) decrease in food intake via a significant (P < 0.05) decrease in meal size. A non-significant decrease in meal number and meal duration occurred. Two other feeding-related activities, meal consumption rate and intermeal sniffs, also decreased. Infusion of TPN-100 into the already anorectic rat led to a further significant (P < 0.0001) decrease in food intake via a significant decrease in both meal size (P < 0.0001) and in meal number (P < 0.0001). A decrease in all other feeding indexes also occurred, resulting in a different feeding pattern. After stopping TPN-100, the TPN-100-induced feeding pattern returned to that of the tumor-induced feeding pattern. That the tumor-induced feeding pattern differs from the TPN-100-induced feeding pattern suggests that the mechanisms whereby these two factors induce anorexia may also differ.