Nocturnal cyclic versus continuous total parenteral nutrition: food intake and feeding pattern in rats

Total parenteral nutrition (TPN), providing the equivalent of 100% of mean daily oral intake for 24 hours, depressed spontaneous food intake (SFI) in rats by a mean greater than 80%. Whether TPN had the same effect on SFI when given either in 12-hour cycles (Cyclic-TPN) or in 24 hours (Continuous-TPN) for 8 days was tested in 16 rats with jugular catheters, placed in metabolic cages modified with an Automated Computerized Rat Eater Meter. This continuously measures food intake and its dependent indexes: meal number, meal size, meal duration, meal sniffs and intermeal sniffs. Both rat groups ate the same amounts of chow before TPN. On starting TPN, food intake decreased by greater than 80% in Cyclic-TPN and greater than 50% in Continuous-TPN during each first infusion period. A nadir in food intake was reached in 48 hours with Cyclic-TPN and in 72 hours with Continuous-TPN. Thereafter, there was no food intake during the 12 hours of Cyclic-TPN, with minimal food intake during the intervening 12 hours of non-TPN normal saline infusion period. In both forms of TPN infusion, a reduction in food intake was achieved by a reduction in meal number and size, and thus in meal duration. Feeding-related sniffing activity was decreased by similar amounts with Cyclic- or Continuous-TPN. Cyclic-TPN for 12 hours had no advantage over Continuous-TPN, in that there was no compensatory enhancement of food intake and meal-related behavior during the cyclic non-TPN normal saline period.