Effects of TPN on brain, liver, and food intake in rats

Postulating that total parenteral nutrition (TPN) has a direct metabolic effect in the brain which may be similar to that in the liver, we studied the effects of TPN on brain glycogen and triglyceride in rats. Control rats (n = 24) received normal saline via jugular catheter for 18 days; TPN rats (n = 24) had normal saline for 10 days and then TPN-100 for 4 days, followed by normal saline for 4 more days. TPN-100 (caloric ratio glucose: fat:amino acid = 50:30:20) provided 100% of the rat's daily caloric needs. Chow and water were available ad libitum during the study. Eight rats from each group were sacrificed after 1 and 4 days of TPN-100, and 4 days after stopping TPN-100. Glycogen in brain and liver glycogen, triglyceride, and glycogen synthetase and phosphorylase were measured, as were plasma glucose and insulin. Data were evaluated using Student's t test. With TPN, the following occurred: (a) an 85% decrease (P < 0.05) of spontaneous food intake; (b) an elevated plasma glucose; (c) a three- to fivefold increase (P < 0.01) in plasma insulin; (d) a 23% increase (P < 0.05) in whole brain glycogen but a 22-33% decrease (P < 0.05) in liver glycogen; (e) liver glycogen synthetase and phosphorylase activity were unchanged while whole brain glycogen synthetase activity decreased by 27% (P < 0.05) and phosphorylase activity increased by 10-16%; and (f) whole brain triglyceride content did not change, although there was a 155-241% increase (P < 0.01) in liver triglyceride.(ABSTRACT TRUNCATED AT 250 WORDS)