The Response to Substrate Infusion and Total Parenteral Nutrition

Abstract

Rates of glucose turnover and oxidation in normal volunteers (N = 16) and in severely ill patients with pancreatitis (N = 9) were isotopically determined. Glucose turnover was determined using primed constant infusions of either 6-3H-glucose or 6-d2-glucose, and glucose oxidation with either U-14C-glucose or U-13C-glucose after appropriate priming of the bicarbonate pool. Urea kinetics were determined using primed constant infusions of either (15N2)-urea or U-14C-urea, whereas free fatty acid (FFA) kinetics were determined by the constant infusion of 1,2-13C palmitate. Basal rates of glucose production and plasma glucose clearance were significantly higher in the patients than in the volunteers. During glucose infusion (4 mg/kg/min) endogenous glucose production was virtually totally suppressed in the volunteers (94 +/- 4%). There was significantly less suppression in the patients, however (44 +/- 1%). In addition, the percentage of available glucose oxidized (i.e., percentage of uptake oxidized) was significantly less in the patients than in the volunteers. The basal rate of urea production was significantly higher in the patients; however, in both patients and volunteers, glucose infusion resulted in a significant decrease. The rate of FFA turnover was similar in the patients and volunteers, and the patients and volunteers were equally sensitive to the suppressive effects of glucose infusion. When the patients were studied during total parenteral nutrition (TPN), there was no further suppression of endogenous glucose turnover than that seen during 2 hours of glucose infusion, and the mean rate of urea turnover measured during TPN (7.0 +/- 1.9 mumol/kg/min) was also not significantly different than the value determined during glucose infusion (8.9 +/- 1.8 mumol/kg/min). It was concluded from these studies that patients with pancreatitis are metabolically similar to septic patients, have an impairment in their ability to oxidize infused glucose when compared with normal volunteers, have an elevated rate of net protein catabolism, and have FFA kinetics similar to those seen in normal humans.