Effects of L-arginine pretreatment on nitric oxide metabolism and hepatosplanchnic perfusion during porcine endotoxemia

Abstract

Background: Sepsis is accompanied by an increased need for and a decreased supply of arginine, reflecting a condition of arginine deficiency.

Objective: The objective was to evaluate the effects of l-arginine pretreatment on arginine-nitric oxide (NO) production and hepatosplanchnic perfusion during subsequent endotoxemia.

Design: In a randomized controlled trial, pigs (20-25 kg) received 3 μg . kg(-1) . min(-1) lipopolysaccharide (LPS; 5 endotoxin units/ng) intravenously and saline resuscitation. l-Arginine (n = 8; 5.3 μmol . kg(-1) . min(-1)) or saline (n = 8) was infused starting 12 h before LPS infusion and continued for 24 h after the endotoxin infusion ended. Whole-body appearance rates, portal-drained viscera (PDV), and liver fluxes of arginine, citrulline, NO, and arginine de novo synthesis were measured by using stable-isotope infusion of [(15)N(2)]arginine and [(13)C-(2)H(2)]citrulline. Hepatosplanchnic perfusion was assessed by using a primed continuous infusion of para-aminohippuric acid and jejunal intramucosal partial pressure of carbon dioxide and was related to systemic hemodynamics.

Results: Arginine supplementation before LPS increased whole-body NO production in the PDV but not in the liver. Furthermore, it increased blood flow in the portal vein but not in the aorta and hepatic artery. During endotoxin infusion, arginine pretreatment was associated with an increased whole-body arginine appearance and NO production in the gut. Additional effects included a preserved mean arterial pressure, the prevention of an increase in pulmonary arterial pressure, an attenuated metabolic acidosis, and an attenuated increase in the intramucosal partial pressure of carbon dioxide.

Conclusion: Arginine treatment starting before endotoxemia appears to be beneficial because it improves hepatosplanchnic perfusion and oxygenation during prolonged endotoxemia, probably through an enhancement in NO synthesis, without causing deleterious systemic side effects.

Figures

FIGURE 1

Experimental design. Study design depicting the experiment to investigate the effects of l-arginine pretreatment [12 h before start of lipopolysaccharide (endotoxin) infusion or control on hepatosplanchnic perfusion variables and arginine–nitric oxide metabolism] as determined by infusion of [N2]arginine and the C1D2-citrulline stable isotopes (shaded areas represent the 2-h infusion period) with blood sampling (arrows) before and after this period of infusion.

FIGURE 2

Whole-body (WB) arginine–nitric oxide (NO) metabolism during l-arginine and saline (control)–pretreated hyperdynamic endotoxemia. Data are presented as medians ± interquartile ranges. A: WB arginine appearance in control (unshaded bars) and l-arginine–supplemented (shaded bars) animals. The data were assessed for variance homogeneity and normality by using Levene's test and the Komolgorov-Smirnov test, after which the data were analyzed by using a linear mixed-model analysis (PG < 0.0001, PT = 0.9, PT×G = 0.3). B: WB arginine de novo synthesis (PG = 0.006, PT = 0.2, PT×G = 0.08). C: WB NO synthesis (PG = 0.001, PT = 0.7, PT×G = 0.01; significant difference at 0 h, P = 0.007). D: WB citrulline appearance (PG = 0.8, PT = 0.5, PT×G = 0.1). *Estimates of fixed effects indicate significant differences between groups at individual time points (P < 0.01). PG, difference between groups (l-arginine treatment); PT, difference over time (endotoxin infusion); PT×G, time × group interaction.

FIGURE 3

Hepatosplanchnic flow and nitric oxide (NO) production during l-arginine and saline (control)–pretreated hyperdynamic endotoxemia. Data are presented as medians ± interquartile ranges. A: Portal-drained viscera (PDV) flow in control (unshaded bars) and l-arginine–supplemented (shaded bars) animals (PG = 0.002, PT = 0.9, PT×G = 0.8). B: Liver flow (PG = 0.01, PT = 0.06, PT×G = 0.6). C: Hepatic artery flow (Hep. Art; PG = 0.03, PT = 0.09, PT×G = 0.04). D: NO flux in the PDV (PG = 0.004, PT = 0.2, PT×G = 0.002). E: NO flux in the liver (PG = 0.3, PT = 0.4, PT×G = 0.02). PG, difference between groups (l-arginine treatment); PT, difference over time (endotoxin infusion); PT×G, time × group interaction. *Estimates of fixed effects indicate significant differences between groups at individual time points (P < 0.01).

FIGURE 4

Mean (±SD) intramucosal jejunal partial pressure of carbon dioxide (PCO2) and arterial-jejunal pCO2-gap during l-arginine–pretreated hyperdynamic endotoxemia. A: Intramucosal pCO2 was significantly lower during endotoxemia in l-arginine–treated animals (▴) than in control animals (▪; PG < 0.0001, PT = 0.8, PTG = 0.2). B: Intramucosal minus arterial pCO2 (Pi-aCO2) was significantly lower in the l-arginine–treated animals than in control animals (PG = 0.02, PT = 1.0, PTG = 0.6). PG, difference between groups (l-arginine treatment); PT, difference over time (endotoxin infusion); PT×G, time × group interaction.