In vivo measurement of nitric oxide production in porcine gut, liver and muscle during hyperdynamic endotoxaemia

Abstract

1. During prolonged endotoxaemia, an increase in arginine catabolism may result in limiting substrate availability for nitric oxide (NO) production. These effects were quantitated in a chronically instrumented porcine endotoxaemia model. 2. Ten days prior to the beginning of the experiments, pigs were catheterized. On day 0, pigs received a continuous infusion of endotoxin (3 microg kg(-1) h(-1)) over 24 h and were saline resuscitated. Blood was drawn from the catheters at 0 and 24 h during primed-infusion of (15)N(2)-arginine and P-aminohippurate to assess (15)N(2)-arginine to (15)N-citrulline conversion and plasma flow rates, respectively, across the portal-drained viscera, liver and hindquarter. 3. During endotoxin infusion a hyperdynamic circulation with elevated heart rate, cardiac index and decreased mean arterial pressure was achieved, characteristic of the human septic condition. 4. Endotoxin induced NO production by the portal-drained viscera and the liver. The increased NO production was quantitatively matched by an increase in arginine disposal. Nitrite/nitrate levels remained unchanged during endotoxaemia. 5. Despite an increased arginine production from the hindquarter and an increased whole-body arginine appearance rate during endotoxin infusion, the plasma arginine concentration was lower in endotoxin-treated animals than in controls. 6 On a whole-body level, the muscle was found to serve as a major arginine supplier and, considering the lowered arginine plasma levels, seems critical in providing arginine as precursor for NO synthesis in the splanchnic region.

Figure 1

Schematic illustration of the catheter implantation. Catheters were placed in the abdominal aorta just above the bifurcation (A1) and just above the right renal vein (A2) and in the inferior caval vein at the corresponding positions (V1 and V2, respectively). Catheters were also placed in the portal (P) vein (via the vena lienalis), the hepatic (H) vein and a splenic (S) vein. The P-Aminohippurate (PAH) dye solution was infused through the A1 and S catheters while isotopes and endotoxin were infused through the V2 catheter. Blood was sampled from the A2, P, H and V1 catheters.

Figure 2

Haemodynamics in endotoxin-treated pigs. Data are mean±s.e.mean. (A) Body temperature (control: n=7; endotoxin: n=7), (B) heart rate (control: n=4, endotoxin, n=5) and (C) mean arterial blood pressure (MAP; control: n=3, endotoxin: n=3) were followed during 24-h saline or endotoxin infusion. (D) Cardiac output was measured in a separate endotoxin-treated pig group (n=6). Statistics by repeated measures ANOVA: (A, B, C) **P<0.01, *P<0.05; significantly different from control group and (D) ⁺P<0.05; significantly different from baseline values (0 h).

Figure 3

Portal-drained viscera (A) net fluxes (+=efflux, −=influx) of arginine, citrulline and ornithine, (B) arginine disposal and production rates, and (C) nitric oxide synthesis rate in the postabsorptive state before (0 h) and 24 h after starvation plus infusion of saline (control) or endotoxin. Statistics by ANOVA: *P<0.05; significantly different from control group and ⁺P<0.05; significantly different from 0 h.

Figure 4

Liver (A) net fluxes (+=efflux, −=influx) of arginine, citrulline and ornithine, (B) arginine disposal and production rates, and (C) nitric oxide synthesis rate in the postabsorptive state before (0 h) and 24 h after starvation plus infusion of saline (control) or endotoxin. Statistics by ANOVA: **P<0.01, *P<0.05; significantly different from control group.

Figure 5

Hindquarter (A) net fluxes (+=efflux, −=influx) of arginine, citrulline and ornithine, (B) arginine disposal and production rates, and (C) nitric oxide synthesis rate in the postabsorptive state before (0 h) and 24 h after starvation plus infusion of saline (control) or endotoxin. Statistics by ANOVA: **P<0.01, *P<0.05; significantly different from control group.