Serial blood sampling from the portal and hepatic vein in conscious unrestrained miniature pigs

Metabolic flux between organs measured by arteriovenous metabolite gradients

Mammalian organs convert dietary nutrients into circulating metabolites and share them to maintain whole-body metabolic homeostasis. While the concentrations of circulating metabolites have been frequently measured in a variety of pathophysiological conditions, the exchange flux of circulating metabolites between organs is not easily measurable due to technical difficulties. Isotope tracing is useful for measuring such fluxes for a metabolite of interest, but the shuffling of isotopic atoms between metabolites requires mathematical modeling. Arteriovenous metabolite gradient measurements can complement isotope tracing to infer organ-specific net fluxes of many metabolites simultaneously. Here, we review the historical development of arteriovenous measurements and discuss their advantages and limitations with key example studies that have revealed metabolite exchange flux between organs in diverse pathophysiological contexts.

Long-term Functional Maintenance of Exteriorized Portal Venous Catheters in a Porcine Animal Model

BACKGROUND

Portal venous access for blood sampling, infusion therapy, and measurement of portal venous pressure is of special interest for experimental studies in surgery, pharmacology, and hepatology. Chronic animal models with continuous portal venous access are rare and especially thrombosis or clotting of permanent catheters is a frequent complication. Aim of this study was to establish a preclinical pig model with a permanent portal venous catheter (PVC).

MATERIALS AND METHODS

PVC implantation was performed in 21 LEWE mini pigs. The catheter was inserted in the distal part of the superior mesenteric vein and fixated with a tobacco-pouch suture. Animals were followed up for 4 wk, directly after implantation of the PVC. Blood gas analyses and portal venous pressures were recorded. Three different groups with continuous infusion via the catheters were defined: NaCl solution (2 mL/h) (group 1), NaCl solution (2 mL/h) + enoxaparin sodium injection (anti-Xa levels of 0.3-0.8 U/mL) (group 2) and heparinized NaCl (2 I.E./mL, 2 mL/h) (group 3).

RESULTS

All 21 PVC implantations were performed without any complications. Application of continuous perfusion with heparinized NaCl (group 3) enabled portal venous access for the entire experiment in 8 of 10 cases (mean of 23.7 d) without any signs of dysfunction. However, for use of NaCl alone or in combination with enoxaparin sodium, catheters were only functional for 6.8 d and 6.9 d, respectively.

CONCLUSIONS

Permanent portal venous access through PVC in mini pigs is achievable by continuous infusion of low-dose heparinized NaCl solution.

Transsplenic portal catheterization combined with a jugular double-lumen catheter for pharmacokinetic and presystemic metabolization studies in pigs

The reliability of a silicone double-lumen catheter implanted into the external jugular vein and tunnelled towards the neck region was investigated in eight pigs. Surgery was uneventful without interference with the normal homoeostasis during 8 days. After injection of amoxicillin/clavulanic acid through the distal port of the catheter, analysis of drug components in the simultaneous blood samples obtained by the proximal port and a Venoject system were comparable in one pig. Histological control of the catheterized jugular veins pointed to an acceptable tissue reaction while bacteriological examination of the tip of the catheters was negative in only three animals. A moulding of the intestinal veins was made in a pig cadaver to determine the optimal length of insertion of a silicone portal catheter from the splenic vein towards the portal vein. Surgery was straightforward in four pigs whereby the catheter was exteriorized towards the back region. No complications were encountered during and after surgery for 9 days. The technique of a double-lumen catheter placed into the jugular vein and a transsplenic portal catheter is a useful tool for the study of the pharmacokinetics and also the first-pass effect of drugs in experimental pigs.

New surgical technique for portal venous port system in Swine

The need for serial blood sampling and continuous infusion using the portal vein for experimental surgery and pharmacological studies is evident. As suitable animal models are rare, we established a new technique to implant a permanent vascular access device to the portal vein in swine. All operations in study animals (n=8) were technically feasible due to a regularly detected side branch of the portal vein within the inferior pancreatic region; complications did not occur. Mean operation time was 48+/-17 min. This study clearly shows that the portal venous access is feasible and can be achieved safely using the inferior pancreatic vein for a permanent vascular access port system.

Liver blood flow measured by indocyanine green in conscious unrestrained miniature pigs

For studies in physiology and biochemistry of the liver the measurement of hepatic blood flow is a fundamental precondition. Therefore, the least invasive method, the measurement of liver blood flow by indocyanine green (ICG) dye elimination, was re-evaluated for the miniature pig, an animal model of increasing interest. The accuracy of spectrophotometric determination of ICG was enhanced by addition of 5% of desoxycholic acid. It was shown that ICG was eliminated exclusively by the liver. An extraction rate of 30%-50% was found in mini-pigs, but an insufficient rate of 5%-10% in pigs of German landrace. A liver blood flow ranging from 70 to 160 ml/100 g X min-1 was measured. These values are in good accordance with datas from simultaneous estimation of blood flow by 133Xenon washout. As shown for a starvation/refeeding cycle, liver blood flow measurement by ICG combined with permanently implanted catheters is a practicable tool for studies of the metabolic and pharmacologic fate of substances resorbed from the gut.