Gut and liver handling of asymmetric and symmetric dimethylarginine in the rat under basal conditions and during endotoxemia.

INTRODUCTION/AIM: Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthase enzymes, whereas symmetric dimethylarginine (SDMA) competes with arginine transport. Although both dimethylarginines may be important regulators of the arginine-NO pathway, their metabolism is largely unknown. In previous studies, evidence was found for the liver in the metabolism of dimethylarginines. We aimed to investigate dimethylarginine handling of the gut and the liver in detail under basal conditions and during endotoxemia. METHODS: Twenty-one male Wistar rats were used for this study. Endotoxemia was induced by lipopolysaccharide (LPS) infusion (8 mg/kg). Blood flow was measured using radiolabeled microspheres according to the reference sample method. Concentration of dimethylarginines were measured by high-performance liquid chromatography. The combination of arteriovenous concentration difference and organ blood flow allowed calculation of net organ fluxes and fractional extraction (FE) rates. RESULTS: Arterial plasma concentration of ADMA was lower in LPS rats, in contrast to a higher SDMA concentration. For the gut, net release of ADMA was found, which was higher in LPS rats. In contrast, for the gut, net uptake of SDMA was found, which was lower in LPS rats. For the liver, a high net uptake of ADMA was found in both groups, while FE was significantly increased in LPS rats. Hepatic handling of SDMA was negligible. CONCLUSION: The liver plays an important role in eliminating ADMA from the circulation and endotoxemia stimulates this capacity. In contrast to the liver, the gut releases ADMA. Endotoxemia results in a reduced systemic ADMA concentration.

Handling of asymmetrical dimethylarginine and symmetrical dimethylarginine by the rat kidney under basal conditions and during endotoxaemia.

BACKGROUND: Asymmetrical dimethylarginine (ADMA) is capable of inhibiting nitric oxide synthase enzymes, whereas symmetrical dimethylarginine (SDMA) competes with arginine transport. The potential role of inflammation in the metabolism of ADMA has been elucidated in an in vitro model using tumour necrosis factor-alpha, resulting in a decreased activity of the ADMA-degrading enzyme dimethylarginine dimethylaminohydrolase (DDAH). The kidney probably plays a crucial role in the metabolism of ADMA by both urinary excretion and degradation by DDAH. We aimed to further elucidate the role of the kidney in a rat model under basal conditions and during endotoxaemia. METHODS: Twenty-five male Wistar rats weighing 275-300 g were used for this study. The combination of arteriovenous concentration differences and kidney blood flow allowed calculation of net organ fluxes. Blood flow was measured using radiolabelled microspheres according to the reference sample method. Concentrations of ADMA, SDMA and arginine were measured by high-performance liquid chromatography. RESULTS: The kidney showed net uptake of both ADMA and SDMA and fractional extraction rates were 35% and 31%, respectively. Endotoxaemia resulted in a lower systemic ADMA concentration (P = 0.01), which was not explained by an increased net renal uptake. Systemic SDMA concentrations increased during endotoxaemia (P = 0.007), which was accompanied by increased creatinine concentrations. CONCLUSIONS: The rat kidney plays a crucial role in the regulation of concentrations of dimethylarginines, as both ADMA and SDMA were eliminated from the systemic circulation in substantial amounts. Furthermore, evidence for the role of endotoxaemia in the metabolism of dimethylarginines was obtained as plasma levels of ADMA were significantly lower in endotoxaemic rats.

Endotoxin impairs endothelium-dependent vasodilation more in the coronary and renal arteries than in other arteries of the rat.

Endotoxemia may result in endothelial dysfunction, and some vascular beds may be affected more than others. To test this hypothesis, we studied, in vitro, the reactivity of isolated rat coronary, renal, superior mesenteric, and hepatic arteries exposed to endotoxin (E. coli, 50 microg. mL(-1)) or saline for 2 h at 37 degrees C. Vascular smooth muscle function was tested using 125 mM KCl, the vasoconstrictors norepinephrine (NE), and the thromboxane analog U46619 (coronary artery). Endothelium-dependent vasorelaxation was tested with acetylcholine (ACh) in preconstricted vessels. Although differing between vessel types, the smooth muscle contractile responses were not affected by endotoxin, either in the presence or absence of L-arginine. Endotoxin impaired the response to ACh in rat coronary arteries (92.7 +/- 4.6% vasodilation in control and 41.3 +/- 11.6% in endotoxin-exposed segments) and in renal arteries (66.7 +/- 5.2% vasodilation in control and 43.2 +/- 4.9% in endotoxin-exposed segments), so that there was a mean 55% decrease vs controls in coronary and a mean 35% decrease in renal arteries. Endotoxin did not affect superior mesenteric and hepatic arteries. Brief endotoxin exposure of isolated rat arteries may thus inactivate endothelial NO synthase, independent of iNOS. The increase in heterogeneity among endothelium-dependent vasodilation after endotoxin may help to explain early blood flow maldistribution in endotoxin shock.

Cold storage sensitizes rat femoral artery to an endotoxin-induced decrease in endothelium-dependent relaxation.

Cold-stored arteries, tissues or organs are transferred in vascular, reconstructive and transplantation surgery. The function of transferred vessels and tissues diminishes when infection complicates transplantation, thereby contributing to morbidity. To evaluate the mechanisms involved, the effects of cold storage on basal vascular reactivity and the sensitivity to the vascular effects of endotoxin were tested in isolated rat femoral artery segments. A crossover design was followed, so that prior to cold storage 4 vessels were incubated for 2 h at 37 degrees C with endotoxin (Escherichia coli 0127:B8, 50 microg mL(-1)) in Krebs solution and 4 with Krebs solution only, while, after cold storage, segments from the former vessels were incubated with Krebs solution only and segments from the latter with endotoxin in Krebs solution. Vascular reactivity was tested in a wire myograph by the addition of depolarizing 125 mM KCl or norepinephrine (NE) as well as the endothelium-dependent vasodilator acetylcholine (ACh) and endothelium-independent vasodilator sodium nitroprusside (SNP). Cold storage did not affect vascular reactivity in the absence of endotoxin. Endotoxin decreased maximum response to NE prior to storage and sensitivity to SNP prior to and after cold storage. After cold storage, endotoxin decreased relaxation to ACh and increased vasoconstriction in response to KCl and NE (P < 0.05). We conclude that cold storage does not alter endothelial and smooth muscle function but sensitizes rat femoral artery to an endotoxin-induced decrease in endothelium-dependent relaxation and thereby to an increase in vasoconstrictor responses, whereas endotoxin alone only decreases receptor-dependent vasoconstrictor responses and sensitivity to NO donors. This may explain in part the detrimental effect of infection on function of cold-stored arterial grafts and tissue/organ transfers.

Tumor necrosis factor-alpha impairs endothelium-dependent relaxation of rat renal arteries, independent of tyrosine kinase.

We hypothesized that tumor necrosis factor-alpha (TNF-alpha) mimics endotoxin in attenuating endothelium-dependent vasodilation and smooth muscle constriction of rat renal arteries, and that tyrosine kinase is involved. Isolated rat renal arteries (n =6 per group), pretreated for 2 h by genistein (4',5,7-trihydroxyisoflavone, 10 microg/mL, a tyrosine kinase inhibitor) or vehicle, were exposed for 2 h to recombinant human (rh) TNF-alpha (100 ng/mL) or vehicle. rhTNF-alpha attenuated (P < 0.05) the constriction response to depolarizing 125 mM KCl (952.6+/-125.3 mg/mm vs. 1191.4+/-136.8 mg/mm in rhTNF-alpha-exposed and control segments, respectively), but did not affect the constriction response to norepinephrine (NE, 0.01-10 microM). Genistein did not affect the constriction response to KCl. The concentration-response relation to NE in genistein-pretreated control segments showed (P < 0.05) a rightward shift, while the maximum constriction was not affected. Genistein did not prevent a reduction (P < 0.05) by rhTNF-alpha in the maximum response to NE (721.7+/-42.4 mg/mm vs. 999.8+/-84.4 mg/mm in controls). The endothelium-dependent relaxation induced by (acetyl choline) ACh (0.001-1.0 microM) was attenuated (P < 0.05) by rhTNF-alpha (39.4%+/-6.7% and 77.4%+/-10.0% in rhTNF-alpha-exposed and control segments, respectively). The reduction (P < 0.05) in maximum ACh-induced relaxation after exposure to rhTNF-alpha was not affected by genistein (44.6%+/-3.4% and 70.8% x 2.2% in genistein-pretreated rhTNF-alpha-exposed and control segments, respectively). Hence, the attenuated endothelium-dependent relaxation and smooth muscle constriction of rat renal arteries following short-term rhTNF-alpha exposure, mimicking the effect of endotoxin, does not involve the activity of tyrosine kinase. The latter may be involved in pharmacomechanical coupling, by increasing Ca2+ sensitivity, but less in the electromechanical coupling of smooth muscle constriction.