Endotoxin impairs the response of rabbit mesenteric artery to electrical stimulation via a prejunctional mechanism

Effect of lipopolysaccharide treatment on neurogenic contraction and noradrenaline release in rat arteries

In the present study, contractile responses and [3H]-noradrenaline overflow evoked by electrical field stimulation were assessed, respectively, in the small mesenteric artery and in tail artery removed from rats pre-treated with either saline or lipopolysaccharide (LPS). In small mesenteric arteries, LPS treatment did not significantly modify the contractile responses elicited by electrical stimulation, in the absence or in the presence of L-arginine. However, in arteries removed from rats treated with LPS, L-arginine addition produced relaxation of vessels pre-contracted with noradrenaline. The amplification of neurogenic contraction by the nitric oxide (NO) synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) was similar in arteries removed from saline and LPS-infused rats. In mesenteric arteries, LPS treatment suppressed the potentiation of the neurogenic responses by the alpha2-adrenoceptor antagonist, yohimbine and by the inhibitor of neuronal uptake of noradrenaline, cocaine. In rat tail artery exposed to L-arginine, LPS treatment produced an increase in [3H]-noradrenaline overflow evoked by electrical stimulation. Altogether, these data suggest that an enhanced noradrenaline release from sympathetic nerves, probably resulting from inhibition of the modulatory effect of both prejunctional alpha2-adrenoceptors and neuronal uptake mechanism, may play a role in the preservation of neurogenic response after LPS treatment despite evidence of the induction of NO synthase.

Urethan anesthesia protects rats against lethal endotoxemia and reduces TNF-α release

Kotanidou, Anastasia, Augustine M. K. Choi, Richard A. Winchurch, Leo Otterbein, and Henry E. Fessler. Urethan anesthesia protects rats against lethal endotoxemia and reduces TNF-α release. J. Appl. Physiol. 81(5): 2304–2311, 1996.—Urethan is a commonly used animal anesthetic for nonrecovery laboratory surgery. However, urethan has diverse biological effects that may complicate the interpretation of experimental findings. This study examined the effect of urethan on the response to an intravenous bolus of lipopolysaccharide (LPS; 30 mg/kg) in rats. In instrumented rats, urethan (1.2 gm/kg ip) completely prevented the fall in arterial pressure immediately after LPS administration but did not prevent late cardiovascular collapse. In uninstrumented rats, urethan also attenuated indexes of organ injury measured 4 h after LPS administration, including mural bowel hemorrhage, hemoconcentration, hypoglycemia, metabolic acidosis, and lung myeloperoxidase activity, a measure of neutrophil sequestration. The peak increase in tumor necrosis factor-α (TNF-α) 90 min after LPS administration was reduced 88% by urethan (2,060 ± 316 vs. 16,934 ± 847 pg/ml; P < 0.001). In uninstrumented animals, urethan at 1.2 gm/kg reduced the 90% mortality rate of a lethal dose of LPS to 0–10% when given up to 24 h before LPS administration but did not reduce mortality when given 2 h after LPS. Urethan neither directly bound LPS by Limulus assay nor inhibited LPS-stimulated TNF-α mRNA expression in cultured mouse peritoneal macrophages, but TNF-α mRNA expression was suppressed by serum from a urethan-treated rat. Moreover, rauwolscine, which shares α2-adrenoceptor-blocking activity with urethan, also prevented death from a subsequent 90% lethal dose LPS bolus. We conclude that urethan or its metabolites protect against LPS, in part, by reducing TNF-α release and speculate that this may be mediated by α2-adrenoceptors. These actions of urethan make it an undesirable anesthetic agent for in vivo studies of sepsis or LPS.

The effect of endotoxin on sympathetic responses in the rat isolated perfused mesenteric bed; involvement of nitric oxide and cyclo-oxygenase products

1. The effects of endotoxin on the vasoconstrictor responses to sympathetic nerve stimulation (SNS) were investigated in the rat isolated perfused mesenteric bed. 2. Rats received either saline (0.1 ml h-1) or endotoxin (2.5 mg kg-1 h-1) intravenously for 4 h; the mesenteric beds were then isolated, perfused with Krebs and prepared for SNS (50 V, 3 ms, 7-40 Hz). 3. SNS caused a frequency-dependent vasoconstrictor response which was abolished by either tetrodotoxin (10(-7) M), prazosin (2.4 x 10(-7) M) or guanethidine (2.4 x 10(-7) M). 4. In mesenteric vascular beds removed from rats infused with endotoxin, there were markedly impaired vasoconstrictor responses to SNS, although responses to noradrenaline were not modified. 5. Removal of the endothelium with distilled water prevented endotoxin-induced impairment of vasoconstrictor responses to SNS, without modifying these responses in preparations from control rats. 6. Pretreatment with dexamethasone (3 mg kg-1 i.p. 1h before commencing endotoxin or saline infusions) did not modify responses to SNS in control rats but prevented the effects of endotoxin. 7. Both L-NAME (10(-3) M) and indomethacin (10(-5) M) restored responses to SNS in preparations from endotoxin-treated rats without modifying these responses in control preparations. However, co-administration of L-NAME and indomethacin markedly augmented responses in both control and endotoxin-treated preparations. 8. The effects of L-NAME were reversed by addition of L-arginine (10(-3) M). 9. The data suggest that endotoxin impairs the release of noradrenaline and that this effect is secondary to increased production of nitric oxide and prostanoids, possibly by the endothelium.