Effect of halothane on phenylephrine-induced vascular smooth muscle contractions in endotoxin-exposed rat aortic rings

Effects of vitamin E and sodium selenate on impaired contractile activity by bacterial lipopolysaccharide in the rat vas deferens

We investigated whether bacterial lipopolysaccharide (LPS) treatment causes any hyporeactivity in rat vas deferens tissue and also whether vitamin E or sodium selenate has any restorative effect on this possible hyporesponsiveness. LPS treatment attenuated contractions to electrical field stimulation (EFS), phenylephrine, or ATP at the prostatic and epididymal ends. Treatment with the inducible nitric oxide synthase (iNOS) inhibitor aminoguanidine or vitamin E could prevent the impairment in contractile responses of both ends to EFS and phenylephrine but sodium selenate could restore these impaired contractions at only the epididymal end. LPS treatment also caused a similar significantly impairment on purinergic or adrenergic component of nerve-evoked contractions in the presence of prazosin or suramin, respectively, and vitamin E or sodium selenate could restored this impairment at both ends. On the other hand, both antioxidant agents failed to restore the impaired ATP-induced contractions in LPS-treated rats at both ends. In conclusion, LPS-treatment caused a hyporeactivity in the rat vas deferens. A possible increased oxidative activity in the vas deferens may be a major reason for the impairment of contractile responses. The restorative effects of vitamin E and/or sodium selenate on this hypocontractility may depend on their antioxidant properties or their inhibitory action on the iNOS.

Anesthetic modulation of immune reactions mediated by nitric oxide

Nitric oxide (NO), when produced via inducible NO synthase (iNOS) in excess under pathological conditions (e.g., inflammation, endotoxemia, and septic shock), may lead to tissue injury and organ dysfunction. The bioavailability of NO and the activity and expression of iNOS are regulated by anesthetic agents. Volatile anesthetics mostly suppress, but in some instances may upregulate, the lipopolysaccharide-and cytokine-induced expression of iNOS in blood vessels and macrophages. Intravenous anesthetics inhibit iNOS expression in macrophages and the liver. Local anesthetics decrease the production of NO by inhibiting iNOS expression in macrophages and increase NO production in glial cells. Based on the literature reported so far, the effects of anesthetics on iNOS expression and activity under conditions of inflammation are controversial, with the observed effects depending on the experimental methods and animal species used. On the other hand, it has been shown that volatile and intravenous anesthetics consistently prevent the development of multiple organ failure elicited by endotoxemia or septic shock. Information, although still insufficient, regarding the interactions between anesthetic agents and the detrimental effects of NO formed during inflammatory processes may help us to construct advanced strategies for anesthetizing and sedating patients with inflammation and sepsis and for anesthetic preconditioning against ischemic injury.

Extracellular Signal-Regulated Kinase (ERK1/2) Contributes to Endotoxin-Induced Hyporeactivity via Nitric Oxide and Prostacyclin Production in Rat Aorta

This study was conducted to determine if mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK1/2) contribute to endotoxin-induced vascular hyporeactivity via nitric oxide (NO) and/or prostacyclin (PGI(2)) production in the rat isolated thoracic aorta. Incubation of endothelium-intact rings with endotoxin (100 microg/ml) for 4 h decreased the E(max) value and increased the EC(50) value of norepinephrine. The endotoxin-induced increase in the EC(50) value of norepinephrine was decreased by phenylene-1,3-bis[ethane-2-isothiourea] dihydrobromide (1,3-PBIT), a selective inducible NO synthase inhibitor, and U0126, a selective inhibitor of ERK1/2 phosphorylation by MAPK kinase. The endotoxin-induced decrease in the E(max) value of norepinephrine was reversed by 1,3-PBIT and further decreased by U0126. 1,3-PBIT and U0126 decreased the endotoxin-induced increase in the tissue nitrite and 6-keto-PGF(1)(alpha) levels. These data suggest that events related to the activation of ERK1/2 contribute to the endotoxin-induced hyporeactivity by increasing NO and PGI(2) production.

Effects of isoflurane, enflurane, and halothane on skeletal muscle microcirculation in the endotoxemic rat

PURPOSE

The cardiovascular effects of volatile anesthetics during sepsis sets patients at high risk for hemodynamic deterioration. We compared the microcirculatory alterations in skeletal muscle under anesthesia with isoflurane, enflurane, and halothane in an endotoxemic rat preparation.

MATERIALS AND METHODS

Twenty-one Sprague-Dawley rats under continuous hemodynamic monitoring and intravital microscopy of the spinotrapezius muscle were studied during two level lipopolysaccharide (0.2 mg/kg and 2 mg/kg) induced sepsis. The effects of equianesthetic concentrations (1.5 minimum alveolar concentration [MAC]) of either isoflurane [n:7], enflurane [n:7], or halothane [n:7] on microcirculatory vasoregulation were measured and histopathologic changes were evaluated.

RESULTS

During low-dose endotoxemia, arteriolar vasodilation under isoflurane was nearly abolished (P < .05). At high-dose endotoxemia, this lack of vasodilatory effect was similar (P < .05). Animals receiving 1.5 MAC of enflurane during low-dose endotoxin presented a significant decrease in arteriolar diameter by -11.3 (+/-2.9%), this response was less during high-dose endotoxemia (-7.0, +/-2.9%). Halothane caused pronounced vasoconstriction by -20 (+/-3.7%) during low-dose endotoxemia and moderate but significant constriction during high-dose endotoxemia (-7.9, +/-2.6%).

CONCLUSIONS

Isoflurane, enflurane, and halothane exert significantly different effects on vasoregulation of skeletal muscle arterioles in the endotoxemic rat.

Endotoxin augments cerebral hyperemic response to halothane by inducing nitric oxide synthase and cyclooxygenase

We examined the cerebral hyperemic response to halothane after treatment with bacterial lipopolysaccharide (LPS). To determine the involvement of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX-2), we tested whether the effect of LPS on halothane-induced hyperemia was altered by pretreatment with the selective iNOS inhibitor, aminoguanidine (100 mg/kg), COX-2 inhibitor, NS-398 (5 mg/kg), or enzyme expression inhibitor, dexamethasone (4 mg/kg). Further, we examined whether the administration of a nitric oxide donor, diethylamine NONOate, would change the cerebral hyperemic response of halothane. Sprague-Dawley rats were anesthetized with 0.5 minimum alveolar anesthetic concentration of halothane and artificially ventilated. Regional cerebrocortical blood flow (rCBF) was assessed by laser-Doppler flowmetry. LPS (1 mg/kg) was administered intracerebroventricularly; artificial cerebrospinal fluid was used in controls. Four hours after LPS infusion, iNOS and COX-2 messenger ribonucleic acid (mRNA) levels (reverse transcription-polymerase chain reaction) and enzyme activities (arginine-citrulline conversion and prostaglandin E(2) enzyme immunoassay) were significantly increased. LPS enhanced halothane-induced 3.9 and 1.6-fold increases in rCBF at 1.0 and 1.5 minimum alveolar concentration, respectively. Co-treatment with NS-398 attenuated, but aminoguanidine or dexamethasone abolished the effect of LPS on halothane-induced rCBF increase. Diethylamine NONOate mimicked the enhanced rCBF response to halothane. These results suggest that LPS augmented halothane-induced cerebrocortical hyperemia by induction of iNOS and COX-2.

Pharmacodynamic characterization of hemoglobin-induced vasoactivity in isolated rat thoracic aorta

The origin and mechanism of vasocontraction observed after vascular exposure to acellular Hbs remain controversial. To help resolve the underlying mechanism, we characterized Hb-induced vasoactivities in terms of Hb purity, heme iron oxidation state, and ligand and pharmacodynamic properties. Isolated rat thoracic aortic rings with intact endothelium were suspended in oxygenated Krebs buffer, and isometric tension responses to various test Hb preparations were measured. In norepinephrine tone-enhanced aortic rings, both crude and purified Hbs exhibited similar dose-response characteristics; stroma-free Hb and HbA0, two Hb preparations with disparate purity, were equally potent in inducing vessel ring contraction. Purified Hb preparations significantly attenuated vasodilatory potency of both acetylcholine, an endothelium-dependent NO generator, and glyceryl trinitrate, an endothelium-independent NO generator. With the exception of nitrosylated Hb, ferrous Hbs, oxy Hb, and carbon monoxy Hb elicited contraction, whereas ferric derivatives, met Hb, and cyanomet Hb did not. In addition, NEM-Hb, an Hb with blocked cysteine residues, did not notably attenuate Hb vasoactivity. These results indicate that Hb itself is directly responsible for inducing contraction in the rat thoracic aortic rings. A primary mechanism for the Hb-induced vasoactivity appears to be heme iron inactivation of endothelium-derived NO. Nonheme interaction with endothelial NO does not appear to play a prominent role in this vascular model. In conclusion, Hb elicits dose-dependent contraction in isolated rat thoracic aorta with intact endothelium. Vasoactivity of Hbs, however, could greatly vary with heme iron oxidation state, nature of heme ligand, and model vessels used in the evaluation.

Abnormal regulation of aortic NOS2 and NOS3 activity and expression from portal vein-stenosed rats after lipopolysaccharide administration

Hyporeactivity to vasoconstrictors in aortae from portal vein-stenosed rats is associated with an increased activity of endothelial NO synthase (NOS3). In contrast, during sepsis, which is common in cirrhosis, vascular hyporeactivity is associated with an induction of inducible NOS2. The aim of this study was to investigate the in vitro reactivity to phenylephrine and the regulation of NOS2 and NOS3 in aortae from portal vein-stenosed rats after lipopolysaccharide (LPS) administration. Aortic vascular reactivity for phenylephrine, aortic NOS activity, and NOS2 and NOS3 protein expression were determined 5 hours after intravenous LPS or saline administration. Moreover, aortic NOS activity was measured after 5-hour in vitro incubation in LPS. LPS induced a significantly smaller decrease in aortic tension in portal vein-stenosed than in sham-operated rats. Under baseline conditions, aortic NOS activity and NOS3 protein expression were higher in portal vein-stenosed than in sham-operated rats, and NOS2 protein expression was not detected in aortae from either group. After LPS administration, NOS activity and NOS2 protein expression increased significantly less in portal vein-stenosed than in sham-operated rat aortae. Similar results were obtained after in vitro incubation with LPS. Endothelium removal or NOS3 inhibition with the calmodulin inhibitor, W7, increased NOS activity in the aortae of portal vein-stenosed rats after LPS incubation. In conclusion, in aortae of portal vein-stenosed rats exposed to LPS, no further decrease in aortic reactivity to phenylephrine was observed, and the induction of NOS2 was down-regulated. Endothelium removal or calmodulin inhibition inhibits NOS3 overactivity and leads to normalized NOS2 activation after LPS in aortae from portal vein-stenosed rats.