Immunochemical Evidence against the Involvement of Cysteine Conjugate [small beta, Greek]-lyase in Compound A Nephrotoxicity in Rats

Background: Compound A, a degradation product of sevoflurane, causes renal corticomedullary necrosis in rats. Although the toxicity of this compound was originally hypothesized to result from the biotransformation of its cysteine conjugates into toxic thionoacyl halide metabolites by renal cysteine conjugate [small beta, Greek]-lyase, recent evidence suggests that alternative mechanisms may be responsible for compound A nephrotoxicity. The aim of this study was to evaluate these issues by determining whether mercapturates and glutathione conjugates of compound A could produce renal corticomedullary necrosis in rats, similar to compound A, and whether renal covalent adducts of the thionacyl halide metabolite of compound A could be detected immunochemically.

Methods: Male Wistar rats were administered, intraperitoneally, N-acetylcysteine conjugates (mercapturates) of compound A (90 or 180 [micro sign]mol/kg) or glutathione conjugates of compound A (180 [micro sign]mol/kg) with or without intraperitoneal pretreatments with aminooxyacetic acid (500 [micro sign]mol/kg) or acivicin (250 [micro sign]mol/kg). Rats were killed after 24 h, and kidney tissues were analyzed for toxicity by histologic examination or for protein adducts by immunoblotting or immunohistochemical analysis, using antisera raised against the covalently bound thionoacyl halide metabolite of compound A.

Results: Mercapturates and glutathione conjugates of compound A both produced renal corticomedullary necrosis similar to that caused by compound A. Aminooxyacetic acid, an inhibitor of renal cysteine conjugate [small beta, Greek]-lyase, did not inhibit the toxicity of the mercapturates, whereas acivicin, an inhibitor of [small gamma, Greek]-glutamyltranspeptidase, potentiated the toxicity of both classes of conjugates. No immunochemical evidence for renal protein adducts of the thionacyl halide metabolite was found in rats 24 h after the administration of the mercapturates of compound A or in the kidneys of rats, obtained from a previous study, 5 and 24 h after the administration of compound A.     

Role of Renal Cysteine Conjugate beta-Lyase in the Mechanism of Compound A Nephrotoxicity in Rats

Background: The sevoflurane degradation product compound A is nephrotoxic in rats, in which it undergoes extensive metabolism to glutathione and cysteine S-conjugates. The mechanism of compound A nephrotoxicity in rats is unknown. Compound A nephrotoxicity has not been observed in humans. The authors tested the hypothesis that renal uptake of compound A S-conjugates and metabolism by renal cysteine conjugate beta-lyase mediate compound A nephrotoxicity in rats.

Methods: Compound A (0-0.3 mmol/kg in initial dose-response experiments and 0.2 mmol/kg in subsequent inhibitor experiments) was administered to Fischer 344 rats by intraperitoneal injection. Inhibitor experiments consisted of three groups: inhibitor (control), compound A, or inhibitor plus compound A. The inhibitors were probenecid (0.5 mmol/kg, repeated 10 h later), an inhibitor of renal organic anion transport and S-conjugate uptake; acivicin (10 mg/kg and 5 mg/kg 10 h later), an inhibitor of gamma-glutamyl transferase, an enzyme that cleaves glutathione conjugates to cysteine conjugates; and aminooxyacetic acid (0.5 mmol/kg and 0.25 mmol/kg 10 h later), an inhibitor of renal cysteine conjugate beta-lyase. Urine was collected for 24 h and then the animals were killed. Nephrotoxicity was assessed by light microscopic examination and biochemical markers (serum urea nitrogen and creatinine concentration, urine volume and urine excretion of protein, glucose, and alpha-glutathione-S-transferase [alpha GST], a marker of tubular necrosis).

Results: Compound A caused dose-related nephrotoxicity, as shown by selective proximal tubular cell necrosis at the corticomedullary junction, diuresis, proteinuria, glucosuria, and increased alpha GST excretion. Probenecid pretreatment significantly (P < 0.05) diminished compound A-induced increases (mean +/- SE) in urine excretion of protein (45.5 +/- 3.8 mg/24 h vs. 25.9 +/- 1.7 mg/24 h), glucose (28.8 +/- 6.2 mg/24 h vs. 10.9 +/- 3.2 mg/24 h), and alpha GST (6.3 +/- 0.8 micro gram/24 h vs. 1.0 +/- 0.2 micro gram/24 h) and completely prevented proximal tubular cell necrosis. Aminooxyacetic acid pretreatment significantly diminished compound A-induced increases in urine volume (19.7 +/- 3.5 ml/24 h vs. 9.8 +/- 0.8 ml/24 h), protein excretion (37.2 +/- 2.7 mg/24 h vs. 22.2 +/- 1.8 mg/24 h), and alpha GST excretion (5.8 +/- 1.5 vs. 2.3 micro gram/24 h +/- 0.8 micro gram/24 h) but did not significantly alter the histologic pattern of injury. In contrast, acivicin pretreatment increased the compound A-induced histologic and biochemical markers of injury. Compound A-related increases in urine fluoride excretion, reflecting compound A metabolism, were not substantially altered by any of the inhibitor treatments.     

The Role of Tumor Necrosis Factor-[Greek small letter alpha] in the Pathogenesis of Aspiration Pneumonitis in Rats

Background: Aspiration pneumonitis is characterized by proteinaceous pulmonary edema and acute infiltration of neutrophils into the alveolar space. This study examined the role of the proinflammatory cytokine, tumor necrosis factor-[Greek small letter alpha] (TNF-[Greek small letter alpha]), on the pathogenesis of the injury produced by the different components that may be present in the aspirate, acid, or gastric particles.

Methods: Rats were injured by intratracheal instillation of a vehicle containing acid or gastric particles. TNF-[Greek small letter alpha] concentration of bronchoalveolar lavage fluid was determined using a bioassay. upregulation of lung TNF-[Greek small letter alpha] mRNA was also measured. The effect of intratracheal anti-rat TNF-[Greek small letter alpha] treatment was assessed by lung protein permeability, blood gases, and lung myeloperoxidase activity.

Results: Injury vehicle alone and acid injury resulted in a small TNF-[Greek small letter alpha] peak 1-2 h after injury in the lavage fluid. Both particulate and acidic particulate groups produced a much more robust TNF-[Greek small letter alpha] signal that reached a plateau at 2-4 h after injury and declined at 8 h. Upregulation of TNF-[Greek small letter alpha] mRNA was only detected in the particulate-containing groups. Acidic particulate exposure yielded a synergistic increase in protein permeability and decrease in blood oxygenation. Anti-TNF-[Greek small letter alpha] treatment reduced protein permeability and myeloperoxidase activity and increased blood oxygenation in the groups exposed to only acid. Such treatment had no effect on either of the particulate containing injuries.     

The Effects of Epidural Morphine on Cardiac and Renal Sympathetic Nerve Activity in [Greek small letter alpha]-Chloralose-anesthetized Cats

Background: Epidural morphine yields postoperative pain relief and hemodynamic stability. However, the effects of epidural morphine on sympathetic tone are unclear. This study was designed to elucidate the effects of epidural morphine on cardiac (CSNA) and renal (RSNA) sympathetic nerve activity by direct measurement in anesthetized cats.

Methods: Thirty mongrel cats anesthetized with [Greek small letter alpha]-chloralose were randomly assigned to one of the following five groups: control (0.2 ml/kg thoracic epidural normal saline; n = 5); thoracic epidural morphine (n = 9); lumbar epidural morphine (n = 6); vagotomized, sinoaortic denervated, thoracic epidural morphine (n = 5); or intravenous morphine (n = 5). Mean arterial pressure (MAP), heart rate (HR), CSNA, and RSNA were measured 0, 15, 30, 60, 90, and 120 min after saline or morphine (200 [micro sign]g/kg) administration and 15 min after reversal with 200 [micro sign]g naloxone given intravenously.

Results: In the control group, no changes in measured variables were found after either thoracic epidural saline or intravenous naloxone. Thoracic and lumbar epidural morphine both significantly reduced MAP, HR, CSNA, and RSNA 30 through 120 min after morphine administration (P < 0.05). These changes were reversed by intravenous naloxone. Changes after thoracic epidural morphine administration in vagotomized, baroreceptor-denervated cats were similar to those in intact cats. Intravenous morphine produced no significant changes except for a decrease in MAP, which was reversed by intravenous naloxone.     

Cysteine Conjugate beta-Lyase-Dependent Metabolism of Compound A (2-[fluoromethoxy]-1,1,3,3,3-pentafluoro-1-propene) in Human Subjects Anesthetized with Sevoflurane and in Rats Given Compound A

Background: Sevoflurane undergoes Baralyme- or soda lime-catalyzed degradation in the anesthesia circuit to yield compound A (2-[fluoromethoxy]-1,1,3,3,3-pentafluoro-1-propene), which is nephrotoxic in rats and undergoes metabolism via the cysteine conjugate beta-lyase pathway in those animals. The objective of these experiments was to test the hypothesis that compound A undergoes beta-lyase-dependent metabolism in humans.

Methods: Human volunteers were anesthetized with sevoflurane (1.25 minimum alveolar concentration, 3%, 2 l/min, 8 h) and thereby exposed to compound A. Urine was collected at 24-h intervals for 72 h after anesthesia. Rats, which served as a positive control, were given compound A intraperitoneally, and urine was collected for 24 h afterward. Human and rat urine samples were analyzed by19 F nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry for the presence of compound A metabolites.

Results: Analysis of human and rat urine showed the presence of the compound A metabolites [S-[2-(fluoromethoxy)-1,1,3,3,3-pentafluoropropyl]-N-acetyl-L-cysteine, (E)- and (Z)-S-[2-(fluoromethoxy)-1,3,3,3-tetrafluoro-1-propenyl]-N-acetyl-L-cyst eine, 2-(fluoromethoxy)-3,3,3-trifluoropropanoic acid, 3,3,3-trifluorolactic acid, and inorganic fluoride. The presence of 2-(fluoromethoxy)-3,3,3-trifluoropropanoic acid and 3,3,3-trifluorolactic acid in human urine was confirmed by gas chromatography-mass spectrometry.     

Pharmacokinetics of [Greek small letter epsilon]-aminocaproic Acid in Patients Undergoing Aortocoronary Bypass Surgery

Background: [Greek small letter epsilon]-Aminocaproic acid (EACA) is commonly infused during cardiac surgery using empiric dosing schemes. The authors developed a pharmacokinetic model for EACA elimination in surgical patients, tested whether adjustments for cardiopulmonary bypass (CPB) would improve the model, and then used the model to develop an EACA dosing schedule that would yield nearly constant EACA blood concentrations.

Methods: Consenting patients undergoing elective coronary artery surgery received one of two loading doses of EACA, 30 mg/kg (group I, n = 7) or 100 mg/kg (group II, n = 6) after CPB, or (group III) a 100 mg/kg loading dose before CPB and a 10 mg [middle dot] kg-1 [middle dot] h-1 maintenance infusion continued for 4 h during and after CPB (n = 7). Two patients with renal failure received EACA in the manner of group III. Blood concentrations of EACA, measured by high-performance liquid chromatography, were subjected to mixed-effects pharmacokinetic modeling.

Results: The EACA concentration data were best fit by a model with two compartments and corrections for CPB. The elimination rate constant k10 fell from 0.011 before CPB to 0.0006 during CPB, returning to 0.011 after CPB. V1 increased 3.8 l with CPB and remained at that value thereafter. Cl1 varied from 0.08 l/min before CPB to 0.007 l/min during CPB and 0.13 l/min after CPB. Cl2 increased from 0.09 l/min before CPB to 0.14 l/min during and after CPB. Two patients with renal failure demonstrated markedly reduced clearance. Using their model, the authors predict that an EACA loading infusion of 50 mg/kg given over 20 min and a maintenance infusion of 25 mg [middle dot] kg-1 [middle dot] h-1 would maintain a nearly constant target concentration of 260 [micro sign]g/ml.     

Acute Depression of Myocardial [Greek small letter beta]-Adrenergic Receptor Signaling during Cardiopulmonary Bypass: Impairment of the Adenylyl Cyclase Moiety

Background: Previously the authors showed that myocardial [Greek small letter beta]-adrenergic ([Greek small letter beta] AR) function is reduced after cardiopulmonary bypass (CPB) in a canine model. Whether CPB results in similar effects on [Greek small letter beta] AR function in adult humans is not known. Therefore the current study tested two hypotheses: (1) That myocardial [Greek small letter beta] AR signaling is reduced in adult humans after CPB, and (2) that administration of long-term preoperative [Greek small letter beta] AR antagonists prevent this process.

Methods: After they gave informed consent, 52 patients undergoing aortocoronary surgery were enrolled. Atrial biopsies were obtained before CPB and immediately before discontinuation of CPB. Plasma catecholamine concentrations, myocardial [Greek small letter beta] AR density, and functional responsiveness (basal, isoproterenol, zinterol, sodium fluoride, and manganese-stimulated adenylyl cyclase activity) were assessed.

Results: Catecholamine levels increased significantly during CPB (P < 0.005). Myocardial [Greek small letter beta] AR adenylyl cyclase coupling decreased during CPB, as evidenced by a 21% decrease in isoproterenol-stimulated adenylyl cyclase activity (750 [430] pmol cyclic adenosine monophosphate per milligram total protein 15 min before CPB compared with 540 [390] at the end of CPB, P = 0.0062, medians [interquartile range]) despite constant [Greek small letter beta] AR density. Differential activation along the [Greek small letter beta] AR signal transduction cascade localized the defect to the adenylyl cyclase moiety. Administration of long-term preoperative [Greek small letter beta] AR antagonists did not prevent acute CPB-induced myocardial [Greek small letter beta] AR dysfunction.     

[small beta, Greek]-Adrenergic Blockade Accelerates Conversion of Postoperative Supraventricular Tachyarrhythmias

Background: Postoperative supraventricular tachyarrhythmia is a common complication of surgery. Because chemical cardioversion is often ineffective, ventricular rate control remains a principal goal of therapy. The authors hypothesized that patients with supraventricular tachyarrhythmia after major noncardiac surgery who receive intravenous [small beta, Greek]-adrenergic blockade for ventricular rate control would experience conversion to sinus rhythm at a rate that differs from those receiving intravenous calcium channel blockade.

Methods: The rate of conversion to sinus rhythm at 2 and 12 h after treatment was examined in 64 cases of postoperative supraventricular tachyarrhythmia. After adenosine administration, patients who remained in supraventricular tachyarrhythmia were prospectively randomized to receive either intravenous diltiazem or intravenous esmolol for ventricular rate control (unblinded). Loading and infusion rates were adjusted to achieve equivalent degrees of ventricular rate control.

Results: Patients were similar with regard to age and Apache III score. Most patients in both groups had atrial fibrillation (esmolol, 79%; diltiazem, 81%), and none experienced stable conversion with adenosine. Patients randomized to receive esmolol experienced a 59% rate of conversion to sinus rhythm within 2 h of treatment, compared with only 33% for patients randomized to receive diltiazem (intention to treat, P = 0.049; odds ratio, 2.9; 95% confidence interval, 1.046 to 7.8). After 12 h of therapy, the number of patients converting to sinus rhythm increased in both groups (esmolol, 85%; diltiazem, 62%), and the rates of conversion no longer differed significantly. Ventricular rates when supraventricular tachyarrhythmia began and after 2 and 12 h of rate control therapy were similar in the two treatment groups. The in-hospital mortality rate and length of stay in the intensive care unit were not significantly influenced by treatment group.     

Specific Actions of Halothane, Isoflurane, and Desflurane on Sympathetic Activity and A [Greek small letter delta] and C Somatosympathetic Reflexes Recorded in Renal Nerves in Dogs

Background: This was a study of the relative effects on directly recorded sympathetic activity of desflurane, isoflurane, and halothane.

Methods: Renal sympathetic nerve activity (RSNA) was recorded with bipolar electrodes in renal nerves exposed retroperitoneally in anesthetized ([Greek small letter alpha]-chloralose), paralyzed (succinylcholine), and artificially ventilated dogs. Somatosympathetic responses were evoked by supramaximal electrical stimulation of radial nerves (0.33 Hz, 30 V, 0.5 ms). Spontaneous and evoked activity were rectified, averaged, and integrated to allow quantitative comparison of the effects of 3-12% desflurane, 0.6-2.4% isoflurane, and 0.4-1.6% halothane.

Results: Increasing concentrations of isoflurane progressively depressed mean RSNA, A [Greek small letter delta], and C reflexes by 40% (P < 0.01), 50% (P < 0.01) and 70% (P < 0.001) respectively at 2.4% concentration. Halothane depressed both reflexes equally by approximately 60% (P < 0.01) at 1.6% concentration, without significant depression of spontaneous RSNA. Desflurane increased and subsequently decreased RSNA by 37% (P < 0.02) and 65% (P < 0.001) at concentrations of 6% and 12% respectively, and although somatosympathetic reflexes remained unchanged up to 9%, both were depressed equally by 70% (P < 0.01) at 12% concentration.     

Direct Effects of [Greek small letter alpha]1- and [Greek small letter alpha]2-Adrenergic Agonists on Spinal and Cerebral Pial Vessels in Dogs

Background: The effects of adrenergic agonists, often used as local anesthetic additives or spinal analgesics, on spinal vessels have not been firmly established. The authors investigated the effects of [Greek small letter alpha]2- and [Greek small letter alpha]1-adrenergic agonists on spinal and cerebral pial vessels in vivo.

Methods: Pentobarbital-anesthetized dogs (n = 28) were prepared for measurement of spinal pial-vessel diameter in a spinal-window preparation. The authors applied dexmedetomidine, clonidine, phenylephrine, or epinephrine in three different concentrations (0.5, 5.0, and 50 [micro sign]g/ml; [2.1, 1.9, 2.5, and 2.3] x [10-6, 10-5, and 10-4] M, respectively) under the window (one drug in each dog) and measured spinal pial arteriolar and venular diameters in a sequential manner. To enable the comparison of their effects on cerebral vessels, the authors also administered these drugs under a cranial window.

Results: On topical administration, each drug constricted spinal pial arterioles in a concentration-dependent manner. Phenylephrine and epinephrine induced a significantly larger arteriolar constriction than dexmedetomidine or clonidine at 5 [micro sign]g/ml (8%, 11%, 0%, and 1%, respectively). Spinal pial venules tended to be less constricted than arterioles. In cerebral arterioles, greater constrictions were induced by dexmedetomidine and clonidine than those induced by phenylephrine and epinephrine (14%, 8%, 0%, and 1%, respectively). Cerebral pial venules tended to exhibit larger constrictions than cerebral arterioles (unlike in spinal vessels).     

Effects of Halothane and Isoflurane on [small beta, Greek]-adrenoceptor-mediated Responses in the Vascular Smooth Muscle of Rat Aorta

Background: Although previous studies have proposed that anesthetics may influence signal transduction systems, their effects on the [small beta, Greek]-adrenoceptor-mediated system have not been fully characterized in vascular smooth muscle. The aim of this study was to determine how halothane and isoflurane affect [small beta, Greek]-adrenoceptor-mediated vasodilation in rat aorta and what mechanisms were involved.

Methods: Isometric tension and the intracellular calcium ion concentration ([Ca2+]i) were measured concomitantly in rat aortic strips from which the endothelium was removed. Strips precontracted with norepinephrine were dilated with the [small beta, Greek]-adrenoceptor agonists, isoproterenol; the adenylyl cyclase activator, forskolin; or the membrane-permeable dibutyryl cyclic adenosine monophosphate (cAMP) with or without halothane or isoflurane. The effects of the anesthetics on each vasodilator were compared with the control responses. [small beta, Greek]-adrenoceptor binding characteristics and affinity for agonists were determined with [(125) I]-iodocyanopindolol with and without halothane or isoflurane. Furthermore, concentrations of cAMP induced by either isoproterenol or forskolin were measured with or without the anesthetics using an enzyme immunoassay procedure.

Results: Halothane and isoflurane attenuated vasodilation and [Ca2+]i decreases induced by isoproterenol, whereas both anesthetics only slightly affected vasodilation and [Ca2+]i decreases induced by forskolin and dibutyryl cAMP. Halothane and isoflurane had no effect on [small beta, Greek]-adrenoceptor binding characteristics and affinity for agonists. Three percent halothane or 4% isoflurane significantly reduced cAMP levels induced by isoproterenol but not by forskolin.     

Cysteine Conjugate beta-Lyase-dependent Biotransformation of the Cysteine S-Conjugates of the Sevoflurane Degradation Product Compound A in Human, Nonhuman Primate, and Rat Kidney Cytosol and Mitochondria

Background: 2-(Fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (compound A) is a fluorinated alkene formed by the degradation of sevoflurane in the anesthesia circuit. Compound A is toxic to the kidneys in rats and undergoes glutathione-dependent metabolism in vivo. Several nephrotoxic halogenated alkenes also undergo cysteine conjugate beta-lyase-dependent biotransformation. These experiments were designed to test the hypothesis that cysteine S-conjugates of compound A undergo beta-lyase-dependent biotransformation.

Methods: S-[2-(Fluoromethoxy)-1,1,3,3,3-pentafluoropropyl]-L-cysteine 4, S-[2-(fluoromethoxy)-1,3,3,3-tetrafluoro-1-propenyl]-L-cysteine 5, and S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine 11 were incubated with rat, human, and nonhuman primate (cynomolgus, rhesus, and marmoset) kidney cytosol and mitochondria. Beta-Lyase activity was determined by measuring pyruvate formation.

Results: Compound A-derived conjugates 4 and 5 as well as conjugate 11, a positive control, were substrates for cytosolic and mitochondrial beta-lyase from human, nonhuman primate, and rat kidney. For all substrates, beta-lyase activity was highest in the rat and lowest in the human and was higher in cytosol than in mitochondria. Conjugate 11 was a much better substrate than conjugates 4 or 5. The biotransformation of conjugates 4, 5, and 11 was inhibited by the beta-lyase inhibitor (aminooxy)acetic acid and was stimulated by the amino group acceptor 2-keto-4-methylthiolbutyric acid, indicating a role for beta-lyase.     

Stereoselective Interaction of Ketamine with Recombinant [micro sign], [small kappa, Greek], and [small delta, Greek] Opioid Receptors Expressed in Chinese Hamster Ovary Cells

Background: The authors examined the interaction of ketamine with recombinant [micro sign], [small kappa, Greek], and [small delta, Greek] opioid receptors and recombinant orphan opioid receptors expressed in Chinese hamster ovary cells (CHO-[micro sign], CHO-[Greek small letter kappa, CHO-[small delta, Greek], and CHOORL1, respectively).

Methods: CHO-[micro sign], CHO-[small kappa, Greek], and CHO-[small delta, Greek] membranes were incubated with the opioid receptor radioligand [(3) H] diprenorphine at room temperature. Ketamine (racemic, R(-) and S(+)) was included at concentrations covering the clinical range. CHOORL1 membranes were incubated with [(125) I]Tyr14 nociceptin and racemic ketamine at room temperature. The effects of racemic ketamine and selective opioid receptor agonists ([micro sign] [D-Ala2, MePhe4, Gly(ol)5] enkephalin (DAMGO); [Greek small letter kappa spiradoline or [small delta, Greek]: [D-pen2, D-pen5] enkephalin (DPDPE)) on forskolin-stimulated cyclic adenosine monophosphate formation also were examined. Data are mean +/- SEM.

Results: Racemic ketamine increased the radioligand equilibrium dissociation constant for [(3) H]diprenorphine from 85 +/- 5 to 273 +/- 11, 91 +/- 6 to 154 +/- 16, and 372 +/- 15 to 855 +/- 42 pM in CHO-[micro sign], CHO-[small kappa, Greek], AND CHO-[small delta, Greek], respectively, The concentration of radioligand bound at saturation was unaffected. In CHO-[micro sign] and CHO-[small kappa, Greek], cells, racemic, ketamine did not slow the rate of naloxone-induced [(3) H]diprenorphine dissociation. Ketamine and its isomers also displaced [(3) H]diprenorphine binding to [micro sign], [small kappa, Greek], and [small delta, Greek] receptors in a dose-dependent manner, with pKi values for racemic ketamine of 4.38 +/- 0.02, 4.55 +/- 0.04, and 3.57 +/- 0.02, respectively. S(+)-ketamine was two to three times more potent than R(-)-ketamine at [micro sign] and [small kappa, Greek] receptors. Racemic ketamine displaced [(125) I]Tyr14 nociceptin with an estimated affinity constant of 0.5 mM. Racemic ketamine inhibited the formation of cyclic adenosine monophosphate (naloxone insensitive) in a dose-dependent manner (concentration producing 50% inhibition [tilde operator] 2 mm) in all cell lines, including untransfected CHO cells. Ketamine (100 [micro sign]M) reversed DAMGO ([micro sign]) and spiradoline ([small kappa, Greek]) inhibition of formation of cyclic adenosine monophosphate.     

Influence of Sevoflurane on the Metabolism and Renal Effects of Compound A in Rats

Background: The sevoflurane degradation product compound A is nephrotoxic in rats. In contrast, patient exposure to compound A during sevoflurane anesthesia has no clinically significant renal effects. The mechanism for this difference is incompletely understood. One possibility is that the metabolism and toxicity of compound A in humans is prevented by sevoflurane. However, the effect of sevoflurane on compound A metabolism and nephrotoxicity is unknown. Thus, the purpose of this investigation was to determine the effect of sevoflurane on the metabolism and renal toxicity of compound A in rats.

Methods: Male rats received 0.25 mmol/kg intraperitoneal compound A, alone and during sevoflurane anesthesia (3%, 1.3 minimum alveolar concentration, for 3 h). Compound A metabolites in urine were quantified, and renal function was evaluated by serum creatinine and urea nitrogen, urine volume, osmolality, protein excretion, and renal tubular histology.

Results: Sevoflurane coadministration with compound A inhibited compound A defluorination while increasing relative metabolism through pathways of sulfoxidation and [beta]-lyase-catalyzed metabolism, which mediate toxicity. Sevoflurane coadministration with compound A increased some (serum creatinine and urea nitrogen, and necrosis) but not other (urine volume, osmolality, and protein excretion) indices of renal toxicity.     

A Role for Erythropoietin in the Attenuation of Radiocontrast-Induced Acute Renal Failure in Rats

Background. Radiocontrast-induced nephropathy (CIN) remains an important iatrogenic cause of acute renal failure in high-risk patients, despite the development of safer contrast media, the improvement of hydration protocols, and the introduction of additional preventive strategies. Erythropoietin (EPO) pretreatment may confer protection against acute renal failure through the induction of stress response genes. Methods. The effect of EPO has been evaluated in a rat model of CIN, induced by iothalamate, following the inhibition of nitric oxide- and prostaglandin-synthesis with indomethacin and N^ω nitro-L-arginine methyl ester (L-NAME). Twenty-two male Sprague-Dawley rats were subjected to saline (CTR) or EPO injections (3000 U/kg and 600 U/kg, 24 and 2 h before the induction of CIN, respectively). Results. The decline in creatinine clearance in CTR animals from 0.38 ± 0.03 to 0.28 ± 0.03 mL/min/100 g (p < 0.005), was prevented by EPO pretreatment (from 0.34 ± 0.02 to 0.32 ± 0.03 mL/min/100 g, NS). The extent of medullary thick ascending limb- and S3-tubular damage in the outer medulla, however, was comparable in the two experimental groups. Conclusions. EPO pretreatment prevents renal dysfunction in a rat model of CIN. Further experimental and clinical studies are required to confirm these preliminary conclusions regarding a potential protective potency of EPO against CIN.     

The Effect of Prophylactic [Greek small letter epsilon]-Aminocaproic Acid on Bleeding, Transfusions, Platelet Function, and Fibrinolysis during Coronary Artery Bypass Grafting

Background: Antifibrinolytic medications administered before skin incision decrease bleeding after cardiac surgery. Numerous case reports indicate thrombus formation with administration of [Greek small letter epsilon]-aminocaproic acid ([Greek small letter epsilon]-ACA). The purpose of this study was to examine the efficacy of [Greek small letter epsilon]-ACA administered after heparinization but before cardiopulmonary bypass in reducing bleeding and transfusion requirements after primary coronary artery bypass surgery.

Methods: Seventy-four adult patients undergoing primary coronary artery bypass surgery were randomized to receive 125 mg/kg [Greek small letter epsilon]-ACA followed by an infusion of 12.5 mg [middle dot] kg-1 [middle dot] h-1 or an equivalent volume of saline. Coagulation studies, thromboelastography, and platelet aggregation tests were performed preoperatively, after bypass, and on the first postoperative day. Mediastinal drainage was recorded during the 24 h after surgery. Homologous blood transfusion triggers were predefined and transfusion amounts were recorded.

Results: One patient was excluded for surgical bleeding and five patients were excluded for transfusion against predefined criteria. One patient died from a dysrhythmia 2 h postoperatively. Among the remaining 67, the [Greek small letter epsilon]-ACA group had less mediastinal blood loss during the 24 h after surgery, 529 +/- 241 ml versus 691 +/- 286 ml (mean +/- SD), P < 0.05, despite longer cardiopulmonary bypass times and lower platelet counts, P < 0.05. Platelet aggregation was reduced in both groups following cardiopulmonary bypass but did not differ between groups. Homologous blood transfusion was similar between both groups.     

Chronic Desipramine Treatment Desensitizes the Rat to Anesthetic and Antinociceptive Effects of the [Greek small letter alpha]2-adrenergic Agonist Dexmedetomidine

Introduction: The effects of long-term administration of the tricyclic antidepressant agent desipramine on the hypnotic, antinociceptive, anesthetic-sparing, and central norepinephrine turnover suppressant action of short-term dexmedetomidine, a highly selective [Greek small letter alpha]2-adrenergic agonist, were studied in rats.

Methods: Rats were given a 3- or 4-week course of twice daily administration of desipramine, 10 mg/kg, or saline. The effect of a hypnotic dose of dexmedetomidine, 250 [micro sign]g/kg given intraperitoneally, on the duration of loss of righting reflex was determined. The tail flick latency response was determined before and after 50 [micro sign]g/kg dexmedetomidine. The minimum anesthetic concentration of halothane and the central norepinephrine turnover rate were determined before and after administration of 30 [micro sign]g/kg dexmedetomidine. Changes in the affinity and density of the [Greek small letter alpha]2-adrenergic receptor in locus coeruleus and spinal cord also were determined.

Results: Treatment with desipramine decreased dexmedetomidine-induced loss of righting reflex duration by 67% and eliminated the antinociceptive effect of dexmedetomidine. Dexmedetomidine produced a 55% decrease in minimum anesthetic concentration in the control group but no reduction in desipramine-treated rats. Desipramine did not change the receptor density or binding affinity of [Greek small letter alpha]2 receptors at the site for hypnotic (locus coeruleus) or antinociceptive (spinal cord) responses. No decrement in the central norepinephrine turnover rate was noted in the locus coeruleus of dexmedetomidine after 3 weeks of treatment with desipramine. The [Greek small letter alpha]1-adrenergic antagonist prazosin at 1 or 5 mg/kg completely (minimum anesthetic concentration reduction), almost completely (antinociceptive), or partially (hypnotic) restored responsiveness to normal.