Mechanisms underlying cerebrovascular effects of cigarette smoking in rats in vivo

BACKGROUND AND PURPOSE

The effects of acute smoking on cerebral circulation are controversial. This study was designed (1) to clarify any differences between the effects of cigarette smoking and nicotine infusion and between the effects of single- and multiple-cigarette smoking on cerebral vessels and (2) to probe the mechanism(s) underlying the vascular responses.

METHODS

In pentobarbital-anesthetized, mechanically ventilated Sprague-Dawley rats, pial vessel diameters were measured with the use of a cranial window preparation. We studied the effects of (1) 60 puffs per minute of mainstream cigarette smoke from cigarettes having 2 nicotine levels (0.1 and 1 mg per cigarette), (2) administration of nicotine (0.05 mg per body IV), and (3) repeated smoking (four 1 mg nicotine-containing cigarettes at 30-minute intervals) (n=6 each).

RESULTS

Inhalation of smoke from a 0.1 or 1 mg nicotine-containing cigarette for 1 minute caused pial arterioles to constrict at 30 seconds (7.2% and 7.3%, respectively) and then to dilate (peak at 5 to 10 minutes; 4.6% and 17.9%, respectively). Nicotine infusion caused pial vasodilation (35.7%) without an initial vasoconstriction. Repeated smoking suppressed the pial vasodilation but not the initial vasoconstriction. The vasodilation induced by a single cigarette was greatly inhibited by pretreatment with mecamylamine or glibenclamide and attenuated by propranolol or Nomega-nitro-L-arginine methyl ester; the initial vasoconstriction was inhibited by seratrodast, a thromboxane A2 receptor antagonist (n=6 in each case).

CONCLUSIONS

Single-cigarette smoking had a significant biphasic effect on cerebral arteriolar tone. The vasodilation was attenuated by repeated smoking. The vasodilation is most likely an effect of nicotine, at least in part mediated via sympathetic activation, NO production, and K+ channel activation. The vasoconstriction is partially due to thromboxane A2 induced by cigarette smoke.

[Comparison of pulse dye densitometry and thermodilution method in cardiac output measurement]

We measured cardiac outputs at forty points from five patients by pulse dye densitometry and compared these with those measured by thermodilution method. We obtained a good correlation (y = 1.090 x = . 0.030, n = 40, 5 cases) and small mean bias (0.348 +/- 0.830 l.min-1, n = 40, 5 cases) between the two methods. We suggest that this method of cardiac output measurement by pulse dye densitometry is not invasive and may be more effective than that by thermodilution method.

[Anaphylactic shock associated with a central venous catheter impregnated with chlorhexidine and silver sulfadiazine]

A 28 year-old male patient developed anaphylactic shock on separate occasions, possibly due to the contact with a central venous catheter impregnated with chlorhexidine and silver sulfadiazine. He was successfully resuscitated. On the second operation, blood basophils disappeared and plasma histamine level increased extremely up to 80 ng.ml-1 soon after anaphylactic shock. One year after the first shock, he did not develop anaphylactic shock following the insertion of a central venous catheter without the impregnation. Pin prick test and scratch test showed positive reactions only to chlorhexidine. Latex-specific anti-IgE antibody was not detected. Therefore, chlorhexidine was confirmed as the causative agent of anaphylactic shock. Because chlorhexidine is extensively used as an antiseptic drug in emergency rooms and intensive care units, we should be aware of the possibility of chlorhexidine induced anaphylactic reactions.

The optimal test dose of epinephrine for epidural injection with lidocaine solution in awake patients premedicated with oral clonidine

We attempted to determine the optimal test dose of epinephrine for use with epidural anesthesia in awake patients premedicated with clonidine. Eighty-eight adult patients were randomized into two groups [oral premedication with clonidine 5 microg/kg (CLON) or no premedication (CONT)]. Before induction of general anesthesia, heart rate (HR) and blood pressure (BP) were measured for 3 min after the i.v. injection of 3 mL of 1.5% lidocaine containing epinephrine (0, 1.25, 2.5, 5, 7.5, or 15 microg) in a randomized, double-blind manner. We calculated 95% confidence intervals for the peak HR and BP increases induced by each dose of epinephrine. At 7.5 microg, epinephrine induced a significantly greater increase in HR and BP in CLON than in CONT. The 95% confidence interval for the HR change induced by 7.5 microg of epinephrine in CLON was nearly the same as the accepted standard dose of epinephrine (15 microg) in CONT. We conclude that premedication with clonidine enhances HR and BP responses to the i.v. administration of epinephrine-containing epidural test solutions. Consequently, 7.5 microg of epinephrine may be sufficient to enable detection of accidental injection into a blood vessel in awake patients premedicated with clonidine 5 microg/kg.

IMPLICATIONS

Clonidine, a commonly used preanesthetic medication, alters patients' cardiovascular responses to drugs such as epinephrine. Our randomized, double-blind study suggests that, in awake patients receiving oral clonidine premedication, 7.5 microg of epinephrine (half the usual dose) is adequate as an indicator of accidental injection into the epidural vessels during epidural anesthesia.

The vascular effects of topical and intravenous alpha2-adrenoceptor agonist clonidine on canine pial microcirculation

To assess the direct cerebrovascular effects of clonidine, we investigated the pharmacological responses of pial vessels to its topical and i.v. administration using a cranial window. Forty-six dogs anesthetized with pentobarbital had the cranial window implanted. We administered six different concentrations of clonidine (10(-8), 10(-7), 10(-6), 10(-5), 10(-4), 10(-3) mol/L) dissolved in artificial cerebrospinal fluid under the window and measured the pial arterial and venous diameters. After pretreating pial vessels with either yohimbine, an alpha2-adrenoceptor antagonist, or glibenclamide, an adenosine triphosphate-sensitive K+-channel blocker, their action was examined after applying clonidine. We also evaluated the effects of i.v. clonidine (5 microg/kg) on pial vascular tone. Topical clonidine produced significant constriction of the pial large and small arteries and veins in a concentration-dependent manner (P < 0.05). Yohimbine abolished the clonidine-induced pial arterial (large P < 0.005; small P < 0.0005) and venous constriction (large and small P < 0.0001). Glibenclamide potentiated the clonidine-induced pial arterial constriction (P < 0.05). I.v. clonidine did not cause significant changes in pial arteries, but it caused significant constriction of small veins. These were associated with a significant decrease in heart rate and an increase in serum potassium level and glucose concentration. In the present study, we demonstrate that the topical application of clonidine constricts both pial arterial and venous vessels in a concentration-dependent manner and suggest that mechanisms of such action are caused by the activation of alpha2-adrenoceptors and adenosine triphosphate-sensitive K+-channels, whereas i.v. clonidine constricts only pial small veins.

IMPLICATIONS

In this study, we describe the direct and i.v. effects of clonidine on pial vessels using a cranial window in anesthetized dogs. The topical application of clonidine constricts pial vessels. This is mediated by the activation of alpha2-adrenoceptors and adenosine triphosphate-sensitive K+-channels. I.v. clonidine constricts only pial small veins.

[Two elderly patients with thoracic herpetic pain and post herpetic neuralgia treated with continuous thoracic sympathetic ganglion block through a placed catheter]

Epidural block is very useful in the treatment of herpetic pain and post herpetic neuralgia. However, in the elderly patients with cardiac disease or diabetes mellitus, severe cardiovascular changes may occur by epidural block. Epidural block caused severe hypotension in two elderly patients with herpetic pain and post herpetic neuralgia who had diabetes mellitus or hypertension. Continuous thoracic sympathetic ganglion block with local anesthetics through a placed catheter reduced their pain and caused almost no changes in cardiovascular system.

[Cerebral oxygen saturation and hemoglobin index under separate brain perfusion]

We monitored bilateral cerebral oxygen saturation and hemoglobin index while the brain received separate perfusion for major vascular surgery. Before surgery, left cerebral oxygen saturation and hemoglobin index were within normal limits but right cerebral oxygen saturation and right hemoglobin index were low. At the end of surgery, right cerebral oxygen saturation was elevated and almost equal to left cerebral oxygen saturation, and right hemoglobin index was elevated too but slightly lower than left hemoglobin index. We found that oxygen delivery to the right cerebral hemisphere improved in comparison with presurgical period. No paralysis or any other neurological complications occurred postoperatively. We conclude that such monitoring is useful during and after anesthesia under separate brain perfusion.

Inhibitory effects of propofol on intracellular signaling by endothelin-1 in aortic smooth muscle cells

BACKGROUND

Blood pressure decreases when propofol is administered. However, the exact mechanism underlying the vascular effects of propofol has not yet been elucidated. Endothelin produced by vascular endothelial cells is a potent vasoactive peptide that elicits prolonged contraction of vascular smooth muscle cells. The effects of propofol on endothelin-1-induced intracellular signaling in an aortic smooth muscle cell line, A10 cells, were examined.

METHODS

Cultured A10 cells were pretreated with propofol for 20 min and then stimulated with endothelin-1. The effect of propofol on the endothelin-1-induced Ca2+ influx into A10 cells was evaluated by measuring intracellular 45Ca2+. The effects of propofol on the endothelin-1-induced activation of phosphatidylinositol-hydrolyzing phospholipase C and phosphatidylcholine-hydrolyzing phospholipase D were evaluated by measuring the formation of inositol phosphates and choline, respectively. The effect of propofol on endothelin-1 binding to its receptor was determined by an [125I] endothelin-1-binding assay.

RESULTS

Propofol inhibited the endothelin-1-induced Ca2+ influx, but this was significant only at supuraclinical concentrations. The endothelin-1-stimulated formation of inositol phosphates was significantly suppressed by propofol. However, propofol had no effect on the formation of inositol phosphates induced by NaF, an activator of heterotrimeric guanosine triphosphate (GTP)-binding proteins. Propofol inhibited the endothelin-1-induced formation of choline. Propofol had no effect on the binding of endothelin-1 to its receptor.

CONCLUSIONS

These results suggest that propofol inhibits endothelin-1-induced intracellular signaling in vascular smooth muscle cells. The inhibitory effect of propofol might be exerted at a point between the endothelin-1 receptor and its GTP-binding protein. However, because all significant effects are observed at high concentrations, clinical relevance is unclear.

[Effects of nicorandil on regional cerebral oxygen saturation]

Nicorandil is usually considered to be a potent antianginal agent characterized as a potassium channel opener. It has been suggested that it may exert similar action on cerebral vessels. We administered nicorandil to surgical patients under general anesthesia. While the regional cerebral oxygen saturation (rSO2) and blood volume index (BVI) were determined continuously, each patient received the drug at dose of 0.08 mg.kg-1.h-1 initially, and after 15 minutes, the dose was increased by 0.08 mg.kg-1.h-1 at a time. This was repeated until the dose reached 0.40 mg.kg-1.h-1. At every dose level, rSO2 and BVI were determined, and the dose-response relationship was obtained. We found that nicorandil also produces cerebral arterial dilation under clinical conditions.

[Hemodynamic effects of continuous epidural infusion with local anesthetics]

Epidural blockade with local anesthetic may cause hypotension resulting from sympathetic block and/or systemic effect produced by absorbed local anesthetic through epidural blood vessels. In the present study, we compared the hemodynamic effects of saline 0.5 ml.h-1, lidocaine 0.5 ml.h-1, bupivacaine 0.5 ml.h-1, lidocaine 2 ml.h-1, and bupivacaine 2 ml.h-1, which were given epidurally combined with morphine. There was not significant difference in hemodynamics among 5 groups. Continuous epidural infusion with a small dose of local anesthetic agent combined with morphine is unlikely to induce apparent hemodynamic effects during postoperative period.

Alteration of redox state of human serum albumin in patients under anesthesia and invasive surgery

Human serum albumin is a mixture of mercapt- (HMA, reduced form) and nonmercaptalbumin (HNA, oxidized form). We studied the mercapt<-->nonmercapt conversion of human serum albumin, which reflects the redox state of the extracellular fluids, in cardiac and other common surgical_ patients using high-performance liquid chromatography. Mean values of [(HMA)/(HMA+HNA)]+/-standard deviation, fHMA+/-sigma], for patients who received common surgery (group 1) and cardiac surgery (group 2) at the start of anesthesia were 0.636+/-0.050 (n = 83) and 0.615+/-0.062 (n = 14), respectively. fHMA values were markedly lower than those for healthy male adults of 0.750+/-0.028 (n = 28). fHMA values increased at 24 h after the start of anesthesia and decreased on the 4th postoperative day in most of the patients. These postoperative changes were prominent in cardiac surgical patients. Although fHMA values after the 7th postoperative day recovered to those at the start of anesthesia in almost all of common surgical patients, those in cardiac surgical patients never recovered even on the 21st postoperative day.

Effects of blood glucose changes and physostigmine on anesthetic requirements of halothane in rats

BACKGROUND

Although hyper- and hypoglycemia induce neurophysiologic changes, there have been no reports on the effects of blood glucose changes on anesthetic requirements. This study examined the effects of hyper- and hypoglycemia on the minimum alveolar concentration (MAC) of halothane in rats. In addition, based on a previous finding that the level of brain acetylcholine was reduced during mild hypoglycemia, the authors examined the influence of physostigmine on MAC during hypoglycemia.

METHODS

In Sprague-Dawley rats, anesthesia was induced and maintained with halothane in oxygen and air. The MAC was determined by observing the response to tail clamping and tested during mild hypoglycemia (blood glucose level, 60 mg/dl) and hyperglycemia (blood glucose level, 300 and 500 mg/dl) induced by insulin and glucose infusion, respectively (experiment 1). The effects of 0.3 and 1.0 mg/kg physostigmine given intraperitoneally on MAC were examined in rats with mild and severe hypoglycemia (blood glucose level, 60 and 30 mg/dl; experiment 2).

RESULTS

In experiment 1, mild hypoglycemia significantly reduced the MAC of halothane (0.76 +/- 0.03%) compared with the control value (0.92 +/- 0.04%), but hyperglycemia did not change MAC. In experiment 2, mild and severe hypoglycemia reduced MAC of halothane in a degree-dependent manner. Physostigmine (1 mg/kg) had no effect on MAC regardless of blood glucose level, but 0.3 mg/kg reduced MAC.

CONCLUSIONS

Hypoglycemia reduced anesthetic requirements in a degree-dependent manner, whereas hyperglycemia had no effects. Although the mechanism of hypoglycemic MAC reduction needs further investigations, physostigmine studies suggest that this may not be related to inhibition of cholinergic transmission.

Non-GABAergic effects of midazolam, diazepam and flumazenil on voltage-dependent ion currents in NG108-15 cells

Non-gamma-Aminobutyric acid (GABA)-mediated effects of benzodiazepines (BZs) have not been widely investigated. However, there is significant evidence in the literature to suggest that several experimental and clinical observations are inconsistent with the commonly accepted GABAergic mechanisms of action for these drugs. The purpose of the present study was to explore electrophysiological effects of midazolam, diazepam and a specific BZ antagonist, flumazenil, using patch-clamp techniques in NG108-15 cells which do not express the GABAA receptor. Midazolam and diazepam decreased Na+, K+ and Ca2+ currents in a dose-related manner. Ca2+ currents were reduced more significantly by diazepam than by midazolam. Flumazenil showed no effects on voltage-dependent ion currents. GABA by itself showed neither effects on the membrane potential nor these ion currents. Midazolam and diazepam, but not flumazenil, exhibited effects on voltage-dependent ion currents in cultured neurons.

Spinal conduction block by intrathecal ketamine in dogs

In addition to its use for intravenous (I.V.) anesthesia, ketamine can provide pain relief in humans when administered spinally. To elucidate the mechanisms of intrathecal (I.T.) ketamine analgesia, we observed differences in the effects of I.V. and I.T. ketamine on intraspinal evoked potentials (ISEPs) in 28 dogs anesthetized with pentobarbital. Bipolar extradural electrodes were inserted at the cervical and lumbar regions of the spinal cord for recording descending ISEPs represented by the two negative deflections, Waves I and II. I.V. ketamine 2 and 10 mg/ kg did not affect the amplitude and latency of Wave I, whereas the large dose (10 mg/kg) significantly decreased the amplitude but not the latency of Wave II. I.T. ketamine 1 and 5 mg/kg caused significant dose-dependent decreases in both Wave I and II amplitudes and prolongations of both Wave I and II latencies. These I.T. effects on ISEPs are consistent with previous in vitro observations that ketamine blocks axonal conduction. We conclude that axonal conduction block may contribute to the analgesic mechanism of I.T. ketamine.

The effects of topical and intravenous ropivacaine on canine pial microcirculation

To assess the direct cerebrovascular effects of ropivacaine, we studied pharmacological responses to its topical and intravenous (IV) administration on vasomotor tone of pial vessels in in vivo experiments using a parietal cranial window in 24 dogs anesthetized with pentobarbital. We directly measured the diameters of pial arteries and veins after the administration of five different concentrations of ropivacaine solution (10(-7) to 10(-3) mol/L) randomly given into the window (n = 10). In six dogs, after pretreating the pial vessels with yohimbine (10(-5) mol/L), the inhibitory action of yohimbine was examined after the application of ropivacaine (10(-3) mol/L). The effects of IV ropivacaine (1 and 4 mg/kg) were also evaluated in the remaining eight dogs. Ropivacaine produced significant constriction of the pial arteries in a concentration-dependent manner (10(-7) to 10(-3) mol/L, P < 0.05) and only exerted a constrictive action on small veins (P < 0.05) at 10(-3) mol/L. Yohimbine had no effect on ropivacaine-induced constriction of pial vessels. IV ropivacaine, 4 mg/kg but not 1 mg/kg, caused pial vascular constriction (large arteries P < 0.005, small arteries P < 0.0001, large veins P < 0.01, small veins P < 0.005) associated with decrease in heart rate (P < 0.001). The results indicate that topical application of ropivacaine constricts pial arterial vessels in a concentration-dependent manner. A large dose of IV ropivacaine produced pial vasoconstriction associated with a decrease in heart rate and no decrease in mean arterial blood pressure. These effects do not appear to be mediated via the mechanism that depends on the activation of alpha2-adrenoceptors. We conclude that ropivacaine in high concentrations could, perhaps directly, cause significant constriction of the central nervous system vasculature.

Direct effects of ropivacaine and bupivacaine on spinal pial vessels in canine. Assessment with closed spinal window technique

BACKGROUND

Ropivacaine produces a vasoconstriction of cutaneous vessels in contrast to vasodilation produced by bupivacaine. To evaluate direct spinal microvascular actions of these local anesthetics, the authors investigated the concentration-related effects of ropivacaine and bupivacaine on spinal pial vascular diameters using the spinal window technique.

METHODS

Anesthetized dogs (n = 14) divided into two groups (ropivacaine, n = 7; bupivacaine, n = 7) were prepared for measurement of spinal pial vessel diameters by intravital microscopy in a spinal window preparation. The authors administered six concentrations of each drug (10(-8)-10(-3) M) under the window and directly measured the spinal pial arteriolar and venular diameters at sequential times. Physiologic data including mean arterial blood pressure (MAP) and heart rate (HR) were determined before and after topical application of each concentration of the drugs. In additional experiments (n = 18), the action of topical ropivacaine and bupivacaine solution on spinal vessels was evaluated in the presence of yohimbine, prazosin, and propranolol.

RESULTS

Ropivacaine significantly constricted whereas bupivacaine dilated pial arterioles and venules, both in a concentration-dependent manner. Microvascular alteration was not blocked with any of the adrenoceptor antagonists tested (yohimbine, prazosin, propranolol), each of which per se did not affect pial vessel diameters. Topical application of ropivacaine or bupivacaine did not induce any change in MAP or HR.

CONCLUSIONS

The present results indicate that ropivacaine constricts and bupivacaine dilates the pial vessels of the spinal cord in a concentration-dependent fashion, and the mechanisms involved in such actions do not seem to be mediated via alpha- or beta-adrenoceptor of spinal vasculature.

[Changes in alpha 2-adrenoceptor binding nature in guinea-pig brain following the development of morphine dependence]

We examined the effect of morphine dependence on alpha 2-adrenoceptors in guinea-pig brain. We also studied the influence of clonidine on the naloxone-induced withdrawal signs. 1. Guinea-pigs were implanted subcutaneously with MS contin (300 mg.kg-1). Two days after implantation, the binding of 3H-UK14304 (alpha 2 selective ligand) to brain membranes prepared from morphine dependent and control animals was determined. Scatchard plot of the saturation binding data revealed an increase in Bmax values and no change in the Kd values from dependent animals. These results indicate that brain alpha 2-adrenoceptors are up-regulated in morphine dependent guinea pigs. 2. Subcutaneous injection of naloxone on the 2 nd day after implantation caused characteristic withdrawal symptoms. Clonidine has been shown to reduce some opiate withdrawal signs in morphine-dependent animals.

[Changes in opioid receptor binding nature in rat brain and spinal cord following formalin or carrageenan-induced nociception]

Previous reports demonstrated the regulation of opioid and their receptor in nociception, but it is not clear how nociceptive activation may alter opioid receptor binding nature. We determined the change of mu, delta and kappa opioid receptor types in brain and spinal cord homogenates obtained from animal models receiving nociceptive treatment. 1) Rats received a subcutaneous injection of formalin and carrageenan into planter aspect of a hindpaw. These agent-injected animals were observed for appearance of pain-related behavior (guarding of the treated paw) within 2-3 hour after treatment. Following these pain behavior, rats were decapitated and brain and spinal cord were removed rapidly. 2) The binding of 3H-DAGO (mu agonist), 3H-DPDPE (delta agonist) and 3H-EKC (kappa agonist) to brain and spinal cord membranes prepared from nociceptive treatment and control rats was determined. Using these tracer 3H-opioid ligands, we failed to see any change in the total number of opioid binding sites (Bmax values) or the affinity constant (Kd values) for binding in whole brain and spinal cord. These results indicate that in these animal models which use experimentally induced inflammation to stimulate a condition of nociception, there appears to be no alteration in the levels of mu, delta or kappa binding sites.

[Bronchospasm due to anaphylactic reaction to Hydroxyethyl starch (HESPANDER)]

A 14-year-old male without any history of allergic disorders developed severe bronchospasm with skin rash 15 min. after the administration of hydroxyethyl starch (HES) during thoratic epidural anesthesia supplemented with N2O-sevoflurane-O2 anesthesia. Aminophylline, hydrocortisone, and epinephrine were administered. These treatments were effective, and the airway pressure was restored to normal ranges within 3 hrs. After the operation, the patient was extubated, because the results of the arterial blood gas examinations recovered to normal ranges. Plasma histamine and complement levels were almost within normal limits, but IgE levels were approximately 5 times higher than normal. Subsequent immediate skin test with hydroxyethyl starch showed an immunologically positive response. These results demonstrate evidence that an anaphylactic reactions could occur just after the start of HES infusion. Severe adverse reactions to HES are very rare, but it is important to keep the possibility always in mind.

New immunodeficient (nude-scid, beige-scid) mice as excellent recipients of human skin grafts containing intraepidermal neoplasms

Engraftment of normal or lesional human skin onto nude or SCID (severe combined immunodeficiency) mice has been used as an in vivo experimental model. However, this model has some limitations, such as shrinkage and loss of the grafted skin over time. To improve the experimental model, we have produced two new SCID-lineage mouse strains, BALB/cA-nude-scid (nu/nu, scid/scid) and BALB/cA-beige-scid (bg/bg, scid/scid) mice, by the method of cross intercross. Intraepidermal neoplastic lesions such as Bowen's disease were grafted onto the back of the mice of these strains. The rate of reduction in the size of the grafts was lower on nude-scid and beige-scid mice than on SCID mice. Rates of survival of neoplastic cells in the grafts were higher in nude-scid mice than in SCID and beige-scid mice (SCID mice 38%, nude-scid mice 55%, beige-scid mice 38%). Neoplastic cells of Bowen's disease grafted onto a beige-scid mouse proliferated and invaded the dermis during 233 days of observation, confirming the progression to invasive squamous cell carcinoma from carcinoma in situ. The present study revealed that nude-scid and beige-scide mice newly produced by us provide a very useful in vivo experimental model for the investigation of carcinogenesis and tumor progression in human skin.

[A case of leukocytosis after massive blood transfusion for postpartum hemorrhagic shock]

We experienced the perioperative management of a hemorrhagic shock associated with postpartum uterine rupture. After the emergency abdominal total hysterectomy, massive blood transfusion was required to maintain the hemodynamics and the laparotomy for hemostasis was performed on the 1st, 2nd and 7th ICU day. Total amount of transfused blood products was 37,000 ml during one week. The patient immediately developed DIC and acute renal failure. Laboratory data showed increased leukocyte count (the peak value was 56,100 microliters-1 on the 12th ICU day), and neutrophilic fraction was more than 90% of leucocyte. After the decrease in CRP, the decrease in total bilirubin concentration was delayed. There were no other signs of infection and no remarkable change in MOF score. There was a discrepancy between this leukocytosis and the severity of organ dysfunction, and the cause of the leukocytosis was unknown.

The effects of bupivacaine and ropivacaine on baroreflex sensitivity with or without respiratory acidosis and alkalosis in rats

Systemic toxicity of local anesthetics causes cardiac and central nervous system (CNS) depression that could be enhanced in the presence of respiratory acidosis. We examined a potential suppression of baroreflex function with bupivacaine and ropivacaine during hypercapnic acidosis or hypocapnic alkalosis. Baroreflex sensitivity (BRS) was randomly tested in rats with one of 13 conditions during intravenous administration of saline (control), bupivacaine 1, 2, or 3 mg/kg, or ropivacaine 2, 4, or 6 mg/kg. The effects of bupivacaine (3 mg/kg) or ropivacaine (6 mg/kg) on BRS were also examined during hypercapnic acidosis or hypocapnic alkalosis. The BRS was assessed using a value of delta heart rate/ delta mean arterial pressure after infusion of phenylephrine (3 micrograms/kg). Both bupivacaine and ropivacaine (at the largest dose) significantly suppressed BRS. Acute respiratory acidosis (pHa 7.24 +/- 0.04, Paco2 63 +/- 4 mm Hg) enhanced BRS. The BRS enhanced during acidosis was also suppressed with bupivacaine and ropivacaine, but less so than in the absence of acidosis. The presence of hypocapnic alkalosis (pHa 7.55 +/- 0.03, Paco2 25 +/- 2 mm Hg) did not affect BRS and reversed BRS suppression caused by both drugs. Thus, bupivacaine and ropivacaine affect neuronal control mechanisms for maintaining cardiovascular stability, and acute changes of respiration could significantly modify such suppression.

The inhibitory effects of local anesthetics on superoxide generation of neutrophils correlate with their partition coefficients

Lidocaine and tetracaine suppress superoxide anion (O2-) generation of neutrophils. We examined the effects of eight local anesthetics on O2- generation in human neutrophils and searched for a potential relationship between the biological activities and the physicochemical properties of presently available eight local anesthetics. Human neutrophils incubated with local anesthetic and a Cypridina luciferin analog as a O2(-)-specific chemiluminescence probe were stimulated by phorbol ester. The chemiluminescence development based on O2- generation was monitored by a luminometer. All of the tested local anesthetics suppressed O2- generation in a concentration-dependent manner. The concentration of each of eight local anesthetics that produced 50% inhibition of peak chemiluminescence (IC50) had a rank order of dibucaine < tetracaine < bupivacaine < ropivacaine < procaine < mepivacaine < lidocaine = prilocaine. A linear relationship was obtained between IC50 values and the values of logarithm of partition coefficient (log P) of eight local anesthetics; log (IC50 in molarity) = -1.252 - 0.514 x log P, r2 = 0.891, P < 0.001. Unlike with staurosporine, which inhibits protein kinase C (PKC), no effect was observed on the O2- generation in the presence of tetrodotoxin (TTX), veratridine (VTD), or amiloride. These results suggest that the inhibitory effects of local anesthetics on O2- generation of neutrophils are predicted by physicochemical properties of the drugs, especially partition coefficients.