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.

Increased activity of small GTP-binding protein-dependent phospholipase D during differentiation in human promyelocytic leukemic HL60 cells

In response to dibutyryl cyclic AMP (dbcAMP) and all-trans retinoic acid, human promyelocytic leukemic HL60 cells differentiate into granulocyte-like cells. In cell lysate and in vitro reconstitution system, phospholipase D (PLD) activity in response to guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) was up-regulated by dbcAMP or all-trans retinoic acid treatment. In the present study, the mechanism(s) for increased PLD activity during differentiation was examined. Western blot analysis revealed that the contents of ADP-ribosylation factor, Rac2, and Cdc42Hs but not RhoA and Rac1 in the cytosolic fraction were elevated during differentiation. However, the cytosolic fraction from undifferentiated cells was almost equally potent as the cytosolic fraction from differentiated cells in the ability to stimulate membrane PLD activity. It was shown that the GTPgammaS-dependent PLD activity in membranes from differentiated cells was much higher than that in membranes from undifferentiated cells, suggesting that the increased PLD activity during differentiation was due to alterations in some membrane component(s). Clostridium botulinum ADP-ribosyltransferase C3 and C. difficile toxin B, which are known as inhibitors of RhoA and Rho family proteins, respectively, effectively suppressed PLD activity in membranes from differentiated cells. In fact, the amount of membrane-associated RhoA was increased during differentiation. Furthermore, the extent of GTPgammaS-dependent PLD activity partially purified from membranes from differentiated cells was greater than that from membranes from undifferentiated cells in the presence of recombinant ADP-ribosylation factor 1. The PLD (hPLD1) mRNA level was observed to be up-regulated during differentiation, as inferred by reverse transcription-polymerase chain reaction. Our results suggest the possibility that the increased Rho proteins in membranes and the changed level of PLD itself may be, at least in part, responsible for the increase in GTPgammaS-dependent PLD activity during granulocytic differentiation of HL60 cells.

[The differences of the cerebral and spinal vessels in sensitivity to PaCO2 and vasoconstrictors]

We investigated the differences in the response to arterial CO2 tension and vasoconstrictors between the cerebral and spinal vasculatures using cranial and spinal window technique which provided the direct observation of pial vessels. Pentobarbital anesthetized dogs (n = 18) (CO2 tension; n = 6 and vasoconstrictor; n = 12) were instrumented for measurement of pial vessel diameters by intravital microscopy in the cranial and spinal window preparation simultaneously. We achieved hypocarbia (20-25 mmHg) followed by adjusting CO2 levels for normocarbia (35-40 mmHg) and for hypercarbia (55-60 mmHg) using CO2 gas addition. After obtaining the desired PaCO2, the measurements were made. In the next experiment, we administered 2 different concentrations of epinephrine or phenylephrine solutions (1:2 x 10(6), 1:2 x 10(5)) through the window, and the measurement was made sequentially. The response of cerebral and spinal vasculature to change in PaCO2 was almost similar. Topical application of both drugs produced a significant constriction of spinal pial arterioles compared with the cerebral ones, while epinephrine but not phenylephrine constricted cerebral pial venules compared with spinal ones. These results suggest that the responses to vasoconstrictor of cerebral and spinal pial vessels are not similar, and high sensitivity of spinal arterioles to vasoconstrictors may possibly contribute to a risk of ischemic damage of the spinal cord.

[Usefulness of alpha 2-adrenoceptor agonists and practical problems associated with their use in clinical anesthesia--II. Effects in regional anesthesia and analgesic effects for pain relief]

In the second part of this review, we summarized the effects of alpha 2-adrenoceptor agonists (clonidine and dexamedetomidine) in regional anesthesia and pain control, and evaluated their usefulness as anesthetic adjuvants and analgesics in the clinical settings. In addition, we referred to practical problems associated with their use.

[Usefulness of alpha 2-adrenoceptor agonists and practical problems associated with their use in clinical anesthesia--1. Premedication, anesthetic adjuvants, and hemodynamic effects]

A great deal of new information on alpha 2-adrenoceptor agonists has recently been accumulated in humans; alpha 2-agonists have several beneficial actions in clinical anesthesia including sedative, anxiolytic as well as analgesic effects, improved hemodynamic stability, and etc. In the first part of this review, we summarized the structure, signal transmission and basic pharmacology of alpha 2-adrenoceptor agonists (clonidine and dexamedetomidine), and evaluated their usefulness for premedication, and as anesthetic adjuvants as well as agents for stabilizing circulation in the clinical settings. In addition, we referred to practical problems associated with their use.

[Effects of continuous epidural administration of fentanyl and morphine on postcesarean pain]

We studied the effects of continuous epidural administration of fentanyl and morphine with bupivacaine for management of postcesarean pain. Eighteen patients received either bolus epidural administration of fentanyl 100 micrograms or morphine 3 mg with 0.5% bupivacaine 4 ml, followed by continuous infusion of fentanyl 33 micrograms.ml-1 with 0.17% bupivacaine or morphine 0.21 mg.ml-1 with 0.17% bupivacaine for 48 hours, respectively. Pain score was assessed at 0 h, 12h, 24h and 48h after leaving the operating room. Pain score increased significantly and progressively in the fentanyl group. In all cases pruritus was noted. Severe pruritus was observed in the morphine group significantly more than in the fentanyl group. The current results indicate that morphine may be preferable to fentanyl for postcesarean pain control using the present opioid doses.

[Postoperative continuous epidural infusion of morphine in a patient with myotonic dystrophy]

Patients with myotonic dystrophy present potential problems during and after anesthesia, especially respiratory dysfunction. A 42-year-old female with myotonic dystrophy associated with slight impairment of respiratory functions and muscular power, underwent abdominal total hysterectomy under epidural anesthesia uneventfully. To relieve pain after the surgery, a bolus of epidural morphine 2 mg was administered through an indwelling lumbar (L1-2) epidural catheter 30 minutes prior to the end of the surgery and followed with continuous epidural infusion of morphine at a rate of 0.083 mg.h-1 using a balloon (Multiday Infuser, Baxter) for three days. She obtained adequate analgesia after the surgery without respiratory depression or other major complications. We demonstrated that the continuous epidural infusion of morphine in a patient with myotonic dystrophy is safe and adequate for postoperative pain relief.

[Nicorandil, as ATP-sensitive K+ channel opener, potentiated morphine analgesia]

Recent reports demonstrated that K+ channels could contribute to signal transmission in the brain and spinal cord, and opioids' action may be related to K+ channels' functions. We investigated the antinociceptive effect of epidurally injected ATP-sensitive K+ channel opener, nicorandil, using tail flick test in rats. Epidural nicorandil (100 micrograms.rat-1) increased % maximum possible effect (%MPE) of epidural morphine (1, 10 micrograms.rat-1) from -3% to 40% (P < 0.05) and 46% to 65%, respectively. Epidural glibenclamide (10 micrograms.rat-1), ATP-sensitive K+ channel blocker, antagonized this effect. Epidural nicorandil alone (10 approximately 100 micrograms.rat-1) showed no antinociceptive effects. Systemic nicorandil (100 micrograms.rat-1, i.m.) did not increase the epidural morphine analgesia. These data suggest that the K+ channel opener could point the way to a new approach to pain treatment.

[Prostaglandin E1 at low-doses improved right ventricular ejection fraction in anesthetic management for CABG]

A 52-year-old male for CABG developed a severe right heart failure, because of the direct injury to the right ventricular wall, after cardiopulmonary bypass. The volume loading therapy could not improve the cardiac function, then we used an infusion of low-dose prostaglandin E1 (0.02-0.04 micrograms.kg-1.min-1) for the acute right heart failure with increased pulmonary vascular resistance. After continuous infusion of this dose, the pulmonary vascular resistance decreased quickly, the right ventricular ejection fraction increased, and the stroke volume index also improved. These hemodynamic changes are the result of the potent vasodilating effect of PGE1, that especially could decrease selectively the pulmonary vascular resistance, and increase the preload of the left ventricle. This dose of PGE1, did not cause a severe systemic hypertension that is a serious complication during vasodilating therapy with any vasoactive drugs. In the present case, we speculated that the low-dose PGE1, is effective to improve the right ventricular function during the acute right heart failure which resulted from the intrinsic right ventricular dysfunction.

[Tizanidine for preanesthetic medication]

The effect of tizanidine given as a premedication on perioperative hemodynamics (mean blood pressure, heart rate), sedation, hypnosis and midazolam requirements for induction were assessed in 68 patients scheduled for elective surgery under general anesthesia. Patients were assigned to three groups. Group 1 was premedicated 90 min prior to induction with tizanidine 4 mg po (n = 28); group 2 was premedicated with tizanidine 2 mg po (n = 12); group 3 received no premedication (n = 28). In group 1, increase of mean blood pressure on anesthesia induction was attenuated significantly and sedative and hypnotic effects were stronger significantly compared with other groups. We also found that the amounts of midazolam necessary for loss of consciousness were significantly less in patients who had received tizanidine 4 mg. In conclusion, tizanidine is a useful drug as preanesthetic medication for general anesthesia.

[Anesthetic management of a patient with renal cell carcinoma extending into the right atrium]

A 60-year-old man with renal cell carcinoma extending through inferior vena cava into the right atrium was scheduled for the removal of the right kidney under general anesthesia and the cardiopulmonary bypass technique. In order to obtain a clear operative field and to minimize the risk for pulmonary embolism of necrotizing tumor, total circulatory arrest under profound hypothermia (20 degrees C) was performed. Anesthesia was maintained with high doses of fentanyl (62 micrograms.kg-1), midazolam and supplemented with enflurane. We attempted to prevent circulatory collapse due to acute pulmonary embolism by tumor fragments during operation. The body temperature of the patient was decreased down to 20 degrees C for protecting central nervous system with the minimal damage. No complications occurred during anesthesia and the post-operative period. For the safe anesthetic management of the patient such as our case, adequate monitoring of circulation and protection of central nervous system are essential.

[Intraoperative acute myocardial infarction during total gastrectomy under general anesthesia combined with thoracic epidural anesthesia]

A 61-year-old, 54-kg man with gastric cancer was scheduled for total gastrectomy under general anesthesia combined with thoracic epidural anesthesia. Approximately 20 minutes after the start of the operation, the patient developed sudden hypotension and ventricular fibrillation. The cardiac rhythm returned to normal after 38 minutes of cardiopulmonary resuscitation. The operation was discontinued and the patient was transferred to an intensive care unit. A 12-lead electrocardiogram (ECG) revealed complete right bundle branch block and elevation of the ST-segment from leads II, III, aVF, V1, and V2 which indicated an inferior myocardial infarction. Laboratory data showed elevated levels of enzymes such as glutamic oxaloacetic transaminase (495 IU.l-1), lactic dehydrogenase (1781 IU.l-1), and creatine kinase-MB (112 IU.l-1). The mildly elevated levels of the enzymes decreased around 10 hours after the termination of the operation, but they increased markedly again without any change in ECG on the second postoperative day. Elevation in serum myoglobin and glutamic pyruvic transaminase and decline in arterial ketone body ratio were also detected. Furthermore, renal failure developed with increase in blood urea nitrogen and creatinine. Because of hepatic failure and renal failure which might have been caused by rhabdomyolysis, the patient needed inotropic support with dopamine, dobutamine, and epinephrine to maintain the circulation. The patient died of reinfarction of the 20th postoperative day despite intensive care such as intraaortic balloon pumping, hemodiafiltration, and continuous intravenous infusion of prostaglandin E1.

[Perioperative managements of a mentally retarded child with obstructive sleep apnea syndrome for adeno-tonsillectomy]

We describe a mentally retarded child with obstructive sleep apnea syndrome (OSAS) in whom it was difficult to maintain upper airway in the perioperative period. The child underwent awake intubation, because the preanesthetic evaluation of the airway with a direct fiberoptic visualization revealed a very narrow airway. Also we considered that if we used an anesthetic agent, a perioperative airway management would be very troublesome. Postoperatively we continuously monitored for apnea and arrhythmias. When the child was sleeping, we found frequently that her thoratic movements were getting weak and percutaneous oxygen saturation went down to about 70 percent. The preoperative direct fiberoptic visualization of the upper airway is effective for the evaluation of the degree of airway obstruction in this child. We also recommend the continuous intensive postoperative monitorings including pulse oximetry, ECG, and apnea monitor which are very important to avoid life-threatening complications such as upper airway obstruction and serious arrhythmias in patients with obstructive sleep apnea syndrome.

Mechanisms of dexmedetomidine-induced cerebrovascular effects in canine in vivo experiments

Dexmedetomidine decreases cerebral blood flow without significantly affecting cerebral oxygen consumption in anesthetized dogs. To assess the direct cerebrovascular effects of dexmedetomidine, we investigated the responses of vasomotor tone to topical application of dexmedetomidine to pial vessels in vivo, using a parietal cranial window. Forty-one dogs were anesthetized with pentobarbital. In 20 dogs, we topically applied six concentrations of dexmedetomidine solution (10(-8), 10(-7), 10(-6), 10(-5), 10(-4), 10(-3) M) and directly measured pial arterial and venous diameters. In 10 dogs, the inhibitory effects of pretreatment of pial vessels with 10(-5) M yohimbine were examined after the application of 10(-5) dexmedetomidine. In the remaining 11 dogs, the effects of 10(-3) M dexmedetomidine were evaluated in the presence of N omega-nitro-L-arginine methyl ester (L-NAME), glibenclamide, or propranolol. Dexmedetomidine significantly constricted pial arteries and veins in a concentration-dependent manner (10(-7) M to 10(-4) M; P < 0.05). Yohimbine blocked dexmedetomidine-induced constriction of pial vessels (both large and small arteries and large veins P < 0.0001; small veins P < 0.005). However, when the highest concentration of dexmedetomidine (10(-3) M) was administered under the window, pial vessel diameter was not significantly altered. In the presence of glibenclamide, 10(-7) and 10(-3) M dexmedetomidine induced a significant decrease in pial arterial diameter compared with 10(-7) and 10(-3) M dexmedetomidine solution alone, respectively (P < 0.05). L-NAME or propranolol did not affect the dexmedetomidine-induced constriction.(ABSTRACT TRUNCATED AT 250 WORDS)

[Opioid receptors altered binding nature in guinea-pig brain following the development of morphine dependence]

Morphine is well known to produce tolerance and dependence. The mechanisms for these phenomena are not clearly understood and there are a number of conflicting reports that chronic morphine administration decreases, increases, or leaves unchanged the number of opioid binding sites. We examined the potency of MScontin (oral controlled-release preparation of morphine) to induce morphine dependence and also determined the change of mu, delta and kappa opioid receptor types in brain homogenates obtained from morphine-dependent guinea-pigs. 1. Guinea-pigs were implanted subcutaneously with MScontin (300 mg.kg-1) and naloxone was employed to precipitate jumping behavior of withdrawal symptoms at various times. The highest degree of physical dependence was observed on the 2nd day after implantation. Therefore, this period was chosen to investigate opioid receptor binding assay. 2. Two days after implantation, the binding of 3H-DAGO (mu agonist), 3H-DPDPE (delta agonist) and 3H-U69593 (kappa agonist) to brain membranes prepared from morphine dependent and control guinea-pigs was determined. Scatchard plot of the saturation binding data revealed an increase in Bmax values (maximum specific binding) and no change in the Kd values (equilibrium dissociation constants) of 3H-opioid ligand bindings obtained from morphine-dependent animals as compared to controls. These results indicate that brain mu, delta and kappa opioid receptors are up-regulated in morphine dependent guinea-pigs.

[The mu, delta and kappa properties of various opioids]

Recently, the highly selective mu, delta and kappa radiolabeled opioid ligands, such as 3H-DAGO (mu ligand), 3H-DPDPE (delta ligand) and 3H-U69593 (kappa ligand) are available. Using the kappa-homogeneous preparations from human placenta and mu-enriched gerbil cerebellum membrane preparations with these highly selective radiolabeled opioid ligands, clinically used opioids were tested for their mu, delta and kappa properties. The mu agonists such as morphine and fentanyl display a very low affinity for delta and kappa receptor. Among the agonist-antagonist, buprenorphine and butorphanol appeared to be the most highly selective agonists for mu and kappa opioid receptors, respectively. Most ligands identified as specific agonists are in fact only selective and appear to interact at more than one receptor type.

[Calcitonin gene-related peptide and human atrial natriuretic hormone levels in response to cardiac operation under high dose fentanyl anesthesia]

To elucidate a role of calcitonin gene-related peptide (CGRP) in anesthesia and surgery with cardiopulmonary bypass (CPB), we measured CGRP which is reported to be a marker for fluid overload, simultaneously with HANP (human atrial natriuretic hormone) in 12 patients during high dose fentanyl anesthesia (50-70 microgram. kg-1). Plasma concentration of CGRP increased to 3 times of the value during preanesthetic phase at 30 min after initiation of CPB. A 3-fold increase compared with control in CGRP occurred 30 min after initiation of CPB. A 3-fold increase in HANP also occurred just before termination of CPB. But, there was no correlation between plasma levels of CGRP and HANP. The changes in CGRP did not relate with those of pulmonary capillary wedge pressure. The results of the present study suggest that the mechanism for the increase is unclear, and CGRP could be influenced during cardiac or coronary artery surgery using CPB.

[The effects of systemic bupivacaine on baroreflex sensitivity in dogs]

To evaluate the effects of systemic bupivacaine on the baroreflex control of heart rate, we investigated the baroreflex sensitivity assessed with a pressor and a depressor test using phenylephrine and nitroglycerin in pentobarbital anesthetized dogs (n = 12). Intravenous injection of bupivacaine (mean plasma concentration of 2.4 +/- 0.9 micrograms.ml-1) caused a significant suppression of the baroreflex sensitivity, defined by the slopes of regression line (in msec of RR interval change per mmHg increase or decrease in systolic blood pressure). The sensitivity obtained with the pressor and the depressor tests decreased from 6.0 +/- 2.3 to 3.5 +/- 1.7, from 2.4 +/- 1.3 to 1.3 +/- 0.8 msec.mmHg-1, respectively (P < 0.01). Suppression of the baroreflex sensitivity during epidural anesthesia with bupivacaine could be due not only to cardiac sympathectomy but also to a direct effect of bupivacaine on the reflex arch including the receptors, the afferent nerve pathways, the CNS, the efferent pathway, and the effector organs. Therefore, the hemodynamic responses to reduction of blood pressure are likely to be inhibited by epidural bupivacaine.