FENTANYL INHIBITS THE UPTAKE OF [3H]NORADRENALINE IN CULTURED NEURONAL CELLS

We have examined how fentanyl modulates [³H]noradrenaline uptakein two cultured neuronal cell preparations, the human neuroblastomaSH-SY5Y and the rat phaeochromocytoma PC12. Fentanyl produceda significant, dose-dependent inhibition of [³noradrenalineuptake at concentrations in excess of 0.1 µmol litre^–1(P <0.05) and 0.3 µmol litre^–1 (P < 0.05)for PC12 and SH-SY5Y cells, respectively. However, these valuesexceed the serum concentration of fentanyl required to produceanalgesia. At the maximum concentration examined (100 µmollitre^–1), fentanyl produced 85–95% inhibition ofuptake. This effect was not antagonized by naloxone, implyinga nonopioid mechanism of action. Imipramine 1 µmol litre^–1reduced [³H]noradrenaline uptake by 65–70% but morphine,in contrast to fentanyl, had no effect (P > 0.1). (Br. J.Anaesth. 1993; 71: 540–543)     

Functional interaction between local anaesthetics and calcium antagonists in guineapig myocardium: 1. Cardiodepressant effects in isolated organs

Both local anaesthetics and calcium antagonists depress cardiacfunction. Therefore, we have studied the interaction of thesecompounds in the isolated myocardium of guineapigs. The negativeinotropic effect of various local anaesthetics was investigatedin left atria in the absence or presence of nitrendipine 10^–7mol litre^–1 (n = 7–8 in each group). In addition,the effect of bupivacaine was studied in the presence of severalcalcium antagonists. The factor by which the negative inotropicpotency (EC₅₀ of local anaesthetics was enhanced significantlyin the presence of nitrendipine varied from mean 1.2 (SD 0.2)(benzocaine) to 3.0 (0.6) (bupivacaine). The EC₅₀ of bupivacainewas lowered by all calcium antagonists. The potentiation factorvaried from 1.4 (0.4) (verapamil) to 3.3 (0.6) (nifedipine).The effects of benzocaine (n = 12) and bupivacaine (n = 11)on the working heart were assessed either alone or after pretreatmentwith nifedipine 10^–8 mol litre^–1. The effects ofbenzocaine on contractility remained unaltered in the presenceof nifedipine, whereas the negative inotropic effect of bupivacaineincreased significantly (for example, a 20% reduction in leftventricular maximum dP/dt occurred with bupivacaine 1 .75 (0.16)x 10^–6 mol litre^–1 alone com pared with 1.1 (0.22)x 10^–6 mol litre^–1 when combined with nifedipine).We conclude that the effects of some local anaesthetics, forexample bupivacaine, on cardiac contractility are enhanced inthe presence of calcium antagonists. The relevance of this interactionin patients remains to be determined.     

DISOPYRAMIDE AND NEUROMUSCULAR TRANSMISSION

The effect of disopyramide on neuromuscular transmission hasbeen studied using the rat isolated phrenic nerve-diaphragmpreparation. The response of the muscle to indirect nerve stimulationwas decreased in the presence of disopyramide 5.6 x l0^–6mol litre^–1 (P<0.05), total blockade occurring at 5.6x 10 ^–4 mol litre^–1. Marked augmentation of theresponse to direct muscle stimulation was recorded in the presenceof disopyramide 1.8 x10^–4– 5.6 x 10^–4 mollitre . Disopyramide 5.6 x 10^–6 mol litre^–1 causeda leftward shift of the log concentration response for tubocurarineand decreased the antagonist effect of neostigmine.     

Actions of morphine on noradrenaline efflux in the rat locus coeruleus are mediated via both opioid and {alpha}2 adrenoceptor mechanisms

A recent report showed that morphine inhibited [³H]clonidinebinding to human platelet ₂ receptors. As the analgesic effectsof morphine and clonidine are clinically additive, we investigatedthe possibility that morphine might stimulate ₂ receptors or₂ mechanisms in rat locus coeruleus (LC) slices. StimulatedLC noradrenaline efflux was measured by fast cyclic voltammetry.Cumulatively applied morphine 10^–8–10^–4mollitre^–1 had no effect on noradrenaline efflux evoked bypseudo-single-pulse stimulations (20 pulses at 100 Hz) whilethe ₂ agonist dexmedetomidine 2 x 10^–10–10^–7mol litre^–1 decreased efflux of noradrenaline in a concentration-dependentmanner. Administration of single concentrations of morphine10^–6–10^–4 mol litre^–1 significantlydecreased efflux of noradrenaline (by 22% and 17%, respectively)and attenuated the effect of dexmedetomidine in a concentration-dependentfashion. Morphine 10^–6–10^–4mol litre^–1also decreased efflux of noradrenaline on long stimulus trains(50 pulses at 50 Hz). These data suggest that the analgesicpotentiation of ₂ and opioid agonists is not mediated via LC₂ receptors.     

COMPARISON OF THE RELAXANT EFFECTS OF DIAZEPAM, FLUNITRAZEPAM AND MIDAZOLAM ON AIRWAY SMOOTH MUSCLE

The mechanisms by which benzodiazepines produce muscle relaxationand respiratory depression are not know, but they may includeactions on peripheral benzodiazepine receptors or central GABAreceptors, or a direct action on airway smooth muscle may alsobe involved. We have compared, therefore, the effects of diazepam,fluni-trazepam and midazolam on airway tone by measuring isometrictension of guineapig trachealis muscle. Cumulative concentrationsof diazepam, flunitrazepam and midazolam caused concentration-dependentrelaxation of resting tone in the tracheal smooth muscle withno significant differences in pD₂ values (–log EC₅₀anindex of potency) or intrinsic activities (% of maximum response)for relaxations for the three compounds. Pretreatment with propranolol10^–6 mol litre^–1, flu-mazenil 1O^–7 and 1 C^–6mol litre^–1 or PK11195 10^–6 mol litre^–1 hadno effect on diazepam- or midazolam-induced relaxation. Diazepam3x Ky6 10^–6 mol litre^–1pretreatment shifted theconcentration-response curves for acetylcholine, histamine andserotonin (5-HT) to the right by a factor of approximately 2.Flunitrazepam 3 x 10^–6 mol litre^–1 pretreatmentalso shifted the curves for histamine and 5-HT similarly tothe right, whereas midazolam pretreatment did not inhibit anyagonist-induced contractions. These results suggest that benzodiazepinesrelax airway smooth muscle, not via neural pathways or centraland peripheral benzodiazepine receptors, but by a direct actionon airway smooth muscle.     

INHIBITION OF THE PLASMA CHOLINESTERASE VARIANTS BY PROPRANOLOL

The inhibitory effect of( ±)propranolol 1.69 x l0^–4–l.69x 10^–7 mol litre^–1 on normal and atypical plasmacholinesterase variants was investigated. The atypical enzymeis less sensitive to inhibition by (±) propranolol oreither of its enanticasiorphs than the usual enzyme. Propranolol8.45 x 10^–6 mol litre^–1 was used as differentialinhibitor of 643 plasma samples from individuals of known genotype.Although the measurement of propranolol inhibition alone isnot always unambiguous for assigning a definite genotype toa given individual, the correlation of propranolol inhibitionwith fluoride inhibition gives clear differentiation of theE₁^uE₁^u and E₁, as well as other phenotypes.     

Functional interaction between local anaesthetics and calcium antagonists in guineapig myocardium: 2. Electrophysiological studies with bupivacaine and nifedipine

The negative inotropic effect of local anaesthetics is potentiatedby several calcium antagonists in guineapig myocardium [1] Therefore,we studied which effects on cardiac ionic currents could beresponsible for this interaction. Concentration- response curvesfor bupivacaine were studied in isolated guineapig atria andpapillary muscles (slow action potentials). Effects on actionpotentials were assessed in the absence (n = 7 atria, n = 8papillary muscles) or presence of nifedipine (8 x 10^–8wmol litre^–1 in n = 8 atria, 10^–8 mol litre^–1in n = 8 papillary muscles). The effect on the Ca²⁺ currentwas assessed directly using the patch-clamp technique in guineapigventricular myocytes. Bupivacaine reduced contractile forceand upstroke velocity of atrial action potentials. Only thenegative inotropic effect was potentiated in the presence ofnifedipine. Force and upstroke velocity of slow action potentialswere diminished by bupivacaine. Both variables were affectedat significantly smaller concentrations of bupivacaine whengiven in combination with nifedipine. The Ca²⁺ current was reducedsignificantly by bupivacaine 5 x 10^–5 mol litre^–1(mean –18 (SD 7)%, n = 9). Its effect was accentuatedin the presence of nifedipine 10^–5 mol litre^–1 (–47(4)%, n = 7).Bupivacaine 3 x 10^–4 mol litre^–1 givenalone exerted a comparable effect (–53 (4)%, n = 4). Variablesindicative of Ca²⁺ channel function (contractile force, upstrokeof slow but not normal action potentials, Ca²⁺ inward current)revealed potentiation of the effects of bupivacaine by nifedipine. Presented in part at the 1993 Annual Scientific Meeting of theGerman Society of Anaesthesiology and Intensive Care Medicine,Würzburg, Germany, and at the 1993 Spring Meeting of theGerman Society of Pharmacology and Toxicology, Mainz, Germany.     

EFFECTS OF THIOPENTONE OR CHLORMETHAZOLE ON HUMAN PLACENTAL STEM VILLOUS ARTERIES

Small placenta/ stem villous arteries were micro dissected fromspecimens obtained at normal term vaginal delivery (n= 25).Ring preparations of the vessels were mounted in organ bathsand isometric tension was measured. Prostaglandin F_2a(PGF_2a)10^{– 7} mol litre^–1 produced concentration-dependentcontractile responses that were inhibited by thiopentone 10^–410^–3/>‘mollitre^–1 and by ch/ormethiazole 3x10^–4-3x 10* mollitre^–1. Thiopentone 10^–410^–3mol litre^–1and chlormethiazole 3x x 10^–4/>-3x x 10^–3 mollitre^–1 decreased the tension in vessels previously treatedwith PGF_2a10^{– 5} mol litre^–1. Chlormethiazole 3x10^–3 mol litre’^–1 inhibited, and thiopenone10^–4-10‘^–3 mol litre abolished contractileresponses to 5-hydroxytryptamine. Contractions induced by angiotensinII were inhibited by thiopentone 1O^–3 mol litre^–1and chlormethiazole 3x 10^{– 3} mol litre^–1. The concentrationsof the two drugs needed to affect contractile activation ofisolated human stem villous arteries exceeded the free plasmaconcentrations reached during anaesthesia induced by the agentsduring Caesarean section, and the present results do not suggestany major effects of thiopentone or chlormethiazole on fetalplacenta/ vascular resistance during the clinical use of thesedrugs.     

Pharmacokinetics of controlled release morphine (MST) in patients with liver carcinoma

Background. There are no studies reported on the pharmacokineticsof controlled release morphine (MST) in patients with hepatocellularcarcinoma, the fifth most common cancer in the world. Methods. We have studied the pharmacokinetic profile of MST(30 mg) in 15 patients with liver carcinoma (eight with primarycarcinoma on top of chronic hepatitis C, and seven with secondarymetastatic liver malignancy as a result of other primary) comparedwith our previously published data for 10 healthy controls.Plasma morphine concentrations were measured in venous bloodsamples at intervals up to 12 h by high-pressure liquid chromatography.Total body clearance (Cl) and systemic bioavailability wereestimated using a compartmental method. Results. Morphine bioavailability showed a substantial increasein patients with primary liver and secondary metastatic carcinomathan that of controls (64.8, 62.1, and 16.8%, respectively).The area under the serum concentration–time curve increased4-fold in primary carcinoma (416 [SEM25] µg h^–1litre^–1) and 3-fold (303 [21] µg h^–1 litre^–1)in metastatic liver patients compared with healthy control (92.5[3] µg h^–1 litre^–1). No significant differencewas found in T_max between the two malignant groups but C_maxwas significantly greater in primary liver carcinoma patients.Impaired morphine elimination was noted in primary carcinomaonly (t_1/2 5.99 [0.39] h). Conclusion. Careful administration of morphine is recommendedin patients with liver cancer.     

ACTIONS OF THE HYPNOTIC ANAESTHETIC, DEXMEDETOMIDINE, ON NORADRENALINE RELEASE AND CELL FIRING IN RAT LOCUS COERULEUS SLICES

We have examined the effects of the highly selective alpha₂adrenoceptor agonist, dexmedetomidine, on noradrenaline releaseand cell firing in isolated, superf used slices of rat locuscoeruleus. Dexmedetomidine decreased both noradrenaline releaseand cell firing rate in a concentration-dependent fashion, withan EC₅₀ of 3.97 (SEM 0.97) x 10^–9morl litre^–1 fornoradrenaline release and 0.92 (0.53) x 10^–9 mol litre^–1for unit activity. Both effects were reversed completely bythe selective alpha₂ antagonist, atipamezole 10^–6 mollitre^–1 These results suggest that cell firing and noradrenalinerelease are under alpha receptor control and that dexmedetomidinepotently stimulates these receptors. We conclude that theseeffects are consistent with the locus coeruleus being a majorsite of action of the hypnotic anaesthetic alpha₂ agonists.     

Effects of halothane and diltiazem on L-type calcium currents in single smooth muscle cells from rabbit portal veins

We have studied the effects of halothane and diltiazem on L-typevoltage-dependent calcium currents (I_Ca) in single smooth musclecells from rabbit portal veins using a whole cell voltage clamptechnique. The threshold of I_Ca was –30 mV and the peakcurrent was reached at 0 mV. Halothane (0.25, 0.5, 1.0, 1.5and 2.07%) decreased I_Ca in a concentration-dependent mannerand shifted the I_Ca activation threshold to the depolarizingside. Halothane 2.0% abolished Diltiazem 10^–8–10^–6mol litre^–1, a calcium channel antagonist, also depressedI_Ca in a concentration-dependent manner. Administration of both0.5% halothane and diltiazem 10 mol litre^–1 (concentrationslower than the clinical therapeutic range) abolished I_Ca however,halothane did not exhibit use-dependent inhibition of I_Ca whereasdiltiazem showed partial use-dependency. We conclude that thedecrease in I_Ca produced by halothane is associated with a directvasodilator effect of this anaesthetic, but is not explainedby block of Ca²⁺ channels similar to the action of diltiazem.Furthermore, administration of low concentrations of both halothaneand diltiazem decreased I_Ca and may reduce the contractilityof the vascular smooth muscle cells.     

DIRECT EFFECTS OF TRIMETAPHAN ON THE DOG MESENTERIC ARTERY AND SAPHENOUS VEIN

Direct vascular effects of trimetaphan camsylate were studiedin the dog mesenteric artery and lateral saphenous vein; vascularstrips were suspended in normal Krebs-Henseleit solution andcontraction produced by phenylephrine 2.4x10^–6 mol litre^–1.Both vessels were relaxed by trimetaphan, maximal relaxationbeing obtained at the concentration of 1.3x10^–2 mol litre^–1;this effect was more marked in the vein strips. Calculated ED₅₀for the relaxing effect of trimetaphan was not significantlydifferent between artery and the vein. It is concluded thatthe sensitivity of arteries and veins to trimetaphan is similar,but that this effect cannot play a significant role in the productionof controlled hypotension.     

ERRATA

The co-ordinate labelled ED₈₅P in figure 4 (p. 543) should readED₅₀P. p. 567: Fluids and electrolytes. The first sentence should read: Ensure intravascular volume repletion with colloid, then give1 litre of saline solution, either 150 or 30 mmol litre^–1,every 4–6 h. In the same section, two subsequent references to "saline 0.3mol litre^–1" should read "saline 30 mmol litre^–1". We apologize to the authors for this confusion, which aroseduring the editorial process.     

EFFECT OF KETAMINE ON TRANSMISSION IN SYMPATHETIC GANGLIA

The effect of ketamine on sympathetic ganglion transmissionhas been studied using the guineapig isolated hypogastric nerve-vasdeferens preparation. Ketamine produced a dose-dependent depressionin the response to preganglionic stimulation (IC₅₀, 2.05 x 10^–4mol litre^–1). No change in the response to postganglionicstimulation was recorded. The anti-cholinergic activity of ketarninewas confirmed using the frog isolated rectus abdominis. ^* Present address: Department of Anaesthesia, University ofShiraz, Iran     

INTERACTION OF ADRENALINE WITH NEOSTIGMINE AND TUBOCURARINE AT THE SKELETAL NEUROMUSCULAR JUNCTION

The effects of neostigmine, and of neostigmine with adrenaline,on the response of the rat isolated hemidiaphragm to stimulationof the phrenic nerve are reported. Neostigmine augmented theresponse: a maximum augmentation occurred at a concentrationof 6.4 x 10^–7 mol litre^–1. At greater concentrationsof neostigmine the response was reduced. Adrenaline in the absenceof neostigmine produced no significant change in the contractionresponse. However, in the presence of neostigmine further augmentationoccurred and achieved a maximum in the presence of adrenaline3.2 x 10^–7–1.3x10^–6 mol litre^–1. Adrenaline4.0 x 10^–8–1.3x10^–6 mol litre^–1 combinedwith neostigmine 4.0x10^–8–6.4 x10^–7 mol litre^–1reversed tubocurarine-in-duced neuromuscular blockade more effectivelythan neostigmine alone(P < 0.001). Adrenaline appeared toenhance the antagonistic effect of neostigmine by increasingacetylcholine release and by enhancing the response at the post-junctionalacetylcholine receptor.     

DOSE-DEPENDENT EFFECT OF METOCLOPRAMIDE ON CHOLINESTERASES AND SUXAMETHONIUM METABOLISM

In obstetric patients undergoing postpartum tubal ligation,we found that metoclopramide produced dose-dependent prolongationof suxamethonium-induced neuromuscular block. Mean block timesafter suxamethonium 1 mg kg^–1 were 8.0 min, 9.83 min and12.45 min for control and metoclopramide 10 mg and metoclopramide20 mg groups, respectively. A laboratory study was thereforeconducted on the inhibition of human plasma cholinesterase (PCHE)and erythrocyte acetylcholinesterase (ACHE) activity by varyingconcentrations of metoclopramide using acetylthiocholine assubstrate. PCHE showed a greater sensitivity to inhibition bymetoclopramide; the concentration of metoclopramide producing50% inhibition of activity (I₅₀) was 3.16x10^–7 mol litre^–1,which is within the therapeutic range. ACHE was less sensitiveto inhibition by metoclopramide (I₅₀ 2.24x10^–5 mol litre^–1).Analysis of enzyme kinetics at varying substrate concentrationsrevealed that metoclopramide produced a potent non-competitive,dose-dependent inhibition of both ACHE and PCHE. The inhibitionconstant, ki, was 1.88x10^–7 mol litre^–1 for PCHEand 9.5x10^–8 mol litre^–1 for ACHE. As metoclopramideis a potent inhibitor of PCHE, interactions might be expectedto occur between metoclopramide and drugs that require PCHEfor biotransformation, such as suxamethonium and ester localanaesthetics. ^*Present address: Department of Anaesthesia, Royal HallamshireHospital, Glossop Road, Sheffield S10 2JF.     

GENERAL ANAESTHETICS INDUCE ONLY HISTAMINE RELEASE SELECTIVELY FROM HUMAN MAST CELLS

We have examined the in vitro effects of increasing concentrationsof propofol (5–70 µg ml^–1), ketamine (10^–6–10^–1mol litre^–1) and thiopentone (10^–5–8 –10^–4 mol litre^–1) on the release of preformed histamineand de novo synthesized mediators (peptide leukotriene C₄ (LTC₄) or prostaglandin D₂ (PGD₂) from human basophils and mastcells isolated from lung parenchyma and skin tissue and fromheart fragments. Propofol, ketamine and thiopentone failed toinduce the release of histamine and de novo synthesis of LTC4from basophils. Propofol induced histamine release from lung(mean 8.6 (SEM 1.6)%) and skin mast cells (3.8 (1.5)%), butnot from heart mast cells. Ketamine caused release of histaminefrom lung (6.2 (0.9) %) and skin mast cells (2.5 (1.5) %). Thiopentonecaused a small amount of histamine release from lung mast cells(3.1 (1.2)%). Propofol, ketamine and thiopentone did not inducede novo synthesis of PGD₂ and L TC₄ from lung and skin mastcells. These results demonstrate that general anaestheticsinduce only histamine release selectively from human mast cells.     

TUBOCURARINE AND PANCURONIUM INHIBIT EVOKED RELEASE OF ACETYLCHOLINE FROM THE MOUSE HEMIDIAPHRAGM PREPARATION

Using a sensitive radioactive method that measures selectivelythe evoked release of acetylcholine, it was demonstrated that,when stimulating at 50 Hz, tubocurarine or pan-curonium 2x10^*mo I litrel or hexamethonium 10^–3 mol litre^–1 significantlydecreased the evoked release of acetylcholine in the mouse invitro phrenic preparation.     

PROPOFOL INHIBITS ENZYMATIC DEGRADATION OF ALFENTANIL AND SUFENTANIL BY ISOLATED LIVER MICROSOMES IN VITRO

We have studied the effect of propofol on the enzymatic degradationof alfentanii and sufentanii utilizing isolated liver microsomesobtained from pig and human liver. Propofol inhibited dose-dependentlythe oxidative metabolic degradation of alfentanii and sufentaniiby both microsomal preparations. The calculated concentrationof propofol causing 50% inhibition of metabolic degradation(IC₅₀) was 32.6 µmol litre^–1 for alfentanii and22.1 pwnol litre^–1 for sufentanii in pig liver microsomes.Similar values of inhibitory activity of propofol (IC values62.8 and 52.9 µmol litre^–1, respectively) were observedusing human microsomes prepared from liver taken from an organtransplant donor. We suggest that propofol in clinically relevantconcentrations interferes with oxidative metabolic degradationof alfentanii and sufentanii in the microsomal fraction of pigand human liver.     

EFFECTS OF TUBOCURARINE ON PLASMA HISTAMINE CONCENTRATION IN THE RAT: Correlation with the Release of Histamine from Isolated Mast Cells

The administration of tubocurarine i.v. in man produces hypotension,probably as a result of the release of histamine. The mechanismsinvolved in this action of tubocurarine on the plasma histamineconcentration in rats, and on the isolated peritoneal mast cellswere investigated. I.v. injections of tubocurarine (> 5mgkg^–1;corresponds to tubocurarine 4 x 10^–4 mol litre^–1in the plasma of the rats) evoked a phasic increase in plasmahistamine concentration. In vitro studies showed that tubocurarine4x 10^–4 mol litre^–1 released about 20% of the histaminecontained in the isolated mast cells. Treatment of the mastceils with carbachol or atropine evoked no histamine release,nor did it modify the tubocurarine-induced release of histamine.These results suggest that the increased histamine concentrationsin the plasma are attributable to an action of tubocurarineon the mast cells which is not mediated through the acetylcholinereceptors distributed on these cells. Present address: Department of Oral Surgery, Faculty of Dentistery,Kyushu University, Fukuoka 812, Japan