Risk factors increasing blood pressure in Japanese colorectal cancer patients treated with bevacizumab.

Bevacizumab has been reported to increase blood pressure. However, the factors, including patient characteristics and laboratory data contributing to this side effect remain unclear. Therefore, we investigated the relationships between increased blood pressure and bevacizumab administration, patient characteristics, and laboratory data. Between April 2007 and January 2018, factor analysis was retrospectively conducted by monitoring increases in blood pressure, the status of bevacizumab administration, patient characteristics, and laboratory data before the first administration in Japanese patients with colorectal cancer who satisfied the criteria for this study. Sixty-seven patients were included, 34 of whom (50.7%) had an increase in blood pressure after bevacizumab administration. On univariate analysis, liver metastasis, antihypertensive drug use, systolic blood pressure at rest before the first bevacizumab administration, body mass index, creatinine, and blood platelet count were significantly different between the two groups. Multivariate analysis was conducted using increased blood pressure as an objective variable and the factors extracted by the univariate analysis as explanatory variables. The results suggested that liver metastasis, antihypertensive drugs, systolic blood pressure at rest before the first bevacizumab administration, and creatinine were associated with the increase in blood pressure. Furthermore, a log-rank test performed based on Kaplan-Meier curves demonstrated that liver metastasis in patients not taking antihypertensive drugs and antihypertensive drug use in patients without liver metastasis were significantly associated with increased blood pressure. Additionally, liver metastasis in patients with antihypertensive drug use was significantly associated with increased blood pressure. Our findings suggest that liver metastasis and antihypertensive drug use, which was previously reported, are risk factors for increased blood pressure.

Characteristics of organic cation transporter in rat renal basolateral membrane.

Characteristics of organic cation transport system were studied in rat renal basolateral membrane and compared with those in brush-border membrane. We first examined the effect of various chemical modifiers on tetraethylammonium uptake by the membrane vesicles. Treatment with N,N'-dicyclohexylcarbodiimide and phenylglyoxal (carboxyl groups and arginine residues specific reagent, respectively) resulted in inhibition of tetraethylammonium transport in both basolateral and brush-border membranes. Tetraethylammonium uptake by brush-border, but not by basolateral, membrane vesicles was decreased by diethyl pyrocarbonate, histidine residues specific reagent, treatment. Treatment of sulfhydryl groups with HgCl2 decreased tetraethylammonium transport in both membranes. However, in contrast to brush-border membrane, unlabeled tetraethylammonium failed to protect against the inhibition of [14C]tetraethylammonium uptake by p-chloromercuribenzene sulfonate in basolateral membrane. We next examined the inhibitory effect of various organic cations on tetraethylammonium uptake. The order of inhibitory potency of organic cations was somewhat different between two membranes. These findings suggest that the characteristics of organic cation transport systems in basolateral and brush-border membranes were different in regard to essential amino acid residues and the affinity of substrates.

Differential sensitivity of organic anion transporters in rat renal brush-border membrane to diethyl pyrocarbonate.

The effect of various chemical modifiers on p-aminohippurate (PAH) uptake by a potential-sensitive system and by an anion exchanger was studied in rat renal brush-border membrane vesicles. Among various chemical modifiers, diethyl pyrocarbonate (DEPC) selectively inhibited potential-sensitive PAH uptake but not the uptake by the anion exchanger. The inhibitory effect of DEPC on potential-sensitive PAH uptake was not due to the facilitated dissipation of membrane potential, which was evidenced by the studies with a potential-sensitive fluorescence dye diS-C3(5). The potential-sensitive PAH uptake was inhibited by DEPC in a concentration-dependent manner, and kinetic analysis showed that the decreased uptake of PAH in DEPC-treated vesicles was due to the decrease of Vmax. The inhibition of the PAH uptake was protected by the presence of organic anions during the DEPC treatment. These findings indicate that PAH transport by the potential-sensitive system and by the anion exchanger is mediated by structurally distinct transporters. Amino acid residue(s) modified by DEPC, most likely a histidine residue, should play an important role in the potential-sensitive transport of PAH in rat renal brush-border membrane.

Transport of procainamide in a kidney epithelial cell line LLC-PK1.

Transport of procainamide, an anti-arrhythmic drug, was investigated in LLC-PK1 kidney epithelial cell line. The uptake of procainamide by LLC-PK1 monolayers cultured in plastic dishes was temperature-dependent, saturable and inhibited by organic cations such as cimetidine and N-acetylprocainamide. An aminocephalosporin antibiotic, cephalexin, also inhibited procainamide uptake, but an organic anion, p-aminohippurate, did not. The uptake of procainamide was greater at an alkaline external pH than at an acidic pH. In addition, procainamide uptake increased when intracellular pH was decreased and the uptake decreased when the intracellular pH was increased by ammonium chloride treatment, indicating the involvement of an H+/procainamide antiport system in apical membrane. The basolateral to apical flux of procainamide across LLC-PK1 monolayers cultured on permeable supports was 2.5-times larger than the apical to basolateral flux, and only the former process was inhibited by other organic cations. These findings suggest that LLC-PK1 cells can transport procainamide by the organic cation transport system and that procainamide is transported unidirectionally from basolateral to apical side across the cell monolayers.

Dopamine and serotonin uptake inhibitors on the release of dopamine and serotonin in the nucleus accumbens of young and aged rats.

Nucleus accumbens (ACC) of young (4 months old) and aged (24 months old) Wistar rats were perfused with dopamine (DA) uptake blocker, cocaine, or the serotonin (5-HT) selective reuptake inhibitor, fluoxetine, through the microdialysis probe membrane, used to assess the dopamine transporter (DAT) or serotonin transporter (SERT) modulation. The basal extracellular DA release in the ACC was significantly lower in aged rats than young rats. Analysis of DA and 5-HT concentrations in the ACC with increased positive GFAP revealed that DA and DOPAC levels of aged rats were decreased to 55 and 60% of those in young rats, respectively. After co-perfusion with cocaine, both DA and 5-HT releases in the ACC were increased in the young and aged groups. However, the magnitude of the increased DA release was lower in aged rats than young rats. Co-perfusion with fluoxetine showed lower magnitude of the increased DA release in aged rats. It appears that the DAT and SERT system responds initially to ACC cell loss with age, and that especially ACC DAT in the aged rat is more degenerative compared with the young rats. These findings suggest that the serotonergic system with SERT in the remaining ACC neurons show an early adaptive response and resistance to the normal aging and maintain the multiple regulatory system in the ACC despite neural loss since the dopaminergic neurons in the aged animals are vulnerable to aging.

Anti-oxidative properties of fluvastatin, an HMG-CoA reductase inhibitor, contribute to prevention of atherosclerosis in cholesterol-fed rabbits.

Studies in vitro reveal that fluvastatin, an HMG-CoA reductase inhibitor, has a strong DPPH radical scavenging activity and achieves concentration-dependent inhibition of copper- and cell-induced oxidation of low-density lipoprotein (LDL). To further examine the anti-oxidative activity of fluvastatin in vivo, we elucidated the effects of chronic treatment with fluvastatin at a dose insufficient to reduce plasma cholesterol levels (2 mg/kg per day) on vasomotion and vascular oxidative stress in thoracic aortas of 0.5% cholesterol-fed rabbits. After 12 weeks of dietary treatment, aortic segments from rabbits fed cholesterol alone showed impaired endothelium-dependent relaxation responses to acetylcholine and A23187 compared to normal chow-fed rabbits in association with a significant increase in plasma total cholesterol levels. In contrast, although plasma total cholesterol levels were not different from those in control cholesterol-fed rabbits, aortic segments from fluvastatin-treated rabbits showed normal relaxation. Compared with rabbits fed cholesterol alone, fluvastatin treatment decreased susceptibility of LDL to ex vivo copper-induced oxidation, reduced vascular superoxide generation, and atheromatous plaque formation. In conclusion, the potent anti-oxidative properties of fluvastatin in addition to its cholesterol-lowering activity appear to contribute to its anti-atherosclerotic effect in vivo.

Regional myocardial ajmaline concentration and antiarrhythmic activity for ischaemia- and reperfusion-induced arrhythmias in rats.

1. Antiarrhythmic actions of ajmaline against ischaemia (left coronary artery occlusion for 15 min) and subsequent reperfusion-induced arrhythmias were investigated in anaesthetized rats. 2. Ajmaline (2 mg kg-1, i.v.) was effective in suppressing ischaemia-induced arrhythmias whether given pre- or post-occlusion. 3. Ajmaline diminished the reperfusion-induced arrhythmias completely when given pre-occlusion but had little effect when given post-occlusion. 4. Reperfusion-induced increases in plasma enzyme activities of lactate dehydrogenase, glutamate-oxaloacetate transaminase and creatine phosphokinase were prevented more effectively when ajmaline was given pre-occlusion rather than post-occlusion. 5. Fifteen min post-occlusion, the ajmaline concentrations in the ischaemic ventricle were 18.42 +/- 1.66 and 1.18 +/- 0.15 micrograms g-1 for pre- and post-occlusion administration, respectively. However, ajmaline concentrations in whole blood and normal ventricle were not significantly different between pre- and post-occlusion administration. 6. We suggest that the beneficial effect of ajmaline against reperfusion-induced arrhythmias is related to the ischaemic myocardial concentration of ajmaline which is markedly affected by the time of drug administration (i.e. pre- and post-occlusion).

Pharmacokinetics and antiarrhythmic activity of ajmaline in rats subjected to coronary artery occlusion.

The pharmacokinetics and the antiarrhythmic action of intravenous ajmaline were investigated in anaesthetized rats subjected to coronary artery occlusion. Ajmaline (0.125-2 mg kg-1, i.v. given just after occlusion) suppressed arrhythmias in a dose-dependent manner, judged by the reduction of premature ventricular complexes. The incidence of malignant arrhythmias (ventricular tachycardia and fibrillation) was preferentially suppressed at the higher doses of ajmaline (1 and 2 mg kg-1). Coronary occlusion induced a change in pharmacokinetics of ajmaline (2 mg kg-1) and its total body blood clearance was significantly decreased from 56.6 ml min-1 kg-1 in sham-operated rats to 43.1 ml min-1 kg-1 in rats after coronary occlusion. Ajmaline exhibited a significantly increased negative dromotropic action (increased PQ interval) in rats after coronary occlusion compared with that in sham-operated rats. The difference seems to be due to the pharmacokinetic change since the concentration-effect relationship was similar in the two groups of rats. We suggest that the measurement of drug levels is important in the assessment of antiarrhythmic agents.

Pharmacokinetics and dromotropic activity of ajmaline in rats with hyperthyroidism.

1. The pharmacokinetics and the dromotropic action (increased PQ interval) of intravenously administered ajmaline (2 mg kg-1) were studied in hyperthyroid rats with sinus tachycardia. The hyperthyroidism was induced by intraperitoneal injection of 3,5,3'-triiodo-L-thyronine (0.5 mg kg-1) for 4 days. 2. The change in the ajmaline concentration in whole blood could be described by a biexponential equation. The steady state distribution volume of ajmaline decreased from 4.81 l kg-1 in control rats to 3.80 l kg-1 in hyperthyroid rats and the total body blood clearance was slightly higher in hyperthyroid rats than in control rats. 3. Ajmaline exhibited a saturable binding to rat plasma proteins, and one kind of binding site was found in the observed range of concentrations. The binding capacity was 2 fold higher in hyperthyroid rats than in control rats. 4. On the basis of the plasma unbound concentration, ajmaline exhibited an increased negative dromotropic activity in hyperthyroid rats compared with control rats. 5. A positive correlation was found between the pacing rate and the dromotropic action of ajmaline on atrioventricular conduction in isolated perfused hearts. There was no significant difference in the rate-dependence of the effect of ajmaline on the heart between control and hyperthyroid rats. 6. Our findings suggest that the increased dromotropic activity of ajmaline is mainly due to the increased heart rate in hyperthyroid rats.

Drug elimination function of rat small intestine: metabolism and intraluminal excretion.

The metabolic and excretory function of the small intestine was investigated after oral and intravenous administration of drugs having an aromatic amino group to rats. After administration of drugs into the intestinal loop at the initial concentration of 0.1 mM, significant excretion of their N-acetylated forms into the lumen was observed. The amount of N-acetyl forms excreted in the lumen were 39.3 +/- 3.5, 63.5 +/- 20.9 and 18.0 +/- 13.8% of disappeared drugs from the lumen for p-aminobenzoic acid (PABA), p-aminosalicylic acid and sulfanilic acid, respectively. The excretion of p-acetamidobenzoic acid (Ac-PABA) after the absorption of PABA was reduced by the coadministration with salicylic acid, benzoic acid and 2,4-dinitrophenol. Salicylic acid noncompetitively inhibited the acetylation of PABA by the intestinal N-acetyltransferase. A good correlation was found between the intestinal N-acetyltransferase activities for drugs and the intraluminal excretion of N-acetyl derivatives after intestinal absorption of drugs. These results indicate that a drug having a higher susceptibility to intestinal N-acetyltransferase would undergo a greater excretion into the lumen in its N-acetyl form after intestinal absorption. After intravenous administration of PABA at a dose of 100 mumole/kg, 4.02 +/- 0.51% of dose was excreted in the lumen as Ac-PABA in 30 min. On the other hand, a significantly smaller fraction (2.72 +/- 0.68% of dose) was excreted in the lumen after intravenous injection of 100 mumole/kg of Ac-PABA. The larger excretion of Ac-PABA after administration of PABA indicates the contribution of intestinal metabolism on the transfer of PABA not only after oral, but also after intravenous administration.

Protective effect of fluvastatin sodium (XU-62-320), a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on oxidative modification of human low-density lipoprotein in vitro.

We investigated the protective effect of fluvastatin sodium on the oxidation of low-density lipoprotein (LDL) induced in vitro by copper ions. The extent of lipid peroxidation was assessed by monitoring the increase of UV absorbance at 234 nm, which is the peak absorbance of a conjugated diene. Fluvastatin sodium (1-30 microM) not only prolonged the lag time of oxidation in the initiation step, but also decreased the rate of oxidation in the propagation step, both concentration dependently. Fluvastatin sodium and alpha-tocopherol showed an additive effect when both compounds were added before oxidation. However, when the lag time was prolonged initially by alpha-tocopherol, and fluvastatin sodium and alpha-tocopherol, were further added into the reaction mixture at the end point of the lag phase, fluvastatin sodium still showed an antioxidative effect, whereas alpha-tocopherol showed a pro-oxidative effect. Therefore, the antioxidative property of fluvastatin sodium differs from that of alpha-tocopherol. In this experiment, as neither the double bond-reduced derivative of fluvastatin sodium nor pravastatin sodium showed any protective effect, we concluded that the antioxidative effect of fluvastatin sodium is not a common property of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, but may be derived from its unique chemical structure. Since the oxidative modification of LDL plays an important role in the genesis of atherosclerosis, fluvastatin sodium may help reduce the risk of atherosclerosis, not only by reducing plasma LDL levels but also by protecting LDL from oxidative modification.

Identification of the major binding protein of salmon calcitonin in the rat.

The major serum binding protein of salmon calcitonin (sCT) in the rat was identified. High-molecular-weight (HMW) forms of sCT, produced by the incubation of radioactive sCT in rat serum, were isolated by gel filtration and analysed by chromatofocusing. The major radioactive peak was eluted at the region of albumin in gel filtration, and this peak had a slightly higher pI than albumin on chromatofocusing. Immunoreactivity of the radioactive peak fraction in chromatofocusing, examined by immunodiffusion, showed that the major protein in the fraction was albumin. Immunoreactivity of the radioactive HMW fraction isolated by gel filtration was studied by immunoprecipitation, indicating that a large portion of the fraction reacted with anti-rat albumin antiserum. These results suggested that the radioactive peak in chromatofocusing represents the complex of sCT and rat albumin. Further, HMW forms of sCT were analysed by immunoelectrophoresis and autoradiography, and most of the radioactivity was found on the precipitation line of albumin. These results demonstrate that the major binding protein of sCT in rat serum is albumin.

Reduced hepatic uptake of propranolol in rats with acute renal failure.

The effect of acute renal failure (ARF) on the hepatic uptake and metabolism of propranolol was investigated in relation to the hepatic clearance of the drug. ARF was induced by the subcutaneous injection of uranyl nitrate to rats. The uptake rate of propranolol in the isolated perfused liver was determined by the multiple-indicator dilution method and was found to decrease from 43.6 +/- 2.0 min-1 (mean +/- S.E.) in control to 29.4 +/- 1.7 min-1 in ARF (P less than 0.001). The recovery fraction of propranolol in effluent venous blood increased about twofold in ARF compared to control (P less than 0.05). The metabolic activity for propranolol was examined using the hepatic microsomal fraction prepared from control and ARF rats. There was no significant difference in the kinetics of oxidative metabolism of propranolol between two groups. These results suggest that the previously reported decrease in the hepatic clearance of propranolol in ARF is due to decreased hepatic uptake of the drug from the blood into the liver cells.

Transport of bestatin in rat renal brush-border membrane vesicles.

Bestatin [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl-L-leucine] is a dipeptide, comprising L-leucine and an unusual beta-amino acid. We studied its transport mechanism in rat renal brush-border membrane vesicles. Uptake of cephradine, an aminocephalosporin, by isolated brush-border membrane vesicles was trans-stimulated and cis-inhibited by bestatin, indicating that these drugs are transported via the same transport system(s). The uptake of bestatin was trans-stimulated by preloading the vesicles with glycylsarcosine, and was cis-inhibited by substrates for the H+/dipeptide cotransport system. Bestatin inhibited tetraethylammonium (an organic cation) uptake, and bestatin uptake was cis-inhibited by substrates for the H+/organic cation antiport system. In addition, bestatin uptake was stimulated by an outward H+ gradient (the driving force for the H+/organic cation antiport system). These findings suggest that bestatin, in spite of being a dipeptide, is transported via not only the H+/dipeptide cotransport system but also the H+/organic cation antiport system in rat renal brush-border membrane.

Bestatin transport in rabbit intestinal brush-border membrane vesicles.

The effect of papain treatment on bestatin uptake by rabbit intestinal brush-border membrane vesicles (BBMVs) was studied. Papain treatment of BBMVs effectively diminished aminopeptidase activity but not bestatin uptake by a H+/dipeptide cotransporter. Bestatin uptake by BBMVs was composed of two saturable components, and after papain treatment the high-affinity component disappeared while the low-affinity component was retained. These findings suggest that high- and low-affinity components represent bestatin binding to aminopeptidase and the true uptake by the H+/dipeptide cotransporter, respectively.

Distribution of patients' test values and applicability of "average of normals" method to quality-control of radioimmunoassays.

Applicability of the Hoffmann's average of normals (Mn) method was evaluated in quality control (QC) of radioimmunoassays (RIA) for thyroxine, 3,5,3'-tri-iodothyronine, thyrotropin, and insulin--assays that are performed routinely in the authors' laboratory. In the first three RIAs, the patterns of the distributions were almost constant and Mn showed significant correlations with values of QC sera and intercepts of the dose-response curve. In insulin RIA, the patterns varied appreciably and Mn showed correlations with parameters that reflect a disturbance in the distribution. Exclusion of assays with abnormal distributions, however, resulted in better correlations of Mn with other QC parameters. These results suggest that average of normals method can be a very useful adjunct to conventional QC methods for RIA. The possibility that the method may be affected by a disturbance in the distribution can be monitored by computation of parameters reflecting such disturbance.

Deficiency of apolipoprotein B synthesis in Suncus murinus.

We reported previously that fatty liver is easily induced in a novel experimental animal, Suncus murinus (suncus) by withholding food. In this study, we focused on lipoprotein and apolipoprotein secretion from the liver. The study of lipoproteins from this animal revealed that small amounts of lipoproteins with apolipoprotein (apo) E but without apo B were observed in the fraction of density less than 1.08 g/ml. In order to learn whether apo B is synthesized by the liver or not, isolated suncus livers were perfused with an addition of [35S]methionine. Small amounts of radioactivity were observed in apo E of VLDL, and fairly large amounts in apo E and A-I in the fraction of LDL + HDL, suggesting that VLDL was secreted with apo E but not with apo B from the liver. Northern blot analysis with use of rat apo B cDNA revealed a weak signal of hybridized rat apo B cDNA between 15 kb and 9 kb in the suncus liver and intestinal mucosa; this is almost the same size as rat apo B mRNA. This finding suggests the presence of apo B mRNA in the suncus. In conclusion, apo B is not secreted from the suncus liver, owing to a defect in intracellular post-transcriptional processing or to ineffective transcription. This might be one of the reasons for fatty deposits in the suncus liver. Suncus may be a candidate for an animal model of abetalipoproteinemia as well as fatty liver due to a defect of apo B synthesis.

Alcohol enhances characteristic releases of dopamine and serotonin in the central nucleus of the amygdala.

The amygdaloid complex (AMY) is implicated in emotional and motivational aspects of behavior, including the formation of positive reinforcement association. AMY may also associated with brain rewarding circuitry. In the present study, the effect of ethanol (EtOH) on the release of dopamine (DA) and serotonin (5-HT) was studied in the central amygdaloid nucleus (CeAMY), and projecting excitatory afferents to the ventral tegmental area (VTA), of freely moving Wistar rats by brain microdialysis. Within 20 min of i.p. injection of EtOH (2 g/kg), the levels of DA and 5-HT in the CeAMY dialysate increased over the baseline value by 270 and 160% (N = 6-7), respectively. Addition of EtOH (25, 50 and 100 mM) to the microdialysis perfusion medium for 1 h caused a 115-150% dose-related increase in the extracellular level of DA in the CeAMY. 100 mM EtOH-induced CeAMY DA release continued to increase for 1 h after the perfusion medium was returned to normal perfusion medium. In contrast, the CeAMY 5-HT level was increased only by the addition of 100 mM EtOH for 1 h to 130% for 80 min. The stimulation of the CeAMY by EtOH through the microdialysis membrane showed delayed responses of DA and 5-HT compared with the i.p. injection of EtOH. Overall, the present findings are not sufficient to conclude whether EtOH acts directly or indirectly on the major monoamine nerve cells in the CeAMY, but the degree of acute EtOH action affected the differences in time at the peak response on EtOH-induced DA and 5-HT releases in the CeAMY via VTA.

Intra-arterial infusion chemotherapy on unresectable hepatocellular carcinoma under occlusion of hepatic arterial flow.

Intra-arterial infusion chemotherapy (IAIC) by occluding hepatic arterial flow augments intrahepatic drug concentrations, resulting in response rates higher than those with conventional infusion methods. We recently developed an intra-hepatic artery catheter and device attached with an implantable double-lumen reservoir that can be used for repeated IAIC in outpatient clinics. Eight patients with unresectable hepatocellular carcinoma were treated by infusion of anticancer drugs using this method. The catheter was inserted into the hepatic artery under laparotomy. The occlusion balloon was attached to the common hepatic artery, and catheters were connected to the subcutaneous double-lumen reservoir. Approximately 0.5 ml of distilled water was injected through the one port of the double-lumen reservoir to inflate the balloon, which compressed the artery within the cylinder-like occluder. 4'-O-tetrahydropyranyladriamycin (THP-ADM) was used as the anticancer agent, and two patients received combined administration with carboplatin. Three to seven repeated infusions were possible without any severe side effects. This treatment was also easy to perform in the outpatient clinic. Six of the eight patients survived for more than 2 years, an improvement over the survival rates obtained in a previous conventional IAIC group. We conclude that IAIC with THP-ADM for unresectable hepatocellular carcinoma under occluding blood flow using our device is more convenient and more effective than other available methods.

A possible role for BDNF, NT-4 and TrkB in the spinal cord and muscle of rat subjected to mechanical overload, bupivacaine injection and axotomy.

Neurotrophins play a crucial role in the regulation of survival and the maintenance of specific functions for various populations of neurons. Neurotrophin-4 (NT-4) is most abundant in skeletal muscle, and is thought to promote sciatic nerve sprouting, inhibit agrin-induced acetylcholine receptor (AChR) clustering, evoke postsynaptic potentiation and induce mitochondrial proliferation. Using Western blot analysis, immunoprecipitation and immunohistochemistry, we investigated the distribution of NT-4 in slow- and fast-type muscles. We also tested the adaptive response of this protein in the mechanically overloaded muscle, in the regenerating muscle following bupivacaine injection and in the denervated muscle. Additionally, we investigated whether TrkB phosphorylation in the spinal cord and in the sciatic nerve occurs through the interaction with BDNF or NT-4 when the innervating muscle is damaged. Markedly more NT-4 was expressed in fast-type muscles compared with the slow types. TrkB protein was more frequently observed around the edge of myofibers (neuromuscular junction) of the soleus muscle compared with the gastrocnemius muscle. TrkB tyrosine phosphorylation occurred in the spinal cord but not in the sciatic nerve 24 h after bupivacaine injection of the innervating muscle. At the same time, the amount of TrkB co-precipitating with BDNF was markedly increased in the spinal cord. A rapid activation of TrkB (1-8 h) was also observed in the spinal cord after axotomy,while the amount of TrkB co-precipitating with NT-4 was markedly lower after axotomy. These results indicate that NT-4 is preferentially distributed in fast-type muscles. Furthermore, by interacting with BDNF and NT-4, the TrkB in the spinal cord may be important for the survival of motoneurons and outgrowth of injured peripheral axons following muscle damage.