Blocking effects of V1 (OPC-21268) and V2 (OPC-31260) antagonists on the negative inotropic response to vasopressin in isolated dog heart preparations

We investigated the effects of V1 IOPC-21268, 1-(1-[4-(3-acetylaminopropoxy)benzoyl]-4-piperidyl)-3,4-dihydro-2( 1H)- quinolinone) and V2 (OPC-31260, 5-dimethylamino-1[4-(2-methylbensoylamino)benzoyl]-2,3,4,5-tetrahy dro-1H- benzazepine) vasopressin receptor antagonists on the negative inotropic response to arginine vasopressin (AVP) in the isolated perfused heart preparations of the dog. AVP (7.5-750 pmol) decreased the atrial and ventricular contractile force when the preparation was perfused with constant pressure or constant flow. AVP induced a small increase in sinus rate. Desmopressin, a selective vasopressin V2 agonist, did not change the sinus rate and atrial or ventricular contractile force. OPC-21268 (0.01-3 mumol) and OPC-31260 (0.01-1 mumol) induced a small negative inotropic effect. Both OPC-21268 and OPC-31260 inhibited the negative inotropic response to AVP in a dose-dependent manner. The doses of 50% inhibition (ID50) for OPC-21268 and OPC-31260 on the inotropic effect were 0.30 +/- 0.16 mumol and 0.084 +/- 0.034 mumol, respectively. Neither OPC-21268 nor OPC-31260 affected the acetylcholine-, adenosine- or norepinephrine-induced inotropic and chronotropic effects. It has been reported that the concentration of OPC-21268 that displaced 50% of specific AVP binding is 0.4 microM for V1 receptors and > 100 microM for V2 receptors and the concentration of OPC-31260 is 0.01 microM for V2 receptors and 1 microM for V1 receptors. We, therefore, suggest that AVP directly causes negative inotropic effects mediated at least in part by V1 receptors in the dog heart.

Detection of IgM antibodies to Chlamydia trachomatis, Chlamydia pneumoniae, and Chlamydia psittaci from Japanese infants and children with pneumonia

Chlamydia trachomatis (C. trachomatis) is now well established as a pathogen of neonatal inclusion conjunctivitis and infantile pneumonia. C. pneumoniae (TWAR) and C. psittaci also cause pneumonia and other respiratory infections. Serum samples from 223 Japanese infants and children with pneumonia were tested for IgM antibodies to C. trachomatis, C. pneumoniae and C. psittaci. IgM antibodies to C. trachomatis were measured by an enzyme immunoassay (EIA) and by a microimmunofluorescence (MIF) test. IgM antibodies to C. pneumoniae and C. psittaci were determined by MIF. Of 223 patients, 48 (21.5%) were positive for IgM antibodies to C. trachomatis, 11 (4.9%) were positive for C. pneumoniae and 5 (2.2%) were positive for C. psittaci. From nasopharyngeal swabs collected from 87 infants with pneumonia (0 to 1 year of age), we attempted to isolate C. trachomatis with tissue culture. C. trachomatis was isolated from 23 (26.4%) of 87 infants with pneumonia, and IgM antibodies to C. trachomatis were detected in 17 (19.5%) of them. Our data suggest a role for chlamydial infection in childhood pneumonia beyond infancy with both C. trachomatis and C. pneumoniae being contributing pathogens.

Potent antagonistic action of OPC-31260, a vasopressin V2 receptor antagonist, on [Arg8]vasopressin-induced vasoconstriction in isolated simian femoral arteries

Using a perfusion technique with isolated vessels, we investigated the effect of OPC-21268 (a selective V1 receptor antagonist) and OPC-31260 (a V2 receptor antagonist) on arginine vasopressin (AVP)- or norepinephrine (NE)-induced vasoconstrictions of isolated simian femoral arteries. The dose-response curve for AVP was shifted to the right in parallel by OPC-31260 but not by OPC-21268. Neither antagonist significantly modified the NE-induced vasoconstriction. On the basis of these results, there are functionally constrictory vasopressin V2 receptors but no V1 receptors in isolated simian femoral arteries.

Identification of human and bovine rotavirus serotypes by polymerase chain reaction

The use of the polymerase chain reaction (PCR) for identifying serotypes of human and bovine rotaviruses was examined. In the identification of 115 human rotavirus samples in stools, results with PCR showed excellent agreement with results of serotyping by an enzyme-linked immunosorbent assay (ELISA) using serotype-specific monoclonal antibodies. Furthermore, the PCR showed a much higher sensitivity (93%) than the ELISA test (82.6%). The PCR method could also be applied for identifying the serotype of bovine rotaviruses.

Sympathetic nerve stimulation activates both beta 1- and beta 2-adrenoceptors of SA and AV nodes in anesthetized dog hearts

We investigated blocking effects of the selective beta 1-adrenoceptor blocker atenolol (0.1-100 micrograms/kg, i.v.), the selective beta 2-adrenoceptor blocker ICI 118,551 (1-1000 micrograms/kg, i.v.) and the combination of the two drugs on positive chronotropic and dromotropic responses to norepinephrine (NE) released by stimulation of the sympathetic nerves in anesthetized, neurally decentralized, open-chest dogs after atropine was given. Stimulation of the intracardiac sympathetic nerves to the SA nodal region or to the AV nodal region selectively increased heart rate or decreased AV conduction time, respectively. ICI 118,551 inhibited the chronotropic or dromotropic response to each stimulation in a dose-dependent manner, but its inhibition of the dromotropic response was less than that of the chronotropic response. Atenolol similarly inhibited either the positive chronotropic or dromotropic response to each stimulation in a dose-related manner. The combination of atenolol and ICI 118,551 attenuated the responses to each stimulation more than atenolol alone. These data indicate that sympathetic nerve stimulation activates both beta 1- and beta 2-adrenoceptors of the SA and AV nodes and that the proportion of beta 2-adrenoceptor-mediated effects on the AV node is less than that on the SA node. These results suggest that neurally released NE in part controls physiological functional cardiac responses mediated through beta 2-adrenoceptors, in addition to the responses predominantly mediated through beta 1-adrenoceptors.

Evaluation of the shell vial pre-CPE method using monoclonal antibodies for the diagnosis of human cytomegalovirus infection in the field of pediatrics

A method of pre-cytopathological effects (CPE) detection in shell vial cultures using monoclonal antibodies (mAb) was evaluated for detection of cytomegalovirus (CMV) in pediatric specimens. The diagnostic value of antibody detection by enzyme immunoassay (EIA) was also evaluated. CMV was isolated from 47 of 1179 specimens tested by the routine tissue culture method. Positive results were obtained in 51 of these 1179 specimens using the pre-CPE method. The pre-CPE shell vial assay was demonstrated to be a rapid and sensitive method of detecting CMV. Detection of the virus by the pre-CPE method was considered much more reliable than by EIA IgM assays for pediatric patients.

[A case of the panencephalopathic type of Creutzfeldt-Jakob disease with retinal involvement]

Neuropathological study of the visual pathway from the retina to the occipital cortex in Creutzfeldt-Jakob disease (CJD) has been scarcely performed. In the present study, pathological involvement of the visual pathway was observed in a 54-year-old man with CJD. The patient had the onset of visual disturbances in December 1985. He subsequently developed progressive dementia, right hemiparesis, ataxia and dysarthria, and rapidly fell into decerebrate posture in February 1986. In March 1986, myoclonus appeared on the whole body and EEG revealed periodic synchronous discharges, while brain CT and CSF findings showed no abnormalities. Myoclonus was observed most frequently from May to October 1986, and then reduced gradually. Brain atrophy on CT started from April 1986, and was progressive till the end stage of the disease. He died in January 1988, and the total clinical course was about 24 months. Neuropathological examination revealed severe degeneration of the cerebral cortex and the white matter. In the cerebral cortex, marked loss of neurons, astrogliosis, and spongiform changes were observed. In the cerebral white matter, the destruction of myelin sheaths and axons were evident. The cerebellum showed prominent loss of granule cells. These findings are consistent with those of the panencephalopathic type of CJD. In the visual pathway, loss of ganglion cells and bipolar cells in the retina, mild demyelination of the optic nerve, neuronal loss in the lateral geniculate body, and severe degeneration in the visual cortex were observed. The present case suggests that the neuropathological investigation in the visual pathway from the retina to the occipital cortex is important for clarifying the pathological processes in the visual system in CJD.

Cardiac electrical responses to catecholamines are differentially mediated by beta 2-adrenoceptors in anesthetized dogs

We investigated the beta 2-adrenoceptor-mediated effects of atrial and ventricular effective refractory period (ERP), SA node pacemaker activity, and AV conductivity induced by sympathetic nerve stimulation or epinephrine infusion in anesthetized dogs. A beta 2-adrenoceptor antagonist, ICI 118,551 up to 100 micrograms/kg, i.v., inhibited the positive chronotropic and dromotropic responses to sympathetic stimulation but did not shorten the atrial or ventricular ERP, ICI 118,551 also attenuated the positive chronotropic and dromotropic responses and the shortening of atrial ERP in response to epinephrine but not the shortening of ventricular ERP. A selective beta 1-adrenoceptor antagonist, atenolol, inhibited each electrical cardiac response to sympathetic stimulation and epinephrine infusion in a similar manner. These results suggest that beta 2-adrenoceptor-mediated electrical cardiac responses to endogenous catecholamines also exist in addition to the predominant beta 1-adrenoceptor-mediated responses, and that the order of the proportion of beta 2-adrenoceptor-mediated cardiac effects was SA node pacemaker activity much greater than AV conductivity = atrial ERP much greater than ventricular ERP in the dog heart.

Effects of YM435, a novel dopamine D1 receptor agonist, on pancreatic exocrine secretion in anesthetized dogs

The effects of YM435, a novel dopamine (DA) D1 receptor agonist, on pancreatic exocrine secretion were investigated in anesthetized dogs. Each drug was injected i.a. as a single bolus. Graded doses of YM435 (0.3-30 nmol) produced dose-dependent increases in the rate of secretion of pancreatic juice, with a maximum effect at approximately 10 nmol, and with a high concentration of bicarbonate and low concentration of protein. SCH23390 (3-30 nmol), a selective D1 receptor antagonist, caused a progressive parallel shift to the right of the dose-response curve for YM435-stimulated pancreatic secretion without changing the maximum response. Schild analysis of the data indicated that the inhibitory constant (Ki) value was 2.9 nmol, and that SCH23390 inhibited YM435-stimulated pancreatic secretion in a competitive manner. Both DA (0.01-3 mumol) and SKF38393 (0.3-30 mumol), a selective D1 receptor agonist, also increased the secretory rate and bicarbonate concentration, and decreased the protein concentration to the same extent as YM435. These results suggest that YM435 is a potent stimulant of pancreatic exocrine secretion by acting on DA D1 receptors of the pancreas in dogs.

Parasympatholytic effects of vecuronium are mediated by nicotinic and muscarinic receptors in hearts of anesthetized dogs

We investigated the blocking effects of vecuronium and pancuronium on the negative chronotropic and dromotropic responses to stimulation of the parasympathetic nerves in the anesthetized, open-chest dog. We stimulated the intracardiac parasympathetic nerves to the SA nodal region (SAP stimulation) or to the atrioventricular nodal region (AVP stimulation). SAP stimulation or AVP stimulation selectively decreased heart rate or increased atrioventricular conduction time, respectively. Vecuronium and pancuronium inhibited the chronotropic response to SAP stimulation and the dromotropic response to AVP stimulation in a dose-dependent manner. The ID50 of each drug for the dromotropic response was less than that for the chronotropic response. The blocking effect of vecuronium on the negative cardiac responses to parasympathetic stimulation was about 10-fold less potent than that of pancuronium. These results suggest that the blocking effects of vecuronium and pancuronium on the negative chronotropic and dromotropic responses to parasympathetic stimulation differ from those of atropine in the heart. In the isolated right atrium perfused with blood from the support dog, vecuronium, injected into the external jugular vein of the support dog, dose-dependently inhibited the negative chronotropic and inotropic responses to carbachol or SAP stimulation and the negative followed by positive chronotropic and inotropic responses to nicotine. The ID50 values for carbachol, nicotine and SAP stimulation were not significantly different. These results suggest that parasympatholytic effects of vecuronium are mediated by not only muscarinic receptors but also neuronal nicotinic receptors in hearts of anesthetized dogs.

Long duration of erythrocyte hypoplasia after bone marrow transplantation

Bone marrow transplantation was performed on a 15 year old girl with chronic myelogenous leukemia. The bone marrow was obtained from her younger sister, who was human leukocyte antigen haplo-identical but major ABO incompatible. As a result, the condition of pure red cell aplasia (PRCA) persisted over a long period of time. In order to overcome major ABO incompatibility, erythrocytes were eliminated from the bone marrow graft before transplantation, and methotrexate and cyclosporine (CsA) were used to prevent graft-versus-host disease (GVHD). Administration of erythropoietin proved ineffective. B19 parvovirus infection could not be detected during that time. Agglutinin titers decreased to less than fourfold in parallel with the recovery of erythrocytes. Reports on similar PRCA have been limited to cases of transplantation with ABO incompatibility and cases where CsA was administered to prevent GVHD. This suggests that ABO incompatibility and CsA might be related to the development of PRCA.

Delayed expression of dystrophin on regenerating muscle from two siblings with Becker muscular dystrophy

We present here a unique expression of dystrophin on biopsied muscle from 2 siblings with Becker muscular dystrophy (BMD). They had neither muscle weakness nor atrophy. Clustered dystrophin-deficient fibers were constituted to regenerating basophilic fibers (mainly type 2C fiber) based on histochemical stainings. We speculate that the developmental delay in the expression of dystrophin is a characteristic finding in regenerating fibers from asymptomatic and young BMD patients, such as the siblings in this report.

Cardiovascular effects of R- and S-enantiomers of Ro 22-9194, (2R)-2-amino-N- (2,6-dimethylphenyl)-N-[3-(3-pyridyl)propyl]propionamide D-tartrate and (2S)-2-amino-N-(2,6-dimethylphenyl)-N-[3-(3-pyridyl)propyl]propionamide L-tartrate, in dog heart preparations

A newly synthesized compound, Ro 22-9194, relates in part of to the chemical structure of lidocaine. The cardiac effects of R- and S-enantiomers of Ro 22-9194 were investigated on isolated right atrial and left ventricular (LV) preparations which were cross-perfused with blood from another donor dog and an anesthetized open-chest dog. Each enantiomer (1-1,000 micrograms) decreased dose-dependently the sinus rate and atrial developed tension in the isolated right atrium (RA). The negative chronotropic responses to R- and S-enantiomers were not significantly different, and the negative inotropic responses to R- and S-enantiomers were also generally comparable. Both R- and S-enantiomers (10-3,000 micrograms) also decreased the ventricular developed tension in a dose-related manner similarly. In neurally decentralized, anesthetized, open-chest dogs, R- and S-enantiomers (0.1-3 mg/kg) injected into the femoral vein dose-dependently prolonged atrioventricular (A-V) conduction time and decreased heart rate (HR) and arterial blood pressure (ABP). Each enantiomer (3 mg/kg intravenously, i.v.) prolonged the interval between His bundle and ventricle rather than the interval between atrium and His bundle. There was no significant difference between R- and S-enantiomer-induced negative dromotropic actions. The duration of the negative dromotropic response to each enantiomer (3 mg/kg i.v.) was longer than that of the decrease in BP. These results suggest that the negative chronotropic, inotropic, and dromotropic effects of R- and S-enantiomers of Ro 22-9194 are not stereospecific in dog heart.

Interactions between recombinant human erythropoietin and serum factor(s) on murine megakaryocyte colony formation

We investigated the interactions between human erythropoietin (hEpo) and serum factor(s) on murine megakaryocyte (MK) colony formation. Serum-free cultures supported the growth of a large number of murine MK colonies in the presence of murine interleukin-3 (mIL-3). The addition of fetal calf serum (FCS) to mIL-3-containing cultures resulted in only a minimal increase in the number of murine MK colonies. In contrast, hEpo alone had no murine MK colony-stimulating activities in serum-free cultures. hEpo required the presence of FCS, murine serum, or human serum in cultures to promote murine MK colony growth and synergized with these sera to stimulate murine MK colony formation. Furthermore, sera from patients with aplastic anemia showed higher synergistic activities with hEpo than sera from hematologically normal persons (normal human serum). When normal human serum was fractionated by gel-filtration chromatography, two peaks with the synergistic activity were observed in the eluent. However, serum did not show any synergistic effects with hEpo on the growth of murine GM colonies or murine colony-forming unit-erythroid-derived colonies. Although human serum synergized with hEpo to stimulate murine MK colony formation, human cytokines such as IL-3, IL-4, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte-CSF (G-CSF) failed to induce murine MK colony formation in Epo-containing cultures. In cultures containing human IL-1 alpha + human IL-6 + hEpo as well as in cultures containing hEpo, human IL-3 and human GM-CSF failed to show stimulatory effects on murine MK colony formation. Moreover, the synergistic activity of human serum with hEpo could not be neutralized by antibodies such as antihuman IL-1 alpha, antihuman IL-3, antihuman IL-4, antihuman IL-6, antihuman G-CSF, and antihuman GM-CSF. Our data show that serum contains a growth factor(s) that synergizes with Epo to stimulate the proliferation and differentiation of MK precursors, and strongly suggest that this factor(s) is an unique growth factor(s) that is distinct from IL-1 alpha, IL-3, IL-4, IL-6, G-CSF, and GM-CSF.

Evidence for a single catalytic site of honeybee alpha-glucosidase I by chemical modification with diethylpyrocarbonate

Honeybee alpha-glucosidase I was inactivated with diethylpyrocarbonate (DEPC). The inactivation followed pseudo-first-order kinetics. The rate of the loss of activity was decreased by the addition of a substrate, maltose. Since there was no spectral change in the tyrosine absorption region, it was recognized that DEPC did not react with this residue. The alpha-glucosidase had one free sulfhydryl group, which was not involved in the catalytic reaction, and was not modified by DEPC. On the other hand, the specific reaction of DEPC with a histidyl residue was spectrophotometrically confirmed by an increase in absorption near 240 nm, and the activity of the inactivated enzyme was restored by hydroxylamine. The modification rate of one histidyl residue by DEPC was almost equal to the rate of the activity loss. These results indicate that there is one histidyl residue at or near the catalytic site, and that honeybee alpha-glucosidase I has a single active site.

[Pharmacokinetic and clinical studies with meropenem in the pediatric field. Pediatric Study Group of Meropenem]

Pharmacokinetic and clinical evaluations in pediatrics were made on meropenem (SM-7338, MEPM), a new parenteral dehydropeptidase-1 stable carbapenem used without any inhibitors, at 33 medical institutions. The results are summarized as follows. 1. Pharmacokinetic studies. MEPM at a dose of 10, 20, or 40 mg/kg was administered to 53 children by 30-minute drip infusion. Peak plasma concentrations (Cmax's) and plasma half-lives (T1/2's) of these doses were 28.5, 47.2 and 130.0 micrograms/ml, and 0.80, 0.93 and 0.94 hours, respectively. A clear dose response was observed in Cmax's and T1/2 values were quite similar to those observed in adults. In the first 6 hours after administration, 54.4 to 68.1% of the administered drug was recovered in urine. The cerebrospinal fluid (CSF) levels of MEPM in patients with purulent meningitis were 0.13 microgram/ml at a dose of 6 mg/kg, and 0.64 to 4.22 micrograms/ml at a dose of 29 to 44 mg/kg within day 4 of onset. The penetration rate of MEPM showed an intermediate value among those for other cephalosporin antibiotics. 2. Clinical study. Clinical efficacies of MEPM were evaluated in 389 cases. The most common doses used were 10 to 20 mg/kg/once, 2 to 3 times a day. The maximum dose was 173 mg/kg/day q.i.d. MEPM gave "excellent" or "good" responses in 242 (97.6%) out of 248 cases in which causative organisms were documented and in 134 (95.0%) out of 141 cases in which causative organisms were not identified. Clinical efficacy rates were 100% in 11 patients with purulent meningitis, 85.7% in 7 with septicemia, 98.8% in 173 with pneumonia, and 100% in 65 with UTI. Bacteriologically, 260 strains (96.7%) out of 269 strains were eradicated by MEPM treatment. Eradication rates were 89.2% for Staphylococcus aureus (37 strains) and 100% for Streptococcus pneumoniae (35 strains). The overall eradication rate for Gram-positive bacteria was 94.6%. Among Gram-negative bacteria, 98.3% out of 172 strains were eradicated. The eradication rate of Haemophilus influenzae (73 strains) was 98.6% and Pseudomonas aeruginosa (11 strains) was 90.9%, and all of Branhamella catarrhalis (15 strains), Escherichia coli (42 strains), and Klebsiella pneumoniae (6 strains) were eradicated. Out of 84 cases for which previous antibiotic therapies of 3 days or longer were not successful, MEPM gave "excellent" or "good" responses in 77 cases (91.7%) and excellent bacteriological responses (95.7%).(ABSTRACT TRUNCATED AT 400 WORDS)

[Clinical pharmacology and efficacy of meropenem]

We studied a newly developed carbapenem, meropenem (MEPM), and obtained the following results. 1. Pharmacokinetics of MEPM in pediatrics was examined in 3 patients. MEPM was injected intravenously at a dose of 16-22 mg/kg by drip infusion for 30 minutes, and its concentrations in serum and urine were determined using bioassay. The average peak value of serum levels of MEPM was 38.4 micrograms/ml and T1/2 beta of MEPM was 1.26 hours. The urinary recovery rate for the first 6 hours after administration was 65.6%. 2. Clinical evaluations of MEPM in pediatrics were done in 14 patients with ages ranging, 1 month to 14 years, with various bacterial infections. Excellent or good clinical responses were observed in all patients, and bacteriological eradication were obtained in 7 out of 8 cases. No serious side effects were observed in any cases, but 2 showed mild and transient GOT, GPT elevations.

[Seizure susceptibility in aged rats--pentylenetetrazol-induced seizures and amygdaloid kindling seizures]

Seizure susceptibility in male aged rats (21-25 mo. age) was investigated by pentylenetetrazol (PTZ)-induced seizures and amygdaloid kindling seizures. Male adult rats (3-4 mo. of age) were used as the control group. During 60 min. after the administration of PTZ (70 mg/kg, s.c.), the aged rats had a higher incidence and a significantly longer duration of generalized convulsion than the control group. On the other hand, the kindling rate of the aged rats was significantly slower than that of the control. The aged rats remained longer at stage 1-2 indicative of partial seizures. However, the aged rats skipped stage 3 on their way to stage 4-5 (generalized seizures), and showed a more violent stage 5 seizure than the control group. They had a longer duration of afterdischarges (AD) through the kindling process with a significantly faster propagation of AD to the contralateral amygdala as compared with the control group. The present study suggests that aged rats are prone to convulsion, while they have a difficulty in acquisition of epileptogenesis.

The influence of tetrodotoxin on the toxic effects of aconitine in vivo

Both aconite toxins (aconitine, mesaconitine, and hypaconitine) and a pufferfish toxin (tetrodotoxin, TTX) were detected in the blood of a legal autopsy case. In order to elucidate the in vivo influence of TTX on the toxic effects of aconitine, a mixture of aconitine and TTX was administered to male ICR mice orally or intraperitoneally. The animal experiments revealed that the time of death due to aconitine was significantly delayed in proportion to the dose of TTX compared with the case for aconitine alone, and that the mortality of aconitine was lowered by TTX when the dose ratio of the two toxins was in a particular range. Accordingly, it is thought that the toxic effects of aconitine are attenuated by TTX in vivo.

Cardiac effects of vecuronium and its interaction with autonomic nervous system in isolated perfused canine hearts

The chronotropic and inotropic effects of vecuronium bromide and its interaction with the autonomic nervous system were investigated in the isolated, cross-circulated right atrial and left ventricular preparations of the dog. Vecuronium, injected into the external jugular vein of the support dog, induced dose-dependent decreases in heart rate and arterial blood pressure, and increased atrial contractile force with no change in sinus rate in isolated atrial preparations. Vecuronium (1-3,000 micrograms), injected into the sinus node artery of the isolated atrium, induced dose-dependent increases in atrial contractile force with small increases in sinus rate. Vecuronium also increased the ventricular contractile force in a dose-dependent manner. The positive inotropic effect was attenuated in part by propranolol, but not by either tetrodotoxin or imipramine. Vecuronium inhibited in a dose-related manner the negative chronotropic and inotropic responses to parasympathetic nerve stimulation and carbachol (CCh) and the negative followed by positive cardiac responses to nicotine, but did not attenuate the positive responses to sympathetic nerve stimulation. The ID50s for the responses to parasympathetic stimulation, CCh, and nicotine were not significantly different. Vecuronium enhanced the positive chronotropic and inotropic responses to sympathetic nerve stimulation, tyramine, norepinephrine, and isoproterenol. These results indicate that (a) vecuronium causes the positive inotropic responses mediated by nonadrenergic mechanisms and beta-adrenoceptors, (b) vecuronium blocks ganglionic and presynaptic nicotinic and postsynaptic muscarinic receptor-mediated responses similarly, and (c) vecuronium enhances beta-adrenoceptor-mediated responses in the dog heart.