Trigeminal uptake and clearance of inhaled manganese chloride in rats and mice.

Inhaled manganese (Mn) can enter the olfactory bulbs via the olfactory epithelium, and can then be further transported trans-synaptically to deeper brain structures. In addition to olfactory neurons, the nasal cavity is innervated by the maxillary division of the trigeminal nerve that projects to the spinal trigeminal nucleus. Direct uptake and transport of inhaled metal particles in the trigeminal system has not been investigated previously. We studied the uptake, deposition, and clearance of soluble Mn in the trigeminal system following nose-only inhalation of environmentally relevant concentrations. Rats and mice were exposed for 10-days (6 h/day, 5 days/week) to air or MnCl2 aerosols containing 2.3 +/- 1.3 mg/m3 Mn with mass median aerodynamic diameter (MMAD) of 3.1 +/- 1.4 microm for rats and 2.0 +/- 0.09 mg/m3 Mn MnCl2 with MMAD of 1.98 +/- 0.12 microm for mice. Mn concentrations in the trigeminal ganglia and spinal trigeminal nucleus were measured 2 h (0-day), 7-, 14-, or 30-days post-exposure using proton induced X-ray emission (PIXE). Manganese-exposed rats and mice showed statistically elevated levels of Mn in trigeminal ganglia 0-, 7- and 14-days after the 10-days exposure period when compared to control animals. The Mn concentration gradually decreased over time with a clearance rate (t1/2) of 7-8-days. Rats and mice were similar in both average accumulated Mn levels in trigeminal ganglia and in rates of clearance. We also found a small but significant elevation of Mn in the spinal trigeminal nucleus of mice 7-days post-exposure and in rats 0- and 7-days post-exposure. Our data demonstrate that the trigeminal nerve can serve as a pathway for entry of inhaled Mn to the brain in rodents following nose-only exposure and raise the question of whether entry of toxicants via this pathway may contribute to development of neurodegenerative diseases.

Potential risk of vasovagal syncope for motor vehicle driving.

Vasovagal syncope is the most common cause of syncope, but its risk for driving remains uncertain. We analyzed the clinical characteristics of patients who had syncope during driving and subsequently underwent the head-up tilt test (HUTT). Of the 245 consecutive patients undergoing HUTT, 23 (9%) had > or =1 episode of syncope during driving. HUTT was positive in 19 (group A) and negative in 4 (group B) patients. No patient had structural heart disease. In group A, the driving incident occurred on the first syncope in 3 patients, and the other 16 patients had 1 to 4 episodes of prior syncope not associated with driving. In group B, the driving incident occurred on the first syncope in 1 patient, and the other 3 patients had prior syncope (3 episodes in each) not associated with driving. Seven group A and 1 group B patients had 2 syncope-related driving incidents, and the remaining patients had only 1 syncope-related driving incident. The syncope-related driving incidents caused personal injury in 7 group A and 2 group B patients. One incident in 1 group A patient caused the death of another driver. After HUTT, all but 1 patient in group A received medical treatment and only 1 patient in group B received empirical beta-blocker therapy. During the follow-up of 51+/-26 months, 1 patient died and another was lost to follow-up. Of the remaining patients, 4 patients had recurrence of syncope and 2 patients had presyncope in group A. One of these patients had another syncope-related driving incident. No group B patient had syncope recurrence. A second etiology of syncope was never found in any patient. We conclude that vasovagal syncope during driving is not uncommon in patients referred for syncope evaluation. Early medical attention to patients with vasovagal syncope may help reduce syncope-related driving incidents.

Usefulness of ibutilide in facilitating successful external cardioversion of refractory atrial fibrillation.

We repeated direct-current cardioversion of atrial fibrillation after ibutilide injection in patients who failed conventional cardioversion. Eleven of 12 patients (92%) had successful cardioversion and avoided the need for internal cardioversion.

The mean ventricular fibrillation cycle length: a potentially useful parameter for programming implantable cardioverter defibrillators.

In programming the implantable cardioverter defibrillator (ICD), the ventricular tachycardia (VT) detection cycle length (CL) is based on the CL of the documented tachycardia but the ventricular fibrillation (VF) detection CL is set arbitrarily. Appropriate programming of VF detection may not only reduce the incidence of inappropriate ICD shocks for non-VF rhythms but can also avoid the fatal underdetection of VF. The mean VFCL may provide a useful parameter for optimal ICD programming for VF detection if it is reproducible. This study examined the intrapatient reproducibility and interpatient variation of the mean VFCL in 30 ICD patients (25 men and 5 women, mean age 63 +/- 13 years). A total of 210 VF episodes (7 +/- 4 per patient, range 3-17) induced by T-wave shocks (166) or AC (44) at the ICD implant (30 patients) and the predischarge test (12 of 30 patients) were analyzed. The mean VFCL was calculated from the stored V-V intervals in the ICDs. Although the mean VFCL varied significantly from 171 +/- 6 to 263 +/- 11 ms (P < 0.01) among different patients, it was reproducible among different VF episodes in an individual patient (maximal variation 4-50 ms, P > 0.05). The mean VFCL was not significantly different between patients with and without antiarrhythmic drugs (210 +/- 32 vs 210 +/- 23 ms, P > 0.05) and was correlated with the ventricular effective refractory period (r = 0.5, P < 0.05). The mean VFCL varies greatly among different patients but remains reproducible in an individual patient, suggesting that the mean VFCL may serve as a reference for ICD programming of VF detection.

Evaluation and management of atrial fibrillation in the emergency department.

AF is the most common sustained cardiac arrhythmia. Recognition and appropriate management of AF is important to optimize care of concurrent medical problems and prevent long-term consequences. DC cardioversion under sedation should be performed in patients with pulmonary edema, angina, or hypotension. Ventricular rate control is the first choice in stable patients with rapid ventricular rate. Anticoagulation should be considered in all patients with AF duration < 48 hours, except for those under 65 years old and having no other risk factors of stroke. Recent data imply that early attempts at cardioversion may increase success rates and decrease AF recurrence rates. Thus, transesophageal echocardiogram-guided early cardioversion may become more widely used.

Autonomic function in manganese alloy workers.

The observation of orthostatic hypotension in an index case of manganese toxicity lead to this prospective attempt to evaluate cardiovascular autonomic function and cognitive and emotional neurotoxicity in eight manganese alloy welders and machinists. The subjects consisted of a convenience sample consisting of an index case of manganese dementia, his four co-workers in a "frog shop" for gouging, welding, and grinding repair of high manganese railway track and a convenience sample of three mild steel welders with lesser manganese exposure also referred because of cognitive or autonomic symptoms. Frog shop air manganese samples 9.6-10 years before and 1.2-3.4 years after the diagnosis of the index case exceeded 1.0 mg/m3 in 29% and 0.2 mg/m3 in 62%. Twenty-four-hour electrocardiographic (Holter) monitoring was used to determine the temporal variability of the heartrate (RR' interval) and the rates of change at low frequency (0.04-0.15 Hz) and high frequency (0.15-0.40 Hz). MMPI and MCMI personality assessment and short-term memory, figure copy, controlled oral word association, and symbol digit tests were used. The five frog shop workers had abnormal sympathovagal balance with decreased high frequency variability (increased ln LF/ln HF). Seven of the eight workers had symptoms of autonomic dysfunction and significantly decreased heart rate variability (rMSSD) but these did not distinguish the relative exposure. Mood or affect was disturbed in all with associated changes in short-term memory and attention in four of the subjects. There were no significant correlations with serum or urine manganese. Power spectrum analysis of 24-h ambulatory ECG indicating a decrease in parasympathetic high frequency activation of heart rate variability may provide a sensitive index of central autonomic dysfunction reflecting increased exposure to manganese, although the contribution of exposures to solvents and other metals cannot be excluded. Neurotoxicity due to the gouging, welding, and grinding of mild steel and high manganese alloys (11-25%) merits air manganese and neuropsychologic surveillance including autonomic function by Holter monitoring of cardiovagal activation.

Causes and consequences of discontinuation of the implantable cardioverter-defibrillator therapy in non-terminally ill patients.

Infection and implantable cardioverter-defibrillator shocks are important contributing factors to discontinuation of cardioverter-defibrillator therapy in non-terminally ill patients. These patients are at a high risk of sudden cardiac death despite continued antiarrhythmic drug therapy.

Long distance transmission of diagnostic cardiovascular information.

Availability of advanced cardiac diagnostic procedures has proven to decrease the morbidity and mortality associated with common cardiovascular diseases. It was requested that the University of Nebraska Medical Center (UNMC) provide a rural hospital with advanced cardiology services. The services included monitoring of inpatients and rapid interpretation of cardiac diagnostic tests. UNMC proposed to solve this problem by building a computer-based system to transmit diagnostic cardiac information from a rural hospital to UNMC for interpretation by a cardiologist. The information transmitted to UNMC was grouped into two categories: 1) cardiovascular ultrasound, 2) ambulatory and 12-lead electrocardiograms. The information consisted of digital and analog waveform information, static images, and 30 fps video. The system provided rapid data transmission to UNMC over a T-1 line. The system utilized a compression technology which did not degrade the interpretation quality of the data. This system has increased the availability of advanced cardiac diagnostic services to general medical practitioners in a rural hospital. In addition, the system has significantly reduced the time and cost to transmit vital cardiac diagnostic information, thus improving the quality of care received by rural patients.

Desensitization of the adipocyte A(1) adenosine receptor during untreated experimental diabetes mellitus.

We examined the changes that occur in the adenosine receptor system during diabetes mellitus. Experimental diabetes mellitus was induced in male Lewis rats with streptozocin (65 mg/kg), and A(1) adenosine receptor binding was characterized with [(125)I]N (6)-2-(4-aminophenyl) ethyladenosine. In adipocytes, high-affinity A(1) adenosine receptor binding decreased from 1466±228 of protein to 312±123 fmol/mg of protein (p<0.01) following 14 d of untreated diabetes mellitus. Neither the dissociation constant (K (d)=1.3±0.2 nM) nor the basal level of adenylate cyclase activity (2.8±1.1 pmol cAMP/mg of protein/min) was altered by diabetes mellitus. The dose-response curve for the inhibition of adenylate cyclase byN (6)-R-phenylisopropyladenosine (R-PIA), however, did show a rightward shift, indicating that diabetic adipocyte membranes were less sensitive to the effects of adenosine than nondiabetic adipocyte membranes. In contrast, the A(1) adenosine receptor-binding characteristics and adenylate cyclase dose-response curve for cerebral cortical tissue were unchanged by diabetes. These findings suggest that diabetes has tissue-specific effects on the A(1) adenosine receptor system. Furthermore, the decreased sensitivity to adenosine potentially worsens the hyperlipidemia associated with diabetes mellitus. Such alterations in the adenosine receptor system may play a previously undescribed role in the pathophysiology of diabetes mellitus and may help explain why some organs are severely affected by diabetes, but others are relatively spared. Understanding these alterations in adenosine receptor function may lead tonovel therapies of this common metabolic disease.

Defibrillator patch electrode constriction: an underrecognized entity.

Pericardial constriction associated with the placement of intrapericardial defibrillator patches is a rare occurrence that is reported only one tenth as often in defibrillator patients as in patients undergoing other types of cardiac operations. Although this discrepancy may be attributable to a lower incidence of constriction with the defibrillator patch electrode procedure, it may also indicate a failure to recognize that progressive right heart failure and signs of low cardiac output that could be due to pericardial constriction and not progressive systolic dysfunction. Because surgical removal of the patches and decortication of the epicardial surface is the only effective therapy, it is important to recognize this uncommon, but profoundly debilitating entity.

Clinical comparison of acute single to dual chamber pacing in chronotropically incompetent patients with left ventricular dysfunction.

Dual chamber, rate responsive (DDDR) pacing is felt to be superior to ventricular, rate responsive (VVIR) pacing since it more closely mimics the normal electrical and hemodynamic activity of the heart. This reasoning has been used to justify the higher initial costs and increased complexity of dual chamber system. This study was designed to determine if objective criteria could be identified during acute testing justify implanting a dual chamber instead of a single chamber system in patients with left ventricular dysfunction. Eight patients with DDDR pacemakers (implanted for chronotropic incompetence) and left ventricular dysfunction underwent exercise radionuclide angiography and graded exercise treadmill testing. Each patient performed the tests in the single (VVIR) and dual (DDDR) chamber modes in a randomized, blinded fashion. We found that objective parameters such as ejection fraction (31% +/- 13% vs 31% +/- 10%), exercise tolerance (6.1 +/- 2.7 min vs 6.3 +/- 2.9 min), oxygen consumption (VO2) (941 +/- 286 mL/min vs 994 +/- 314 mL/min), carbon dioxide production (VCO2) (995 +/- 332 mL/min vs 1054 +/- 356 mL/min), and maximum attainable workload (43 +/- 24 W vs 46 +/- 22 W) did not differ between the single and dual chamber pacing modes. These findings suggest that in the acute setting, the additional cost and complexity of dual chamber, rate responsive pacing cannot be justified by objective improvements in exercise tolerance in patients with underlying left ventricular dysfunction.

Treatment of supraventricular tachycardias with transcatheter delivery of radiofrequency current.

Medical therapy for the treatment of supraventricular tachycardias is frequently ineffective and associated with significant side effects, whereas curative surgical approaches have generally been limited by their considerable morbidity and cost. Greater understanding of the mechanisms underlying supraventricular tachycardias has improved our ability to precisely map endocardial areas critical to arrhythmogenesis. Advances in catheter ablation techniques and particularly the use of radiofrequency current to generate thermal energy for ablation have resulted in dramatic success rates for curative catheter ablation. This review examines the physics of radiofrequency current ablation and its application to the treatment of atrial fibrillation, atrial flutter, AV nodal reentrant tachycardia, and arrhythmias associated with the Wolff-Parkinson-White syndrome. The limitations, risks, and cost-effectiveness of this technique relative to medical and surgical approaches are also evaluated.

Glycoprotein nature of the A2-adenosine receptor binding subunit.

Mammalian A2-adenosine receptor binding subunits (A2AR) can be visualized by covalent labeling with the photoaffinity crosslinking ligand 125I-2-[4-[2-[2-[(4-aminophenyl)methylcarbonylamino] ethylaminocarbonyl]ethyl]phenyl]ethylamino-5'-N-ethylcarboxamidoad enosine or directly with the azide derivative described in this paper. The protein comprising the A2-adenosine receptor binding subunit migrates with a Mr of 45,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In this study, the glycoproteins representing the radiolabeled A1- and A2-adenosine receptor binding subunit from bovine brain were compared by partial peptide maps and following treatment with exo- and endoglycosidases. Peptide maps using two separate proteases reveal that the A1- and A2-adenosine receptor binding subunits share no common peptide fragments by two-dimensional gel electrophoresis. Endoglycosidase F treatment of labeled A2AR results in a single labeled peptide of Mr 38,000 without intermediate peptides, suggesting a single N-linked carbohydrate chain. The labeled A2AR demonstrates a sensitivity to neuraminidase, as evidenced by an increased mobility on gel electrophoresis, suggesting the receptors contain a glycan component containing terminal sialic acid. Treatment of the labeled A2AR with alpha-mannosidase reveals two distinct populations of A2ARs, one of which is sensitive and the other resistant to the enzyme. The nonadditivity of sequential treatments with the two exoglycosidases suggests, a heterogeneous population of A2AR containing either complex- or high mannose-type carbohydrate chains. These data suggest the A2AR is a Mr 45,000 glycoprotein with a single carbohydrate chain of either the complex or high mannose type. In addition, the A1- and A2ARs are distinct glycoproteins, as evidenced by their differing molecular weights (before and after deglycosylation) and distinct peptide maps.

Demonstration of both A1 and A2 adenosine receptors in DDT1 MF-2 smooth muscle cells.

Adenosine receptors of the A1 and A2 subtypes were characterized in membranes from DDT1 MF-2 smooth muscle cells. These cells possess a high density of A1 adenosine receptors (Bmax = 0.8-0.9 pmol/mg of protein), as measured by both agonist and antagonist radioligands. Agonists compete for [125I]N6-[2-(4-amino-3-iodophenyl)ethyl]-adenosine (A1 receptor-selective radioligand) binding with the following potency series: (R)-phenylisopropyladenosine [(R)-PIA] greater than 5'-N-ethylcarboxamide adenosine (NECA) greater than (S)-PIA, indicative of their interaction with A1 adenosine receptors. Agonist competition for [3H]8-(4-[[[(2-aminoethyl)amino]carbonyl)methyl)oxy]phenyl)-1, 3-dipropylxanthine [( 3H]XAC) (an antagonist radioligand for the A1 adenosine receptor) was described by a two-state model of 1.3 nM (high affinity state, KK) and 370 nM (low affinity state, KL), with 70% of the receptors in the high affinity state (RH). Addition of guanosine 5'-[beta, alpha-imido]triphosphate (100 microM) shifted the (R)-PIA competition curves to the right to lower affinities. Photoaffinity labeling with the agonist photoprobe [125I]N6-[2-(4-amino-3-iodophenyl) ethyl]adenosine indicates that the A1 adenosine receptor binding subunit is a Mr 38,000 protein. Adenosine receptor agonists [(R)-PIA, NECA, and (S)-PIA] inhibited isoproterenol-stimulated adenylate cyclase activity in DDT1 MF-2 cell membranes with IC50 values of 62, 538, and 750 nM, respectively. Inhibition of adenylate cyclase by (R)-PIA was attenuated by the A1 receptor antagonist XAC and following inactivation of Gi with pertussis toxin (100 ng/ml). Using a recently developed A2 adenosine receptor agonist radioligand 2-[4-(2-[( 4-aminophenyl]methylcarbonyl)ethyl) phenyl]ethylamino-5'-N-ethylcarboxamido adenosine (125I-PAPA-APEC), we have demonstrated the presence of A2 adenosine receptors in this cell line. Saturation curves with 125I-PAPA-APEC indicated the Bmax and Kd values to be 0.21 pmol/mg of protein and 4.0 nM, respectively. In competition experiments, NECA was more potent at inhibiting 125I-PAPA-APEC binding than (R)-PIA, with their respective IC50 values being 5.6 and 351 nM. The photolabeled A2 adenosine receptor migrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an Mr of 42,000. Finally, adenosine receptor agonists stimulated adenylate cyclase activity by approximately 2-3 fold with the following potency series: PAPA-APEC greater than or equal to NECA greater than (R)-PIA, indicative of their interaction at A2 receptors. These data represent the first demonstration of the presence of both A1 and A2 receptors in a single cell line, DDT1 MF-2 smooth muscle cells.

Agonist derived molecular probes for A2 adenosine receptors.

The adenosine agonist 2-(4-(2-carboxyethyl)phenylethylamino)-5'-N- ethylcarboxamidoadenos ine (CGS21680) was recently reported to be selective for the A2 adenosine receptor subtype, which mediates its hypotensive action. To investigate structure/activity relationships at a distal site, CGS21680 was derivatized using a functionalized congener approach. The carboxylic group of CGS21680 has been esterified to form a methyl ester, which was then treated with ethylenediamine to produce an amine congener. The amine congener was an intermediate for acylation reactions, in which the reactive acyl species contained a reported group, or the precursor for such. For radioiodination, derivatives of p-hydroxyphenylpropionic, 2-thiophenylacetic, and p-aminophenylacetic acids were prepared. The latter derivative (PAPA-APEC) was iodinated electrophilically using [125I]iodide resulting in a radioligand which was used for studies of competition of binding to striatal A2 adenosine receptors in bovine brain. A biotin conjugate and an aryl sulfonate were at least 350-fold selective for A2 receptors. For spectroscopic detection, a derivative of the stable free radical tetramethyl-1-piperidinyloxy (TEMPO) was prepared. For irreversible inhibition of receptors, meta- and para-phenylenediisothiocyanate groups were incorporated in the analogs. We have demonstrated that binding at A2 receptors is relatively insensitive to distal structural changes at the 2-position, and we report high affinity molecular probes for receptor characterization by radioactive, spectroscopic and affinity labelling methodology.

Identification of the A2 adenosine receptor binding subunit by photoaffinity crosslinking.

A high-affinity iodinated agonist radioligand for the A2 adenosine receptor has been synthesized to facilitate studies of the A2 adenosine receptor binding subunit. The radioligand 125I-labeled PAPA-APEC (125I-labeled 2-[4-(2-[2-[(4- aminophenyl)methylcarbonylamino]ethylaminocarbonyl]- ethyl)phenyl]ethylamino-5'-N-ethylcarboxamidoadenosine) was synthesized and found to bind to the A2 adenosine receptor in bovine striatal membranes with high affinity (Kd = 1.5 nM) and A2 receptor selectivity. Competitive binding studies reveal the appropriate A2 receptor pharmacologic potency order with 5'-N-ethylcarboxamidoadenosine (NECA) greater than (-)-N6-[(R)-1-methyl- 2-phenylethyl]adenosine (R-PIA) greater than (+)-N6-[(S)-1-methyl-2- phenylethyl]adenosine (S-PIA). Adenylate cyclase assays, in human platelet membranes, demonstrate a dose-dependent stimulation of cAMP production. PAPA-APEC (1 microM) produces a 43% increase in cAMP production, which is essentially the same degree of increase produced by 5'-N- ethylcarboxamidoadenosine (the prototypic A2 receptor agonist). These findings combined with the observed guanine nucleotide-mediated decrease in binding suggest that PAPA-APEC is a full A2 agonist. The A2 receptor binding subunit was identified by photoaffinity-crosslinking studies using 125I-labeled PAPA-APEC and the heterobifunctional crosslinking agent N-succinimidyl 6-(4'-azido-2'-nitrophenylamino)hexanoate (SANPAH). After covalent incorporation, a single specifically radiolabeled protein with an apparent molecular mass of 45 kDa was observed on NaDodSO4/PAGE/autoradiography. Incorporation of 125I-labeled PAPA-APEC into this polypeptide is blocked by agonists and antagonists with the expected potency for A2 receptors (see above) and is decreased in the presence of 10(-4) M guanosine 5'-[beta, gamma-imido]triphosphate. Photoaffinity crosslinking of the A1 adenosine receptor binding subunit with 125I-labeled 8-[4-[2-(4- aminophenylacetylamino)ethyl]carbonylmethyloxyphenyl]-1,3-di propylxanthine (PAPAXAC) (an A1 selective photoaffinity probe) in the same tissue reveals a 38-kDa peptide that exhibits the appropriate A1 receptor pharmacology. 125I-labeled PAPA-APEC, therefore, has identified the A2 receptor binding subunit as a 45-kDa protein that is unique and distinct from the A1 binding subunit.