The effects of inhomogeneities and anisotropies on electrocardiographic fields: a 3-D finite-element study

The aim of this study was to quantify the effects of selected inhomogeneities and anisotropies on computed electric potential fields associated with the electrocardiographic forward problem. The model construction was based on the Utah Torso model and included geometry for major anatomical structures such as subcutaneous fat, skeletal muscle, and lungs, as well as for epicardial fatpads, major arteries and veins, and the sternum, ribs, spine, and clavicles. Measured epicardial potentials served as the electrical source for solutions to the electrocardiographic forward problems computed using the finite element method (FEM). The geometry of the torso model for each simulation was constant, but different combinations of conductivities were assigned to individual organs or tissues. Comparisons of different conductivity combinations followed one of two basic schemes: 1) a homogeneous torso served as the reference against which we compared simulations with a single organ or tissue and assigned its nominal conductivity, or 2) a fully inhomogeneous torso served as the reference and we removed the effect of individual organs or tissues by assigning it the homogeneous conductivity value. When single inhomogeneities were added to an otherwise homogeneous isotropic model, anisotropic skeletal muscle (at a 15:1 anisotropy ratio) and the right and left lung had larger average effects (12.8, 12.7, and 12.1% relative error (RE), respectively) than the other inhomogeneities tested. Our results for removing single inhomogeneities show that the subcutaneous fat, the anisotropic skeletal muscle (with the degree of anisotropy equal to 7:1), and the lungs have larger average impacts on the body surface potential distributions than other elements of the model (with values of 14.9, 12.6, and 11.7% RE, respectively). The results also show that the size of the effect depended strongly on the distribution of epicardial potentials. The results of this study suggest that accurate representation of tissue inhomogeneity has a significant effect on the accuracy of the forward solution, with regions near the torso surface playing a larger role, in general, than those near the heart.

Effect of dedicated monitor watchers on patients' outcomes

BACKGROUND: In 55% of progressive care units, someone is assigned to watch the cardiac monitors at all times, but the effect of this practice on patients' outcomes has not been examined. OBJECTIVE: To evaluate the effect of continual observation of telemetry units by a monitor watcher on mortality, frequency of transfer to a critical care unit, and the occurrence of five life-threatening dysrhythmias. METHODS: Data for this quasi-experimental study were collected on 1185 patients for a 9-month period in 1993 when the cardiac progressive care unit had a monitor watcher and on 1198 patients for a 9-month period in 1994 when the unit had no monitor watcher. RESULTS: We found no significant differences in mortality, frequency of transfer to a critical care unit, or the occurrence of three of the five dysrhythmias examined. The presence of a monitor watcher was associated with significantly fewer episodes of sustained ventricular tachycardia but more bradyarrhythmias. For both sustained ventricular tachycardia and bradyarrhythmias, the monitor watcher variable remained in the final multivariate logistic regression models. CONCLUSIONS: The presence of a monitor watcher was not associated with lower rates of most adverse outcomes evaluated; however, fewer episodes of sustained ventricular tachycardia occurred when a monitor watcher was present. Sustained ventricular tachycardia is life-threatening, disturbing to the patient, and may result in a longer hospital stay while medical therapy is being adjusted. The results of this study support the use of a monitor watcher to prevent sustained ventricular tachycardia.

Effect of dedicated monitor watchers on patients' outcomes

BACKGROUND

In 55% of progressive care units, someone is assigned to watch the cardiac monitors at all times, but the effect of this practice on patients' outcomes has not been examined.

OBJECTIVE

To evaluate the effect of continual observation of telemetry units by a monitor watcher on mortality, frequency of transfer to a critical care unit, and the occurrence of five life-threatening dysrhythmias.

METHODS

Data for this quasi-experimental study were collected on 1185 patients for a 9-month period in 1993 when the cardiac progressive care unit had a monitor watcher and on 1198 patients for a 9-month period in 1994 when the unit had no monitor watcher.

RESULTS

We found no significant differences in mortality, frequency of transfer to a critical care unit, or the occurrence of three of the five dysrhythmias examined. The presence of a monitor watcher was associated with significantly fewer episodes of sustained ventricular tachycardia but more bradyarrhythmias. For both sustained ventricular tachycardia and bradyarrhythmias, the monitor watcher variable remained in the final multivariate logistic regression models.

CONCLUSIONS

The presence of a monitor watcher was not associated with lower rates of most adverse outcomes evaluated; however, fewer episodes of sustained ventricular tachycardia occurred when a monitor watcher was present. Sustained ventricular tachycardia is life-threatening, disturbing to the patient, and may result in a longer hospital stay while medical therapy is being adjusted. The results of this study support the use of a monitor watcher to prevent sustained ventricular tachycardia.

Accuracy of detection of clinically important dysrhythmias with and without a dedicated monitor watcher

BACKGROUND: Although dedicated monitor watchers are used in many progressive care units with telemetry monitors, this costly practice has not been evaluated. OBJECTIVE: To compare the accuracy of detection of clinically important dysrhythmias with and without a dedicated monitor watcher. METHODS: On a 26-bed cardiac progressive care unit, documentation of four categories of dysrhythmias during a 7-week period when a monitor watcher was present was compared with that during a 7-week period when no monitor watcher was present. The Hewlett-Packard CareVue Clinical Event Review, a full-disclosure system, was used as the gold standard. RESULTS: Accuracy of detection of nonsustained ventricular tachycardia, supraventricular tachycardia, and pauses was significantly better with a monitor watcher than without. Although the detection of life-threatening rhythms was correct a higher percentage of the time with a monitor watcher, the difference was not significant. CONCLUSIONS: The efficiency and quality of patient care can be enhanced by using a dedicated monitor watcher. The results of this study raise the question of whether improved accuracy of detection of dysrhythmias results in better outcomes for patients.

Accuracy of detection of clinically important dysrhythmias with and without a dedicated monitor watcher

BACKGROUND

Although dedicated monitor watchers are used in many progressive care units with telemetry monitors, this costly practice has not been evaluated.

OBJECTIVE

To compare the accuracy of detection of clinically important dysrhythmias with and without a dedicated monitor watcher.

METHODS

On a 26-bed cardiac progressive care unit, documentation of four categories of dysrhythmias during a 7-week period when a monitor watcher was present was compared with that during a 7-week period when no monitor watcher was present. The Hewlett-Packard CareVue Clinical Event Review, a full-disclosure system, was used as the gold standard.

RESULTS

Accuracy of detection of nonsustained ventricular tachycardia, supraventricular tachycardia, and pauses was significantly better with a monitor watcher than without. Although the detection of life-threatening rhythms was correct a higher percentage of the time with a monitor watcher, the difference was not significant.

CONCLUSIONS

The efficiency and quality of patient care can be enhanced by using a dedicated monitor watcher. The results of this study raise the question of whether improved accuracy of detection of dysrhythmias results in better outcomes for patients.

Computational and numerical methods for bioelectric field problems

Fundamental problems in electrophysiology can be studied by computationally modeling and simulating the associated microscopic and macroscopic bioelectric fields. To study such fields computationally, researchers have developed a variety of numerical and computational techniques. Advances in computer architectures have allowed researchers to model increasingly complex biophysical systems. Modeling such systems requires a researcher to apply a wide variety of computational and numerical methods to describe the underlying physics and physiology of the associated three-dimensional geometries. Issues naturally arise as to the accuracy and efficiency of such methods. In this paper we review computational and numerical methods of solving bioelectric field problems. The motivating applications represent a class of bioelectric field problems that arise in electrocardiography and electroencephalography.

(Carboxyalkyl)benzyl propargyl ethers as selective inhibitors of leukocyte-type 12-lipoxygenases

A series of (carboxyalkyl)benzyl propargyl ethers was synthesized and tested as inhibitors of 12-lipoxygenase (12-LO) from porcine leukocyte cytosol. Optimum activity was displayed by 3-[4-[(2-tridecynyloxy)methyl]phenyl]propanoic acid. Altering the length of the alkyl side chain attached to the acetylenic group reduced activity. Changing the substitution pattern in the (carboxyalkyl)benzyl group from para to meta or ortho also reduced activity. Analogs in which the triple bond was replaced by a double bond or an allene displayed reduced activity, whereas fully saturated analogs were inactive. High concentrations (10 microM) of the most potent acetylenic (carboxylalkyl)benzyl ethers did not inhibit human platelet 12-LO, human neutrophil 5-LO, rabbit reticulocyte 15-LO, or soybean 15-LO. Thus, this class of compounds represents the first example of isoform specific LO inhibitors.

Role of radiotherapy and hyperthermia in the management of malignant melanoma

The overall response rates of malignant melanoma (MM) to ionizing radiation are similar to those of other malignant neoplasms. This is based on recent radiobiological data on MM cell lines and radiobiological analyses of large clinical experiences, using a spectrum of fractionation schedules on diverse MM lesions. In contrast to other carcinomas, MM exhibits an unusual spectrum of radiobiological responses characteristic for early- and late-response tissues implying that there is a wide range of sensitivities to radiation fraction sizes. This is confirmed by clinical response and tumor control data from prospective trials in which different fractionation schedules produced control rates between 40 and > 90%. These experiences suggest that primary MM lesions as well as skin and lymph node metastases may be more responsive to larger fraction sizes than parenchymal metastases. The same holds true when irradiation is used as an adjuvant for locoregional treatment of the primary MM and draining lymphatics. Total doses for maximum tumor control rates remain to be established for the different fractionation schemes of proven effectiveness. Hyperthermia in combination with regionally applied cytotoxic agents or irradiation has produced encouraging enhancements in MM cytotoxicity. However, due to contradicting results, these data need to be validated by additional clinical investigation.

The N-terminal domain of Escherichia coli enzyme I of the phosphoenolpyruvate/glycose phosphotransferase system: molecular cloning and characterization

The bacterial phosphoenolpyruvate/glycose phosphotransferase system (PTS) comprises a group of proteins that catalyze the transfer of the phosphoryl group from phosphoenolpyruvate (PEP) to sugars concomitant with their translocation. The first two steps of the phosphotransfer sequence are PEP <--> Enzyme I (EI) <--> HPr (the histidine-containing phosphocarrier protein). We have proposed that many functions of the PTS are regulated by EI, which undergoes a monomer/dimer transition. EI monomer (63.5 kDa) comprises two major domains: a flexible C-terminal domain (EI-C) and a protease-resistant, structurally stable N-terminal domain (EI-N) containing the active site His. Trypsin treatment of Salmonella typhimurium EI yielded EI-N, designated EI-N(t). Homogeneous recombinant Escherichia coli EI-N [i.e., EI-N(r)], has now been prepared in quantity, shows the expected thermodynamic unfolding properties and, similarly to EI-N(t), is phosphorylated by phospho-HPr, but not by PEP. In addition, binding of EI-N(r) to HPr was studied by isothermal titration calorimetry: K/a = 1.4 x 10(5) M(-1) and delta H = +8.8 kcal x mol(-1). Both values are comparable to those for HPr binding to intact EI. Fluorescence anisotropy [dansyl-EI-N(r)] and gel filtration of EI-N(r) show that it does not dimerize. These results emphasize the role of EI-C in dimerization and the regulation of intact EI.

Thermodynamic analysis of small ligand binding to the Escherichia coli repressor of biotin biosynthesis

BirA is the transcriptional repressor of biotin biosynthesis and a biotin holoenzyme synthetase. It catalyzes synthesis of biotinyl-5'-AMP from the substrates biotin and ATP. The adenylate is the activated intermediate in the biotin transfer reaction as well as the positive allosteric effector for site-specific DNA binding. The affinity of BirA for the adenylate is considerably greater than its affinity for biotin, and both binding reactions are coupled to changes in the conformation of the protein. The temperature dependencies of the two binding interactions have been determined using kinetic techniques. Van't Hoff analysis of the equilibrium dissociation constants derived from the kinetic data indicate that while the two binding processes are characterized by large negative enthalpies, the entropic contributions are small for both. Binding enthalpies have also been determined by isothermal titration calorimetry. Consistent with the results of the van't Hoff analyses, the calorimetric enthalpies are large and negative. The greater precision of the calorimetric measurements allowed more accurate estimation of the entropic contributions to the binding processes, which are of opposite sign for the two ligands. In addition, the heat capacity changes associated with the two binding reactions are small. The measured thermodynamic parameters for binding of biotin and bio-5'-AMP to BirA have been utilized to dissect out structural contributions to the binding energetics. Results of these calculations indicate equivalent contributions of burial of polar and apolar surface area to both binding processes. The total loss of solvent accessible surface area is, however, greater for biotin binding. The analysis indicates furthermore that although both binding reactions are coupled to losses in configurational entropy, the magnitude of the conformational change is significantly larger for biotin binding.

Oxygen binding to fallow-deer (Dama dama) hemoglobin: stepwise enthalpies at pH 7.4

High-precision thin-layer gas-solution microcalorimetry has been used to study the oxygen binding properties of fallow-deer (Dama dama) hemoglobin under physiological conditions. This method measures directly the enthalpy of macromolecular ligand binding by changing the ligand activity in a manner analogous to that of the Gill thin-layer optical apparatus ([1], D. Dolman and S. J. Gill, Anal. Biochem., 87 (1978) 127-134). By logarithmically lowering the partial pressure of oxygen we have generated differential heat binding curves of oxygen binding to fallow-deer hemoglobin in phosphate buffer at pH 7.4. In order to enlarge the data field, the temperature dependence of the oxygen affinity was examined by generating binding curves at a number of different temperatures allowing for separation of enthalpy and free energy parameters. This type of experimental analysis makes no assumption of optical linearity between the various heme groups and reveals initially that overall oxygen binding to fallow-deer hemoglobin is less exothermic and of lower affinity than for human hemoglobin A0. In addition, previous optical work on the ancestrally related reindeer hemoglobin (Rangifer tarandus; [2], B. Giardina, O. Brix, M. Nuutinen, S. Sherbini, A. Bardgard, G. Lazzarino and S. Condo, FEBS Lett., 247 (1989) 135) has indicated that the enthalpy associated with its final two oxygen binding steps is minimal. Our calorimetric determination with fallow-deer hemoglobin also reveals this tendency. Presumably, this adaptation would make it easier for these animals to maintain a consistent hemoglobin oxygen saturation level under environmental conditions where the temperature fluctuates.

Responses of the longitudinal muscle and the muscularis mucosae of the rat duodenum to adenine and uracil nucleotides

1. Previous studies have shown that the rat duodenum contains P1 and P2Y purinoceptors via which it relaxes to adenosine and adenosine 5'-triphosphate (ATP) respectively. It has also been shown to contract to uridine 5'-triphosphate (UTP) and adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma-S), and based on their differential inhibition by the P2 antagonist suramin it has been suggested that they act via two separate receptors. In addition, the rat duodenum has been shown to dephosphorylate ATP rapidly via ectonucleotidases and adenosine deaminase. In this study the responses of two preparations from the rat duodenum, the longitudinal muscle and the muscularis mucosae, were investigated using a series of nucleotides and suramin. 2. 2-Methylthioadenosine 5'-triphosphate (2-MeSATP), ATP, ATP-gamma-S and adenosine 5'-alpha,beta-methylene-triphosphonate (AMPCPP) each relaxed the longitudinal muscle, with an agonist potency order of 2-MeSATP > ATP = ATP-gamma-S > AMPCPP, while UTP and uridine 5'-diphosphate (UDP) were not observed to elicit relaxation. This indicates the presence of a relaxant P2Y-purinoceptor on the longitudinal muscle. The longitudinal muscle did not contract to any of the agonists at concentrations of 300 microM, apart from ATP-gamma-S which caused very weak contractions. 3. ATP-gamma-S, adenosine 5'-methylenediphosphonate (AMPCP), AMPCPP, ATP, UTP, adenosine 5'-diphosphate (ADP), UDP and 2-MeSATP each contracted the muscularis mucosae with an agonist potency order of ATP-gamma-S > or = AMPCP > or = AMPCPP = ATP = UTP = ADP = UDP >> 2-MeSATP, although maximal responses were not obtained at concentrations of 300 microM. The muscularis mucosae did not relax to any of the agonists at concentrations of 300 microM. 4. Suramin (1 mM) inhibited relaxations induced by ATP on the longitudinal muscle, shifting the relaxation concentration-response curve to the right. This further supports the presence of a P2Y-purinoceptor on this muscle layer. Suramin (1 mM) inhibited contractions induced by AMPCPP, but not those induced by ATP, UTP or ATP-gamma-S, in the muscularis mucosae. Desensitization of the muscularis mucosae was seen with AMPCPP, but not with UTP or ATP-gamma-S, and no cross-desensitization between AMPCPP and UTP or ATP-gamma-S was observed. This suggests there are two receptors which mediate contraction on the rat duodenum muscularis mucosae, one suramin-sensitive and the other suramin-insensitive. 5. ATP was rapidly degraded by the muscularis mucosae to ADP, adenosine 5'-monophosphate (AMP) and inosine, with no adenosine being detected. A similar rate of degradation was seen for UTP with UDP, uridine 5'-monophosphate (UMP) and uridine being formed and for 2-MeSATP with 2-methylthioadenosine 5'-diphosphate (2-MeSADP), 2-methylthioadenosine 5'-monophosphate (2-MeSAMP) and 2-methylthioadenosine being formed. AMPCPP and ATP-gamma-S were both degraded more slowly, AMPCPP being degraded to AMPCP, and ATP-gamma-S to ADP, AMP and inosine. Suramin (1 mM), did not significantly affect the rate and pattern of degradation of these nucleotides, apart from AMPCPP which was degraded slightly more slowly in the presence of suramin. 6. These results show that there is a P2Y-purinoceptor which mediates relaxation in the rat duodenum longitudinal muscle. They also show that there is a contraction-mediating suramin-sensitive receptor on the rat duodenum muscularis mucosae which is desensitized by AMPCPP, and thus is probably of the P2X subtype. In addition, there is a contraction-mediating suramin-insensitive receptor on the rat duodenum muscularis mucosae which is not desensitized by UTP or ATP-gamma-S, and at which ATP and UTP show equal potency, and is thus probably of the P2U subtype. In addition, the rat duodenum muscularis mucosae contains ectonucleotidases and adenosine deaminase, which rapidly degrade nucleotides, although the inhibition by suramin of this deg

Screening of cyclic peptide phage libraries identifies ligands that bind streptavidin with high affinities

The screening of combinatorial peptide libraries has emerged as an important tool in the discovery of novel substrates or ligands for enzyme and receptor targets. For example, screening linear peptide libraries using streptavidin as a model receptor system has previously identified many low-affinity peptide ligands, all of which contain the common motif His-Pro-Gln (HPQ). We reasoned that constraining the conformational freedom of linear peptides by cyclization in a library would yield peptide ligands of increased affinity. Three different cyclic peptide libraries were constructed in an M13 phage display system as N-terminal pIII protein fusions. The random peptide sequences were flanked by two cysteine residues, which allows efficient disulfide bond formation and cyclization during phage assembly. These cyclic peptide libraries were screened with streptavidin as the model receptor system. Many sequences, all of which contained the motif His-Pro-Gln (HPQ), were discovered, and in the preceding paper, the structures of complexes of streptavidin-bound cyclic and linear peptides are described (Katz, 1995). Analysis of binding kinetics and affinities demonstrated that the conformationally constrained cyclic peptides bound streptavidin with affinities up to 3 orders of magnitude higher than linear peptides identified in previous library screens. These results demonstrate the potential of screening conformationally constrained peptide libraries for high-affinity novel receptor ligands or enzyme substrates.

The tumor volume and clonogen number relationship: tumor control predictions based upon tumor volume estimates derived from computed tomography

PURPOSE

While tumor volume is an important parameter predicting clinical outcome, its relationship to clonogen number remains uncertain. This uncertainty is related to many factors, among them treatment response heterogeneity, which obscures the influence of patients and treatment-related parameters. In this study, we analyze the effect of tumor volume on local and regional recurrence in a setting tightly controlled for dose, treatment time, and patient selection. The hypothesis that changes in clonogen number scale directly with changes in tumor volume is tested.

METHODS AND MATERIALS

Using digital reconstruction of diagnostic computed tomography (CT) scans, primary and total tumor volumes were estimated in 51 cases of advanced squamous cell carcinoma of the head and neck. All patients were managed with a concomitant boost accelerated superfractionated schedule to a median dose of 70.2 Gy. Clinical data were fitted to a mixture model to relate tumor volume parameters to control probability where volume and clonogen number were related by the relationship m = a.Vb, where m is initial clonogen number, a is a proportionality constant, V is tumor volume, and b is the volume exponent.

RESULTS

Tumor volume estimates for primary tumor ranged from 3-196 cm3 and for total tumor volume 5-196 cm3. Actuarial local-regional control is 63%. The estimated volume exponent b is 0.85 (95%, confidence interval (c.i.): 0.40-1.29) for primary tumor volume and 1.1 (95%, c.i.: 0.33-1.85) for total tumor volume.

CONCLUSION

This study quantifies the adverse influence of tumor volume on local-regional disease control in advanced head and neck cancer. The derived volume exponent approximates to one, the theoretical expectation if the growth fraction is roughly constant and clonogen number increases linearly with volume. Finally, these results suggest that radiobiological parameters are more reliably estimated from clinical data with narrowly defined strata.

The influence of quantitative tumor volume measurements on local control in advanced head and neck cancer using concomitant boost accelerated superfractionated irradiation

PURPOSE

Current methods to clinically define head and neck tumor bulk are qualitative and imprecise. Although the American Joint Committee on Cancer (AJCC) staging system is important for this purpose, limitations exist. This study will investigate the prognostic value of computed tomography (CT) derived tumor volume measurements in comparison to AJCC stage and other significant variables.

MATERIALS AND METHODS

Seventy-six patients with advanced head and neck squamous cell carcinoma were treated with concomitant boost accelerated superfractionated irradiation. Doses ranged from 68.4-73.8 Gy (median 70.2 Gy). Good quality pretherapy CT scans were available in 51 patients. Total tumor volume (TTV) estimates were derived from these scans using digital integration of primary tumor and metastatic lymphadenopathy. Actuarial and multivariate statistical techniques were applied to analyze local control.

RESULTS

Thirty-six-month local control was 63%. TTV ranged from 5-196 cm3 (median 35 cm3) for all cases, 5-142 cm3 (median 17 cm3) for those controlled, and 16-196 cm3 (median 47 cm3) for local failures. There was a significant increase in failures above 35 cm3. Univariate analysis found that TTV, T-stage, N-stage, and primary site were each significant prognostic variables. Local control for TTV < or = 35 cm3 was 92% at 36 months vs. 34% for TTV > 35 cm3 (p = 0.0001). Multivariate analysis, however, found that TTV, primary site, and sex were important as independent variables; T and N stage were not independently significant unless TTV was removed from the model.

CONCLUSIONS

This study demonstrates the prognostic significance of TTV in advanced carcinoma of the head and neck. This variable appears to be a more predictive than AJCC clinical stage. Quantitative tumor volume measurements may prove to be a useful parameter in future analyses of head and neck cancer.

Affective disorders in hospitalized children and adolescents with mental retardation: a retrospective study

We contrasted a sample of children and adolescents with affective disorders and mental retardation with a comparison group on behavioral symptoms, associated diagnoses, and psychopharmacologic treatment. Fifty consecutive patients with both impaired intellectual functioning and at least one affective disorder admitted to a psychiatric inpatient unit for children and adolescents with developmental disabilities and psychiatric disorders were matched to a group of 50 inpatients without depression. Behavioral symptoms such as suicidal ideation or gestures, crying, irritability, sleep problems, agitation, mood lability, and social withdrawal/isolation occurred significantly more often in the affective group than in the comparison group. Aggression, however, was the most frequent behavior concern for both groups, whereas disruption/destruction was identified significantly more often in the comparison group. Regarding Axis I diagnoses, the comparison group was more often identified with externalizing disorders (ADHD, ODD), though there was a high rate of comorbidity in the affective disorder group. The behavioral symptoms used to diagnosis normally developing children and adolescents appear to be applied in making affective disorders diagnoses in this sample of children and adolescents with mental retardation.

Thermodynamic analysis of the structural stability of the tetrameric oligomerization domain of p53 tumor suppressor

The structural stability of an amino acid fragment containing the oligomerization domain (residues 303-366) of the tumor suppressor p53 has been studied using high-precision differential scanning calorimetry (DSC) and circular dichroism spectroscopy (CD). Previous NMR solution structural determinations have revealed that the fragment forms a symmetric 29.8 kDa tetramer composed of a dimer of dimers (p53tet) [Lee, W., Harvey, T. S., Yin, Y., Yau, P., Litchfield, D., & Arrowsmith, C. H. (1994) Nature Struct. Biol. 1, 877-890]. Thermal unfolding of the tetramer is reversible and can be described as a two-state transition in which the folded tetramer is converted directly to unfolded monomers (N4<==>4U). According to the DSC and CD data, the population of intermediate species consisting of folded monomers or dimers is insignificant, indicating that isolated dimeric or monomeric structures have a much lower stability than the dimer and do not become populated during thermal denaturation under the conditions studied. The transition temperature of unfolding is found to be highly dependent on protein concentration and to follow the expected behavior for a tetramer that dissociates upon unfolding. Experiments conducted at pH 4.0 in 25 mM sodium acetate at a tetramer concentration of 145.8 microM have a transition temperature (Tm) of 75.3 degrees C while at 0.5 microM the value drops to 39.2 degrees C. The enthalpy change of unfolding at 60 degrees C is 26 kcal (mol of monomer)-1 with a heat capacity change of 387 cal (K.mol of monomer)-1. The stability of p53tet is dependent on pH and salt concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Psychiatric and behavioral disorders in hospitalized preschoolers with developmental disabilities

Describes the types of psychiatric and behavioral disturbance present in 169 preschoolers with developmental disabilities admitted to a specialized psychiatric inpatient unit. Differences in the proportion of some diagnoses and behavior problems across cognitive functioning level and across age were found. Seventy-two percent of the sample had one or more medical diagnosis. Similarities and differences with earlier reports in the literature are discussed.

MS-551 protects against ventricular fibrillation in a chronic canine model of sudden cardiac death

We studied the electrophysiologic and antifibrillatory properties of MS-551 (1,3-dimethyl-6-((2-[N-hydroxy-ethyl)-3-(4-nitrophenyl) propylamino] ethylamino) 2,4(1H,3H) pyrimidinedione hydrochloride) in a conscious canine model of sudden cardiac death. Three to 5 days after surgically induced myocardial infarction (MI: 2-h occlusion of the left anterior descending coronary artery, LAD), animals were subjected to programmed electrical stimulation (PES) to identify those at risk for sudden cardiac death. MS-551 was administered (2.0, 3.0, or 4 x 2.0 mg/kg intravenously, i.v.). Vehicle-treated animals received 0.9% sodium chloride solution for injection. MS-551 (multiple-dose regimen) increased ventricular effective refractory period (VERP) from 112 +/- 4 to 137 +/- 4 ms (p < 0.05) as compared with vehicle treatment, which did not alter VERP (125 +/- 6 to 121 +/- 5 ms). MS-551 prolonged QTc interval from a predrug value of 293 +/- 8 to 333 +/- 18 ms postdrug. The size of surgically induced MI did not differ among groups: 2.0 mg/kg, 23 +/- 4%; 3.0 mg/kg, 28 +/- 2%; 4 x 2.0 mg/kg, 25 +/- 3%; and vehicle, 28 +/- 3% of the left ventricle. Single bolus administration of MS-551 (2.0 or 3.0 mg/kg i.v.) did not confer significant protection against sudden cardiac death. However, repeated administration of MS-551 protected against sudden cardiac death in 8 of 10 dogs as compared with 2 of 12 in the vehicle-treated group (p < 0.05). The data indicate that a multiple-dose regimen of MS-551 provides protection against ischemia-induced ventricular fibrillation (VF) in the postinfarcted heart. The mechanism by which MS-551 achieves its antifibrillatory effect most likely depends on its ability to prolong VERP of myocardium without altering ventricular conduction velocity.

Contractile effects of uridine 5'-triphosphate in the rat duodenum

1. Previous studies have shown that the rat duodenum relaxes to adenosine and adenosine 5'-triphosphate (ATP) via P1 and P2Y purinoceptors respectively, but in preliminary studies uridine 5'-triphosphate (UTP) was found to contract this tissue. The non-selective P2 antagonist suramin and a number of nucleotides were therefore used to investigate this response further. 2. ATP, UTP, adenosine 5'-diphosphate (ADP), adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma-S), guanosine 5'-triphosphate (GTP) and uridine 5'-diphosphate (UDP) each relaxed the duodenum, with an agonist potency order of ATP = ADP > ATP-gamma-S >> GTP >> UTP = UDP, consistent with the presence of a P2Y purinoceptor mediating relaxation. 3. ATP-gamma-S, UTP and UDP each contracted the duodenum with an agonist potency order of ATP-gamma-S > UTP > UDP, although maximal responses to these agonists were not obtained at a concentration of 267 microM (ATP-gamma-S) and 300 microM (UTP and UDP). No contractions were observed with any of the other agonists at concentrations up to 300 microM. 4. Indomethacin (25 microM) did not inhibit the contractions induced by UTP, indicating that they were not mediated via production of prostaglandins. 5. Suramin (100 microM and 1 mM) inhibited relaxations induced by ATP, shifting the concentration-response curve to the right, with the maximal response to ATP being decreased by the higher concentration of suramin (1 mM). Suramin (1 mM) inhibited relaxations induced by ATP-gamma-S, shifting the concentration-response curve to the right, and completely abolished contractions induced by ATP-gamma-S. In contrast, suramin (100 JAM and 1 mM) had no effect on contractions induced by UTP.Contractions induced by UTP were, however, less sustained in the presence of suramin, which also affected the basal tone of some tissues when precontracted with carbachol (0.1 microM). In the presence of suramin (I mM), no contractions to ATP were observed.6. These results confirm that in the rat duodenum there is a P2Y purinoceptor that mediates relaxation in response to a number of purine nucleotides, and at which the pyrimidine nucleotides UTP and UDP are almost inactive. There are also receptors at which UTP and ATP-y-S act to cause contraction.Suramin discriminates between the contractile effects of these two agonists, which may indicate the presence of a suramin-insensitive pyrimidinoceptor as well as a suramin-sensitive receptor for ATP-y-S.An alternative explanation is that the differential effects of suramin are via its actions as an antagonist in addition to its action as an ectonucleotidase inhibitor.

Efficacy of methylphenidate and behavioral intervention on classroom behavior in children with ADHD and mental retardation

Using a combination of an alternating treatment and double-blind placebo-controlled drug design, the independent and combined effects of two behavioral interventions and two doses of methylphenidate (MPH) in 3 children with Attention Deficit Hyperactivity Disorder (ADHD) and mental retardation (MR) were assessed. In this single subject design, 2 of the 3 subjects responded positively to medication as measured by increased on-task behavior. The first behavioral intervention, a token economy for on-task behavior, was ineffective for increasing either on-task behavior or work accuracy when combined with placebo. However, improvement in work accuracy was realized with implementation of a second behavioral intervention that specifically targeted accuracy independent of drug conditions. The current findings highlight both the positive effects and limitations of the two commonly used treatment modalities for ADHD. Future studies should continue to extend this area of investigative efforts to produce more data-based knowledge as to the appropriate doses of treatment, both pharmacological and behavioral, with children with both ADHD and mental retardation.

Protective effects of the SOD-mimetic SC-52608 against ischemia/reperfusion damage in the rabbit isolated heart

An experimental model of myocardial ischemia/reperfusion injury was used to assess the cardioprotective effects of SC-52608, a low molecular weight superoxide dismutase mimetic. Langendorff perfused rabbit isolated hearts were subjected to 30 min of global ischemia followed by 45 min of reperfusion. Hearts perfused in the presence of 20 microM SC-52608 exhibited a decrease in the release of creatine kinase and intracellular potassium compared to hearts receiving vehicle (control). A progressive increase in left ventricular end-diastolic pressure developed upon reperfusion in all hearts, but was significantly greater in control hearts when compared to hearts treated with SC-52608 (P < 0.05). In addition, results obtained with a radiolabeled monoclonal antibody to the intracellular protein myosin, indicate an increased degree of irreversible damage in vehicle-treated hearts. Myocardial protection was not significant in an additional group of hearts treated with 10 microM SC-52608. The hemodynamic, biochemical, morphological, as well as the antimyosin binding data, demonstrate that pretreatment with SC-52608 protects the myocardium from damage associated with global ischemia and reperfusion. The mechanism by which SC-52608 mediates the observed protective effect is most likely related to its ability to scavenge superoxide.

Discrimination training in the treatment of pica and food scavenging

Pica and scavenging are serious, sometimes life-threatening behavior problems among a significant percentage of individuals with mental retardation. This study describes procedures developed to reduce life-threatening pica and food scavenging in two adolescents with severe to profound mental retardation. Treatment was designed to teach the subjects to discriminate safe from unsafe items by training them to ingest only those items put on a specified placemat and to communicate with simple signs or gestures to obtain more food to be put on the mat. Discrimination was achieved by praising subjects when they selected and ingested items from their placemats and delivering a mild punisher when attempts to ingest nonplacemat items were made. A multiple baseline design across settings was used to evaluate the effects of the treatment package in three inpatient settings. All environments were "baited" with both edible and inedible items. Our treatment procedures appeared to be effective in reducing pica in each of the settings. Generalization of treatment effects to natural environments for one of the two subjects was documented.