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Biomedical subjects

S Levine

Publications and source records attributed to S Levine.

At least 379 records · Page 21Linked to original sources
PubMed1983

Theory of the electrokinetic behavior of human erythrocytes.

We develop a theory of electrophoresis of human erythrocytes that predicts mobilities significantly smaller than those based on the classical Smoluchowski relation. In the classical treatment the charge is assumed to be spread uniformly on the hydrodynamic surface. The present model takes into account that most of the charge, due mainly to sialic acid, is contained in the glycocalyx. The glycocalyx is modeled as a permeable layer of polyelectrolyte molecules anchored to the cell membrane. The charge is assumed to be uniformly distributed throughout this layer. The fluid flow in the layer is treated as being dominated by Stokes friction arising from idealized polymer segments. The Navier-Stokes equations are solved to give the dependence of electroosomotic velocity with distance from the cell surface. An expression for the electrophoretic mobility is obtained which contains two parameters (a) the thickness of the glycocalyx and (b) the mean polymer segment radius. The best fit to experimental data is obtained if these are given the values 75 A and 7 A, respectively. Deviation from experimental data at low ionic strength (less than 0.05 M) occurs. However, this deviation is in the direction one would expect if at low ionic strength the polyelectrolyte layer expands slightly due to decreased charge shielding.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1983

Adrenal responses to reinforcement and extinction: role of expectancy versus instrumental responding.

Plasma corticosterone levels were evaluated during operant conditioning in order to determine the effect of reinforced and nonreinforced responding (extinction) on adrenal activation. The influence of instrumental responding was assessed by comparing trained rats with yoked subjects that received a matched reward schedule in the absence of an operant task. Reinforcement sessions resulted in a significant decrease in adrenal secretion at 20 min, but not at 5 min, whereas extinction caused a rapid increase in corticosterone levels at 5 min and an even greater elevation by 20 min. Comparison of the operant and yoked subjects showed that this effect of reinforcement and extinction was not dependent on instrumental responding, but rather on the receipt or withdrawal of the expected reward.

Animals↗
PubMed1983

Immediate and proactive effects of controllability and predictability on plasma cortisol responses to shocks in dogs.

Controllability and predictability are important modulators of the behavioral effects of aversive stimulation on animals. An experiment was conducted to further investigate both the immediate and proactive effects of controllability and predictability of shocks on adrenocortical responsivity. In an initial stress induction phase, the controllability and predictability of electric shocks were independently varied in groups of dogs, and plasma cortisol responses were measured. In a subsequent test phase, all groups of dogs received identical shocks in a novel situation. Cortisol responses to these test shocks were analyzed as a function of the controllability and predictability of previous induction shocks. The results showed that during stress induction, uncontrollable shocks produced significantly greater cortisol elevations that controllable shocks but that predictability had no significant effect on cortisol responses. However, unpredictable shocks during stress induction acted proactively to significantly increase cortisol response to novel test shocks, whereas prior controllability did not modulate subsequent responsivity to novel shocks.

Animals↗
PubMed1983

Respiratory syncytial virus polypeptides. III. The envelope-associated proteins.

Four proteins, GP1, VGP48, GP26 and VPM27, are associated with the envelope of respiratory syncytial (RS) virus. The status of GP1 has been uncertain, because a cellular glycoprotein migrates at the same position when Laemmli's discontinuous buffer system is used for PAGE, and because BSC-1 cells infected with the RSN-2 strain of RS virus appear not to contain GP1. However, additional evidence suggests that GP1 is a viral structural protein. (i) It is removed from cells by trypsin, while the cellular glycoprotein is not; (ii) it is separated from the cellular glycoprotein when the infected cells are analysed by neutral SDS-PAGE; (iii) it is present in the purified RSN-2 strain of RS virus produced by BSC-1 cells; (iv) it is also present in the purified Long strain of RS virus produced by either human or monkey cells. When purified Long strain virus is analysed by PAGE under non-reducing conditions, the glycoproteins VGP48 and GP26 migrate together, and VPM27 separates into two proteins, which one-dimensional peptide mapping suggests are not different proteins. These observations suggest that VGP48 and GP26 exist in the virion as a single molecule joined by disulphide bonds, and so resemble a paramyxovirus fusion protein, and that probably there are two forms of VPM27 which differ in either position or number of disulphide bonds.

Electrophoresis, Polyacrylamide Gel↗
PubMed1983

Effect of helium on the ventilatory response to hypoxia under normocapnic and hypercapnic conditions.

We studied the effect of helium (He) on ventilatory (VI) responses to progressive isocapnic hypoxia. Accordingly, in normal male subjects (age 23-46), we compared hypoxic rebreathes using He as a carrier gas with those utilizing nitrogen (N2) as a carrier gas. When alveolar CO2 tension (PACO2) was maintained at 40 mm Hg, we noted no difference in VI responses to hypoxia between N2 and He trials. In contrast, when PACO2 was maintained at 50 mm Hg, VI responses to hypoxia during the He trials were consistently greater than those noted during the N2 experiments. These results indicate that substitution of He for N2 does not augment VI responses to normocapnic hypoxia; however, this substitution does enhance VI responses to hypercapnic hypoxia.

Adult↗
PubMed1983

Inhibition of passive localized experimental allergic encephalomyelitis by interferon.

Recently it has been reported that interferon (IFN) suppresses experimental allergic encephalomyelitis (EAE) in actively immunized Lewis rats. In the present study the effect of IFN on a localized form of passively transferred EAE has been investigated. Localization and acceleration of the disease was obtained by injection of EAE lymph node cells into rats which had, 3 days previously, been prepared with a thermal brain injury. Within 24 h of cell transfer perivenular lymphocytic infiltrates (EAE lesions) were observed in the brain. Administration of IFN (40,000 U/kg) right after EAE lymph node cell injection resulted in a significant reduction or elimination of EAE lesions. The possibility that IFN is acting exclusively on the afferent arc is eliminated, and the results suggest that IFN may be acting, although not solely, through modulations of components of the efferent arc. IFN was equally effective in suppressing EAE in adrenalectomized animals. This demonstrates that the immunosuppressive effects observed in this study are not due to endogenously produced corticosteroids.

Adrenalectomy↗
PubMed1983

Short- and long-term efficacy of high-dose oral diltiazem for angina due to coronary artery disease: a placebo-controlled, randomized, double-blind crossover study.

The effects of oral diltiazem (360 mg/day) on exercise tolerance, left ventricular performance, and plasma lactate and catecholamine levels were studied in 13 patients with atherosclerotic coronary artery disease in a placebo-controlled, randomized, double-blind protocol. Exercise duration to the onset of ischemic ST segment depression, time to angina pectoris, and time to peak exercise improved by 120, 174, and 144 sec, respectively (p less than .0001). Left ventricular ejection fraction, as determined by radionuclide angiography, increased in patients at rest from 52 +/- 11% (mean +/- SD) during placebo therapy to 58 +/- 11% during diltiazem therapy (p less than .001); at peak exercise ejection fraction increased from 44 +/- 11% during placebo treatment to 52 +/- 15% during diltiazem therapy (p less than .01). The mean plasma norepinephrine level in patients at rest increased from 498 +/- 221 pg/ml during placebo treatment to 667 +/- 272 pg/ml during diltiazem therapy (p less than .05). Resting standing blood pressure and supine and standing diastolic blood pressures decreased significantly with diltiazem. In all 10 patients followed over a long term, oral diltiazem caused persistent improvement in exercise performance at 12 to 20 weeks, without evidence of placebo effects. Thus, diltiazem is highly effective in divided doses of 360 mg/day for the therapy of chronic angina pectoris due to coronary artery disease.

Aged↗
PubMed1983

Immunogenicity of Ty21a attenuated "Salmonella typhi" given with sodium bicarbonate or in enteric-coated capsules.

Ty21a, a stable attenuated mutant of Salmonella typhi, is a safe, protective oral vaccine when 3 doses of 10(9) cells in saline are taken after neutralization of gastric acidity by 1 g NaHCO3. To identify a more convenient method to administer vaccine and to determine the feasibility of immunizing with a single dose, we studied the immune response of children and adults to different formulations of Ty21a with a newly developed, sensitive, enzyme-linked immunosorbent assay (ELISA). In this ELISA, a rise in S. typhi O antibody was defined as a change in net optical density of greater than or equal to 0.15 (more than 3 SD from the mean difference in optical density in a negative control population). Three hundred and thirty-five Chilean children were given 3 doses of 10(9) Ty21a in 150 ml of milk with 0.8 g NaHCO3 or in enteric-coated capsules. In each group, 5% seroconverted by Widal O but 41% by IgG ELISA O antibody titers; mean antibody levels by group were identical. Studies were also carried out in healthy college students in a non-endemic area (U.S.A.) who had no history of prior typhoid immunization. In total, 141 U.S. adults received vaccine formulated in either one of two ways: 1) in gelatin capsules administered with two additional gelatin capsules containing a total of 0.8 gm NaHCO3 or 2) in enteric-coated capsules. Thirty-six persons received one dose, 30 got two doses and 16 ingested three doses of enteric-coated vaccines, while 44 persons receiving one dose and 15 got two doses of vaccine in the gelatin capsule formulation. Rates of seroconversion of ELISA O antibody were similar in all the groups. Ty21a vaccine was not recovered from multiple stool, jejunal fluid or blood cultures of the U.S. vaccine recipients. Based on these observations a large-scale field trial of efficacy has been initiated in 90.000 schoolchildren 6-20 years of age in Santiago, Chile, of whom one-third received one dose of enteric-coated vaccine, one-third got two doses and the remainder received placebo.

Adolescent↗
PubMed1983

Depletion of lymphoid tissues by tilorone. Ultrastructure and synergistic interaction with antilymphocyte serum.

Antilymphocyte serum (ALS) caused lymphocyte depletion and shrinkage of thymus-dependent areas in spleen and lymph nodes of rats. Tilorone also depleted T lymphocytes, but light- and electron-microscopic examination revealed hyperplasia and vacuolation of the interdigitating cells that remained in the thymus-dependent areas, rather than shrinkage. These changes were not mediated by the adrenal gland. The combination of agents had a synergistic effect on the thymus-dependent areas in the spleen, lymph nodes, Peyer's patches, and bronchial-associated lymphoid tissue, all of which were severely depleted but maintained their normal dimensions. The combination of ALS and a tilorone analog that was capable of depleting lymph node but not spleen, gave a synergistic effect only in lymph node and not in spleen. Tilorone effects were transient, whereas ALS produced a long-lasting depletion. Administration of the two drugs at different times were synergistic only during the brief period of tilorone's effectiveness. The synergistic effects on T lymphocytes correlated well with immunosuppressive potency of the combined drugs on a T-lymphocyte-mediated auto-immune disease.

Animals↗
PubMed1982

Experimental allergic encephalomyelitis: simple method for producing the localized form.

In the past, the lesions of experimental allergic encephalomyelitis (EAE) have been induced to localize around brain tissue damaged by anoxia or direct physical or chemical attack. The procedure for producing the requisite antecedent brain injury has been simplified by use of a single subcutaneous injection of a neurotoxic chemical, thereby eliminating the need for surgery. The EAE lesions are concentrated in a very small area and can be obtained in one day after the passive transfer of a relatively small number of lymph node cells from immunized donors.

Animals↗
PubMed1982

Periventricular localization of a toxic encephalopathy induced by a mechanism involving choroid plexus.

An aliphatic triamine has been reported to cause lesions in rats in the vicinity of the area postrema and the median eminence of the hypothalamus, sites known to lack a blood-brain barrier. The present study revealed that some of the rats developed lesions in the cerebellum as well. The cerebellar lesions were related topographically to the choroid plexus in the underlying fourth ventricle. This periventricular distribution could be due to passage of the triamine from blood to choroid plexus and cerebrospinal fluid and then to parenchyma. In further experiments, the permeability of the plexus was increased by inducing choroid plexitis with cyclophosphamide. Subsequent administration of the triamine induced periventricular cerebellar lesions in higher incidence and at lower dose levels than in normal rats. Thus, the induction of choroid plexitis supported the aforementioned hypothesis and also suggested that it might be a useful model for periventricular localization of other types of lesions or diseases.

Animals↗
PubMed1982

Brain lesions in a case of cystinosis.

Cystinosis usually spares the brain or causes only deposition of cystine crystals without destructive lesions in choroid plexus or, rarely, in brain parenchyma. A case of cystinosis is presented with unusually long survival and with bilateral necrosis, numerous concretions, and extensive demyelination of internal capsule and brachium pontis. No cystine crystals could be demonstrated in these lesions although they were present in the choroid plexus. The symmetry and unique distribution of the lesions as well as their histopathology suggested a progressive process caused by the metabolic dysfunction of cystinosis. The validity of this hypothesis will be determined by future experience as renal transplants enable more patients to survive into adult life.

Adult↗