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Biomedical subjects

S Klein

Publications and source records attributed to S Klein.

At least 397 records · Page 22Linked to original sources
PubMed1979

Nonlinear kernels of the human ERG.

In this paper we examine the use of a symmetric binary random stimulus for eliciting the ERG, and for calculating the first-order and second-order kernels of a nonlinear functional expansion of the response. We show that if the stimulus is represented in a non-dimensional form, then the units in which all kernels are measured are the same as the units used to measure the response, microvolts in the case of the ERG; further, contributions from all kernels to the response can be added without scale factors. We present the first-order and second-order kernels measured for a population of 15 normal subjects in a clinical setting. The measurements were made at various levels of adaptation ranging from photopic to scotopic conditions. The second-order kernels illustrate the processes of rapid adaptation (less than 100 ms) in the retina.

Adult↗
PubMed1979

Response of visual mechanisms to stimulus onsets and offsets.

Transient and sustained visual mechanisms were studied with single, flickering bars of various widths. Wide bars were largely detected on the basis of temporal luminance transients whereas thin bars were detected on the basis of the sustained contrast. A rapidly flickering uniform field selectively masked wide flickering bars, which suggests that different mechanisms detect wide versus thin flickering bars. For coarse spatial patterns, stimulus onsets were slightly more visible than stimulus offsets, and the response to onsets and offsets approximately summated.

Darkness↗
PubMed1978

[Retinal thromboses with metabolic disturbances (author's transl)].

In 31 out of 35 patients with retinal thromboses metabolic disturbances were found. 11 patients showed disturbances of lipid, purine and carbohydrate metabolism and hypertension. In 19 further cases hyperuricaemia was found, usually combined with hypotriglyceridaemia. Two young women with branch vein thrombosis and pathological metabolic values were taking hormonal contraceptives. The possible relationships between vein thromboses and metabolic disturbances are discussed.

Adult↗
PubMed1977

Delayed hypersensitivity in tumor-bearing mice. In vitro activation of "eclipsed" spleen cells.

At various stages during the progressive growth of a transplanted sarcoma in BALB/c mice, the delayed hypersensitivity response to tumor antigen was determined using the food-pad swelling test (FPS) and the leukocyte migration inhibition assay (LMI). A close correlation was observed between the in vivo and in vitro assays. "Early" recognition of tumor antigen was detected 24 h after tumor inoculation by both techniques and this positive response was maintained until day 15. As the tumor grew larger, the delayed hypersensitivity response in vivo vanished, while the delayed hypersensitivity response in vitro disappeared about 3 days later. This suppression or "eclipse" of the anti-tumor cellular immune response was specific for the type of tumor used, and could be reversed in vitro by means of a low pH treatment of lymphoid cells.

Animals↗
PubMed1977

Effect of heparin modification on its activity in enhancing the inhibition of thrombin by antithrombin III.

Studies were conducted to determine the effect of modifying specific functional groups of heparin on its antithrombin III-enhancing activity. The derivatives employed were heparin methyl ester, heparinylglycine and N-desulfated heparin. The carboxyl-modified derivatives increase the rate of inhibition of thrombin by antithrombin III, although not to the same extent as heparin. N-Desulfated heparin is devoid of any activity. Heparin methyl ester is more potent than heparinylglycine in activating antithrombin III, as exhibited by its immediate effect on the thrombin-fibrinogen reaction. However, heparinylglycine is the more effective of the two, in increasing the rate of thrombin deactivation by antithrombin III. The results indicate that although free carboxyl groups of heparin are not crucial for its binding to antithrombin III, they are important for the combination of the latter with thromobin. In contrast, N-sulfates are critical for the interaction of heparin with antithrombin III.

Animals↗
PubMed1977

Induction of delta-Aminolevulinic Acid Formation in Etiolated Maize Leaves Controlled by Two Light Systems.

A short illumination of etiolated maize (Zea mays) leaves with red light causes a protochlorophyll(ide)-chlorophyll(ide) conversion and induces the synthesis of delta-aminolevulinic acid (ALA) during a subsequent dark period. In leaves treated with levulinic acid, more ALA is formed in the dark than in control leaves. Far red light does not cause a conversion of protochlorophyll(ide) into chlorophyll(ide) and does not induce accumulation of ALA in the dark. Both red and far red preilluminations cause a significant potentiation of ALA synthesis during a period of white light subsequent to the dark period. The results indicate a dual light control of ALA formation. The possible role of phytochrome and protochlorophyllide as photoreceptors in this control system is discussed.

Journal Article↗
PubMed1977

Diminution of bone mass in childhood diabetes.

Photon absorption measurements of forearm bone density in 196 insulin-dependent patients, age 6--26 years, were compared with findings in 124 controls. Expected density, gm. Ca/cm.2 bone width (M/W), was calculated from regressions of M/W on ulnar length for white and black male and female controls. There were no significant correlations between M/W differences from expected and serum Ca, Mg, P, or alkaline phosphatase levels, estimated physical activity level, insulin dosage, or the presence of joint contracture. White females averaged 8.2 per cent (+/- 1 S.E.M.) loss of M/W, as against white male average loss of 4.7 per cent +/- 1 and black female loss of 2 per cent +/- 2 (p less than 0.001); the black male population was too small for separate analysis. M/W loss greater than 10 per cent was seen in 29 per cent of white males, 19 per cent of blacks, and 48 per cent of white females (p less than 0.02). When the groups were further divided into those with duration of diabetes less than or equal to five years and those with duration greater than five years, significant reduction in M/W average loss over time was seen with white females (10.6 per cent +/- 1.2 to 3.7 per cent+/- 1.5, p less than 0.0001). Expression of this defect in bone mineralization is controlled by race and sex acting independently of each other.

Adolescent↗
PubMed1975

The nitrosation products of creatine and creatinine in model systems.

The formation of N-nitrososarcosine from creatine, creatinine-5-oxime and l-methylhydantoin-5-oxime from creatinine was investigated in model solutions under various conditions (temperature, pH, concentration of sodium nitrite). N-nitrososarcosine was formed from creatine only in strongly acidic medium and its concentration increased with temperature and concentration of sodium nitrite. No N-nitrososarcosine was detected at 0 degrees C and in the presence of an equimolar amount of sodium nitrite. Creatinine-5-oxime and l-methylhydantoin-5-oxime was formed from creatinine in a broad region of pH, the highest concentration of these compounds was found in pH 3.6. The main reaction product was l-methylhydantoin-5-oxime. At a given pH, the concentrations of these two oximes increased generally with increased temperature and/or concentration of sodium nitrite. No oxime were detected at O degrees C and in the presence of equimolar amounts of sodium nitrite. Likewise was studied the influence of temperature on the decomposition of the above mentioned compounds. The activation energies of the studied reactions in acidic medium were 4.12 (n-nitrososarcosine), 19.3 (creatinine-5-oxime), and 20.2 kcal/mol (l-methylhydantoin-5-oxime), respectively.

Biodegradation, Environmental↗