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Biomedical subjects

M Landau

Publications and source records attributed to M Landau.

At least 73 records · Page 4Linked to original sources
PubMed1988

Determination of triacylglycerols in serum by capillary gas chromatography with trinonadecanoylglycerol as internal standard.

An accurate capillary gas-chromatographic method with trinonadecanoylglycerol as internal standard for determining triacylglycerols in human serum and other biological sources is described. After serum extraction, total triacylglycerol and triacylglycerol species (differing in the number of carbon atoms in the acyl radicals) are directly determined without any further sample manipulation. In addition, from the same gas-chromatographic run the data obtained by the integrator record are compared with those of a computer data acquisition system. Evaluation of the triacylglycerol values resulted in a coefficient of variation (CV) of 2.08% (computer evaluation). Simultaneous evaluation of data obtained from tripalmitoylglycerol and tristearoylglycerol standards resulted in CV of 2.04 and 1.99%, respectively (computer evaluation), and 6.63 and 4.84%, respectively (integrator evaluation). Gas chromatography at lower elution temperature resulted in better separations but enhanced CV values up to about 4%. Triacylglycerol values were not influenced by storage of plasma at -20 degrees C up to 4 days prior to extraction.

Chromatography, Gas↗
PubMed1987

Hysteresis phenomena between periodic and stationary solutions in a model of pacemaker and nonpacemaker coupled cardiac cells.

We were interested in investigating the behaviour of a cardiac electrophysiological model including coupled pacemaker (PM) and nonpacemaker (NPM) cells. To this aim, a modified version of the model of Van Capelle and Durrer was used. First, few discrete values were assigned to coupling resistance (CR) and respective cell sizes and numerical simulations versus time showed three possible kinds of response pattern: sustained rhythmic activity, subthreshold oscillations, and complete inhibition. Then, after setting a fixed value to PM cell size, we undertake a thorough study of the system by using bifurcation-continuation techniques and CR was chosen as the continuation parameter. On the maximum action potential--CR plane representation, we could describe five behavioural zones: complete inhibition, coexistence of complete inhibition and NPM large oscillations, NPM large oscillations, coexistence of NPM large oscillations and subthreshold oscillations, subthreshold oscillations. Within the zones of qualitatively different coexisting solutions, a detailed exploration clearly demonstrated the presence of hysteresis cycles. Indeed, the status of the system depended on its immediate previous story within narrow ranges of CR values. Such a coexistence of stable solutions for identical values of CR may suggest an explanation of the intermittant activity elicited from abnormal ectopic foci observed in certain ventricular rhythm disturbances. In addition, a Hopf bifurcation point, from which emerged stationary and periodic solutions, was followed on the PM cell size--CR plane and from this representation we could deduce that the smaller the PM cell, the higher the CR must be for the PM cell to escape from the NPM cell inhibition.

Cell Membrane↗
PubMed1985

Characterization of a pigment-dispersing hormone in eyestalks of the fiddler crab Uca pugilator.

A pigment-dispersing hormone (PDH) from eyestalks of the fiddler crab Uca pugilator has been purified by gel filtration, ion-exchange chromatography, partition chromatography, and reversed-phase liquid chromatography. Based on automated gas-phase sequencing and subsequent identification of carboxyl-terminal amide, we have assigned the primary structure of this peptide as Asn-Ser-Glu-Leu-Ile-Asn-Ser-Ile-Leu-Gly-Leu-Pro-Lys-Val-Met-Asn-Asp-Ala-NH (2). We have confirmed the sequence by synthesizing this peptide and demonstrating that the synthetic PDH and the native PDH display identical chromatographic behavior and biological activity. This hormone is a member of a family of invertebrate neuropeptides that includes a light-adapting/pigment-dispersing octadecapeptide hormone from the prawn Pandalus borealis. In assays for melanophore pigment dispersion in destalked fiddler crabs, Uca PDH was 21-fold more potent than Pandalus PDH. These two hormones share a hexapeptide core sequence (residues 5-10: -Ile-Asn-Ser-Ile-Leu-Gly-) as well as the amino- and carboxyl-terminal residues but differ at positions 3, 4, 11, 13, 16, and 17. These results point to speciesrelated or group-specific structural differences among crustacean PDHs.

Journal Article↗
PubMed1983

[Effect of the treatment of psoriasis with dithranol in comparison with a combination of dithranol and a corticosteroid].

Symmetric lesions of ten psoriasis patients were treated with anthralin and a combination of anthralin and steroid to compare the effect of these two therapies. After treatment, tissue was excised from the papules. An in vitro double-labeling autoradiography with 3H- and 14C-thymidine was then carried out. The thickness of the epidermis was also measured. The anthralin therapy leads to significantly greater inhibition of proliferation than the combined therapy with steroid. On the other hand, the combined therapy significantly shortens the duration of the S-phase, which is pathologically lengthened in psoriasis patients. The combined therapy also leads to significantly greater thinning of the epidermis.

Adrenal Cortex Hormones↗