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At least 91 records · Page 5Linked to original sources
PubMed1996

Spectral analysis in cyclic changes of human sleep evaluation.

In this study cyclic changes of human sleep structure were examined. For whole-night polysomnograms of 35 healthy volunteers of both sexes, manual hypnograms were created and divided into NREM-REM cycles. EEG signals from C3-A2 derivation were analysed by computer using a Fast Fourier Transform (FFT). For consecutive NREM-REM cycles of individual sleep stages, EEG power density contents for delta, theta, alpha, sigma and beta waves were analysed. For consecutive sleep cycles, a clear decrease in NREM sleep duration, especially slow wave sleep duration, was obtained. In addition, a decrease in power density of delta waves was observed. For consecutive sleep cycles, increases in REM sleep duration and in power density of theta and alpha waves were obtained. In consecutive sleep cycles, high amplitude delta slow waves are replaced by higher frequency and lower amplitude waves. Thus stages of NREM sleep are replaced by stages of REM.

Adult↗
PubMed1999

Fluorescence decay time distribution analysis of cyclic enkephalin analogues. Influence of the solvents and configuration of amino acids in position 2 and 3 on changes in conformation.

The lifetime distribution calculations were applied to study the influence of configuration of amino-acid residues in positions 2 and 3 on changes in conformation of the peptide chain of cyclic analogues of enkephalins containing a fluorescence energy donor and acceptor in different solvents. In all the solvents studied the lifetime distributions were bimodal. This testified to the presence of two families of conformations. In this paper the relationship between the population of each conformation and configuration of the residues in position 2 and 3, and the solvent used is discussed.

Amino Acid Sequence↗
PubMed1990

[Synthesis and analysis of cyclic analogs of angiotensin].

Five angiotensin cycloanalogues have been synthesised by classical methods of peptide chemistry, cyclisation being carried out via pentafluorophenyl esters. Cycloanalogues (I-IV) with a fixed potential turn in the C-terminal part of the angiotensin molecule inferred on the basis of physico-chemical data do not possess angiotensin-like activity. Compounds (V) with enlarged cycle shows decreased pressor effects as compared with angiotensin. By means of circular dichroism chiroptical properties of the compounds in water and ethanol were examined.

Amino Acid Sequence↗
PubMed1985

Rapid automated high-performance liquid chromatographic analysis of cyclic adenosine 3',5'-monophosphate. Synthesis in brain tissues.

A rapid and sensitive automated system for measuring cyclic adenosine 3',5'-monophosphate (cAMP) synthesized from either radiolabelled adenine or adenosine 5'-triphosphate (ATP) in intact and broken cell tissue preparations, respectively, is described. After incubation with radiolabelled precursor, tissue samples are deproteinized and then injected directly onto a reversed-phase high-performance liquid chromatographic column. The column effluent fraction which contains cAMP is collected into scintillation vials and assayed for tritium by liquid scintillation spectrometry. Since the high-performance liquid chromatographic and fraction collection procedures are automated, over fifty samples can be analyzed in duplicate in a single day. The utility of this assay is illustrated by investigations of the effects of beta-adrenergic receptor stimulation on cAMP synthesis in tissue slices prepared from rat cerebral cortex and dopamine on cAMP synthesis in striatal membrane preparations.

Adenine↗
PubMed1982

Implementation of micromethods to resolve problems of human breast tumor heterogeneity in analysis of cyclic 3':5'-nucleotide phosphodiesterase.

Individual human infiltrating ductal carcinomas and fibroadenomas were sectioned frozen to yield an alternating sequence of stained and lyophilized material. Stained preparations were used as references permitting microdissection of regions of tumor involvement in the corresponding dried sections. Tissues quantities of 5 to 25 micrograms dry weight were incubated under mineral oil in reaction volumes of 5 microliters and analyzed for cyclic adenosine 3':5'-monophosphate phosphodiesterase (PDE). The observed affinity constants for the 27,000 x g soluble PDE from benign tumors were 4.7 and 49.9 microM, while those for malignant tumors were 6.3 and 28.5 microM. The soluble enzyme of both tumor types eluted in three peaks on DEAE-Sephacel microcolumns. Both tumor types possessed a PDE activator eluting at 350 mM NaCl, although endogenous PDE activities were unaffected by additions of either this activator or 200 microM ethylene glycol bis(beta-aminoethyl ether)N,N,N',N'-tetraacetic acid. Individual microsections of benign tumors contained total PDE levels 2-fold higher than those of malignant tumors. Homogenates prepared from pooled microsections of the same tumors possessed only one-half of the total activity. Differential losses of enzyme in various preparation schemes as well as the use of tumor samples differing in cell density were suggested to account for some of the apparently conflicting literature values for breast tumor PDE.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1979

Stereochemical studies on cyclic peptides. Part X. Conformational analysis of hydrogen bonded cyclic pentapeptides.

Conformational aspects of 4 leads to 1 hydrogen bonded cyclic pentapeptides are considered in this paper from the point of view of "contact criteria" and potential energy calculations. Three types of such hydrogen bonded conformations, designated A1, A2 and B, are possible, involving some amount of strain on the bond angles. The energy of hydrogen bonded cyclopentaglycyl is somewhat less than that of the five-fold symmetrical conformation. The stereochemical feasibility of introducing L- and D-alanyl resudues in these structures has also been studied and the possible types for different sequences of alanyl residues have been determined. The results are discussed further in the light of the limited data available from crystal structure and nuclear magnetic resonance studies on cyclic pentapeptides.

Amino Acid Sequence↗
PubMed1998

Migration, stem shape, and surface finish in cemented total hip arthroplasty.

In many recent publications it was suggested that the amount of early subsidence of a femoral stem in total hip arthroplasty is indicative for later revision. In this article it is argued that stems can be designed according to alternative objectives, resulting in different shapes and surface roughness, each producing its own characteristic postoperative subsidence pattern. It was investigated whether these inherent subsidence patterns can be estimated in preclinical testing. For that purpose two stems, both without a collar, relying on cement fixation only, were compared regarding their stress transfer, migration, and induced micromotion behavior. Finite element analysis, cyclic bench testing of substitute bone reconstructions, and clinical radiostereophotogrammetric analysis were applied. The stems investigated were the Exeter, which is assumed to be a force closed fixation design, relying on subsidence under load as a method of maintaining stability, and the SHP, as a shape closed fixation design, meant to be contained by the cement mantle. Both designs were true to their design concepts in the analyses, in the sense that migrations and micromotions of the Exeter stems far exceeded those of the SHP stems. It was found that preclinical studies such as finite element analysis or bench tests give reasonable indications of in vivo postoperative behavior. It is concluded that early clinical migration values should be considered relative to stem shape and surface finish, when prediction of later revision probability is the issue.

Aged↗
PubMed2000

Hansch analysis of antimalarial cyclic peroxy ketals with physicochemical and electrotopological parameters.

Hansch analysis of some antimalarial cyclic peroxy ketals (IV) having structural variations at the para substituted phenyl ring and an alicyclic ring of different size reveals that electronic and steric parameters of the phenyl ring substituents are important for explaining the variation in the activity while hydrophobicity parameter is of little significance. Electron withdrawing substituents with higher MR (molar refractivity) or V(W) (van der Waals volume) are preferred for the activity. Use of structural descriptors suggests that presence of a seven membered alicyclic ring attached to the peroxy bridge containing ring is conducive to the activity. Application of electrotopological state atom index (ETSAI) suggests a pharmacophore containing the peroxy bridge. This is corroborated by earlier observation on importance of oxygen atoms of the peroxy linkage of artemisinin for antimalarial activity. Although incorporation of ETSAI into Hansch model does not improve the relations, the electronic parameter sigma is found to be significantly correlated with it.

Algorithms↗