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Biomedical subjects

P Back

Publications and source records attributed to P Back.

At least 19 recordsLinked to original sources
PubMed1994

Practical aspects of shielded gradient-coil design for localised in vivo NMR spectroscopy and small-scale imaging.

For a number of NMR applications the availability of screened gradients is crucial to minimize the effect of eddy currents on the NMR signal. In this paper we review two types of shielded gradient design: the target field and minimum inductance methods. The two designs are compared and construction details are presented. A novel coil design constructed with a double-sided primary and a single layered screen is outlined. Experimental results for both target field and minimum inductance coils are presented and compared.

Magnetic Resonance Spectroscopy↗
PubMed1984

The isolation of tetrahydroxy bile acids as methyl esters from human urine and their characterization by 1H- and 13C-nuclear magnetic resonance spectroscopy.

Treatment with phenobarbital causes an increased urinary excretion of tetrahydroxylated bile acids in patients suffering from intrahepatic cholestasis. The main components were isolated from urine by means of column and thin-layer chromatography and were studied as methyl esters by nuclear magnetic resonance spectroscopy. The results obtained strongly support the contention that the main components are 1 beta-, 6 alpha- and 6 beta-hydroxylated derivatives of cholic acid.

Bile Acids and Salts↗
PubMed1982

Phenobarbital-induced alterations of bile acid metabolism in cases of intrahepatic cholestasis.

Bile acid profiles from plasma and urine of six patients suffering from intrahepatic cholestasis were studied before and during treatment with phenobarbital. All patients responded to this treatment by decreasing their plasma bile acid levels. Using gas chromatographic and mass spectrometric methods for separation and identification of the bile acids, especially the occurrence of major atypical bile acids was quantitatively evaluated. The plasma bile acid lowering effect of phenobarbital in intrahepatic cholestasis can be partly explained by an increased formation of tetrahydroxylated bile acids, which are rapidly excreted by renal pathways. These tetrahydroxylated bile acids, present as nonsulfated compounds, have high renal excretory flow rates exceeding those of bile acid sulfates. Their enterohepatic circulation, however, seems to be low, since only small amounts of tetrahydroxylated bile acids can be found in bile. It is mainly the 1- and 6-hydroxylation that is stimulated by phenobarbital. The exact site of formation of tetrahydroxylated bile acids, however, is still unknown. These findings may provide a rationale for the institution of a phenobarbital treatment in cases of intrahepatic cholestasis.

Adolescent↗
PubMed1980

[Changes in bile acid metabolism in cholestasis].

The metabolism of bile acids is grossly disturbed under the conditions of cholestasis. Atypical bile acids are formed, which are mainly excreted into the urine. With regard to the origin of these atypical bile acids analyses of human meconium support the hypothesis that bile acid metabolism in cholestasis reverts to a fetal biosynthetic pattern. Problems may arise in cholestatic liver disease, if the elimination of atypical bile acids is impaired.

Bile Acids and Salts↗
PubMed1980

[Atypical bile acids (author's transl)].

The metabolism of bile acids in man is disturbed under the conditions of cholestasis. Besides of the main bile acids atypical bile acids can be found, which are mainly eliminated by renal excretion as sulphate esters and glucuronides. The pattern of urinary bile acids up to now renders no conclusions with respect to the underlying disease, although intrahepatic cholestasis seems to be in some way connected with disturbances in the metabolism of 3 beta-hydroxy-5-cholenoic acid, a bile acid, which exerts cholestatic effects by itself. The metabolites to be found seem to reflect a derepression of a genotypical synthesis program, which is not phenotypically apparent in healthy adults, but which may have been active during prenatal developmental stages of the liver.

Bile Acids and Salts↗
PubMed1980

Developmental pattern of bile acid metabolism as revealed by bile acid analysis of meconium.

The developmental metabolism of bile acids can be partly studied by the analysis of bile acid patterns in meconium. Employing modern analytical techniques, it has been found that besides the main bile acids of humans (cholic, chenodexoycholic, deoxycholic, and lithocholic acids) several "atypical" bile acids occur in meconium. It is unlikely that these "atypical+ bile acids are derived from materno--fetal transfer, and they therefore probably reflect a special fetal bile acid metabolism. Hydroxylations at positions 1 and 6 of the steroid skeleton are regularly encountered. These hydroxylations, as well as the occurrence of 3 beta-hydroxy-delta 5 compounds and of bile acids of the 5 alpha series, suggest that fetal bile acid synthesis differs markedly from that of the adult. These observations are of interest in relation to the origin of unusual bile acids found in the cholestatic condition of the adult. It appears that a resurgence of the fetal biosynthetic patterns takes place under the conditions of cholestatic liver disease.

Bile Acids and Salts↗
PubMed1976

Bile acid glucuronides, II[1]. Isolation and identification of a chenodeoxycholic acid glucuronide from human plasma in intrahepatic cholestasis.

The isolation of a glucurono-conjugate of a bile acid has been performed from human plasma in a case of chronic intrahepatic cholestasis. By means of a series of chromatographic steps, esterification with diazomethane and acetylation a mixture of methylester polyacetates of steroid glucuronides was obtained, which could be separated by thin-layer chromatography. Methyl 7alpha-acetoxy-3alpha-O-(methyl 2, 3, 4-tri-O-acetyl-beta-D-glucopyranosyluronate)5beta-cholan-24-oate, synthesized via the Koenigs-Knorr condensation reaction, was used as reference substance. From comparison of the chromatogrphic behaviour and the mass spectrum of the natural compound and the synthetic product the structure of the bile acid derivative isolated from plasma could be established as a peracetylated methylester of chenodeoxycholic acid-3-beta-D-glucuronide.

Bile Acids and Salts↗
PubMed1976

Bile acid glucuronides, III[1, 2]. Chemical synthesis and characterization of glucuronic acid coupled mono-, di- and trihydroxy bile acids.

The synthesis of bile acid-3-beta-D-monoglucuronides has been accomplished via the Koenigs-Knorr condensation reaction using methyl 2, 3, 4-tri-O-acetyl-1-deoxy-alpha-bromo-D-glucopyranuronate as coupling reagent. Chemical characteristics as melting points, elemental analyses, IR-spectra, isobutane-chemical ionization mass spectra and, in case of the derivative of 3alpha-hydroxy=5beta-cholanoate, NMR-spectra were recorded and can serve as a means of identification of these recently detected naturally occurring derivatives of bile acids in isolation procedures from biological sources.

Bile Acids and Salts↗