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Biomedical subjects

B Singer

Publications and source records attributed to B Singer.

At least 163 records · Page 9Linked to original sources
PubMed1979

[Unilateral dysplasia of the circle of Willis with multiple distal stenoses (author's transl)].

Neurological and clinical examinations were found to be normal in a woman aged 40 years who had had a single generalized epileptic seizure. Rediological examinations demonstrated a spiral-shaped calcification above and laterally to the left sella turcica. This corresponded to changes in the C 1 segment of the left carotid sinus, which was partly stenosed distally, with left unilateral abnormalities of the circle of Willis and multiple distal stenoses of the left sylvian and vertebro-basilar arteries. Scanning demonstrated that these had been present for a long time, but it is not possible to establish the diagnosis on an etiological basis as no similar radiological findings have been published.

Adult↗
PubMed1978

[Diffuse polymorphous inclusions in a patient treated with perhexiline maleate (author's transl)].

Case report of polyneuritis and liver dysfunction induced by perhexiline maleate in a 64 years old male patient. The ultrastructural study of nerve, liver, muscle and skin biopsies shows polymorphous, membrane bound, often multilamellar, lysosome-like inclusions, the content of which is probably complex lipids. The histochemical study of liver reveals a lipid storage, consisting mainly of triglycerides and of smaller amount of phospholipids and free fatty acids, the pattern of which is abnormal. The biochemical study of nerve tissue shows a decrease of phospholipids levels and some qualitative disturbances in gangliosides. These changes, some of which are similar to those reported in amphiphilic drug intoxications, are prevalent in high lipid metabolism cells such as hepatic and Schwann cells.

Biopsy↗
PubMed1978

Preparation and template activities of polynucleotides containing O2- and O4-alkyluridine.

O2-Ethyl-UDP and O4-methyl-UDP have been prepared and copolymerized in various proportions with UDP or CDP, using polynucleotide phosphorylase. The copolymers were used as templates for DNA-dependent RNA polymerases in the presence of Mn2+. Both of the O-alkylated uridines caused a similar misincorporations. When copolymerized with U they led to incorporation of CMP and GMP into the poly(A). No AMP or UMP incorporation seemed to be caused by the introduction of O-alkyluridines into either poly(U) or poly(C). The mispairing of O2- and O4-alkyluridine to behave like C or G represents mutagenic events. O2 alkylation of U or T is, in contrast to O4 alkylation, a relatively frequent result of treatment of double-stranded nucleic acids with N-nitroso alkylating agents. In single-stranded nucleic acids both O2 and O4 alkylations of U and T occur to similar extents. Thus, the observed mutagenic effects of O2 and O4 alkylation of U may be involved in the high carcinogenicity of these alkylating agents.

Alkylation↗
PubMed1977

Sites in nucleic acids reacting with alkylating agents of differing carcinogenicity of mutagenicity.

The site of alkylation of a nucleic acid, in vivo, is greatly dependent on the type of alkylating agent. Most alkylating agents of low mutagenicity or carcinogenicity (such as dimethylsulfate) react primarily with the ring nitrogens. The carcinogenic N-nitroso compounds have a great affinity for alkylating oxygens and react with all ring oxygens as well as the phosphodiesters and, in the case of RNA, with the 2'-O of ribose. Ethylating agents, though in absolute terms less reactive than the corresponding methylating agents, show even greater affinity toward oxygens. It appears that the ethyl nitroso compounds that are carcinogenic are also the most reactive with oxygens.

Alkylating Agents↗
PubMed1977

The effect of angiotensin I converting enzyme inhibitor (SQ 20881) on the release of prostaglandins by rabbit kidney, in vivo.

1. Prostaglandin E- and F-like material has been estimated in renal venous blood of the left kidney of anaesthetized rabbits following renal nerve section. Prostaglandins were estimated by bioassay following solvent extraction and column chromatography. 2. Electrical stimulation of the renal nerves of the left kidney to reduce renal blood flow by approximately 15% for 15 min resulted in a significant increase in the concentration of prostaglandin E-like material in the renal venous blood. The peak values were normally seen either in the last 5 min of the stimulation period or in the first 5 min after the end of the stimulation period. The concentration of prostaglandin F-like material was not significantly altered. 3. Similar reduction of renal blood flow of the left kidney by renal artery constriction also resulted in a significant increase in the concentration of prostaglandin E- but not F-like material in renal venous blood. The timing and magnitude of the response was comparable with that observed with renal nerve stimuation. 4. The effect of an angiotensin I converting enzyme inhibitor, SQ 20881, on the response to both renal nerve stimulation and renal artery constriction has been studied. The administration of the drug did not significantly reduce the release of prostaglandins from the denervated kidneys, however, the increase in prostaglandin E-like material, in response to both stimuli, was abolished. 5. The results suggest that the increase in prostaglandin E-like material released from the kidney in response to low frequency stimulation or to modest reductions in renal blood flow is dependent on the release of renin and that the effect is mediated by the formation of angiotensin II and not angiotensin I.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1976

All oxygens in nucleic acids react with carcinogenic ethylating agents.

Over 80% of ethylnitrosourea and ethylnitrosoguanidine modification of nucleic acids is on oxygens. The reactivity of oxygens (other than ribose and phosphate) in single-stranded RNA is: O2 of C greater than O2 of U greater than O6 of G greater than O4 of U. In double-stranded DNA the order is: O2 of T equals O6 of G greater than O4 of T greater than O2 of C. Oxygen reactivity of single-stranded DNA resembles RNA. The glycosidic bond of O2-alkylpyrimidines is labilised.

Alkylation↗
PubMed1976

Alkylation of ribose in RNA reacted with ethylnitrosourea at neutrality.

Ribose oxygens in TMV-RNA are ethylated by the carcinogen ethylnitrosourea in neutral aqueous solution (pH 6.1-7.3). 2'-O-ethyluridine, and 2'-O-ethylcytidine have been identified as reaction products. The four 2'-O-ethyl nucleosides are found in approximately equal amounts and the total extent of ribose alkylation is about 15% of the total ethylation. This finding, in conjunction with earlier results showing that all ring and phosphate oxygens can be ethylated, signifies that every oxygen in RNA or polyribonucleotides can react with ethylnitrosourea. The possible biological significance of ribose alkylation, resulting from chemical rather than enzymatic reaction, is discussed. The preparation of the new derivative 2'(3')-Oethylguanosine is described.

Alkylation↗
PubMed1976

Sites of alkylation of poly(U) by agents of varying carcinogenicity and stability of products.

Several alkylating agents of widely varying reported carcinogenicity (dimethylsulfate, diethylsulfate, ethylmethanesulfonate, methylnitrosourea, ethylnitrosourea and ethylnitrosoguanidine) were reacted with poly(U) at pH values ranging from 4.5 to 7.5. All nucleophilic centers (internal phosphate groups, ribose hydroxyls, and O2, N-3 and O4 sites of the uracil base) were found reactive, though to different extents, at neutrality and in slightly acid solution. The distribution of products is a function of the alkylating agent and pH. The nitroso compounds are more reactive toward oxygens than are dialkylsulfates and alkylalkanesulfonates. The ratio of N : O alkyl products is strongly pH dependent, primarily due to the N-3 being most reactive at the higher pH values, while the diester is most reactive at the lower pH values. The extent of reaction of the O2, O4 or 2'-O or ribose is not greatly affected over the pH range tested. At pH 5.0 alkyl ribophosphotriesters mainly lose alchol to re-form a stable phosphodiester. With increasing OH- concentration, the favored reaction is chain scission at the 3'-O-P bond.

Alkylating Agents↗
PubMed1976

[Circulatory disorders induced by amantidine].

Amantadine has been used since 1969 in the treatment of Parkinson's disease. In 1970, were described the special symptoms noted in the lower limbs due to this drug. The authors, after a review of the various disturbances, have studied 10 cases by Capillaroscopy. They emphasize the interest of the study of this abnormality of the micro-circulation, producing vaso-constriction of the arterioles and venules.

Aged↗
PubMed1976

The sodium-retaining effect of renal nerve activity in the cat: role of angiotensin formation.

1. The effect of low-frequency stimulation of the renal nerves on renal function and renin release has been investigated. The experiments were performed in unilaterally nephrectomized, anaesthetized cats in which the nerves to the remaining kidney were sectioned. 2. When stimulation frequency was adjusted to reduce renal blood flow by approximately 15% for 15 min, glomerular filtration rate was hardly affected. The ratio sodium clearance/glomerular filtration rate was significantly reduced and plasma renin activity was significantly increased. 3. When the renal nerves were similarly stimulated in the presence of the beta-adrenergic receptor blocking agent, propranolol, the glomerular filtration rate was significantly reduced and the rise in plasma renin activity was significantly inhibited. The reduction of sodium clearance/glomerular filtration rate was as great as in the control animals. 4. The results are consistent with the view that the maintenance of glomerular filtration rate, during renal nerve stimulation which reduced renal blood flow, may be mediated by the local generation of angiotensin. The results also suggest that angiotensin does not play an important role in the sodium retention associated with increased renal nerve activity.

Aminohippuric Acids↗