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Biomedical subjects

G Cohen

Publications and source records attributed to G Cohen.

At least 307 records · Page 17Linked to original sources
PubMed1984

Enzymatic and nonenzymatic hydrolysis of D,L-dipivefrin.

D,L-dipivefrin hydrochloride was administered bilaterally to rabbit eyes five or 150 minutes after unilateral application of a cholinesterase inhibitor. Aqueous humor levels of D,L-epinephrine, measured 30 minutes later by high-performance liquid chromatography, were not significantly different in the two eyes. Nonenzymatic conversion of D,L-dipivefrin to D,L-epinephrine was measured in tissue-free (pH 7.4) solutions; after three hours less than 1% of D,L-dipivefrin became D,L-epinephrine. Homogenates of corneal epithelium were 16 times more effective in converting D,L-dipivefrin to D,L-epinephrine than after heat-inactivation. The ocular hypotension produced by 0.25% D,L-dipivefrin eyedrops was unaffected by prior administration of 0.25% echothiophate iodide eyedrops provided the D,L-dipivefrin was administered after the echothiophate-induced ocular hypertensive phase. It was concluded that D,L-dipivefrin was converted to D,L-epinephrine in vivo primarily by enzymatic hydrolysis and that cholinesterase inhibitors did not affect this conversion.

Animals↗
PubMed1984

Regional differences in the effect of pargyline on dopamine concentrations in the rat hypophysis.

Dopamine concentrations were estimated in different regions of the infundibular-pituitary system of the rat. The highest values were found in the pituitary stalk where they are comparable to the concentrations in the striatum, and higher than in the median eminence. In the anterior lobe the dopamine (DA) concentrations of the upper pole (10% of the lobe tissue) were 2-5 times higher than in the rest of the lobe. Anterior lobe DA was significantly higher in rats about 6 months old than in rats about 3 months old. After inhibition of MAO, the DA concentrations in the isolated neural lobe (NL) were more than doubled. In contrast there was no increase in the DA concentrations of the intermediate lobe, an observation which is in agreement with our previous finding that DA synthesis in the intermediate lobe after electrical stimulation of the pituitary stalk is much slower than in the neural lobe. Pargyline treatment caused an increase in the DA concentrations in the anterior lobe by about 150%. This rise (together with a DA increase in the stalk-infundibulum) may be related to the decrease in circulating prolactin which occurs in pargyline treated rats.

Aging↗
PubMed1984

Direct demonstration that the abundant 6-kilobase herpes simplex virus type 1 mRNA mapping between 0.23 and 0.27 map units encodes the major capsid protein VP5.

The two partially colinear 6-kilobase (kb) and 1.5-kb mRNAs mapping between 0.23 and 0.27 map units on the herpes simplex virus type 1 genome were precisely located. The 5' end of the 6-kb mRNA was located 28 bases downstream of the sequence ATATATT and was 10 bases to the left of the BamHI site at 0.268. This position is ca. 90 bases to the left of our earlier reported sequence (R. J. Frink, K. G. Draper, and E. K. Wagner, Proc. Natl. Acad. Sci. U.S.A. 78:6139-6143, 1981). We used a polyclonal antibody made against purified herpes simplex virus type 1 VP5 to demonstrate that the 155,000-dalton translation product of the 6-kb mRNA is this capsid protein. The antibody did not react with the 35,000-dalton translation product of the 1.5-kb mRNA. We also confirmed our identification of VP5 as the translation product of the 6-kb mRNA by comparison of tryptic peptides of the in vitro-translated protein and authentic VP5.

Antibodies, Viral↗
PubMed1984

Dose efficiency of screen-film systems used in pediatric radiography.

Twenty-one screen-film systems were examined using contrast-detail-dose methods in order to determine which were most dose-efficient for use in pediatric radiography. With a given screen, dose efficiency in the noise-limited region (contrast approximately equal to 0.05) was more or less constant (within the range of experimental error) with changes in film speed. When screens with decreased phosphor thickness were used, dose efficiency deteriorated markedly. For a given speed of up to two times Par, rare-earth phosphors offered no advantage over calcium tungstate systems with regard to low-contrast dose efficiency; however, they did increase the speed of the system. Anti-crossover film proved to be an effective means of improving high-contrast detail while maintaining low-contrast dose efficiency.

Calcium Compounds↗
PubMed1984

Oxy-radical toxicity in catecholamine neurons.

This article summarizes the evidence that oxy-radicals are involved in the destruction of catecholamine neurons by polyphenolic neurotoxins. Superoxide-mediated damage by 6-hydroxydopamine can be suppressed by intracellular catecholamines, which act as scavengers of the superoxide radical. Administration of exogenous hydroxyl radical-scavenging agents protects peripheral sympathetic neurons from destruction by 6-hydroxydopamine, 6- aminodopamine or 5,7-dihydroxytryptamine. Intraneuronal monoamine oxidase may drive cellular senescence of the nigrostriatal tract in patients with Parkinson's disease by generating hydrogen peroxide and derived oxy-radicals during the metabolism of endogenous dopamine.

Animals↗
PubMed1984

[Recent tracheobronchial ruptures caused by closed injuries of the thorax. Diagnosis and complications in 18 cases].

Tracheo-bronchial ruptures are serious complications of thoracic trauma. The authors report their experience of 18 cases: 3 tracheal ruptures, 3 tears in the tracheal or bronchial membrane, 11 unilateral bronchial ruptures and 1 bilateral bronchial rupture. Diagnostic endoscopy was performed immediately in 9 cases, with a delay of 2 to 3 days in 6 cases and with a longer delay (15th, 23rd and 25th days) in 3 cases. The treatment was non-operative in the 3 cases with membranous tears. The other patients were operated by resection of the contused area and end-to-end anastomosis of the ruptured extremities: within 24 hours following the diagnosis in 10 cases, and after a delay in the 5 other cases. The post-operative course was uncomplicated in 13 cases; 1 patient developed a bronchial stenosis requiring pneumonectomy and 4 patients died, including 2 from infective lesions due to delay in the diagnosis.

Adolescent↗
PubMed1983

Production of formaldehyde and acetone by hydroxyl-radical generating systems during the metabolism of tertiary butyl alcohol.

t-Butyl alcohol is not a substrate for alcohol dehydrogenase or for the peroxidatic activity of catalase and, therefore, it is used frequently as an example of a non-metabolizable alcohol. t-Butyl alcohol is, however, a scavenger of the hydroxyl radical. The current report demonstrates that t-butyl alcohol can be oxidized to formaldehyde plus acetone by hydroxyl radicals generated from four different systems. The systems studied were: (a) two chemical systems, namely, the iron catalyzed oxidation of ascorbic acid and the Fenton reaction between H2O2 and iron; (b) an enzymatic system, the coupled oxidation of xanthine by xanthine oxidase; and (c) a membrane-bound system, NADPH-dependent microsomal electron transfer. The oxidation of t-butyl alcohol appeared to be mediated by hydroxyl radicals, or by a species with the oxidizing power of the hydroxyl radical, because the production of formaldehyde plus acetone was (a) inhibited by competing scavengers of the hydroxyl radical; (b) stimulated by the addition of iron-EDTA; and (c) inhibited by catalase. The last observation suggests that H2O2 served as the precursor of the hydroxyl radical in all three systems. A possible mechanism is hydrogen abstraction to form the alkoxyl radical [CH3)3-C-O.), spontaneous fission of the alkoxyl radical to produce acetone and the methyl radical (CH3.), interaction of the methyl radical with O2 to form the methyl peroxy radical (CH300.), and decomposition of the later to formaldehyde. These results extend the alcohol oxidizing capacity of the microsomal alcohol oxidizing system to a tertiary alcohol. Since t-butyl alcohol is not a substrate for alcohol dehydrogenase or catalase, the ability of microsomes to oxidize t-butyl alcohol lends further support for a role for hydroxyl radicals in the microsomal alcohol oxidation system. In view of the production of formaldehyde, and the reactivity as well as further metabolism of this aldehyde, caution should be used in interpreting experiments in which t-butyl alcohol is used as a presumed "non-metabolizable" alcohol. t-Butyl alcohol may be a valuable probe for the detection of hydroxyl radicals in intact cells and in vivo.

Acetone↗
PubMed1983

A deletion of heterochromatin only of the Y chromosome in an azoospermic male.

A patient with a deletion of the distal portion of the long arm (q21) of chromosome Y is described clinically and cytogenetically. The proband has a normal male habitus but with azoospermia. The proband was investigated because of infertility. Male relatives were also investigated cytogenetically. The deleted Y chromosome was measured and compared with the normal Y of male family members. The results suggest that no Y euchromatin was lost.

Adult↗
PubMed1983

Increased microsomal oxidation of hydroxyl radical scavenging agents and ethanol after chronic consumption of ethanol.

The oxidation of ethanol by rat liver microsomes is increased after chronic ethanol consumption. Previous experiments indicated that hydroxyl radicals play a role in the mechanism whereby microsomes oxidize ethanol. Experiments were therefore carried out to evaluate the role of these radicals in ethanol oxidation by microsomes from ethanol-fed rats, and to determine whether the increase in ethanol oxidation by these induced microsomes correlates with an increase in the generation of hydroxyl radicals. Rat liver microsomes from ethanol-fed rats catalyzed the oxidation of two typical hydroxyl radical scavenging agents, dimethylsulfoxide and 2-keto-4-thiomethylbutyric acid, at rates which were two- to threefold greater than rates found with control microsomes. This increased rate of oxidation of hydroxyl radical scavengers was similar to the increased rate of microsomal oxidation of ethanol. Azide, which inhibits contaminating catalase in microsomes, increased the oxidation of dimethyl sulfoxide and 2-keto-4-thiomethylbutyric acid by both microsomal preparations. This suggests that H2O2 may serve as the microsomal precursor of the hydroxyl radical. Cross competition for oxidation between ethanol and the hydroxyl radical scavenging agents was observed. Moreover, the oxidation of ethanol, dimethyl sulfoxide, or 2-keto-4-thiomethylbutyric acid was inhibited by other compounds which interact with hydroxyl radicals, e.g., benzoate, and the free-radical, spin-trapping agent, 5,5-dimethyl-1-pyrroline-N-oxide. These results suggest that the increase in the rate of ethanol oxidation found with microsomes from ethanol-fed rats may be due, at least in part, to an increase in the rate of production of hydroxyl radicals by these induced microsomes. Increased production of oxyradicals may possibly result in oxidative damage to the liver cell as a result of ethanol consumption.

Alcoholism↗