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Biomedical subjects

J Cabanes

Publications and source records attributed to J Cabanes.

At least 37 records · Page 2Linked to original sources
PubMed1988

Development of young rats and rabbits exposed to a strong electric field.

Body growth and circulating levels of hormones were assessed in young rats and rabbits exposed to a 50-Hz electric field of 50 kV/m. Eight-week-old male rats were exposed 8 h/day for 4 weeks and rabbits were exposed 16 h/day from the last 2 weeks of gestation to 6 weeks after birth. The body and the organ growth of exposed rats were not statistically different from those of sham-exposed controls. No important differences from controls were observed in plasma levels of corticosterone, TSH, ACTH, and T4 or in adrenal levels of epinephrine, norepinephrine, and corticosterone although T3 was slightly, but significantly, decreased. No large histological changes in the thyroid or adrenals were noted. In rabbits, organ and body weights of exposed animals were comparable to those of controls. Plasma levels of various hormones (ACTH, GH, T3, T4, corticosterone, cortisol), serum glucose, triglycerides, and cholesterol were not significantly altered. Adrenal content of cortisol was lower, however, in exposed rabbits. No histological changes of the thyroid or adrenal glands were observed.

Adrenal Glands↗
PubMed1988

[Effects of exposure of spontaneously leukemic mice (AKR mice) to an electric field].

Spontaneously leukemic AKR mice were exposed from 6 weeks age to a 50 kV/m electric field 12 hrs./day. In this study, carrying on 50 exposed and 50 sham-exposed mice, like in the two preceding experiments, the exposed group mortality is lightly retarded, and reaches 100% only 10 weeks after the sham-exposed group. These differences are not however statistically significative.

Animals↗
PubMed1987

Chemical and enzymatic oxidation of 4-methylcatechol in the presence and absence of L-serine. Spectrophotometric determination of intermediates.

A pathway for 4-methylcatechol oxidation by tyrosinase (monophenol, dihydroxy-L-phenylalanine:oxygen oxidoreductase, EC 1.14.18.1) in the presence of L-serine is proposed. Characterization of intermediates in this oxidative reaction and stoichiometry determination have both been performed. It has been possible to detect spectrophotometrically 4-methyl-o-benzoquinone as the first intermediate in this pathway after oxidizing 4-methylcatechol with epidermis tyrosinase or sodium periodate at pH 6.5. The steps for 4-methylcatechol transformation in the presence of L-serine could be: 4-methylcatechol----4-methyl-o-benzoquinone----5-methyl-4N-serine-catechol----5 - methyl-4N-serine-o-benzoquinone. Matrix analysis of the spectra obtained with a rapid-scan spectrophotometer verified that 4-methyl-o-benzoquinone was transformed into 5-methyl-4N-serine-o-benzoquinone at a constant ratio, the stoichiometry for this conversion being the equation: 2-(4-methyl-o-benzoquinone) + L-serine----4-methylcatechol + 5-methyl-4N-serine-o-benzoquinone.

Animals↗
PubMed1987

Enzymatic oxidation by frog epidermis tyrosinase of 4-methylcatechol and p-cresol. Influence of L-serine.

A study has been made of the kinetics of cresolase and catecholase activities of tyrosinase on the p-cresol/4-methyl-catechol pair in the presence of L-serine. For this, a spectrophotometer assay for both activities based on the spectrophotometric and stoichiometric characteristics of the chemical reactions in the evolution of 4-methyl-o-benzoquinone is proposed. The presence of L-serine in the reaction medium caused a modification in the lag period and the steady-state rate expressed during the cresolase activity of tyrosinase, but no modification was observed during the expression of catecholase activity. These results can be explained taking into account the complex mechanism proposed for tyrosinase which included the chemical steps involved in the process. Furthermore, a singular form of regulation of enzymatic activity by L-serine has been clarified, not by any direct interaction between the protein molecule and the nucleophile, but by modification of the chemical reactions involved in the mechanism of tyrosinase.

Animals↗
PubMed1987

A kinetic study of the melanization pathway between L-tyrosine and dopachrome.

In the pathway of melanin biosynthesis originating from L-tyrosine, the dopachrome accumulation at physiological pH is produced with a pronounced lag period, during which the level of L-dopa increases, following a sigmoidal kinetics to reach a steady-state. A kinetic model has been proposed for the overall pathway of melanization from L-tyrosine to dopachrome; it explains the lag period present during the dopachrome accumulation as well as the influence of L-tyrosine and tyrosinase over this lag period. Use of this model is also valid to explain the kinetics of L-dopa accumulation in the reaction medium, as has been tested by simulation.

Animals↗
PubMed1987

[Effect of a low-intensity magnetic field on the proliferation of several models of cultured cells].

The effects of a ELF magnetic field (50 Hz) of low intensity (5 x 10(-4) T) were studied on the growth of 3 cell cultures: fibroblasts L 929, keratinocytes and HeLa. After a 24 to 72 hours exposure to the field no modification of growth rate and viability of the cells was observed in comparison to controls. This conclusion can be expressed for the conditions adopted in our experiments.

Animals↗
PubMed1987

Kinetic study of sinephrine oxidation by mushroom tyrosinase.

Mushroom tyrosinase catalyzes the oxidation of sinephrine showing a marked lag period during appearance of adrenochrome and simultaneously adrenaline accumulation in the reaction medium can be detected. The adrenaline accumulation follows a sigmoidal curve until a constant level of adrenaline is reached when the system is in the steady-state. These experimental results agree with a model of enzymatic catalysis that includes the chemical evolution of adrenoquinone and permit us to explain these phenomenon as well as the influence that enzyme and sinephrine concentration present on the lag period and the level of adrenaline accumulated in the steady-state.

Adrenochrome↗
PubMed1984

Kinetic study on the slow inhibition of epidermis tyrosinase by m-coumaric acid.

The inhibition by m-coumaric acid of oxidation of L-dopa by epidermis tyrosinase (monophenol,dihydroxy-L-phenylalanine:oxygen oxidoreductase, EC 1.14.18.1) is characterized by a prolonged transient phase. Kinetic data correspond to that for a postulated mechanism that involves rapid formation of a reduced enzyme-m-coumaric acid complex that subsequently undergoes a relatively slow reversible reaction. An overall inhibition constant for m-coumaric acid of 0.05 mM was calculated. The value of the Ki for the dissociation of m-coumaric acid from the rapidly formed complex was calculated as 0.53 mM. The first-order rate constants for the slow isomerization of the enzyme-inhibitor complex were calculated as 3.0 +/- 0.1 min-1 for the forward step and 0.31 +/- 0.06 min-1 for the reverse step.

Animals↗
PubMed1984

[Development of young rabbits exposed to an intense electric field].

Newborn rabbits were exposed 18 hours a day for 6 weeks to an intense electric field; then they were killed, the body weight and the weights of the main organs had the same values as the control ones. The compositions of liver and interscapular brown fat were not modified. There was no significant effect of the electric field either on plasma levels of ACTH, GH, T3, T4, corticosterone, cortisol or on plasma levels of glucose, triglycerides and cholesterol. The histology of thyroid and adrenals showed no evident alterations. Ultrastructural examinations of the cerebellum did not show the previously described alterations observed in Purkinje nerve cells. It is concluded that in the present experimental conditions, the chronic exposure of newborn rabbits to an intense electric field did not modify the biological and structural parameters which were examined and had no effect on the animal growth and development.

Adipose Tissue, Brown↗
PubMed1983

Bicompartmental analysis of cerebrospinal fluid circulation. Theory and clinical applications.

A new model for cerebrospinal fluid (CSF) circulation is proposed. Specific activity/time curves for CSF kinetics determined after intraventricular injection of a radiotracer were produced by fitting a biexponential function to data points and developing a two-compartmental model. Calculation of kinetic parameters of the model provides quantitative data about CSF dynamics. The study of each compartment separately and of the intercompartmental relationship is possible with this model. Sequential scan images and graphic plots of the variations of radioactivity in both compartments, derived from this model, add supplementary information in the evaluation of patients. Ventriculography was performed in 80 patients, who fell into four groups: those with normal CSF circulation, hydrocephalus, infantile hydrocephalus, and functioning ventricular shunts. Normal and hydrocephalic patients showed significant differences between the two groups in the means of some numerical parameters calculated from the new model. An increase of intraventricular radioactivity at 24 hours (p less than 10(-4)) and of the volume of Compartment 1 (p less than 0.01) with decreased volume of Compartment 2 (p less than 10(-4)) and total flow outside the system (p less than 10(-3)) were found in patients with hydrocephalus. The limiting values for normal patients were also estimated. Communicating and obstructive hydrocephalus could be differentiated by this method; however, no differences in mean values were found relating to the etiology or clinical course of the hydrocephalus. Normal-pressure hydrocephalus and cerebral atrophy produced significantly different mean values for the volume of Compartment 2 (p less than 0.01), flow out of the system (p less than 0.01), and intercompartmental flow (p less than 0.01).

Cerebral Ventriculography↗
PubMed1979

Melanotic spinothoracic schwannoma.

A dumb-bell mediastinal melanotic schwannoma is described, and the rarity of this type of tumour emphasised. The tumour was resected by simultaneous laminectomy and posterior thoracotomy. The patient is well four years after operation. The pathology of the tumour is described and the origin of melanotic cells is discussed.

Female↗
PubMed1979

Cerebral venous angiomas.

The literature on venous angiomas is generally confusing, although recent reports confirm the existence of this entity. A survey of the published cases, with addition of two of our own, is presented in the current study. Characteristic histological and angiographic features are described. The value of radioisotope techniques is emphasized with regard to the modifications which these angiomas cause in cerebral circulation.

Adult↗
PubMed1978

Hydrocephalus after posterior fossa operations.

Sixteen patients with hydrocephalus which developed after operations on the posterior fossa were studied by radioisotope ventriculography. The results indicate that postoperative hydrocephalus is of communicating type, and that block of the basal cisterns is always present. Mechanisms involved in its pathogenesis are discussed, and it is felt that pre-existent adhesions in basal cisterns, surgical bleeding and cerebrospinal fluid (CSF) extra-arachnoidal collections are possible causes of the hydrocephalus.

Cerebellar Neoplasms↗