PubMed Health⌕ Search

Biomedical subjects

C Montero

Publications and source records attributed to C Montero.

At least 55 records · Page 3Linked to original sources
PubMed1991

Artemia purine phosphoribosyltransferases. Purification and characterization.

Adenine phosphoribosyltransferase (APRTase) and hypoxanthine-guanine phosphoribosyltransferase (HGPRTase) have been purified from Artemia cysts and nauplii to apparent homogeneity, as determined by SDS-PAGE. The purification includes affinity chromatography on AMP-Sepharose, which binds both enzymes, and they are eluted at different 5-phospho-alpha-D-ribosyl diphosphate (PP-Rib-P) concentrations. The purified enzymes from Artemia cysts were similar to nauplii enzymes with respect to Mr in denaturing gel electrophoresis and gel filtration, pH and cation dependence and kinetic constants for substrates and inhibitors. By Sephadex G-100 filtration, the native Mr of the adenine and hypoxanthine-guanine enzymes was estimated to be Mr 28,000 and 66,000, respectively. Analysis by SDS-PAGE revealed that the APRTase was a dimer of Mr 15,000 sub-units and the HGPRTase, a tetramer of four identical Mr 19,000 sub-units. The pH profile of the HGPRTase shows two apparent buffer-independent pH optima, at 7.0 and 9.5, while the APRTase has just one, at about pH 8-9. The purine phosphoribosyltransferase activity with adenine was highest, about tenfold the HGPRTase activity with hypoxanthine and fivefold that with guanine. Both enzymes exhibited similar requirements for divalent cations, either Mg2+, Mn2+ or Zn2+, while Ca2+ is highly inhibitory. The Km values of APRTase for adenine and PP-Rib-P are 2 and 30 microM, respectively, and the Km values of HGPRTase for hypoxanthine, guanine and PP-Rib-P are less than 1, less than 1 and 15 microM, respectively. Plots of the reciprocal enzyme activities versus reciprocal concentrations of one substrate at several fixed levels of the second one yield a pattern of inhibition by guanine and hypoxanthine. Product-inhibition studies indicated that AMP is a competitive inhibitor with respect to PP-Rib-P in the APRTase reaction, while the HGPRTase shows a mixed inhibition by GMP.

Adenine Phosphoribosyltransferase↗
PubMed1991

A high performance liquid chromatographic assay for AMP-deaminase activity in the erythrocytes of healthy subjects and patients with inherited purine disorders.

A novel method for measuring AMP-deaminase activity in human erythrocytes is presented, based on the determination of the reaction product, IMP, using high performance liquid chromatography. IMP formation was found to be proportional both to the incubation time and the amount of haemolysate over a wide range. The minimal detectable AMP-deaminase activity was more than 1000 times lower than the mean activity found in healthy controls (1083 nmol/h/mg Hb). No marked difference of activity was found in the patients with the following inherited purine disorders: familial juvenile gouty nephropathy and deficiencies of adenosine deaminase, hypoxanthine-guanine phosphoribosyltransferase or adenine phosphoribosyltransferase. The activity in the erythrocytes of patients with chronic renal failure was also similar to controls. The existence of subjects with low erythrocyte AMP-deaminase activity in the population has been confirmed.

AMP Deaminase↗
PubMed1991

Blockade of the antigen-antibody reaction using benzil condensation with the guanidyl residue of arginine.

Benzil blockade of the guanidyl group of arginine was tried on sections of paraffin-embedded tissue fixed in two different fixatives, in an attempt to evaluate the relevance of this amino acid to the reaction of several proteins with their corresponding antibodies. The two fixatives were 10% formaldehyde, and Bouin's fluid without acetic acid. Both polyclonal and monoclonal antibodies against proteins or peptides (lysozyme, adrenocorticotropic hormone, growth hormone, placental lactogen, and prolactin) were used on human biopsies or material from autopsies. The blockade was effective when monoclonal antibodies were used, whereas no effect or only a small decrease of the intensity of the reaction was observed with polyclonal antibodies. The least definitive result was obtained with prolactin, where a complete blockade was never achieved with monoclonal antibodies. Calcitonin, a peptide that does not contain arginine, was used as a control not susceptible to benzil blockade; no blockade of immunostaining was observed.

Adrenocorticotropic Hormone↗
PubMed1991

[A comparison between three questionnaires and laboratory tests for the detection of alcoholism in general practice].

By means of a case/control study, an attempt was made to identify the different questionnaires and biological tests which might be used in the General Practice consulting room for the detection of alcoholic patients. A comparison was made between the CABE, MALT, and Skinner questionnaires, and the MCV, AST, ALT, GGT triglyceride, cholesterol, uric acid, bilirubin and glycemia biological tests. Sensitivity, specificity, predictive value and diagnostic efficiency were studied in a group of 37 confirmed alcoholics and 25 controls making up a population with a high prevalence of alcoholism. Later we analysed the changes which affect the values of the different tests when applied to a population with a low prevalence of alcoholism, in other words, the utility of the tests in general practice was evaluated. The study concludes that the diagnostic performance of the questionnaires together with case history is higher than that of biological tests in general practice, and that the routine application tests in general practice, and that the routine application of the CAGE questionnaire and to a lesser extent of the Skinner questionnaire make it possible to identify those patients suspected of alcoholism and to improve the predictive value of the biological tests applied thereafter. Nevertheless further study is necessary to confirm the diagnostic effectiveness of these questionnaires in the general population of health centre patients.

Adult↗
PubMed1990

S-adenosylmethionine increases erythrocyte ATP in vitro by a route independent of adenosine kinase.

The mechanism by which S-adenosylmethionine (SAM) and adenosine (Ado) increase ATP levels in intact human erythrocytes in vitro has been compared. The use of erythrocytes from healthy controls and from subjects totally deficient in adenine phosphoribosyltransferase (APRT), plus inhibitors of adenosine kinase (AK) and adenosine deaminase (ADA) separately and together, has enabled us to demonstrate that this increment in ATP levels occurred via totally different metabolic routes. The results show that: (i) whilst the Ado-induced increment in ATP was AK dependent, that produced by SAM was independent of AK: and (ii) the SAM-induced increment in ATP was totally dependent on APRT and that some of the increment produced by Ado might also be APRT dependent. The above data are consistent with the metabolism of SAM to ATP by a route recently identified by us whereby ATP is formed from deoxyadenosine: namely binding to the enzyme S-adenosylhomocysteine hydrolase with subsequent release of adenine and further conversion to ATP via APRT.

Adenine Nucleotides↗
PubMed1989

Demonstration of sugar residues in the ultimobranchial tubule and thyroid C-cells of the rat using peroxidase labelled lectins.

The distribution of various sugars, that contribute to the composition of the carbohydrate components of the glycoprotein in the ultimobranchial tubule and the thyroid C-cells has been studied, using eight peroxidase-labelled lectins (Dolichos biblorus, Glycine max, Bauhinia purpurea, Helix pomatia, Arachis hipogaea, Ulex europaeus I, Limax flavus and Sophora japonica). The results obtained seem to show that there are receptors for Dolichos biflorus, Glycine max, Bauhinia purpurea, Helix pomatia, Arachis hipogaea, Ulex europaeus I and Limax flavus in the ultimobranchial tubule, suggesting the existence of N-acetylgalactosamine, galactose, L-fucose and sialic acid. However, the C-cells show only a positive reaction with Ulex europaeus I indicating the existence of fucosyl residues in those cells. All these findings support the contention that the ultimobranchial body might contribute decisively not only to the formation of C-cells but also, partially, to the constitution of certain follicular cells.

Animals↗
PubMed1989

Rapid improvement of visual defects with parenteral depot-bromocriptine in a patient with a non-functioning pituitary adenoma.

The management of non-functioning pituitary adenomas with bromocriptine is controversial, and surgical treatment is usually prescribed when the visual field is affected. Here we report, what we believe to be the first case of a patient with a non-functioning pituitary adenoma who experienced normalization of visual field defects and a substantial improvement in visual acuity after the parenteral administration of depot-bromocriptine. The patient's tolerance to the drug was excellent. The results of the immunohistochemical study of the surgically removed tumor were negative for PRL, GH, LH, FSH, TSH and ACTH. In our opinion, the use of depot-bromocriptine may represent an alternative to surgery in patients with non-functioning pituitary adenomas associated with visual lesions.

Adenoma↗
PubMed1989

Histochemical blockade of the antigen-antibody reaction using immunoperoxidase demonstration of lysozyme in paneth cells and lamina propria mononucleocytes of human small intestine as a model system.

Nitrosation and acetylation, two histochemical blocking procedures for amino groups, were used to establish the extent to which these groups intervene in the antigen-antibody reaction in immunohistochemistry. We used the peroxidase-antiperoxidase method (PAP) to demonstrate lysozyme in Paneth cells and in lamina propria mononucleocytes of human small intestine as a model system. We studied the relationship of these groups to fixation, concentration of the primary antiserum, and length of blockade, as well as the possibility of reversing blockade as proof of specificity. Our findings support the contention that amino groups are also an important factor in antigen-antibody binding, even in fixed tissue. Fixatives influence the binding process in many ways, with acetylation producing a more successful result than nitrosation in tissue fixed in Bouin without acetic acid, whereas the reverse is true in formaldehyde-fixed tissue.

Acetates↗
PubMed1988

Randomized trial of chemotherapy versus chemotherapy plus radiotherapy for stage I-II Hodgkin's disease.

A total of 277 patients with untreated Hodgkin's disease, clinical stages I-II, were randomized to cyclophosphamide, vinblastine, procarbazine, and prednisone (CVPP) alone for 6 monthly cycles or to CVPP plus radiation therapy (RT), 3,000 rad, to involved areas (CVPP plus RT). One or more of the following factors were considered as unfavorable prognosis: age greater than 45 years, more than two lymph node areas involved, or bulky disease. In the favorable group, disease-free survival (77% vs. 70%) or overall survival (92% vs. 91%) at 84 months for CVPP versus RT plus CVPP was similar. Patients with unfavorable prognosis treated with RT plus CVPP had longer disease-free survival (75% vs. 34%) (P = .001) and overall survival (84% vs. 66%) than patients treated with CVPP alone.

Adolescent↗
PubMed1988

Mucosubstances in medullary carcinoma of the thyroid.

We have studied mucosubstances in 12 cases of medullary carcinoma of the thyroid using histochemical techniques and a number of different lectins. Immunohistochemical staining for calcitonin and carcinoembryonic antigen was also performed. We have found that the presence of mucosubstances is a constant finding in medullary carcinomas; they were present extracellularly in 100% of cases and intracellularly in 53.3%. In both these compartments there was a predominance of neutral over acid mucosubstances. Receptors for UEA-I, Con A, RCA-I, Succ-WGA and SBA were found in many cells in the majority of cases, but there were differences in the affinity from one case to another. Because of this lack of specificity lectin histochemistry is not of diagnostic value in medullary carcinomas of the thyroid. The possible relationships of the lectin-binding results to glycosylated hormone precursors and carcinoembryonic antigen are discussed.

Adolescent↗
PubMed1988

Size changes of a growth hormone- and prolactin-producing adenoma during and after sandostatin treatment.

A 46-year-old woman with acromegaly and marked hyperprolactinemia was treated chronically with sandostatin (50 micrograms b.i.d. up to 100 micrograms t.i.d.). Plasma growth hormone (GH) was reduced by 90% of basal values and prolactin (PRL) dropped from initially 204 to 74 ng/ml. Serial CAT scans detected a volume reduction of the pituitary adenoma of 46.7%, but discontinuation of therapy was followed by re-expansion of the tumor. Tissue collected at transsphenoidal adenomectomy was examined by immunohistology and found positive for both GH and PRL. This characteristic would explain the dual hormonal response to the specific GH inhibitor sandostatin.

Adenoma↗
PubMed1987

A rare cause of acromegaly: ectopic production of growth hormone-releasing factor by a bronchial carcinoid tumor.

Ectopic production of growth hormone-releasing factor (GRF) is a rare cause of acromegaly. In addition to its production by gangliocytomas, both hypothalamic and intrasellar, in rare cases various neuroendocrine neoplasms produce the substance, with resultant growth hormone cell hyperplasia of the pituitary and acromegaly. We report an endocrinologically well-documented case of a GRF-producing bronchial carcinoid tumor in which the associated acromegaly was cured by lobectomy.

Acromegaly↗