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M A Valenzuela

Publications and source records attributed to M A Valenzuela.

At least 37 records · Page 2Linked to original sources
PubMed1996

Characterization of ATP-diphosphohydrolase from rat mammary gland.

ATP-diphosphohydrolase (or apyrase) hydrolyses nucleoside di- and triphosphates in the presence of millimolar concentration of divalent cations. It is insensitive towards sulfhydryl and aliphatic hydroxyl-selective reagents and to specific inhibitors of ATPases. We present further evidence that ATPase and ADPase activities present in rat mammary gland correspond to apyrase. Two kinetic approaches have been employed, competition plot and chemical modification with group-selective reagents. The M(r) of these activities was determined by 60Co radiation-inactivation. The kinetic approaches employed, competition plot (which discriminate whether competitive reactions occur at the same site) and chemical modification, point to the presence of a single protein which hydrolyses ATP and ADP. The similar M(r) values of ATPase and ADPase activities also support this proposal. ATPase and ADPase activities of mammary gland show a similar sensitivity or insensitivity towards several chemical modifiers. These results suggest that this enzyme is ATP-diphosphohydrolase, also known as apyrase. The results obtained are compared with the ones obtained by us and other authors with the enzyme isolated from other sources.

Adenosine Triphosphatases↗
PubMed1996

ATP-diphosphohydrolase activity in rat renal microvillar membranes and vascular tissue.

Ecto-nucleotidases may have a role in the regulation of purinoceptor-mediated responses. ATP-diphosphohydrolase or apyrase has been described as an ecto-nucleotidase, which is characterized by a low specificity for its substrates and bivalent cations. The aim of this work was to demonstrate the presence of apyrase as an ecto-enzyme in the rat kidney. ATPase-ADPase activities of the renal microvillar membrane preparation, which correspond to "right side out' membranes, were characterized. The detection of ATP-diphosphohydrolase in the renal vasculature was done through perfusion of isolated rat kidney. ATPase-ADPase activities of the microvillar membrane preparation and apyrase share similar kinetic properties. These include: low substrate and bivalent metal specificities and insensitivity towards inhibitors like: oligomycin, ouabain, verapamil, levamisole and Ap5A. The M(r) or native ATPase and ADPase activities was determined by the 60Co irradiation-inactivation technique being around 65 kDa for both hydrolytic activities. Immunowestern blot analysis also supports the presence of apyrase in microvilli. Perfusion of isolated rat kidney with ATP and ADP, in the presence or absence of different inhibitors or apyrase antibodies indicated the existence of this enzyme in the vascular endothelium. The identification of ATP-diphosphohydrolase as an ecto-enzyme both in microvilli and vasculature support the proposal that the enzyme may have an important role in the extracellular metabolism of nucleotides.

Adenosine Triphosphatases↗
PubMed1996

ATP-diphosphophydrolase activity in rat heart tissue.

Extracellular nucleotides interact with specific receptors on the cell surface and are locally metabolized by ecto-nucleotidases. Biochemical characterization of the ATPase and ADPase activities detected in rat heart sarcolemma, under conditions where mitochondrial ATPase and adenylate kinase were blocked, supports our proposal that both activities correspond to a single enzyme, known as ATP-diphosphohydrolase or apyrase. The physiological function of this enzyme could be dephosphorylation of the nucleotides present in the interstitial heart compartment acting together with 5'-nucleotidase. Both hydrolytic activities have similarities in: sarcolemma localization, bivalent metal ion dependence, optimum pH, effect of several amino acid residue modifiers, competitive inhibition of nucleotide analogs, and broad nucleoside di-and triphosphate specificity. The ATPase activity could not be separated from the ADPase either through isoelectrofocusing or electrophoresis under acid conditions.

Amino Acids↗
PubMed1996

Comparison of the biochemical properties, regulation and function of ATP-diphosphohydrolase from human placenta and rat kidney.

ATP-diphosphohydrolase (apyrase. EC 3.6.1.5) has both ATPase and ADPase activity that are stimulated by bivalent metals, with Ca2+ being the most effective. The possible physiological function of this enzyme, associated with placental and renal microvilli, is related to the extracellular metabolism of nucleotides. A comparison of the biochemical properties of human placenta and rat kidney apyrase is presented, showing similarities in Mr. bivalent metal stimulation, nucleotide nonspecificity, insensitivity towards specific ATPase inhibitors, and lack of essential sulfhydryl and aliphatic hydroxyl groups. We describe the treatment of membrane preparations from both tissues with different detergents and the isoelectric focusing of the solubilized proteins to partially purify apyrase. An ectoenzyme localization is assigned both in microvillus membranes and in the vasculature on the basis of organ perfusion experiments with nucleotides in the presence of antibodies. Placental and kidney microvillus membranes inhibited ADP-induced platelet aggregation, in agreement with an extracellular role. Initial studies on enzyme regulation suggested the existence of at least two types of modulatory proteins: an activating protein in the cytosol of both tissues, and an inhibitory protein associated with placental microsomes. Possible hormonal regulation was investigated in kidneys using in vivo estradiol treatment, but only slight changes in total apyrase activity were observed.

Animals↗
PubMed1995

[POEMS syndrome. A case report].

A 48 years old male is reported. He presented with lower limb progressive and severe polyneuropathy, hypertrichosis, endocrinological alterations (hypothyroidism and hypogonadism) and organomegaly (hepatosplenomegaly and lymphadenopathies). This syndrome was associated with an osteosclerotic myeloma. The patient died two months after admission.

Hepatomegaly↗
PubMed1994

Human placental ATP-diphosphohydrolase: biochemical characterization, regulation and function.

1. Kinetic and physico-chemical studies on human placental microsomal fraction confirmed that the ATPase and ADPase activities detected in this fraction correspond to the enzyme ATP-diphosphohydrolase or apyrase (EC 3.6.1.5). These include substrate specificity, and coincident M(r) and pI values of both ATPase-ADPase activities. 2. This enzyme hydrolyses both the free unprotonated and cation-nucleotide complex, the catalytic efficiency for the latter being considerably higher. 3. Microsomal apyrase is insensitive to ouabain and Ap5A. The highly purified enzyme was only inhibited by o-vanadate, DES and slightly by DCCD. 4. Apyrase seems to be a glycoprotein from its interaction with Concanavalin-A. 5. Preliminary studies on the essential amino acid residues suggest the participation of Arg, Lys and His residues, and discard the requirement of -SH, COO-, -OH, and probably also Tyr and Trp. 6. Two kinetic modulatory proteins of apyrase were detected in placental tissue. An activating protein was found in the soluble fraction and an inhibitory protein was loosely bound to the membranes. 7. The proposed in vivo function for apyrase is related to the inhibition of platelet aggregation due to its ADPase activity, which is supported by the direct effect on washed platelets and by its plasma membrane localization.

Adenosine Diphosphate↗
PubMed1993

[Experimental evidence that endogenous TSH modulates microsomal antigen expression: clinical implications].

The purpose of this work was to study if TSH has a role in TPO antigen expression in vivo. Using the cytotoxicity assay we measured TPO expression and correlated it with TSH serum levels in 3 groups of rats: control, hypothyroid and hypothyroid supplemented with thyroxine. For comparative purposes, in the cytotoxicity assay we used rat monoclonal antiTPO or human sera with high titles for antiTPO antibodies. Hypothyroid rats showed marked elevations of TSH serum levels and TPO antigen expression in their thyrocytes when compared to the control and supplemented group. A positive correlation between TPO antigen and TSH levels was observed (r = 0.69, p < 0.001). There was an excellent correlation between TPO results using rat monoclonal or human sera antibodies (r = 0.94 p < 0.0001). It is concluded that TSH modulates TPO antigen expression. These data are of clinical relevance considering that TSH modulates the expression of other antigens that can maintain the immune response and perpetuate the immune disease in patients with Graves disease treated with antithyroid drugs. Thus, the avoidance of TSH hypersecretion with administration of thyroxine could be useful to treat these patients.

Analysis of Variance↗
PubMed1992

Changes in apyrase activity in uterus and mammary gland during the lactogenic cycle.

1. The purpose of this present research was to explore the possible roles of ATP-diphosphohydrolase (apyrase) in two tissues with high energetic demands during cell proliferation and differentiation. 2. Changes in apyrase activities during the pregnancy lactation cycle were examined in the rat uterus and mammary gland. 3. A significant decrease in apyrase activity (ATPase-ADPase) was observed in the pregnant uterus; this observation correlates with a minor inhibitory effect on platelet aggregation. 4. In mammary gland, the enzyme activity increases during lactation in parallel with an increase in blood supply, synthesis of glycoproteins and cell proliferation. 5. Apyrase activity did not change during the estrous cycle. Estradiol administration to rats slightly increased (20%) both ATPase-ADPase activities. 6. The probable function of apyrase is finally discussed, based on its substrate specificity and subcellular localization.

Animals↗
PubMed1992

[Pregnancy in a class-T diabetic patient].

We report the pregnancy of a 35 year old diabetic woman with a positive Australia antigen, 3 years after a successful cadaver kidney transplant. Immunosuppressive therapy with prednisone, azathioprine and cyclosporine was maintained. Pregnancy was complicated by an acute rejection episode on week 13, mild hypertension and intrahepatic cholestasis on week 22. Cesarean section and tubal ligation were performed at 32 and a half weeks. A 2020 g female infant was delivered, with Apgar scores of 8 and 9 at 1 and 5 min, respectively. Mild respiratory distress, jaundice and hypocalcemia were noted. The Australia antigen was negative. No fetal anomalies were detected. The high risk of pregnancy in a class T diabetic patient is confirmed in this case.

Acute Disease↗
PubMed1991

ATPase-ADPase activities of rat placental tissue.

1. Calcium-stimulated ATPase-ADPase activities were studied in a microsomal fraction of rat placental tissue. 2. The kinetic characteristics correspond to those of ATP-diphosphohydrolase, also known as apyrase (E.C. 3.6.1.5). 3. These characteristics include the lack of specificity towards nucleoside di- and triphosphates, activation by Ca2+, Mg2+ or Mn2+, insensitivity to specific inhibitors of some ATPase and absence of an effect of sulphydryl reagents. 4. Chemical modification of tyrosine, tryptophan, arginine and carboxylic residues decreases both ATPase and ADPase activities. 5. The substrate analogue, 5'-(beta, gamma-methylene)triphosphate, protected both enzyme activities against all the modifying amino acid reagents tested. 6. Placental fractions (homogenate and microsomes) inhibit ADP-dependent platelet aggregation. 7. The solubilized microsomal enzyme has a molecular mass of 67 kDa by size-exclusion chromatography; the pI is 9.36. 8. A differential effect is observed on the activation produced by Concanavalin A on microsomal and solubilized fractions when treated in the presence and absence of alpha-methylmannoside.

Adenosine Triphosphatases↗
PubMed1991

[Insulinoma and pregnancy. Clinical case].

A 25 year old woman developed severe episodes of hypoglycemia during the first weeks of pregnancy. Insulin blood levels of 53 uU/ml and Peptide C levels of 6.5 ng/dl were shown associated to a blood glucose level of 34 mg/dl. Echotomographic examination of the abdomen was unrewarding. Surgical exploration revealed a 1.5 cm tumor located at the junction of the body and tail of the pancreas, which was removed. Hypoglycemia disappeared and pregnancy continued uneventfully ending in a normal delivery at 40 weeks. The newborn was normal and no motor or psychologic abnormalities have been noted during follow up to 2 years of age.

Adult↗
PubMed1989

Comparative subcellular distribution of apyrase from animal and plant sources. Characterization of microsomal apyrase.

1. Apyrase (ATP: diphosphohydrolase) has been found in the microsomal fraction of rat salivary gland, mammary gland and uterus. 2. This enzyme, already described in plant tissue, is mainly present as a soluble polypeptide in tubers of Solanum tuberosum. 3. A fraction of this enzyme is associated with the microsomal fraction with a higher specific activity than the soluble one, for either ATP or ADP as substrate. 4. Apyrase bound to microsomes from rat and potato tissues was characterized in its substrate specificity and effect of inhibitors. 5. The Km values for ATP and ADP, optimum pH and metal ion requirement were determined. 6. A characteristic common to the microsomal and soluble apyrases is the stimulatory effect of a potato activator protein of soluble plant apyrase. 7. The microsomal-bound apyrase from rat and potato tissues were solubilized and subjected to size-exclusion chromatography. 8. The mammary gland and salivary gland apyrases eluted as molecular aggregates, in contrast to the uterus and potato enzyme.

Animals↗
PubMed1989

[Efficacy of propylthiouracil in the treatment of amiodarone-induced hyperthyroidism].

Amiodarone is a benzofuranic derivative widely used in cardiologic practice because of its excellent antiarrhythmic properties. Due to its high iodine content, it interferes with thyroid physiology and can cause either hyper or hypothyroidism. Amiodarone-induced hyperthyroidism should be considered as a serious complication since it develops in cardiac patients, the clinical diagnosis can be difficult and because conventional methods of therapy are said to be often ineffective. We analyze the outcome of 10 pts, chronically treated with Amiodarone (16-60 mo, mean 37.6 mo) who develop hyperthyroidism during the antiarrhythmic therapy. All patients had multinodular goiter. Overt clinical picture for thyrotoxicosis was seen in 7 of them and lab tests showed: rT3 = 101.1 +/- 14.9 ng/dl; T3 = 220.2 +/- 25 ng/dl; T4 = 15.6 +/- 1.9 micrograms/dl, TSH = 0.8 +/- 0.2 microU/ml and TRH response 0.0 microU/ml. Thyroid microsomal antibodies were negative in 3 pts studied. After Amiodarone was discontinued, patients were followed-up monthly. In 2, normalization of clinical and laboratory indexes were obtained at 40-60 d and no other medication was given. In the remaining, due to the intensity of clinical manifestations, PTU treatment was started (300 mg/d) After 4 mo, euthyroidism was achieved in 6 and it persisted after discontinuation of PTU has patient failed to respond to PTU, 131I was administered with excellent results. Patients have been followed-up up to 3 years after therapy without observing thyrotoxic relapses nor deterioration of their cardiological condition.2+ conventional therapies (PTU or 131I) have been, very effective.

Adult↗
PubMed1989

[Glucose overload test. Screening of gestational diabetes in population of pregnant women with risk factors for diabetes. Clinical experience].

UNLABELLED: Clinical utility of the Overload Test with 50 g. of Oral Glucose (PSG) is evaluated, in 513 pregnancies with risk factors for diabetes. Of the 933 PSG which were made, 13.7% were positive (limit value: plasma glucose of much less than 150 mg/dl at 1 hour); the test were made after 20 weeks of gestation in 82.8% of the cases. Of the 128 positive PSG, 73 positive Oral Glucose Tolerance Test were obtained (O'Sullivan criteria). The prevalence of gestational diabetes found in this group was 15.2%. There was no difference on the most frequent risk factors (family history, obesity and macrosomia) between the general population in the study and the group of Gestational diabetes. CONCLUSION: PSG, because of its easy application, low cost and excellent tolerance is a test which should be included among the prenatal routine test as screening for gestational diabetes in our media.

Adult↗
PubMed1989

[Clinical experience in diabetes and pregnancy].

We followed patients with pregnancy and diabetes in an outpatient clinic. 240 had gestational diabetes, 16 had type II and 5 type I diabetes. 85% of 110 patients with gestational diabetes had normal glucose tolerance test post partum (AGT). Type I patients were younger (25 years old) than AGT (32) or type II (33) patients. Complications frequently observed among diabetics included hypertension, premature membrane rupture and polyhydroamnios (the latter only among AGT and type II patients). Insulin was required for diabetes control in 14% of cases. Cesarean section was more frequent in diabetics than in a control population (21%): AGT 45%, type II 45% and type I 60%. Larger newborns occurred in 21% of AGT and 22% of type II as compared to 6% in controls. Neonatal mortality was 2.1% in AGT patients (0.8% in controls). Hyperbilirrubinemia, polyglobulia and hypocalcemia were more frequent among newborns of diabetic patients.

Adult↗