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Biomedical subjects

M Nieto

Publications and source records attributed to M Nieto.

At least 55 records · Page 3Linked to original sources
PubMed1994

Prediction of a putative fusion peptide in the S protein of hepatitis B virus.

Sequence analysis of the S protein of hepatitis B virus (HBV) reveals a stretch of 23 hydrophobic amino acids in the amino-terminal region which shows a high degree of similarity with known fusogenic peptides from other viruses. Additionally, this sequence also appears to be highly conserved within the hepadnavirus family. Taken together, the different criteria used in this work suggest fusogenic activity in the amino-terminal region of the S protein of the envelope of HBV.

Amino Acid Sequence↗
PubMed1994

Rapid heterologous desensitization of muscarinic and thrombin receptor-mediated phospholipase D activation.

Activation of the M3 muscarinic receptor in 1321N1 human astrocytoma cells leads to increased phospholipase D (PLD)-catalyzed hydrolysis of phosphatidylcholine, which is maximal within 1 min of exposure to agonist. Studies examining the kinetics of phosphatidylethanol formation indicate that there is no further PLD activation beyond this time. Thrombin, a mitogen for quiescent 1321N1 cells, also activates PLD only transiently. The PLD response does not recover for up to 1 hr and cells that have been exposed to carbachol or thrombin do not respond to subsequent challenge with the heterologous agonist. In contrast to the desensitization observed with agonists, phorbol-12-myristate-13-acetate induces a sustained stimulation of PLD. In addition, cells pretreated with carbachol or thrombin show a normal response to phorbol-12-myristate-13-acetate, suggesting that the enzymatic activity of PLD is not compromised. Guanosine-5'-O-(3-thio)triphosphate activation of PLD in cell-free homogenates is also unaffected by prior treatment of the cells with agonist. Agonist-stimulated PLD activation in 1321N1 cells is mediated by protein kinase C (PKC). Thrombin and carbachol cause comparable changes in redistribution of both PKC-alpha and PKC-epsilon. The increase in membrane-associated PKC-alpha is transient and is reinitiated by addition of the heterologous agonist, whereas PKC-epsilon remains membrane associated for at least 60 min and is not further increased by addition of the heterologous agonist. We suggest that desensitization of PLD activation results from the down-regulation of an as yet undefined mediator required for agonist receptor coupling to PLD and that PKC-epsilon might participate in this down-regulation.

Astrocytoma↗
PubMed1992

Familial spastic paraplegia with neuropathy and poikiloderma. A new syndrome?

We report a case study spanning three generations of familial spastic paraplegia, distal amyotrophy and poikiloderma. This study is the first description of an association between these three disorders. The gait disorder, the sensory and motor involvement and the skin disorder coincide in all the affected members, suggesting autosomal dominant inheritance with complete penetrance.

Child↗
PubMed1988

Progesterone abbreviates the nuclear retention of estrogen receptor in the rat oviduct and counteracts estrogen action on egg transport.

Progesterone has synergistic or antagonistic effects on several estrogenic actions. The effects of progesterone on estrogen-induced accelerated ovum transport and on the dynamics of estrogen receptors in the rat oviduct were examined. The involvement of the progesterone receptors in these phenomena was assessed. On Day 1 of pregnancy, rats were treated with estradiol, estradiol plus progesterone, or either one plus the progesterone receptor-blocking agent RU486. Control animals received the oil vehicle alone. The number of eggs remaining in the oviduct was assessed 24 h after treatment. Cytoplasmic and nuclear estrogen receptor levels in the oviduct, as well as plasma concentrations of estradiol and progesterone, were measured at various intervals--up to 11 h and 24 h after treatment, respectively. Accelerated oviductal egg transport induced by estrogen was blocked by the concomitant administration of progesterone. This effect of progesterone was not associated with changes in estrogen circulating levels and was preceded by a reduction in the total amount of estrogen receptors and by a shortened retention of estrogen receptors in the nucleus. The effects of progesterone on egg transport and on the levels of estrogen receptors were reversed by blocking the progesterone receptor with RU486, suggesting that both effects were receptor-mediated. These findings demonstrate that progesterone antagonizes the effect of estrogen on oviductal egg transport in the rat, and suggest that this antagonism is mediated by a reduction both in the amount of estrogen receptors and in their retention time in the nucleus.

Animals↗
PubMed1988

Estrogen and progesterone receptors in the oviduct during egg transport in cyclic and pregnant rats.

We investigated the temporal relationships between ovum transport and changes in the concentration of nuclear steroid receptors in the oviduct of cyclic and pregnant rats. A lack of parallelism between estrogen and progesterone fluctuations in plasma and their respective nuclear receptor concentrations in the oviduct predominated during egg transport. In pregnant animals, oviductal egg transport took 24 h longer than in nonpregnant animals. In both conditions, transport was initiated while the action of estrogen and progesterone on the oviduct--measured as nuclear receptor accumulation--was decreasing. Three or four days later, depending on whether the animal was pregnant, the eggs entered the uterus shortly after an increase in the nuclear receptor accumulation of both hormones. Treatment with RU486, a progesterone receptor-blocking agent known to cause premature arrival of eggs in the uterus, advanced estrogen receptor accumulation in the oviduct of pregnant rats. These data suggest that the arrival of eggs in the uterus is timed by a transitory increase in nuclear estrogen receptor in the oviduct that does not necessarily reflect a similar change of circulating estradiol. Moreover, in pregnant rats, the onset of this estrogenic action is delayed by a progesterone receptor-mediated effect that hinders nuclear estrogen receptor accumulation.

Animals↗
PubMed1988

Simple, rapid enzymatic determination of glycerophosphocholine in human seminal plasma.

We have devised a new enzymatic determination of sn-glycero-3-phosphocholine (GPC) in human seminal plasma. This is based on GPC hydrolysis by a phosphodiesterase (PDE), free choline being then determined by the choline oxidase method. The whole procedure involves a first incubation in the presence of choline oxidase and catalase, to eliminate the excess of choline present in seminal plasma (10-fold, compared with GPC). Absorbance and concentration are linearly related up to at least 100 nmol per assay, analytical recovery ranges between 89% and 105%, and intra- and interassay CVs are 3.2% and 5.6%, respectively, at the highest substrate concentration. Using this procedure, we found seminal plasma from 21 fertile men to contain 5.22 (SD 3.33) mumol per ejaculate--within the same range as previously reported values obtained chromatographically. After vasectomy, GPC in seminal plasma decreased to 28% of its original value, as determined in 10 volunteers. Thus this new method displays appropriate characteristics of specificity, reliability, and convenience, allowing its use in routine evaluation of male fertility.

Alcohol Oxidoreductases↗
PubMed1987

Ovum transport in pregnant rats is little affected by RU486 and exogenous progesterone as compared to cycling rats.

In cycling and pregnant rats, the eggs stay in the oviduct for approximately 66 and 90 h, respectively. The influence of progesterone in these timings was investigated. An excess or a simulated deficit of progesterone was induced with exogenous progesterone or the antiprogesterone RU486, respectively, beginning on the day of ovulation. The effect of these treatments on egg transport in cycling and pregnant rats was assessed in detail and complemented with determinations of estradiol and progesterone circulating levels and progesterone receptor levels in the oviduct. Accelerated transport of ova followed treatment with RU486 in cycling and pregnant rats but with different features. In cycling rats, acceleration began 24 h after the onset of treatment and was not associated with changes in estradiol levels; in pregnant rats, it started 72 h after treatment and was associated with a 5-fold increase in estradiol circulating levels. Thus, RU486 failed to accelerate ovum transport during the first three days of treatment in pregnant rats, in spite of the fact that no progesterone receptors were available in the oviduct as early as 24 h of treatment. Progesterone administration caused egg retention in the oviducts and a 50% reduction in circulating estradiol levels in cycling rats, whereas in pregnant rats progesterone excess did not change estradiol circulating levels and had no effect on the location of embryos on Days 4 and 5. These results demonstrate a different physiological importance of endogenous progesterone in slowing down oviductal ovum transport in cycling and pregnant rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Characteristics of the binding of platelet-activating factor to platelets of different animal species.

The binding of platelet-activating factor (PAF-acether) to human, rabbit and rat platelets was investigated by incubating washed platelets at 37 degrees C with radiolabeled [3H]PAF-acether. Scatchard plot analysis of the binding showed that human and rabbit platelets possess two different types of binding sites. One of them was saturable and of high affinity (KD 1.58 +/- 0.36 nM in human and 0.9 +/- 0.5 nM in rabbits), and the other one had nearly infinite binding capacity. By contrast, rat platelets only showed non-specific binding. Addition of unlabeled PAF-acether 5 min after the addition of [3H]PAF-acether showed that internalization of 66 +/- 9% of the specific binding in human and 52 +/- 6.9% in rabbit platelets had occurred. Specific binding of [3H]PAF-acether in rabbit platelets correlated well with [3H]serotonin release in response to different doses of PAF-acether and with the uptake of calcium by the platelets. By contrast, PAF-acether did not induce [3H]serotonin release or calcium uptake by rat platelets. The following data suggest that the potential of PAF-acether to activate platelets depends on the interaction with a specific membrane receptor rather than on a non-receptor-mediated alteration of the platelet membrane: (1) platelets from animal species sensitive to PAF-acether show saturability and specificity of binding; (2) platelets from one animal species non-sensitive to PAF-acether lack specific binding; (3) PAF-acether does not induce calcium uptake by platelets from an animal species which lacks specific binding sites.

Animals↗
PubMed1984

Enzootic Brugia infection in a two-year-old Colombian girl.

Mature male and female filarial worms were present in a lymphatic vessel near a retro-auricular lymph node removed from a 2-year old Colombian girl. Although apparently mature microfilariae were present in the uterus of the female, none was detected in blood samples (Knott's) of peripheral blood taken during day or night. The identification of the worms as a species of Brugia is suggested by their location in a dilated lymphatic vessel, morphology of adults, and the distribution pattern of tail nuclei of the microfilariae. This case is similar to another Colombian case reported from the Departamento del Santander del Sur, and suggests that zoonotic filarial infections may not be uncommon in Colombia.

Brugia↗
PubMed1984

[Hyperthermic radiosensitization of a strain of hematopoietic cells from mouse bone marrow, CFU-S].

Employing the technique of the spleen colony-formation the authors investigated the survival curve of the mouse hematopoietic stem cells resulting from increasing doses of X rays (D0 = 0.79 Gy and n = 1.59). The effect of the hyperthermic radiosensitization was measured by comparison with the effects observed in the irradiated CFU-S population previously exposed to hyperthermia. The treatment lasted 60 minutes at 42 degrees C and 12 minutes at 44 degrees C considering the thermal inactivation kinetics in such a way that the survival rate were the same in both cases. The results obtained for D0 = 0.52 Gy and n = 1.0 during 60 minutes at 42 degrees C, and for D00 = 0.61 Gy and n = 1.0 during 12 minutes at 44 degrees C showed that: 1) a synergic effect upon the CFU-S population is produced by the combination of hyperthermia and radiation, 2) for the same survival rate, the radiosensitivity increase produced after the thermic treatment a 42 degrees C and 44 degrees C is of the same order, and 3) such treatments, in both cases, produced a loss of a radioinduced sublethal damage accumulation.

Animals↗
PubMed1983

A chemical carcinogen, 3-methylcholanthrene, alters T-cell function and induces T-suppressor cells in a mouse model system.

The in-vivo effects of a polycyclic aromatic hydrocarbon (PAH), 3-methylcholanthrene (MCA), on in-vitro mitogen activation, cell-mediated lympholysis (CML) and T-cell subset distribution in mouse splenic lymphocyte populations were measured. Three inbred mouse strains were treated with a single intraperitoneal injection of corn oil alone or with different doses of MCA in oil (0.5-50 mg kg -1). One to ninety days after injection, splenic lymphocytes were isolated, and assayed for blastogenesis, CML and the percent T-helper and T-suppressor cells using monoclonal antibodies. High doses of MCA suppressed mitogen activation (15.2-53.6%) and CML (69-90%) within 24 hr in lymphocytes from PAH-responsive mice (C57 and C3H). Blastogenesis was stimulated and CML was suppressed to a lesser degree (5-45%) in lymphocytes from non-responsive mice (DBA). MCA induced an increase in T-suppressor cells in responsive mice, but there was no change in DBA mice. These studies suggest a correlation between immunocytotoxicity of PAH compounds on T-cell subsets and the responsiveness of mouse strains to these carcinogens.

Animals↗
PubMed1982

Changes in nuclear estrogen receptor level in the rat oviduct during ovum transport.

The purpose of this study was to assess variations in the concentration of nuclear estrogen receptor in the oviduct during normal embryo transport and to determine its temporal relationship with the passage of eggs to the uterus. Groups of 6--8 rats were sacrificed at different intervals from 0800 h on Day 1 to 1700 h on Day 4 of pregnancy to determine the concentration of nuclear estrogen receptor in the oviduct, the plasmatic estrogen level and the location of eggs in the genital tract. No significant variations in the amount of nuclear estrogen receptor were observed throughout the first 3 days. However, on Day 4 of pregnancy, concomitant with an elevation of plasma estrogen level there was a significant increase in nuclear estrogen receptor which started 4 to 5 h before the first ova began to reach the uterus. The receptor concentration attained a 3-fold elevation over previous days and returned to basal levels when 30% of the ova had been transferred to the uterus. These results provide evidence that estrogen exerts a direct action on the oviduct during embryo transport and that the passage of embryos to the uterus is preceded by a well-defined increment of estrogenic action on the oviduct. This temporal relationship is in keeping with the concept that estrogen receptor mediated events taking place in the oviduct may be involved in timing the transport of ova through the tubouterine junction.

Animals↗
PubMed1980

The active centres in penicillin-sensitive enzymes.

The interaction between beta-lactam antibiotics and the penicillin-sensitive enzymes is a multiple-step process. Binding of the beta-lactam ring of the penam (or 3-cepham) nucleus occurs at binding site no. 1. Interaction between the N-14 substituent of the bound molecule and binding site no. 2 induces changes in binding site no. 1. In turn, the catalytic site thus created increases the chemical reactivity of the beta-lactam amide bond. As the beta-lactam ring opens and acylates an enzyme serine residue, the interaction between the thiazolidine (or dihydrothiazine) ring and binding site no. 3 stabilizes the acyl-enzyme complex. Enzyme regeneration slowly proceeds either by direct elimination of the penicilloyl moiety or via C-5-C-6 splitting of the bound metabolite. The fragment arising from thiazolidine yields free N-formyl-D-penicillamine while the enzyme-linked N-acylglycyl fragment is immediately attacked by an exogenous nucleophile correctly positioned on the acceptor site. Similarly, the enzyme action on L-X-D-Ala-D-Ala terminated peptides is mediated via a binding site no. 1 that combines with D-Ala-D-Ala, a binding site no. 2 that interacts with the side chain of the preceding L-residue, an inducible catalytic site and an acceptor site. Enzymes are known that form a transitory L-X-D-Ala-enzyme complex where the acyl group is ester-linked to the same serine residue as that involved in the formation of the penicilloyl-enzyme complex (Waxman et al., this symposium). Other enzymes, however, may function as catalyst templates. Depending on the enzymes, the independence of the beta-lactam and L-X-D-Ala-D-Ala active centres is more or less pronounced.

Amino Acid Sequence↗
PubMed1978

Thermal denaturation of Micrococcus lysodeikticus adenosine triphosphatase. Influence of temperature on the circular dichroism, fluroescence and enzymic activity of the protein.

The soluble ATPase (adenosine triphosphatase) from Micrococcus lysodeikticus underwent a major unfolding transition when solutions of the enzyme at pH 7.5 were heated. The midpoint occurred at 46 degrees C when monitored by changes in enzymic activity and intrinsic fluorescence, and at 49 degrees C when monitored by circular dichroism. The products of thermal denaturation retained much secondary structure, and no evidence of subunit dissociation was detected after cooling at 20 degrees C. The thermal transition was irreversible, and thiol groups were not involved in the irreversibility. The presence of ATP, adenylyl imidodiphosphate, CaCl2 or higher concentrations of ATPase conferred stability against thermal denaturation, but did not prevent the irreversibility one denaturation had taken place. In the presence of guanidinium chloride, thermal denaturation occurred at lower temperatures. The midpoints of the transition were 45 degrees C in 0.25 M-, 38 degrees C in 0.5 M-and 30 degrees C in 0.75 M-denaturant. In the highest concentration of guanidinium chloride a similar unfolding transition induced by cooling was observed. Its midpoint was 9 degrees C, and the temperature of maximum stability of the protein was 20 degrees C. The discontinuities occurring the the Arrhenius plots of the activity of this enzyme had no counterpart in variations in the far-u.v. circular dichroism or intrinsic fluorescence of the protein at the same temperature.

Adenosine Triphosphatases↗
PubMed1977

Activation parameters and molecular changes induced by substrate hydrolysis of the adenosine triphosphatase of Micrococcus lysodeikticus. A comparison of three different soluble forms of the enzyme.

The Arrhenius plots for the active and low activity soluble forms of the ATPase purified from the membranes of Micrococcus lysodeikticus grown at 30 degrees C presented discontinuities at 30 and 33 degrees C, respectively. Their activation parameters differed, being highest for the low activity form of the enzyme. Both forms underwent changes in their molecular properties as a consequence of being enzymically active, i.e., upon incubation with substrates at an adequate temperature. These changes consisted of a decrease in the relative mobilities of some of their subunits in dodecyl sulphate polyacrylamide gel electrophoresis, and the temperature at which they occurred depended on the energy of activation of the particular form of the ATPase used. The low activity form required an incubation temperature of 50 degrees C, whereas for an active form 37 degrees C was sufficient.

Adenosine Triphosphatases↗