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Biomedical subjects

S Estrada

Publications and source records attributed to S Estrada.

At least 19 recordsLinked to original sources

Recollection rejection of false narrative statements.

Our research was focused on a false-memory editing operation that is posited in fuzzy-trace theory-recollection rejection. The main objectives were (a) to extend model-based measurement of this operation to a narrative task that ought to ensure high levels of recollection rejection and (b) to study five manipulations that ought to influence recollection rejection by affecting the accessibility of verbatim traces of narrative statements: recency of narrative presentation, narrative repetition, type of false-memory item, testing delay, and repeated testing. The results showed that the narrative task did indeed yield high levels of recollection, with an estimated 49% of gist-consistent distractors being rejected in this way on initial memory tests. Consistent with current theoretical conceptions of false-memory editing, the results also showed that recollection rejection increased as a function of manipulations that should enhance the accessibility of verbatim traces of narrative statements, with repeated testing delivering especially large increases in verbatim accessibility.

Attention↗

Reproductive response in supplemented heifers in the humid tropics of Costa Rica.

To evaluate the effect of two supplementary diets to determine the consequence on productive and reproductive performance in heifers (Bos indicus x Bos taurus) averaging between 24 and 36 months of age and grazing tropical pastures, two trials were conducted. Thirty animals (initial BW 325.1+/-33.6 kg) were divided in two groups in the initial study: supplemented (SG) and control (CG); SG received a concentrate (5.5% CP and 2.85 Mcal/kg of DE dry matter basis) at 1% of body weight (BW). In the second study, 45 heifers (initial BW 332.6+/-29.3 kg) were assigned in two treatments, with the same amount of supplement (1% BW) but with a greater nutrient content (13% CP and 3.15 Mcal/kg of DE). The proportion of animals with a corpus luteum at the end of each study was greater in the supplemented groups (P<0.05). Ovarian follicular dynamics was similar between groups in the first study, but in the second study there were more heifers in the SG group with follicles larger than 9 mm in diameter (P<0.05). Pregnancy rate was similar for SG and CG (P>0.05). The response to a regimen of estrous synchronization in both trials was numerically superior in the SG group. No differences were observed in the length of estrus. Daily gain and body condition score were similar for supplemented and control groups (0.27 compared with -0.06 in the first study and 0.90 kg compared with 0.60 in the second study, respectively). Dietary supplementation improved the number of animals initiating estrous cycles and the expression of estrus when compared with unsupplemented control heifers. The dietary regimens imposed in these studies appear to be an adequate for the management of growing heifers destined to a reproductive program.

Animal Nutritional Physiological Phenomena↗

Ultrasonographic screening of embryo development in cattle (Bos indicus) between days 20 and 40 of pregnancy.

Through a transrectal ultrasonography (Aloka SSD 500 microplus equipment, linear transducer of 7.5 MHz) a total of 267 observations were performed in a group of 50 females mainly Bos indicus, raised under humid tropical conditions and pregnant from day 20 every other day until day 40 post-artificial insemination (AI). The objective was to measure the size of the amniotic vesicle and the longitudinal and transversal axis of the embryo, to determine the day in which it is possible to measure this structure and detect the heart contractions in the screened embryos. The accuracy in identifying the amniotic vesicle was 60% (12/20) on day 20 of the first screening with embryos having an average length of 0.44 +/- 0.20 cm. Accuracy in detecting the embryo was 66.6 and 100% between days 20 and 24 post-breeding, respectively. The mean length of the embryos on day 20 was of 0.20 +/- 0.07 cm and the transversal shape had a mean length of 0.07 +/- 0.02 cm. The accuracy of detecting heart contractions was 50% (9/18) on day 24 post-breeding and for day 26 the accuracy was 100%. At the end of the screening (day 40), embryos had means of 1.92 +/- 0.24 (longitudinal) and 0.85 +/- 0.11 cm (transverse). The embryo can be detected from day 24 post-AI and the heart contractions from day 26 with 100% reliability.

Animals↗

Leaving previously implanted central venous catheters (ports) in place does not increase morbidity in patients undergoing autologous peripheral stem cell transplantation.

We sought to assess if leaving in place a previously inserted noncolonized or infected implantable catheter (IC) is associated with an increase in morbidity in patients undergoing autologous peripheral stem cell transplantation (APSCT). Medical records from all patients between March 1997 and January 2002 undergoing APSCT with an IC in place were reviewed. Case group (IC in place) was compared with a control group (no IC) from 6 days prior to 60 days after APSCT. In all, 43 cases were matched with 43 controls by underlying disease, age and sex. In both groups, duration of neutropenia and use of antimicrobial prophylaxis were comparable. Underlying malignancies were lymphoma (22/24), multiple myeloma (14/12), leukemia (3/3), and others (7/7) in case and control groups. Cases and controls had comparable rates of risk for fever, bloodstream infection, use of vancomycin and amphotericin B, and death, as well as comparable lengths of stay and readmissions. ICs were used in 20 of 43 patients. Using the IC did not significantly increase the risk of fever, bloodstream infection, length of stay, and/or readmissions after APSCT but was associated with increased use of antibacterial and antifungal agents. Leaving in place a previously inserted, noncolonized or infected IC did not increase morbidity in patients undergoing APSCT.

Adult↗

Spasmolytic stilbenoids from Maxillaria densa.

2,5-dihydroxy-3,4-dimethoxyphenanthrene (1), fimbriol-A (2), nudol (3), gymnopusin (4) and erianthridin (5) isolated from Maxillaria densa provoked a concentration-dependent inhibition of the spontaneous contractions of the rat ileum with potencies comparable to papaverine. In order to establish the mode of action of stilbenoids 1-5, their effect on the contractions induced by different spasmogens (histamine, barium chloride and L-NAME) was investigated. In general, the results suggested that the relaxant activity of the products does not involve a direct nitrergic or antihistaminergic mode of action or an interference with calcium influx into the smooth muscle cells.

Animals↗

Pregnancy rate in zebu cows with two different postpartum intervals exposed to a two-bull rotational system.

In order to evaluate the reproductive effect of a rotational breeding system, the pregnancy rate of 69 Zebu cows was assessed, 32 late postpartum (211 +/- 93 days postpartum, LP) and 37 early postpartum (averaging 63 +/- 8 days after calving, EP). In the LP group, 60% (19/32) were cycling before exposure to the bulls but only 38% (14/37) in the EP group. The two groups were dissimilar from the start (p < 0.05). The cows were exposed in a rotational breeding system, with six Brahman bulls with previous sexual experience paired off in three groups (A-B, C-D and E-F). The cows were exposed to each pair of bulls for a period of 3 weeks, with one week in between each period, when the females were without the presence of a male. In the LP group, the pair of bulls A B obtained a pregnancy rate of 72% (23/32), whereas for bulls C-D the pregnancy rate was 33% (3/9) and for bulls E-F the pregnancy rate was 67% (4/6). In contrast, for the EP cows, bulls A-B obtained a pregnancy rate of 32% (12/37), bulls C-D a pregnancy rate of 67% (12/18) and for bulls E-F a pregnancy rate of 55% (6/11). The percentage pregnancy obtained using the pair of bulls A-B differed (p < 0.05) between LP and EP, whereas for bulls C-D and E-F it was similar. The pregnancy rate was different (p < 0.05) in the first 3 weeks of mating for the LP group, the highest number of cows becoming pregnant during the first 3 weeks of the study. In contrast, the highest number of pregnancies in EP occurred evenly during the last 6 weeks. This study suggests that the reproductive performance of pairs of bulls in a 9-week rotational programme with the overall pregnancy rate is similar (94% in the LP and 81% in the EP). However, the time taken for the females to become pregnant, and hence the performance of the bulls, is related to the average number of days postpartum for the cows.

Animals↗

Effect of alternating bulls as a management tool to improve the reproductive performance of suckled Zebu cows in the humid tropics of Costa Rica.

A study was undertaken to evaluate the effect of alternating bulls between a single and a multiple sire mating (MSM) program on the reproductive performance of suckled Zebu cows raised under range conditions in the humid tropics of Costa Rica. Multiparous Zebu cows (n=94) suckling calves were distributed between two experimental trials (A and B) consisting of 47 animals each. A single sire mating (SSM) system was alternated weekly with a MSM system with three bulls. This period lasted for 8 weeks. To facilitate estrous expression, four cows were strategically synchronized (estrus-stimulated) in alternate weeks. Courtship predominated over mounting under non-stimulated estrus, for each mounting performed an average of 6.0 and 6.3 courtship activities were recorded in the SSM and MSM, respectively. Under the influence of strategic synchronization corresponding values were 3.9 and 4.2 in the SSM and MSM, respectively (P>0.05). Blood samples for progesterone evaluation were taken twice weekly. All cows in trial A were in anestrus at the start of the study. By second week, 5 out of the 47 cows had initiated estrous cycles and by the third week six were pregnant. In contrast in trial B, 9 out of 47 had initiated estrous cycles before interacting with the bulls and on week 3, only two females had become pregnant and three had initiated estrous cycles. Significant differences were found in the cumulative percentage of cows pregnant between trials A and B (P<0.05). Even though these results occurred, the rotation of the bulls (one or three), or the type of cows (estrus-stimulated or not) did not influence the results in this study.

Anestrus↗

Heparin antagonists are potent inhibitors of mast cell tryptase.

Tryptase may be a key mediator in mast cell-mediated inflammatory reactions. When mast cells are activated, they release large amounts of these tetrameric trypsin-like serine proteases. Tryptase is present in a macromolecular complex with heparin proteoglycan where the interaction with heparin is known to be essential for maintaining enzymatic activity. Recent investigations have shown that tryptase has potent proinflammatory activity, and inhibitors of tryptase have been shown to modulate allergic reactions in vivo. Many of the tryptase inhibitors investigated previously are directed against the active site. In the present study we have investigated an alternative approach for tryptase regulation. We show that the heparin antagonists Polybrene and protamine are potent inhibitors of both human lung tryptase and of recombinant mouse tryptase (mouse mast cell protease 6). Protamine inhibited tryptase in a competitive manner whereas Polybrene showed noncompetitive inhibition kinetics. Treatment of tetrameric, active tryptase with Polybrene caused dissociation into monomers, accompanied by complete loss of enzymatic activity. The present report thus suggests that heparin antagonists potentially may be used in treatment of mast cell-mediated diseases such as asthma.

Animals↗

A note on the effects of calf stimuli on the response of Zebu cows to Synchro-mate-B.

The effect of Synchro-mate-B (SMB) was measured on the estrous response and the establishment of cyclicity using different calf stimuli. Multiparous Zebu cows, were divided in three groups. In the first, 32 animals were treated with SMB leaving the calves present (SMB+CP). In the second, 33 cows were treated with SMB and calves partially removed (fence-line contact) for 48h (SMB+CPR). In the third group (n=33), cows received SMB and calves were removed for 48h (SMB+CCR) with no visual or olfactory contact. A control group (CG, n=33) involved neither SMB or calf separation. Blood samples for progesterone assessment were obtained at 11 and 4d prior to SMB treatment and on days 7 and 11 after the average return to estrous for each group. All animals were observed continuously for mounting activity during 72h after SMB implant removal. A significant difference (P<0.05) in estrous response was found between SMB-treated and non-treated animals, regardless of calf management (56 versus 8%, respectively). Cows with SMB+CCR and SMB+CPR came into estrous sooner (P<0.05) (26.5+/-2.6 and 18.1+/-4.94h, respectively), than those that remained with their calf present (40.4+/-12.8h). Cows with SMB+CCR displayed longer (P<0.05) periods of mounting behavior (13.0+/-4.4h) in comparison with SMB+CPR and SMB+CP (7.4+/-1.8 and 8.1+/-4.0h), respectively. Furthermore, 84% (P<0.05) of the cows in the SMB+CCR had high concentrations of progesterone after mounting behavior was displayed, in comparison with 68 and 54% in the other two groups, respectively. No difference was found (P>0.05) in the number of mounts per hour in estrous. It was concluded that: (1) SMB increases the number of cows that display estrous; (2) temporary weaning shortens the period from SMB implant withdrawal to mounting activity, and (3) SMB+CCR, increases the length of sexual receptivity and the number of cows that continue to cycle.

Journal Article↗

Sexual behaviour of Zebu bulls in the humid tropics of Costa Rica: single versus multiple-sire groups.

This study compares the courtship and mounting behaviour of Bos indicus bulls in single- and multiple-sire groups in Costa Rica (latitude 10 degrees 25'N, longitude 84 degrees 32'W, annual precipitation of 3096mm, temperature of 24 degrees C and humidity of 85.3%). Four, 3-4 year-old Brahman bulls with previous sexual experience were used to sire a group of 120 multiparous cows (average of 128 days post-partum and a body condition score of 2.5) allocated to two groups of 60 each: (1) single-sire mating group (SSM) and (2) multiple-sire mating group of three bulls (MSM). Bulls were rotated among groups every 7 days for 28 days. The frequency, type and duration of sexual activities (mounting and mounting attempts) and courtship activities (smelling and licking genital area, butting, supporting the head over a female and the sign of Flehmen) were calculated for each mating group. Descriptive and non-parametric statistics (Wilcoxon, Mann-Withney tests) were used to calculate differences between mating programmes. Sexual activities tended to be more frequent in the SSM group than the MSM group (267 versus 124, P>0.05). Differences in the ratios of sexual to courtship activities between both groups were significant (1:3 in SSM and 1:6 in MSM, P>0.05). Pregnancy rate averages were 28 and 37%, respectively, (P>0.05). It is concluded that under these conditions multiple-sire mating and single-sire mating achieved similar pregnancy rates.

Animals↗

The N-terminal region of cystatin A (stefin A) binds to papain subsequent to the two hairpin loops of the inhibitor. Demonstration of two-step binding by rapid-kinetic studies of cystatin A labeled at the N-terminus with a fluorescent reporter group.

The three-dimensional structures of cystatins, and other evidence, suggest that the flexible N-terminal region of these inhibitors may bind to target proteinases independent of the two rigid hairpin loops forming the remainder of the inhibitory surface. In an attempt to demonstrate such two-step binding, which could not be identified in previous kinetics studies, we introduced a cysteine residue before the N-terminus of cystatin A and labeled this residue with fluorescent probes. Binding of AANS- and AEDANS-labeled cystatin A to papain resulted in approximately 4-fold and 1.2-fold increases of probe fluorescence, respectively, reflecting the interaction of the N-terminal region with the enzyme. Observed pseudo-first-order rate constants, measured by the loss of papain activity in the presence of a fluorogenic substrate, for the reaction of the enzyme with excess AANS-cystatin A increased linearly with the concentration of the latter. In contrast, pseudo-first-order rate constants, obtained from measurements of the change of probe fluorescence with either excess enzyme or labeled inhibitor, showed an identical hyperbolic dependence on the concentration of the reactant in excess. This dependence demonstrates that the binding occurs in two steps, and implies that the labeled N-terminal region of cystatin A interacts with the proteinase in the second step, subsequent to the hairpin loops. The comparable affinities and dissociation rate constants for the binding of labeled and unlabeled cystatin A to papain indicate that the label did not appreciably perturb the interaction, and that unlabeled cystatin therefore also binds in a similar two-step manner. Such independent binding of the N-terminal regions of cystatins to target proteinases after the hairpin loops may be characteristic of most cystatin-proteinase reactions.

Animals↗

The contribution of N-terminal region residues of cystatin A (stefin A) to the affinity and kinetics of inhibition of papain, cathepsin B, and cathepsin L.

The affinity and kinetics of binding of three N-terminally truncated variants of the cysteine proteinase inhibitor cystatin A to cysteine proteinases were characterized. Deletion of Met-1 only minimally altered the inhibitory properties of the protein. However, deletion also of Ile-2 resulted in reduced affinities of 900-, >/=3-, and 200-fold for papain and cathepsins L and B, respectively. Further truncation of Pro-3 substantially increased the inhibition constants to approximately 0.5 microM for papain and cathepsin L and to 60 microM for cathepsin B, reflecting additionally 2 x 10(3)-, 2 x 10(4)-, and 400-fold decreased affinities, respectively. The reductions in affinity shown by the latter mutant indicate that the N-terminal region contributes about 40% of the total free energy of binding of cystatin A to cysteine proteinases. Moreover, Pro-3 and to a lesser extent Ile-2 are the residues responsible for this binding energy. The reduced affinities for papain and cathepsin L were due only to higher dissociation rate constants, whereas both lower association and higher dissociation rate constants contributed to the decreased affinity for cathepsin B. These differential effects indicate that the N-terminal portion of cystatin A primarily functions by stabilizing the complexes with enzymes having easily accessible active-site clefts, e.g., papain and cathepsin L. In contrast, the N-terminal region is required also for an initial binding of cystatin A to cathepsin B, presumably by promoting the displacement of the occluding loop and allowing facile interaction of the rest of the inhibiting wedge with the active-site cleft of the enzyme.

Animals↗

New phenanthrene derivatives from maxillaria densa(1)

Two new phenanthrene derivatives, 2,5-dihydroxy-3, 4-dimethoxyphenanthrene (1) and 9,10-dihydro-2,5-dihydroxy-3, 4-dimethoxyphenanthrene (2), were isolated from an extract prepared from the whole plant of the orchid Maxillaria densa with spasmolytic activity. In addition, four known compounds, namely 2,7-dihydroxy-3, 4-dimethoxyphenanthrene, 9,10-dihydro-2,7-dihydroxy-3, 4-dimethoxyphenanthrene (3), 2,5-dihydroxy-3,4, 9-trimethoxyphe-nanthrene, and 2,7-dihydroxy-3,4, 9-trimethoxyphenanthrene, were obtained. The structures of the isolated compounds were elucidated by spectroscopic methods. In the case of phenanthrene derivatives 1 and 3, the structures were unambiguously assigned by X-ray analysis.

Journal Article↗

Nitric oxide/cGMP mediates the spasmolytic action of 3,4'-dihydroxy-5,5'-dimethoxybibenzyl from Scaphyglottis livida.

Five aromatic compounds, 3,4'-dihydroxy-5,5'-dimethoxybibenzyl (1), batatasin III (2), coelonin (3), 3,7-dihydroxy-2,4-dimethoxyphenanthrene (4), and 3,7-dihydroxy-2,4,8-trimethoxyphenanthrene (5) were isolated from the orchid Scaphyglottis livida (Lindley) Schltr. Compounds 1-5 induced a concentration-dependent inhibition of the spontaneous contractions of the rat ileum with potencies comparable or higher to that of papaverine. The relaxation evoked by compounds 1-4 was blocked by L-NAME, an inhibitor of nitric oxide synthase. It was also demonstrated that 1 increased cyclic GMP content in rat ileum rings. Compound 1-induced elevation of cGMP was inhibited by L-NAME and ODQ, inhibitors of nitric oxide synthase and soluble guanylyl cyclase, respectively. These results indicate that nitric oxide/cGMP formation constitute the signaling pathway in the spasmolytic action of compound 1.

Animals↗

The role of Gly-4 of human cystatin A (stefin A) in the binding of target proteinases. Characterization by kinetic and equilibrium methods of the interactions of cystatin A Gly-4 mutants with papain, cathepsin B, and cathepsin L.

The importance of the evolutionarily conserved Gly-4 residue for the affinity and kinetics of interaction of cystatin A with several cysteine proteinases was assessed by site-directed mutagenesis. Even the smallest replacement, by Ala, resulted in approximately 1000-, approximately 10- and approximately 6000-fold decreased affinities for papain, cathepsin L, and cathepsin B, respectively. Substitution by Ser gave further 3-8-fold reductions in affinity, whereas the largest decreases, >10(5)-fold, were observed for mutations to Arg and Glu. The kinetics of inhibition of papain by the mutants with small side chains, Ala and Ser, were compatible with a one-step bimolecular reaction similar to that with wild-type cystatin A. The decreased affinities of these mutants for papain and cathepsin L were due exclusively to increased dissociation rate constants, but the reduced affinities for cathepsin B were due also to decreased association rate constants. The latter finding indicates that the intact N-terminal region serves as a guide directing cystatin A to the active site of cathepsin B, as has been proposed for cystatin C. The kinetics of binding of the mutants with charged side chains, Arg and Glu, to papain were consistent with a two-step binding mechanism, in which the mutant side chains are accommodated in the complex by a conformational change. The NMR solution structure of the Ala and Trp mutants showed only minor changes compared with wild-type cystatin A, indicating that the large reductions in affinity for proteinases are not due to altered structures of the mutants. Instead, a side chain larger than a hydrogen atom at position 4 affects the interaction with the proteinase most likely by interfering with the binding of the N-terminal region.

Binding, Competitive↗

Two-step mechanism of inhibition of cathepsin B by cystatin C due to displacement of the proteinase occluding loop.

Stopped-flow kinetics showed that the inhibition of the lysosomal cysteine proteinase, cathepsin B, by its endogenous inhibitor, cystatin C, occurs by a two-step mechanism, in which an initial, weak interaction is followed by a conformational change. The initial interaction most likely involves binding of the N-terminal region of the inhibitor to the proteinase. Considerable evidence indicates that the subsequent conformational change is due to the inhibitor displacing the occluding loop of the proteinase that partially obscures the active site. The presence of this loop, which allows the enzyme to function as an exopeptidase, thus complicates the inhibition mechanism, rendering cathepsin B much less susceptible than other cysteine proteinases to inhibition by cystatins.

Binding Sites↗

[Ultrastructural aspects of lesions caused by Mycobacterium spp in AIDS].

Samples from necrotizing lesions in eight autopsy cases of AIDS were examined with transmission electron microscopy. They were selected among 35 autopsies of Mycobacterium spp infection and AIDS, and were part of a series of 230 autopsy cases of AIDS performed from 1984 to 1995 in the Anatomopathologic Institute at Central University of Venezuela. Ultrastructural aspects of micobacteriae, their relationship with macrophages and tissue alterations are discussed and related to the immune defcit observed in AIDS patients.

AIDS-Related Opportunistic Infections↗