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Biomedical subjects

M A Ramos

Publications and source records attributed to M A Ramos.

At least 19 recordsLinked to original sources
PubMed2006

Ram effect: adult rams induce a greater reproductive response in anestrous ewes than yearling rams.

The introduction of rams to previously isolated anestrous ewes ensures induction of ovulation and estrus in part of the flock, and allows for the potential to conceive. However, there is little known about the desirable characteristics of the rams used to induce these behavioral and physiological responses. Adult rams may be more effective than young rams in induction of these responses. The primary aim of the present study was to compare the response in ewes stimulated by adult or yearling rams. During the non-breeding season, two groups of 121 ewes were stimulated with adult (AR) or yearling (YR) rams. When adult rams were used, significantly more ewes had ovulations (78.5 compared with 61.1%) and came into estrus (47.9 compared with 35.5%). There were more corpora lutea per ewe exposed to rams (0.95+/-0.59 compared with 0.65+/-0.51) and per ewe that had ovulations (1.18+/-0.41 compared with 1.06+/-0.25) and a greater conception rate (58.6 compared with 20.9%) as a result. Subsequently, to determine what signals led to the greater response to adult rams, the courtship behavior of adult and yearling rams toward anestrous ewes was compared in 46 pen tests. There were no significant differences in the frequency of any of the recorded courtship behaviors (anogenital sniffing: 21.9+/-3.4 versus 25.7+/-3.2; lateral approaches: 7.1+/-1.5 compared with 9.9+/-2.9; flehmen: 2.1+/-0.4 compared with 2.2+/-0.4; mount attempts: 0.1+/-0.1 compared with 0.1+/-0.1, for AR and YR, respectively), latency to the onset of courtship behavior (13.1+/-7.0 compared with 17.3+/-6.2s) or the time engaged in courtship behavior (173.1+/-24.6 compared with 199.0+/-26.5s). The difference in the signals produced by adult and yearling rams skin glands was assessed by stimulating ewes with masks containing wool from adult (n=45) or yearling (n=48) rams. More ewes had ovulations (24/45 compared with 11/48) and came into estrus (21/45 compared with 10/48) when wool from adult rams was used. As in Experiment 1, pregnancy and conception rates were greater when adult rams were used, another trial was designed to determine if there were differences in mating and mounting frequency between adult and yearling rams. Seven adult and six yearling rams were subjected to three pen tests each with three estrual ewes. Adult rams mounted more (21.7+/-4.5 compared with 9.8+/-0.7) and tended to ejaculate more frequently (2.9+/-0.5 compared with 1.8+/-0.4) than yearling rams. It is concluded that adult rams induce a greater reproductive response in anestrous ewes than yearling rams, inducing a greater ovulation percentage and estrous response in ewes, resulting in greater ovulation numbers, pregnancy and conception rates. This greater stimulation is, in part, explained by differences in the signals provided in the wool (presumably odors) produced by adult rams. The lesser percentage of pregnancies obtained when yearling rams are used may be explained by differences in mounting behaviors and ejaculation frequency.

Age Factors↗
PubMed2006

Relationship between male-male and male-female sexual behavior in 5-6-month-old male lambs.

To characterize male-male sexual behavior during lamb development, to relate it with lamb body and testicular growth, and with sexual behavior toward estrual ewes, 40 Milchschaf male lambs, weaned at 45 days of age, were kept with ewes that were nursing younger lambs. Experimental lambs were weighed and scrotal circumference was measured every 2 weeks. Male-male sexual behavior was observed during 1-2 h every 2 weeks after birth until 7 months of age. Observations were recorded more intensively (3-4 h on five different days) for 2 weeks (5-6 months of age) as male-male sexual behavior increased during that period. Both mounting and mounted lambs were identified. An individual mounting index (MI) was calculated. To study male-female sexual behavior, lambs were individually located with two estrual ewes, and during 5 min the number of ano-genital sniffing, lateral approaches, mounts, and mounts with ejaculation were recorded. From those data, a libido index was also calculated. Male-male mounts (n=308) were observed. Courtship behavior was displayed in 25% of interactions; mounts were accepted in 72.1% of attempted mounts. Mounts without previous courtship were accepted more frequently than mounts with previous courtship (P=0.002). Lamb weight and scrotal circumference were not different according to MI groups. Lambs that mounted more times estrual ewes (first tertile) had greater (P=0.04) MI (0.61+/-0.10) than lambs with medium (0.27+/-0.09) and less (0.30+/-0.10) MI. The regression between MI and heterosexual libido index was r=0.33 (P<0.05). In summary, intensive male-male sexual activity during a short period of male lamb development was observed. There was a positive relationship between sexual behavior of male lambs towards other male lambs and towards estrual ewes.

Aging↗
PubMed2006

Structural analysis of dextran-based hydrogels obtained chemoenzymatically.

This work reports the results of structural analysis in novel dextran-acrylate (dexT70-VA) hydrogels generated chemoenzymatically. Porous structure as well as hydrogel surface and interior morphologies were evaluated by mercury intrusion porosimetry (MIP), nitrogen adsorption (NA), and scanning electron microscopy (SEM) analyses, as a function of the degree of substitution (DS), and initial water content used in the preparation of the hydrogel. MIP analysis showed that the overall networks were clearly macroporous with pore sizes ranging from 0.065 to 10 microm. As expected, the average pore size decreased as DS increased and as initial water content decreased. Moreover, the porosity values ranged from 75 up 90%, which shows that these hydrogels present an interconnected pore structure. Nitrogen adsorption analyses showed that the specific surface area of dexT70-VA hydrogels increased either by increasing the DS or by decreasing the initial water content of the hydrogel. SEM results revealed that the surface of hydrogels with lower DS presented either a porous structure or a polymeric "skin" covering the pores, whereas hydrogels with higher DS were totally porous. Furthermore, the interior morphology varied according to the DS and the initial water content of the hydrogels. Finally, the average pore size was also determined from the swelling of hydrogel using a theoretical model developed by Flory-Rehner. The comparison of the SEM and MIP results with the ones obtained by the equilibrium swelling theory of Flory-Rehner shows that this approach highly underestimates the average pore size.

Biocompatible Materials↗
PubMed2003

Preliminary estimation of the rainfall chemical composition evaluated through the scavenging modeling for north-eastern Amazonian region (Amapá state, Brazil).

Numerical modeling of scavenging processes has been compared with data obtained for rainwater and aerosol chemistry at Serra do Navio, in the state of Amapá in the Brazilian Amazon region. Sulfate, nitrate and ammonium concentrations were determined in rainwater samples collected from May 1995 until June 1997. The levels of these same chemicals were also determined in aerosols for the same period and region. Scavenging processes have been evaluated on a rainfall event basis, via numerical modeling, in order to simulate the rainwater concentrations and compare them with the observed data. RAMS (Regional Atmospheric Modeling System) was used to simulate cloud structures. A model of below-cloud scavenging was evaluated, as well. The determinations made from the results of the scavenging model are the following: a) aerosol vertical profiles are quite important to rainwater concentrations; b) modeled sulfate in rainwater is a better fit to the observed data values than ammonium and nitrate; c) the obtained sulfate aerosol concentrations samples are similar to ones found in the literature, although the sulfate concentrations in rainwater are much lower than other studies in the literature; d) the in-cloud scavenging process dominates, e) our modeled results, using an input gas vertical profile extracted from the ABLE2B experimental data set, present a smaller ratio between gas and aerosol scavenging than found in other studies in the literature, other studies may have had larger rainfall times, which increase the importance of gas phase scavenging.

Aerosols↗
PubMed2002

Chemical isomerism as a key to explore free-energy landscapes in disordered matter.

The effects of a minor chemical modification on the microscopic structure of a material in its glass and crystal phases are investigated by the concurrent use of neutron diffraction and computer simulation. Significant changes in short-, intermediate-, and long-range order are found, resulting from the change in molecular structure. These differences are explainable by a shift in the balance between directional and excluded-volume interactions.

Journal Article↗
PubMed2002

Glochidium metamorphosis in the endangered freshwater mussel Margaritifera auricularia (Spengler, 1793): a histological and scanning electron microscopy study.

The metamorphosis of the glochidium of the critically endangered Margaritifera auricularia in the gills of a host is studied here for the first time. Siberian sturgeon, Acipenser baeri, were infected with glochidia and regularly inspected using scanning and optical microscopy. The mature glochidia immediately attach to the epithelium of the sturgeon gill filaments, piercing the secondary lamellae and the connective tissues, blood cells, and vessels within the lamellae. Once the epithelium is pierced, overlapping host lamellae cover the glochidium and form a cyst. Metamorphosis takes place inside the cyst. Sixteen days after infection the glochidium becomes spherical in shape and the larval muscle is reabsorbed. The two adductor muscles of the juvenile are observed 34 days after infection at 16-20 degrees C. Metamorphosis is complete in approximately 51 days at 18-22 degrees C and in 65 days at 16-17 degrees C. Released juveniles have a spherical shell with a thin rim of new shell material and a finely ciliated foot. Juvenile mean measurements are: length = 190 microm, width = 193 microm, and height = 210 microm.

Animals↗
PubMed2001

Development and validation of a cholate binding capacity method for DMP 504, a bile acid sequestrant.

DMP 504, a highly cross-linked insoluble polymer, is a bile acid sequestrant developed by the DuPont Pharmaceuticals Company for serum cholesterol reduction. Since DMP 504 is insoluble, it was necessary to develop unique specific analytical methods to measure and control the quality of different lots of the drug. Since the mechanism of action of DMP 504 is believed to be by sequestration of bile acids, the in-vitro binding capacity of the polymer for cholic acid was chosen as a surrogate of in-vivo performance and used to assess potency of the compound. In this method, individual aliquots of DMP 504 at three different levels were incubated with a cholate solution of known concentration. The residual cholate solution was filtered and analyzed by a reversed-phase HPLC method using refractive index detection. When the bound cholate was plotted versus the mass of DMP 504, the resulting curve was linear. The slope of this curve is the cholate binding capacity of DMP 504. This method has been shown to be precise and robust. Precision of the method was shown to have an RSD of 2.0% with injection precision of 0.4% and stability of cholate solutions up to 73 h. It is also a unique binding capacity method due to its multi-point determination, and it has been shown to be a suitable quality control method for ensuring lot-to-lot consistency of drug substance.

Cholates↗
PubMed2001

Inhibition of gene expression in Entamoeba histolytica with antisense peptide nucleic acid oligomers.

Peptide nucleic acids (PNAs) may be a potent tool for gene function studies in medically important parasitic organisms, especially those that have not before been accessible to molecular genetic knockout approaches. One such organism is Entamoeba histolytica, the causative agent of amebiasis, which infects about 500 million people and is the cause of clinical disease in over 40 million each year, mainly in the tropical and subtropical world. We used PNA antisense oligomers to inhibit expression of an episomally expressed gene (neomycin phosphorotransferase, NPT) and a chromosomal gene (EhErd2, a homolog of Erd2, a marker of the Golgi system in eukaryotic cells) in axenically cultured trophozoites of E. histolytica. Measurement of NPT enzyme activity and EhErd2 protein levels, as well as measurement of cellular proliferation, revealed specific decreases in expression of the target genes, and concomitant inhibition of cell growth, in trophozoites treated with micromolar concentrations of unmodified antisense PNA oligomers.

Animals↗
PubMed2001

VEGF protects against oxidized LDL toxicity to endothelial cells by an intracellular glutathione-dependent mechanism through the KDR receptor.

Although the accumulation of vascular endothelial growth factor (VEGF) has been observed in human atherosclerotic lesions, the exact role of this growth factor in atherogenesis remains unknown. We hypothesized that VEGF in the vascular wall might have a preventive effect on endothelial cell damage during atherosclerosis. To test our hypothesis, we examined whether VEGF protects against the toxicity of oxidized low density lipoprotein (Ox-LDL) in cultured endothelial cells derived from bovine aortas (BAECs). Preincubation of BAECs with VEGF prevented Ox-LDL-induced toxicity in a preincubation time- and VEGF concentration-dependent manner. Addition of N(omega)-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, did not reverse the protective effect of VEGF on Ox-LDL toxicity. Incubation of BAECs with VEGF increased intracellular glutathione (GSH) content in a time-dependent manner. Combined addition of VEGF and L-buthionine sulfoximine, a GSH synthesis inhibitor, reversed both GSH levels and the protective effect of VEGF on Ox-LDL-induced cytotoxicity. Placenta growth factor, which ligates to the VEGF Flt-1 receptor but not KDR/Flk-1, failed to prevent Ox-LDL toxicity and had no effect on intracellular GSH levels. An anti-KDR antibody completely blocked these beneficial activities of VEGF. These results suggest that VEGF prevents Ox-LDL-induced endothelial cell damage via an intracellular GSH-dependent mechanism through the KDR/Flk-1 receptor.

Animals↗
PubMed2000

B lymphopenia in uremia is related to an accelerated in vitro apoptosis and dysregulation of Bcl-2.

BACKGROUND: Lymphopenia has been described in patients with chronic renal failure (CRF). It is postulated that the decline in lymphocytes is due to accelerated apoptosis. We investigated whether dysregulation of programmed cell death plays a role in the immunodeficiency described in CRF. METHODS: Peripheral blood lymphocytes (PBL) from pre-dialysis uraemic patients (nHD) and haemodialysed patients (HD) were cultured with no stimulus for 96 h. Apoptosis of lymphocytes was measured by propidium iodide staining and flow cytometry. Expression of Fas and Bcl-2 was also analysed by flow cytometry. RESULTS: Peripheral blood B cells were significantly lower in pre-dialysis and haemodialysis uraemic patients compared to control. Lymphocytes from both groups of patients had a higher rate of apoptosis in vitro than those from healthy controls. This effect was more pronounced in B lymphocytes and a significant correlation between the B lymphopenia and the percentage of apoptotic B cells after 48 h of culture without stimulus was observed. The increased lymphocyte apoptosis in CRF was accompanied by a significantly lower in vitro Bcl-2 expression. However, Fas did not seem to play a role in spontaneous lymphocyte apoptosis in end-stage renal disease. CONCLUSIONS: Our data indicate that B lymphopenia in CRF may be partially attributed to an increased susceptibility to cell death by apoptosis that is associated with a decreased expression of Bcl-2.

Adolescent↗
PubMed2000

Matrix metalloproteinase and alphavbeta3 integrin-dependent vascular smooth muscle cell invasion through a type I collagen lattice.

Smooth muscle cell (SMC) migration from the tunica media to the intima is a key event in the development of atherosclerotic lesions and in restenosis after angioplasty. SMCs require not only migratory but also degradative abilities that enable them to migrate through extracellular matrix proteins, which surround and embed these cells. We used a collagen type I lattice as a coating on top of a porous filter as a matrix barrier in a chamber to test the invasive behavior of SMCs in response to a chemoattractant (invasion assay) and compared that behavior with simple SMC migration through collagen type I-coated filters (migration assay). Inhibitors of matrix metalloproteinase, KB-R8301, tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), TIMP-2, and peptide 74, attenuated platelet-derived growth factor-BB (PDGF-BB)-directed SMC invasion across the collagen lattice, whereas no effect was seen with these inhibitors on simple SMC migration through collagen-coated filters. RGD peptide inhibited SMC invasion but did not affect SMC migration. Anti-alphavbeta3 integrin antibody attenuated PDGF-BB-directed SMC invasion, whereas other antibodies against RGD-recognizing integrins, namely alphavbeta5 and alpha5, had no effect. None of these antibodies had any effect on simple SMC migration. RGD peptide and anti-alphavbeta3 antibody inhibited the attachment and spreading of SMCs on denatured collagen but not on native collagen. These findings indicate that there is a difference in the mechanisms between simple SMC migration across a collagen-coated filter and SMC invasion through a fibrillar collagen barrier. A proteolytic process is required for SMC invasion, and the degradation of matrix proteins alters the relationship between matrix protein molecules and SMC surface integrins.

Animals↗
PubMed1999

Induction of apoptotic cell death in vascular endothelial cells cultured in three-dimensional collagen lattice.

Endothelial cells derived from fetal bovine aorta (BAECs) undergo apoptosis in three-dimensional (3-D) type I collagen lattice in the absence of specific angiogenic factor. In the presence of angiogenic factor, BAECs survive and form a capillary-like tube structure in 3-D culture. In the present study we elucidate the mechanisms of BAECs apoptosis or survival and tube formation in 3-D culture. When BAECs embedded in collagen lattice were cultured with angiogenic factor (fibroblast growth factor-2 (FGF-2) or 4beta-phorbol 12-myristate 13-acetate (PMA)) in the presence of PD98059, a specific inhibitor of mitogen-activated protein kinase kinase, BAECs did not form tube structures and underwent apoptosis in collagen lattice. Function-blocking antibody against alphavbeta3 integrin also inhibited tube formation and induced apoptosis in 3-D culture in the presence of angiogenic factors. Exposure of BAECs to FGF-2 and PMA had no effect on the alphavbeta3 integrin expression but induced the activation of alphavbeta3 integrin. PD98059 attenuated alphavbeta3 integrin activation in response to angiogenic factor. KB-R8301, a hydroxamic acid-based matrix metalloproteinase (MMP) inhibitor, prevented apoptotic cell death in the absence of angiogenic factor in 3-D culture and enhanced capillary-like tube formation in the presence of angiogenic factor, which was not inhibited by the anti-alphavbeta3 integrin antibody. The results suggest that angiogenic factor-induced alphavbeta3 integrin activation through the MEK-ERK pathway regulates the BAEC fate between apoptosis and angiogenesis in collagen lattice. MMP derived from BAECs seems to play a key role in the release of cryptic ligands for alphavbeta3 integrin from intact collagen.

Angiogenesis Inducing Agents↗
PubMed1998

Angiogenic stimuli are essential for survival of vascular endothelial cells in three-dimensional collagen lattice.

Cultured vascular endothelial cells derived from bovine aorta (BAECs) can survive and proliferate in the condition of two-dimensional monolayer culture in the presence of serum without any specific growth factors. When BAECs were embedded in collagen lattice, they underwent apoptotic death within 2 days unless the cultures were repeatedly supplied with angiogenic growth factor such as fibroblast growth factor-2 (FGF-2). Supplementation with FGF-2 induced endothelial cell differentiation, resulting in capillary-like tube formation inside collagen lattice. Following tube formation, withdrawal of FGF-2 induced disruption of the tube structures associated with the characteristic apoptotic cell death. These effects of FGF-2 were regulated by tyrosine phosphorylation, but not mediated through protein kinase C pathway. This model of endothelial cell apoptosis inside collagen lattice may represent in vivo endothelial cell-matrix interaction during angiogenesis process, indicating that apoptotic death of endothelial cells may regulate angiogenesis and the regression of vessels.

Animals↗
PubMed1998

Inhibition of angiogenesis on glycated collagen lattices.

Advanced glycation endproduct (AGE) accumulation in extracellular matrix proteins has been demonstrated in diabetic patients with a significant correlation with the severity of diabetic complications. AGE accumulation induces matrix protein cross-link formation, resulting in an increased stiffness of matrix fibres and the reduction of the susceptibility of matrix proteins to proteolytic degradation. We examined whether glycation-induced collagen cross-linking may affect vascular endothelial cell behaviours such as invasion, proliferation and differentiation, using the in vitro angiogenesis model of capillary-like structure formation in three-dimensional matrices of collagen type I. Endothelial cells cultured on collagen gel with angiogenic factors (the combination of fibroblast growth factor-2 and vascular endothelial growth factor) invaded the underlying collagen matrix, and organized capillary-like cord structures in the gel. We found that endothelial cell invasion into glycated collagen gel was significantly attenuated without any effect on proteinase activity including cell-associated plasminogen activator and matrix metalloproteinase in the conditioned medium. In addition, subsequent capillary-like cord formation was also inhibited in glycated collagen gel. In contrast, endothelial cell proliferation was enhanced on glycated collagen gel with or without angiogenic factors compared with control collagen gel. These results suggest that the structural alterations of extracellular matrix proteins through the glycation-induced cross-link formation affect the interaction between endothelial cell and extracellular matrix, resulting in the impairment of an adequate neovascularization in diabetic patients.

Angiogenesis Inducing Agents↗