RESUMO
Methane (CH4) is a greenhouse gas (GHG) produced and released by eructation to the atmosphere in large volumes by ruminants. Enteric CH4 contributes significantly to global GHG emissions arising from animal agriculture. It has been contended that tropical grasses produce higher emissions of enteric CH4 than temperate grasses, when they are fed to ruminants. A number of experiments have been performed in respiration chambers and head-boxes to assess the enteric CH4 mitigation potential of foliage and pods of tropical plants, as well as nitrates (NO3-) and vegetable oils in practical rations for cattle. On the basis of individual determinations of enteric CH4 carried out in respiration chambers, the average CH4 yield for cattle fed low-quality tropical grasses (>70% ration DM) was 17.0 g CH4/kg DM intake. Results showed that when foliage and ground pods of tropical trees and shrubs were incorporated in cattle rations, methane yield (g CH4/kg DM intake) was decreased by 10% to 25%, depending on plant species and level of intake of the ration. Incorporation of nitrates and vegetable oils in the ration decreased enteric CH4 yield by â¼6% to â¼20%, respectively. Condensed tannins, saponins and starch contained in foliages, pods and seeds of tropical trees and shrubs, as well as nitrates and vegetable oils, can be fed to cattle to mitigate enteric CH4 emissions under smallholder conditions. Strategies for enteric CH4 mitigation in cattle grazing low-quality tropical forages can effectively increase productivity while decreasing enteric CH4 emissions in absolute terms and per unit of product (e.g. meat, milk), thus reducing the contribution of ruminants to GHG emissions and therefore to climate change.
Assuntos
Gases de Efeito Estufa , Metano , Ração Animal/análise , Animais , Bovinos , Dieta/veterinária , Leite , Poaceae , Rúmen , RuminantesRESUMO
Intensive silvopastoral systems (ISS) are a sustainable alternative to monoculture systems (MS). The presence of trees and legumes improves animal welfare due to the increased food quality and quantity and the presence of shade while providing a variety of environmental services. As cattle behaviour is greatly affected by environmental conditions, knowledge on the behavioural trade-offs that cattle make to meet their demands while foraging in different grazing systems is important, as this will help us understand the perceived advantages of ISS. This pilot study assessed the behaviour of heifers in an ISS (n=8 heifers) and MS (n=8 heifers) in the Mexican tropics during the dry and rainy seasons, and its relationship with forage availability, mean travelled distance and the temperature humidity index (THI). In both seasons, daily foraging times were longer in the MS than the ISS (P<0.01). The duration of rumination was higher for ISS (P<0.01) and the duration of lying was higher for the dry season (P<0.05). The decrease in foraging times in relation to THI was significantly higher in the ISS than in the MS (mean slope±SE: ISS=-4.64±0.34; MS=-2.34±0.22; t=-14.20, P<0.001). The results suggest that the forage availability and access to shade in the ISS allow cattle to rest longer and increase rumination, whereas cattle in MS spend more time searching for food and foraging at times of the day were the temperatures were higher as a compensatory strategy, which potentially decreases cattle's welfare and production qualities when compared with the ISS. In conclusion, ISS are likely to generate positive behavioural trade-offs that result in better welfare conditions and higher productive potential.
Assuntos
Criação de Animais Domésticos/métodos , Comportamento Alimentar , Animais , Bovinos , Feminino , Umidade , México , Projetos Piloto , Estações do Ano , TemperaturaRESUMO
The objective of this study was to evaluate the influence of tree foliage species supplemented in ruminant diets based on Pennisetum purpureum on the in vitro digestibility and fermentation, microbial biomass synthesis and enteric methane production. Seven experimental diets were evaluated, including a control treatment based on P. purpureum (PT) grass, and six additional treatments supplemented with 30.0% foliage from Neomillspaughia emargiata (NE), Tabernaemontana amygdalifolia (TA), Caesalpinia gaumeri (CG), Piscidia piscipula (PP), Leucaena leucocephala (LL) and Havardia albicans (HA). A randomised complete block design repeated in two periods (block) was used. The highest gas production (P < 0.05) was recorded in treatments TA and PT (237 and 228 mL g-1, respectively). The highest in vitro digestibility of dry matter (IVDMD) and organic matter (IVOMD) (P < 0.05) was recorded in the control treatment PT (57.9% and 66.1%, respectively). Treatments LL, NE, TA and PP promoted greater microbial biomass synthesis (290, 223, 220 and 213 mg g-1, respectively) (P < 0.05). The proportion of propionic acid also increased in these latter treatments and in treatments CG and HA (P < 0.05). Additionally, treatments LL, PP, NE and TA decreased methane production (25.8, 29.5, 30.6 and 31.8 L kg-1 of digested dry matter, respectively). In conclusion, supplementation with L. leucocephala, P. piscipula, N. emargiata and T. amygdalifolia in ruminant diets based on P. purpureum is one feed alternative that can promote greater efficiency and synthesis of microbial biomass, increase the proportions of propionic and butyric acid and decrease the production of enteric methane by 15.6 to 31.6%.
Assuntos
Dieta , Fabaceae , Fermentação , Metano , Pennisetum , Rúmen , Animais , Bovinos , Amônia/metabolismo , Ração Animal/análise , Biomassa , Dieta/veterinária , Suplementos Nutricionais , Digestão , Microbioma Gastrointestinal , Metano/metabolismo , México , Folhas de Planta , Polygonaceae , Rúmen/metabolismo , Rúmen/microbiologia , Ruminantes , ÁrvoresRESUMO
The aim of this work was to evaluate the effect of quebracho tannins extract (QTE) on feed intake, dry matter (DM) digestibility, and methane (CH4) emissions in cattle fed low-quality Pennisetum purpureum grass. Five heifers (Bos taurus × Bos indicus) with an average live weight (LW) of 295 ± 19 kg were allotted to five treatments (0, 1, 2, 3, and 4% QTE/kg DM) in a 5 × 5 Latin square design. Intake, digestibility, and total methane emissions (L/day) were recorded for periods of 23 h when cattle were housed in open-circuit respiration chambers. Dry matter intake (DMI), organic matter intake (OMI), dry matter digestibility (DMD), and organic matter digestibility (OMD) were different between treatments with 0 and 4% of QTE/kg DM (P < 0.05). Total volatile fatty acid and the molar proportion of acetate in the rumen was not affected (P < 0.05); however, the molar proportion of propionate increased linearly (P < 0.01) for treatments with 3 and 4% QTE. Total CH4 production decreased linearly (P < 0.01) as QTE increased in the diet, particularly with 3 and 4% concentration. When expressed as DMI and OMI by CH4, production (L/kg) was different between treatments with 0 vs 3 and 4% QTE (P < 0.05). It is concluded that the addition of QTE at 2 or 3% of dry matter ration can decrease methane production up to 29 and 41%, respectively, without significantly compromising feed intake and nutrients digestibility.
Assuntos
Anacardiaceae/química , Dieta/veterinária , Digestão/efeitos dos fármacos , Comportamento Alimentar/efeitos dos fármacos , Metano/metabolismo , Taninos/administração & dosagem , Poluentes Atmosféricos/metabolismo , Ração Animal/análise , Fenômenos Fisiológicos da Nutrição Animal , Animais , Bovinos , Suplementos Nutricionais/análise , Relação Dose-Resposta a Droga , Feminino , Pennisetum/fisiologia , Extratos Vegetais/administração & dosagem , Árvores/químicaRESUMO
An experiment was carried out to determine the effect of supplementing ground pods of Enterolobium cyclocarpum in a basal ration of Pennisetum purpureum grass on feed intake, rumen volatile fatty acids (VFAs), and protozoa and methane (CH4) production by hair sheep. Four male sheep (Pelibuey × Katahdin) with a mean live weight of 27.0 kg (SD ± 0.5) were supplemented with 0.00, 0.15, 0.30, and 0.45 kg of dry matter (DM) of E. cyclocarpum pods daily; equivalent to 0.00, 4.35, 8.70, and 13.05 g of crude saponins, respectively. Dry matter intake (DMI), organic matter intake (OMI), and molar proportions of propionic acid increased linearly (P < 0.05) as pods of E. cyclocarpum in the ration were increased. Higher intakes of DM and OM were found when lambs were fed 0.45 kg DM per day of E. cyclocarpum, and the highest proportion of propionic acid (0.21 and 0.22, respectively) was obtained with 0.15 and 0.30 kg of DM per lamb of E. cyclocarpum, while apparent digestibility of neutral detergent fiber (NDF) and molar proportion of acetic acid were reduced (P < 0.05). Rumen CH4 production decreased (P < 0.05) when 0.30 and 0.45 kg of DM/lamb/day of E. cyclocarpum were fed (21.8 and 25.3 L CH4/lamb/day, respectively). These results suggest that to improve the feeding of sheep fed tropical grass, it is advisable to supplement the basal ration with up to 0.30 kg DM of E. cyclocarpum pods.
Assuntos
Digestão/efeitos dos fármacos , Fabaceae , Fermentação/efeitos dos fármacos , Metano/metabolismo , Saponinas/administração & dosagem , Ração Animal/análise , Animais , Fibras na Dieta , Suplementos Nutricionais , Ingestão de Alimentos , Ácidos Graxos Voláteis/metabolismo , Masculino , Pennisetum , Rúmen/metabolismo , Rúmen/parasitologia , Saponinas/metabolismo , Ovinos , Carneiro DomésticoRESUMO
Silvopastoral systems can be a good alternative for sustainable livestock production because they can provide ecosystem services and improve animal welfare. Most farm animals live in groups and the social organization and interactions between individuals have an impact on their welfare. Therefore, the objective of this study was to describe and compare the social behaviour of cattle (Bos indicus×Bos taurus) in a silvopastoral system based on a high density of leucaena (Leucaena leucocephala) combined with guinea grass (Megathyrsus maximus), star grass (Cynodon nlemfuensis) and some trees; with a monoculture system with C. nlemfuensis, in the region of Merida, Yucatán. Eight heifers in each system were observed from 0730 to 1530 h each day for 12 consecutive days during the dry season and 12 consecutive days during the rainy season. The animals followed a rotation between three paddocks, remaining 4 days in each paddock. The vegetation was characterized in the paddocks of the silvopastoral system to estimate the average percentage of shade provided. To make a comparison between systems, we used a t test with group dispersion, and Mann-Whitney tests with the frequency of affiliative and agonistic behaviours. We assessed differences in linearity and stability of dominance hierarchies using Landau's index and Dietz R-test, respectively. The distance of cows with respect to the centroid of the group was shorter, and non-agonistic behaviours were 62% more frequent in the intensive silvopastoral system than in the monoculture one. Heifers in the silvopastoral system had a more linear and non-random dominance hierarchy in both seasons (dry season: h'=0.964; rainy season: h'=0.988), than heifers in the monoculture system (dry season: h'=0.571, rainy season: h'=0.536). The dominance hierarchy in the silvopastoral system was more stable between seasons (R-test=0.779) than in the monoculture system (R-test=0.224). Our results provide the first evidence that heifers in the silvopastoral system maintain more stable social hierarchies and express more sociopositive behaviours, suggesting that animal welfare was enhanced.
Assuntos
Criação de Animais Domésticos/métodos , Bovinos/fisiologia , Comportamento Social , Bem-Estar do Animal , Animais , Fabaceae/crescimento & desenvolvimento , Feminino , México , Poaceae/crescimento & desenvolvimento , Estações do Ano , Clima TropicalRESUMO
The objective of this work was to evaluate the effect of metabolizable energy intake (MEI) on changes in fat depots of adult Pelibuey ewes fed roughage diets under tropical conditions. Eighteen 3-year-old Pelibuey ewes with similar body weight (BW) of 37.6 ± 4.0 kg and body condition score (BCS) of 2.5 ± 0.20 were randomly assigned to three groups of six ewes each in a completely randomized design. Ewes were housed in metabolic crates and fed three levels of MEI: low (L), medium (M), and high (H) for 65 days to achieve different BW and BCS. At the end of the experiment, the ewes were slaughtered. Data recorded at slaughter were: weights of viscera and carcass. Internal fat (IF, internal adipose tissue) was dissected, weighed, and grouped as pelvic (around kidneys and pelvic region), omental, and mesenteric regions. Carcass was split at the dorsal midline in two equal halves, weighed, and chilled at 6°C during 24 h. After refrigeration, the left half of the carcass was completely dissected into subcutaneous and intermuscular fat (carcass fat). Dissected carcass fat (CF) of the left carcass was adjusted as whole carcass. At low levels of MEI, proportion of IF and CF was approximately 50%; however, as the MEI was increased, the proportion of IF was increased up to 57% and 60% for M and H, respectively. Omental and pelvic fat depots were those which increased in a larger proportion with respect to the mesenteric fat depot. Regression equations between the weight of each body fat depot and BW had a coefficient of determination (r (2)) that ranged between 0.37 for mesenteric fat and 0.87 for CF. The regression with BCS had a r (2) that ranged between 0.57 for mesenteric and 0.71 for TBF. BW was the best predictor for TBF, CF, omental fat, and pelvic fat; whereas, BCS was better than BW in predicting IF and mesenteric fat. Inclusion of both BW and BCS in multiple regressions improved the prediction for all fat depots, except for pelvic fat, which was best estimated by BCS alone. The greater slope of the regression for the pelvic fat depot equation, relative to TBF (1.40), EBW (4.02), and BCS (2.36), suggested that pelvic fat has a greater capacity to accumulate and mobilize fat. These results indicated that adult Pelibuey ewes seem to store a considerable proportion of absorbed energy in the IF depots rather than in the carcass.
Assuntos
Tecido Adiposo/anatomia & histologia , Composição Corporal , Distribuição da Gordura Corporal , Dieta/veterinária , Ingestão de Energia , Carneiro Doméstico/fisiologia , Criação de Animais Domésticos , Animais , Peso Corporal , Feminino , México , Análise de Regressão , Clima TropicalRESUMO
Extracellular adenosine removal is via human equilibrative nucleoside transporters 1 (hENT1) and 2 (hENT2) in the endothelium, thus regulating adenosine-induced revascularization and angiogenesis. Since human endothelial progenitor cells (hEPCs) promote revascularization, we hypothesize differential expression of nucleoside transporters in hEPCs. hEPCs were cultured 3 (hEPC-3d) or 14 (hEPC-14d) days. RT-PCR for prominin 1, CD34, octamer-4, kinase insert domain receptor, oxidized low-density lipoprotein (lectin-like) receptor 1 and tyrosine endothelial kinase was used to evaluate phenotypic differentiation. Flow cytometry was used to estimate CD34(+)/KDR(-) (non-differentiated), CD34(-)/KDR(+) (differentiated) or CD34(+)/KDR(+) (mixed) cell populations. Adenosine transport was measured in absence or presence of sodium, S-(4-nitrobenzyl)-6-thio-inosine (NBTI, 1-10 µM), inosine, hypoxanthine or guanine (0.1-5 mM), hENTs protein abundance by western blot, and hENTs, hCNT1, hCNT2 and hCNT3 mRNA expression by real time RT-PCR. hEPC-3d cells were CD34(+)/KDR(-) compared with hEPC-14d cells that were CD34(-)/KDR(+). hEPC-3d cells exhibit hENT1-like adenosine transport (NBTI-sensitive, Na(+)-independent), which is absent in hEPC-14d cells. hEPC-14d cells exhibit two transport components: component 1 (NBTI insensitive, Na(+)-independent) and component 2 (NBTI insensitive, Na(+)-dependent, Hill coefficient â¼1.8), the latter resembling CNT3-like transport. hEPC-3d cells express hENT1 protein and mRNA, which is reduced (â¼90%) in hEPC-14d cells, but instead only hCNT3 mRNA is expressed in this cell type. hENT2, hCNT1 and hCNT2 were undetectable in hEPCs. Thus, hEPCs exhibit a differential expression of hENT1 and hCNT3 functional nucleoside transporters, which could be related with its differentiation stage.
Assuntos
Células Endoteliais/fisiologia , Transportador Equilibrativo 1 de Nucleosídeo/biossíntese , Transportador Equilibrativo 2 de Nucleosídeo/biossíntese , Células-Tronco/fisiologia , Adenosina/metabolismo , Transporte Biológico , Western Blotting , Diferenciação Celular/fisiologia , Células Endoteliais/metabolismo , Transportador Equilibrativo 1 de Nucleosídeo/genética , Transportador Equilibrativo 2 de Nucleosídeo/genética , Humanos , Cinética , RNA/química , RNA/genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Células-Tronco/metabolismo , Tioinosina/análogos & derivados , Tioinosina/farmacologiaRESUMO
The aim was to evaluate the effect of corn oil supplementation during postpartum anoestrus on ovarian activity, pregnancy rate, progesterone (P(4)), and lipid metabolites (cholesterol, CHO; low and high density lipoproteins; LDL and HDL, respectively) concentrations in blood of F(1) (Bos taurus x Bos indicus) grazing cows. Cows were randomly assigned to an experimental group, fed with a supplement containing 4% corn oil on dry matter basis (OG, n = 11), and a control group with the same supplement without corn oil (CG, n = 12). Both supplements contained equivalent amounts of crude protein and metabolizable energy and were fed for 34 days continuously. All cows were induced to estrous 12 days after beginning of supplementation by using a synthetic progestagen and artificially inseminated 56 h after retiring the implants. Pregnancy diagnosis was performed by transrectal palpation 45 days after insemination, evaluating simultaneously ovarian activity. P(4) and lipid metabolites (CHO, HDL, LDL) concentrations were determined in blood samples collected at 3-day intervals, from the beginning of corn oil supplementation and up to 10 days after artificial insemination. Ovarian activity was affected by treatment (p < 0.05), finding ovarian structures in 72.7% of OG cows and in 50% of CG cows. Concentration of P(4) and CHO was higher for OG with respect to CG (2.52 +/- 0.65 vs 1.88 +/- 0.62 ng/ml and 117.79 +/- 11.57 vs 85.71 +/- 12.11 mg/dl, respectively), whereas pregnancy rate and blood concentrations of HDL and LDL were not affected by treatment (p > 0.05). Addition of corn oil to the supplement stimulated ovarian activity and increased serum concentrations of progesterone and cholesterol in grazing B. taurus x B. indicus cows with low body condition score showing postpartum anoestrus.
Assuntos
Bovinos/fisiologia , Óleo de Milho/farmacologia , Metabolismo dos Lipídeos/efeitos dos fármacos , Ovário/efeitos dos fármacos , Progesterona/sangue , Animais , Bovinos/sangue , Colesterol/sangue , Dieta/veterinária , Suplementos Nutricionais , Feminino , Lipoproteínas HDL/sangue , Lipoproteínas LDL/sangue , Ovário/fisiologia , Período Pós-Parto/efeitos dos fármacos , Período Pós-Parto/fisiologia , Gravidez , Taxa de GravidezRESUMO
Vitamin C is a wide spectrum antioxidant essential for humans, which are unable to synthesize the vitamin and must obtain it from dietary sources. There are two biologically important forms of vitamin C, the reduced form, ascorbic acid, and the oxidized form, dehydroascorbic acid. Vitamin C exerts most of its biological functions intracellularly and is acquired by cells with the participation of specific membrane transporters. This is a central issue because even in those species capable of synthesizing vitamin C, synthesis is restricted to the liver (and pancreas) from which is distributed to the organism. Most cells express two different transporter systems for vitamin C; a transporter system with absolute specificity for ascorbic acid and a second system that shows absolute specificity for dehydroascorbic acid. The dehydroascorbic acid transporters are members of the GLUT family of facilitative glucose transporters, of which at least three isoforms, GLUT1, GLUT3 and GLUT4, are dehydroascorbic acid transporters. Ascorbic acid is transported by the SVCT family of sodium-coupled transporters, with two isoforms molecularly cloned, the transporters SVCT1 y SVCT2, that show different functional properties and differential cell and tissue expression. In humans, the maintenance of a low daily requirement of vitamin C is attained through an efficient system for the recycling of the vitamin involving the two families of vitamin C transporters.
Assuntos
Ácido Ascórbico/metabolismo , Transportador de Glucose Tipo 1/metabolismo , Transportador de Glucose Tipo 3/metabolismo , Transportador de Glucose Tipo 4/metabolismo , Transportadores de Ânions Orgânicos Dependentes de Sódio/metabolismo , Simportadores/metabolismo , Humanos , Transportadores de Sódio Acoplados à Vitamina CRESUMO
Oxidized low density lipoproteins (oxLDL), macrophages and T-lymphocytes are present in atherosclerotic lesions. We and others have shown that oxLDL is cytotoxic for macrophages, endothelial, smooth muscle and activated T-lymphocytes and induce apoptosis. Here we demonstrate that (i) oxidized LDL (oxLDL), oxidized VLDL (oxVLDL) and hydrogen peroxide (H2O2) induce apoptosis in human T-lymphocytes and (ii) mitogen-activated protein kinases are involved in this process. Apoptosis was monitored by immunofluorescence microscopy and flow cytometry for annexin V binding, Apo 2.7 expression, the TUNEL reaction and caspase 3 activity. In the presence of oxLDL (100 microg/ml), oxVLDL (50 microg/ml) and H2O2 (5 mM), the fraction of apoptotic cells increased within 6 hours to more than 70%. Preincubation of lymphocytes with the MAPKK inhibitor PD-98059 and the p38MAPK inhibitor SB-203580 almost completely abolished these effects. Furthermore, oxLDL and H2O2 but not native LDL strongly enhanced phosphorylation of JNK, p38MAPK and p42/44MAPK. The results suggest that in the resting lymphocyte apoptosis triggered by oxidized lipoproteins and oxidative stress depends on the activation of p44/42MAPK and p38MAPK cascades.
Assuntos
Apoptose/efeitos dos fármacos , Lipoproteínas LDL/farmacologia , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Linfócitos T/metabolismo , Anexina A5/metabolismo , Caspase 3/análise , Caspase 3/metabolismo , Células Cultivadas , Relação Dose-Resposta a Droga , Inibidores Enzimáticos/farmacologia , Flavonoides/farmacologia , Humanos , Imidazóis/farmacologia , Proteínas Quinases Ativadas por Mitógeno/antagonistas & inibidores , Oxirredução , Estresse Oxidativo , Piridinas/farmacologia , Fatores de TempoRESUMO
Non-Hodgkin's lymphoma (NHL) of the gastrointestinal (GI) tract is the most common extranodal lymphoma, accounting for approximately 40% of all extranodal NHLs. Initial treatment of duodenal lymphoma includes surgery, chemotherapy and radiotherapy, alone or in combination. Here, we present a case of stage I primary duodenal follicular lymphoma (FL) showing a complete response after rituximab therapy. Rituximab alone can be an effective alternative treatment for duodenal FL.
Assuntos
Anticorpos Monoclonais/uso terapêutico , Antineoplásicos/uso terapêutico , Neoplasias Duodenais/tratamento farmacológico , Linfoma Folicular/tratamento farmacológico , Anticorpos Monoclonais/administração & dosagem , Anticorpos Monoclonais Murinos , Antineoplásicos/administração & dosagem , Humanos , Masculino , Pessoa de Meia-Idade , RituximabRESUMO
Oxidative stress releases intracellular calcium, which plays a pathogenic role in mammalian cell death. Here we report a search for the source of oxidative calcium in HeLa cells based on confocal epifluorescence microscopy. H(2)O(2) caused a rapid increase in cytosolic calcium, which was followed by mitochondrial Ca(2+) loading. Combined mitochondrial uncoupling with full depletion of thapsigargin-sensitive stores abrogated inositol 1,4,5-trisphosphate-mediated calcium release but failed to inhibit H(2)O(2)-induced calcium release, observation that was confirmed in MDCK cells. Prevention of peroxide-induced acidification with a pH clamp was also ineffective, discarding a role for endosomal/lysosomal Ca(2+)/H(+) exchange. Lysosomal integrity was not affected by H(2)O(2). Mature human erythrocytes also reacted to peroxide by releasing intracellular calcium, thus directly demonstrating the cytosolic source. Glutathione depletion markedly sensitized cells to H(2)O(2), an effect opposite to that achieved by DTT. Iron chelation was ineffective. In summary, our results show the existence of a previously unrecognized sulfhydryl-sensitive source of pathogenic calcium in the cytosol of mammalian cells.
Assuntos
Cálcio/metabolismo , Citosol/metabolismo , Ácido Egtázico/análogos & derivados , Células Epiteliais/metabolismo , Peróxido de Hidrogênio/farmacologia , Animais , Morte Celular/efeitos dos fármacos , Morte Celular/fisiologia , Linhagem Celular , Cães , Ácido Egtázico/farmacologia , Retículo Endoplasmático/fisiologia , Células Epiteliais/efeitos dos fármacos , Espaço Extracelular/fisiologia , Células HeLa , Humanos , Peróxido de Hidrogênio/antagonistas & inibidores , Concentração de Íons de Hidrogênio , Mitocôndrias/efeitos dos fármacos , Mitocôndrias/fisiologia , Fatores de TempoRESUMO
The sodium-vitamin C co-transporters SVCT1 and SVCT2 transport the reduced form of vitamin C, ascorbic acid. High expression of the SVCT2 has been demonstrated in adult neurons and choroid plexus cells by in situ hybridization. Additionally, embryonic mesencephalic dopaminergic neurons express the SVCT2 transporter. However, there have not been molecular and kinetic analyses addressing the expression of SVCTs in cortical embryonic neurons. In this work, we confirmed the expression of a SVCT2-like transporter in different regions of the fetal mouse brain and in primary cultures of neurons by RT-PCR. Kinetic analysis of the ascorbic acid uptake demonstrated the presence of two affinity constants, 103 microM and 8 microM. A K(m) of 103 microM corresponds to a similar affinity constant reported for SVCT2, while the K(m) of 8 microM might suggest the expression of a very high affinity transporter for ascorbic acid. Our uptake analyses also suggest that neurons take up dehydroascorbic acid, the oxidized form of vitamin C, through the glucose transporters. We consider that the early expression of SVCTs transporters in neurons is important in the uptake of vitamin C, an essential molecule for the fetal brain physiology. Vitamin C that is found at high concentration in fetal brain may function in preventing oxidative free radical damage, because antioxidant radical enzymes mature only late in the developing brain.
Assuntos
Ácido Ascórbico/metabolismo , Proteínas de Transporte/metabolismo , Embrião de Mamíferos/metabolismo , Neurônios/metabolismo , Transportadores de Ânions Orgânicos Dependentes de Sódio , Proteínas/metabolismo , Simportadores , Animais , Proteínas de Transporte/genética , Células Cultivadas , Córtex Cerebral/citologia , Citocalasina B/farmacologia , Citocalasinas/farmacologia , Inibidores Enzimáticos/farmacologia , Imuno-Histoquímica , Cinética , Camundongos , Camundongos Endogâmicos C57BL , Ouabaína/farmacologia , Proteínas/genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Sódio/metabolismo , Transportadores de Sódio Acoplados à Vitamina CRESUMO
Glucose transporters play an essential role in the acquisition of glucose by the brain. Elevated expression of glucose transporter-1 has been detected in endothelial cells of the blood-brain barrier and in choroid plexus cells of the blood-cerebrospinal fluid barrier. On the other hand, there is a paucity of information on the expression of glucose transporters in the ependymal cells that line the walls of the cerebral ventricles. The tanycytes are specialized ependymal cells localized in circumventricular organs such as the median eminence that can be segregated into at least three types, alpha, beta1 and beta2. The beta2 tanycytes form tight junctions and participate in the formation of the cerebrospinal fluid-median eminence barrier. Using immunocytochemistry and in situ hybridization, we analyzed the expression of hexose transporters in rat and mouse hypothalamic tanycytes. In both species, immunocytochemical analysis revealed elevated expression of glucose transporter-1 in alpha and beta1 tanycytes. Intense anti-glucose transporter-1 staining was observed in cell processes located throughout the arcuate nucleus, in the end-feet reaching the lateral sulcus of the infundibular region, and in cell processes contacting the hypothalamic capillaries. On the other hand, there was very low expression of glucose transporter-1 in beta2 tanycytes involved in barrier function. In contrast with the results of the cytochemical analysis, in situ hybridization revealed that tanycytes alpha, beta1, and beta2 express similar levels of glucose transporter-1 mRNA. Further analysis using anti-glial fibrillary acidic protein antibodies to identify areas rich in astrocytes revealed that astrocytes were absent from areas containing alpha and beta1 tanycytes, but were abundant in regions containing the barrier-forming beta2 tanycytes. Overall, our data reveal a lack of correlation between participation in barrier function and expression of glucose transporter-1 in hypothalamic tanycytes. Given the virtual absence of astrocytes in areas rich in alpha and beta1 tanycytes, we speculate whether the tanycytes might have astrocyte-like functions and participate in the metabolic coupling between glia and neurons in the hypothalamic area.
Assuntos
Barreira Hematoencefálica/fisiologia , Encéfalo/metabolismo , Líquido Cefalorraquidiano/metabolismo , Epêndima/citologia , Hipotálamo/citologia , Hipotálamo/metabolismo , Proteínas de Transporte de Monossacarídeos/biossíntese , Regulação para Cima , Animais , Astrócitos/metabolismo , Núcleo Celular/metabolismo , Proteína Glial Fibrilar Ácida/biossíntese , Transportador de Glucose Tipo 1 , Imuno-Histoquímica , Hibridização In Situ , Camundongos , Camundongos Endogâmicos C57BL , Modelos Biológicos , Neuroglia/metabolismo , Neurônios/metabolismo , RNA Mensageiro/metabolismo , RatosRESUMO
We studied the expression and function of the granulocyte-macrophage colony stimulating factor (GM-CSF) receptor in male germ cells. RT-PCR showed expression of mRNAs encoding the alpha- and beta-subunits of the GM-CSF receptor in human testis, and the presence of the alpha- and beta-proteins was confirmed by immunoblotting with anti-alpha and anti-beta-antibodies. Immunolocalization studies showed the level of expression of GM-CSF alpha- and beta-subunits in the germ line in the testis and in ejaculated spermatozoa. Receptor binding studies using radiolabeled GM-CSF revealed that bull spermatozoa have about 105 high-affinity sites with a K(d) of 222 pM and approximately 1100 low-affinity sites with a K(d) of 10 nM. GM-CSF signaled, in a time- and dose-dependent manner, for an increased uptake of glucose and vitamin C.
Assuntos
Ácido Ascórbico/metabolismo , Glucose/metabolismo , Receptores de Fator Estimulador das Colônias de Granulócitos e Macrófagos/biossíntese , Transdução de Sinais , Testículo/metabolismo , Animais , Sítios de Ligação , Bovinos , Relação Dose-Resposta a Droga , Eletroforese em Gel de Ágar , Fator Estimulador de Colônias de Granulócitos e Macrófagos/metabolismo , Humanos , Immunoblotting , Imuno-Histoquímica , Hibridização In Situ , Cinética , Masculino , Ligação Proteica , Transporte Proteico , RNA Mensageiro/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Sêmen/metabolismo , Espermatozoides/metabolismo , Fatores de TempoRESUMO
The four-state simple carrier model (SCM) is employed to describe ligand translocation by diverse passive membrane transporters. However, its application to systems like facilitative sugar transporters (GLUTs) is controversial: unidirectional fluxes under zero-trans and equilibrium-exchange experimental conditions fit a SCM, but flux data from infinite-cis and infinite-trans experiments appear not to fit the same SCM. More complex kinetic models have been proposed to explain this "anomalous" behavior of GLUTs, but none of them accounts for all the experimental findings. We propose an alternative model in which GLUTs are channels subject to conformational transitions, and further assume that the results from zero-trans and equilibrium-exchange experiments as well as trans-effects corresponds to a single-occupancy channel regime, whereas the results from the infinite-cis and infinite-trans experiments correspond to a regime including higher channel occupancies. We test the plausibility of this hypothesis by studying a kinetic model of a two-site channel with two conformational states. In each state, the channel can bind the ligand from only one of the compartments. Under single-occupancy, for conditions corresponding to zero-trans and equilibrium-exchange experiments, the model behaves as a SCM capable of exhibiting trans-stimulations. For a regime including higher degrees of occupancy and infinite-cis and infinite-trans conditions, the same channel model can exhibit a behavior qualitatively similar to a SCM, albeit with kinetic parameters different from those for the single-occupancy regime. Numerical results obtained with our model are consistent with available experimental data on facilitative glucose transport across erythrocyte membranes. Hence, if GLUTs are multiconformational channels, their particular kinetic properties can result from transitions between single and double channel occupancies.