RESUMEN
The dry ecosystems in the ignimbrite meseta of Guanacaste, northwest Costa Rica is mapped. Plant community distribution is intimately related to the type of relief, soils and humidity. In the upper parts of the meseta, characterised by soils which are stony, sandy, and acidic, herbacious vegetation such as savanna and edaphic steppe is dominant. By contrast, woodland is found on the deep and organically rich soils of the valley floors. Within the herbaceous formations dwarf varieties of Byrsonima crassifolia (nance), Curatella americana (raspa guacal) and Quercus oleoides (encino) are found because of the acid and infertile soils.
Asunto(s)
Ecosistema , Plantas , Suelo , Clima , Costa Rica , Plantas/clasificación , LluviaRESUMEN
The intra-venous (i.v.) hypotensive action of the final aqueous fraction of Pimenta dioica was studied in Spontaneously Hypertensive Rats (SHR). The rats were anaesthetized (sodium pentobarbital 50 mg/kg), the trachea, right carotid artery and jugular vein were cannulated for adequate ventilation, direct blood pressure measurement and intra-venous administration of extracts, solutions and drugs. The arterial line was connected to a pressure transducer (Viggo-Spectramed model P23 XL) and a polygraph (Grass model 7H) and monitored continuously during the first five minutes after plant extract administration and then at 5 and 15 minute intervals for one hour. Responses were taken as the maximum pressure changes observed during this period. Increasing doses of the final aqueous fraction were given i.v. to groups of six SHR each. It produced a dose dependent decrease in blood pressure and the ED50 was 45 mg/kg. To discard that the hypotensive effect of the extracts was due to its ionic composition, a solution containing KCl, NaCl, CaCl2 and MgCl2 equivalent to the ion contents present in a dose of 50 mg/kg of total aqueous extract was injected to Sprague-Dawley rats (SDN) using the same method as described above. It did not produce significant changes in blood pressure. Pharmacological antagonistic studies were done injecting either autonomic ganglion, alpha adrenoceptor, beta adrenoceptor and cholinergic receptor blockers prior to extract administration in SHR rats. Atropine, propranolol and phentolamine did not affect the hypotensive effect of the final aqueous fraction. With hexamethonium (autonomic ganglion blocker) the hypotensive response was diminished in a significant way (p < 0.05). The hypotensive action of the final aqueous extract was not mediated through cholinergic, alpha or beta adrenergic receptors. The extract may posses vasorelaxing activity which could not be evident after autonomic ganglion blockade due to extreme vasodilation present prior to extract administration. Future studies should address the question of a possible direct vasodilating effect of the extracts.
Asunto(s)
Antihipertensivos/farmacología , Presión Sanguínea/efectos de los fármacos , Frecuencia Cardíaca/efectos de los fármacos , Extractos Vegetales/farmacología , Animales , Antihipertensivos/uso terapéutico , Relación Dosis-Respuesta a Droga , Evaluación Preclínica de Medicamentos , Hipertensión/tratamiento farmacológico , Masculino , Extractos Vegetales/uso terapéutico , Ratas , Ratas Sprague-DawleyRESUMEN
Feedback modulation of voltage-dependent Ca2+ channels by ATP is a well documented phenomenon in bovine chromaffin cells. However, its influence in the control of hormone release is at present poorly understood. By using combined patch-clamp and fura-2 fluorescence measurements we provide evidence that the three Ca2+ channel types (L, N and P/Q) expressed in bovine chromaffin cells are inhibited by ATP (30 microM), and that their involvement in the secretory response, as assayed by capacitance measurements, is roughly proportional to their contribution to the whole-cell Ca2+ current (ICa) both in the absence and presence of ATP. ATP did not modify the capacitance increase observed in cells dialyzed with Ca(2+)-EGTA buffers (1.5 microM free Ca2+), thus excluding a direct effect of ATP on the secretory machinery. Voltage predepolarizations or long chemical (2 s, 70 mM KCl) depolarizations attenuate the effect of ATP on exocytosis by partially relieving the inhibition of ICa Likewise, a strong stimulation that depletes the readily releasable pool of vesicles prevents an inhibitory effect of ATP on the secretory response. While these results lend support to the hypothesis of autocrine modulation of exocytosis by endogenously released ATP acting on P2y-purinoceptors to inhibit ICa, feedback regulation of the rate of release will be a complex function of the occupancy of those receptors and of the electrical and secretory activity of the cell.
Asunto(s)
Adenosina Trifosfato/farmacología , Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio/fisiología , Células Cromafines/efectos de los fármacos , Exocitosis/efectos de los fármacos , Algoritmos , Animales , Canales de Calcio/efectos de los fármacos , Canales de Calcio Tipo L/efectos de los fármacos , Canales de Calcio Tipo L/metabolismo , Canales de Calcio Tipo N/efectos de los fármacos , Canales de Calcio Tipo N/metabolismo , Canales de Calcio Tipo P/efectos de los fármacos , Canales de Calcio Tipo P/metabolismo , Catecolaminas/metabolismo , Bovinos , Separación Celular , Estimulación Eléctrica , Electrofisiología , Técnicas In Vitro , CinéticaRESUMEN
The hypotensive activity of ethanolic and aqueous extracts of Pimenta dioica and several fractions of the aqueous extract was observed in anaesthetized normotensive rats. General effects of the extracts and fractions were assessed through Hippocratic screening showing a central nervous system (CNS) depressant effect. The intravenous (i.v.) administration of the aqueous extract of Pimenta dioica (30, 70, 100 mg/kg) produced a dose-related significant fall in mean arterial blood pressure (MAP). The ED50 was 53.94 mg/kg. The hypotensive effect of identical doses (100 mg/kg) of the aqueous extract (95% decrease) was significantly greater (P < 0.05) than the effect of the ethanolic extract (67% decrease). The final aqueous fraction produced the greatest hypotensive activity compared to the other fractions of the total aqueous extract. There were no significant changes in the heart rate and no abnormalities were observed in the EKG. The mechanisms of action of the extracts have not been determined. Structural elucidation of the compounds responsible for this activity is under investigation.
Asunto(s)
Antihipertensivos/toxicidad , Presión Sanguínea/efectos de los fármacos , Extractos Vegetales/toxicidad , Análisis de Varianza , Animales , Antihipertensivos/administración & dosificación , Antihipertensivos/farmacología , Antihipertensivos/uso terapéutico , Depresores del Sistema Nervioso Central/toxicidad , Relación Dosis-Respuesta a Droga , Electrocardiografía/efectos de los fármacos , Etanol/química , Femenino , Frecuencia Cardíaca/efectos de los fármacos , Inyecciones Intravenosas , Dosificación Letal Mediana , Masculino , Extractos Vegetales/administración & dosificación , Extractos Vegetales/farmacología , Extractos Vegetales/uso terapéutico , Hojas de la Planta/metabolismo , Ratas , Ratas Sprague-Dawley , Agua/químicaRESUMEN
Water and electrolyte transport in turtle urinary bladder closely resembles that present in the mammalian collecting tubule. Although cAMP is known to participate in the control of mucosal transport processes, the GTP-binding inhibitory Gi and stimulatory Gs proteins which link receptors on the cell surface to the adenylate cyclase system remain to be identified in this urinary epithelium. To this end, individual cells harvested from the mucosal surface of the turtle bladder were isolated using a discontinuous density Ficoll gradient. Examination by electron microscopy of the material from the different layers of the Ficoll gradient confirmed that bands II and III contained carbonic anhydrase-rich cells and granular cells, respectively. Identification of Gi and Gs in carbonic anhydrase-rich and granular cells was accomplished using pertussis (PT) and cholera toxins to promote [32P] ADP ribosylation of the proteins. Separation of Gi and Gs from other cell proteins was accomplished using polyacrylamide gel electrophoresis and autoradiography. Pretreatment of cells with 0.2% triton X-100 substantially magnified the ADP-ribosylation of Gi by PT. A doublet form of Gi was present in the 40-kD region and indicated heterogeneity of the PT substrate in granular and carbonic anhydrase-rich cells. Gs was observed as a single polypeptide at the 42-kD region in both cell types. A distinct 45-kD peptide not present in mammalian collecting tubule was identified by both toxins in granular cells and by cholera toxin in carbonic anhydrase-rich cells. In summary, this investigation identified and characterized Gi and Gs proteins in carbonic anhydrase-rich and granular cells from the mucosa of turtle urinary bladder.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Proteínas de Unión al GTP/análisis , Tortugas/metabolismo , Vejiga Urinaria/química , Toxina de Adenilato Ciclasa , Animales , Autorradiografía , Anhidrasas Carbónicas/análisis , Centrifugación por Gradiente de Densidad , Toxina del Cólera/metabolismo , Electroforesis en Gel de Poliacrilamida , Epitelio/química , Epitelio/ultraestructura , Microscopía Electrónica , Peso Molecular , Membrana Mucosa/química , Membrana Mucosa/ultraestructura , Toxina del Pertussis , Poli(ADP-Ribosa) Polimerasas/metabolismo , Vejiga Urinaria/enzimología , Vejiga Urinaria/ultraestructura , Factores de Virulencia de Bordetella/metabolismoRESUMEN
To evaluate the relative importance of the V-type H(+)-ATPase in proximal bicarbonate reabsorption in vivo, proximal tubules of male and female Wistar rats (180 to 260 g) were perfused with bicarbonate-Ringer solution with and without the addition of 2 microM bafilomycin A1. Bafilomycin significantly increased stationary pH from 6.75 +/- 0.05 (N = 39) to 6.86 +/- 0.03 (N = 82), the stationary concentration of bicarbonate from 5.24 +/- 0.62 to 6.33 +/- 0.46 mM and the half-time of acidification from 3.72 +/- 0.22 to 4.65 +/- 0.25 s, and significantly decreased net bicarbonate reabsorption from 3.17 +/- 0.21 to 2.55 +/- 0.15 nmol s-1 cm-2, that is, by 20%. Since bafilomycin is considered to be a specific inhibitor for V-type H(+)-ATPase, these data establish 1) the existence of this type of transport in the rat proximal tubule and 2) that approximately a fifth of the total proximal bicarbonate reabsorption is due to this mechanism of transport.
Asunto(s)
Antibacterianos/farmacología , Bicarbonatos/farmacocinética , Túbulos Renales Proximales/metabolismo , Macrólidos , Absorción , Animales , Transporte Biológico Activo , Electrofisiología , Femenino , Concentración de Iones de Hidrógeno/efectos de los fármacos , Túbulos Renales Proximales/enzimología , Masculino , Potenciales de la Membrana/efectos de los fármacos , Perfusión , ATPasas de Translocación de Protón/antagonistas & inhibidores , ATPasas de Translocación de Protón/metabolismo , Ratas , Ratas WistarRESUMEN
To evaluate the relative importance of the V-type H(+)-ATPase in proximal bicarbonate reabsorption in vivo, proximal tubules of male and female Wistar rats (180 to 260 g) were perfused with bicarbonate-Ringer solution with and without the addition of 2 microM bafilomycin A1. Bafilomycin significantly increased stationary pH from 6.75 +/- 0.05 (N = 39) to 6.86 +/- 0.03 (N = 82), the stationary concentration of bicarbonate from 5.24 +/- 0.62 to 6.33 +/- 0.46 mM and the half-time of acidification from 3.72 +/- 0.22 to 4.65 +/- 0.25 s, and significantly decreased net bicarbonate reabsorption from 3.17 +/- 0.21 to 2.55 +/- 0.15 nmol s-1 cm-2, that is, by 20 per cent . Since bafilomycin is considered to be a specific inhibitor for V-type H(+)-ATPase, these data establish 1) the existence of this type of transport in the rat proximal tubule and 2) that approximately a fifth of the total proximal bicarbonate reabsorption is due to this mechanism of transport
Asunto(s)
Animales , Masculino , Femenino , Ratas , Antibacterianos/farmacología , Bicarbonatos/farmacocinética , Túbulos Renales Proximales/metabolismo , Absorción , Transporte Biológico Activo , Concentración de Iones de Hidrógeno , Electrofisiología , Potenciales de la Membrana/efectos de los fármacos , Perfusión , ATPasas de Translocación de Protón/antagonistas & inhibidores , ATPasas de Translocación de Protón/metabolismo , Ratas Wistar , Túbulos Renales Proximales/enzimologíaRESUMEN
This study systematically evaluates the effect of changes in the acid-base composition of the incubation media on the electrogenic H+ and HCO3- secretion (voltage clamp method and serosal ouabain) in the isolated turtle urinary bladder. Since the various cell types would change their acidity in a similar direction but to a variable degree, measured mean cell pH values (5,5-dimethyl-2,3-oxazolidinedione method) were used for an overall assessment of the changes in the acid-base status of the acid-transporting cells. Although addition of exogenous CO2 (0.7-3%) increased H+ secretion (JH+) 2- to 4-fold from a CO2-free control period, a further increase in the percent of CO2 did not enhance JH+ demonstrating a permissive but not a stimulatory role of CO2. Cyclic AMP plus 3-isobutyl-1-methylxanthine-induced electrogenic HCO3 secretion (JHCO3-) remained unaltered at 10% CO2 from a 5% CO2 control period. Cell acidosis resulting from either alterations in the PCO2/HCO3- levels or from NH4Cl in the bathing solution did not enhance JH+; by contrast maximal levels of acidification were found at cell pH values of about 7.40 and comparable effects on JH+ were found with a variety of PCO2/HCO3- combinations that led to a similar intracellular acidity.