RESUMO
Endogenous opioids are known to mediate some of the cardiovascular sequelae of sepsis. Inhibition of adrenergic action has been implicated as a physiological path by which endogenous opioids cause deleterious changes in cardiovascular function during endotoxin shock, but where and to what extent this accounts for changes in regional vascular resistance remains unclear. In this study, we addressed this question by examining the role of alpha-adrenergic actions in cardiovascular performance and the regional perfusion changes caused by naloxone during endotoxin shock. Rats had catheters inserted into the tail artery, left cardiac ventricle, and jugular vein. Twenty-four hours later, rats received saline or endotoxin (2 mg/kg) challenge intravenously over 30 min, followed at 40 min by intravenous naloxone (or saline) treatment (4 mg/kg + 2 mg/kg x h) in the presence or absence of phentolamine (100 micrograms/kg + 600 micrograms/kg x h) or yohimbine (40 micrograms/kg + 4 micrograms/kg x h). Radiolabeled microspheres were used to determine cardiac outputs and blood flows at 0, 30, 60, and 120 min after beginning endotoxin infusion. Naloxone attenuated the endotoxin-induced decline in mean arterial pressure (MAP) and cardiac output (CO), but had no effect on increased systemic vascular resistance (SVR). Phentolamine blocked naloxone's ability to increase MAP and CO, but permitted an increase in SVR by naloxone. In the presence of yohimbine, naloxone still increased MAP, but not CO nor SVR. Regional vascular responses varied, with naloxone demonstrating a vasoconstrictive effect despite alpha-adrenergic receptor blockade in some beds, and no effect in others. The response of individual organs in the hepatosplanchnic circulation was heterogenous as well. These data suggest that some effects of endogenous opioids during endotoxin shock are mediated via inhibition of alpha-adrenergic effects, but that some cardiovascular effects of endogenous opioids are independent of adrenergic control during endotoxin shock.
Assuntos
Antagonistas Adrenérgicos alfa/farmacologia , Naloxona/uso terapêutico , Antagonistas de Entorpecentes/uso terapêutico , Fentolamina/farmacologia , Choque Séptico/fisiopatologia , Ioimbina/farmacologia , Animais , Velocidade do Fluxo Sanguíneo/efeitos dos fármacos , Pressão Sanguínea/efeitos dos fármacos , Débito Cardíaco/efeitos dos fármacos , Endotoxinas/farmacologia , Hemodinâmica/efeitos dos fármacos , Hipotensão/induzido quimicamente , Masculino , Ratos , Ratos Sprague-Dawley , Resistência Vascular/efeitos dos fármacos , Vasoconstrição/efeitos dos fármacosRESUMO
BACKGROUND: Bile acid exposure produces cellular hypercalcemia in gastric and hepatic cells. It is not known, however, whether this event contributes to cell injury or if it results from passive equilibration of calcium ion concentrations across the membranes of irreversibly damaged cells. This study was performed to determine whether the cellular hypercalcemia produced by bile acid exposure in gastric cells is reversible and to determine whether the source of this hypercalcemia is from intracellular stores of calcium, extracellular sources, or both. METHODS: Cytosolic free calcium concentrations ([Ca]i) were measured in rabbit gastric mucosal cells that had been loaded with the intracellular probe FURA-2. Measurements were performed in suspensions of dispersed cells by using standard spectrofluorometry and in primarily cultured cells by using fluorescence videomicroscopy. Measurements were made before and after exposure to 0.2, 0.5, and 1.0 mmol/L deoxycholic acid (DC). These measurements were made in the presence of 1 mmol/L extracellular calcium and in the absence of any extracellular calcium (0.5 mmol/L EGTA). RESULTS: In experiments with dispersed cells and spectrofluorometry, [Ca]i increased from a pretreatment level of 194 +/- 8 nmol/L to 396 +/- 21 nmol/L within 3 minutes of exposure to 0.2 mmol/L DC. When these cells were washed and resuspended in DC-free medium, [Ca]i] decreased to 180 +/- 5 nmol/L. In experiments with cultured cells and fluorescence videomicroscopy, rapid, reversible hypercalcemia was observed after exposure to 0.5 and 1.0 mmol/L DC. Removal of extracellular calcium from the incubating medium reduced both the magnitude and duration of the observed hypercalcemia. CONCLUSIONS: These data show that the cellular hypercalcemia that accompanies DC-induced injury in gastric cells is a reversible event. The initial increase in [Ca]i appears to come from both intracellular and extracellular sources, although sustained hypercalcemia requires a source of extracellular calcium. As a reversible event, cellular hypercalcemia may be an important pathophysiologic feature of bile acid induced injury of the upper gastrointestinal tract.
Assuntos
Colagogos e Coleréticos/farmacologia , Ácido Desoxicólico/farmacologia , Mucosa Gástrica/citologia , Hipercalcemia/induzido quimicamente , Animais , Cálcio , Células Cultivadas , Espaço Extracelular , Hipercalcemia/patologia , Coelhos , Espectrometria de FluorescênciaRESUMO
Lack of decrease in the level of calcium ions in the cytoplasm after incubation of cell suspension with deoxycholic acid (DC) may be an early sign of cellular damage. The purpose of the study was to find out whether an increase in free calcium level in the cytoplasm preceded other signs of damage and whether calcium channel blockade may inhibit calcium increase in the cytoplasm. The cell suspension from the gastric mucosa in rabbits was incubated with DC in various concentrations. The calcium level was measured by means of spectrofluorimetry after prior incubation with FURA 2/AM. The viability of cells was determined by measuring oxygen consumption and using trypan blue test. Deoxycholic acid in the concentration of 0.2 mM produced an increase in [Ca2+]i from 177 +/- 5 to 285 +/- 24 nM. Incubation of the cell suspension with 0,5 mM DC also produced an abrupt increase in [Ca2+]i from 177 +/- 5 nM to 639 +/- 49 nM. In addition, the studies showed that 0,2 mM DC despite increasing free calcium level in the cytoplasm did not reduce the cell viability. It was revealed on the basis of oxygen consumption and trypan blue test. The studies showed that an increased intracellular [Ca2+]i may be a very early sign of their damage.
Assuntos
Cálcio/metabolismo , Citoplasma/efeitos dos fármacos , Ácido Desoxicólico/farmacologia , Mucosa Gástrica/efeitos dos fármacos , Animais , Citoplasma/metabolismo , Mucosa Gástrica/metabolismo , Homeostase/efeitos dos fármacos , Consumo de Oxigênio/efeitos dos fármacos , Coelhos , Verapamil/farmacologiaRESUMO
Naloxone, an opioid antagonist, has been shown to improve cardiovascular status during endotoxin shock, including splanchnic perfusion. Enhancement of adrenergic action has been implicated as a physiological path by which naloxone effects changes in cardiac function during endotoxin shock, but the mechanism for changes in various splanchnic vascular beds has not been examined. In this study, we examined the role of beta-adrenergic actions in cardiovascular performance and the splanchnic perfusion changes caused by naloxone during endotoxin shock. Rats were instrumented with catheters in the tail artery, left cardiac ventricle, and jugular vein. Twenty-four hours later, rats received saline or endotoxin (2 mg/kg) challenge intravenously over 30 min, followed at 40 min by i.v. naloxone (or saline) treatment (4 mg/kg + 2 mg/kg.hr) in the presence or absence of propranolol (1 mg/kg + 1 mg/kg.hr). Radiolabelled microspheres were used to determine cardiac outputs and blood flows at 0, 30, 60, and 120 min after beginning endotoxin infusion. Blood pressure was not affected by endotoxin challenge, but cardiac output and most organ blood flows fell over time. beta-Adrenergic blockade did not alter this response. Naloxone improved cardiac output and blood flow to the stomach, small intestine, colon, and spleen but not to other splanchnic organs. Naloxone also increased renal and coronary blood flows. The improvements in cardiac output with naloxone were ablated in the presence of propranolol, as were the increases in gastric, colonic, splenic, coronary, and renal blood flows. However, the beneficial effect of naloxone on small bowel blood flow was not diminished by blockage of beta receptors. These results suggest that the effects of opioid antagonism are mediated, in part, by enhancing endogenous beta-adrenergic actions in vivo. Improvements in the splanchnic circulation are selectively altered by naloxone during endotoxin shock, some independent of beta-adrenergic actions. Understanding this phenomenon can lead to the appropriate use of opioid antagonism, should it prove clinically useful in the treatment of septic shock.
Assuntos
Hemodinâmica/efeitos dos fármacos , Naloxona/farmacologia , Receptores Adrenérgicos beta/fisiologia , Choque Séptico/fisiopatologia , Circulação Esplâncnica/efeitos dos fármacos , Animais , Masculino , Perfusão , Ratos , Ratos Sprague-DawleyRESUMO
The potential of adenosine to regulate organ blood flow (ml/min/100 g tissue) in the intact rabbit upper alimentary tract was evaluated using the radioactive microsphere technique. Adenosine (1.0 mumole/kg/min) produced significant, greater than threefold increases in esophageal mucosal blood flow (37 +/- 2 to 127 +/- 47) and threefold increases in antral mucosal (39 +/- 3 to 144 +/- 24) and transmural small intestinal blood flow (duodenum, 60 +/- 13 to 187 +/- 22; jejunum, 42 +/- 3 to 138 +/- 16; ileum, 27 +/- 2 to 80 +/- 22). Inosine did not reproduce these effects. P1-purinergic receptor antagonism with theophylline blocked the effects of adenosine. 5'-(N-Ethylcarboxamido)adenosine, an agonist of A2-subtype, P1-purinergic receptors, increased gastrointestinal organ blood flow similarly to adenosine with nmole/kg/min doses. Similar doses of the A1-subtype agonist, N5-cyclohexyladenosine, were ineffective, but mumole/kg/min doses produced small effects on esophageal mucosa and ileum. Our results indicate that in rabbit alimentary organs, adenosine preferentially increases blood flow to esophageal mucosa, antral mucosa, and small intestine. Its effects are mediated by the A2-subtype of P1-purinergic receptors.
Assuntos
Adenosina/farmacologia , Esôfago/irrigação sanguínea , Mucosa Gástrica/irrigação sanguínea , Intestino Delgado/irrigação sanguínea , Antro Pilórico/irrigação sanguínea , Fluxo Sanguíneo Regional/efeitos dos fármacos , Adenosina/análogos & derivados , Adenosina-5'-(N-etilcarboxamida) , Animais , Duodeno/irrigação sanguínea , Fundo Gástrico/irrigação sanguínea , Íleo/irrigação sanguínea , Inosina/farmacologia , Jejuno/irrigação sanguínea , Mucosa/irrigação sanguínea , Músculo Liso/irrigação sanguínea , Especificidade de Órgãos , Antagonistas de Receptores Purinérgicos P1 , Coelhos , Receptores Purinérgicos P1/fisiologia , Teofilina/farmacologia , Vasodilatadores/farmacologiaRESUMO
Ca2+ entry into the cell may be an early event in the pathophysiology of bile salt-induced gastric mucosal injury. The aim of this study was to characterize the rise in cytosolic free Ca2+ associated with bile salt injury and its association with cell injury and death. Rabbit gastric mucosal cells were preloaded with the Ca2+ indicator fura 2-acetoxymethyl ester (fura 2-AM) for 20 min at 37 degrees C and then exposed to graded concentrations of the bile salt deoxycholate (DC). Cytosolic free Ca2+ concentration ([Ca2+]i) was estimated by spectrofluorometry. The resting [Ca2+]i in gastric cells was 177 +/- 15 nM (n = 6). When cells were subjected to 0.5 mM DC, there was a time-dependent rise in [Ca2+]i. An increase in [Ca2+]i was observed within 2 min, at which time [Ca2+]i rose from 177 +/- 15 to 480 +/- 30 nM. The maximal increase in [Ca2+]i was observed after 20 min of exposure to 0.5 mM DC (639 +/- 49 nM), and [Ca2+]i remained unchanged for at least 2 h. The increase in [Ca2+]i depended on the concentration of DC. The minimum effective dose of DC was 0.2 mM, with which [Ca2+]i was increased by 1.6-fold (from 177 to 285 nM). At 0.5 mM DC also caused a rise in 45Ca2+ influx into the cells and reduced the viability of gastric cells from 96% to 58% at 2 h. The DC-induced rise in cytosolic free Ca2+ depended on the presence of extracellular Ca2+. In the absence of extracellular Ca2+ there was no rise in cytosolic Ca2+ and gastric cells were protected from cell death caused by DC. The DC-induced cell death was reduced from 26% to 10% and from 37% to 16% at 60 and 90 min, respectively, by removal of extracellular Ca2+. The association of DC with gastric cells was not altered by removing extracellular Ca2+. This suggests decreased DC-induced injury in the absence of extracellular Ca2+ is due to the protection from cellular hypercalcemia rather than some other mechanism related to reduced binding and/or association of DC to gastric cells. These experiments show that rising [Ca2+]i appears to be an early pathophysiological event in bile salt-induced cellular injury and that extracellular Ca2+ is critical to produce this effect.
Assuntos
Cálcio/metabolismo , Ácido Desoxicólico/farmacologia , Mucosa Gástrica/efeitos dos fármacos , Animais , Transporte Biológico/efeitos dos fármacos , Sobrevivência Celular/efeitos dos fármacos , Ácido Desoxicólico/metabolismo , Ácido Egtázico/análogos & derivados , Ácido Egtázico/farmacologia , Corantes Fluorescentes , Fura-2/análogos & derivados , Mucosa Gástrica/citologia , Mucosa Gástrica/fisiologia , Membranas Intracelulares/metabolismo , Concentração Osmolar , CoelhosRESUMO
Bowel anastomoses are conventionally performed using a handsewn technique or a stapling device. Each has potential benefits and disadvantages. The most clinically significant complications of the bowel anastomosis are anastomotic leakage and stricture formation. The indices of healing and tissue cohesion were compared dynamically over time in 24 dogs randomized to undergo either a standard two-layer handsewn anastomosis or a stapled anastomosis with the Premium CEEA (United States Surgical Corporation, Norwalk, CT). Animals were sacrificed at 1, 4, 7, and 28 days postoperatively. Each anastomosis was evaluated for anastomotic index, burst pressure, collagen content, and histologic appearance. The anastomotic index was similar on postoperative day (POD) 1, 4, and 7; but on day 28 all handsewn anastomoses had larger diameters than the widest CEEA anastomosis. Burst pressure was higher in handsewn anastomoses at all intervals. Collagen content tended to be higher on POD 7 in the CEEA anastomoses. Histological evaluation showed more complete epithelialization and less inflammation in handsewn anastomoses on POD 28. The higher level of collagen in the CEEA anastomoses on POD 7 may be implicated in the tendency toward stricture formation found with this type of anastomosis. This study demonstrates that the greater speed and ease of the stapled anastomosis is offset by the greater strength, reduced tendency to stricture, and more complete healing of the handsewn anastomosis.