Role of endogenous platelet-activating factor in caerulein-induced acute pancreatitis in rats: Protective effects of a PAF-antagonist

The role of endogenous platelet-activating factor (PAF) in the pathogenesis of acute pancreatitis was investigated by determining whether CV-6209, a selective PAF antagonist, confers protection against caerulein-induced acute pancreatitis in rats. Continuous intravenous infusion of caerulein (5 micrograms/kg x h) induced time-dependent increase in serum pancreatic enzymes, pancreatic weight, and protein content of the pancreas, and produced histologic evidence of acute pancreatitis. Pretreatment with CV-6209 (1 mg/kg) significantly inhibited the elevation of serum pancreatic enzymes, pancreatic weight, and protein content of the pancreas. Caerulein-induced tissue oedema and recruitment of leucocytic cells were markedly ameliorated with CV-6209. Platelet-activating factor may be released endogenously and may play a role during acute pancreatitis.     

Contribution of platelet activating factor to hemodynamic and sympathetic responses to bacterial endotoxin in conscious rats

The effect of the platelet activating factor (PAF) antagonist WEB 2086 on blood pressure; heart rate; and plasma glucose, lactate, and catecholamine concentrations were examined following either PAF or endotoxin administration in conscious rats. PAF infusion (50 ng/kg/min for 60 min) resulted in a sustained hypotension, with tachycardia and elevated plasma norepinephrine (NE; 1.8-fold increase), epinephrine (E; 6.7-fold increase), and dopamine (DA; 1.0-fold increase) at 30 min after beginning infusion. Plasma NE, E, and DA became 4.1 (NE)-, 17.4 (E)-, and 3.3 (DA)-fold higher than control at 60 min after beginning infusion. Both the hemodynamic and plasma catecholamine alterations induced with PAF were completely blocked with WEB 2086 pretreatment. Bacterial endotoxin treatment (5 mg/kg, i.v. bolus) produced well-characterized responses of hypotension, tachycardia, hyperglycemia, hyperlactacidemia, and an elevation in plasma catecholamines. Whereas complete blockade of the hypotensive and tachycardic effect of endotoxin was achieved with WEB 2086 at 30 min following endotoxin, the increases in plasma catecholamines and lactate elicited by endotoxin were attenuated but remained significantly higher than control levels. Hyperglycemia following endotoxin was not altered by WEB 2086 treatment. In endotoxic rats pretreated with WEB 2086 there was significant hypotension, tachycardia, and hyperlactacidemia and an elevation in plasma catecholamines at both 60 and 120 min, but all were less severe compared to non-WEB 2086-treated endotoxic animals. The results demonstrate that WEB 2086 completely blocked early endotoxin-induced hypotension and tachycardia but not catecholamine elevation following endotoxin. This work suggests that sympathetic activation following endotoxin may be mediated by factors other than hypotension.     

Effect of LTB4 receptor antagonists in endotoxic shock in the rat.

This study examined 1) the effects of infusion of LTB4 and 2) the potential role of LTB4 in the sequelae to endotoxic shock in the rat. Control rats were anesthetized with Ketamine/xylazine and given LTB4 (2 micrograms/kg) bolus i.v. followed by a 1 microgram/kg/min infusion for 10 min. LTB4 induced systemic hypotension and a three-fold increase in circulating band neutrophils which contributed to a 70% increase (P less than 0.05) in the total peripheral neutrophil count. LTB4 did not cause changes in circulating mature (segmented) neutrophils, lymphocytes, platelets, or hematocrits. Pretreatment (1 min) with LY233978, an LTB4 antagonist (10 mg/kg bolus i.v.), inhibited LTB4-induced systemic hypotension (-16.1 +/- 6.1 mmHg [n = 3] vs. -38.8 +/- 5.9 mmHg [n = 4], P less than 0.05). Salmonella enteritidis endotoxin (10 mg/kg bolus i.v.) induced systemic hypotension, hemoconcentration, leukopenia, and thrombocytopenia, which was greatest at 5 and 15 min postendotoxin. The leukopenia was characterized by lymphopenia, band neutropenia, and segmented neutropenia. LY233978 (10 mg/kg bolus i.v. immediately before endotoxin administration and followed by an infusion at 0.67 mg/kg/min for 90 min) attenuated endotoxin-induced hemoconcentration at 60 and 90 min postendotoxin (P less than 0.05), and systemic hypotension at 15 min postendotoxin (P less than 0.05). The LTB4-receptor antagonist LY255283 (10 mg/kg bolus i.v., 10 min before endotoxin followed by a 5 mg/kg bolus i.v. 30 min postendotoxin) completely inhibited endotoxin-induced systemic hypotension and partially attenuated endotoxin-induced hemoconcentration from 15 min to 90 min postendotoxin (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiovascular improvement due to RA642, a pyrimido-pyrimidine derivative, in canine endotoxin shock

The cardiovascular effects of a pyrimido-pyrimidine derivative, RA642, were studied during endotoxin shock in pentobarbital-anesthetized dogs. In the control group, 30 min after intravenous administration of Escherichia coli endotoxin (1 mg/kg) mean blood pressure (MBP) and cardiac output (CO) fell significantly from 125 +/- 8 mmHg (mean +/- SE) to 65 +/- 8 mmHg and from 1.57 +/- 0.17 liter/min to 0.84 +/- 0.13 liter/min, respectively. Left ventricular (LV)dP/dtmax, renal blood flow (RBF), heart rate (HR), and central venous pressure (CVP) were also reduced significantly after endotoxin administration. Following the injection of vehicle 30 min after the endotoxin, all cardiovascular parameters in the control group remained decreased. A rapid significant rise in portal venous pressure (PoP) occurred and was maintained until the end of the experiment. Endotoxin caused an initial transient rise of total peripheral resistance (TPR) followed by a prolonged decrease. In the treated group, RA642 (0.25 mg/kg, IV), injected 30 min after the endotoxin, produced significant increases in MBP (from 62 +/- 6 mmHg to 93 +/- 7 mmHg), CO (from 0.92 +/- 0.111 liter/min to 1.28 +/- 0.18 liter/min), LVdP/dtmax (from 1600 +/- 100 mmHg/sec to 2100 +/- 300 mmHg/sec), and RBF (from 46 +/- 10 ml/min to 61 +/- 11 ml/min) within 15 min. There was a gradual return toward the pretreatment levels in each parameter 30 min after the endotoxin. The values of each parameter in the treated group were maintained significantly higher than those in the control group until the end of the experiment (90 min after the treatment). RA642 caused a rapid return of the reduced HR and the elevated PoP to the preendotoxin level. CVP recovered somewhat, though insignificantly, toward the preendotoxic value by the treatment. Following treatment, TPR was maintained at the pretreatment level. The results of this study provide evidence that RA642 exerts beneficial cardiovascular actions in endotoxin shock, restoring blood flow to vital organs without jeopardizing normal perfusion pressure and without increasing heart rate.     

Role of endogenous platelet-activating factor in the regulation of pancreatic blood flow during caerulein stimulation

The role of endogenous platelet-activating factor (PAF) in the control of pancreatic blood flow during caerulein stimulation was investigated. Pancreatic blood flow in anesthetized rats was measured continuously by laser Doppler flowmetry for 2h during the intravenous infusion of caerulein (0.25 μg/kg per h). Pancreatic blood flow showed a gradual, consistent, and significant increase, reaching 114.2±2.3% of the basal value after 120 min. Changes in pancreatic blood flow induced by caerulein were completely inhibited by a cholecystokinin (CCK) antagonist (loxiglumide, 5 mg/kg per h, i.v.) and by a specific PAF antagonist (CV-6209, 1 mg/kg, i.v.-bolus). Systemic blood pressure remained stable in all groups. These results suggest an important role of endogenously yielded PAF in regulating pancreatic blood flow during caerulein stimulation to the pancreas.     

Evidence for a role of platelet activating factor in the pathogenesis of irreversible but not reversible myocardial injury after reperfusion in dogs

The role of platelet activating factor (PAF) in myocardial injury after either brief (15 minutes, stunned myocardium) or prolonged (90 minutes, infarcted myocardium) coronary artery occlusion and 3 hours of reperfusion of the left anterior descending coronary artery was investigated in barbital-anesthetized dogs. Regional myocardial blood flow was measured by radioactive microspheres, regional segment shortening by sonomicrometry, and infarct size by the triphenyltetrazolium chloride stain. Infarct size expressed as a percentage of the area at risk was significantly reduced by the intravenous administration of two structurally unrelated PAF antagonists, BN 52021 (10 mg/kg and 1 mg/kg/hr) and CV-3988 (3 mg/kg and 0.3 mg/kg/hr). Infarct size was 38% +/- 5% in the saline (control) group, (n = 7), 22% +/- 5% in the BN 52021 group (n = 7), and 19% +/- 5% in the CV-3988 group (n = 8). However, the intravenous administration of BN 52021 (5 and 10 mg/kg) and CV-3988 (5 mg/kg) had no effect on functional recovery (regional segment shortening) in the stunned myocardium after brief occlusion and reperfusion. Regional myocardial blood flow, hemodynamic data, and the incidence of cardiac arrhythmias were not significantly affected by PAF antagonists in both series of experiments at any time. These data suggest that PAF may play an important role in the pathogenesis of an evolving myocardial infarction that follows a prolonged coronary artery occlusion and reperfusion. Furthermore, PAF antagonists may have a beneficial role in reduction of the injury produced during an acute infarction. Finally, these data indicate that PAF does not appear to be an important mediator of myocardial stunning.     

Role of platelet-activating factor in pulmonary edema after coronary ligation in dogs.

To evaluate whether PAF is related to the precipitation of pulmonary edema after myocardial ischemia, we studied the effect of a specific PAF antagonist, CV-6209, on the extravascular lung water level measured by the thermal-dye double indicator dilution method, ETV, after coronary ligation in dogs. Eight dogs served as sham control animals (group 1). The proximal left anterior descending coronary artery was ligated for 45 min in eight dogs (group 2), and the coronary artery was ligated after pretreatment with CV-6209 (1 mg/kg) in eight dogs (group 3). The ETV increased significantly after coronary ligation in groups 2 and 3. The amount of increase in ETV in group 2 was significantly larger than in group 3. Thus, CV-6209 can prevent the accumulation of extravascular lung water after coronary ligation without producing changes in pulmonary vascular dynamics, indicating that PAF may play an important role in pulmonary edema after myocardial ischemia.     

Comparative hemodynamics and cardiovascular effects of endotoxin and platelet-activating factor in rat

We have compared the cardiovascular effect of endotoxin with platelet-activating factor (PAF) in rats. Endotoxin injected into perfusate of isolated rat heart did not induce significant changes in heart function, whereas PAF induced elevation of coronary perfusion pressure (CPP), decrease in ventricular pressure (VP), decrease in coronary flow (CF), but no significant changes in heart rate (HR). Neither endotoxin nor PAF caused contraction or relaxation of isolated rat arteries. However, endotoxin in the presence of macrophages caused contractions of rat aortic strips. These contractions were potentiated when platelets were present in the macrophage preparation. PAF in the presence of platelets caused profound contraction of the aortic strips, and this action of PAF was entirely blocked by either PAF antagonists or thromboxane antagonists. Injection of endotoxin into rats (i.v.) caused a decrease in blood pressure (BP) without significantly affecting the HR. At higher concentrations (greater than or equal to 10 mg/kg), endotoxin caused ventricular tachycardia (VT) associated with ventricular fibrillation (VF). PAF in vivo caused a rapid and sustained decrease in BP, with an ED50 of 3 micrograms/kg. PAF antagonists significantly prevented overall mortality induced by PAF and short-term endotoxin-induced mortality, but not the long-term (week) mortality. Endotoxin (10 mg/kg) injected into rats caused the release of PAF into the circulation, reaching a maximum after 2-5 min. Tritiated PAF injected into rats i.v. was metabolized over 60 min into lyso-PAF (approximately 30%), acyl-PAF (approximately 10%), and some degraded products (approximately 10%), and the remainder was found in the form of PAF. The results of the present study suggest that PAF may play a significant role in the pathogenesis of endotoxin shock. The action of PAF requires the participation of cells such as platelets, macrophages, neutrophils, and monocytes and involvement of arachidonic acid metabolites.     

Effects of recombinant human superoxide dismutase on increased lung vascular permeability and respiratory disorder in endotoxemic rats

A 4 hr intravenous infusion of Escherichia coli endotoxin in a total dose of 100 mg/kg produced significant morphological and functional pulmonary alterations in pentobarbitone anesthetized rats. Lung vascular permeability index was increased from 2.11 +/- 0.34 in normal rats to 4.82 +/- 0.65 in untreated endotoxemic rats. Treatment of endotoxemic rats with recombinant human superoxide dismutase (r-HSOD) in doses of 0.1, 0.215, and 0.464 mg/kg.min i.v., infused concomitantly with endotoxin, dose-dependently reduced the permeability index to 3.28 +/- 0.96, 2.83 +/- 0.55 (P less than 0.05), and 2.16 +/- 0.65 (P less than 0.05). The wet lung weight was 523 +/- 15 and 664 +/- 46 mg/100 g bwt in normal and in untreated endotoxemic rats, respectively. r-HSOD dose-dependently inhibited the endotoxin-induced increase in wet lung weight to 617 +/- 40, 577 +/- 31, and 559 +/- 39 (P less than 0.05) mg/100 g bwt. r-HSOD (0.464 mg/kg.min) did not affect permeability index and wet lung weight in normal, nonintoxicated rats. Endotoxin infusion produced a significant increase in respiratory rate (max. +69%) and blood gas alterations, indicating a hyperventilatory hypocapnia in endotoxemic control rats. Infusion of r-HSOD (0.464 mg/kg.min) significantly inhibited the endotoxin-induced tachypnoe (max. +13%) and blunted the alterations in arterial hydrogen carbonate content and carbon dioxide tension. In conclusion, infusion of r-HSOD dose-dependently and significantly inhibited pulmonary edema formation and hyperventilatory dyspnoe in endotoxemic rats.     

Portal hypotensive effects of combined terlipressin and DL-028, a synthetic alpha 1 adrenoceptor antagonist administration on anesthetized portal hypertensive rats

AIMS/BACKGROUND: The purpose of this study was to investigate the therapeutic effects of terlipressin, alone or in combination with DL-028, a synthetic alpha 1-adrenoceptor antagonist on anesthetized portal hypertensive rats. METHODS: Portal hypertension was induced by either partial portal vein ligation (PVL) or bile duct ligation (BDL) in Sprague-Dawley rats. Each portal hypertensive rat received only one of the two regimens: vehicle plus terlipressin or DL-028 plus terlipressin. Terlipressin dosage was 0.017 mg/kg/min infused for 3 min, while vehicle or DL-028 (0.50 microgram/kg/min) was continuously infused for 40 min, starting 10 min before terlipressin infusion. RESULTS: In PVL rats, infusions of vehicle plus terlipressin induced significant, maximum reduction of portal venous pressure (PVP, -11.0 +/- 1.8%) and prominent elevation of mean arterial pressure (MAP, 50.3 +/- 9.0%) from baseline. Infusions of DL-028 plus terlipressin induced maximum PVP reduction (-17.5 +/- 2.8%) and MAP elevation (39.8 +/- 7.4%). In BDL rats, infusion of vehicle plus terlipressin also induced significant, maximum reduction of PVP (-6.8 +/- 2.1%) and prominent elevation of MAP (61.4 +/- 7.8%) from baseline. Infusions of DL-028 plus terlipressin induced maximum PVP reduction (-17.9 +/- 2.2%) and MAP elevation (47.9 +/- 7.4%). Compared to vehicle plus terlipressin, DL-028 significantly enhanced portal hypotensive effects of and attenuated systemic pressor effects of terlipressin in both PVL and BDL rats. CONCLUSIONS: Our results suggest that terlipressin, alone or in combination with DL-028, induced portal hypotensive effects in portal hypertensive rats. The combination of terlipressin with DL-028 was beneficial in enhancing the portal hypotensive effects and ameliorating the systemic pressor effects of terlipressin.     

Role of nitric oxide in endotoxin-induced hepatic microvascular dysfunction in rats chronically fed ethanol

BACKGROUND: Nitric oxide (NO) appears to be involved in the pathogenesis of endotoxin-induced liver injury. However, little is known about how NO acts on the hepatic microcirculation, especially in alcohol-fed animals. We examined the roles of NO in endotoxin-induced hepatic microvascular dysfunction in control and ethanol-fed rats. METHODS: One lobe of the liver was observed with an intravital microscope. Flow velocity of fluorescein isothiocyanate-labeled erythrocytes in sinusoids was measured with an off-line velocimeter. Portal pressure and mean arterial pressure also were measured. RESULTS: After administration of endotoxin to control, the flow velocity decreased after 30 min. Portal pressure increased after 45 min. However, in ethanol-fed rats, both the flow velocity and portal pressure temporarily increased in the early phase. Thereafter, the flow velocity decreased and portal pressure increased. At 30 min after administration of the endotoxin, pretreatment with 10 mg/kg of an NO synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA), enhanced the endotoxin-induced decrease in the velocity of erythrocytes in the midzonal region of both control and ethanol-fed rats. Although 0.5 mg/kg of L-NMMA enhanced the endotoxin-induced reduction of erythrocyte velocity in the midzonal region of ethanol-fed rats, L-NMMA enhanced the endotoxin-induced reduction of erythrocyte velocity in the pericentral region of control rats. At 60 min after the endotoxin administration, L-NMMA did not affect the endotoxin-induced decrease of erythrocyte velocity in either control or ethanol-fed rats. Although 10 mg/kg of L-NMMA increased mean arterial pressure both in control and ethanol-fed rats, 0.5 mg/kg of L-NMMA did not change mean arterial pressure in either control or ethanol-fed rats. CONCLUSIONS: These results suggest that NO is involved in endotoxin-induced hepatic microvascular dysfunction, which may contribute to the sequential liver injury, especially in alcohol-fed animals.     

Effect of platelet-activating factor antagonist and leukotriene antagonist on endotoxin shock in the rat: role of the leukocyte.

The effects of platelet-activating factor (PAF) antagonist (CV-3988) and leukotrienes (LTs) antagonist (ONO-1078) on endotoxin-induced sequelae in the rat were assessed. Pretreatment with either CV-3988 (6 mg/kg, i.v.) or ONO-1078 (150 mg/kg, p.o.) did not improve survival rate following the administration of Escherichia coli lipopolysaccharide (LPS) compared with that of control rats pretreated with solvents of the drugs. Rats pretreated with both CV-3988 and ONO-1078 exhibited significantly (P less than 0.01) enhanced survival following lipopolysaccharide (LPS) administration. Percentage survivals 48 hr after the administration of LPS were 20%, 32%, 24%, and 68% in the pretreatment with solvents, CV-3988, ONO-1078, and CV-3988 combined with ONO-1078 groups, respectively. Pretreatment with CV-3988 combined with ONO-1078 inhibited the change of plasma transaminase 3 hr after LPS administration. The neutropenia, due to the administration of vinblastine (1 mg/kg, i.v.), increased the survival rate following the administration of LPS without pretreatment with PAF and LT antagonists. Antishock action of CV-3988 and ONO-1078 could not be seen in neutropenic rats. These data suggest that combined pretreatment with PAF antagonist and LT antagonist inhibited leukocyte-mediated tissue injury in LPS-induced endotoxemia.     

A New Platelet-Activating Factor Antagonist (CV-6209) in Preservation of Heart and Lung for Transplantation

The objective of this experimental protocol was to evaluate theprotective effect of a new, potent platelet-activating factor (PAF)antagonist CV-6209 and the use of this compound in combination withallopurinol on ischemia-reperfusion injury in a swine model of heart-lungtransplantation. Forty-two swine were divided into three groups, with sevendonors and seven recipients in each. In group A, the PAF antagonist CV-6209was administered in a single dosage of 1 mg/kg by slow intravenousinjection at 1 hour before crossclamping of the aorta in both donors andrecipients. In group B the combination of allopurinol and the PAFantagonist CV-6209 was used. Allopurinol was administered as a pretreatmentregime of 50 mg/kg/day for 3 days prior to ischemia. The PAFantagonist dosage and regime of administration were the same as in group A,and both donors and recipients were pretreated with this combination. GroupC was the control in which heart-lung transplantations were performedwithout interventional therapies. Based on the comparison of pre- andpost-transplantation assessments of cardiac and pulmonary functionalintegrity within groups, and post-transplantation among groups, animals ingroups A and B were significantly (P < 0.05) better protected fromischemia-reperfusion injury than animals in group C. The difference betweengroups A and B, however, was insignificant at all times. Morphologicalfindings are in agreement with measures of physiological variation amongexperimental groups. It is suggested that the new PAF antagonist CV-6209 iseffective in the prevention of heart and lung ischemia-reperfusion injurywith and without allopurinol pretreatment.     

Protective effect of platelet-activating factor antagonist on hepatic energy metabolism following transient hepatic inflow occlusion in rabbits.

To investigate whether or not platelet-activating factor (PAF) is a mediator of the liver injury resulting from transient hepatic inflow occlusion (Pringle's maneuver), the effect of pretreatment with a potent PAF antagonist (CV6209) on hepatic energy metabolism was evaluated following 30 min of inflow occlusion in rabbits. At 60 min after declamping, the arterial ketone body ratio (AKBR; acetoacetate/3-hydroxybutyrate), reflecting hepatic mitochondrial redox state (NAD+/NADH), increased to 1.10 +/- 0.05 (mean +/- SEM) in the CV6209 (5 mg/kg)-pretreated group (group 1, n = 5) compared with 0.72 +/- 0.06 (P less than 0.01) in the untreated group (group 2, n = 5). Hepatic energy charge at 60 min after declamping was significantly higher in group 1 than in group 2 (0.871 +/- 0.010 vs. 0.800 +/- 0.023; P less than 0.05). Pretreatment with CV6209 had no significant influence on these parameters in sham-operated animals. The present study demonstrates that pretreatment with CV6209 has a protective effect against the impairment of hepatic energy metabolism following transient hepatic inflow occlusion.     

Priming by platelet-activating factor of endotoxin-induced lung injury and cardiovascular shock.

Platelet-activating factor (PAF) is a glycerophospholipid known for its unusual potent vasoactive and proinflammatory activities. The present study examined whether PAF might serve as a priming factor in endotoxin-induced tumor necrosis factor-alpha (TNF alpha) synthesis, cardiovascular shock, and lung injury in anesthetized rats. Intravenous infusion of PAF (1 pmol/kg/min for 60 minutes, n = 5) alone or endotoxin (0.1 micrograms/kg i.v. bolus, n = 5) failed to alter blood pressure, serum TNF alpha and thromboxane B2, platelet and leukocyte count, and hematocrit, nor was lung histology, myeloperoxidase activity, and water content changed. In contrast, the combined administration of PAF and endotoxin markedly elevated serum TNF alpha (1,359 +/- 362 pg/ml, n = 5, p less than 0.01) and thromboxane B2 (43 +/- 5 pg/100 microliters, n = 8, p less than 0.01) along with hypotension, hemoconcentration, leukopenia, and thrombocytopenia. Most notably, the combined regimen caused neutrophil aggregation, adhesion, and accumulation into the lung parenchyma along with platelet-fibrin deposits in postcapillary venules, pulmonary edema, and increased lung myeloperoxidase activity. The role of PAF in this process was confirmed by 1) the prevention of the priming effect by pretreatment with the PAF antagonist BN 50739 (n = 5), and 2) the failure of lyso-PAF, the cardinal nonactive PAF-metabolite, to prime for endotoxin-induced production of TNF alpha (n = 4). These data suggest that PAF could serve as a key mediator in priming for endotoxin-induced tissue injury, especially the typical pulmonary pathophysiology of adult respiratory distress syndrome, a severe pathological outcome of septic shock, burns, and multiple organ injury.     

Hypotension- and endotoxin-induced alterations in calcitonin gene-related peptide: modulation by dexamethasone

Plasma levels of calcitonin gene-related peptide (CGRP) were studied in anesthetized rats during and after recovery from hemorrhagic hypotension as well as following administration of bacterial endotoxin. Hypotension of 35-40 mmHg maintained for 2 hr resulted in significant (P less than .05) elevation of plasma CGRP levels. Plasma levels at 120 min of hypotension were 49.5 +/- 5.9 pg/ml, over 4-fold above average control levels (11.1 +/- 1.1 pg/ml). Plasma CGRP levels at 90 min of hypotension (20.2 +/- 2.4 pg/ml) or before were not more than 2.5-fold above control levels. Ninety minutes after the return of shed blood in the 30 min group, blood pressure (83 +/- 3 mmHg) and CGRP (17.2 +/- 2.2 pg/ml) were not different from saline controls (88 +/- 3 mmHg and 15.1 +/- 1.7 pg/ml CGRP). However, if hypotension was maintained for 120 min before the return of shed blood, blood pressure following 90 min recovery was significantly lower (59 +/- 5 mmHg) and CGRP levels significantly higher (39.2 +/- 5.6 pg/ml) than saline control values (82 +/- 5 mmHg and 19.5 +/- 2.7 pg/ml). Dexamethasone treatment of the 120 min hypotension group when shed blood was returned resulted in CGRP values not different from saline treated, but hypotension persisted. Administration of bacterial endotoxin (16.7 mg/kg) to anesthetized rats caused significant elevations (P less than .05 vs. saline treatment at 3 hr) in plasma CGRP levels from aorta (82.2 +/- 5.0 pg/ml), vena cava (79.4 +/- 12.9), and portal vein (117.7 +/- 29 pg/ml) compared to levels in saline-treated control rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endotoxin-induced ascites formation in the rat: partial mediation by platelet-activating factor

Systemic endotoxemia has been observed in patients with acute and chronic liver failure, and bacterial endotoxin is known to increase vascular permeability. We investigated in the normal rat the effects of intraportal endotoxin administration and the possible mediation of these effects by platelet-activating factor. Injection of endotoxin lipopolysaccharide (10 and 25 mg per kg) in the rat resulted in rapid ascites formation, as well as systemic hypotension, hemoconcentration and acute erosions of the gastrointestinal mucosa. These effects were significantly attenuated by pretreatment with L652,731 and CF-3988, specific platelet-activating factor antagonists. Administration of 25 mg per kg endotoxin also resulted in significant elevations of platelet-activating factor biosynthesis in vitro by samples of duodenum, liver and lung. The effects of endotoxin were mimicked by intraportal infusion of platelet-activating factor (50 ng per kg per min), which induced ascites and gastrointestinal lesions. Platelet-activating factor reduced circulating plasma volume and increased peritoneal permeability to albumin as assessed by the ascites to plasma ratio of labeled albumin. These results, therefore, support a role for platelet-activating factor in mediating endotoxin-induced ascites and gastrointestinal erosions.     

Attenuation of endotoxin-induced increase in glucose metabolism by platelet-activating factor antagonist

Platelet-activating factor (PAF) has recently been proposed as a putative mediator of various pathophysiologic events during endotoxemia. The aim of the present study was to determine the relative importance of PAF in producing the alterations in carbohydrate metabolism following endotoxin. Chronically catheterized conscious rats were treated with SRI 63-441, a specific PAF receptor antagonist, or saline prior to Escherichia coli endotoxin (100 micrograms/100 g body weight, LD10) administration. Hemodynamic and whole-body glucose kinetic changes, the latter assessed by a constant intravenous infusion of [6-3H] glucose, were determined throughout the 4-hr experimental protocol. Endotoxin induced a transient 30-35% reduction in mean arterial blood pressure (MABP) in animals treated with saline. The PAF-antagonist attenuated this hypotensive effect, and MABP was only reduced by 14-18%. Endotoxin increased plasma glucose and lactate levels, as well as the rate of glucose appearance (Ra) in saline-treated rats. The PAF antagonist reduced the hyperglycemia by 60-75% and tended to prevent the hyperlactacidemia. The endotoxin-induced elevation in glucose Ra was also attenuated by 55%. A similar degree of hyperglucagonemia was observed following endotoxin in both groups, and plasma insulin concentrations were not different. However, plasma catecholamine levels were significantly lower (30-70%) in endotoxemic rats treated with the PAF antagonist. These results suggest that the enhanced production of PAF following endotoxin may be responsible, at least in part, for the early hemodynamic changes. The role of PAF as a mediator of endotoxin-induced glucose dyshomeostasis, however, may be secondary to its hemodynamic effects.     

Biological responses to liposome-encapsulated hemoglobin (LEH) are improved by a PAF antagonist

Liposome-encapsulated hemoglobin (LEH) is an experimental oxygen-carrying blood substitute. Previous studies in our laboratory with hydrogenated soy lecithin-based LEH indicated that while this solution maintained some physicochemical and oxygen-carrying properties of red blood cells, it evoked several transient (30-120 min) untoward biological responses, such as hypertension, tachycardia, thrombocytopenia, hemoconcentration, and elevation of plasma thromboxane B2 (TXB2). Such biochemical, hematological, and hemodynamic derangements are also produced by platelet-activating factor (PAF). The purpose of this study was to test the biological responses to administration of a newly produced synthetic distearoyl phosphatidylcholine-based LEH (s-DSPC-LEH) in the normal conscious rat (n = 6-11) and to examine the role of PAF in these processes. Systemic (IV) administration of S-DSPC-LEH caused transient hypotension (-23 +/- 8 mmHg, P less than 0.05), bradycardia (-24 +/- 11 bpm, P less than 0.05) followed by tachycardia (+62 +/- 21 bpm, P less than 0.05), decreased cardiac index (217 +/- 21 ml/min/kg, P less than 0.01), increased peripheral resistance (0.570 +/- 0.003 mmHg/ml/min/kg, P less than 0.01), transient leukocytosis (+6,870 +/- 1,801/microliters, P less than 0.05), hemoconcentration (+5.2 +/- 0.4%, P less than 0.01), thrombocytopenia (-160 +/- 18 X 10(3)/microliters, P less than 0.01), and increase in plasma TXB2 (45.0 +/- 1.9 pg/100 microliters, P less than 0.01). Separate infusion of the liposome vehicle or free hemoglobin, the two components of s-DSPC-LEH, did not evoke any consistent responses. Administration of the PAF antagonist BN 50739 (10 mg/kg, i.p.) 30 min prior to LEH prevented the hemodynamic changes and hemoconcentration induced by s-DSPC-LEH. These data suggest that hemoglobin/phospholipid interactions might account for the transient side effects of s-DSPC-LEH, possibly through interactions with blood elements and the resultant production of PAF and TXA2. Furthermore, PAF antagonists incorporated into or co-administered with LEH might enhance its biological applications.     

Effects of a competitive antagonist of bradykinin on blood pressure and renal blood flow in anesthetized rats

To examine a possible role of endogenous bradykinin in the regulation of blood pressure (BP) and renal blood flow (RBF), a newly synthesized competitive antagonist of bradykinin (B4147) was studied in anesthetized rats. Also, the question of whether the hypotensive effect of the converting enzyme inhibitor, captopril, is mediated partly by an accumulation of endogenous bradykinin was considered. The intravenous infusion of B4147 (25 micrograms/min) inhibited the depressor effect of exogenous bradykinin (0.5 microgram, i.v.) by 69%. After an intravenous injection of B4147 at doses of 25, 50 and 100 micrograms, BP increased and RBF decreased in a dose-dependent fashion. The increase in BP was not blocked by pretreatment with an angiotensin II antagonist (1-Sar-8-Ile angiotensin II; 20 micrograms/kg per min) or an alpha 1-blocker (prazosin; 0.1 mg/kg). The administration of captopril (1 mg/kg) decreased mean BP from 110 +/- 3.5 to 71 +/- 1.9 mmHg (P less than 0.001). However, the injection of B4147 (50 micrograms) after the administration of captopril elicited an increase in BP of 43% of the initial decrease induced by captopril. These results suggest that the effects of B4147 on BP and RBF are not mediated through angiotensin II or sympathetic alpha 1-stimulation. Endogenous bradykinin could contribute to the maintenance of BP and RBF in anesthetized rats, probably counter-balancing the vasoconstrictor mechanisms. It is also suggested that bradykinin may partly participate in the acute hypotensive effect induced by the converting enzyme inhibitor captopril.