Vascular smooth muscle desensitization in rabbit epigastric and mesenteric arteries during hemorrhagic shock.

The decompensatory phase of hemorrhage (shock) is caused by a poorly defined phenomenon termed vascular hyporeactivity (VHR). VHR may reflect an acute in vivo imbalance in levels of contractile and relaxant stimuli favoring net vascular smooth muscle (VSM) relaxation. Alternatively, VHR may be caused by intrinsic VSM desensitization of contraction resulting from prior exposure to high levels of stimuli that temporarily adjusts cell signaling systems. Net relaxation, but not desensitization, would be expected to resolve rapidly in an artery segment removed from the in vivo shock environment and examined in vitro in a fresh solution. Our aim was to 1) induce shock in rabbits and apply an in vitro mechanical analysis on muscular arteries isolated pre- and postshock to determine whether VHR involves intrinsic VSM desensitization, and 2) identify whether net VSM relaxation induced by nitric oxide and cyclic nucleotide-dependent protein kinase activation in vitro can be sustained for some time after relaxant stimulus washout. The potencies of phenylephrine- and histamine-induced contractions in in vitro epigastric artery removed from rabbits posthemorrhage were decreased by ∼0.3 log units compared with the control contralateral epigastric artery removed prehemorrhage. Moreover, a decrease in KCl-induced tonic, relative to phasic, tension of in vitro mesenteric artery correlated with the degree of shock severity as assessed by rates of lactate and K(+) accumulation. VSM desensitization was also caused by tyramine in vivo and PE in vitro, but not by relaxant agents in vitro. Together, these results support the hypothesis that VHR during hemorrhagic decompensation involves contractile stimulus-induced long-lasting, intrinsic VSM desensitization.

Intravenous perfluorocarbon emulsion increases nitrogen washout after venous gas emboli in rabbits.

Intravenous perfluorocarbon emulsion (IV-PFC) has been shown to provide hemodynamic protection from gas embolism (Venous-VGE or arterial-AGE). The objective of this study was to investigate the mechanism of PFC protection from controlled VGE by quantifying the effects of IV-PFC emulsion on pulmonary elimination of nitrogen (N2). All rabbits received an intravenous pretreatment of PFC emulsion (Oxygent, 2.7 g/kg) or saline, then either a continuous room air infusion (0.25 ml/kg for 10 minutes) or a bolus of air (0.8 ml/kg within 10 seconds) through the femoral vein. Expiratory N2 peaked higher with PFC infusion immediately after air injection. The recovery to baseline of end tidal N2 was faster for PFC-treated animals (40 +/- 4.7 vs. 58 +/- 6.5 minutes). In PFC-treated animals, expired CO2, O2, arterial pressure and central venous pressure returned to baseline faster than the saline group. This study demonstrated that PFC increased pulmonary N2 washout. Correspondingly, PFC treatment better preserved the animals' hemodynamics after VGE injury. The use of IV-PFC promises to be a breakthrough non-recompression therapy for gas embolism in the treatment of Decompression Sickness (DCS) and in surgery.

Role of fatty acids in the recovery of cardiac function during resuscitation from hemorrhagic shock.

This study tested the hypothesis that removal of fatty acids as a fuel source would improve cardiac efficiency at the expense of reduced cardiac contractile function in the isolated working heart after hemorrhage-retransfusion. Non-heparinized male Sprague-Dawley rats were anesthetized with ketamine-xylazine and were hemorrhaged to a mean arterial blood pressure of 40 mmHg for 1 h. Two-thirds volume of shed blood was reinfused together with 0.9% NaCl in a volume equal to 2.3 times the shed blood volume, followed by continuous infusion of 0.9% NaCl at 10 mL/kg per h for 3 h. Hearts were removed and perfused in closed, recirculating working mode for 60 min to measure hydraulic work and cardiac efficiency. Rates of glycolysis and glucose oxidation were assessed with [5-3H/U-14C] glucose (11 mM) in the absence or presence of 0.4 mM palmitate. Compared to baseline measurements, hemorrhage-retransfusion significantly reduced arterial blood glucose (228+/-7 versus 118+/-12 mg/dL) and non-esterified fatty acid concentrations (0.36+/-0.01 versus 0.30+/-0.02 mM), while elevating blood lactate (0.8+/-0.1 versus 2.5+/-0.4 mM). Perfusion of sham hearts with glucose-only did not alter cardiac work compared to shams perfused with glucose plus palmitate. However, shocked hearts perfused with glucose-only demonstrated a significant reduction in cardiac work compared to shocked hearts perfused with glucose plus palmitate and compared to sham hearts perfused with glucose only (P < 0.05, repeated measures ANOVA). Shocked hearts perfused with glucose plus palmitate showed no reduction in cardiac work compared to shams. Shocked hearts perfused with glucose-only had increased glucose oxidation rates compared to shams perfused with glucose plus palmitate. In sham hearts perfused with glucose-only, myocardial glycogen and triacylglycerol contents were significantly reduced compared to hearts freeze-clamped in situ. These endogenous fuels were not decreased in shocked hearts. These data indicate that hemorrhagic shock renders the heart unable to mobilize endogenous fuels, and suggest that withdrawal of fatty acid oxidation will impair myocardial energy metabolism during resuscitation.

Depletion of lactate by dichloroacetate reduces cardiac efficiency after hemorrhagic shock.

We have demonstrated previously that dichloroacetate (DCA) treatment in rodents ameliorates, via activation of the pyruvate dehydrogenase complex, the cardiovascular depression observed after hemorrhagic shock. To explore the mechanism of this effect, we administered DCA in a large animal model of hemorrhagic shock. Mongrel hounds were anesthetized with 1.5% isoflurane and were measured for hemodynamics, myocardial contractility, and myocardial substrate utilization. They were hemorrhaged to a mean arterial pressure of 35 mm Hg for 90 min or until arterial lactate levels reached 7.0 mM (1137 +/- 47 mL or 49 +/- 2% total blood volume). Animals were chosen at random to receive DCA dissolved in water or an equal volume of saline at the onset of resuscitation. Two-thirds of the shed blood volume was returned immediately after giving an equivalent volume of saline. Two hours after the onset of resuscitation, mean arterial pressure was not different between DCA and control groups (79 +/- 3 vs. 82 +/- 3 mm Hg, respectively). Arterial lactate levels were significantly reduced by DCA (0.5 +/- 0.06 vs. 2.0 +/- 0.2 mM). However, DCA treatment was associated with a decreased stroke volume index (0.56 +/- 0.06 vs. 0.82 +/- 0.08 mL/kg/beat) and a decreased myocardial efficiency (19 vs. 41 L x mm Hg/mL/100 g tissue). During resuscitation by DCA, myocardial lactate consumption was reduced (21.4 +/- 3.7 vs. 70.7 +/- 16.3 micromole/min/100 g tissue) despite a three-fold increase in myocardial pyruvate dehydrogenase activity, while free fatty acid levels actually began to rise. Although increased lactate oxidation should be beneficial during resuscitation, we propose that DCA treatment led to a deprivation of myocardial lactate supply, which reduced net myocardial lactate oxidation, thus compromising myocardial function during resuscitation from hemorrhagic shock.

Lactate improves cardiac efficiency after hemorrhagic shock.

This study was undertaken to examine the role of lactate on cardiac function and metabolism after severe acute hemorrhagic shock. Anesthetized, nonheparinized rats were bled to a mean arterial pressure of 25-30 mm Hg for 1 h; controls were not bled. Their hearts were removed, and cardiac work and efficiency (work/oxygen consumption) were measured in the isolated working heart mode for 60 min. The hearts were perfused with one of five substrate combinations: 1) glucose (11 mM), 2) glucose + 0.4 mM palmitate, 3) glucose + 0.4 mM palmitate + 8.0 mM lactate, 4) glucose + 1.2 mM palmitate, or 5) glucose + 1.2 mM palmitate + 8.0 mM lactate. After perfusion, hearts were freeze-clamped, and tissue contents of free coenzyme-A (CoA), acetyl CoA, and succinyl CoA were measured, as was myocardial pyruvate dehydrogenase (PDH) activity. The addition of 8.0 mM lactate significantly improved cardiac work in shocked hearts perfused with 0.4 mM palmitate and increased cardiac efficiency in the presence of either 0.4 mM or 1.2 mM palmitate. Compared to control hearts, shocked hearts exhibited a 20-30% decrease in PDH activity. Shocked hearts perfused with lactate demonstrated no increase in acetyl CoA content but did have a significant increase in tissue succinyl CoA compared to control hearts perfused with lactate or shocked hearts perfused without lactate. In the heart recovering from severe hemorrhagic shock, lactate improves cardiac efficiency in the presence of free fatty acids, possibly by a anaplerosis of the tricarboxylic acid cycle.

A comparison of resuscitation with packed red blood cells and whole blood following hemorrhagic shock in canines.

Resuscitation with crystalloid and packed red blood cells has for the most part replaced the use of plasma and whole blood in the initial treatment of hemorrhagic shock. The effects of such changes on cardiovascular function following hemorrhagic shock remain largely unexplored. We examined cardiovascular function in anesthetized canines subjected to severe hemorrhagic shock. Mongrel canines of either gender were anesthetized with isoflurane and instrumented for measurement of arterial pressure, cardiac output, coronary flow, and left ventricular pressure and volume for the determination of end systolic elastance (Ees). Following a 30-min stabilization period, blood was rapidly removed to induce fixed pressure (mean arterial pressure = 35 mmHg) hemorrhagic shock for 90 min or until an arterial lactate of 7.0 mM was achieved. Animals were then resuscitated with 2/3 of the shed volume as lactated Ringer's and an equal volume of either whole blood (WB, n = 8) or packed red blood cells (PRBC, n = 10) resuspended in lactated Ringer's (LR) solution to replace expressed plasma volume. PRBC resuscitated dogs showed lower values of mean arterial pressure, cardiac output, rates of ventricular contraction and relaxation and myocardial work. Increasing the maintenance infusion rate of LR (10 mL/kg/h) following PRBC infusion normalized mean arterial pressure, but not other indices of cardiovascular function. Thus, WB, but not PRBC resuscitation restores normal myocardial function during resuscitation from severe hemorrhagic shock.

Heart function after severe hemorrhagic shock.

OBJECTIVE: Test whether brief deep hemorrhagic hypotension or prolonged moderate hemorrhagic hypotension impairs intrinsic heart function. METHODS: Pentobarbital-anesthetized, non-anticoagulated rats were cannulated via the carotid artery. This study focuses on three main groups: 1) hemorrhage to a mean arterial blood pressure (MAP)=25 mm Hg for 1 h (1 h severe shock), 2) hemorrhage to MAP=40 mm Hg for 3 h (3 h moderate shock), 3) no hemorrhage (control). Hearts were either freeze-clamped in-situ for tissue analysis (n=6 per group) or were removed to study in vitro cardiac function and efficiency using a working heart perfusion (n=12 per group, glucose (11 mM)/palmitate (0.4 mM), 3% BSA buffer). Following perfusion, hearts were freeze-clamped and analyzed for free CoA, acetyl-, succinyl-, and malonyl-CoA, ATP content and for TNF-alpha content. RESULTS: Isolated working hearts obtained following 1 h of severe shock generated 20% less hydraulic work than hearts obtained from control rats or rats subjected to 3 h of moderate shock. The cardiac efficiency (work/O2 consumption) was also significantly reduced with 1 h severe shock (0.76 +/- 0.07 after 15 min perfusion) versus control (0.96 +/- 0.06) or 3 h prolonged shock (1.10 +/- 0.09). Myocardial Co-A ester, ATP and TNF-alpha concentrations were not different between control and shocked hearts, although TNF-alpha concentrations increased significantly in all hearts during ex vivo perfusion. CONCLUSIONS: Depth of hypotension is more important than duration in causing intrinsic cardiac dysfunction. This post-hemorrhagic cardiac dysfunction is not a result of substrate limitation to the heart, nor myocardial TNF-alpha accumulation, but is more likely a result of impaired transfer of energy from molecular oxygen into external cardiac work.

Inhibition of poly(ADP-ribose) synthetase improves vascular contractile responses following trauma-hemorrhage and resuscitation.

Hyporeactivity of vessels to constrictor agents is thought to contribute to cardiovascular decompensation following trauma-hemorrhage and resuscitation. In this study, we determined if inhibition of poly(ADP-ribose) synthetase (PARS) activity prevented the development of vascular hyporeactivity in rats following trauma-hemorrhage and resuscitation. Trauma consisted of a laparotomy that was closed and rats were hemorrhaged into a reservoir containing citrate to 40 mm Hg for 90 min. Resuscitation included 2/3 of the shed blood plus 2 1/3 of the shed volume as Ringer's lactate. Sham animals received the laparotomy and were time-matched. Induction of iNOS was assessed by reverse transcription-polymerase chain reaction (RT-PCR). Aortic rings isolated 6 h after the initiation of hemorrhage (4.5 h after resuscitation) showed decreased responsiveness to norepinephrine (peak developed tension 0.31+/-0.01 g/mg tissue) compared with sham rings (0.43+/-0.02 g/mg tissue), but no change in EC50 for this response (approximately 5x10(-8) M). Addition of the PARS inhibitor, 3-aminobenzamide, at the onset of resuscitation prevented the decrease in response of aortic rings. The addition of the structural analogue, 3-aminobenzoic acid, which does not inhibit PARS, did not prevent the decrease in vascular reactivity. These agents did not alter vascular responses to norepinephrine in sham animals. iNOS induction was not associated with depressed contractile function. These results indicate that decreased vascular reactivity was prevented by inhibition of PARS and that PARS activation was independent of iNOS induction following trauma-hemorrhage and resuscitation.

Effects of citrated whole blood transfusion in response to hemorrhage.

BACKGROUND AND PURPOSE: Standard treatment for massive hemorrhage in dogs is infusion of whole blood or of packed red blood cells with fresh frozen plasma if whole blood is not available. Although most whole blood is collected using a citrate-based anticoagulant, knowledge of citrate's relevant non-anticoagulant effects is not widespread. Citrate's anticoagulant activity is achieved through chelation of divalent metal cations (e.g., magnesium, calcium), which may exacerbate cardiovascular and metabolic insults attributable to hemorrhage. METHODS: Blood pressures, gas tensions, metabolites, and electrolytes; myocardial metabolites, pressures, and contractility; cardiac output; and left cranial descending and circumflex coronary artery flows were measured in 21 anesthetized dogs after hemorrhage was induced by collection of blood into a citrated reservoir to mean arterial pressure of 45 mm Hg for approximately 60 min (until arterial lactate concentration was 7.0 mmol/L), followed by a 1-h transfusion and 2 h of maintenance. RESULTS: Arterial ionized calcium concentration, total peripheral resistance, and myocardial function decreased significantly during hemorrhage. All aforementioned responses but myocardial function continued to decrease during the initial 20 min of transfusion, then began to recover. Total peripheral resistance and end-systolic elastance were the only factors significantly related to calcium concentration. CONCLUSION: Transfusion with citrated whole blood may significantly alter calcium concentration, negatively affecting myocardial and vascular function.

Combination of dobutamine and myocardial contrast echocardiography to differentiate postischemic from infarcted myocardium.

OBJECTIVES: This study tested whether the combination of dobutamine echocardiography (DE) and myocardial contrast echocardiography (MCE) was superior to either technique alone in identifying postischemic myocardium and in differentiating it from necrotic myocardium. BACKGROUND: Wall motion abnormalities at rest occur in postischemic myocardium in the presence of infarction, stunning or hibernation, alone or in combination. Various investigators have suggested that either DE or MCE can be used to identify the presence of myocardial viability. METHODS: We studied a total of 53 mongrel dogs in an open chest model of coronary occlusion of various durations followed by reperfusion and dobutamine administration (10 microg/kg body weight per min). MCE with aortic root injections of Albunex (area under the curve) and DE (percent thickening fraction) were performed at the different stages. Postmortem triphenyltetrazolium chloride (TTC) staining was used to identify myocardial necrosis. RESULTS: Thirteen dogs underwent brief (15 min) occlusions and developed no necrosis (Group I). Of 40 dogs that underwent prolonged (30 to 360 min) occlusions, 14 had no infarction (Group II), whereas 26 did (Group III: 12 papillary muscle, 7 subendocardial, 7 transmural). MCE (expressed as percent change from baseline) demonstrated changes that paralleled the blood flow changes observed by radiolabeled microspheres at all interventions (r = 0.67, p < 0.0001). Regional ventricular function improved with dobutamine administration in the ischemic region in all three groups. The sensitivity (88%) for detecting myocardial viability was superior when the two techniques were combined; however, a poor specificity (61%) was observed. CONCLUSIONS: Contractile reserve and perfusion data are complementary when assessing regional wall motion abnormalities in postischemic myocardium. DE alone cannot differentiate postischemic from infarcted myocardium; simultaneous data on myocardial perfusion are required. The combination of DE and MCE is superior to either technique alone for identifying the absence of myocardial necrosis.

Potential clinical implications of abnormal myocardial perfusion patterns immediately after reperfusion in a canine model: a myocardial contrast echocardiography study.

During myocardial infarction, lack of myocardial opacification after reperfusion has been associated with poor or no recovery of function. We have previously documented the presence of perfusion abnormalities after brief coronary occlusions without infarction and the absence of perfusion abnormalities after prolonged occlusions with infarction. To characterize myocardial perfusion patterns immediately after reperfusion, we studied 53 animals in two groups in a coronary occlusion-reperfusion model. Temporary occlusions (group 1, 15 minutes; group 2, 30 to 360 minutes) were performed, followed by reperfusion with and without dobutamine. Myocardial contrast echocardiography was performed with aortic root injections of sonicated 5% serum human albumin (Albunex) during each intervention. Group 1 dogs showed no evidence of myocardial infarction. In group 2, 26 of 40 dogs had infarctions. After reperfusion, no perfusion abnormalities were seen in 13 of 26 group 2 dogs with infarctions; perfusion abnormalities were identified after reperfusion in 2 of 13 group 1 and in 8 of 14 group 2 dogs without infarctions. In animals subjected to prolonged ischemia, the absence of perfusion abnormalities after reperfusion did not rule out the presence of necrosis. Similarly, in animals without infarction subjected to ischemia, the presence of a perfusion defect after reperfusion did not represent the presence of necrosis but an abnormal microvascular reserve. These results suggest that early after reperfusion, assessment of perfusion by myocardial contrast echocardiography has significant limitations in the evaluation of myocardial viability and salvage.

Adenovirus-mediated in vivo gene transfer in a rabbit model of allograft vasculopathy.

BACKGROUND: The long-term success of heart transplantation continues to be in jeopardy because of the development of accelerated vascular myointimal proliferation. Transfer of genes encoding products that can modulate the adverse consequences of phenomena that cause myointimal proliferation, into the allograft vessel wall, may modify these pathologic processes. The purpose of this study was to assess the feasibility of gene transfer and to evaluate the duration of gene expression in a rabbit heterotopic aortic transplant model of allograft vasculopathy. METHODS: The abdominal aortas of 32 outbred New Zealand rabbits were harvested and cross-sectionally bisected (n = 64). Six donor and recipient animals were used in a preliminary study to examine neointimal proliferation without accompanying gene transfer. Of the remaining 26 rabbits (52 allografts), one half of each allograft aorta was administered a control solution, while the other half was incubated with a replication-defective, recombinant, adenoviral vector-encoding, cytomegalovirus promoter-regulated beta-galactosidase. After a 20-minute incubation period, bilateral aorto-carotid transplantations were performed in 26 recipient rabbits. All animals received cyclosporine immunosuppression (10 mg/kg/day subcutaneously). The allografts were harvested at 3, 7, 10, 21, and 28 days after transplantation and assayed for beta-galactosidase activity. RESULTS: Neointimal areas showed an initially slow increase for the first 10 days, followed by a rapid increase up to 21 days, and tended to plateau thereafter. Significant beta-galactosidase was apparent in aortic sections dissected from host rabbits for all time points, except at 28 days. At the 21-day time point, the aortic section from one rabbit was positive, whereas the other two remained negative. However, the one positive section showed intense beta-galactosidase activity, suggesting variability in the experimental model. At 28 days, all aortic sections were negative. CONCLUSIONS: Our findings confirm that genes delivered by this method are expressed for the duration of early rapid intimal proliferation in this heterotopic rabbit model of aortic allograft vasculopathy. These findings suggest that this animal model can be used to assess the therapeutic potential of gene transfer at the time of vascular transplantation and may provide a novel therapeutic approach to prevent or ameliorate the genesis of allograft vasculopathy.

Lack of effect of exercise training on dehydroepiandrosterone-sulfate.

Although functions of dehydroepiandrosterone (DHEA) and its sulfate ester are unknown, investigators have found an inverse relation between DHEA-sulfate levels and coronary artery disease, suggesting its importance as an inverse coronary risk factor. In previous studies, where behavioral therapy was used to try to reduce stress and social isolation, DHEA levels increased--although other confounding factors, including enhanced physical activity, also were affected. To determine the influence of physical activity alone on plasma DHEA-sulfate levels in patients with coronary artery disease, the authors studied the effects of exercise training by measuring plasma DHEA-sulfate levels and other parameters in 96 patients at baseline and after 12 weeks of cardiac rehabilitation and exercise training. They confirmed that DHEA-sulfate levels decreased with age (r = 0.41; P < 0.0001) and that DHEA-sulfate levels correlated with body mass index (r = 0.32; P < 0.001), but not with other baseline risk factors. Exercise training during cardiac rehabilitation resulted in a 43% increase in exercise capacity (P < 0.0001) and was associated with improvement in other cardiac risk factors; however, there were no significant changes in plasma DHEA-sulfate levels (106 +/- 77 micrograms/dL versus 102 +/- 76 micrograms/dL). Although behavior therapy in combination with exercise training was shown to lead to concomitant increases in DHEA-sulfate and physical activity, exercise training alone has no significant impact on DHEA-sulfate, thereby strengthening the suggested role of behavioral changes in modifying this hormone.

Retroviral suicide vector does not inhibit neointimal growth in a porcine coronary model of restenosis.

We attempted to attenuate neointimal formation following vascular injury using a retroviral suicide vector. Epicardial coronary arteries of adult miniature swine were injured by deployment of oversized tantalum stents. One week later, injured segments were exposed to packaged retroviral constructs with or without the herpes simplex virus thymidine kinase gene. Ganciclovir treatments were initiated 48 hours later in both control and experimental swine and continued for two weeks. Four weeks following vascular injury, both control and experimental arteries were harvested and histologically prepared for image analysis. Despite adequate marker gene expression, there was no significant difference in the neointimal area or neointimal/media ratio between control and experimental groups. While the HSVtk ganciclovir system attenuates cell proliferation in other systems, retroviral vector targeting of vascular smooth muscle cells for elimination may be too inefficient to prevent restenosis following angioplasty.

Effect of verapamil and captopril on endothelial injury in the diabetic hypertensive rat.

Microvascular and macrovascular complications are a major cause of increased morbidity and mortality in patients with diabetes mellitus and hypertension. Atherosclerosis is the major cause of these complications. Recently, Hebden and colleagues demonstrated endothelial injury in a rat model with streptozotocin-induced diabetes mellitus and deoxycorticosterone acetate-induced hypertension. To determine if captopril and verapamil reduce endothelial injury in this model of diabetic hypertensive (DH) rats, we evaluated mean medial thickness and intimal cell changes in four groups of rats: control, untreated DH rats, captopril-treated DH rats, and verapamil-treated DH rats. Mean medial thickness increased from 63.5 +/- 4.8 microns in control rats (n = 7) to 107.2 +/- 7.5 microns in untreated DH rats (n = 8), (P < .05). Verapamil and captopril blunted DH-induced medial thickening to 90.1 +/- 4.9 and 93.7 +/- 8.3 microns, respectively (P < .05 compared with control and untreated rats). An endothelial injury index (EI), consisting of white blood cells adhered to the intimal surface and rounded endothelial cells per 25-microns arc in aortic vessels, was determined for each group. The EI increased from 0.2 +/- 0.1 cells/25-microns arc in control rats to 6.3 +/- 4.0 cells/25-microns arc in untreated DH rats. Both verapamil and captopril diminished the EI in DH rats to 0.8 +/- 0.2 and 2.7 +/- 0.3 cells/25-microns arc, respectively (P < .05 compared with untreated DH rats). In addition, verapamil decreased the EI in DH rats to a greater degree than captopril (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamics in transgenic mice with overexpression of atrial natriuretic factor.

The circulatory effects associated with lifelong plasma atrial natriuretic factor (ANF) elevation were examined by generating transgenic mice, which constitutively express a fusion gene consisting of the transthyretin promoter and the ANF structural gene. These mice have chronically elevated ANF levels as compared with their nontransgenic siblings. Transgenic animals exhibited immunoreactive ANF levels that were nearly fivefold higher than those measured in nontransgenic littermates. Systemic and regional hemodynamics and blood volumes were explored by using modifications of the reference microsphere and dilution techniques. Mean arterial pressure was reduced by 24 mm Hg, associated with a 27% reduction in total heart weight. This chronic reduction in blood pressure was due to a 21% reduction in total peripheral resistance, whereas cardiac output, stroke volume, and heart rate were not significantly altered, despite a 15% elevation in plasma volume. Transgenic mice displayed reductions of 35%, 33%, 32%, and 19% in muscle, skin, brain, and renal vascular resistance, respectively, whereas coronary and splanchnic resistances were not significantly altered. The findings complement earlier data from chronically infused normotensive mammals and suggest that these mice are an excellent model for investigating the effects of lifelong ANF elevation.

Endothelin blockade lowers total peripheral resistance in hemorrhagic shock recovery.

To determine whether endothelin (ET) has a role in maintaining circulatory support during hypotensive hemorrhage, we (1) examined cardiac and systemic hemodynamics after a 6-mL hemorrhage in the presence and absence of the ETA receptor blocker BQ-123, (2) examined cardiac and systemic hemodynamics during BQ-123 infusion in nonhemorrhaged rats, (3) measured changes in circulating immunoreactive endothelin (IR-ET) after a 6-mL hemorrhage, and (4) infused pathophysiological doses of ET-1 into rats anesthetized with thiobutabarbital. Twenty minutes after hemorrhage, cardiac output and mean arterial pressure had stabilized in part because of an increase in systemic vascular resistance from 0.86 +/- 0.04 (baseline) to 1.04 +/- 0.05 (20 minutes) mm Hg/mL per minute. The rise in systemic vascular resistance was temporally associated with a significant (24%) increase in circulating IR-ET from 29 +/- 2 to 36 +/- 3 pg/mL 20 minutes after hemorrhage. During BQ-123 infusion mean arterial pressure at 5, 10, and 20 minutes after hemorrhage was 9 +/- 2, 23 +/- 4, and 23 +/- 3 mm Hg lower than values obtained after hemorrhage alone (P < .05). Mean arterial pressure was unaffected by BQ-123 infusion at baseline and 30 minutes after hemorrhage. Systemic vascular resistance was not affected at baseline by BQ-123 infusion. However, systemic vascular resistance was significantly lower 5, 10, 20, and 30 minutes after hemorrhage during BQ-123 infusion compared with hemorrhage alone at each time point. Infusion of BQ-123 into nonhemorrhaged rats had no effect on mean arterial pressure, systemic vascular resistance, or cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac output and regional hemodynamics during recurrent seizures in rats.

Altered cardiovascular function in status epilepticus may contribute to mortality and morbidity in patients. We investigated changes in cardiac output and regional hemodynamics during 2 h of recurrent PTZ-induced seizures in anesthetized, paralyzed rats using radioactive microspheres, thermodilution methods, and the pulsed Doppler technique. Cardiac output fell 30-60% during recurrent seizures in 17 of 27 animals. The fall in cardiac output was sudden in onset and occurred primarily in association with seizures accompanied by prolonged increases in MABP but no change in central venous pressure. Total peripheral resistance (TPR) rose during early seizures in association with vasoconstriction of renal and certain splanchnic vascular beds. Ictal increases in TPR became attenuated during late seizures, due to failure of renal and splanchnic beds to constrict. Therefore, derangements in both cardiac and vascular function occur during late seizures. These derangements may contribute to both cerebral hypoperfusion and sudden death in status epilepticus.

Exercise training improves cardiac performance in diabetic rats.

Diabetes mellitus is often associated with a cardiomyopathy characterized by alterations in cardiac metabolism and declines in cardiac performance. We sought to determine whether exercise training would attenuate the depressed cardiac performance seen in diabetic animals. Female rats were divided into four groups: sedentary control, trained control, sedentary diabetics, and trained diabetics. After 1 week of training, we induced diabetes by intravenous injection of streptozotocin (65 mg/kg). We trained animals on a treadmill using a progressive protocol that plateaued at 27 m/min for 1 hr/day, 5 days/week for a total of 8 weeks. We measured cardiac output at a variety of left atrial filling pressures with an isolated working heart apparatus; glucose was the sole metabolic substrate for the heart. Training increased succinate dehydrogenase activity in the soleus muscle of exercised rats, but did not change heart and body weights or plasma glucose and thyroid hormone levels. The diabetic groups exhibited depressed cardiac outputs at high workloads compared to nondiabetics. Training increased the cardiac output of both sedentary and diabetic animals at high, but not low, preloads. We suggest that exercise can attenuate the severity of diabetic cardiomyopathy.

Prior arterial injury enhances luciferase expression following in vivo gene transfer.

We determined the time course of gene expression following DNA/Lipofectin transfection of normal or previously injured arterial segments using direct intraluminal infusion following surgical exposure. Constructs possessing the firefly luciferase cDNA regulated by Simian virus 40, Rous sarcoma virus, or alpha-actin promoter were incubated together with Lipofectin for 30 minutes. Arterial segments were assayed for luciferase activity following harvest at 2-21 days. Without prior injury, luciferase activity was only 2.5-fold greater than background two days following gene transfer. Arterial injury three days before gene transfer resulted in luciferase activity 12.5-fold over background levels. This observation has clinical implications with regard to gene therapy following angioplasty, a procedure that is associated with endothelial cell denudation and smooth muscle cell proliferation. Maintenance of gene expression for several days could ameliorate the early smooth muscle migration and proliferation following arterial injury.