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A G Greenburg

Publications and source records attributed to A G Greenburg.

At least 19 recordsLinked to original sources
PubMed2005

Hemoglobin mediated contraction of the isolated rat thoracic aorta: why is precontraction necessary?

A primary mechanism for the hemoglobin (Hb) mediated vascular contraction is believed to be Hb scavenging of endothelial nitric oxide (NO). In the isolated rat thoracic aorta, however, the Hb mediated contraction occurs only after an agonist-induced precontraction. Why? To investigate the question, a rat thoracic aortic ring model was used. Isometric vessel ring tension responses to selected pharmacologic contractile agonists were assessed and compared. The Hb mediated additional contraction occurred in vessel rings precontracted with adrenergic agonists as well as other types of contractile agonists. Even after agonist induced contraction, removal of the vascular endothelium or inhibition of endothelial NO synthase with Nomega-nitro-L-arginine methyl ester prevented the Hb mediated additional contraction. Additionally, imposition of passive tension without an agonist pretreatment did not allow Hb mediated contraction. In conclusion, in the isolated rat thoracic aorta, the endothelial NO synthase is minimally active in the basal state but upregulated upon treatment with a contractile agonist. This may explain why the Hb mediated additional contraction occurs only after an agonist induced precontraction.

Adrenergic Agonists↗
PubMed2004

Active myogenic tone: a requisite for hemoglobin mediated vascular contraction?

Acellular free hemoglobin (Hb), when intravenously administered to animals and humans, elicits vascular contraction. A primary mechanism for the Hb mediated vasoconstriction is Hb scavenging of nitric oxide (NO), a potent relaxation factor, constitutively secreted by the vascular endothelium. However, in the isolated rat thoracic aorta in basal state, Hb does not elicit contraction. To investigate this apparent paradox, we assessed isolated rat aortic ring isometric contraction responses to Hb under different myogenic tone states: (1) following equilibration at a submaximal tension, (2) following agonist induced contraction, or (3) following a passive mechanical stretch. In vessel rings at basal state, Hb as high as 4 microM did not elicit any measurable contractions. In contrast, in vessel rings tone enhanced with norepinephrine, Hb as low as 0.1 microM Hb elicited a significant additional contraction. In vessel rings with passively induced tone, 4 microM Hb did not elicit a notable contraction. Similarly, in vessel rings in basal state, 0.17-1 mM acetylcholine, a NO dependent vasodilator, did not elicit relaxation. In these vessel rings, exogenous 8-Br-cGMP, a membrane permeable cGMP analog, did not elicit relaxation. In conclusion, in the isolated rat thoracic aorta, Hb mediated contraction may be contingent upon the state of myogenic tone.

Animals↗
PubMed2004

Temporal effect of hemoglobin resuscitation on sepsis survival.

Hemoglobin (Hb)-based oxygen carriers are promising resuscitation fluids for hemorrhagic shock. However, infusion of large amounts of Hb-based material could interfere with reticuloendothelial function potentiating postresuscitation sepsis mortality. We investigated the temporal relationship between hemorrhage-resuscitation and sepsis survival. Male SD rats were subjected to hemorrhage and resuscitated with shed blood volumes of purified human hemoglobin solution (HS). Sepsis was induced by cecal ligation and puncture (CLP) 24 h before, 0, 24, or 72 h after hemorrhage/resuscitation (H/R) and survival was monitored. In additional animals with or without Hb resuscitation, hepatic heme oxygenase-1 (HO-1) gene expression and HO activity were assessed. Seven-day survival for animals resuscitated with HS prior to sepsis induction was significantly higher than other groups. Animals resuscitated with HS showed hepatic HO-1 gene expression while non-HS resuscitated animals did not. In addition, hepatic HO activity levels were significantly higher in HS resuscitated animals than non-HS resuscitated animals. In conclusion, HS resuscitation does not appear to enhance postresuscitation sepsis mortality. Rather, when conducted concomitantly or prior to sepsis, HS resuscitation appears to improve survival from a subsequent sepsis challenge.

Animals↗
PubMed2001

Contraction coupled endothelial nitric oxide release: a new paradigm for local vascular control?

INTRODUCTION: Nitric oxide (NO), a potent vasodilator, is presumed to be constitutively released in most mammalian blood vessels. In isolated rat thoracic aorta, however, hemoglobin (Hb), a nitric oxide scavenger, elicited contraction only when the vessels were precontracted with an alpha adrenergic agonist. Does vascular contraction induce endothelial NO release? METHODS: Thoracic aortic rings from male Sprague-Dawley rats were prepared with or without the endothelium. Vessel rings were contracted with several distinct types of contractile agonists and NO release was probed using a Hb contraction assay in the presence and absence of nitro-l-arginine methyl ester (NAME), a NO synthase inhibitor. RESULTS: In vessel rings precontracted with norepinephrine, potassium chloride, arginine vasopressin, prostaglandin F(2alpha), or serotonin, Hb elicited significant additional contractions. In contrast, Hb failed to elicit significant contractions in vessel rings without the functional endothelium or vessels pretreated with NAME. The Hb mediated additional contraction was not inhibited by calmidazolium, a calmodulin antagonist, and protein kinase inhibitors staurosporine and 2,5-dihydromethylcinnamate. Intercellular gap junction inhibitor 2,3-butanedione monoxime at a low dose (<2 mM) significantly attenuated the NE/Hb mediated contractions but at a high dose (>15 mM) completely prevented both contractions. The contraction coupled NO release may be mediated through a mechanism distinct from the Ca(2+)-calmodulin-dependent endothelial NOS pathway. CONCLUSIONS: In the isolated rat thoracic aorta, endothelial NO release may be coupled to contractile stimulus. This vascular property appears to render a unique local control mechanism independent of baroreflex and other central mechanisms.

Adrenergic Agonists↗
PubMed2001

Nitric oxide scavenging modulates an experimental vasoplesia in-vitro.

Endogenous overproduction of nitric oxide (NO) is believed to be a primary cause of refractory hypotension in septic shock. Under this condition, effectiveness of vasopressors is diminished due to hyporeactivity of blood vessels, a condition termed as vasoplesia. Effective reduction of NO levels should alleviate the condition. In this study, we investigated whether NO scavenging could modulate the endotoxin mediated vasoplesia in-vitro. Further, we explored whether NO scavenging in combination with a moderate NO synthase (NOS) inhibition would also be effective in modulating NO mediated vasoplesia. Experimental vasoplesia was produced in-vitro by incubating isolated rat thoracic aortic rings with lipopolysaccharide (LPS). Vessel rings were then treated with N(omega)-nitro-L-arginine methyl ester (L-NAME; a NOS inhibitor), human hemoglobin (Hb; a NO scavenger), or both L-NAME and Hb. Vascular reactivity was assessed by measuring vessel ring isometric tension changes to norepinephrine (NE) doses; the median effective doses (logEC50) of NE before and after each experimental treatment were compared. Following a 6-hour LPS treatment, vascular reactivity logEC50 values for NE were significantly increased compared with control vessel rings incubated without LPS. Treatment with either L-NAME alone or Hb alone significantly improved the vessel ring reactivity to NE. When both L-NAME and Hb were used concomitantly, vascular reactivity was also significantly improved. These results indicate that NO scavenging with Hb is as effective as NO synthesis inhibition with NAME in modulating the endotoxin induced vasoplesia. In conclusion, NO scavenging, alone or in combination with a moderate NOS inhibition, may render an alternative therapeutic approach to NOS synthesis inhibition in modulating the vasoplesia in septic shock.

Animals↗
PubMed2001

Alpha adrenergic activation and hemoglobin mediated contraction in the isolated rat thoracic aorta.

A primary mechanism for Hb mediated vascular contraction appears to be Hb scavenging of endothelium derive nitric oxide (NO), a potent vasodilator. In isolated rat thoracic aorta, however, Hb elicits contraction only after precontraction. The present study investigated a possible role of the alpha adrenergic activation in the Hb mediated contraction. Thoracic aortic rings harvested from normal male SD rats were prepared in a tissue bath and isometric tension changes were evaluated. In vessel rings precontracted with 50nM norepinephrine (NE), 1 microM Hb produced an additional 21.8+/-13.2% increase in tension. Pretreatment with 70nM phentolamine, an alpha adrenergic antagonist, prevented the 50nM NE induced contraction. In these vessels, subsequent treatment with 2-4 microM Hb did not elicit contraction. In vessel rings precontracted with 37mM KCl, 2 microM Hb produced an additional 21.8+/-20.1% tension increase (P<0.05). Pretreatment with phentolamine did neither prevent KCl induced contraction nor affect subsequent Hb mediated additional contraction. To test whether there is a threshold level of basal tension for Hb to trigger contraction, a group of vessel rings were passively stretched to match the tension generated by NE before Hb treatment. In these passively stretched vessel rings, Hb did not produce a significant contraction. Pretreatment with 10mM EGTA, a Ca++ chelator, significantly reduced NE induced contraction (9.7+/-5.9 vs 137.7+/-60.0%, P<0.01) but did not prevent it. EGTA also significantly reduced 2 microM Hb induced contraction (27.2+/-29.3% vs 8.9+/-7.7%, P<0.05). In contrast, pretreatment with verapamil, a Ca++ channel blocker, did not completely block NE and Hb induced contractions. In conclusion, alpha adrenergic activation is not a requisite for the Hb mediated contraction in isolated rat aortic rings. The mechanism how prior tone enhancement allows Hb mediated contraction remains unclear but results from this study suggest a factor that controls cytosolic Ca++ levels may be involved.

Adrenergic alpha-Agonists↗
PubMed2000

Pharmacodynamic characterization of hemoglobin-induced vasoactivity in isolated rat thoracic aorta.

The origin and mechanism of vasocontraction observed after vascular exposure to acellular Hbs remain controversial. To help resolve the underlying mechanism, we characterized Hb-induced vasoactivities in terms of Hb purity, heme iron oxidation state, and ligand and pharmacodynamic properties. Isolated rat thoracic aortic rings with intact endothelium were suspended in oxygenated Krebs buffer, and isometric tension responses to various test Hb preparations were measured. In norepinephrine tone-enhanced aortic rings, both crude and purified Hbs exhibited similar dose-response characteristics; stroma-free Hb and HbA0, two Hb preparations with disparate purity, were equally potent in inducing vessel ring contraction. Purified Hb preparations significantly attenuated vasodilatory potency of both acetylcholine, an endothelium-dependent NO generator, and glyceryl trinitrate, an endothelium-independent NO generator. With the exception of nitrosylated Hb, ferrous Hbs, oxy Hb, and carbon monoxy Hb elicited contraction, whereas ferric derivatives, met Hb, and cyanomet Hb did not. In addition, NEM-Hb, an Hb with blocked cysteine residues, did not notably attenuate Hb vasoactivity. These results indicate that Hb itself is directly responsible for inducing contraction in the rat thoracic aortic rings. A primary mechanism for the Hb-induced vasoactivity appears to be heme iron inactivation of endothelium-derived NO. Nonheme interaction with endothelial NO does not appear to play a prominent role in this vascular model. In conclusion, Hb elicits dose-dependent contraction in isolated rat thoracic aorta with intact endothelium. Vasoactivity of Hbs, however, could greatly vary with heme iron oxidation state, nature of heme ligand, and model vessels used in the evaluation.

Animals↗
PubMed2000

A phase I study of oxidized raffinose cross-linked human hemoglobin.

OBJECTIVE: To evaluate the safety of oxidized-raffinose cross-linked human hemoglobin, Hemolink, in normal healthy volunteers. DESIGN: Randomized, placebo-controlled, double-blind study. SETTING: Clinical research facility of a contract research organization. PATIENTS: Forty-two healthy adult male volunteers of which 33 received Hemolink. INTERVENTIONS: Oxidized-raffinose cross-linked and polymerized hemoglobin as a 10% (w/v) solution, in doses of 0.025-0.6 g/kg or an equivalent volume of lactated Ringer's solution, was infused intravenously on day 1, and subjects were monitored for 3 days in the clinical facility with < or =6 wks follow-up. Major organ function was assessed pre- and postinfusion, by hemodynamic, electrocardiographic, pulmonary function, and clinical chemistry measurements. MEASUREMENTS AND MAIN RESULTS: Doses of 1.7-42 g of hemoglobin were administered with no serious adverse events noted. Abdominal pain of moderate to severe intensity was seen in some subjects at doses >0.4 g/kg and was alleviated with smooth muscle relaxants. There was a dose-dependent increase in mean arterial pressure with a plateau of approximately 14% above baseline at 0.1 g/kg. There was a concomitant reduction in heart rate, with no electrocardiographic abnormalities found. Respiratory function was not affected. There was a dose-dependent increase in serum bilirubin with values above the upper limit of normal at doses of > or =0.4 g/kg. Small increases in aspartate aminotransferase and alanine aminotransferase were noted in some patients, whereas alkaline phosphatase and gamma-glutamyltransferase remained in the normal range. Serum amylase concentrations were normal in 31 of 33 patients receiving Hemolink, whereas lipase was within the normal range in 21 of 33 patients. LDH was increased in a dose-dependent fashion. Two patients had increased creatine kinase concentrations, with a normal creatine kinase-MB mass fraction. All hematologic variables were within the normal range. The half-life of the oligomeric (>64 kDa) fraction of Hemolink was 18-20 hrs. CONCLUSION: Oxidized-raffinose cross-linked hemoglobin, Hemolink, at doses < or =0.6 g/kg were well tolerated in healthy volunteers with no evidence of organ dysfunction. Further investigation of its potential use in surgical and trauma settings appears warranted.

Adult↗
PubMed1998

Cell-free hemoglobin preserves renal function during normothermic ischemia.

INTRODUCTION: The purpose of this study is to determine whether an infusion of polymerized hemoglobin solution is capable of suppressing the tubular damage and loss of renal function normally seen during a clinically relevant period of warm ischemia. METHODS: Male rats (350-450 g) were randomized to treatment with control (5% human serum albumin, HSA, n = 6) or test solution (9% polymerized hemoglobin, PHB, n = 6). Following a right nephrectomy, the left renal artery was perfused with 4 ml of HSA or PHB at 37 degreesC. The left renal artery was temporarily occluded for 50 min. At 72 h, creatinine (Cr), blood urea nitrogen (BUN), and percentage hemoglobin (Hb) were measured and the kidney was removed. Stained kidney sections were graded for ischemic injury (0-4, 0 = normal and 4 = necrosis of the proximal tubule). All results were expressed as means +/- SEM and statistical analysis was performed by t test. RESULTS: Treatment with PHB resulted in lower Cr (1.2 +/- 0.23 mg/dl vs 3.26 +/- 0.60 mg/dl, P < 0.01) and BUN (60.5 +/- 12.7 mg/dl vs 151 +/- 20.2 mg/dl, P < 0.01) at 72 h compared to HSA controls. Total hemoglobin was not significantly different at 72 h. The weight of all treated kidneys increased; however, the increase was significantly less in the PHB-treated group (34 +/- 9.1% vs 70 +/- 7. 4%, P < 0.01). PHB-treated kidneys had less evidence of histologic damage compared to those in the HSA group (0.75 +/- 0.11 vs 2.50 +/- 0.64, P < 0.05). CONCLUSIONS: During normothermic renal ischemia, renal artery infusion of PHB resulted in preservation of renal function and histologic architecture. PHB solutions may be useful in preserving organ function during prolonged periods of in vivo ischemia.

Animals↗
PubMed1998

Clinical implications of blood substitutes.

Red cell substitutes are developing rapidly and progressing in their clinical testing. The original concept of a shelf storable oxygen carrying solution for use in trauma and other emergency situations still remains valid. Of interest is the potential for red cell substitutes to be used in other areas of surgery, traditionally the realm of autologous transfusion. This article describes some of the logic behind defining which areas of application are potentially useful in the surgical arena.

Blood Substitutes↗
PubMed1998

A pilot randomized trial comparing symptomatic vs. hemoglobin-level-driven red blood cell transfusions following hip fracture.

BACKGROUND: The indications for transfusion have never been evaluated in an adequately sized clinical trial. A pilot study was conducted to plan larger clinical trials. STUDY DESIGN AND METHODS: Hip fracture patients undergoing surgical repair who had postoperative hemoglobin levels less than 10 g per dL were randomly assigned to receive 1) symptomatic transfusion: that is, transfusion for symptoms of anemia or for a hemoglobin level that dropped below 8 g per dL or 2) threshold transfusion: that is, patients receive 1 unit of packed RBCs at the time of random assignment and as much blood as necessary to keep the hemoglobin level above 10 g per dL. Outcomes were 60-day mortality, morbidity, functional status, and place of residence. RESULTS: Among 84 eligible patients enrolled, mean (+/- SD) prerandomization hemoglobin was 9.1 (+/- 0.6) g/ dL. The median number of units transfused in the threshold transfusion group was 2 (interquartile range, = 1-2), and that in the symptomatic transfusion group was 0 (6; interquartile range, = 0-2) (p < 0.001). Mean hemoglobin levels were approximately 1 g per dL higher in the threshold group than in the symptomatic group: for example, on Day 2, 10.3 (+/- 0.9) g per dL versus 9.3 (+/- 1.2) g per dL, respectively (p < 0.001). At 60 days, death or inability to walk across the room without assistance occurred in 16 (39.0%) of the symptomatic transfusion group and 19 (45.2%) of the threshold transfusion group. Death occurred by 60 days in 5 (11.9%) of the symptomatic transfusion group and 2 (4.8%) in the threshold transfusion group (relative risk = 2.5; 95% CI, 0.5-12.2). Other outcomes were similar for the two groups. CONCLUSIONS: Symptomatic transfusion may be an effective blood-sparing protocol associated with the transfusion of appreciably fewer units of RBCs and lower mean hemoglobin levels than are associated with the threshold transfusion policy. However, it is unknown whether these two clinical strategies have comparable mortality, morbidity, or functional status. A definitive trial is needed.

Adult↗
PubMed1997

New transfusion strategies.

The "new transfusion strategies" are designed to minimize exposure to allogeneic transfusion while maximizing the use of autologous red cells. While not always possible in all clinical situations, this approach appears to be the current transfusion strategy paradigm. Physician and patient concerns about the risk of transfusion therapy are driving these strategies. When combined with management of the elements of cardiopulmonary physiology responsible for cardiac output and tissue perfusion, the autologous techniques of hemodilution, cell salvage, and predeposit are reasonable strategies for achieving the desired goals of allogeneic transfusion avoidance. Of the 11 policies and interventions proposed by the Blood Management Conference6 several need to be iterated as underpinnings for these strategies. They include: 1. assessing transfusion needs on a patient case basis; 2. transfusions are to be given and effect-benefit assessed before proceeding with additional transfusion; 3. limited exposure to allogeneic blood if possible; 4. minimize perioperative blood loss ranging from surgical technique to decreasing laboratory assessments; and 5. maximize oxygen delivery physiology as a first step in improving basic oxygen delivery.

Blood Component Transfusion↗
PubMed1997

Decreased whole blood factor IX activity following hemodilution with hemoglobin A-zero in-vitro.

Previous studies of hemoglobin-based oxygen carriers and their effects on coagulation have shown conflicting results. This study re-examined the effect of hemoglobin solution on blood coagulation in whole blood using highly purified human hemoglobin Ao (HbAo). Citrated human whole blood samples were diluted 1:1 with HbAo (7gHb/dl) or human serum albumin (HSA; 5g/dl) as a protein control, and both activated partial thromboplastin time (aPTT) and prothrombin time (PT) were measured using a mechanically based whole blood coagulometer. Multiple runs were performed with the same volunteer donor sample. The mean aPTT time of HbAo-diluted samples (105.9 +/- 19.9 sec., n = 41) was significantly longer than the undiluted controls (46.4 +/- 5.6 sec., n = 54) or HSA-diluted blood (77.1 +/- 12.7 sec., n = 41) indicating an abnormal intrinsic coagulation pathway. There was no significant difference between the PT times of the HbAo and HSA-diluted samples. To examine the cause of the prolonged aPTT times with HbAo dilution, we performed activity assays of intrinsic factors XII, XI, IX, and VIII in a citrated human whole blood system diluted 1/5 and 1/10 with normal saline solution (NSS), and then 1:1 with either HbAo, HSA, or NSS. Only the Factor IX activity was significantly depressed by hemodilution (1/5 HbAo 50.20 +/- 8.11; HSA 61.05 +/- 6.72; NSS 74.75 +/- 9.83. 1/10 HbAo 46.50 +/- 5.57; HSA 64.97 +/- 11.01; NSS 67.92 +/- 16.03). These results suggest that in-vitro hemodilution with HbAo causes a hypocoagulatory response through interference with Factor IX function.

Blood Coagulation↗
PubMed1996

Pathophysiology of anemia.

Inherent in any decision to treat a patient for anemia is an appreciation of the underlying cause of a decrease in the oxygen-carrying capacity of blood. Equally important is an understanding of how this acute or chronic decrease in oxygen delivery affects individual patients. Anemia generally results from blood loss, decreased red blood cell (RBC) production, poor RBC maturation, or increased RBC destruction. This article reviews the pathophysiology of anemia, with specific emphasis on its physiologic consequences in the surgical patient, and provides a contemporary definition of anemia for use in that context. Taking a broader, more functional view of anemia paves the way for understanding and appreciating the newer techniques of RBC conservation and transfusion avoidance, as well as of pharmacologic methods available to counter this disorder.

Anemia, Hypochromic↗