Prostacyclin administration during cardiopulmonary bypass in man

Epoprostenol Therapy for a Pediatric Patient With Subacute Heparin-Induced Thrombocytopenia and a Ventricular Assist Device Undergoing Heart Transplant: A Case Report

Concerns remain regarding the use of direct thrombin inhibitors for cardiopulmonary bypass anticoagulation in pediatric patients with heparin-induced thrombocytopenia undergoing complex cardiac surgery. We describe the safe and effective use of epoprostenol sodium as an alternative therapy before heparin exposure for a pediatric patient with subacute heparin-induced thrombocytopenia and a ventricular assist device undergoing heart transplant.

Prostacyclin, cardiopulmonary bypass and the alveolar capillary membrane

In a double blind controlled study of 24 patients undergoing coronary artery bypass grafting, 12 received an infusion of prostacyclin at 20 ng/kg/min during cardiopulmonary bypass in an attempt to reduce the previously reported increased alveolar capillary membrane permeability that occurs postoperatively. Prostacyclin significantly reduced platelet activation but had no effect in reducing complement activation or transpulmonary neutrophil sequestration. Alveolar epithelial permeability as assessed by measuring the clearance of inhaled 99mTc-DTPA from lung to blood did not change postoperatively in either group.

In order to fully evaluate pulmonary damage following cardiopulmonary bypass a marker for pulmonary endothelial damage may need to be used.

Cardiac surgery with cardiopulmonary bypass in patients with type II heparin-induced thrombocytopenia

BACKGROUND

The use of cardiopulmonary bypass (CPB) in patients with a history of type II heparin-induced thrombocytopenia (HIT) may be associated with complications related to their anticoagulation management.

METHODS

Between January 1997 and December 1999, among 4,850 adults patients who underwent cardiac surgery in our institution, 10 patients presented with preoperative type II HIT. In 4 patients, anticoagulation during CPB was achieved with danaparoid sodium. In 6 other patients, heparin sodium was used after pretreatment with epoprostenol sodium.

RESULTS

No significant change in platelet count occurred in any patient. No intraoperative thrombotic complication was encountered. Total postoperative chest drainage ranged from 250 to 1,100 ml in patients pretreated with epoprostenol and 1,700 to 2,470 ml in patients who received danaparoid sodium during CPB (p < 0.05, Mann-Whitney U test).

CONCLUSIONS

During CPB, inhibition of platelet aggregation by prostacyclin may be a safe anticoagulation approach in patients with type II HIT.

Platelet protective effect of TAK-029, a novel glycoprotein IIb/IIIa antagonist: an in vitro study

Previous studies have indicated that exposure of fibrinogen receptors associated with the glycoprotein IIb/IIIa complex contributes to platelet loss during cardiopulmonary bypass. TAK-029 is a newly developed reversible, nonpeptide inhibitor of platelet glycoprotein IIb/IIIa receptors. In this study, we tested the platelet preserving effect of TAK-029 in an in vitro model. The methods included the comparison of the release of beta-thromboglobulin (beta-TG) between a TAK-029 group (n = 5) and a control group (n = 5) in a mock circulation under a shear force generated by a centrifugal pump. To evaluate the degree of beta-TG release, deltabeta-TG/deltaT was calculated where deltabeta-TG is the increase in beta-TG and deltaT is the time. The results showed that the value of deltabeta-TG/deltaT in the TAK-029 group was significantly lower than it was in the control group (4.22 +/- 0.27 x 10(2) ng/ml vs. 7.33 +/- 0.66 x 10(2) ng/ml, respectively). In conclusion, TAK-029 reduced the platelet activation under the shear forces of an in vitro model, suggesting that TAK-029 is a potential candidate for platelet protection during cardiopulmonary bypass.

Prostacyclin counteracts the increase in capillary permeability induced by tumour necrosis factor-alpha

OBJECTIVE

To analyse how prostacyclin interferes with the short-term local circulatory effects of tumour necrosis factor-alpha (TNF alpha) in a skeletal muscle.

DESIGN

An autoperfused sympathectomised cat gastrocnemius muscle enclosed in a plethysmograph.

INTERVENTIONS

Arterial blood flow, total and segmental vascular resistances (large-bore arterial vessels, arterioles and veins), hydrostatic capillary pressure, tissue volume and capillary filtration coefficient were followed during local intra-arterial infusion of TNF alpha at various rates (2.5, 5.0 and 7.5 micrograms/kg per min) and during intra-arterial infusion of prostacyclin simultaneously with the highest dose of TNF alpha. The capillary filtration coefficient reflects the capillary surface for fluid exchange.

RESULTS

Arterial infusion of TNFx had no influence on vascular resistance up to 5.0 micrograms/kg per min but induced vasodilation at 7.5 micrograms/kg per min. No effects on the recorded hydrostatic capillary pressure were observed. The capillary filtration coefficient and the capillary filtration increased with the infusion rate of TNF alpha, the former by 55%. Simultaneous arterial infusion of prostacyclin (350 ng/kg per min) caused further vasodilation and an increase in hydrostatic capillary pressure and completely restored the capillary filtration coefficient to control. The TNF alpha-induced filtration was partly restored.

CONCLUSIONS

The local circulatory effect of TNF alpha is small apart from a graded increase in the capillary filtration coefficient, most likely reflecting an increase in the capillary permeability. The prostacyclin-induced decrease in capillary filtration coefficient most likely reflects a restoration of capillary permeability. The TNF alpha-induced transcapillary filtration is not fully reduced by prostacyclin due to a simultaneous increase in hydrostatic capillary pressure.

Effects of prostacyclin on myocardial hemodynamics and metabolism after coronary artery bypass grafting

OBJECTIVE

To study the effects of incremental infusion rates of prostacyclin on myocardial blood flow and metabolism and central hemodynamics shortly after coronary artery bypass grafting.

DESIGN

A pharmacodynamic dose-response study.

SETTING

A multi-institutional university hospital.

PARTICIPANTS

Twelve patients with two- or three-vessel coronary artery disease and with an ejection fraction greater than 0.5 were studied in the operating room after sternal closure and elective coronary artery bypass grafting.

INTERVENTIONS

Prostacyclin was administered at infusion rates of 2.5, 5, 10, and 20 ng/kg/min. Systemic and pulmonary hemodynamics and global (coronary sinus) as well as regional (great cardiac vein) myocardial blood flow and metabolic variables were measured.

MEASUREMENTS AND MAIN RESULTS

Infusion rates of 10 and 20 ng/kg/min decreased mean arterial blood pressure (13% and 21%, respectively), systemic vascular resistance (31% and 42%), and pulmonary vascular resistance (11% and 33%), increased cardiac output (28% and 37%), heart rate (9% and 13%), and stroke volume (15% and 20%), but had no effect on central filling pressures. Prostacyclin caused no changes in great cardiac vein flow or coronary sinus flow. Furthermore, prostacyclin caused no changes in regional myocardial oxygen extraction, indicating that prostacyclin did not induce direct coronary vasodilation. There were no electrocardiographic or obvious metabolic signs of myocardial ischemia during prostacyclin infusion.

CONCLUSION

Prostacyclin may be a useful afterload-reducing compound after coronary artery bypass grafting because it has no direct coronary vasodilatory effect, which minimizes the risk of myocardial ischemia.

A comparison of prostacyclin and sodium nitroprusside for the treatment of heart failure after cardiac surgery

OBJECTIVE

To study the effects of the two vasodilators, prostacyclin and sodium nitroprusside, on central hemodynamics in heart failure after cardiac surgery.

DESIGN

Randomized cross-over study.

SETTING

Multi-institutional university hospital.

PARTICIPANTS

Ten patients.

INCLUSION CRITERIA

cardiac index less than 2.5 L/min/m2; pulmonary capillary wedge pressure greater than 15 mmHg, systemic vascular resistance index greater than 2,500 dynes.s.cm-5/m2, and treatment with inotropic support. Five patients were treated with intra-aortic balloon counterpulsation.

INTERVENTIONS

After control measurements, mean arterial pressure was decreased by 10% to 20% with each vasodilator in each patient.

MEASUREMENTS AND RESULTS

Sodium nitroprusside induced decreases in mean pulmonary arterial pressure (-21%), pulmonary capillary wedge pressure (-29%), central venous pressure (-17%), and systemic vascular resistance (-25%), and increases in cardiac output (+7%) and stroke volume (+6%) compared with control. Prostacyclin decreased mean pulmonary arterial pressure (-14%), pulmonary capillary wedge pressure (-19%), central venous pressure (-7%), and systemic (-40%) and pulmonary (-25%) vascular resistances, whereas cardiac output (+25%) and stroke volume (+22%) increased compared with control. Prostacyclin, compared with sodium nitroprusside, induced a more pronounced increase in cardiac output and stroke volume, associated with less pronounced decreases in cardiac filling pressures and more profound decreases in systemic and pulmonary vascular resistances.

CONCLUSION

Prostacyclin appears to be a useful agent, superior to sodium nitroprusside, in the treatment of postoperative heart failure in patients with normal or mildly elevated cardiac filling pressures, where vasodilator treatment is indicated.

Low-dose Iloprost infusion improves insulin action and non-oxidative glucose metabolism in hypertensive patients

Fourteen hypertensive (174.3/98.3 mmHg) non-diabetic patients were given a euglyceamic glucose clamp along with infusion of 0.9% NaCl and the prostacyclin (PGI2) analogue Iloprost (0.7 ng x kg x min(-1)). Substrate oxidation was also determined by indirect calorimetry. Over the last 60 min of the clamp, Iloprost vs saline improved whole body glucose disposal (WBGD) (35 vs 28.3 micromol x kg(-1) LBM) and non-oxidative glucose metabolism (24.7 vs 18.1 micromol x kg(-1) LBM x min(-1). Iloprost delivery was associated with a significant decrease in membrane microviscosity (0.253 vs 0.205), but did not affect arterial blood pressure and heart rate. In nine patients, skeletal muscle blood flow (SMBF) and insulin-stimulated glucose uptake (GU) were also studied. At the end of the study, despite a similar SMBF (37 vs 38 ml x min(-1) x kg(-1)), GU (0.55 vs 0.46 mmol x l(-1)) was significantly increased by Iloprost infusion. Percentage decrease in membrane microviscosity was correlated with percentage increase in WBGD (r = 0.65) and non-oxidative glucose metabolism (r = 0.68). In conclusion, low-dose Iloprost infusion improves insulin action and non-oxidative glucose metabolism in hypertensive patients.

Pharmacodynamic profile of prostacyclin

Since the 1930s and the discovery by von Euler of a vasoactive, lipid-soluble substance that he erroneously assumed was generated by the prostate gland and therefore should be called "prostaglandin," the family of prostaglandins has grown to some 90 substances. These lipid mediators are derived from arachidonic acid in the "arachidonic acid cascade." In 1976, while looking for the enzyme that generates the unstable prostanoid thromboxane A2 from arachidonic acid, Moncada and Vane discovered prostaglandin I2 and renamed it "prostacyclin." Prostacyclin is the main product of arachidonic acid in all vascular tissues tested to date and strongly vasodilates all vascular beds studied. It is also the most potent endogenous inhibitor of platelet aggregation yet discovered, both inhibiting aggregation and dispersing existing aggregates. It acts through activation of adenylate cyclase, leading to increased levels of cyclic adenosine monophosphate. It also appears to have a "cytoprotective" activity, as yet not completely understood. Its effects are short-lasting, disappearing within 30 minutes of cessation of infusion. A stable, freeze-dried preparation of prostacyclin (epoprostenol) is available for administration to humans, and several analogs with therapeutically desirable characteristics are currently being clinically tested and should become commercially available soon. Clinical application of prostacyclin is bedeviled by 2 characteristics: it is pharmacologically unstable, so care must be taken in its use, and the correct dosage regimens have not yet been established.

Effect of intracardiac repair on biosynthesis of thromboxane A2 and prostacyclin in children with a left to right shunt

OBJECTIVE

To investigate the effect of intracardiac repair on the abnormal biosynthesis of prostacyclin (PGI2) and thromboxane A2 (TXA2) in children with congenital heart disease and increased pulmonary blood flow.

DESIGN

A prospective study with immunoaffinity chromatography and gas chromatography-mass spectrometry to measure the urinary excretion products of PGI2 (2,3-dinor-6-oxo-prostaglandin (PG) F1 alpha (2,3-dinor-6-oxo-PGF1 alpha)) and TXA2 (2,3-dinor-TXB2) before operation, in the first 12-24 h after operation, and at discharge from hospital.

SETTING

A supraregional referral centre for patients with congenital heart disease.

PATIENTS

15 patients aged 2 to 60 months (median 7 months) with a left to right shunt who underwent intracardiac repair.

RESULTS

The preoperative 2,3-dinor-TXB2 excretion rate was greater than that found previously in a control group of 16 healthy children with a median (range) age of 24 (6-36) months (1159(201) v 592(122) ng/g creatinine in controls, P = 0.006). The excretion rate rose after operation to 9600(3832) ng/g creatinine (P = 0.01) and decreased before discharge to 1071(191) ng/g creatinine (NS), but remained greater than that of the control group (P = 0.014). Before operation 2,3-dinor-6-oxo-PGF1 alpha excretion rates were similar to those of the healthy children (482(68) v 589(95) ng/g creatinine in controls) but increased after operation to 19,668(11,162) ng/creatinine (P = 0.002) and fell at discharge to 1621(245) ng/g creatinine although this was higher than both preoperative and control rates (P = 0.005 and P = 0.0002 respectively). The preoperative ratio of 2,3-dinor-TXB2 to 2,3-dinor-6-oxo-PGF1 alpha excretion was greater than that of the control group (3.2(0.8) v 1.3(0.22) in controls, (P = 0.005)), decreased significantly after operation to 0.9(0.13) (P = 0.016), and changed little, to 0.7(0.12), before discharge. The last two ratios were similar to those in normal children and significantly lower than those before operation (P = 0.004).

CONCLUSION

In children with a left to right shunt the ratio of the excretion rates of the metabolites of TXA2 and PGI2 was abnormal before operation, which favoured vasoconstriction and platelet aggregation, but had decreased at discharge from hospital. The increase in excretion of PGI2 metabolites over TXA2 metabolite after intracardiac repair augurs well for pulmonary vascular recovery.

Conjugated estrogens reduce endothelial prostacyclin production and fail to reduce postbypass blood loss

Intravenous conjugated estrogens correct bleeding times and reduce bleeding in uremia, gastrointestinal telangiectasias, and liver disease. One study found a similar benefit in patients undergoing open heart surgery. The mechanism by which conjugated estrogens improve bleeding times is unknown. We report on the effect of estrogens on endothelial prostacyclin production and bleeding in coronary bypass surgery. In a randomized, double-blind trial, 16 male patients undergoing elective coronary artery bypass surgery received four daily infusions of conjugated estrogens (0.6 mg/kg/day) or placebo, preoperatively. Groups were similar with respect to age, preoperative hemostatic profiles, and pump time. Conjugated estrogens significantly reduced greater saphenous vein endothelial prostacyclin production in the estrogen group compared to control subjects. Postoperative blood loss was not reduced, with a trend toward increased blood loss in the treatment group. We have shown that conjugated estrogens reduce endothelial prostacyclin production and fail to reduce blood loss in coronary bypass surgery.

Effects of taprostene, a stable prostacyclin analogue, on haemodynamics, platelet function and arachidonate metabolism in healthy volunteers

In order to assess the effect of taprostene on haemodynamics, platelet function and arachidonate metabolism in 4 healthy volunteers an intravenous infusion of 25 ng.kg-1.min-1 was given for 6 h. During the infusion period systolic blood pressure dropped from 130 to 111 mm Hg and diastolic blood pressure from 77 to 69 mm Hg. The heart rate rose from 77 to 84 beats/min. During the taprostene infusion the slope and height of the ADP and collagen induced platelet aggregation curves were significantly inhibited and the sensitivity of platelets to PGI2 and PGE1 was increased. Plasma and serum thromboxane B2, conversion of exogenous radiolabelled arachidonic acid, WU-test, circulating endothelial cell count, concentration of platelet factor 4, beta-thromboglobulin, malondialdehyde and the PGI2-synthesis stimulating plasma factor did not show any clear drug-related alteration. It is concluded that infusion of taprostene 25 ng.kg-1.min-1 caused measurable inhibition of platelet function ex vivo.

Prostacyclin and vascular function: implications for hypertension and atherosclerosis

Prostacyclin and endothelium-derived relaxing factor (or nitric oxide) are unstable mediators produced by the vascular endothelium, that are important for local regulation of platelet behavior and blood flow. This review focuses on the basic biochemistry and pharmacology of prostacyclin, its interactions with nitric oxide and nitrovasodilator drugs, and the implications of disturbances in this system for vascular disease, particularly hypertension and atherosclerosis. Prostacyclin and its stable analogs are also finding limited therapeutic applications in preservation of platelet function, pulmonary hypertension, and investigation into the cytoprotective and antiatherosclerotic properties is continuing.

Quantification of extracorporeal platelet deposition in cardiopulmonary bypass: effects of ZK 36374, a prostacyclin analogue

The degree of extracorporeal platelet sequestration in 32 patients undergoing cardiopulmonary bypass has been assessed using 111In labelled platelets and both a shadow shield whole body monitor and a standard gamma camera. The effects of ZK 36374, a prostacyclin analogue, on deposition of platelets in the oxygenator and atrial line filter were also investigated. Total platelet deposition in the placebo group ranged from 2.2% to 31.7%, mean 13.9 +/- 7.8%; n = 15, and was significantly higher than the deposition in the treatment group, range 0.7% to 9.4%, mean 3.9 +/- 2.6%; n = 16, P less than 0.001. There was also a highly significant correlation between the gamma camera and whole body monitor measurements, r = 0.99, P less than 0.001, with no systematic difference between the techniques. This study demonstrates that accurate quantitative assessment of platelet deposition can be achieved with either the gamma camera or whole body monitor. In addition, significant reduction in platelet sequestration in the extracorporeal circuit can be achieved by using ZK 36374 during the bypass operation.

Epoprostenol (PGI2, prostacyclin) during high-risk hemodialysis: preventing further bleeding complications

The frequency of hemodialysis-associated hemorrhage was studied prospectively in two successive, parallel, heparin-controlled studies using epoprostenol (PGI2; average dose, 4.1 ng/kg.min) as the sole antithrombotic agent. Sixty-three patients with active or recently active bleeding underwent 163 hemodialysis treatments in each of which prospective bleeding risk was assessed. PGI2 was associated with up to 50% overall reduction in the frequency of bleeding, particularly in the highest risk circumstances. PGI2 also allowed successful completion of the full, prospectively prescribed hemodialysis time in the most treatments (82% versus 93% with heparin). Furthermore, the efficiency of hemodialysis using PGI2, as indicated by the reduction in concentration of blood urea nitrogen and serum creatinine, was equal to that using heparin, even though there was a tendency toward modest reduction in residual volume of the hollow fiber dialyzer and slightly more frequent early termination of treatment from dialyzer clotting with PGI2. No severe vasodilatory side effects of PGI2 were observed during these studies. Hypotension was equally frequent during hemodialysis with heparin as with PGI2. The current results suggest that PGI2 should be considered as a substitute for heparin during high-risk hemodialysis because PGI2 may reduce the incidence of dialysis-associated bleeding without severe adverse side effects.

Placebo-controlled study of Iloprost (ZK 36374) in cardiopulmonary bypass surgery

The effects of infusion of Iloprost (ZK 36374), a prostacyclin analogue, on platelet function, postoperative blood loss and microaggregate deposition on filters and oxygenators were studied in patients undergoing routine coronary operations. In this double-blind randomized study of 50 male patients, 25 received Iloprost and 25 a placebo. Platelet deposition was assessed using Indium-labelled platelets. Comparison of Iloprost and placebo groups showed the mean number of platelets to be significantly higher in the Iloprost group at the end of cardiopulmonary bypass and in early postoperative recovery. Similarly, spontaneous aggregation of platelets was higher in the placebo group. The mean percentages of platelets sequestrated in the extracorporeal circuit were significantly higher in the placebo group. There was no difference in either the amount or pattern of postbypass bleeding between Iloprost and the control patients. Infusion of the tested drug was responsible for significant hypotension, which was correctable with fluid administration alone. Thus, Iloprost diminishes the fall in circulatory platelet count during cardiopulmonary bypass, preserves platelet function, diminishes platelet deposition on filters and oxygenators, but also causes arterial hypotension.

Platelet damage by protamine and the protective effect of prostacyclin: an experimental study in dogs

Protamine is given after cardiopulmonary bypass to reverse the effect of heparin. However, the adverse effects of an overdose have not been fully evaluated. In this canine study, a standard dose of one bolus of heparin (300 IU per kilogram of body weight) was neutralized by an infusion of protamine hydrochloride in a 1:2 ratio. Platelet number and function were severely reduced by this overdose of protamine, and this finding correlated with a prolongation of the bleeding time. Giving a titrated dose of protamine hydrochloride to reverse heparin activity, measured by the activated clotting time, affected neither platelet number nor function. When prostacyclin (0.5 microgram/kg/min) was infused during administration of an overdose of protamine, platelets again were not affected by the excess of protamine.

Effect of prostacyclin (PGI2) on water and solute transport in the human jejunum

Prostacyclin is an arachidonic acid metabolite, synthesised throughout the gastrointestinal tract, which has different effects on water and electrolyte transport across a variety of mammalian gastrointestinal epithelia. Using a perfusion technique in the human jejunum of 11 healthy subjects in vivo, the effect of intravenous prostacyclin, 4 ng/kg/min, on jejunal water and solute transport from a glucose electrolyte solution was investigated. In the prostacyclin group (n = 5), prostacyclin was infused intravenously from 70-150 minutes, and buffer administered iv from 0-70 and 150-210 minutes. In the buffer group (n = 6), iv buffer was administered from 0-210 minutes. In the prostacyclin group, net jejunal absorption of water was inhibited from 90-120 min (p less than 0.05), 150-180 min (p less than 0.01) and 180-210 min (p less than 0.01), of sodium was inhibited from 90-120 min (p less than 0.05), 120-150 min (p less than 0.05), 150-180 min (p less than 0.01) and 180-210 min (p less than 0.01), and of chloride was inhibited from 90-120 min (p less than 0.05), 120-150 min (p less than 0.005), 150-180 min (p less than 0.01) and 180-210 min (p less than 0.01). Prostacyclin had no effect on net movement of glucose, potassium or bicarbonate. These results are consistent with a role for prostacyclin in the endogenous humoral regulation of water and electrolyte transport in the human jejunum.

Effect of prostacyclin and adenosine triphosphate on vasospasm of canine basilar artery

Cerebral vasospasm is one of the most important factors influencing morbidity and mortality of intracranial operations or diseases. Platelet aggregation and adhesion is increased in spastic vessels. Degradation of platelets liberates mediators, which in turn increase vasospasm, thus creating a vicious cycle. Healthy vessels cope with this by increasing the synthesis of prostacyclin. The purpose of this study was to increase experimentally the levels of arterial prostacyclin and adenosine triphosphate (ATP) in animals through intraarterial injection of these substances because they are lower in spastic vessels. Prostacyclin promotes antiaggregation and dilatation, increases blood flow, inhibits thromboxane A2, and prevents synthesis of angiotensin II. Most of these effects were done by increasing cyclic adenosine monophosphate (cAMP). After injecting autogenous blood into the cisterna magna of male dogs, both the acute and chronic phases of vasospasm and the degenerative changes in the arterial wall were observed. Injecting ATP increased the severity of vasospasm. During vasospasm it was found that when prostacyclin is used intraarterially, vasodilatation began, but degeneration of the arterial wall could not be prevented. In the group of animals in which both ATP and prostacyclin were used, there was no degeneration of the arterial wall and the basilar artery was seen to be normal when viewed under the electron microscope.

Effects of prostacyclin infusion on renal function during cardiopulmonary bypass

Infusion of prostacyclin inhibits platelet activation during cardiopulmonary bypass (CPB) but also results in systemic arterial hypotension. Therefore, the effects of CPB and prostacyclin on renal function were studied in 36 male patients undergoing aortocoronary bypass. Nineteen patients (Group 1) received prostacyclin, 50 ng per kilogram of body weight per minute, during CPB, and 17 patients (Group 2) served as controls. There was pronounced hypotension in Group 1 only. Urine production during CPB averaged 88 +/- 140 ml and 2,306 +/- 1,112 ml in Groups 1 and 2, respectively. No patient had renal failure. Glomerular filtration rate (GFR), as measured by clearance of chromium 51-labeled ethylenediaminetetraacetic acid, was increased in Group 1 from 86 +/- 14 to 99 +/- 22 ml/1.73 m2/min (p less than 0.05) the day after operation, but remained unchanged in Group 2 (81 +/- 15 to 82 +/- 21 ml/1.73 m2/min). The increased GFR in Group 1 can be regarded as an expected adaptation to the change in body fluids after CPB. Therefore, the unchanged GFR in Group 2 must be regarded as caused by insufficient adaptation or impaired renal function. Proximal tubular function was evaluated by determination of beta 2-microglobulin in urine. In both groups, urinary beta 2-microglobulin and the ratio of urinary beta 2-microglobulin to urinary creatinine were increased the day after operation. The hypotension in Group 1 did not exacerbate the damage to tubular function.

In vivo interaction of prostacyclin with an inhibitor of cyclic nucleotide phosphodiesterase, HL 725

Prostacyclin (PGI2) inactivates platelets by stimulation of adenylate cyclase, and its effect can be potentiated in vitro by simultaneous inhibition of cyclic AMP phosphodiesterase. The interaction of synthetic PGI2 and the potent phosphodiesterase inhibitor HL 725 was studied in a model of systemic platelet activation by intravenous injection of collagen. Platelet aggregate formation was evaluated by continuous on-line measurement of the circulating platelet count. Collagen injection in rabbits receiving vehicle caused a 30 +/- 3% decrease in the circulating platelet count. Infusion of PGI2 (0.05, 0.1 and 0.75 micrograms kg-1 min-1) dose-dependently inhibited this decrease. HL 725 (0.5, 1 and 3 micrograms kg-1 min-1) caused a slight but significant effect. Combinations of PGI2 and HL 725, respectively, at 0.25 + 1.0 and 0.1 + 0.5 micrograms kg-1 min-1 inhibited platelet aggregate formation to a greater extent than when either substance was used alone and produced a comparable inhibition to PGI2 at 0.75 micrograms kg-1 min-1. Collagen induced an acute fall in the mean arterial blood pressure (MABP) which also was inhibited by PGI2, HL 725 and their combinations. The infusion of a combination of PGI2 and HL 725 before collagen produced a decrease in the MABP which was greater than when either compound was used on its own. Thus, PGI2 and the phosphodiesterase inhibitor HL 725 interact in vivo to inhibit platelet aggregation and lower MABP.

Adenosine spares platelets during cardiopulmonary bypass in man without causing systemic vasodilatation

The effect of infusing adenosine during cardiopulmonary bypass (CPB) on platelet count and mean arterial blood pressure (MABP) was studied in 13 patients (age 42-74), with 12 patients (age 47-66) as controls. Adenosine infusion (0.1 mg/kg/min in a central vein) caused a ten- to twentyfold increase of the adenosine concentration in the venous blood to the oxygenator, while the arterial levels were close to basal values (0.3 +/- 0.1 microM). The platelet count was significantly higher in the treated than in the placebo group during and 30 min after CPB, but not on the postoperative day. The groups did not differ with regard to the postoperative blood loss from tube drainage. Adenosine did not cause major systemic vasodilation (MABP less than 30 mmHg) in any case, and the blood pressure levels showed no intergroup difference during CPB. However, seven control patients but none in the adenosine group required vasodilator treatment (sodium nitroprusside) during CPB to prevent MABP from exceeding 70 mmHg. We conclude that adenosine infusion during CPB in man spares platelets, with minor changes in blood pressure.

The effects of prostacyclin (PGI2) on haematological and haemodynamic parameters, and lung histology in puppies undergoing cardiopulmonary bypass surgery with profound hypothermia

Puppies 6-12 kg underwent cardiopulmonary bypass with profound hypothermia. Thirteen animals received 200 ng kg-1 min-1 of PGI2 during bypass whilst 11 control animals received equivalent volumes of glycine buffer (placebo) over a similar period. Results indicated preservation of platelets, leukocytes and fibrinogen levels, together with shortened activated partial thromboplastin times and fewer fibrinogen degradation products post-bypass in PGI2-treated animals. There was an initial fall in blood pressure and systemic vascular resistance in PGI2 treated animals, but pulmonary pressures and resistances, cardiac outputs, and heart rates showed no significant differences from controls. Higher and more satisfactory end of bypass and post-bypass blood pressure levels, together with a lesser fall-off in mean total pulmonary compliance, and shortened bypass times were achieved in treated animals. PGI2 appeared to afford some protection against lung damage as observed by histological studies. All beneficial effects appeared to be significantly greater amongst smaller animals. The results indicate possible benefits from the use of PGI2 in infant open heart surgery.

Expression of the platelet procoagulant activity in vivo in thrombus formation in an extracorporeal shunt in the rat

The interaction of platelets and the coagulation system has been investigated in vivo on a cotton thread implanted in an arteriovenous shunt in the rat. Depletion of the circulating platelet count with anti-platelet antibody reduces both thrombus deposition and 125I-labelled fibrinogen incorporation demonstrating the platelet behaviour with either anagrelide or prostacyclin decreases thrombus deposition by a greater extent than that expected from the platelet content of the thrombus. Treatment with warfarin also dramatically decreases both formation and 51Cr-labelled platelet deposition demonstrating the important role of the coagulation system in platelet aggregation in this model. Treatment with Arvin or with heparin also reduced the thrombus weight. It is concluded that this is a model of bidirectional platelet interaction with the coagulation system and may have similarities with thrombosis which occurs in extracorporeal shunts in man.

Disadvantages of prostacyclin infusion during cardiopulmonary bypass: a double-blind study of 50 patients having coronary revascularization

Prostacyclin (PGI2) has been suggested for use in cardiopulmonary bypass (CPB) because of its positive effects on platelet number and function. Fifty patients who underwent coronary artery bypass grafting using a bubble oxygenator received heparin, 3 mg per kilogram of body weight, and then were randomly assigned to receive PGI2, 25 ng/kg/min, beginning 5 minutes before and until the end of CPB (26 patients) or a placebo (24 patients). Both groups were similar in sex, age, heparin dose, protamine dose, and CPB time. During CPB, mean arterial pressure fell significantly with PGI2 (76 +/- 2 mm Hg to 53 +/- 2 mm Hg; p less than 0.05) and necessitated pressor substances. Platelet counts fell significantly in both groups with the start of CPB, but after 60 minutes were similar in both groups (118 +/- 9 X 10(3) versus 130 +/- 8 X 10(3); not significant [NS]) and were unchanged 3 hours after CPB. Total chest tube output was 647 +/- 51 ml (placebo group) versus 576 +/- 34 ml (PGI2 group) (NS); 18 of the patients given PGI2 required 26 transfusions compared with 16 transfusions in 8 of the patients given a placebo (p less than 0.05). In PGI2 patients, arterial oxygen tension on 100% oxygen fell from 281 +/- 18 mm Hg before CPB to 223 +/- 17 mm Hg immediately after CPB (p less than 0.05). The placebo patients did not show a change in this variable.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of intravenous ZK36-374, a stable prostacyclin analogue, on normal volunteers

Prostacyclin (PGI2) therapy has been evaluated in many vascular diseases. However, it is unstable and a potent vasodilator, able to lower blood pressure. Although such effects may be desirable in some situations, they are unwanted in others. ZK36-374 (Schering AG) is a carbacyclin derivative with a similar action to PGI2; however, it is chemically stable and has less of a hypotensive action. We evaluated the effects of a 4-hour I.V. infusion of ZK36-374 at a maximum dose of 2ng/Kg/min. in ten normal volunteers. Prior to the infusion and at 2 and 4 hours, blood was sampled for estimation of platelet aggregation in both platelet rich plasma and whole blood. Beta-thromboglobulin, 6-keto-PGF1 alpha and TXB2 were measured by radioimmunoassay, as were other coagulation and rheological tests. The infusion was well tolerated with facial flushing, jaw trismus and some nausea at max dose. Blood pressure and pulse rate were not significantly altered. During infusion of ZK36-374, the rates of platelet aggregation to 2 microns ADP and 2 micrograms collagen in PRP were significantly decreased when compared to baseline, as was whole blood aggregation to 2 microns ADP and 0.5 microgram collagen. Beta TG also fell significantly, as did the levels of 6-keto-PGF1 alpha and TXB2. Fibrinolysis, blood viscosity, and red cell deformability were unchanged. ZK36-374 is an effective anti-platelet agent without major toxic or hypotensive effects.

Evidence suggestive of diffuse brain damage following cardiac operations

In 37 patients regional cerebral blood flow (rCBF) was measured by single photon emission computerised tomography (SPECT) after inhalation of xenon-133 before and within the first 10 days after open heart surgery for acquired or congenital heart disease. None of the patients had motor deficits postoperatively and no focal abnormalities were disclosed by the rCBF tomograms. However, rCBF was generally reduced and mean CBF fell from a normal value of 53.5 to 44.7 ml/100 g X min (p less than 0.001). Changes in rCBF occurred uniformly throughout the brain. The reduction in CBF correlated positively with increasing years (p less than 0.05), duration of extracorporeal circulation (p less than 0.05), and low mean arterial blood pressure during the bypass (p less than 0.02). It was generally more pronounced after valve replacement than after coronary bypass (p less than 0.16). In 11 patients investigated 1 year after surgery CBF remained slightly reduced, 50.5 ml/100 g X min (p less than 0.05). No CBF reduction occurred in a control group of 15 patients who underwent carotid endarterectomy or extracranial-intracranial shunt operations. The findings are consistent with the suggestion that the extracorporeal circulation causes early postoperative central nervous system dysfunction.

Does prostacyclin prevent cognitive deficits after open heart surgery?

Two groups of open heart surgery patients, one receiving prostacyclin and one placebo, were assessed one week pre-operatively and 3 months post-operatively, using a battery of clinical tests measuring a variety of cognitive functions. No significant differences between the groups were detected, apart from a visual retention deficit at 3 months in the prostacyclin group. The results cast doubt on previous findings suggesting that prostacyclin reduces cognitive deficits following open heart surgery.

Nobel lecture. Adventures and excursions in bioassay--the stepping stones to prostacyclin

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Effects of prostacyclin during cardiopulmonary bypass in men on plasma levels of beta-thromboglobulin, platelet factor 4, thromboxane B2, 6-keto-prostaglandin F1 alpha and heparin

A randomized double-blind study was carried out on 40 male patients requiring aorto-coronary bypass surgery. 20 patients received a constant dose of 8 ng kg-1 min-1 of prostacyclin (PGI2), beginning two minutes before extracorporeal circulation (ECC) and ending together with ECC. Compared to the placebo-treated patient group (n = 20), PGI2-treatment significantly reduced the ECC-induced release of platelet alpha-granule proteins, beta-thromboglobulin (1178 ng/ml vs. 1926 ng/ml) and platelet factor 4 (837 ng/ml vs. 1245 ng/ml) into plasma (mean of max. values). Furthermore the decrease of platelet counts during ECC was less pronounced in PGI2-treated patients. Application of PGI2 had no effect on the increase in thromboxane B2 (TxB2) plasma levels, which amounted to 0.6 ng/ml at the end of ECC. PGI2-treatment resulted in significantly elevated plasma concentrations of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) (2.1 ng/ml) throughout the infusion off prostacyclin. 6-keto-PGF1 alpha plasma levels increased up to 1.2 ng/ml in the control group patients, indicating a stimulation of endogenous PGI2 formation during ECC.

Effects of prostacyclin and indomethacin on experimental delayed cerebral vasospasm

Isolated canine basilar artery contracted by prostaglandin E2, hemoglobin, or serum was relaxed in a dose-dependent manner by the addition of 10(-8)M to 10(-6)M prostacyclin (PGI2), and was scarcely relaxed by 10(-9)M PGI2. In other studies, intravenous administration of PGI2 (25 or 75 ng/kg/min), indomethacin (4 mg/kg), or indomethacin (4 mg/kg) plus PGI2 (25 ng/kg/min) failed to reverse angiographic delayed vasospasm produced in vivo in the canine basilar artery by an intracisternal injection of blood. In addition, no significant increase occurred in mean values of regional cerebral blood flow (rCBF) with any treatments, and mean rCBF difference in dogs treated by PGI2 infusion at 25 ng/kg/min was 2.5 +/- 1.2 ml/100 gm/min and only significantly increased (p less than 0.01). Mean arterial blood pressure was significantly reduced by PGI2 infusion at 25 (p less than 0.05) or 75 ng/kg/min (p less than 0.005).