Heparin reversal by protamine in humans--complement, prostaglandins, blood cells, and hemodynamics

Red blood cell transfusion-related dynamics of extracellular vesicles in intensive care patients: a prospective subanalysis

Extracellular vesicles (EVs) accumulate during packed red blood cell (PRBC) storage. To date, the involvement of EVs in transfusion-related immunomodulation (TRIM) has not been prospectively evaluated in intensive care unit (ICU) patients. This was a prospective subanalysis of a recent observational feasibility study in postoperative ICU patients after: (1) open aortic surgery (Aorta), (2) bilateral lung transplantation (LuTx), and (3) other types of surgery (Comparison). Patient plasma was collected three times each before and after leukoreduced PRBC transfusion at 30-min intervals. The total number of EVs and EVs derived from erythrocytes (EryEVs), total platelets (total PEVs), activated platelets, granulocytes (GEVs), monocytes, and myeloid cells in PRBC samples and patient plasma were analyzed by flow cytometry. Statistical analysis was performed by Spearman's correlation test, linear mixed models and pairwise comparisons by Wilcoxon matched-pairs test. Twenty-three patients (Aorta n = 5, LuTx n = 9, Comparison n = 9) were included in the final analysis. All EV subgroups analyzed were detectable in all PRBCs samples (n = 23), but concentrations did not correlate with storage time. Moreover, all EVs analyzed were detectable in all plasma samples (n = 138), and EV counts were consistent before transfusion. Concentrations of total EVs, EryEVs, total PEVs, and GEVs increased after transfusion compared with baseline in the entire cohort but not in specific study groups. Furthermore, the change in plasma EV counts (total EVs and EryEVs) after transfusion correlated with PRBC storage time in the entire cohort. Extracellular vesicles were detectable in all PRBC and plasma samples. Individual EV subtypes increased after transfusion in the entire cohort, and in part correlated with storage duration. Future clinical studies to investigate the role of EVs in TRIM are warranted and should anticipate a larger sample size.Trial registration: Clinicaltrials.gov: NCT03782623.

Red blood cell transfusion-related eicosanoid profiles in intensive care patients—A prospective, observational feasibility study

Introduction: Eicosanoids are bioactive lipids present in packed red blood cells (PRBCs), and might play a role in transfusion-related immunomodulation (TRIM). We tested the feasibility of analyzing eicosanoid profiles in PRBC supernatant and in plasma samples of postoperative intensive care unit (ICU) patients transfused with one unit of PRBCs.

Methods: We conducted a prospective, observational feasibility study enrolling postoperative ICU patients: 1) patients treated with acetylsalicylic acid following abdominal aortic surgery (Aorta); 2) patients on immunosuppressants after bilateral lung transplantation (LuTx); and 3) patients undergoing other types of major surgery (Comparison). Abundances of arachidonic acid (AA) and seven pre-defined eicosanoids were assessed by liquid chromatography and tandem mass spectrometry. PRBC supernatant was sampled directly from the unit immediately prior to transfusion. Spearman’s correlations between eicosanoid abundance in PRBCs and storage duration were assessed. Patient plasma was collected at 30-min intervals: Three times each before and after transfusion. To investigate temporal changes in eicosanoid abundances, we fitted linear mixed models.

Results: Of 128 patients screened, 21 were included in the final analysis (Aorta n = 4, LuTx n = 8, Comparison n = 9). In total, 21 PRBC and 125 plasma samples were analyzed. Except for 20-hydroxyeicosatetraenoic acid (HETE), all analyzed eicosanoids were detectable in PRBCs, and their abundance positively correlated with storage duration of PRBCs. While 5-HETE, 12-HETE/8-HETE, 15-HETE, 20-HETE, and AA were detectable in virtually all plasma samples, 9-HETE and 11-HETE were detectable in only 57% and 23% of plasma samples, respectively.

Conclusions: Recruitment of ICU patients into this transfusion study was challenging but feasible. Eicosanoid abundances increased in PRBC supernatants during storage. In plasma of ICU patients, eicosanoid abundances were ubiquitously detectable and showed limited fluctuations over time prior to transfusion. Taken together, larger clinical studies seem warranted and feasible to further investigate the role of PRBC-derived eicosanoids in TRIM.

Combination of aptamer and drug for reversible anticoagulation in cardiopulmonary bypass

Unfractionated heparin (UFH), the standard anticoagulant for cardiopulmonary bypass (CPB) surgery, carries a risk of post-operative bleeding and is potentially harmful in patients with heparin-induced thrombocytopenia-associated antibodies. To improve the activity of an alternative anticoagulant, the RNA aptamer 11F7t, we solved X-ray crystal structures of the aptamer bound to factor Xa (FXa). The finding that 11F7t did not bind the catalytic site suggested that it could complement small-molecule FXa inhibitors. We demonstrate that combinations of 11F7t and catalytic-site FXa inhibitors enhance anticoagulation in purified reaction mixtures and plasma. Aptamer-drug combinations prevented clot formation as effectively as UFH in human blood circulated in an extracorporeal oxygenator circuit that mimicked CPB, while avoiding side effects of UFH. An antidote could promptly neutralize the anticoagulant effects of both FXa inhibitors. Our results suggest that drugs and aptamers with shared targets can be combined to exert more specific and potent effects than either agent alone.

Mannose-binding lectin-associated serine protease-1 is a significant contributor to coagulation in a murine model of occlusive thrombosis

Bleeding disorders and thrombotic complications constitute a major cause of death and disability worldwide. Although it is known that the complement and coagulation systems interact, no studies have investigated the specific role or mechanisms of lectin-mediated coagulation in vivo. FeCl(3) treatment resulted in intra-arterial occlusive thrombogenesis within 10 min in wild-type (WT) and C2/factor B-null mice. In contrast, mannose-binding lectin (MBL)-null and MBL-associated serine protease (MASP)-1/-3 knockout (KO) mice had significantly decreased FeCl(3)-induced thrombogenesis. Reconstitution with recombinant human (rh) MBL restored FeCl(3)-induced thrombogenesis in MBL-null mice to levels comparable to WT mice, suggesting a significant role of the MBL/MASP complex for in vivo coagulation. Additionally, whole blood aggregation demonstrated increased MBL/MASP complex-dependent platelet aggregation. In vitro, MBL/MASP complexes were captured on mannan-coated plates, and cleavage of a chromogenic thrombin substrate (S2238) was measured. We observed no significant differences in S2238 cleavage between WT, C2/factor B-null, MBL-A(-/-), or MBL-C(-/-) sera; however, MBL-null or MASP-1/-3 KO mouse sera demonstrated significantly decreased S2238 cleavage. rhMBL alone failed to cleave S2238, but cleavage was restored when rMASP-1 was added to either MASP-1/-3 KO sera or rhMBL. Taken together, these findings indicate that MBL/MASP complexes, and specifically MASP-1, play a key role in thrombus formation in vitro and in vivo.

Voltage-dependent modulation of cardiac ryanodine receptors (RyR2) by protamine

It has been reported that protamine (>10 µg/ml) blocks single skeletal RyR1 channels and inhibits RyR1-mediated Ca²⁺ release from sarcoplasmic reticulum microsomes. We extended these studies to cardiac RyR2 reconstituted into planar lipid bilayers. We found that protamine (0.02–20 µg/ml) added to the cytosolic surface of fully activated RyR2 affected channel activity in a voltage-dependent manner. At membrane voltage (V_m; SR lumen - cytosol) = 0 mV, protamine induced conductance transitions to several intermediate states (substates) as well as full block of RyR2. At V_m>10 mV, the substate with the highest level of conductance was predominant. Increasing V_m from 0 to +80 mV, decreased the number of transitions and residence of the channel in this substate. The drop in current amplitude (full opening to substate) had the same magnitude at 0 and +80 mV despite the ∼3-fold increase in amplitude of the full opening. This is more similar to rectification of channel conductance induced by other polycations than to the action of selective conductance modifiers (ryanoids, imperatoxin). A distinctive effect of protamine (which might be shared with polylysines and histones but not with non-peptidic polycations) is the activation of RyR2 in the presence of nanomolar cytosolic Ca²⁺ and millimolar Mg²⁺ levels. Our results suggest that RyRs would be subject to dual modulation (activation and block) by polycationic domains of neighboring proteins via electrostatic interactions. Understanding these interactions could be important as such anomalies may be associated with the increased RyR2-mediated Ca²⁺ leak observed in cardiac diseases.

Regulation of human internal mammary and radial artery contraction by extracellular and intracellular calcium channels and cyclic adenosine 3', 5' monophosphate

BACKGROUND

The internal mammary (IMA) and radial arteries (RA), which are routinely used in coronary artery bypass grafting, show a significant incidence of postoperative vasospasm. The present study evaluated the respective roles of calcium (Ca2+)-dependent and cyclic adenosine 3', 5' monophosphate-dependent (cAMP) signaling in mediating contraction and relaxation of the IMA and RA.

METHODS

We examined the contractile responses of the IMA and RA to potassium chloride, a depolarizing agent; phenylephrine, an alpha-adrenergic agonist; and U46619, a thromboxane analogue, in the absence and presence (0.045 to 1.500 mM) of extracellular Ca2+.

RESULTS

Potassium chloride elicited little or no contraction in the absence of extracellular Ca2+. Contractions elicited by U46619 were similar in the IMA and RA, both in the absence and presence of extracellular Ca2+. By contrast, phenylephrine elicited significantly greater extracellular Ca2+-dependent contraction of the IMA than the RA. Estimation of cyclic guanosine 3', 5' monophosphate (cGMP) and cAMP revealed levels of cAMP to be about fourfold higher than cGMP in both the RA and IMA. Whereas forskolin and milrinone elicited similar relaxation of IMA and RA precontracted with either U46619 or phenylephrine and increased adenylate cyclase-catalyzed cAMP production, isoproterenol-induced relaxation of the arteries precontracted with U46619 was significantly impaired compared with arteries precontracted with phenylephrine.

CONCLUSIONS

Our findings suggest that thromboxane A2 receptor-dependent pathways activate contraction of IMA and RA through both extracellular Ca2+-dependent and Ca2+-independent pathways. In addition, adenylate cyclase appears to play a key role in attenuating thromboxane A2 and alpha-adrenergic receptor-mediated contraction through both pathways.

Thromboxane Receptor Stimulation Suppresses Guanylate Cyclase-Mediated Relaxation of Radial Arteries

BACKGROUND

The internal mammary artery (IMA) and the radial artery (RA) are routinely used in coronary artery bypass grafting. However, RA grafts have a higher incidence of postoperative vasospasm and comparatively poor patency rates. The present study was undertaken to investigate the signaling pathways mediating contraction and relaxation in the IMA and RA with the aim of better understanding the mechanism underlying the propensity of RA grafts to spasm.

METHODS

We examined the contractile responses of the IMA and RA to KCl (a depolarizing agent), phenylephrine (an alpha-adrenergic agonist), and U46619 (a thromboxane analogue).

RESULTS

Contractions induced by KCl or U46619 did not significantly differ in IMA and RA. By contrast, phenylephrine evoked significantly greater contraction of the IMA than the RA. Contractions induced by both phenylephrine and U46619 were dose-dependently inhibited by nifedipine (an L-type calcium channel blocker). Estimation of thromboxane A2 (TxA2) and prostacyclin (PGI2) synthesis revealed that the TxA2 to PGI2 ratio in the RA was twice that in the IMA. Moreover, acetylcholine-induced and nitroglycerin-induced relaxation of RA precontracted with U46619 was significantly impaired, as compared with RA precontracted with phenylephrine. These data suggest that inhibition of nitroglycerin-induced soluble guanylate cyclase activity by U46619 was at least partially responsible for the diminished vasodilatory response of RA to nitric oxide.

CONCLUSIONS

Our findings suggest that by reducing nitric oxide-stimulated soluble guanylate cyclase activity, the higher TxA2 to PGI2 ratios in RA, and the elevated serum TxA2 levels seen during coronary artery bypass grafting operations, may underlie the vasospasm and poor patency rates seen with the RA.

Protamine is a low molecular weight polycationic amine that produces actions on cardiac muscle

Protamine is a polycationic amine used clinically to reverse heparin overdose. Here we characterized the actions of protamine on the cardiovascular system of anesthetized rats and in isolated Langendorff rat hearts in order to define a possible mechanism of action on cardiovascular tissue. In anesthetized rats, protamine reduced blood pressure in a dose-dependent fashion and reduced heart rate. Only at a dose of 32 mg/kg did protamine increase the Q-aT interval of the electrocardiogram (EKG) to 62 +/- 6 msec from a control of 54 +/- 5 msec (p < 0.05). Protamine dose-dependently reduced cardiac output by 74 +/- 5% and stroke volume by 62 +/- 15 %, suggesting that it directly affects cardiac contractility. An analysis of blood chemistry suggests that protamine does not alter plasma electrolyte or serum enzyme levels at the doses administered. Protamine produced aberrant rhythms in normal rat hearts when administered between 1-32 mg/kg. The P-Q segment of the EKG for each of the arrhythmic complexes was reduced to 24 +/- 1 msec compared to 32 +/- 3 msec in normal EKG complexes suggestive of anomalous atrio-ventricular or pre-excitation conduction. Isolated rat heart studies confirmed that protamine produced a reduction in cardiac contractility. Our studies suggest that the cardiovascular depressant actions of protamine result from a direct effect on the heart and that protamine may produce aberrant conduction within the heart which may result in deleterious effects in heart function, especially conditions associated with myocardial disease.

The effect of differing rates and injection sites on the amount of protamine delivered before detection of hemodynamic alterations in dogs

OBJECTIVES

To determine the effect of the route and rate of protamine administration on the amount of protamine that could be delivered before a hemodynamic reaction occurred in dogs.

STUDY DESIGN

Prospective randomized experimental study.

ANIMALS

Twenty adult mixed-breed dogs weighing 25.1+/-2.5 kg.

METHODS

Before vascular surgery, the dogs were heparinized to reach an activated clotting time (ACT) of 300 seconds. After completion of the vascular surgery, protamine was administered intravenously until a hemodynamic reaction was recorded. The 4 groups of dogs were given protamine at 5 mg/min (slow) or 10 mg/min (fast) via the cephalic or the jugular veins. Systemic and pulmonary arterial pressures, central venous pressure (CVP), and pulmonary arterial occlusion pressure (PAOP) were recorded before and after protamine administration. The dose of protamine was recorded when a reaction occurred, which was defined as mean arterial pressure (MAP) <60 mm Hg or mean pulmonary arterial pressure (MPAP) >20 mm Hg or more than double the baseline value.

RESULTS

Significant decreases in systolic arterial pressure (SAP), MAP, and diastolic arterial pressure (DAP) and significant increases in systolic (SPAP), mean (MPAP), and diastolic (DPAP) pulmonary arterial pressures were recorded after protamine administration. The cephalic slow group had significantly fewer protamine reactions than other groups (chi-square = 8.57, P = .03, df = 3). Significantly more protamine could be delivered from the cephalic vein (52.5+/-14.5 mg) compared with the jugular vein (37.6+/-16 mg) before a reaction occurred (P = .048).

CONCLUSION

The rate of administration did not have an effect on the amount of protamine delivered. Adverse reactions were minimized when protamine was administered via the cephalic vein at a slow rate.

CLINICAL RELEVANCE

We would recommend delivering protamine after cardiopulmonary bypass or vascular surgery through a peripheral venous route.

The effects of heparin and extracorporeal circulation on platelet counts and platelet microaggregation during cardiopulmonary bypass

BACKGROUND

Cardiopulmonary bypass is associated with platelet activation and reduced platelet counts. Platelet activation may artifactually lower platelet counts by causing aggregation. In vivo platelet activation may increase existent platelet microaggregation ex vivo. We studied platelet counts and existent platelet microaggregation at different stages of cardiopulmonary bypass.

METHODS

Twenty-one patients were studied before and after heparinization (300 U. kg(-1)) and at the end of cardiopulmonary bypass. Unaggregated (or single) platelets were counted in hirudin-anticoagulated blood, and total platelets were counted in ethylenediaminetetraacetic acid-anticoagulated blood.

RESULTS

The total platelet count, 198 +/- 61 x 10(9). L(-1), was unaffected by heparin and stayed at 197 +/- 60 x 10(9). L(-1) (P =.7) but fell during extracorporeal circulation; the hemodilution-corrected count was 163 +/- 52 x 10(9). L(-1) (P =.0004). Heparinization reduced the unaggregated platelet count from (mean +/- 1 SD) 178 +/- 62 x 10(9). L(-1) to 155 +/- 60 x 10(9). L(-1) (P =.0001). Extracorporeal circulation had little additional effect. The hemodilution-corrected count was 142 +/- 48 x 10(9). L(-1) (P =.6).

CONCLUSIONS

Heparinization caused platelet activation and increased existent platelet microaggregation ex vivo. During extracorporeal circulation, there was a reduction in total platelets that was greater than could be explained by hemodilution alone, but the unaggregated platelet count did not change significantly when corrected for hemodilution. Furthermore, the increased platelet microaggregation observed after heparinization was no longer evident after this loss. These findings suggest that during extracorporeal circulation, the platelets that formed into microaggregates after heparinization were lost from the circulation in preference to single platelets.

Isoflurane and sodium nitroprusside reduce the depressant effects of protamine sulfate on isolated ischemic rat hearts

The administration of protamine sulfate (protamine) to reverse the action of heparin is associated with adverse reactions. We studied the effects of protamine and isoflurane on isolated, perfused rat hearts previously subjected to cardioplegic ischemia. Hearts were perfused with oxygenated Krebs-Henseleit (KH) solution for 30 min, then subjected to cardioplegic ischemia for 30 min (KCl 16 mEq/L at 31 degrees C) and 5 min reperfusion. Drug exposure lasted 15 min, and the recovery period was 60 min. Test groups were control, protamine (10 microg/mL), isoflurane (1.5%), protamine +/- isoflurane, sodium nitroprusside (SNP) (2.5 ng/mL), and SNP +/- protamine. Left ventricular developed pressure (LVP), coronary flow, and myocardial oxygen consumption were depressed by protamine to 30% +/- 4%, 47% +/- 4%, and 39% +/- 4% of baseline (P < 0.001 versus control), respectively. Isoflurane and SNP afforded partial protection from the effects of protamine: LVP was 57% +/- 5% and 51% +/- 3% of baseline, respectively (P < 0.05 versus protamine alone and control); coronary flow was 70% +/- 6% and 97% +/- 12% of baseline, respectively (P < 0.05 versus protamine alone; P < 0.05 for isoflurane versus control); and O2 consumption was 69% +/- 6% and 88% +/- 15% of baseline, respectively (P < 0.05 versus protamine; P < 0.05 for isoflurane versus control). In this model, protamine-induced myocardial depression and coronary vasoconstriction were less pronounced in the presence of either isoflurane or SNP.

IMPLICATIONS

We examined the interactions of isoflurane, sodium nitroprusside, and protamine in a rat heart model and found that both isoflurane and sodium nitroprusside partially protect the heart from the depressant effects of protamine. This finding is significant, as these drugs are often used in heart surgery.

Extracorporeal heparin adsorption following cardiopulmonary bypass with a heparin removal device--an alternative to protamine

OBJECTIVES

To evaluate the therapeutic efficacy and applicability of a heparin removal device (HRD) based on plasma separation and poly-L-lysine (PLL) affinity adsorption as an alternative to protamine in reversing systemic heparinization following cardiopulmonary bypass (CPB).

DESIGN

A prospective study.

SETTING

University research laboratory.

SUBJECTS

Adult female swine (n=7).

INTERVENTIONS

Female Yorkshire swine (n=7, 67.3+/-3.5 [SEM] kg) were subjected to 60 mins of right atrium-to-aortic, hypothermic (28 degrees C) CPB. After weaning from CPB, the right atrium was recannulated with a two-stage, dual-lumen cannula which was connected to an HRD via extracorporeal circulation. Blood flow was drained at 1431.2+/-25.4 mL/min from the inferior vena cava, through the plasma separation chamber of the HRD (where heparin was bound to PLL), and reinfused into the right atrium. The HRD run time was determined by a previously established mathematical model of first-order exponential depletion.

MEASUREMENTS AND MAIN RESULTS

Heart rate, mean arterial pressure, pulmonary arterial pressure, central venous pressure, kaolin and celite activated clotting time (ACT), activated partial thromboplastin time (APTT), heparin concentration, and plasma free hemoglobin were obtained before, during, and after the use of the HRD. Pre-CPB ACT was 167+/-89 secs (kaolin) and 99+/-7 secs (celite), and APTT was 34+/-5 secs. The HRD run time averaged 27.4 +/-1.5 mins targeted to remove 90% total body heparin. Use of the HRD was not associated with any adverse hemodynamic reactions or increases in plasma free hemoglobin. The heparin concentration immediately following CPB was 4.85+/-0.24 units/mL, with ACT >1000 secs and APTT >150 secs in all animals. During heparin removal, total body heparin content followed first-order exponential depletion kinetics. At the end of the HRD run, heparin concentration decreased to 0.51+/-0.09 units/mL, with kaolin ACT returning to 177+/-22 secs, celite ACT returning to 179+/-17 secs, and APTT returning to 27+/-3 secs (p > .05 vs. pre-CPB baseline for all variables).

CONCLUSIONS

The HRD is capable of reversal of anticoagulation following CPB without significant blood cell damage or changes in hemodynamics. The HRD, therefore, can serve as an alternative to achieve heparin clearance in clinical situations where use of protamine may be contraindicated.

Involvement of fibrinogen in protamine-induced pulmonary hypertension

Protamine reversal of heparin anticoagulation occasionally results in pulmonary hypertension as well as systemic hypotension. To examine the contribution of blood components to this induction of pulmonary hypertension, we developed an isolated rat lung perfusion model and perfused heparinized plasma, heparinized serum, and Hepes (4% bovine serum albumin, 20 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid, 5 mM glucose, in warm physiological saline) buffer solution with or without fibrinogen. Perfusion with heparinized plasma and Hepes buffer solution with fibrinogen caused pulmonary hypertension; perfusion with heparinized serum or Hepes buffer solution without fibrinogen did not, suggesting that fibrinogen is involved in the induction of pulmonary hypertension. We also labeled protamine with 125I and compared the amounts of protamine accumulating in the lung with different concentrations of fibrinogen. The amount of protamine trapped in the lung increased according to the concentration of fibrinogen. Fibrinogen may accelerate the reaction between pulmonary endothelial cells and protamine or protamine-heparin complexes. In the mechanism of protamine-induced pulmonary hypertension, fibrinogen, as well as heparin and protamine, may be an essential component.

The isolated post ischaemic rat heart is more vulnerable to protamine sulphate than the non-ischaemic heart

Protamine sulphate is currently used for the reversal of heparin anticoagulation but is known to cause direct myocardial depression. The purpose of this study was to compare the effects of protamine sulphate on the isolated heart with and without cardioplegic ischaemia. Isolated rat hearts (Langendorff preparation) were electrically paced at 300 beats/min and perfused with Krebs-Henseleit solution. Five groups were tested: (1) control: no ischaemia, no protamine; (2) no ischaemia, protamine; (3) no ischaemia, protamine (time-matched control to groups 4 and 5); (4) control: ischaemia, no protamine; and (5) ischaemia, protamine. Protamine sulphate was infused for 15 min at 10 microg/ml. In groups 4 and 5, cardioplegic ischemia was maintained for 30 min at 30 degrees C before protamine exposure. Protamine decreased myocardial performance in a time- and dose-dependent manner. Protamine depressed mean (s.d.) myocardial left ventricular pressure in both non-ischaemic hearts (groups 2 and 3, to 49(4)% and 50(4)% from baseline, respectively) and post ischaemic hearts (group 5, to 28(8%). Mean (s.d.) left ventricular-developed pressure only partially recovered after protamine in post-ischaemic hearts (to 55(13)% of baseline) compared with full recovery of the non-ischaemic group. Protamine depressed coronary flow to 70(5)% and 74(8)% in non-ischaemic hearts (groups 2 and 3, respectively) and to 58(7)% in group 5. Coronary flow recovered completely at the end of the experiments in all protamine-treated groups. In conclusion, isolated rat hearts subjected to cardioplegic ischaemia are more vulnerable to protamine than are non-ischaemic hearts.

Enhancement of the leukocyte-endothelial cell interaction in collecting venules of skeletal muscle by protamine

OBJECTIVE

A transient but severe systemic leukopenia regularly occurs after the antagonization of heparin by protamine in patients and in animals. The aim of the present study was to investigate the site and mechanisms of white blood cell retention during this transient leukopenia by studying the leukocyte-endothelial cell interaction in skeletal muscle venules.

METHODS

Syrian golden hamsters were equipped with a dorsal skinfold chamber for intravital fluorescence microscopy and arterial and venous catheters for drug infusion, blood pressure measurement, and blood sampling. Microhemodynamic parameters and leukocyte-endothelial cell interactions were observed in one single collecting venule per animal after intravenous infusion of saline solution (control, n = 10), of protamine (n = 9), and after infusion of heparin followed by either intravenous protamine (n = 9) or intraarterial protamine (n = 9).

RESULTS

All parameters remained unchanged in the control group. Whereas venular diameters remained unchanged, protamine transiently increased arterial blood pressure and venular erythrocyte velocity in all groups. Systemic leukocyte counts and the venular leukocyte discharge concentration decreased concurrently after protamine administration by about 60% to 70% at 2 minutes while the fraction of rolling leukocytes and the number of adherent leukocytes remained unchanged. Two and one-half minutes later, systemic leukocyte counts and venular discharge concentrations normalized while the fraction of leukocytes rolling slowly along or adhering firmly to the venular endothelial wall increased considerably and similarly in all groups receiving protamine. Myeloperoxidase (an indicator of polymorphonuclear leukocytes) determination in 20 separate hamsters 2 minutes after protamine infusion revealed increased myeloperoxidase activity exclusively in the lungs.

CONCLUSION

The response of leukocytes to protamine infusion with or without prior heparinization is biphasic: initial retention of leukocytes in the lungs is followed by enhanced leukocyte-endothelial cell interaction in the systemic circulation.

Perioperative distribution of pulmonary vascular resistance in patients undergoing coronary artery surgery

This study was undertaken to measure distribution of pulmonary vascular resistance (PVR) perioperatively in patients undergoing coronary artery bypass grafting (CABG) and to examine the effects of cardiopulmonary bypass (CPB) on pulmonary capillary pressure (Pc) relative to wedge pressure (Pw). Pulmonary artery catheters were placed before anesthetic induction in 18 patients scheduled for elective CABG and systemic hemodynamic variables were measured. Pulmonary artery pressure was recorded during balloon inflation and stored for off-line determination of Pc. Data were collected prior to induction (baseline), as well as after induction and intubation, skin incision, sternotomy, protamine administration, and chest closure. At each data point, downstream (capillary plus venous segments) resistance (Rds) contributed approximately 60% of total PVR and did not change significantly during the operation. PVR decreased (P < 0.05) after CPB and protamine administration, primarily due to a decrease in the absolute magnitude of the upstream (arterial) resistance. Administration of large-dose opioid anesthesia had no significant effect (P > 0.05) on total PVR or on segmental distribution of vascular resistance. At all data points, Pc was significantly larger than Pw (P < 0.05). This study demonstrates that perioperative measurement of Pc is feasible, that during CABG under these conditions, relative contribution of arterial and venous resistances remain relatively unchanged, that Pc is always larger than Pw, and that the administration of large-dose opioid anesthesia has a minimal effect on pulmonary vascular hemodynamics.

Protamine-induced pulmonary venoconstriction in heparinized pigs

Reversal of heparin anticoagulation with protamine may be associated with acute pulmonary vasoconstriction. The specific site of pulmonary vasoconstriction has not been determined. This study was designed to determine the site of protamine-induced pulmonary vasoconstriction and the role of nitric oxide (NO) after protamine injection. Pigs were anesthetized and instrumented with catheters for monitoring pulmonary arterial, systemic arterial, and central venous pressures. Pulmonary capillary pressure was estimated using the arterial occlusion concept, while left atrial pressure was estimated from the equilibrium wedge pressure. Hemodynamic measurements were made during baseline, before and after heparin (200 U/kg), at peak pressure response after protamine injection (2 mg/kg), and 10 and 30 min thereafter. In the control group, pulmonary vascular resistance (PVR) values during baseline and after heparin were identical (2.7 +/- 0.4 mm Hg.L-1.min-1). At peak protamine response (1-2 min) PVR increased to 8.0 +/- 1.6, but returned to baseline value after 10 min (2.8 +/- 0.3) and remained stable for 30 min (2.2 +/- 0.3). The increase in PVR after protamine was primarily due to an increase in venous resistance from 1.0 +/- 0.2 to 4.9 +/- 1.4 mm Hg.L-1.min-1, and a much smaller increase in arterial resistance from 1.7 +/- 0.3 to 3.4 +/- 0.6 mm Hg.L-1.min-1. A second group was treated with nitrow-L-arginine (LNA, 20 mg/kg) to inhibit NO release, and then heparin and protamine were administered as in the first group. Heparin had no effect on pressures, but protamine increased PVR by the same magnitude as in Group 1.(ABSTRACT TRUNCATED AT 250 WORDS)