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A H Stephenson

Publications and source records attributed to A H Stephenson.

At least 37 records · Page 2Linked to original sources
PubMed1996

Effect of eicosanoid inhibition on the development of pulmonary edema after acute lung injury.

In experimental models of acute lung injury, cyclooxygenase inhibition improves oxygenation, presumably by causing a redistribution of blood flow away from edematous lung regions. This effect on perfusion pattern could also reduce alveolar edema formation. On the other hand, pulmonary pressures usually increase after cyclooxygenase inhibition, an effect that could exacerbate edema accumulation. Therefore we tested the following hypothesis: the total accumulation of pulmonary edema in dogs during a 24- to 28-h period of observation after acute lung injury caused by oleic acid will be less in a group of animals treated with meclofenamate (n = 6) or with the thromboxane-receptor blocker ONO-3708 (n = 5) than in a group of animals treated with oleic acid alone (placebo, n = 6). Lung water concentrations (LWC), the regional pattern of pulmonary perfusion, and protein permeability were measured with the nuclear medicine imaging technique of positron emission tomography. After 24-28 h, LWC was significantly less (P < 0.05) in the ONO-3708 group than in the meclofenamate group (a similar trend was seen compared with the placebo group, P = 0.12). After 24-28 h, pulmonary arterial pressures were highest in the meclofenamate group. Regardless of group, the only significant correlation with the change in LWC was with the integral of pulmonary pressures over the 24- to 28-h period. The data suggest that thromboxane inhibition will reduce edema accumulation in acute lung injury but that this effect depends on reducing as much as possible the simultaneous development of pulmonary hypertension from other causes.

Animals↗
PubMed1996

Hypotheses regarding the role of pericytes in regulating movement of fluid, nutrients, and hormones across the microcirculatory endothelial barrier.

A decade ago, we initiated studies to define relationship(s) between products of 5-lipoxygenase-mediated arachidonic acid metabolism and altered microvascular permeability. Patients with permeability (nonhydrostatic) pulmonary edema (adult respiratory distress syndrome) and intact animal models of permeability edema, produced with agents that required neutrophils (phorbol myristate acetate) and those that did not (ethchlorvynol), invariably revealed the presence of leukotrienes; in contrast, leukotrienes were not detected in cases of hydrostatic pulmonary edema. In isolated perfused canine lung, we identified increases in microvascular permeability coefficients in response to the injurious agent. Permeability coefficients were not increased when injurious agents were given in the presence of 5-lipoxygenase inhibitors. To define further the relationships between leukotriene generation and edema formation, we postulated that leukotrienes effected contraction of capillary pericytes, thereby increasing pore size of endothelial intercellular junctions and enhancing movement across the microvascular barrier. We isolated pericytes from bovine retinas, identified them morphologically and by staining characteristics, and, in preliminary experiments, found that they do not possess the 5-lipoxygenase enzyme; however, when cocultured with neutrophils, which possess 5-lipoxygenase but cannot synthesize sulfidopeptide leukotrienes because of their lack of glutathione S-transferase, sulfidopeptide leukotriene synthesis ensued. In view of the anatomic position of pericytes, evidence that they participate in endothelial transport, their ability to contract, and evidence of cell-to-cell communication, we propose that pericytes control the movement of fluid, solutes, hormones, and small and large molecules across the microvascular endothelium.

Animals↗
PubMed1995

Prostaglandin H synthetase-mediated metabolism of dopamine: implication for Parkinson's disease.

Differences in prostaglandin H synthetase (PHS) activity in the substantia nigra of age- and postmortem interval-matched parkinsonian, Alzheimer's, and normal control brain tissue were assessed. Prostaglandin E2 (PGE2, an index of PHS activity) was higher in substantia nigra of parkinsonian brain tissue than Alzheimer's or control tissue. Incubation of substantia nigra slices with arachidonic acid (AA) increased PGE2 synthesis. Dopamine stimulated PHS synthesis of PGE2. [3H]Dopamine was activated by PHS to electrophilic intermediate(s) that covalently bound to DNA, microtubulin protein, bovine serum albumin, and sulfhydryl reagents. When AA was replaced by hydrogen peroxide, PHS/H2O2-supported binding proceeded at rates similar to those observed with PHS/AA. Indomethacin and aspirin inhibited AA-mediated cooxidation of dopamine but not H2O2-mediated metabolism. PHS-mediated metabolism of dopamine was not affected by monoamine oxidase inhibitors. Substrate requirements and effects of specific inhibitors suggest cooxidation of dopamine is mediated by the hydroperoxidase activity of PHS. 32P-postlabeling was used to detect dopamine-DNA adducts. PHS/AA activation of dopamine in the presence of DNA resulted in the formation of five dopamine-DNA adducts, i.e., 23, 43, 114, 70, and 270 amol/micrograms DNA. DNA adduct formation was PHS, AA, and dopamine dependent. PHS catalyzed cooxidation of dopamine in dopaminergic neuronal degeneration is discussed.

Absorption↗
PubMed1995

Effect of L-NAME on pressure-flow relationships in isolated rabbit lungs: role of red blood cells.

Nitric oxide (NO) is produced by and relaxes pulmonary arteries and veins; however, a role for NO as a participant in the control of pulmonary vascular resistance (PVR) remains to be defined. Here we investigated the hypothesis that for NO to serve as a determinant of PVR in the rabbit requires the presence of blood. In isolated blood-perfused rabbit lungs, NG-nitro-L-arginine methyl ester (L-NAME, 100 microM) increased PVR and the slope of the pressure-flow relationship. These effects of L-NAME were prevented by pretreatment with L-arginine. In contrast, in lungs perfused with a physiological salt solution, L-NAME had no effect on PVR or the pressure-flow relationship. The addition of washed red blood cells (RBCs) to physiological salt solution, but not the addition of plasma and platelets, restored the response to L-NAME. This effect of RBCs was not reproduced by increasing perfusate viscosity with dextran. These results suggest that, in the rabbit lung, NO is a determinant of PVR in the presence of blood. Moreover, that aspect of blood that permits the generation of NO appears to be related to the RBC and not to perfusate viscosity.

Animals↗
PubMed1995

Relationship of arachidonic acid release to porcine coronary artery relaxation.

In porcine coronary artery endothelium-dependent relaxation to bradykinin is in part attributed to a chemically unidentified factor, termed endothelium-derived hyperpolarizing factor (EDHF). We hypothesize that arachidonic acid, acting through a cyclooxygenase-independent mechanism, is responsible for EDHF production. To define the relationship between EDHF production and arachidonic acid release, we investigated the role of phospholipase C in bradykinin-induced relaxation and prostaglandin I2 production (an index of arachidonic acid release) in porcine coronary artery. The phospholipase C inhibitor U73122 (1 mumol/L) abolished bradykinin-induced, nitric oxide-mediated relaxation but did not inhibit either bradykinin-induced, EDHF-mediated relaxation or prostaglandin I2 production. However, when given at a larger dose (20 mumol/L) U73122 abolished both bradykinin-induced, EDHF-mediated relaxation and prostaglandin I2 production. Similarly, the calcium-ATPase inhibitor thapsigargin, given at a dose (1 mumol/L) that abolished bradykinin-induced increases in intracellular calcium concentration in cultured porcine coronary artery endothelial cells, eliminated both bradykinin-induced. EDHF-mediated relaxation and prostaglandin I2 production. Although thapsigargin abolished bradykinin-induced prostaglandin I2 production, the basal production of prostaglandin I2 was enhanced and contraction of endothelium-intact rings was attenuated. These latter responses are most likely related to enhanced basal arachidonic acid release and associated EDHF production. These observations suggest that phospholipase C activation and increased intracellular calcium concentration are required for both bradykinin-induced arachidonic acid release and EDHF production in porcine coronary artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Effect of indomethacin on increases in leukotriene B4 and pulmonary edema in response to phorbol ester administration in dogs.

The administration of leukotrienes (LTs) into the pulmonary circulation results in edema formation and increased vascular permeability. We reported previously that the administration of phorbol myristate acetate (PMA, 20 micrograms/kg) to intact anesthetized dogs results in a reduction in circulating white blood cells as well as the development of pulmonary edema concomitant with the appearance of LTs in the lungs. In contrast, when a smaller dose of PMA (10 micrograms/kg) was administered, neither extravascular lung water nor LTs increased, although there was a similar reduction in circulating white blood cells. In the present study, we used a property of indomethacin, namely, its capacity to augment the formation of LTs, to examine further the relationship between LT generation and pulmonary edema formation in response to PMA administration. In intact pentobarbital-anesthetized dogs pretreated with saline (N = 9), the administration of PMA at a dose of 10 micrograms/kg, i.v., did not result in any change in extravascular lung water or in LTB4 present in bronchoalveolar lavage fluid (BALF). In contrast, in six animals pretreated with indomethacin (5 mg/kg), the administration of this dose of PMA resulted in increases in both extravascular lung water (P < 0.05) and LTB4 (P < 0.05) in BALF. These results provide support for the hypothesis that leukotrienes are requisite for PMA-induced increases in extravascular lung water.

Animals↗
PubMed1994

Relaxation of porcine coronary artery to bradykinin. Role of arachidonic acid.

Bradykinin-induced relaxation of precontracted, porcine coronary artery (PCA) rings is mediated by distinctly different endothelium-derived relaxing factors depending on the contractile agent used. Thus when contracted with KCl, bradykinin-induced relaxation of PCA rings is mediated solely by nitric oxide (NO), whereas when contracted with the thromboxane mimetic U46619, a small component of the relaxation is attributable to NO and a large component is attributable to a non-NO mechanism that is independent of cyclooxygenase activity. We hypothesized that the non-NO component was mediated by arachidonic acid (AA) or by a non-cyclooxygenase product of AA metabolism. Bradykinin-induced relaxations of PCA rings precontracted with U46619 in the presence of indomethacin (10 mumol/L) were moderately attenuated by the NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 100 mumol/L), whereas when precontracted with KCl, L-NAME abolished the relaxations. AA produced endothelium-dependent relaxations of rings precontracted with U46619 that were unaffected by L-NAME, whereas AA did not relax rings precontracted with KCl. In rings precontracted with U46619, in the presence of L-NAME and indomethacin the phospholipase inhibitors quinacrine (50 mumol/L) and 4-bromophenacyl bromide (10 mumol/L) attenuated bradykinin- but not AA-induced relaxations. Inhibitors of both lipoxygenase (BW 755c [100 mumol/L] and nafazatrom [20 mumol/L]) and cytochrome P-450 (proadifen [10 mumol/L] and clotrimazole [10 mumol/L]) pathways did not eliminate bradykinin- or AA-induced relaxations, although clotrimazole partially attenuated AA-induced relaxations. These findings suggest that bradykinin-induced relaxation of PCA rings is mediated by AA through a mechanism that is not dependent on cyclooxygenase, lipoxygenase, or cytochrome P-450 pathways.

Animals↗
PubMed1993

Thromboxane receptor stimulation/inhibition and perfusion redistribution after acute lung injury.

Perfusion redistribution (PR) after acute oleic acid (OA) lung injury may be the result of changes in the tissue concentration ratio of thromboxane (Tx) and prostacyclin (A. H. Stephenson et al. J. Appl. Physiol. 73: 2126-2134, 1992). We tested this hypothesis by determining whether the Tx mimetic U-46619 would mimic PR caused by cyclooxygenase inhibition with meclofenamate and whether the Tx receptor antagonist ONO-3708 would inhibit PR even in the presence of meclofenamate. Measurements of regional pulmonary blood flow (PBF) and lung water concentration were made with the nuclear medicine imaging technique of positron emission tomography. Measurements were made at baseline and 2 h after OA. At baseline, the spatial distribution of PBF was similar in all experimental groups. Two hours after OA, fractional PBF was reduced to the edematous lung in all groups given OA, but the magnitude of change was greater in those groups receiving meclofenamate or U-46619 compared with the change in the group given OA only. Thus, although the Tx mimetic produced the same amount of PR as meclofenamate, Tx inhibition did not prevent PR after meclofenamate. Therefore, the ratio of Tx to prostacyclin per se is not the critical determinant of PR.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1992

Eicosanoid balance and perfusion redistribution of oleic acid-induced acute lung injury.

We have proposed that endogenous prostacyclin opposes the vasoconstriction responsible for redistribution of regional pulmonary blood flow (rPBF) away from areas of increased regional lung water concentration (rLWC) in canine oleic acid- (OA) induced acute lung injury (D. P. Schuster and J. Haller. J. Appl. Physiol. 69: 353-361, 1990). To test this hypothesis, we related regional lung tissue concentrations of 6-ketoprostaglandin (PG) F1 alpha and thromboxane (Tx) B2 in tissue samples obtained 2.5 h after administration of OA (0.08 ml/kg iv) to rPBF and rLWC measured by positron emission tomography. After OA only (n = 16), rLWC increased in dependent lung regions. Some animals responded to increased rLWC by redistribution of rPBF away from the most edematous regions (OA-R, n = 6), whereas others did not (OA-NR, n = 10). In another six animals, meclofenamate was administered after OA (OA-meclo). After OA, tissue concentrations of 6-keto-PGF1 alpha were greater than TxB2 in all groups, but concentrations of 6-keto-PGF1 alpha were not different between OA-R and OA-NR animals. TxB2 was increased in the dependent regions of animals in both OA-R and OA-NR groups compared with controls (no OA, n = 4, P < 0.05). The tissue TxB2/6-keto-PGF1 alpha ratio was smaller in controls and OA-NR in which no perfusion redistribution occurred than in OA-R and OA-meclo in which it did occur. This TxB2/6-keto-PGF1 alpha ratio correlated significantly with the magnitude of perfusion redistribution.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Ketoprostaglandin F1 alpha↗
PubMed1992

Enhanced microvascular permeability of PMA-induced acute lung injury is not mediated by cyclooxygenase products.

Products of cyclooxygenase activity have been proposed to mediate the pulmonary hypertension and increased microvascular permeability associated with phorbol myristate acetate- (PMA) induced acute lung injury. Previously, we reported that thromboxane (Tx) does not mediate PMA-induced pulmonary hypertension in intact anesthetized dogs. In the present study, PMA was administered to isolated canine lungs perfused with autologous blood at constant flow to investigate a possible role for Tx in the PMA-induced increase in microvascular permeability. Changes in permeability were assessed by determining changes in the capillary filtration coefficient (Kfc). In lobes pretreated with papaverine to prevent PMA-induced increases in pulmonary vascular resistance, Kfc increased from a baseline value of 0.2 +/- 0.03 to 1.5 +/- 0.29 ml.min-1.cmH2O-1.100 g wet lobe wt-1 (P < 0.01) 30 min after PMA (5.8 x 10(-8) M, n = 10). Concomitantly, TxB2, the stable metabolite of TxA2, increased from 138 +/- 44 to 1,498 +/- 505 pg/ml (P < 0.05) in the blood. Both the selective Tx synthase inhibitor, OKY-046 (7 x 10(-4) M, n = 6), and the cyclooxygenase inhibitor, indomethacin (10(-4) M, n = 7), prevented the PMA-induced increase in TxB2, but neither compound attenuated the PMA-induced increase in Kfc. ONO-3708 (10(-6) M), a selective prostaglandin (PG) H2/TxA2 receptor antagonist, prevented the vasoconstriction resulting from administration of U-46619, a stable PGH2/TxA2 receptor agonist, but it did not prevent the PMA-induced increases in Kfc (n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)

6-Ketoprostaglandin F1 alpha↗
PubMed1992

OKY-046 prevents increases in LTB4 and pulmonary edema in phorbol ester-induced lung injury in dogs.

Thromboxanes (Txs) were implicated as possible participants in the altered microvascular permeability of acute lung injury when the Tx synthase inhibitor, OKY-046, was reported to prevent pulmonary edema induced by phorbol myristate acetate (PMA). Recently, however, we found that OKY-046, at a dose just sufficient to block Tx synthesis in intact dogs, did not prevent PMA-induced pulmonary edema but rather merely reduced it modestly. The present study was designed to explore other mechanisms whereby OKY-046 might prevent PMA-induced pulmonary edema. The finding that 5-lipoxygenase (5-LO) metabolites of arachidonic acid were increased within the lung after PMA administration, coupled with the report that OKY-046 inhibited slow-reacting substance of anaphylaxis formation, permitted formulation of the hypothesis that OKY-046, at a dose in excess of that required to inhibit Tx synthesis, inhibits the formation of a product(s) of 5-LO and, thereby, prevents edema formation. In vehicle-pretreated pentobarbital-anesthetized male mongrel dogs (n = 4), PMA (20 micrograms/kg i.v.) increased pulmonary vascular resistance (PVR) from 4.4 +/- 0.3 to 26.3 +/- 8.8 mmHg.l-1 x min (P < 0.01) and extravascular lung water from 6.7 +/- 0.5 to 19.1 +/- 6.2 ml/kg body wt (P < 0.05). Concomitantly, both TxB2 and leukotriene B4 (LTB4) were significantly increased in the lung. Pretreatment with OKY-046 (100 mg/kg i.v., n = 8) prevented PMA-induced increases in TxB2, LTB4, and pulmonary edema formation but did not prevent the increase in PVR.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Ketoprostaglandin F1 alpha↗
PubMed1990

Production of leukotrienes in phorbol ester-induced acute lung injury.

Leukotrienes, when administered into the pulmonary circulation of intact animals or isolated perfused lungs, have been associated with the formation of pulmonary edema. In addition, leukotrienes were identified in edema fluid and in bronchoalveolar lavage fluid (BALF) both from patients with the adult respiratory distress syndrome (ARDS) and from dogs with ethchlorvynol-induced acute lung injury (ALI). To determine whether the identification of leukotrienes in BALF was a finding common to ALI, etiology notwithstanding, we produced acute lung injury in dogs with phorbol myristate acetate (PMA). PMA produces a model of ALI thought to differ mechanistically from ethchlorvynol-induced ALI. Leukotriene C4 (LTC4), D4 (LTD4) and B4 (LTB4) were measured in BALF before and after PMA administration in intact pentobarbital-anesthetized dogs. The intravenous administration of 20 or 30 micrograms/kg of PMA produced increases in pulmonary vascular resistance (PVR) and extravascular lung water (EVLW), whereas, 10 or 15 micrograms/kg caused only a modest increase in PVR with no increase in EVLW. LTD4 and LTB4 were increased in BALF solely in those animals that developed increases in EVLW. These results, when viewed together with those reported in humans with ARDS and in dogs with ethchlorvynol-induced ALI, support the hypothesis that leukotriene detection in BALF is a feature common to ALI, etiology notwithstanding.

Animals↗
PubMed1990

Thromboxane does not mediate pulmonary hypertension in phorbol ester-induced acute lung injury in dogs.

Thromboxane (Tx) has been suggested to mediate the pulmonary hypertension of phorbol myristate acetate- (PMA) induced acute lung injury. To test this hypothesis, the relationship between Tx and pulmonary arterial pressure was evaluated in a model of acute lung injury induced with PMA in pentobarbital sodium-anesthetized male mongrel dogs. Sixty minutes after administration of PMA (20 micrograms/kg iv, n = 10), TxB2 increased 10-fold from control in both systemic and pulmonary arterial blood and 8-fold in bronchoalveolar lavage (BAL) fluid. Concomitantly, pulmonary arterial pressure (Ppa) increased from 14.5 +/- 1.0 to 36.2 +/- 3.5 mmHg, and pulmonary vascular resistance (PVR) increased from 5.1 +/- 0.4 to 25.9 +/- 2.9 mmHg.l-1.min. Inhibition of Tx synthase with OKY-046 (10 mg/kg iv, n = 6) prevented the PMA-induced increase in Tx concentrations in blood and BAL fluid but did not prevent or attenuate the increase in Ppa. OKY-046 pretreatment did, however, attenuate but not prevent the increase in PVR 60 min after PMA administration. Pretreatment with the TxA2/prostaglandin H2 receptor antagonist ONO-3708 (10 micrograms.kg-1.min-1 iv, n = 7) prevented the pressor response to bolus injections of 1-10 micrograms U-46619, a Tx receptor agonist, but did not prevent or attenuate the PMA-induced increase in Ppa. ONO-3708 also attenuated but did not prevent the increase in PVR. These results suggest that Tx does not mediate the PMA-induced pulmonary hypertension but may augment the increases in PVR in this model of acute lung injury.

Animals↗
PubMed1989

Regulation of human neutrophil functions by adenine nucleotides.

Previous work has shown that platelet-derived adenine nucleotides modulate neutrophil superoxide anion (O2-) generation. Additional studies were undertaken to characterize the effects of authentic adenosine (ADO) and its nucleotide derivatives on the inflammatory functions of human neutrophils. Stimulus-specific inhibition of neutrophil O2- generation by ADO in response to FMLP was verified. In addition, the ability of ATP, ADP, and AMP to limit neutrophil O2- generation induced by FMLP (0.2 to 0.5 microM) was demonstrated. The concentration producing 50% inhibition for nucleotide inhibition of neutrophil O2- generation was in the rank order of ADO (0.1 microM) less than AMP (0.5 microM) less than ADP less than or equal to ATP (5 microM). Guanine and inosine nucleotides (0.01 to 100 microM) did not inhibit FMLP-stimulated neutrophil O2- generation. Neutrophil degranulation in response to FMLP was only modestly inhibited by adenine nucleotides and ADO. Adenosine and ADP failed to affect chemotaxis of neutrophils stimulated with FMLP. The inability of non-metabolizable analogs to mimic the inhibitory effects of authentic ATP or ADP on the neutrophil O2- response suggested that metabolism of added nucleotides is necessary for their effectiveness. Both TLC and HPLC confirmed that ATP and ADP were converted to AMP and ADO after their incubation with unstimulated or FMLP-activated neutrophils. The addition of adenosine deaminase to neutrophil reaction mixtures in which conversion of added nucleotides was apparent removed detectable ADO but failed to completely abrogate the inhibition of neutrophil O2- generation by accumulated AMP. The kinetics of inhibition of FMLP-induced neutrophil O2- generation by ATP and ADP also indicated that conversion of these nucleotides to ADO and/or AMP may be essential for their ability to reduce neutrophil responses.

Adenine Nucleotides↗
PubMed1989

Proposed role for leukotrienes in the pathophysiology of multiple systems organ failure.

The leukotrienes are a group of biologically active products of arachidonic acid metabolism that have been demonstrated to possess the capability to alter vascular reactivity as well as vascular permeability when applied topically to tissues or infused into the vascular bed of various organs. These biologic effects of the exogenous leukotrienes have led to the speculation that these arachidonic acid metabolites could be important mediators in the pathophysiologic events that culminate in the development of acute lung injury and MSOF. Increased production of inflammatory mediators is undoubtedly a contributing factor to the pathophysiologic events that culminate in MSOF. LTB4 has been shown to be a potent stimulator of neutrophil chemotaxis and adhesion. It is possible that LTB4 may be responsible for initiation or amplification of the inflammatory response in this syndrome. The sulfidopeptide leukotrienes have profound effects on cardiac function, which may be mediated through effects on both coronary blood flow and cardiac contractility. These arachidonic acid metabolites are also capable of altering blood flow to several vascular beds and, when synthesized endogenously and released, may be important in the regulation of the peripheral circulation. Endogenous leukotrienes may have physiologic or pathophysiologic effects on cardiac output and its distribution to peripheral vascular beds or on systemic blood pressure. In view of the observations that alterations in cardiac output, blood pressure, and individual organ blood flow have been demonstrated in the clinical setting of ARDs and MSOF, it is attractive to suggest that the leukotrienes may contribute to the hemodynamic alterations observed in these clinical conditions. In addition to their effects on vascular smooth muscle and the myocardium, the leukotrienes have been shown to increase the permeability of blood vessels. In the case of the sulfidopeptide leukotrienes, the enhanced vascular permeability appears to be a direct effect of these lipoxygenase metabolites. Although LTB4 may directly increase vascular permeability, several lines of evidence suggest that the recruitment and activity of neutrophils is required for edema formation to develop following application of this leukotriene. Enhanced capillary permeability, at least in the pulmonary circulation, is a hallmark of ARDS and is also frequently present in MSOF. The leukotrienes, either through direct effects on vessels or through recruitment of inflammatory cells, are likely contributors to the nonhydrostatic edema associated with these syndromes.

Animals↗
PubMed1988

Inhibition of neutrophil superoxide anion generation by platelet products: role of adenine nucleotides.

Previously, we demonstrated the stimulus-specific ability of platelet lysate or release products to inhibit neutrophil functions in response to f-met-leu-phe (fMLP) or phorbol myristate acetate (PMA). The present study further characterizes these activities and identifies one of the platelet inhibitors of neutrophil superoxide anion (O2-) generation. Sephadex G-200 chromatography revealed two fMLP-specific inhibitory activities in platelet lysate. One component eluted with materials less than 13 kilodaltons (kD) molecular weight, whereas the second fractionated at the void volume (Mr greater than 200 kD). PMA-specific inhibitor(s) cofractionated at the void volume with the lysate's fMLP-inhibitory activity. Release products of activated platelets contained low-molecular-weight (less than 13 kD), fMLP-specific inhibitor activity but failed to demonstrate PMA-specific inhibition of neutrophil O2- generation. Biochemical characterization identified two distinct high-molecular-weight inhibitors in platelet lysate. Pretreatment with adenosine deaminase (ADA) completely abrogated the maximum inhibitory effect (43.8 +/- 7.5%) of the high-molecular-weight, fMLP-specific lysate component but failed to reduce maximum PMA-specific inhibition (93.0 +/- 2.0%) of neutrophil O2- generation. Likewise, while the lysate's fMLP-specific inhibitor was heat stable, heating reduced the PMA-specific inhibition 56.5 +/- 10.4%. Equal sensitivity to ADA, resistance to trypsin, and heat stability were demonstrated by the low-molecular-weight inhibitor(s) in platelet lysate and release products. Neither high- nor low-molecular-weight platelet inhibitors scavenged O2-. High-performance liquid chromatography (HPLC) of the low-molecular-weight inhibitory activity from both platelet lysate and release products revealed physiological levels of adenine nucleotides. Addition of pure adenine nucleotides at physiological levels (1-10 microM) mimicked the effectiveness of the platelet inhibitor. We conclude that stimulus-specific limitation of neutrophil O2- generation by platelet adenine nucleotides may represent a mechanism for reducing inadvertent tissue damage during inflammation.

Adenine Nucleotides↗