A Retrospective Observational Study of Anticoagulation Practices in Critically ill Patients with Atrial Fibrillation Admitted to the Intensive Care Unit.

BACKGROUND: Atrial Fibrillation (AF) is the most common arrhythmia in critically ill patients. AF precipitates thromboembolic (TE) events. International guidelines recommend long-term anticoagulation for AF patients dependent upon the risk of TE versus major bleeding events. The CHA2DS2VASc and HAS-BLED scores are used to calculate these risks, but have not been validated in intensive care. Little is known about the risk/benefit ratio of prescribing anticoagulation to patients with AF in the intensive care setting. METHODS: This observational study included patients who were admitted to intensive care and had AF episodes during admission. We aimed to 1) describe the anticoagulation strategies used in critically ill patients with AF, 2) determine the percentage of patients who received guideline-compliant anticoagulation and 3) compare anticoagulation strategies in patients with new onset AF (NOAF) and known AF. Demographic data was extracted from electronic health records. Therapeutic anticoagulation prescribed during AF episodes and outcomes were collected. CHA2DS2VASc and HAS-BLED scores were calculated and correlated with TE and bleeding events. RESULTS: The incidence of AF in our cohort was 13.8%. Anticoagulation was administered in 34.0% of patients. Anticoagulation use did not affect morbidity or mortality outcomes. Patients with pre-existing AF were anticoagulated more often compared to patients with NOAF. CHA2DS2VASc scores and TE events, and HAS-BLED scores and bleeding events did not correlate well. CONCLUSION: AF is common in critical care. Current guidelines on anticoagulation in AF may not be directly transferable to the critical care setting.

Pyruvate: immunonutritional effects on neutrophil intracellular amino or alpha-keto acid profiles and reactive oxygen species production.

For the first time the immunonutritional role of pyruvate on neutrophils (PMN), free α-keto and amino acid profiles, important reactive oxygen species (ROS) produced [superoxide anion (O(2) (-)), hydrogen peroxide (H(2)O(2))] as well as released myeloperoxidase (MPO) acitivity has been investigated. Exogenous pyruvate significantly increased PMN pyruvate, α-ketoglutarate, asparagine, glutamine, aspartate, glutamate, arginine, citrulline, alanine, glycine and serine in a dose as well as duration of exposure dependent manner. Moreover, increases in O(2) (-) formation, H(2)O(2)-generation and MPO acitivity in parallel with intracellular pyruvate changes have also been detected. Regarding the interesting findings presented here we believe, that pyruvate fulfils considerably the criteria for a potent immunonutritional molecule in the regulation of the PMN dynamic α-keto and amino acid pools. Moreover it also plays an important role in parallel modulation of the granulocyte-dependent innate immune regulation. Although further research is necessary to clarify pyruvate's sole therapeutical role in critically ill patients' immunonutrition, the first scientific successes seem to be very promising.

Continuous S-(+)-ketamine administration during elective coronary artery bypass graft surgery attenuates pro-inflammatory cytokine response during and after cardiopulmonary bypass.

BACKGROUND: Coronary artery bypass surgery (CABG) with cardiopulmonary bypass (CPB) leads to elevated circulating plasma cytokines. In this prospective randomized study, the effect of an S-(+)-ketamine-based anaesthetic protocol on perioperative plasma cytokine levels was compared with standard anaesthesia with propofol and sufentanil during CPB. METHODS: Patients undergoing elective on-pump CABG were randomly allocated to anaesthesia with sufentanil-propofol-midazolam (Sufentanil) or S-(+)-ketamine-propofol-midazolam (Ketamine). Blood samples were obtained before induction of anaesthesia (baseline) and also at 1, 6, and 24 h after aortic unclamping. Plasma levels of the interleukins (IL)-6, IL-8, IL-10, and tumour necrosis factor (TNF)-alpha were determined by enzyme-linked immunosorbent assay. RESULTS: One hundred and twenty-eight patients were studied (Ketamine: n=60; Sufentanil: n=68). All measured cytokines increased during and after CPB. However, the increase in the pro-inflammatory cytokines IL-6 and IL-8 6 h after aortic unclamping was significantly lower in the Ketamine group compared with the Sufentanil group [mean (sd): IL-6 56.75 (46.28) pg ml⁻¹ (Ketamine) vs 172.64 (149.93) pg ml⁻¹ (Sufentanil), P<0.01; IL-8 7.74 (14.72) pg ml⁻¹ (Ketamine) vs 26.3 (47.12) pg ml⁻¹ (Sufentanil), P<0.01]. In contrast, the anti-inflammatory cytokine IL-10 showed higher levels 1 h after unclamping in the Ketamine group compared with the Sufentanil group [mean (sd): 69.59 (78.78) vs 24.63 (37.7) pg ml⁻¹, P<0.001]. CONCLUSION: Our data demonstrate that S-(+)-ketamine possesses anti-inflammatory potential. Anaesthesia with S-(+)-ketamine may have beneficial effects in attenuating the CPB-induced systemic inflammatory response.

Effects of alpha-ketoglutarate on neutrophil intracellular amino and alpha-keto acid profiles and ROS production.

The aim of this study was to determine the effects of alpha-ketoglutarate on neutrophil (PMN), free alpha-keto and amino-acid profiles as well as important reactive oxygen species (ROS) produced [superoxide anion (O(2) (-)), hydrogen peroxide (H(2)O(2))] and released myeloperoxidase (MPO) activity. Exogenous alpha-ketoglutarate significantly increased PMN alpha-ketoglutarate, pyruvate, asparagine, glutamine, asparatate, glutamate, arginine, citrulline, alanine, glycine and serine in a dose as well as duration of exposure dependent manner. Additionally, in parallel with intracellular alpha-ketoglutarate changes, increases in O(2) (-) formation, H(2)O(2)-generation and MPO activity have also been observed. We therefore believe that alpha-ketoglutarate is important for affecting PMN "susceptible free amino- and alpha-keto acid pools" although important mechanisms and backgrounds are not yet completely explored. Moreover, our results also show very clearly that changes in intragranulocytic alpha-ketoglutarate levels are relevant metabolic determinants in PMN nutrition considerably influencing and modulating the magnitude and quality of the granulocytic host defense capability as well as production of ROS.

The whole blood phagocytosis assay: a clinically relevant test of neutrophil function and dysfunction in community-acquired pneumonia.

OBJECTIVE: To refine and validate a neutrophil function assay with clinical relevance for patients with community-acquired pneumonia (CAP). DESIGN: Two phase cross-sectional study to standardise and refine the assay in blood from healthy volunteers and test neutrophil phagocytic function in hospital patients with CAP. PARTICIPANTS: Phase one: Healthy adult volunteers (n = 30). Phase two: Critical care patients with severe CAP (n = 16), ward-level patients with moderate CAP (n = 15) and respiratory outpatients (no acute disease, n = 15). RESULTS: Our full standard operating procedure for the assay is provided. Patients with severe CAP had significantly decreased neutrophil function compared to moderate severity disease (median phagocytic index 2.8 vs. 18.0, p = 0.014). Moderate severity pneumonia neutrophil function was significantly higher than control samples (median 18.0 vs. 1.6, p = 0.015). There was no significant difference between critical care and control neutrophil function (median 2.8 vs. 1.6, p = 0.752). CONCLUSIONS: Our whole blood neutrophil assay is simple, reproducible and clinically relevant. Changes in neutrophil function measured in this pneumonia cohort is in agreement with previous studies. The assay has potential to be used to identify individuals for clinical trials of immunomodulatory therapies, to risk-stratify patients with pneumonia, and to refine our understanding of 'normal' neutrophil function in infection.

Intracellular alpha-keto acid quantification by fluorescence-HPLC.

Procedures for the analysis of free alpha-keto acids in human fluids (i.e. plasma, cerebrospinal fluid, urine, etc.) as well as for studying the dynamic free alpha-keto acid pools in differentiated tissues and organ cells have been the subject of growing clinical interest in the study of metabolic regulatory and pathophysiological phenomena. Due to the high instability and polarity of the alpha-keto acids being examined, the development of a quantitative and reproducible analysis of metabolically relevant intracellular alpha-keto acids still presents a substantial methodological challenge. The aim of small sample size, rapid, non-damaging and "metabolism-neutral" cell isolation, careful sample preparation and stability, as well as reproducible analytics technology is not often achieved. Only few of the methods described can satisfy the rigorous demands for an ultra-sensitive, comprehensive and rapid intracellular alpha-keto acid analysis.

Which mechanisms are involved in taurine-dependent granulocytic immune response or amino- and alpha-keto acid homeostasis?

We examined the effects of beta-alanine (taurine analogue and taurine transport antagonist), taurine (regarding its role in neutrophil (PMN) immunonutrition) and taurine combined either with L-NAME (inhibitor of *NO-synthase), SNAP (*NO donor), DON (glutamine-analogue and inhibitor of glutamine-requiring enzymes), DFMO (inhibitor of ornithine-decarboxylase) and beta-alanine on neutrophil amino- and alpha-keto acid profiles or important PMN immune functions in order to establish whether taurine transport-, nitric oxide-, glutamine- or ornithine-dependent mechanisms are involved in any of the taurine-induced effects. According to the present findings, the taurine-mediated effect appears to be based primarily on a modulation of important transmembraneous transport mechanisms and only secondarily on directly or indirectly induced modifications in intragranulocytic amino- and alpha-keto acid homoeostasis or metabolism. Although a direct relation to the parallel observed immunological modifications can only be presumed, these results show very clearly that compositional modifications in the free intragranulocytic amino- and alpha keto-acid pools coinciding with changes in intragranulocytic taurine levels are relevant metabolic determinants that can significantly influence the magnitude and quality of the granulocytic immune response.

Comparison of S-(+)-ketamine- with sufentanil-based anaesthesia for elective coronary artery bypass graft surgery: effect on troponin T levels.

BACKGROUND: S-(+)-ketamine anaesthesia carries potential benefits for the cardiovascularly compromised patient. However, the use of S-(+)-ketamine in ischaemic coronary artery disease is controversial. In a prospective, randomized, clinical trial, we have investigated whether an S-(+)-ketamine-based anaesthetic protocol leads to increased cardiac troponin T levels (cTnT) after coronary artery bypass grafting (CABG). METHODS: Two hundred and nine patients undergoing elective CABG were randomized to receive either i.v. anaesthesia with sufentanil-midazolam-propofol (SMP; n=108) or S-(+)-ketamine-midazolam-propofol (KMP; n=101). Haemodynamic variables were maintained within the normal range. Invasive haemodynamic monitoring was performed using a pulmonary artery catheter. Plasma cTnT levels were sampled before induction and 1, 6, and 24 h after aortic unclamping. Cardiovascular adverse events, such as electrocardiographic signs of ischaemia, perioperative myocardial infarction, and death, were recorded. RESULTS: Patient characteristics, cardiac profile, intraoperative management, and the incidence of cardiovascular adverse events were comparable between the groups. Plasma cTnT levels increased after operation in both groups. cTnT levels were significantly lower in the KMP group 6 h after aortic unclamping compared with the SMP group (P=0.004), but did not differ 24 h after aortic unclamping [median (range): SMP 0.4 (0.01-3.9) vs KMP 0.4 (0.07-6.6) microg litre(-1), P=0.338]. CONCLUSIONS: S-(+)-ketamine does not accentuate postoperative cTNT rises in haemodynamically stable elective CABG patients.

Pathways involved in alanyl-glutamine-induced changes in neutrophil amino- and alpha-keto acid homeostasis or immunocompetence.

We examined the effects of DON [glutamine-analogue and inhibitor of glutamine-requiring enzymes], alanyl-glutamine (regarding its role in neutrophil immunonutrition) and alanyl-glutamine combined with L-NAME, SNAP, DON, beta-alanine and DFMO on neutrophil amino and alpha-keto acid concentrations or important neutrophil immune functions in order to establish whether an inhibitor of *NO-synthase [L-NAME], an *NO donor [SNAP], an analogue of taurine and a taurine transport antagonist [beta-alanine], an inhibitor of ornithine-decarboxylase [DFMO] as well as DON could influence any of the alanyl-glutamine-induced effects. In summary, irrespective of which pharmacological, metabolism-inhibiting or receptor-mediated mechanisms were involved, our results showed that impairment of granulocytic glutamine uptake, modulation of intracellular glutamine metabolisation and/or de novo synthesis as well as a blockade of important glutamine-dependent metabolic processes may led to significant modifications of physiological and immunological functions of the affected cells.

Oxygen exchange and C-reactive protein predict safe discharge in patients with H1N1 influenza.

BACKGROUND: : Pandemic influenza has potential to overwhelm healthcare resources. There is uncertainty over performance of existing triage tools for hospital admission and discharge decisions. AIM: : Our aim was to identify clinical criteria that predict safe discharge from hospital and develop a pragmatic triage tool to guide physician decision-making. DESIGN: : We retrospectively examined an existing database of patients who presented to the Royal Liverpool University Hospital during the 2010-11 influenza pandemic. METHODS: Inclusion criteria: patients ≥18 years, with PCR confirmed H1N1 influenza. Exclusion criteria: died in the emergency department or case notes unavailable. Successful discharge was defined as discharge within 24 h of presentation and no readmission within 7 days. RESULTS: Eighty-six patients were included and 16 were successfully discharged. Estimated P/F ratio and C-reactive protein predicted safe discharge in a multivariable logistic regression model (AUC 0.883). A composite univariate predictor (estimated P/F minus C-reactive protein, AUC 0.877) was created to calculate specific cut off points for sensitivity and specificity. A pragmatic decision tool was created to incorporate these thresholds and relevant guidelines. Discharge: SpO 2 (in air) ≥ 94% and CRP <50. Observe: SpO 2 ≥ 94% and CRP >50 or SpO 2 ≤ 93% and CRP <50. Admit: SpO 2 ≤ 93% and CRP >50. CONCLUSIONS: We identified that oxygen exchange and CRP, a marker of acute inflammation, were the most important predictors of safe discharge. Our proposed simple triage model requires validation but has the potential to aid clinical decisions in the event of a future pandemic, and potentially for seasonal influenza.

Endogenous morphine.

It is now well accepted that endogenous morphine is present in animals, both in invertebrates and vertebrates. It is a key signaling molecule that plays an important role in downregulating physiological responses, such as those in the immune system, including immune elements in the CNS. It has been demonstrated that a specific mu-opiate-receptor subtype, mu3, mediates these downregulatory effects through release of NO. This article examines morphine as an endogenous signaling molecule, in terms of its role in neural and immune regulation.

Basal nitric oxide limits immune, nervous and cardiovascular excitation: human endothelia express a mu opiate receptor.

Nitric oxide (NO) is a major signaling molecule in the immune, cardiovascular and nervous systems. The synthesizing enzyme, nitric oxide synthase (NOS) occurs in three forms: endothelial (e), neuronal (n) and inducible (i) NOS. The first two are constitutively expressed. We surmise that in many tissues there is a basal level of NO and that the actions of several signaling molecules initiate increases in cNOS-derived NO to enhance momentary basal levels that exerts inhibitory cellular actions, via cellular conformational changes. It is our contention that much of the literature concerning the actions of NO really deal with i-NOS-derived NO. We make the case that cNOS is responsible for a basal or 'tonal' level of NO; that this NO keeps particular types of cells in a state of inhibition and that activation of these cells occurs through disinhibition. Furthermore, naturally occurring signaling molecules such as morphine, anandamide, interleukin-10 and 17-beta-estradiol appear to exert, in part, their beneficial physiological actions, i.e., immune and endothelial down regulation by the stimulation of cNOS. In regard to opiates, we demonstrate the presence of a human endothelial mu opiate receptor by RT-PCR and sequence determination, further substantiating the role of opiates in vascular coupling to NO release. Taken together, cNOS derived NO enhances basal NO actions, i.e., cellular activation state, and these actions are further enhanced by iNOS derived NO.

Morphine suppresses complement receptor expression, phagocytosis, and respiratory burst in neutrophils by a nitric oxide and mu(3) opiate receptor-dependent mechanism.

We investigated whether morphine and fentanyl influence surface receptor expression, phagocytic activity and superoxide anion generation of neutrophils in a whole blood flow cytometric assay. Morphine suppressed complement and Fcgamma receptor expression and neutrophil function in a concentration- and time-dependent manner. Morphine-induced changes were similar to those caused by the nitric oxide (NO) donor S-nitroso-N-acetyl-penicillamine and were abolished by preincubation with the NO synthase inhibitor N-nitro-L-arginine as well as naloxone. Fentanyl had no immunosuppressive effects. These results suggest that these neutrophil functions are inhibited by morphine-stimulated NO release mediated by the mu(3) opiate receptor subtype found on immunocytes.

NF-kappaB, nitric oxide and opiate signaling.

NF-kappaB, a DNA binding factor, has been implicated in inflammatory cytokine activation. NF-kappaB is activated by IkappaBalpha, its inhibitor, which is phosphorylated and proteolytically degraded. In this regard, NF-kappaB is also responsive to reactive oxygen intermediates and calcium. Reports also have emerged that demonstrate that nitric oxide inhibits NF-kappaB transcriptional activation in a variety of cells, including monocytes and endothelial cells. Recently, we have demonstrated that morphine, not opioid peptides, via the mu3 opiate receptor is coupled to constitutive nitric oxide release in these same cells. In this regard, we provide a scenario whereby morphine modulates NF-kappaB activation via nitric oxide. This pathway appears to be the key step in regulating inducible nitric oxide synthase expression, controlling the balance between constitutive nitric oxide synthase and the inducible form.

Morphine inhibits AP-1 activity and CD14 expression in leukocytes by a nitric oxide and opioid receptor-dependent mechanism.

BACKGROUND: Activator protein 1 is a transcription factor involved in the regulation of proinflammatory mediators. Activation of phagocytes by lipopolysaccharide depends on the expression of CD14 on the cell surface. In this study, we investigated the effects of morphine and nitric oxide on CD14 expression and activator protein 1 activation in human blood monocytes and neutrophils as well as the leukocyte cell line HL-60. METHODS: Whole blood was incubated with morphine, the nitric oxide donor S-nitroso-N-acetyl-penicillamine, naloxone or nitric oxide synthase inhibitors Nomega-nitro-l-arginine and Nomega-nitro-l-arginine-methylester and stimulated with lipopolysaccharide. Activator protein 1 nuclear content was determined by flow cytometry in human blood neutrophils and monocytes. CD14 expression on neutrophils was measured after incubation with fluorescein isothiocyanate-labelled antibodies. Electric mobility shift assay served for evaluation of activator protein 1 nuclear binding in HL-60 cells. RESULTS: Incubation of whole blood with morphine and subsequent stimulation with lipopolysaccharide decreased activator protein 1 nuclear content. Exposure to naloxone before morphine treatment abolished morphine-induced inhibition of activator protein 1 activity in human blood monocytes and neutrophils. Nitric oxide synthase inhibitors also reversed morphine's effects. CD14 expression on neutrophils was reduced after morphine treatment. These effects were antagonized by nitric oxide synthase inhibitors and naloxone. CONCLUSION: Morphine inhibits activator protein 1 activation by a mu opioid receptor pathway coupled to nitric oxide as second messenger. The decrease in CD14 expression caused by morphine may play a role in inhibition of activator protein 1 activation following lipopolysaccharide treatment of phagocytes.

Nitric oxide and polyamine pathway-dependent modulation of neutrophil free amino- and alpha-keto acid profiles or host defense capability.

We have examined the effects of N(omega)-nitro-L-arginine-methylester-hydrochloride [L-NAME; inhibitor of nitric oxide synthase], S-nitroso-N-acetyl-penicillamine [SNAP; nitric oxide donor], alpha-difluoro-methyl-ornithine [DFMO; inhibitor of ornithine decarboxylase] arginine or ornithine as well as the combination of arginine or ornithine with L-NAME, SNAP or DFMO on intracellular free amino- and alpha-keto acid profiles and the immune function markers superoxide anion and hydrogen peroxide generation as well as released myeloperoxidase activity in neutrophils (PMN). Although the underlying mechanisms still remain unclear, we believe from our results that nitric oxide as well as polyamine-dependent pathways are involved in the signal transmission of free radical molecule, beneficial nutritional therapy or maleficient pharmacological stress-induced alterations in PMN nutrient composition. Relevant changes in intragranulocyte free amino- and alpha-keto acid homeostasis and metabolism, especially, may be one of the determinants in PMN nutrition that positively or negatively influences and modulate neutrophil host defence capability and immunocompetence.

[Activation of granulocytes and antiproteases in open heart surgery]. / Aktivierung von Granulozyten und Antiproteasen bei herzchirurgischen Eingriffen mit extrakorporaler Zirkulation.

OBJECTIVE: Cardiovascular surgical procedures with extracorporeal circulation (ECC) lead to neutrophil activation followed by the release of proteases such as neutrophil elastase (NE) and oxidants. The mis-balance between proteases and their physiological inhibitors may contribute to morbidity in the postoperative period. In this study, the effects of cardiac surgery on neutrophil mediators were evaluated. Release of neutrophil elastase and plasma levels of the natural NE antagonists alpha (1)-proteinase inhibitor (API) and secretory leukocyte proteinase inhibitor (SLPI) were measured. The oxidative burst and the phagocytic activity were also evaluated. Tissue destruction was quantified by measuring the serum concentration of fibronectin. METHODS: Blood samples were obtained from 30 patients undergoing elective coronary artery bypass grafting (n = 30). NE and SLPI concentrations were measured by ELISA, API and fibronectin plasma levels were determined by nephelometry. Neutrophil phagocytic activity and oxidative burst were evaluated by flow cytometry. RESULTS: Neutrophil elastase plasma concentrations rose during ECC (245 +/- 107 microg/ml versus 44 +/- 14 microg/ml after induction, p < 0.001), whereas SLPI and API were decreased after onset of ECC. 24 h after ECC SLPI (54 +/- 17 ng/ml versus 41 +/- 10 ng/ml, p < 0.05) and API (3 +/- 0.5 g/l versus 1.6 +/- 0.3 g/l, p < 0.05) increased significantly compared to baseline values. A minor increase in phagocytic activity was observed after the onset of ECC. There were no significant changes in the oxidative burst. CONCLUSION: Cardiac surgery with ECC leads to neutrophil activation and elastase release. The imbalance between NE and the NE inhibitors API and SLPI may increase the risk for tissue damage due to granulocyte activation after cardiac surgery.

Alterations in neutrophil (PMN) free intracellular alpha-keto acid profiles and immune functions induced by L-alanyl-L-glutamine, arginine or taurine.

The objective of this study was to determine the dose as well as duration of exposure-dependent effects of L-alanyl-L-glutamine, arginine or taurine on polymorphonuclear neutrophil (PMN) free alpha-keto acid profiles and, in a parallel study, on PMN immune functions. Exogenous L-alanyl-L-glutamine significantly increased PMN alpha-ketoglutarate, pyruvate PMN superoxide anion (O2-) generation, hydrogen peroxide (H2O2) formation and released myeloperoxidase (MPO) activity. Arginine also led to significant increases in alpha-ketoglutarate, pyruvate, MPO release and H2O2 generation. Formation of O2- on the other hand was decreased by arginine. Incubation with taurine resulted in lower intracellular pyruvate and alpha-ketobutyrate levels, decreased O2- and H2O2 formation and a concomitant significantly increased MPO activity. We therefore believe that considerable changes in PMN free-alpha-keto-acid profiles, induced for example by L-alanyl-L-glutamine, arginine or taurine, may be one of the determinants in cell nutrition that considerably modulates the immunological competence of PMN.

Benzodiazepine receptor-dependent modulation of neutrophil (PMN) free amino- and alpha-keto acid profiles or immune functions.

We have examined the effects of midazolam, Ro 5-4864 (agonist for "peripheral" [p] benzodiazepine receptors [BR]), PK 11195 (antagonist for pBR), flumazenil (antagonist for "central" BR), naloxone (antagonist for opiate receptors) and the combination of midazolam and Ro 5-4864, PK 11195, flumazenil or naloxone on intracellular amino- and alpha-keto acids and the immune function markers superoxide anion (O(2)(-)), hydrogen peroxide (H(2)O(2)) and released myeloperoxidase (MPO) activity in neutrophils (PMN). Only midazolam and Ro 5-4864 led to significant changes in the dynamic PMN free amino- and alpha-keto acid pools. Concerning PMN immune function markers, midazolam and Ro 5-4864 significantly decreased O(2)(-) and H(2)O(2) formation and released MPO. When midazolam and Ro 5-4864 were applied together they appeared to act additively. Pre-incubation with PK 11195 partially neutralized the midazolam effects whereas flumazenil or naloxone showed no effects. We therefore believe that pBR are involved in the signal transmission of anesthetic-induced cellular metabolic changes in PMN.

Effects of endogenous and synthetic opioid peptides on neutrophil function in vitro.

BACKGROUND: Opioid peptides released from immunocytes during inflammation and stress in critically ill patients are associated with an altered immune response. Moreover, concentrations of opioid peptides are increased in peripheral blood and at the sites of inflammatory reactions. METHODS: Using flow cytometric assay of whole human blood, we investigated direct effects of endogenous and synthetic opioid peptides on surface expression of complement receptors CD35 and CD11b/CD18 and Fcã receptor III CD16, and superoxide anion generation of neutrophils. RESULTS: The endogenous opioid peptides beta-endorphin(1-31) and met-enkephalin, representing the N-terminal fragment of beta-endorphin(1-31), and the synthetic delta opioid receptor agonists D-Ala(2)-D-Leu(5)-enkephalin and D-Pen(2)-enkephalin produced concentration-dependent stimulation of neutrophil activity. Incubation with met-enkephalin 10(-7) M or beta-endorphin(1-31) 10(-7) M led to an increase in receptor expression of up to 10% (met-enkephalin) and 15% (beta-endorphin(1-31)). After incubation with D-Ala(2)-D-Leu(5)-enkephalin or D-Pen(2/5)-enkephalin, receptor expression was increased by up to 30%. This correlated with concentration-dependent stimulation of the production of reactive oxygen intermediates, as shown by an increase of up to 40% in oxidative burst activity. All effects were abolished after preincubation with naloxone or with the selective delta opioid antagonist naltrindole, whereas the selective micro receptor antagonist d-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH(2) showed only partial inhibitory effects. CONCLUSIONS: Our data suggest a delta opioid receptor-mediated stimulatory effect on neutrophil function. beta-Endorphin(27-31), the C-terminal fragment of beta-endorphin(1-31), did not alter neutrophil function, indicating that beta-endorphin(1-31) mediates its effect on neutrophils via the N-terminal fragment. This study may contribute to a better understanding of neuroimmune interaction.