Plasma Kinin Research Articles

Plasma Kinins- A Pharmacological Perspective

Background: Plasma kinins are known for decades but the understanding of them is not up-to the mark and the complexity is the reason. There are many drugs and trials undertaken with these as drug targets but only very few have been successfully marketed and used. Rest all others have resulted in failure during various phases of the trial.
 Purpose: The purpose of this review is to explain and explore the complexity of plasma kinins and explore the relations between Kinins, and analyze the failures in drug development with these receptors as targets.
 Implication: This extensive review might help in understanding the complexity and ensure the reduction of drug development failures in these molecules as drug targets
 Conclusion: Kinins have an important role in the homeostatic functions of the body physiologically. The pathophysiological roles in inflammation are also known. The complexity of these systems is well established.

Mass spectrometric study of variation in kinin peptide profiles in nasal fluids and plasma of adult healthy individuals

BackgroundThe kallikrein-kinin system is assumed to have a multifunctional role in health and disease, but its in vivo role in humans currently remains unclear owing to the divergence of plasma kinin level data published ranging from the low picomolar to high nanomolar range, even in healthy volunteers. Moreover, existing data are often restricted on reporting levels of single kinins, thus neglecting the distinct effects of active kinins on bradykinin (BK) receptors considering diverse metabolic pathways. A well-characterized and comprehensively evaluated healthy cohort is imperative for a better understanding of the biological variability of kinin profiles to enable reliable differentiation concerning disease-specific kinin profiles.MethodsTo study biological levels and variability of kinin profiles comprehensively, 28 healthy adult volunteers were enrolled. Nasal lavage fluid and plasma were sampled in customized protease inhibitor prespiked tubes using standardized protocols, proven to limit inter-day and interindividual variability significantly. Nine kinins were quantitatively assessed using validated LC–MS/MS platforms: kallidin (KD), Hyp4-KD, KD1-9, BK, Hyp3-BK, BK1-8, BK1-7, BK1-5, and BK2-9. Kinin concentrations in nasal epithelial lining fluid were estimated by correlation using urea.ResultsCirculating plasma kinin levels were confirmed in the very low picomolar range with levels below 4.2 pM for BK and even lower levels for the other kinins. Endogenous kinin levels in nasal epithelial lining fluids were substantially higher, including median levels of 80.0 pM for KD and 139.1 pM for BK. Hydroxylated BK levels were higher than mean BK concentrations (Hyp3-BK/BK = 1.6), but hydroxylated KD levels were substantially lower than KD (Hyp4-KD/KD = 0.37). No gender-specific differences on endogenous kinin levels were found.ConclusionsThis well-characterized healthy cohort enables investigation of the potential of kinins as biomarkers and would provide a valid control group to study alterations of kinin profiles in diseases, such as angioedema, sepsis, stroke, Alzheimer’s disease, and COVID-19.

Reliable measurement of plasma kinin peptides: Importance of preanalytical variables

BackgroundThe kallikrein‐kinin system is involved in many (patho)physiological processes and kinin peptides are considered potential clinical biomarkers. Variance in blood specimen collection and processing, artificial ex vivo bradykinin formation, and rapid degradation of kinins have contributed to divergence in published plasma levels, therefore limiting their significance. Thus, reliable preanalytical settings are highly required. ObjectivesThis study aimed to develop and evaluate a standardized preanalytical procedure for reliable kinin quantification. The procedure was based on identification of the most impactful variables on ex vivo plasma level alterations. MethodsSuitable protease inhibitors and blood specimen collection and handling conditions were systematically investigated. Their influence on plasma levels of seven kinins was monitored using an established in‐house liquid chromatography–tandem mass spectrometry platform. ResultsIn nonstandardized settings, ex vivo rise of bradykinin was found to already occur 30 seconds after blood sampling with high interindividual variation. The screening of 17 protease inhibitors resulted in a customized seven‐component protease inhibitor, which efficiently stabilized ex vivo kinin levels. The reliability of kinin levels was substantially jeopardized by prolonged rest time until centrifugation, phlebotomy methodology (eg, straight needles, catheters), vacuum sampling technique, or any time delays during venipuncture. The subsequently developed standardized procedure was applied to healthy volunteers and proved it significantly limited interday and interindividual kinin level variability. ConclusionThe developed procedure for blood specimen collection and handling is feasible in clinical settings and allows for determination of reliable kinin levels. It may contribute to further elucidating the role of the kallikrein‐kinin system in diseases like angioedema, sepsis, or coronavirus disease 2019.

Targeted LC-MS/MS platform for the comprehensive determination of peptides in the kallikrein-kinin system

The kallikrein-kinin system (KKS) is involved in many physiological and pathophysiological processes and is assumed to be connected to the development of clinical symptoms of angioedema or COVID-19, among other diseases. However, despite its diverse role in the regulation of physiological and pathophysiological functions, knowledge about the KKS in vivo remains limited. The short half-lives of kinins, their low abundance and structural similarities and the artificial generation of the kinin bradykinin greatly hinder reliable and accurate determination of kinin levels in plasma. To address these issues, a sensitive LC-MS/MS platform for the comprehensive and simultaneous determination of the four active kinins bradykinin, kallidin, des-Arg(9)-bradykinin and des-Arg(10)-kallidin and their major metabolites bradykinin 2-9, bradykinin 1-7 and bradykinin 1-5 was developed. This platform was validated according to the bioanalytical guideline of the US Food and Drug Administration regarding linearity, accuracy, precision, sensitivity, carry-over, recovery, parallelism, matrix effects and stability in plasma of healthy volunteers. The validated platform encompassed a broad calibration curve range from 2.0–15.3 pg/mL (depending on the kinin) up to 1000 pg/mL, covering the expected concentrations in disease states. No source-dependent matrix effects were identified, and suitable stability of the analytes in plasma was observed. The applicability of the developed platform was proven by the determination of endogenous levels in healthy volunteers, whose plasma kinin levels were successfully detected in the low pg/mL range. The established platform facilitates the investigation of kinin-mediated diseases (e.g. angioedema, COVID-19) and enables the assessment of the impact of altered enzyme activities on the formation or degradation of kinins.Graphical abstract

Associations Between Plasma Kinin B1 Receptor Levels and the Presence and Severity of Coronary Artery Disease.

Aim: Kinin B1 receptor (KB1R) was shown to be up-regulated in human carotid atherosclerotic lesions. Serum KB1R levels were also reported to be high in patients with stroke. However, KB1R deficiency increased atherosclerotic lesions. Therefore, the role of KB1R in atherosclerosis remains unclear. Moreover, no study has reported blood KB1R levels in patients with coronary artery disease (CAD). Methods: We measured plasma KB1R levels in 375 patients undergoing coronary angiography. The severity of CAD was represented as the numbers of ＞50% stenotic vessels and segments and the severity score. Results: CAD was found in 197 patients, of whom 89 had 1-vessel disease (1-VD), 62 had 2-VD, and 46 had 3-VD. Plasma KB1R levels were higher in 197 patients with CAD than in 178 without CAD (median 83.3 vs. 73.7 pg/mL, p ＜0.01). A stepwise increase in KB1R levels was found depending on the number of stenotic vessels: 77.1 in 1-VD, 87.8 in 2-VD, and 88.5 pg/mL in 3-VD ( p ＜0.025). A high KB1R level (＞90.0 pg/mL) was present in 30% of patients with CAD(-), 39% of 1-VD, 50% of 2-VD, and 48% of 3-VD ( p ＜0.025). KB1R levels correlated with the number of stenotic segments and the severity score (r=0.14 and r=0.17, p ＜0.01). In multivariate analysis, KB1R levels were an independent factor associated with CAD. Odds ratio for CAD was 1.62 (95%CI=1.02-2.58) for high KB1R level ＞90.0 pg/mL. Conclusion: Plasma KB1R levels in patients with CAD were high and were associated with the presence and severity of CAD independent of atherosclerotic risk factors.

Therapeutic Values of Human Urinary Kallidinogenase on Cerebrovascular Diseases.

The term “tissue kallikrein” is used to describe a group of serine proteases shared considerable sequence homology and colocalize in the same chromosomal locus 19q13. 2–q13.4. It has been widely discovered in various tissues and has been proved to be involved in kinds of pathophysiological processes, such as inhibiting oxidative stress, inflammation, apoptosis, fibrosis and promoting angiogenesis, and neurogenesis. Human Urinary Kallidinogenase (HUK) extracted from human urine is a member of tissue kallikrein which could convert kininogen to kinin and hence improve the plasma kinin level. Medical value of HUK has been widely investigated in China, especially on acute ischemic stroke. In this review, we will summarize the therapeutic values of Human Urinary Kallidinogenase on acute ischemic stroke and its potential mechanisms.

Investigation of the proton relay system operative in human cystosolic aminopeptidase P.

Aminopeptidase P, a metalloprotease, targets Xaa-Proline peptides for cleavage [1–4]. There are two forms of human AMPP, a membrane-bound form (hmAMPP) and a soluble cytosolic form (hcAMPP)[5]. Similar to the angiotensin-I-converting enzyme, AMPP plays an important role in the catabolism of inflammatory and vasoactive peptides, known as kinins. The plasma kinin, bradykinin, was used as the substrate to conduct enzymatic activity analyses and to determine the Michaelis constant (Km) of 174 μM and the catalytic rate constant (kcat) of 10.8 s-1 for hcAMPP. Significant differences were observed in the activities of Y527F and R535A hcAMPP mutants, which displayed a 6-fold and 13.5-fold for decrease in turnover rate, respectively. Guanidine hydrochloride restored the activity of R535A hcAMPP, increasing the kcat/Km 20-fold, yet it had no impact on the activities of the wild-type or Y527F mutant hcAMPPs. Activity restoration by guanidine derivatives followed the order guanidine hydrochloride >> methyl-guanidine > amino-guanidine > N-ethyl-guanidine. Overall, the results indicate the participation of R535 in the hydrogen bond network that forms a proton relay system. The quaternary structure of hcAMPP was determined by using analytical ultracentrifugation (AUC). The results show that alanine replacement of Arg535 destabilizes the hcAMPP dimer and that guanidine hydrochloride restores the native monomer-dimer equilibrium. It is proposed that Arg535 plays an important role in hcAMMP catalysis and in stabilization of the catalytically active dimeric state.

Release of biologically active kinin peptides, Met-Lys-bradykinin and Leu-Met-Lys-bradykinin from human kininogens by two major secreted aspartic proteases of Candida parapsilosis

In terms of infection incidence, the yeast Candida parapsilosis is the second after Candida albicans as causative agent of candidiases in humans. The major virulence factors of C. parapsilosis are secreted aspartic proteases (SAPPs) which help the pathogen to disseminate, acquire nutrients and dysregulate the mechanisms of innate immunity of the host. In the current work we characterized the action of two major extracellular proteases of C. parapsilosis, SAPP1 and SAPP2, on human kininogens, proteinaceous precursors of vasoactive and proinflammatory bradykinin-related peptides, collectively called the kinins. The kininogens, preferably the form with lower molecular mass, were effectively cleaved by SAPPs, with the release of two uncommon kinins, Met-Lys-bradykinin and Leu-Met-Lys-bradykinin. While optimal at acidic pH (4–5), the kinin release yield was only 2–3-fold lower at neutral pH. These peptides were able to interact with cellular kinin receptors of B2 subtype and to stimulate the human endothelial cells HMEC-1 to increased secretion of proinflammatory interleukins (ILs), IL-1β and IL-6. The analysis of the stability of SAPP-generated kinins in plasma suggested that they are biologically equivalent to bradykinin, the best agonist of B2 receptor subtype and can be quickly converted to des-Arg9-bradykinin, the agonist of inflammation-inducible B1 receptors.

Bradykinin and the Pathogenesis of Hereditary Angioedema

Bradykinin and the Pathogenesis of Hereditary Angioedema

Hereditary angioneurotic oedema: characterization of plasma kinin and vascular permeability-enhancing activities.

The mediator(s) responsible for localized enhanced vascular permeability that characterizes an exacerbation of hereditary angioneurotic oedema (HAE) is thought to be a product of either contact or complement system activation. In contrast to normal individuals, plasma from these patients generates both kinin and vascular permeability-enhancing activity following incubation at 37 degrees C. Depletion of C1 inhibitor in both normal and C2-deficient plasma, but not in contact factor-deficient plasmas, resulted in generation of these activities. The kinin activity from incubated HAE plasma was susceptible to kininase inactivation and was blocked by a Bk2 receptor antagonist. Furthermore, this activity was isolated from HAE plasma; amino acid sequence analysis proved it to be bradykinin. Similarly, the vasopermeability-enhancing activity from ethanol-fractionated or boiled HAE plasma, collected during either attack or remission, co-eluted with bradykinin on reverse-phase high performance liquid chromatography (HPLC). These studies conclusively demonstrate that bradykinin is the major kinin and mediator of enhanced vascular permeability generated during incubation of HAE plasma. The role of other bioactive products, such as the C2 kinin, at local sites of oedema formation remains to be further defined.

Metallopeptidase activities in hereditary angioedema: Effect of androgen prophylaxis on plasma aminopeptidase P

Aminopeptidase P (APP) plays an important role in the catabolism of kinins in human plasma, mostly for des-Arg(9)-bradykinin. Impaired degradation of this active bradykinin metabolite was found to be associated with a decreased APP activity in hypertensive patients who experienced angioedema while being treated with angiotensin I-converting enzyme inhibitors. The pathophysiology of hereditary angioedema is presently attributed only to a quantitative/qualitative C1 inhibitor (CI-INH) defect with increased bradykinin release. In the context of androgen prophylaxis, increased CI-INH function cannot fully explain protection from angioedema attacks alone because of the limited reversion of the CI-INH defects. Therefore we hypothesized that androgen prophylaxis could enhance plasma APP activity. Patients with hereditary angioedema were investigated for plasma metallopeptidase activities responsible for kinin catabolism (APP, angiotensin I-converting enzyme, and carboxypeptidase N) and for CI-INH function in treated and untreated patients. APP activity was asymmetrically distributed in untreated patients (n = 147): the mean value was significantly lower than the value in a reference healthy and unmedicated population (n = 116; P < or = .001). Prophylaxis with androgen induced a significant increase in APP activity (P < or = .001), whereas it did not affect the other metallopeptidase activities. In both patient groups, APP activity showed a significant inverse relationship to disease severity (P < or = .001). In addition to the effect on circulating CI-INH levels, the increase in APP levels brought on by androgens could contribute to a more effective control of the kinin accumulation considered to be responsible for the symptoms of angioedema.

Bradykinin-related peptides from Phyllomedusa hypochondrialis

Bradykinin related peptides (BRPs) present in the water-soluble secretion and freshly dissected skin fragments of Phyllomedusa hypochondrialis were investigated by mass spectrometry techniques. Eighteen BRPs, along with their post-translational modifications, were characterized in the secretion by de novo MS/MS sequencing and direct MALDI imaging experiments of the frog skin. These molecules revealed strong sequence similarities to the main plasma kinin of some mammals and reptiles. Such a diversity of molecules, within the same peptide family, belonging to a single amphibian species may be related to functional specializations of these peptides and a variety of corresponding receptors that might be present in a number of different predators. Also, a novel analog, [Val] 1,[Thr] 6-bradykinyl-Gln,Ser had its biological activity positively detected in cell culture expressing the human bradykinin B 2 receptor and in guinea pig ileum preparations.

Loss of sodium modulation of plasma kinins in human hypertension.

We studied the effect of salt intake and hypertension on the systemic kallikrein-kinin system (KKS), as measured by bradykinin (BK) 1-5, a stable circulating bradykinin metabolite, and the tissue KKS, as measured by urinary kallikrein excretion. Venous BK 1-5, urinary kallikrein, and components of the renin-angiotensin-aldosterone system were measured in 35 normotensive and 19 hypertensive subjects who were maintained on a high (200 mmol/day) or low (10 mmol/day) salt diet. Salt restriction decreased mean arterial pressure (MAP) (P < 0.001 overall) and the plasma angiotensin-converting enzyme (P = 0.017) and increased plasma renin activity (P < 0.001) and serum aldosterone (P < 0.001). There was an interactive effect of salt intake and hypertension on plasma BK 1-5 (P = 0.043), with BK 1-5 significantly lower during low compared with high salt intake in normotensive (24.7 +/- 2.6 versus 34.9 +/- 5.6 fmol/ml, P = 0.002) but not hypertensive subjects (30.6 +/- 4.6 versus 27.5 +/- 2.8 fmol/ml, P = 0.335). In normotensives, the change in plasma BK 1-5 from high to low salt intake correlated with the change in MAP (r = 0.533, P = 0.004). Urinary kallikrein was higher during low compared with high salt intake (P < 0.001) in both groups. There was no effect of salt intake on urinary BK 1-5. In summary, the systemic and renal KKSs act in tandem to modulate the response to salt intake. The systemic system is activated during high salt intake and counterbalances increased vascular response to pressors. With sodium restriction, the renal system is activated and counterbalances the increased sodium-retaining state induced by activation of the renin-angiotensin-aldosterone system. With hypertension, these modulating effects are diminished or lost, supporting a role for both systems in the development/maintenance of hypertension.

Acute biliary pancreatitis: when should the endoscopist intervene?

A 63-year-old usman is admitted to the hospital with acute pancreatitis of presumed biliary origin. Laboratory results include white blood cell count (WBC) 18,500; hemoglobin 13.0; platelets 191,000; alanine aminotransferase (ALT) 330; aspartate aminotransferase (AST) 260; alkaline phosphatase 250; bilirubin 1.4; glucose 225; blood urea nitrogen (BUN) 47; creatinine 1.4; and prothrombin time 12 seconds. Ultrasound shows gallstones in the gallbladder; the common bile duct is 5 mm without stones identified.

Activation of the Plasma Kinin Forming Cascade along Cell Surfaces

Proteins of the plasma kinin-forming cascade bind to endothelial cells and activation of the cascade can be initiated along the surface. The light chain of high molecular weight kininogen (HK) (domain 5) and factor XII bind to gC1qR, the heavy chain of HK (domain 3) binds to cytokeratin 1 and the interactions are zinc dependent. Prekallikrein binds to domain 6 of HK. Antisera to gC1qR and cytokeratin 1 inhibit binding and activation. Incubation of normal plasma with endothelial cells leads to gradual conversion of prekallikrein to kallikrein, while plasma deficient in factor XII or HK are inactive within a 2-hour time frame. Thus factor XII is critical for activation to proceed. Augmentation of these reactions may occur when C1 inhibitor is functionally deficient or with ACE inhibitors which also inhibit kininases.

Kinin receptors and their antagonists as novel therapeutic agents.

Plasma kinins are a family of peptides which play an important role in a variety of pathophysiological conditions. As a consequence of the progress in the area of kinin receptors, specific kinin receptor antagonists will be available in near future in order to provide more selective therapeutic modalities for the treatment of diseases such as asthma, cardiovascular diseases, inflammation, pain, etc. Although the initial observation leading to discovery of kinins has been performed in 1909, important progress on the development of specific kinin receptor antagonists has been made in last two decades. This review emphasizes the physiological functions of kinins along with their receptor subtypes and post-receptor events in the cellular signaling. In this article, the latest developments in the kinin receptor antagonists including nonpeptide ones have been reviewed.

Bradykinin B2-receptor antagonism attenuates fatal cardiocirculatory breakdown induced by severe experimental pancreatitis.

To investigate the impact of the long-acting bradykinin B2 receptor antagonist HOE 140 (Icatibant) on survival time in a model of severe porcine pancreatitis. Randomized, controlled intervention trial. Thirty domestic pigs of either gender anesthetized by intravenous application of piritramide, midazolam, and pancuronium and mechanically ventilated. Pancreatitis was induced by an injection of sodium taurocholate (5%, 1 mL/kg body weight [BW]) and enterokinase (10 U/kg BW). Control animals (group 1, n = 10) underwent the spontaneous course of the disease. In two treatment groups, Icatibant was administered either in a low (100 nmol/kg BW; group 2, n = 10) or in a high dosage (5000 nmol/kg BW; group 3, n = 10). Mean survival time was significantly prolonged by Icatibant (controls, 6.6 hrs; group 2, 9.8 hrs; p = .022; group 3, 10.9 hrs; p = .007). Six hours postinduction, the decline of total peripheral resistance (52% of baseline) and cardiac index (92% of baseline) in controls was significantly improved by Icatibant, both in the low (16% and 44%; p < .05) and high (6% and 45%; p < .05) dosage. The concentrations of free, nonreceptor-bound kinin in plasma 6 hrs postinduction were significantly lower in controls than in groups 2 and 3 animals (111+/-50 vs. 208+/-40 and 237+/-52 fmol/mL, respectively). Six hours postinduction, the pretreatment with Icatibant was associated with significantly higher plasma concentrations of phospholipase A2 (controls, +1194%; group 2, +2000%; group 3, +2285% of baseline values) and interleukin-1 receptor antagonist (controls, 1900+/-800; group 2, 3100+/-800; group 3, 3600+/-800 pg/mL). In contrast, the increase of urinary trypsinogen activation peptides indicating local pancreatic damage (589+/-114 nmol/L in controls) was substantially attenuated by pretreatment with Icatibant (group 2, 467+/-102, NS; 352+/-91 nmol/L in group 3; p = .022 vs. controls). Systemic inflammatory reactions, however, as quantified by C-reactive protein and the extracellularly discharged neutrophil cytosolic inhibitor leukocyte neutral proteinase inhibitor were not influenced by the bradykinin B2-receptor antagonist. Pretreatment with the bradykinin B2 receptor antagonist Icatibant resulted in prolonged survival time and in delayed impairment of major macrocirculatory and pulmonary variables. Icatibant resulted in elevated concentrations of free, circulating kinin. This was associated with increased concentrations of phospholipase A2 and interleukin-1 receptor antagonist, suggesting that circulating kinins strengthen the activation of some mediator cascades, the association of which with the kinin metabolism requires further experimental clarification. Other variables indicating a systemic inflammatory response (C-reactive protein, leukocyte neutral proteinase inhibitor) remained unaffected by Icatibant. Bradykinin antagonism distinctly ameliorated the local pancreatic damage, indicated by increased urinary concentrations of trypsinogen activation peptides. It is concluded that the kinin metabolism plays an important role in the pathophysiology of systemic complications after severe experimental pancreatitis.

Inactivation of bradykinin by angiotensin-converting enzyme and by carboxypeptidase N in human plasma.

Because bradykinin (BK) appears to have cardioprotective effects ranging from improved hemodynamics to antiproliferative effects, inhibition of BK-degrading enzymes should potentiate such actions. The purpose of this study was to find out which enzymes are responsible for the degradation of BK in human plasma. Human plasma from healthy donors (n = 10) was incubated with BK in the presence or absence of specific enzyme inhibitors. At high (micromolar) concentrations, BK was mostly (>90%) degraded by carboxypeptidase N (CPN)-like activity. In contrast, at low (nanomolar) substrate concentrations, at which the velocity of the catalytic reaction is equivalent to that under physiological conditions, BK was mostly (>90%) converted into an inactive metabolite, BK-(1-7), by angiotensin-converting enzyme (ACE). BK-(1-7) was further converted by ACE into BK-(1-5), with accumulation of this active peptide. A minor fraction (<10%) of the BK was converted into another active metabolite, BK-(1-8), by CPN-like activity. The present study shows that the most critical step in plasma kinin metabolism, i.e., inactivation of BK, is mediated by ACE. Thus inhibition of plasma ACE activity would be cardioprotective by elevating the concentration of BK in the circulation.

The involvement of plasma kinins in the cardiovascular effects of Leiurus quinquestriatus scorpion venom in anaesthetised rabbits

The present study was undertaken to investigate the involvement of kinins in the cardiovascular and respiratory effects of LQQ venom. Blood pressure, heart rate, electrocardiogram (ECG) and respiration were studied in anaesthetised rabbits, in the presence and absence of aprotinin and icatibant, a B 2 bradykinin antagonist. Plasma bradykinin concentrations were also measured following venom injection. LQQ venom caused a triphasic effect on blood pressure comprising an immediate fall, a pronounced rise and a progressive decline until death. Bradycardia, myocardial damage, arrhythmias, respiratory distress and pulmonary oedema were also exhibited. Pretreatment with aprotinin attenuated the venom-induced hypotension, bradycardia, ECG and respiratory changes and prolonged survival. Pretreatment of atropinized animals with icatibant gave similar protection. In animals treated with LQQ venom, plasma bradykinin was significantly higher than controls, although there was considerable inter-animal variation in plasma kinin concentrations and the elevation was seen relatively late after venom administration. The data provides some support for the hypothesis that kinins are involved in the cardiovascular and lethal effects of LQQ venom in rabbits.

Activation of plasma kinin system correlates with severe coagulation disorders in patients with ovarian hyperstimulation syndrome

The aim of this study was to evaluate status of plasma kinin system in patients with ovarian hyperstimulation syndrome (OHSS), in order to investigate whether activation of the plasma kinin system correlates with increased blood coagulability. In the first part of the study, concentrations of plasma prekallikrein (PK) in OHSS cycles (n = 13) were monitored from the day of human chorionic gonadotrophin (HCG) administration to the mid-luteal phase, and were compared with those of control cycles (n = 17). The average value of PK in OHSS cycles began to decrease on day 8, and by day 10 was significantly lower than that of control cycles (86 +/- 6 versus 106 +/- 4%, P <0.01). The time course of changes in PK concentration correlated well with the clinical condition of OHSS patients. In the second part of the study, we obtained data from 26 patients who were hospitalized because of severe OHSS, to investigate the correlation between PK and other haemostatic markers. OHSS patients with severe PK reduction (<80% normal, n = 9) demonstrated significantly higher values of plasma thrombin-antithrombin III and plasmin-alpha2 antiplasmin, and more severe haemoconcentration, compared to those OHSS patients who had no reduction in PK (n = 17). In conclusion, our data suggest that activation of the plasma kinin system occurs specifically and occasionally in OHSS patients, and is associated with increased blood coagulability. Thus, when an OHSS patient demonstrates a low value of plasma PK, more careful management is required to prevent thromboembolic complications.