Blood Kinin Research Articles

Change in Blood Kinin and Plasma Porcine Pancreatic Kallikrein Concentrations after Oral Administration of Kallikrein Formulation in Dog

Oral formulation of tissue kallikrein consists primarily of porcine pancreatic kallikrein (PPK) and is used to improve peripheral circulation, menopausal symptoms, and impaired chorioretinal circulation. Although gastrointestinal absorption of tissue kallikrein after oral administration has been reported in nonclinical and clinical studies, the increase in the concentration of pharmacologically active kinins, which are produced from kininogens by tissue kallikrein, has not been investigated. In this study, kallikrein formulation was orally administered to dogs and an increase in PPK in plasma was confirmed, along with an increase in the blood kinin level. After oral administration of kallikrein formulation (10 U/kg or 20 U/kg PPK) to dogs, PPK concentration in plasma reached maximum 3 h after administration, and then decreased time-dependently. The maximum concentration was 6.01 ± 1.44 pg/ml in the 10 U/kg group and 10.88 ± 3.59 pg/ml in the 20 U/kg group (mean ± S.E.M, n = 5). After oral administration of kallikrein formulation (40 U/kg PPK) to dogs, the blood kinin concentration in the PPK-treated group was significantly increased 2 h after administration as compared to the purified water-treated group (before administration: 48.8 ± 2.1 ng/ml vs. 48.1 ± 1.9 ng/ml, 2 h after administration: 55.5 ± 1.6 ng/ml vs. 49.6 ± 1.4 ng/ml; mean ± S.E.M, n = 4, p < 0.05). In conclusion, PPK was considered to be absorbed after oral administration and to exert its pharmacological action via kinins produced by kininogen degradation in dogs.

An Acidic Kininogenase in Rat Ventricular Myocardium

Canine ventricles have been reported to contain a cathepsin D-like kininogenase, which might confer protection on the heart during ischaemia. The aim of this study was to investigate the presence and levels of a similar kininogenase in normal and ischaemic rat hearts. Aqueous extracts of rat ventricles were tested for the ability to release bradykinin-like immunoreactivity from human low-molecular-weight kininogen and high-molecular-weight kininogen at acidic pHs. The enzymes involved were separated using gel filtration followed by the testing of fractions for cleavage of D-Val-Leu-Arg-pNA and low-molecular-weight kininogen. Extracts from normal and ischaemic ventricles were compared for the ability to release bradykinin-like immunoreactivity from low-molecular-weight kininogen. Kinin levels in mixed venous blood were compared before and after ischaemia. By assessing their effect on isolated oestrous rat uteri and on protease inhibitors, further characterization of acidic kininogenases in the extracts was performed. Extracts of rat ventricles released bradykinin-like immunoreactivity only from low-molecular-weight kininogen. Using the isolated oestrous rat uterus, gel filtration and protease inhibitors, the enzyme involved was identified as a cathepsin D-like enzyme with an optimum pH of 4.7 and a molecular weight of 42.8 +/- 4.9 kDa. It is an arginine amidase and releases bradykinin-like immunoreactivity from low-molecular-weight kininogen. Ischaemia reduced the amount of bradykinin-like immunoreactivity released by the ventricular extract (P < or = 0.05) and increased levels of free kinin in venous blood from the right atrium. Rat ventricles contain a cathepsin D-like acidic protease that cleaves low-molecular-weight kininogen to release bradykinin-like immunoreactivity. The acidic protease may protect the heart during ischaemia.

Local generation of kinins in working skeletal muscle tissue in man.

The effect of standardized isometric forearm work on circulating and local kinin concentrations was investigated in 12 healthy volunteers using the forearm catheter technique. Radioimmunological kinin determination in arterial blood and in the venous effluent of forearm muscle tissue was performed using a modification of Shimamoto's technique of blood sampling and kinin extraction. Under basal conditions, there was no arterio-venous difference of kinins. Throughout the whole experiment, arterial--reflecting systemically circulating--kinins did not change. In muscle venous blood, immunoreactive kinins were not significantly elevated during work, whereas a marked increase was detected in the recovery period (5.0 +/- 0.6 vs. 10.2 +/- 2.0 pmol/l; p less than 0.01). The data demonstrate, that kinins are locally generated in calculated amounts (32.7 +/- 8.4 fmol/(100 g x min) that are known to be sufficient to induce local vasodilatory and metabolic effects at the site of muscle contraction, but below the threshold for systemic cardiovascular actions.

Effect of a kinin antagonist on the acute antihypertensive activity of enalaprilat in severe hypertension.

The purpose of this study was to assess the role of kinins in the acute antihypertensive effect of the converting enzyme inhibitor (CEI) enalaprilat in rats with severe hypertension induced by aortic ligation between both renal arteries. For this study, we used a bradykinin analogue, D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-DPhe-Thi-Arg-TFA, with in vivo antagonistic properties. Hypertensive rats were infused intra-aortically for 15 minutes with either saline (30 microliters/min) or the kinin antagonist (40 micrograms/kg/min). Five minutes after the infusion was begun, a bolus injection of enalaprilat (60 micrograms/kg) was given. The blood pressure of the saline-infused animals decreased 48 +/- 6 mm Hg (from 180 +/- 7 to 132 +/- 7 mm Hg), while that of the rats treated with the antagonist decreased only 21 +/- 4 mm Hg (from 175 +/- 3 to 154 +/- 3 mm Hg). The difference between both decrements was significant (p less than 0.01). In another group of hypertensive animals (n = 9), we measured kinin concentration in plasma from arterial blood before and after administration of CEI (41 +/- 10 vs 68 +/- 20 pg/ml, respectively; NS). These results are consistent with the hypothesis that kinins play a role in the acute antihypertensive effect of CEIs in rats with severe hypertension. However, since arterial blood kinin concentrations were not increased significantly after CEI administration, the effect of the CEI may be due to an increase in tissue kinins, which could act as autacoids regulating vascular resistance.

The analytical value for kinin concentration in blood depends on the antiserum used in the bradykinin radioimmunoassay.

Recently published blood kinin concentrations are subject a wide scatter, due to sampling time and technique. In our study we tested the influence of the used antibradykinin antiserum on the measured kinin concentration in blood. Blood was collected from the anticubital vein by a teflon cannula and inactivated immediately by hydrochloric acid in the syringe. Subsequent extraction was performed using diethylether, n-butanol, distilled water and Biorex-70. The blood extract containing the kinins was divided into four samples and measured by four radioimmunoassays using different antibradykinin antibodies. All four assays were performed under standard conditions and at the same time. The resulting kinin values were similar in two assays: 7.4 +/- 2.6 ng/l and 5.6 +/- 1.3 ng/l. In the two other assays, however, the measured kinin concentrations differed markedly from these values: 127.5 +/- 46.7 ng/l and 693.0 +/- 85.7 ng/l. These results indicate clearly that the antibody used in the assay can be a major factor determining the range of the recorded kinin concentration.

Dyspnea in patients with hyperbradykininism and excessive venous pooling

In the original description of the syndrome of hyperbradykininism, dyspnea on exertion was not described. However, in five women with the syndrome, ages 31 to 58, four of whom had at least one elevated value of blood kinin as determined by radioimmunoassay, dyspnea on exertion was a prominent complaint. During treadmill walking at a constant power requirement against gravity, expired air gas collections and equilibrium carbon dioxide rebreathing were performed. Seventeen apparently healthy women, ages 18 to 48, served as control subjects. Although oxygen uptake was the same in both groups by design (oxygen uptake 0.91 liters per minute, 0.11 standard deviation [sd], in the control subjects; oxygen uptake 0.97 liters per minute, 0.12 [sd]in the patients), cardiac output was significantly reduced in the patients (cardiac output 8.4 liters per minute, 1.3 [sd], in the control subjects; cardiac output 6.3 liters per minute, 0.9 [sd], in the patients, p <0.01). End-tidal carbon dioxide tension was significantly lower in the patients (end-tidal carbon dioxide tension 41 torr, 3 [sd], for the control subjects; end-tidal carbon dioxide tension 33 torr, 7 [sd], for the patients). In one patient, repeated studies over a 12-month period demonstrated a positive relationship between end-tidal carbon dioxide tension and the respiratory exchange ratio. (Respiratory exchange ratio = 0.01 + 0.027 · end-tidal carbon dioxide tension, 0.073 standard error of the estimate [See], 0.71 regular correlation coefficient, n = 20). This relationship was opposite to that expected with voluntary overbreathing; it was interpreted to mean that reduced cardiac output with exercise occurred to a variable degree and was the cause of hyperpnea and hypocapnia. In the same patient, studies at exercise with and without the Jobst (antigravity) garment and studies at exercise in the supine and erect position were consistent with the hypothesis that dyspnea and exercise intolerance were caused by venous pooling when standing. It is concluded that hyperbradykininism is characterized not only by orthostatic hypotension and tachycardia with light-headedness, as originally described, but also by severe dyspnea on exertion with exercise intolerance. The mechanism remains obscure, and the treatment is unsatisfactory, but temporary improvement in the abnormal physiology can be achieved in some patients with the use of an antigravity garment.

The mechanism of the hypotensive effect of captopril (converting enzyme inhibitor) with special reference to the kallikrein-kinin and renin-angiotensin systems.

In order to clarify the mechanism of the hypotensive action of captopril, the acute and chronic effects of this drug on the kallikrein-kinin and renin-angiotensin systems were investigated respectively in 14 and 19 patients with hypertension. To determine the acute effect, a dose of 50 mg of captopril was administered once orally. For the chronic effect, 75-300 mg of the drug was administered daily for 14 days. In observations of the acute effect, blood pressure decreased significantly at 30 min. and maximally at 60-180 min. after administration with no change in heart rate. Significant increases in blood kinin levels and plasma renin activity (PRA), and a decrease in plasma angiotensin II levels were also observed. A marked augmentation was also found in urinary kinin excretion, but not in urinary kallikrein excretion. Moreover, the changes in blood pressure significantly correlated negatively with basal PRA, basal plasma angiotensin II and the changes in blood kinin levels, and positively with the changes in plasma angiotensin II. In our study of the chronic effect of captopril, similar changes in blood kinin levels, PRA, plasma angiotensin II levels, blood pressure and heart rate to the acute effect study were observed. Significant correlations of the changes in blood pressure were found negatively with basal PRA, basal plasma angiotensin II levels and the changes in blood kinin levels and positively with the changes in plasma angiotensin II levels. In addition, significant increases in urine volume and urinary sodium excretion occurred following administration of captopril for 14 days, and both increases negatively correlated with the changes in blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of furosemide and captopril on submaxillary gland blood flow and arterial pressure

The effects of furosemide and captopril were studied in nephrectomized rats with and without submaxillary gland. Captopril increased blood flow, but did not modified blood pressure. Furosemide plus captopril decreased significantly blood pressure. These results suggest a release of kallikrein by furosemide and probably a formation of kinin from plasma kininogen. On the other hand, rats sialodectomized showed no alterations in blood pressure in response to both drugs. These data suggest that submaxillary gland kallikrein participates in the mechanism of blood pressure regulation and blood flow of the gland at least in our experimental conditions. Glandular kallikreins are serine proteases which release kinins from substrates called kininogen. They are found in extracts and secretions of all exocrine glands. This proteases have been implicated in the regulation of exocrine glands and kidney blood flow, in water and electrolyte balance, in blood pressure regulation and in the pathogenesis of experimental and clinical hypertension ( Carretero et al., 1978; Martinez Seeber et al., 1982). Glandular kallikreins of exocrine glands and kidney are secreted into the exocrine secretions and urine and also into the vascular compartment, where a local blood flow could be affected. According to Gautvik et al. (1980), rat submandibular gland is an organ rich in kallikrein, and significants amounts of the gland enzyme are release into the circulation after stimulation (Orstavik et al., 1982). Hilton and Lewis (1956) first proposed that glandular kallikrein-kinin system in salivary glands regulates vasodilation, probably through the effect of kallikrein on plasma kininogen. It has also been demonstrated that release of glandular kallikrein into the circulation increase the generation of kinin in blood (Scicli et al., 1982). In the present study the effect of furosemide and Captopril on submaxillary gland were determined in order to establish whether the drugs affect the local blood flow of the gland and the arterial pressure.

Acute effects of MK421, a new angiotensin converting enzyme inhibitor, in man.

Acute effects of MK421 were examined in 11 male normal volunteers. Oral administration of 5 mg of MK421 did not induce any changes in blood pressure or pulse rate. Plasma renin activity increased significantly from 7.3 +/- 2.9 ng/ml to 22.2 +/- 7.1 (p less than 0.05), whereas plasma aldosterone concentration did not change. Blood kinin, or urinary excretion of kallikrein and of prostaglandin E did not change. However, urinary excretion of sodium increased significantly from 44.0 +/- 6.8 mEq/4 hr to 56.5 +/- 6.5 (p less than 0.02) following the administration of MK421. The present results show that an increased renin release induced by MK421 is independent of change in blood pressure, and also suggest that MK421 may have a direct action on the renal tubules.

Chlorpropamide-alcohol flushing and blood kinins.

In a pilot study six patients with noninsulin dependent diabetes, three positive and three negative to chlorpropamide-alcohol flushing (CPAF), were tested. The patients were tested both without and with chlorpropamide premedication. Blood kinin concentrations were determined before and after ingestion of small quantities of alcohol. No rise in blood kinin concentrations were found during the flush suggesting that kinins do not play a major part in chlorpropamide-alcohol flushing.

An improved method for the determination of human blood kinin levels by sensitive kinin radioimmunoassay.

A highly sensitive and specific radioimmunoassay for kinin (minimal detectable amount, 0.5 pg/tube) was applied to measure the blood kinin level. A five ml blood sample was collected with a siliconized needle and plastic syringe which contained 2.5 ml of 0.8 N-HCl. The blood kinin was extracted with butanol, following reextraction with water. According to this procedure, the mean recovery (mean +/- SE) calculated from added 125I-bradykinin (500 CPM) and the known amounts of cold bradykinin were 50.4 +/- 0.8% and 51.1 +/- 2.2%, respectively. In comparison with other sampling methods in 6 normal subjects, the blood samples taken without HCl in syringes showed a higher level (24.4 +/- 10.1 pg/ml) than the samples with HCl (5.3 +/- 1.3 pg/ml). And very high levels were obtained in the plasma samples collected by the method of Talamo or Vinci (0.53 +/- 0.24 ng/ml and 3.5 +/- 1.3 ng/ml, respectively). The kinin content in blood samples taken with HCl was stable at -20 degrees C for at least one month, but increased significantly at room temperature or 4 degrees C for 48 hours. Blood samples were obtained from 17 normal subjects, and 3 patients with acute myocardial infarction. Blood kinin levels in the patient with acute myocardial infarction, 121 +/- 20.9 pg/ml, were significantly higher than those in normal subjects (3.8 +/- 0.5 pg/ml). From these results, it was concluded that high levels of blood kinin reported previously may have resulted from inadequate sampling procedures. Thus, in order to measure blood kinin accurately, inactivation of the kinin generating and destroying enzymes must be done immediately after the sampling. In addition, this radioimmunoassay method should be very useful in investigating the pathophysiological role of blood kinin in various diseases.

Role of the Renin-Angiotensin-Aldosterone and Kallikrein-Kinin Systems in the Control of Fluid and Electrolyte Metabolism, Renal Function, and Arterial Blood Pressure

The long-term effects of angiotensin I converting enzyme (kininase II) inhibition with Captopril on fluid and electrolyte metabolism, aldosterone secretion, renal function, and arterial pressure were evaluated in conscious sodium deficient dogs. Plasma aldosterone concentration (PAC), plasma renin activity (PRA), urinary sodium excretion (UNaV), arterial pressure (AP), renal blood flow (RBF), glomerular filtration rate (GFR), blood kinin concentration (BK), urinary kinin excretion (UK), and urinary kallikrein activity (UKA) were determined during long-term inhibition of angiotensin I converting enzyme (kininase II). In response to Captopril administration (20 mg/kg/day) PAC decreased from 38.9 +/- 6.7 to 14.3 +/- 2.3 ng/dl, PRA increased from 3.58 +/- 0.53 to 13.7 +/- 1.6 ng/ml/hr, UNaV increased from 0.65 +/- 0.27 to 6.4 +/- 1.2 mEq/day, AP decreased from 102 +/- 3 to 65 +/- 2 mmHg, RBF increased from 136 +/- 7 to 156 +/- 8 ml/min, GFR decreased from 65 +/- 8 to 36 +/- 7 ml/min, BK increased from 0.17 +/- 0.02 to 0.41 +/- 0.04 ng/ml, UK increased from 7.2 +/- 1.5 to 31.4 +/- 3.2 micrograms/day, and UKA decreased from 23.6 +/- 3.1 to 5.3 +/- 1.2 E.U./day. Aldosterone infusion in sodium deficient dogs maintained on Captopril failed to alter urinary sodium excretion, renal function, or arterial blood pressure. However, angiotensin II infusion (3 ng/kg/min) restored aldosterone secretion, renal function, and arterial blood pressure within three days to levels observed in untreated sodium deficient dogs. The marked alterations in renal function and urinary sodium excretion during angiotensin II infusion indicate that angiotensin II is several times more potent than aldosterone in the long-term control of sodium excretion. Also, our studies demonstrated that the long-term hypotensive and natriuretic actions of inhibitors of angiotensin I converting enzyme (kininase II) are mediated by inhibition of angiotensin II formation.

Virulent and Avirulent Strains of Babesia bovis: The Relationship Between Parasite Protease Content and Pathophysiological Effect of the Strain

A virulent strain of Babesia bovis ("L" strain) was rendered avirulent by irradiation with 35 krads with a gamma source. Another virulent strain of B. bovis ("C" strain) was made avirulent by rapid blood passage through 12 splenectomised calves. Both the parent virulent and their respective avirulent strains were injected into susceptible cattle. A nonfatal disease was observed in those intact cattle that had received avirulent parasites; however, a fatal disease was produced in those animals that had received virulent parasites and in splenectomised calves that had received avirulent parasites. Blood kinin levels rose and plasma kininogen levels fell significantly in those animals infected with both virulent strains. Nonsignificant changes occurred with these parameters in animals infected with avirulent parasites. Preparations of disrupted parasites were obtained from the four parasite populations. Both virulent strains contained high levels of protease. The avirulent forms contained insignificant amounts. As parasite doubling times and maximum parasitaemias were the same for all four parasite populations, we conclude that these enzymes are not obligatory for parasite multiplication in the vertebrate host. Their role in producing pathological changes in the host is discussed.

Kinins in relation to renin activity in renal and inferior caval veins in normal individuals and patients with primary aldosteronism

Blood kinin concentration and plasma renin activity (PRA) were determined in the renal veins and in the inferior caval vein (ICV) below the level of the renal veins in 9 normal individuals (5 men and 4 women) and 7 patients with primary aldosteronism (3 men and 4 women). PRA in the renal veins and ICV was significantly lower and plasma aldosterone concentration in ICV significantly higher in the patients as compared to the normals. Kinin concentration in the renal veins and ICV did not differ significantly between the patients and the normals (0.31 +/- 0.04 (mean +/- SEM) vs 0.45 +/- 0.03 and 0.27 +/- 0.05 vs 0.45 +/- 0.06 microgram/l, respectively). In the normal individuals kinin concentration and PRA were inversely related in the left renal vein (r = -0.80; P less than 0.02), whereas this relation did not reach statistical significance in the right renal vein (r = -0.60; P less than 0.10). Kinin concentration in both renal veins was positively correlated to kinin concentration in ICV (r = 0.73; P less than 0.05 and r = 0.83; P less than 0.02 for the right and left renal vein, respectively). These results indicate that intrarenal kinin formation and renin release are inversely related in normal subjects. Furthermore, they suggest that one and the same enzyme, possibly renal kallikrein, may be implicated in the kinin formation in the systemic as well as in the renal circulation. Intrarenal kinin formation seems not to be increased in primary aldosteronism.

The kallikrein-kinin system and its role in the hypotensive shock syndrome of animals infected with the haemoprotozoan parasites Babesia, Plasmodium and Trypanosoma

1. Severe hypotension occurs in the terminal stages of acute Babesia bovis and Plasmodium falciparum infections and in experimental chronic Trypanosoma brucei infections. 2. A rise in whole blood kinin and a corresponding fall in plasma kininogen occurs in babesial, malarial and trypanosomal infections. 3. Significant plasma kallikrein activation occurs during acute B. bovis and P. knowlesi infections, and a large turnover in plasma kallikrein occurs in trypanosomiasis. The activation of plasma kallikrein is inhibited in both babesiosis and trypanosomiasis by the proteinase inhibitor aprotinin. 4. Plasma kallikrein and Hageman Factor are activated in B. bovis infections by parasite proteases. Antigen/antibody complexes result in plasma kallikrein activation in chronic trypanosomiasis.

Mobilization of colonic kallikrein following pelvic nerve stimulation in the atropinized cat.

1. Pelvic nerve stimulation (p.n.s.) in cats induces atropine-resistant colonic vasodilatation and colonic contraction. The effects of this on cat colon are mimicked by synthetic bradykinin infusions. The present study examines the effect of p.n.s. on the activation of kallikrein, the kinin-forming enzyme present in colonic tissue and its effects on the plasma kinin system in the atropinized cat.2. Mean level (+/- S.D.) of mucosal kallikrein was found to be about 37 times higher in unstimulated colonic mucosa (300 +/- 100 ng bradykinin equivalents min(-1)g(-1)) than in the underlying muscle (8.2 +/- 6.3 ng bradykinin equiv min(-1)g(-1)).3. After a p.n.s. of 5 min, mean kallikrein level in colonic muscle was 7.3 +/- 3.5 ng bradykinin equiv min(-1)g(-1), which was not significantly different from the control muscle kallikrein. However, there was an 86% fall in mucosal kallikrein to 41.3 +/- 34.7 ng bradykinin equiv min(-1)g(-1) after 5 min p.n.s., indicating a rapid activation and secretion of mucosal kallikrein.4. Secretion of mucosal kallikrein was paralleled by specific depletion of plasma kininogen, the precursor of active kinin in blood draining the colon. The mean plasma kininogen level fell to 79 and 68% of the prestimulated value (3.1 +/- 1.1 S.D. mug bradykinin equiv per ml. plasma) after 5 and 10 min p.n.s. respectively. Total plasma protein and haematocrit remained unaltered excluding non-specific changes due to protein extravasation or haemodilution and indicating utilization of the plasma kinin precursor.5. Following 2 hr p.n.s., raised levels of kallikrein were detected in both colonic muscle (28 +/- 2.0 bradykinin equiv min(-1)g(-1)) and mucosa 434 +/- 118 ng bradykinin equiv min(-1)g(-1)). Preliminary studies using a kallikrein inhibitor indicated that the increased kallikrein levels originated from plasma.6. Direct stimulation of the parasympathetic pelvic nerve in the atropinized cat thus produced activation of the plasma kinin system in the colon and formation of free kinins may be responsible for the mucosal vasodilatation and strong motor contraction which is not blocked by large doses of atropine. The observation that prolonged stimulation causes extravasation of plasma kallikrein, a potential inflammatory mediator, into the tissues may be of clinical significance.

Changes in components of kinin system and hemodynamics in acute myocardial infarction

Kinin is known to have potent pain-producing and hypotensive actions and has been suggested as one of the causes of chest pain and shock in acute myocardial infarction. Since most of the previous reports 3–7 have been based on measurements of kininogen, the inactive precursor of kinin, peripheral blood kinin as well as kininogen was measured in this study. Kinin and kininogen levels were determined over a period of one month or until death from the onset in 23 cases of acute myocardial infarction, along with simultaneous measurements of hemodynamic indices. Sixteen of the 23 cases survived more than one month, and seven patients died of pump failure within 3 days of the infarction. In the survival group, increased kinin and decreased kininogen levels were observed in the initial stage, reaching a maximal change on the second day. The alterations in kinin levels were significantly correlated with concomitant lowering of blood pressure, decreased total vascular resistance, and prolongation of circulation time. In the non-survival group, there was no increase in kinin levels in spite of a decrease in kininogen. Accordingly, no significant correlation was found between kinin and hemodynamic changes. The lack of change in kinin in the latter group was thought to account for the strong kininase activity. Thus, these data indicate that kinin is not the cause of cardiogenic shock. Rather, the increased kinin level observed in survivors might indicate beneficial vasodilation effects, possibly by increasing coronary flow and reducing the afterload of the left ventricle.

Effects of t-AMCHA and EACA on the Plasma Kallikrein System

Varied amounts of t-AMCHA or EACA added to non-contact fresh dog plasma generates kininogenase and TAME esterase activities. These phenomena may be abolished by prior addition of lima bean trypsin inhibitor. t-AMCHA or EACA had no effect on partially purified kallikrein, but had a significant inhibitory influence on plasma kininase. The generation of prekallikrein activator with t-AMCHA was ascertained by gel filtration on a Sephadex G-100 column. The blood kinin level increased about 50% one hr after administration of t-AMCHA. It is suggested from these results that t-AMCHA may initiate the true activation of the kallikrein system by activating the Hageman factor.

Inhibition of kinin formation by a kallikrein inhibitor during extracorporeal circulation in open-heart surgery.

Involvement of the kinin system was studied in 58 patients during extracorporeal circulation in open heart surgery. At the onset of extracorporeal circulation, there was no increase of free kinin in blood and no reduction of plasma kininogen, when the latter was expressed as mug bradykinin/mg plasma protein. With the lapse of time, kinin in the blood increased significantly, and decrease of kininogen was also significant. The longer the circulation time, the greater the consumption of kininogen. The site of the kinin formation was presumed to be the heart-lung machine since the level of kinin increased slightly and kininogen decreased gradually in the blood leaving the machine, compared with those levels entering the machine. The difference in kininogen was significantly different from zero at termination of extracorporeal circulation. Administration of a kallikrein-trypsin inhibitor, trasylol (A. G. Bayer), infused into the heart-lung machine, prevented the decrease of kininogen. Reduction of the total peripheral resistance during this circulation was also prevented. The hemoconcentration, presumably the result of vascular permeability increase caused by increased kinin, was prevented by trasylol in cases in which extracorporeal circulation lasted over 60 minutes. Trasylol applied thus appears to be an effective counteragent for circulatory disturbances which occur during extracorporeal circulation.

Determination of blood kinin levels by radioimmunoassay

A radioimmunoassay has been developed which enables measurement of kinin levels in blood of man and dogs. The levels found are not due to production of kinin by kallikrein activation during collection. The material detected by this assay is immunologically similar to synthetic bradykinin (BK) and has the same susceptibility to proteolytic enzymes. Levels found in venous blood in man average 0·07 ng/ml (S.D. 0·03 ug/ml). In a dog receiving an infusion of synthetic BK the levels detected downstream from the infusion site rose progressively with increased dose. Dogs show a positive arterio-venous difference across the vascular bed of the hind limb.