ENZYMATIC STUDIES ON BRADYKININ AND SIMILAR PEPTIDES

Angiotensin I-converting enzyme inhibitors block protein kinase C epsilon by activating bradykinin B1 receptors in human endothelial cells

Angiotensin I-converting enzyme (ACE) inhibitors are widely used to treat patients with cardiovascular and kidney diseases, but inhibition of ACE alone does not fully explain the beneficial effects. We reported that ACE inhibitors directly activate bradykinin B1 receptor at the canonical Zn2+ binding site, leading to prolonged nitric oxide (NO) production in endothelial cells. Protein kinase C (PKC) epsilon, a novel PKC isoform, is up-regulated in myocardium after infarction, suggesting a role in the development of cardiac dysfunction. In cytokine-treated human lung microvascular endothelial cells, B1 receptor activation by ACE inhibitors (enalaprilat, quinaprilat) or peptide ligands (des-Arg10-Lys1-bradykinin, des-Arg9-bradykinin) inhibited PKC epsilon with an IC50 = 7 x 10(-9) M. Despite the reported differences in binding affinity to receptor, the two peptide ligands were equally active, even when inhibitor blocked the cleavage of Lys(1), thus the conversion by aminopeptidase. The synthetic undecapeptide (LLPHEAWHFAR) representing the binding site for ACE inhibitors on human B(1) receptors reduced PKC epsilon inhibition by enalaprilat but not by peptide agonist. A combination of inducible and endothelial NO synthase inhibitors, 1400W [N-(3(aminomethyl) benzyl) acetamidine dihydrochloride] and N omega-nitro-L-arginine (2 microM), significantly reduced inhibition by enalaprilat (100 nM), whereas the NO donor (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl) amino]diazen-1-ium-1,2-diolate (100 microM) inhibited PKC epsilon activity just as the B1 ligands did. In conclusion, NO generated by B1 receptor activation inhibits PKC epsilon.

The kallikrein-kininogen-kinin system: lessons from the quantification of endogenous kinins

The purpose of the present review is to describe the place of endogenous kinins, mainly bradykinin (BK) and des-Arg(9)-BK in the kallikrein-kininogen-kinin system, to review and compare the different analytical methods reported for the assessment of endogenous kinins, to explain the difficulties and the pitfalls for their quantifications in biologic samples and finally to see how the results obtained by these methods could complement and extend the pharmacological evidence of their pathophysiological role.

Metabolism of Bradykinin by Peptidases in Health and Disease

This chapter provides an overview of the metabolism of bradykinin (BK) by peptidases in health and disease. The enzymatic breakdown of kinins affects the duration of their biological actions as the plasma half-life of intravenously injected BK is in the range of seconds. Kinins are cleaved in vitro and in vivo by enzymes that belong to families, such as zinc-metallopeptidases, astacin-like metallopeptidases, and catheptic enzymes. Vane noted the importance of the pulmonary circulation in the metabolism of vasoactive substances, such as BK as well as angiotensin 1 and 5- hydroxytryptamine. It is clear after decades of research that angiotensin 1-converting enzyme (ACE) on the vascular endothelial cell surface is the most important inactivator of blood-borne BK. BK may act primarily in an autocrine and paracrine fashion, establishing the importance of local regulation of its activity by enzymes on cell surfaces. Thus, the assortment of other enzymes that can inactivate BK is important in a variety of physiological and pathological situations. Most physiological systems have redundant pathways of metabolism so that the abolishment of one pathway is compensated for by the presence of others. This is demonstrated by the pharmacological inhibition of ACE in hypertension.

THE PRESERVATION OF BRADYKININ BY PHENOTHIAZINES IN VITRO

Chlorpromazine and phenoxybenzamine have been shown to potentiate the actions of bradykinin in vivo. To test whether this phenomenon could be due to inhibition of the enzymatic destruction of bradykinin, bradykinin was incubated with either tissue extracts or with carboxypeptidase B. Bradykinin was rapidly destroyed by acetonedried powders of brain and serum of various animals as well as by purified carboxypeptidase B. The rate of disappearance of bradykinin activity was decreased in the presence of phenothiazine derivatives, phenoxybenzamine and hydroxyzine, but not by compounds of a larger group including other psychotropic drugs, tranquillizers and ganglionic and adrenergic blocking agents. Spectrophotometric studies of the hydrolysis of hippuryl-L-arginine confirmed the presence of a carboxypeptidase B-like activity in brain. The substances that acted as inhibitors of bradykinin destruction were also enzyme inhibitors as measured by this technique. Previous incubation of carboxypeptidase B with phenothiazines and zinc ions greatly reduced the enzymatic inhibition by the phenothiazines, which indicated a possible chelating action by these inhibitors on the metalo-enzyme carboxypeptidase B.

KININ-FORMING AND DESTROYING ACTIVITIES OF SALIVA

Kininase activity is present in saliva obtained from the oral cavity but not in saliva obtained by cannulation of the parotid or submandibular ducts. This activity originates from squamous epithelial cells from the oral mucous membranes. Experiments with various inhibitors indicated that the kininase activity of squamous epithelial cells differs from that of plasma, and resembles that of erythrocytes. Kinin-forming activity is present both in the glandular secretion and in the squamous epithelial cells.

Activated human plasma carboxypeptidase B is retained in the blood by binding to alpha2-macroglobulin and pregnancy zone protein

A 66-kDa glycosylated carboxypeptidase, plasma pro-carboxypeptidase B (pro-plasma CPB), has recently been identified in human blood (Eaton, D. L., Malloy, B. E., Tsai, S. P., Henzel, W., and Drayna, D. (1991) J. Biol. Chem. 266, 21833-21838). The pro-enzyme binds to plasminogen and the active enzyme is specific for COOH-terminal Lys or Arg residues. These properties implicate a role in the fibrinolytic or coagulation system. However, we show that the molecular mass of the active plasma CPB is approximately 36 kDa, which is below the glomerular filtration limit. Since activated plasma CPB no longer binds plasminogen, the active enzyme may not be retained in the circulation. To investigate this, we performed plasma elimination studies in mice which showed that 125I-plasma CPB remains in the circulation despite its small size. Native polyacrylamide gel electrophoresis of blood samples removed from the mice revealed that plasma CPB migrated as a high molecular weight band. Similar bands were observed in vitro when 125I-plasma CPB was added to plasma from humans and other species. The plasma CPB-binding proteins were purified from human plasma and identified as alpha2-macroglobulin (alpha2M) and pregnancy zone protein. Only the active enzyme bound to the two alpha-macroglobulins, and the interaction was specific for alpha2M in its native conformation, but not its receptor recognized forms. The complex between human alpha2M and plasma CPB dissociated during SDS-polyacrylamide gel electrophoresis and transverse urea gel electrophoresis suggesting that the interaction was noncovalent and depended on the tertiary structure of the native alpha2M molecule. The catalytic activity of plasma CPB was not significantly affected by its binding to alpha2M. The specific binding of plasma CPB to alpha-macroglobulins suggest that these proteins may function as a "shuttle" in vivo to modulate the clearance of plasma CPB from the circulatory system.

Removal of Arg141 from the alpha chain of human hemoglobin by carboxypeptidases N and M

Both human plasma carboxypeptidase N (CPN) and membrane-bound carboxypeptidase M (CPM) released the C-terminal arginine (alpha-Arg141) of the alpha chain of human adult hemoglobin. An arginase contamination present in the hemoglobin preparation, which converted the released arginine to ornithine, was removed by gel filtration. CPM was about 20 times more efficient than CPN or its active subunit in hydrolyzing oxyhemoglobin and cleaved oxyhemoglobin twice as fast as deoxyhemoglobin. The hydrolysis of the peptide bond of alpha-Arg141 accelerated the dissociation rate of the tetramer deoxy-des-alpha-Arg141 hemoglobin to dimers 2500-fold over that of deoxyhemoglobin, as measured by haptoglobin binding. Moreover, the dissociation of the deoxy-des-alpha-Arg141 hemoglobin tetramer to dimers was not affected by 2,3-diphosphoglyceric acid. Des-alpha-Arg141 hemoglobin had a higher oxygen affinity (P50, 5.51 mm Hg; control, 19.94 mm Hg [P50 is the partial pressure of oxygen that gives 50% of the saturation of hemoglobin]) and a lower apparent cooperativity (Hill coefficient: n, 1.02; control, 2.24) than unhydrolyzed hemoglobin. After hemoglobin was incubated in human plasma, its oxygen-binding parameters, the P50, and the Hill coefficient decreased drastically due to cleavage by CPN. In the perfused rat heart, des-alpha-Arg141 hemoglobin was a more effective coronary vasoconstrictor than hemoglobin, possibly because it dissociated to dimers in the coronary vascular bed. A covalently cross-linked hemoglobin was less active than native hemoglobin. The coronary vasoconstriction was caused by multiple factors, including interference with vasodilation by nitric oxide and eicosanoids. Thus, the hydrolysis of hemoglobin by CPM and CPN demonstrated the contribution of the alpha-Arg141 residue to sustaining the tetrameric structure of hemoglobin and its normal oxygen affinity and vasoactivity.

A micromethod for the determination of the activities of kininases in rat plasma. Kinetics and inhibitory characteristics

Kininase II (EC 3.4.15.1) (KII) and kininase I (KI) (EC 3.4.12.7) activities of rat plasma were characterized by the hydrolysis of hippuryl-L-histidyl-L-leucine (HHL), hippuryl-L-arginine (HLA) [expressed as carboxypeptidase N1 (CN1) activity] and hippuryl-L-lysine (HLL) [expressed as carboxypeptidase N2 (CN2) activity]. Using a spectrophotometric assay, biochemical characteristics of the three enzymes were investigated. The Michaelis-Menten constants were as follows: KII: Km 2.55 +/- 0.22 mM, Vmax 0.357 +/- 0.017 mumol/min/mL; CN1: Km 6.93 +/- 0.32 mM, Vmax 0.748 +/- 0.019 mumol/min/mL; and CN2: Km 35.8 +/- 1.52 mM, Vmax 13.11 +/- 0.40 mumol/min/mL. EDTA and O-phenanthroline inhibited the three enzyme assays at the same Ki, whereas captopril and 2-mercaptomethyl-3-guanidinoethylthiopropanoic acid (MERGETPA), allowed for the demonstration of the specificity of each assay. Furthermore, Ki values of MERGETPA against both CN1 (4.75 microM) and CN2 (2.36 microM) activities do not support the hypothesis that KI activity may be accounted for by the presence of isoenzymes in rat plasma.

Psoriasis: highly reactive early cellular inflammation

Psoriasis is the result of highly reactive early cellular inflammation. Psoriasis simultaneously has a rapidly proliferating epidermis, a vigorous acute inflammatory reaction, an accelerated rate of dermal breakdown and repair, and vascular and fibroblast proliferation. Understanding the primary role of early cellular inflammation allows explanation of other factors. All clinical, experimental and therapeutic facts can be explained on this basis. There are extensive biologic changes. Early cellular inflammation is influenced by genetic and environmental factors. It is proposed that the defect is quantitative rather than qualitative. Psoriasis commonly localizes at sites of injury. Several authors have noted that the first histologic change in psoriasis is the spurting of granulocytes from the dermal papillae. This is a cyclical event. Connective tissue-active peptides released from granulocytes produce a ninefold increase in the size of the dermal papille. This results in a ninefold increase in the size of the germinative cell base of the epidermis. The vast literature on rapid epithelial proliferation in psoriasis measures a secondary phenomenon. The concept presented does not provide an answer to the biochemistry of early cellular inflammation except to point out the initial importance of dilution of tissue fluids. The author considers early cellular inflammation to result from multiple, simultaneous, overlapping, amplifying and inhibitory systems. There are multiple ways to arrive at the final biologic effect which is too essential to depend on a single series of events. There is a large amount of empiric knowledge on psoriasis which can aid in understanding early cellular inflammation.

Mechanism of digestion of bradykinin and lysylbradykinin (kallidin) in human serum. Role of carboxypeptidase, angiotensin-converting enzyme and determination of final degradation products

Degradation of bradykinin and lysylbradykinin was studied in plasma and serum, and the results were compared to those seen with mixtures of carboxypeptidase N and angiotensin-converting enzyme (ACE), the two recognized kininases in blood. Angiotensin-converting enzyme was an effective kininase in mixtures with carboxypeptidase N at physiologic concentration and digested bradykinin to the dipeptides Phe- Arg and Ser-Pro plus the pentapeptide Arg-Pro-Pro-Gly-Phe. Carboxypeptidase N slowly removed the C-terminal Arg from bradykinin to yield des-Arg9-bradykinin (DBK); the latter was digested by ACE to yield the aforementioned pentapeptide and the tripeptide Ser-Pro-Phe. In serum, however, the C-terminal Arg was removed from bradykinin about five times faster than was accounted for by the activity of carboxypeptidase N. The primary substrate of ACE in serum, therefore, was des-Arg9-bradykinin and not bradykinin. The products of this reaction, pentapeptide and tripeptide, were unstable in serum and were cleaved by enzymes that have not yet been characterized. One product, free phenylalanine, was used to monitor these reactions by HPLC. Our studies indicate that the final products of bradykinin degradation were the tripeptide Arg-Pro-Pro, one mole each of Ser, Pro, Gly, and Arg, and two moles of phenylalanine. Since the serum level of carboxypeptidase N did not account for the rapid kinin degradation seen, other carboxypeptidases may have been operative, perhaps released as a result of blood clotting, or a serum cofactor may augment carboxypeptidase N activity.

Converting enzyme activity of free airway cells

The pulmonary circulation was previously shown to inactivate and even activate a number of autacoids. Further studies showed that these enzymatic activities were localized in vascular endothelial cells. The present results shows that guinea pig free airway cells (FACs) convert angiotensin I to angiotensin II and inactivate bradykinin, whereas they do not inactivate serotonin, prostaglandin E2, histamine, and noradrenaline. In the presence of a converting enzyme inhibitor (SQ14225), the angiotensin I was not converted into angiotensin II, but bradykinin was still inactivated, although the speed of inactivation was decreased. Furthermore, when FACs were separated as adherent and nonadherent cells, the cleavage of angiotensin I by adherent cells was similar to that of the total cell suspension. The inactivation of bradykinin was more pronounced in incubation with nonadherent than with the adherent cells. Using selected enzyme inhibitors, we also showed that the conversion of angiotensin by FAC is the result of specific kinase II activity most likely located in macrophages, whereas the bradykinin inactivation is the result of the cooperation of many enzymes including kinase I and II produced by various cell types.

Studies of the digestion of bradykinin, lysyl bradykinin, and kinin-degradation products by carboxypeptidases A, B, and N

We have compared the digestion of bradykinin, lysyl bradykinin, and kinin degradation products by carboxypeptidases N, B and A (CPN, CPB and CPA). Carboxypeptidase N removed the C-terminal arginine from bradykinin or lysyl bradykinin to leave the des-Arg derivative of each, and no further degradation occurred regardless of enzyme concentration or time of incubation. However, both CPB and CPA degraded the des-Arg derivatives to remove the C-terminal phenylalanine. The inhibitory effect of phosphate ions upon this activity of CPB (but not CPA) suggests that CPA may be responsible for the formation of free phenylalanine seen upon degradation of kinins in plasma or serum. However, angiotensin converting enzyme degraded des-Arg9-bradykinin in plasma or serum prior to such Phe removal to yield the pentapeptide Arg-Pro-Pro-Gly-Phe and the tripeptide Ser-Pro-Phe. We demonstrated that CPB degraded Arg-Pro-Pro-Gly-Phe but not Ser-Pro-Phe; this reaction was also inhibited by phosphate ions. Carboxypeptidase A, on the other hand, liberated Phe from both peptides in phosphate-buffered saline and accounted, at least in part, for the free phenylalanine detected. Carboxypeptidase N did not digest the aforementioned pentapeptide or tripeptide. It is clear that carboxypeptidase B and carboxypeptidase A had overlapping activities, depending upon the substrate tested, and were distinguished by the effects of different ionic environments. We further suggest a role for carboxypeptidases other than CPN in the degradation of kinins in human plasma or serum.

Kininase one-an'-a-half: the newest member of the kininase family

A kininase I-like enzyme (carboxypeptidase) was purified to homogeneity from human urine and compared to the 48,000 mol. wt. (48K) active subunit of carboxypeptidase N. The urinary carboxypeptidase had a mol. wt. of 73,000 in gel filtration and 76,000 in SDS-polyacrylamide gel electrophoresis. It had a pH optimum of 7.0 and differed from the 48K subunit in stability, susceptibility to trypsin, and enzymatic activity. The urinary enzyme did not cross-react with antibody to carboxypeptidase N in "Western blotting". Urine from a patient genetically deficient in plasma carboxypeptidase N (21% of normal) contained normal levels of urinary carboxypeptidase with similar properties to that from pooled human urine. Membrane fractions from several tissues contained a similar carboxypeptidase activity. The activity was highest in a microvillous membrane fraction from human placenta (65 nmol/min/mg with Bz-Gly-Lys as substrate). High specific activities were also found in membrane fractions of human kidney (18 nmol/min/mg) and lung (8 nmol/min/mg). The membrane-bound enzyme was distinguished from lysosomal and catheptic carboxypeptidases as well as "enkephalin convertase" by the use of specific inhibitors. These results show that urine contains a carboxypeptidase capable of cleaving arginine or lysine from the C-terminus of peptides. The enzyme does not arise from plasma carboxypeptidase N, but may be released into the urine from the renal brush border.

Kinin cleavage by human erythrocytes

An aminopeptidase-P has been purified 230-fold from human erythrocytes. The purified enzyme cleaved arginine from des-(Arg9)-bradykinin (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe) had a molecular weight in nondenaturing buffers of 155,000 +/- 6,900 daltons, was not inactivated by chelating agents, had a pH optimum of 7.2, and was stimulated by manganous ions. The aminopeptidase-P was stable in intact erythrocytes for at least 21 days. Extensively washed and intact human erythrocytes cleaved arginine from exogenously supplied des-(Arg9)-bradykinin; arginine was the earliest-appearing reaction product. Purified aminopeptidase-P also cleaved a group of X-proline dipeptides including leucyl-proline, methionyl-proline, phenylalanyl-proline, arginyl-proline, and alanyl-proline. The total intra-erythrocytic aminopeptidase-P activity of the "average 70-kg man" was 2,600 units, approximately five times the amount of activity in the total lung mass. The human erythrocyte aminopeptidase-P activity was not tightly bound to the erythrocyte membrane. Intact erythrocytes also exhibited some kinin-converting enzyme activity.

Kallikrein and prekallikrein of the isolated basolateral membrane of rat kidney

A basolateral membrane (BLM) enriched fraction of the homogenized rat kidney contained kallikrein and prekallikrein which differ from urinary kallikrein. Triton X-100 (0.1%) or melittin (10(-7) - 10(-5)M) solubilized the membrane-bound enzyme. Prekallikrein was activated by trypsin and plasmin. Active kallikrein and activated prekallikrein cleaved the chromogenic substrate S-2266 and released bradykinin from kininogen. Aprotinin and antiserum to rat urinary kallikrein inhibited BLM kallikrein. Gel electrophoresis separated activated BLM prekallikrein and kallikrein; prekallikrein even after activation moved slower (Rf = 0.3) in electrophoresis at an alkaline pH than active kallikrein (Rf = 1). Gel filtration resolved BLM kallikrein to two proteins of low (4 X 10(4) M) and high (1.5 X 10(5) M) molecular weight. After isoelectric focusing of the activated BLM fraction, two kallikreins with pIs of 3.9 and 5.3 were obtained. The BLM fraction also contained renin which became active after Triton treatment. Renin activity was not enhanced by trypsin or acid pH indicating that there was no prorenin present. Thus, BLM of rat kidney contains a kallikrein which is different from urinary kallikrein. This kallikrein, when released from basal membrane, may appear in renal lymph and venous effluent.

Experimental gingivitis in ODU plaque-susceptible rats. V. The presence of bradykinin in the gingival tissue and the bradykinin inactivating factor in rat dental plaque

Plaque formation and gingival inflammation were found in ODU plaque-susceptible rats. A study was performed to determine the relationship between the presence of bradykinin in gingival tissue and the inflammatory capacity of rat plaque. Bradykinin content in gingival tissue and the bradykinin inactivating activity of dental plaque of 12-month-old ODU rats were measured. The presence of bradykinin was observed in the gingival tissue of the ODU rat and a bradykinin inactivating factor was found in the rat plaque. The factor was destroyed at 60 degrees C for 30 minutes, at pH 1.5 or by treatment with perchloric acid. The optimum pH of the factor was approximately 8.0. Chelate reagents, such as O-phenanthroline and EDTA . 4Na, strongly inhibited the bradykinin inactivating factor. The protease inhibitor, Trasylol, also inhibited this factor. The SH reagent, L-cysteine, inhibited weakly and Zn++ inhibited less. The investigation suggested that the rat plaque posseses the ability to inactivate bradykinin and plays an important role in modifying the inflammatory response caused by bradykinin in gingival tissue.

An aminopeptidase of human neutrophil leucocytes--its possible role in enhanced vascular permeability

An aminopeptidase of human leukocyte lysosomes was partially purified by chromatography on SP-Sephadex, Sephadex G-200 and QAE-Sephadex. By QAE-Sephadex and isolelectric focusing it showed microheterogeneity, focusing at pH 3.7 and 4.1. By gel filtration its molecular weight was estimated to be approx. 200,000. The enzyme had leucine amino peptidase activity and pharmacological assays indicated that it converted lysyl- or methionyl-lysyl-bradykinin to bradykinin. Conversion of lysyl-bradykinin to bradykinin could be confirmed also by chromatography on CM-cellulose. When the neutrophil-derived enzyme acted on methionyl-lysyl-bradykinin it increased its effect of enhancing vascular permeability, when injected intradermally into guinea pits. Thus the enzyme may play a role in neutrophil leukocyte-mediated vascular phenomena of the inflammatory reaction.

A review of macromolecular transport and secretion at the cellular level

This is a review of current information concerning mechanisms involved in transport and secretion of macromolecules in exocrine glands. Emphasis has been placed on information available for pancreatic acinar cells. The review was prompted by the availability of considerable amounts of new information developed during the past several years. Exportable proteins in the pancreatic acinar cells are synthesized on ribosomes attached to the endoplasmic reticulum. Following synthesis, nascent proteins are transported from ribosomes attached to the endoplasmic reticulum into intracisternal spaces bound by the endoplasmic reticulum. The proteins are then carried to the Golgi complex by transitional elements. Zymogen granules are formed in the Golgi complex and migrate to the cell apex. Appropriate stimulation leads to fusion of the zymogen granule membrane and apical plasmalemma followed by a break in the membrane and consequent release of the granule content into the ductules. The extact molecular events involved in the process of secretion are not known. The roles of cAMP and cGMP in pancreatic secretion are supported by indirect evidence only. The role of calcium in secretion is apparent, but further investigation is needed to delineate the exact mechanism of its action. Membrane depolarization and associated ionic fluexes seem to play a significant role.

The bradykininase activities of extracts of dog lung

1. Homogenates of dog lungs freed from blood inactivate bradykinin. The bradykininase activity is present in soluble and particulate subcellular fractions.2. The fraction with the highest relative specific activity is that sedimenting between 8,700 g and 78,000 g. This fraction has been studied in more detail.3. There is evidence for two bradykinin inactivating enzymes in this fraction with apparent K(m) values of 7.5 muM and 120 muM.4. The bradykininase activity is not dependent on the concentration of chloride ion.5. The bradykininase activity is inhibited by EDTA, 2:3-dimercaptopropanol, nickel ions and some of the peptides from the venom of Bothrops jararaca and of Agkistrodon halys blomhoffii but not by 2-mercaptoethanol or N-ethylamaleimide.6. Angiotensin II in either 15 or 170 mM chloride ion is not an inhibitor of bradykininase activity but angiotensin I at either chloride concentration is an inhibitor. It is proposed that chloride is not necessary for binding of angiotensin I to converting enzyme but is necessary to ensure the correct orientation of substrate for hydrolysis to proceed.

The inactivation of bradykinin in the pulmonary circulation of isolated lungs

1. The isolated lungs of guinea-pigs, rats and dogs, perfused with Krebs bicarbonate solution via the pulmonary artery, inactivated 95, 98 and 99% respectively of the bradykinin infused through them.2. This inactivation process was not inhibited by 2-mercaptoethanol (1 mM) or EDTA (500 muM).3. The inactivation was inhibited by 2:3-dimercaptopropanol (100 muM), N-ethylmaleimide (100 muM), and several of the bradykinin potentiating peptides from Bothrops jararaca, in both natural and synthetic forms.4. The effect of these compounds, 2-mercaptoethanol, EDTA, 2:3-dimercaptopropanol, N-ethylmaleimide and Bothrops peptides on the pulmonary bradykininase activity is the same as their effect on pulmonary angiotensin I converting enzyme.

Altered Urinary Kallikrein Excretion in Rats with Hypertension

The urinary excretion of kallikrein, an enzyme which cleaves a vasodilator kinin from kininogen substrate, was examined in three types of hypertensive rats. Enzyme activity was measured by both esterase activity (isotopic assay) and bioassay with purified rat urinary kallikrein as a standard. Excretion of kallikrein was found to increase with age in spontaneously hypertensive rats, but levels were lower and stable in normotensive Wistar control animals. Rats with desoxycorticosterone-salt hypertension excreted markedly more, whereas rats with renal hypertension excreted significantly less kallikrein than did control animals. The alterations in kallikrein excretion were unrelated to changes in urine volume and protein excretion. The findings indicate that the kallikrein-kinin system may be involved in different forms of hypertension in the rat.

Inhibitory effects of aprotinin on kallikrein and kininases in dog's blood

1. The blood-bathed organ technique was used in dogs to estimate kinin generation in the blood. Strips of cat jejunum were used as assay tissues.2. Infusions of kallikrein at 0.5-8 mU / ml into the blood in the extracorporeal circuit led to a generation of kinin at 0.6-10 ng / ml. The kinin generated was at the same concentration after incubation of kallikrein with blood for 15 s or 120 seconds. Intravenous infusions of kallikrein at (8-125 mU / kg) / min led to similar blood concentrations of kinin. These infusions induced substantial falls in blood pressure.3. Aprotinin inhibited the generation of kinin by kallikrein, but the concentration needed in vivo was 20,000 times higher than would be expected from the definition of the units.4. After intravenous injection of large doses of aprotinin, the kallikrein-inhibiting activity passed off within 40-60 minutes. At the same time, there was a gradual reduction in kininase activity, so that the half life of bradykinin in blood increased from a mean of 13 s to 40 seconds. This effect reached a maximum 1-3 h after injection of aprotinin.5. It is suggested that a metabolite of aprotinin is responsible for the kininase inhibition and that this effect may limit the usefulness of aprotinin in man.