The brown Norway rats and the kinin system

Proteomic changes of the bovine blood plasma in response to heat stress in a tropically adapted cattle breed

Background

Identifying molecular mechanisms responsible for the response to heat stress is essential to increase production, reproduction, health, and welfare. This study aimed to identify early biological responses and potential biomarkers involved in the response to heat stress and animal's recovery in tropically adapted beef cattle through proteomic analysis of blood plasma.

Methods

Blood samples were collected from 14 Caracu males during the heat stress peak (HSP) and 16 h after it (heat stress recovery-HSR) assessed based on wet bulb globe temperature index and rectal temperature. Proteome was investigated by liquid chromatography-tandem mass spectrometry from plasma samples, and the differentially regulated proteins were evaluated by functional enrichment analysis using DAVID tool. The protein-protein interaction network was evaluated by STRING tool.

Results

A total of 1,550 proteins were detected in both time points, of which 84 and 65 were downregulated and upregulated during HSR, respectively. Among the differentially regulated proteins with the highest absolute log-fold change values, those encoded by the GABBR1, EPHA2, DUSP5, MUC2, DGCR8, MAP2K7, ADRA1A, CXADR, TOPBP1, and NEB genes were highlighted as potential biomarkers because of their roles in response to heat stress. The functional enrichment analysis revealed that 65 Gene Ontology terms and 34 pathways were significant (P < 0.05). We highlighted those that could be associated with the response to heat stress, such as those related to the immune system, complement system, hemostasis, calcium, ECM-receptor interaction, and PI3K-Akt and MAPK signaling pathways. In addition, the protein-protein interaction network analysis revealed several complement and coagulation proteins and acute-phase proteins as important nodes based on their centrality and edges.

Conclusion

Identifying differentially regulated proteins and their relationship, as well as their roles in key pathways contribute to improve the knowledge of the mechanisms behind the response to heat stress in naturally adapted cattle breeds. In addition, proteins highlighted herein are potential biomarkers involved in the early response and recovery from heat stress in tropically adapted beef cattle.

A pooled analysis of nine studies in one institution to assess effects of whole heart irradiation in rat models

PURPOSE

Over the years, animal models of local heart irradiation have provided insight into mechanisms of and treatments for radiation-induced heart disease in human populations. However, it is not completely clear which manifestations of radiation injury are most commonly seen after whole heart irradiation, and whether certain biological factors impact experimental results. Combining 9 homogeneous studies in rat models of whole heart irradiation from one laboratory, we sought to identify experimental and/or biological factors that impact heart outcomes. We evaluated the usefulness of including (1) heart rate and (2) bodyweight as covariates when analyzing biological parameters, and (3) we determined which echocardiography, histological, and immunohistochemistry parameters are most susceptible to radiation effects. Finally, (4) as an educational example, we illustrate a hypothetical sample size calculation for a study design commonly used in evaluating radiation modifiers, using the pooled estimates from the 9 rat studies only for context. The results may assist investigators in the design and analyses of pre-clinical studies of whole heart irradiation.

MATERIALS AND METHODS

We made use of data from 9 rat studies from our labs, 8 published elsewhere in 2008-2017, and one unpublished study. Echocardiography, histological, and immunohistochemical parameters were collected from these studies. Using mixed effects analysis of covariance models, we estimated slopes for heart rate and bodyweight and estimated the radiation effect on each of the parameters.

RESULTS

Bodyweight was related to most echocardiography parameters, and heart rate had an effect on echocardiography parameters related to the diameter of the left ventricle. For some parameters, there was evidence that heart rate and bodyweight relationships with the parameter depended on whether the rats were irradiated. Radiation effects were found in systolic measures of echocardiography parameters related to the diameter of the left ventricle, with ejection fraction and fractional shortening, with atrial wall thickness, and with histological measures of capillary density, collagen deposition, and mast cells infiltration in the heart.

CONCLUSION

Accounting for bodyweight, as well as heart rate, in analyses of echocardiography parameters should reduce variability in estimated radiation effects. Several echocardiography and histological parameters were particularly susceptible to whole heart irradiation, showing robust effects compared to sham-irradiation. Lastly, we provide an example approach for a sample size calculation that will contribute to a rigorous study design and reproducibility in experiments studying radiation modifiers.

Investigational plasma kallikrein inhibitors for the treatment of diabetic macular edema: an expert assessment

Introduction: Plasma kallikrein is a  mediator of vascular leakage and inflammation. Activation of plasma kallikrein can induce features of diabetic macular edema (DME) in preclinical models. Human vitreous shows elevated plasma kallikrein levels in patients with DME. Because of the incomplete response of some patients to anti-VEGF agents, and the treatment burden associated with frequent dosing, there is still considerable need for VEGF-independent targeted pathways.Areas covered: This review covers the role of plasma kallikrein in the pathogenesis of DME and the therapeutic potential of plasma kallikrein inhibitors. It discusses early clinical studies of plasma kallikrein pathway modulation for DME, which have been associated with some improvement in visual acuity but with limited improvement in macular edema. This review also highlights KVD001, which is furthest along the development pathway, THR-149, which has recently completed a phase 1 study, and oral agents under development.Expert opinion: Plasma kallikrein inhibitors have a potential role in the treatment of DME, with mixed functional/anatomic results in early clinical trials. Given the large unmet need in DME treatment, further studies are warranted.

Role of the bradykinin B2 receptor in a rat model of local heart irradiation

PURPOSE

Radiation-induced heart disease (RIHD) is a delayed effect of radiotherapy for cancers of the chest, such as breast, esophageal, and lung. Kinins are small peptides with cardioprotective properties. We previously used a rat model that lacks the precursor kininogen to demonstrate that kinins are involved in RIHD. Here, we examined the role of the kinin B2 receptor (B2R) in early radiation-induced signaling in the heart.

MATERIALS AND METHODS

Male Brown Norway rats received the B2R-selective antagonist HOE-140 (icatibant) via osmotic minipump from 5 days before until 4 weeks after 21 Gy local heart irradiation. At 4 weeks, signaling events were measured in left ventricular homogenates and nuclear extracts using western blotting and real-time polymerase chain reaction. Numbers of CD68-positive (monocytes/macrophages), CD2-positive (T-lymphocytes), and mast cells were measured using immunohistochemistry.

RESULTS

Radiation-induced c-Jun phosphorylation and nuclear translocation were enhanced by HOE-140. HOE-140 did not modify endothelial nitric oxide synthase (eNOS) phosphorylation or alter numbers of CD2-positive or mast cells, but enhanced CD68-positive cell counts in irradiated hearts.

CONCLUSIONS

B2R signaling may regulate monocyte/macrophage infiltration and c-Jun signals in the irradiated heart. Although eNOS is a main target for kinins, the B2R may not regulate eNOS phosphorylation in response to radiation.

Cardiac inflammation after local irradiation is influenced by the kallikrein-kinin system

Radiotherapy of intrathoracic and chest wall tumors may lead to exposure of the heart to ionizing radiation, resulting in radiation-induced heart diseases (RIHD). The main manifestations of RIHD become apparent many years after treatment and include cardiomyopathy and accelerated atherosclerosis. This study examines the role of the kallikrein-kinin system (KKS) in RIHD by investigating the cardiac radiation response in a kininogen-deficient Brown Norway Katholiek (BN/Ka) rat model. BN/Ka rats and wild-type Brown Norway (BN) rats were exposed to local heart irradiation with a single dose of 18 Gy or 24 Gy and were observed for 3 to 6 months. Examinations included in vivo and ex vivo cardiac function, histopathology, gene and protein expression measurements, and mitochondrial swelling assays. Upon local heart irradiation, changes in in vivo cardiac function were significantly less in BN/Ka rats. For instance, a single dose of 24 Gy caused a 35% increase in fractional shortening in BN rats compared with a 16% increase in BN/Ka rats. BN rats, but not BN/Ka rats, showed a 56% reduction in cardiac numbers of CD2-positive cells, and a 57% increase in CD68-positive cells, together with a 52% increase in phosphorylation of extracellular signal-regulated kinase 1/2 (Erk1/2). Local heart irradiation had similar effects on histopathology, mitochondrial changes, and left ventricular mRNA levels of NADPH oxidases in the two genotypes. These results suggest that the KKS plays a role in the effects of radiation on cardiac function and recruitment of inflammatory cells. The KKS may have these effects at least in part by altering Erk1/2 signaling.

Kininogens: More than cysteine protease inhibitors and kinin precursors

Two kininogens are found in mammalian sera: HK (high molecular weight kininogen) and LK (low molecular weight kininogen) with the exception of the rat which encompasses a third kininogen, T-Kininogen (TK). Kininogens are multifunctional glycosylated molecules related to cystatins (clan IH, family I25). They harbor three cystatin domains but only two of them are tight-binding inhibitors of cysteine cathepsins. HK and LK, but not TK, are precursors of potent peptide hormones, the kinins, which are released proteolytically by tissue and plasma kallikreins. Besides these classical features novel functions of kininogens have been recently discovered; they are described in the second part of this review. HKa, which corresponds to the kinin-free two-chain HK and its isolated domain D5 (kininostatin), possesses angiostatic and pro-apoptotic properties, inhibits the proliferation of endothelial cells and participates in the regulation of angiogenesis. Moreover, some HK-derived peptides display potent and broad-spectrum microbicidal properties against both Gram-positive and Gram-negative bacteria, and thus may offer a promising alternative to conventional antibiotic therapy. Of seminal interest, a kininogen-derived peptide inhibits activation of the contact phase system of coagulation and protects mice with invasive Streptococcus pyogenes infection from pulmonary lesions. On the other hand, TK is a biomarker of aging at the end of lifespan of elderly rats. However, although TK has been initially identified as an acute phase reactant, and earlier known as alpha-l-acute phase globulin, the increase of TK in liver and plasma is not known to relate to any inflammatory event during the senescence process.

Gender-specific association between the kininogen 1 gene variants and essential hypertension in Chinese Han population

BACKGROUND

Kininogens serve as the precursors of potent vasoactive kinin peptides and also function as cysteine proteinase inhibitors.

METHOD

Given its potential role in blood pressure homeostasis, a tagging single nucleotide polymorphism (SNP) based case-control study was conducted to explore the association between kininogen 1 gene common variants and essential hypertension in Chinese Han population. Four tagging SNPs were selected on the basis of the HapMap database and further genotyped in 2411 patients with essential hypertension and 2348 controls from the International Collaborative Study of Cardiovascular Disease in Asia (InterASIA in China).

RESULTS

A significant gender-specific association between the kininogen 1 gene common variants and essential hypertension was observed. In male, but not female participants, rs2304456 CC genotype and rs4686799 TT genotype were significantly related to hypertension [odds ratio (OR) = 2.20, 95% confidence interval (CI): 1.24-3.90, P = 0.007 and OR = 1.31, 95% CI: 1.04-1.66, P = 0.025, respectively]. The haplotypes G-C-C-T and the A-A-T-T were significantly associated with essential hypertension in the male population with adjusted OR 1.43 (P < 0.001) and OR 1.24 (P = 0.001), respectively. The haplotype G-A-C-T was in significant association with essential hypertension (OR = 1.42, P = 0.003) as well as systolic blood pressure (P = 0.005) and diastolic blood pressure (P = 0.015).

CONCLUSION

This is the first association study of the kininogen 1 gene with essential hypertension. Both single-locus and haplotype analyses indicated the kininogen 1 gene was associated with essential hypertension and blood pressure traits in the Chinese male population.

Human plasma kallikrein-kinin system: physiological and biochemical parameters

The plasma kallikrein-kinin system (KKS) plays a critical role in human physiology. The KKS encompasses coagulation factor XII (FXII), the complex of prekallikrein (PK) and high molecular weight kininogen (HK). The conversion of plasma prekallikrein to kallikrein by the activated FXII and in response to numerous different stimuli leads to the generation of bradykinin (BK) and activated HK (HKa, an antiangiogenic peptide). BK is a proinflammatory peptide, a pain mediator and potent vasodilator, leading to robust accumulation of fluid in the interstitium. Systemic production of BK, HKa with the interplay between BK bound-BK receptors and the soluble form of HKa are key to angiogenesis and hemodynamics. KKS has been implicated in the pathogenesis of inflammation, hypertension, endotoxemia, and coagulopathy. In all these cases increased BK levels is the hallmark. In some cases, the persistent production of BK due to the deficiency of the blood protein C1-inhibitor, which controls FXII, is detrimental to the survival of the patients with hereditary angioedema (HAE). In others, the inability of angiotensin converting enzyme (ACE) to degrade BK leads to elevated BK levels and edema in patients on ACE inhibitors. Thus, the mechanisms that interfere with BK liberation or degradation would lead to blood pressure dysfunction. In contrast, anti-kallikrein treatment could have adverse effects in hemodynamic changes induced by vasoconstrictor agents. Genetic models of kallikrein deficiency are needed to evaluate the quantitative role of kallikrein and to validate whether strategies designed to activate or inhibit kallikrein may be important for regulating whole-body BK sensitivity.

Genetically altered animal models in the kallikrein-kinin system

Transgenic and gene-targeting technologies allowing the generation of genetically altered animal models have greatly advanced our understanding of the function of specific genes. This is also true for the kallikrein-kinin system (KKS), in which some, but not yet all, components have been functionally characterized using such techniques. The first genetically altered animal model for a KKS component was supplied by nature, the brown Norway rat carrying an inactivating mutation in the kininogen gene. Mice deficient in tissue kallikrein, B1 and B2 receptors, some kinin-degrading enzymes, and factor XII followed, together with transgenic rat and mouse strains overexpressing tissue kallikrein, B1 and B2 receptors, and degrading enzymes. There are still no animal models with genetic alterations in plasma kallikrein, kininases I and some other degrading enzymes. The models have confirmed an important role of the KKS in cardiovascular pathology, inflammation, and pain, and have partially elucidated the distinct function of the two receptors. This created the basis for rational decisions concerning the putative use of kinin receptor agonists and antagonists in therapeutic applications. However, a more thorough analysis of the existing models and the generation of new, more sophisticated transgenic models will be necessary to clarify the still elusive issue as to where and by which mechanisms the kinins exert their actions.

T-kininogen can either induce or inhibit proliferation in Balb/c 3T3 fibroblasts, depending on the route of administration

T-kininogen (T-KG) is a precursor of T-kinin, the most abundant kinin in rat serum, and also acts as a strong and specific cysteine proteinase inhibitor. Its expression is strongly induced during aging in rats, and expression of T-KG in Balb/c 3T3 fibroblasts results in inhibition of cell proliferation. However, T-KG is a serum protein produced primarily in the liver, and thus, most cells are only exposed to the protein from the outside. To test the effect of T-KG on fibroblasts exposed to exogenous T-KG, we purified the protein from the serum of K-kininogen-deficient Katholiek rats. In contrast to the results obtained by transfection, exposure of Balb/c 3T3 fibroblasts to exogenously added T-KG leads to a dose-dependent increase in [3H]-thymidine incorporation. This response does not require kinin receptors, but it is clearly mediated by activation of the ERK pathway. As a control, we repeated the transfection experiments, using a different promoter. The results are consistent with our published data showing that, under these circumstances, T-KG inhibits cell proliferation. We conclude that T-KG exerts opposite effects on fibroblast proliferation, depending exclusively on the way that it is administered to the cells (transfection versus exogenous addition).

Inhibitory effects of proanthocyanidins from Ribes nigrum leaves on carrageenin acute inflammatory reactions induced in rats

Background

The anti-inflammatory effects of proanthocyanidins (PACs), isolated from blackcurrant (Ribes nigrum L.) leaves, were analysed using carrageenin-induced paw oedema and carrageenin-induced pleurisy in rats.

Results

Pretreatment of the animals with PACs (10, 30, 60 and 100 mg/kg, i.p.) reduced paw oedema induced by carrageenin in a dose and time-dependent manner. PACs also inhibited dose-dependently carrageenin-induced pleurisy in rats. They reduced (A) lung injury, (B) pleural exudate formation, (C) polymorphonuclear cell infiltration, (D) pleural exudate levels of TNF-α, IL-1β and CINC-1 but did not affect IL-6 and IL-10 levels. They reduced (E) pleural exudate levels of nitrite/nitrate (NOx). In indomethacin treated rats, the volume of pleural exudate was low, its content in leukocytes and its contents in TNF-α, IL-1β, IL-6 and IL-10 but not in NOx were reduced. These data suggest that the anti-inflammatory properties of PACs are achieved through a different pattern from those of indomethacin.

Conclusion

These results suggest that the main mechanism of the anti-inflammatory effect of PACs mainly lies in an interference with the migration of the leukocytes. Moreover, PACs inhibited in vivo nitric oxide release.

Roles for the kallikrein-kinin system in inflammatory exudation and pain: lessons from studies on kininogen-deficient rats

Roles for the kallikrein-kinin system in inflammation have been investigated extensively, and many reviews on this topic have been published during the 50 years since the discovery of bradykinin in 1949. Recent progress in the field has been remarkable with the help of experiments using gene-targetted transgenic or knockout mice, which have added further valuable information in addition to previous results obtained from pharmacological and biochemical studies using purified and isolated components of the system. Furthermore, much knowledge has been accumulated as a result of the development of various bradykinin agonists and antagonists. In this review, we focused on the data obtained from the kininogen-deficient rat, which is a natural mutant, and discuss the results in comparison with those from bradykinin receptor knockout mice. These data have clarified that endogenous bradykinin exerts a most important role in inflammatory exudation along with prostanoids, preferentially to histamine, serotonin, or neuropeptides. In inflammatory pain perception also, bradykinin produced in the local perivascular spaces stimulates polymodal pain receptors in conjunction with co-helpers such as prostanoids, vanilloids, and neuropeptides. These important roles are concluded based on consistent results obtained from experiments using several antagonists of bradykinin, kininogen-deficient rats, and bradykinin receptor knockout mice.

Reflex secretion of proteins into submandibular saliva in conscious rats, before and after preganglionic sympathectomy

1. An indwelling catheter was placed in the left submandibular duct of rats, under pentobarbitone anaesthesia, and connected to an outflow cannula that emerged above the skull. 2. Saliva was collected from the outflow cannula in conscious rats, the same day after recovery from anaesthesia, under four different reflex conditions: grooming, heat exposure, rejection of a bitter tasting substance and feeding on softened chow, repeated in different orders. 3. Saliva flow was greatest for grooming and least for rejection. Protein concentrations were least with heat but much greater and similar for the other stimulations. Acinar peroxidase activity was high for feeding, intermediate for grooming and rejection, and again lowest with heat. Tubular tissue kallikrein activities were moderately low, being greatest with feeding and least with grooming. Secretory immunoglobulin A (SIgA) concentration was least with heat and similar for the other stimulations. 4. The next day, under pentobarbitone anaesthesia, the left preganglionic sympathetic trunk was sectioned (sympathetic decentralization) and, after recovery, the preceding stimulations were repeated. Flow of saliva showed little change, but protein and peroxidase concentrations and outputs decreased dramatically with grooming, rejection and feeding to levels similar to those with heat, which showed little change. Tissue kallikrein was lowered less dramatically, but the reductions in output were significant except with heat. Patterns of proteins resolved by electrophoresis changed for grooming, rejection and feeding and became similar to saliva from heat, which showed little change. No significant effects on SIgA concentrations occurred. 5. Gland weights from the sympathetically decentralized side were greater than from the intact side at the end of the experiments and histologically showed retention of acinar mucin. 6. Thus reflex sympathetic drive varied with the different stimulations; it was least during heat, but it had pronounced effects on acinar secretion of proteins during the other stimulations. At the same time this sympathetic drive had less impact on tissue kallikrein secretion from tubules and had little influence on flow or the concentration of SIgA secreted.

Towards understanding the kallikrein-kinin system: insights from measurement of kinin peptides

The kallikrein-kinin system is complex, with several bioactive peptides that are formed in many different compartments. Kinin peptides are implicated in many physiological and pathological processes including the regulation of blood pressure and sodium homeostasis, inflammatory processes, and the cardioprotective effects of preconditioning. We established a methodology for the measurement of individual kinin peptides in order to study the function of the kallikrein-kinin system. The levels of kinin peptides in tissues were higher than in blood, confirming the primary tissue localization of the kallikrein-kinin system. Moreover, the separate measurement of bradykinin and kallidin peptides in man demonstrated the differential regulation of the plasma and tissue kallikrein-kinin systems, respectively. Kinin peptide levels were increased in the heart of rats with myocardial infarction, in tissues of diabetic and spontaneously hypertensive rats, and in urine of patients with interstitial cystitis, suggesting a role for kinin peptides in the pathogenesis of these conditions. By contrast, blood levels of kallidin, but not bradykinin, peptides were suppressed in patients with severe cardiac failure, suggesting that the activity of the tissue kallikrein-kinin system may be suppressed in this condition. Both angiotensin converting enzyme (ACE) and neutral endopeptidase (NEP) inhibitors increased bradykinin peptide levels. ACE and NEP inhibitors had different effects on kinin peptide levels in blood, urine, and tissues, which may be accounted for by the differential contributions of ACE and NEP to kinin peptide metabolism in the multiple compartments in which kinin peptide generation occurs. Measurement of the levels of individual kinin peptides has given important information about the operation of the kallikrein-kinin system and its role in physiology and disease states.

Rodent submandibular gland peptide hormones and other biologically active peptides

The cervical sympathetic trunk-submandibular gland neuroendocrine axis plays an integral role in physiological adaptations and contributes to the maintenance of systemic homeostasis, particularly under the 'stress conditions' seen with tissue damage, inflammation, and aggressive behavior. The variety of polypeptides, whose release from acinar and ductal cells is under sympathetic nervous system control, offers coordinated and progressive levels of endocrine communication. Proteolytic enzymes (e.g. the kallikreins and furin maturases) are involved in the conversion of inactive precursors (e. g. Pro-EGF and SMR1) into biologically active molecules (e.g. EGF, SMR1-pentapeptide), which act on local or distant targets and thereby modulate the homeostatic process.

Bradykinin and its receptors in non-mammalian vertebrates

The generation of bradykinin (BK) in blood by the action of the kallikrein-kinin system has been studied intensively in mammals but the system has received relatively little attention in non-mammalian vertebrates. The plasma of crocodilians and Testudines (turtles and tortoises) contains all the components of the kallikrein-kinin system found in mammals (prekallikrein activator, prekallikrein, kininogen, and kininases) and activation results in generation of [Thr6]-BK. Plasma of birds and snakes probably lacks a prekallikrein activator analogous to mammalian Factor XII but treatment with exogenous proteases (pig pancreatic kallikrein and/or trypsin) generates [Thr6, Leu8]-BK (chicken), [Ala1, Thr6]-BK (python) and [Val1, Thr6]-BK (colubrid snakes). The skins of certain frogs, particularly of the genus Rana, contain very high concentrations of BK-related peptides but their pathway of biosynthesis involves the action of cellular endoproteinase(s) cleaving at the site of single arginyl residues rather than by the action of the kallikrein-kinin system. Evidence for a prekallikrein activator in fish plasma is lacking but treatment with exogenous proteases generates [Arg0, Trp5, Leu8]-BK (trout and cod), [Trp5]-BK (bowfin and gar), [Met1, Met5]-BK (sturgeon). The cardiovascular actions and effects upon gastrointestinal smooth muscle of these peptides in their species of origin differ markedly. For example, intra-arterial injections of the native BK peptides into unanesthetized fish produce transient hypertension in the cod, complex depressor and pressor responses in the trout and bowfin and hypotension in the sturgeon. Pharmacological studies in snakes and fish and with the recombinantally expressed chicken BK receptor have demonstrated that the BK receptors in the tissues of non-mammalian vertebrates have appreciably different ligand binding properties from the well-characterized mammalian B1 and B2 receptors.

Characterization of bradykinin-related peptides generated in the plasma of six sarcopterygian species (African lungfish, amphiuma, coachwhip, bullsnake, gila monster, and Gray's monitor)

Incubation of heat-denatured plasma from six species occupying different evolutionary positions within the Sarcopterygian lineage [the dipnoan, Protopterus annectens (African lungfish); the urodele, Amphiuma tridactylum (three-toed amphiuma); the colubrid snakes, Pituophis melanoleucus sayi (bullsnake) and Masticophis flagellum (coachwhip); and the lizards Heloderma suspectum (Gila monster) and Varanus Grayi (Gray's monitor)] with trypsin generated bradykinin-related peptides that were detected by radioimmunoassay using an antiserum raised against mammalian bradykinin (BK). The peptides were purified by HPLC and their primary structures were established as lungfish [Tyr1,Gly2,Ala7,Pro8]BK, amphiuma [Phe1,Ile2, Leu5]BK, bullsnake and coachwhip [Val1,Thr6]BK, Gila monster [Leu2, Thr6]BK, and Gray's monitor [Thr6]BK. Monitor BK is identical to the peptide generated in turtle and alligator plasma and coachwhip/bullsnake BK shows one amino acid substitution (Ala1 --> Val) compared with the peptide generated in the plasma of the python. The data provide further evidence for the widespread occurrence of a kallikrein-kininogen system in nonmammalian vertebrates but indicate that the primary structure of BK has been poorly conserved during evolution.

Low-salt diet downregulates plasma but not tissue kallikrein-kinin system

The kallikrein-kinin system (KKS) is involved in the regulation of blood pressure and in the sodium and water excretion. In humans, the KKS is divided functionally into a plasma KKS (pKKS) generating the biologically active peptide bradykinin and into the tissue (glandular) KKS (tKKS) generating the active peptide kallidin. The objective of this study was to examine the effect of a low-NaCl diet on the concentration of both pKKS and tKKS in plasma and urine in 10 healthy volunteers. After a 4-day low-NaCl diet, the urinary sodium and chloride excretions had decreased from 234 to 21.2 mmol/24 h and from 198 to 14.6 mmol/24 h, respectively. The plasma levels of ANG I, aldosterone, and angiotensin converting enzyme (ACE) significantly increased from 50.4 to 82.8 pg/ml, from 129 to 315 pg/ml, and from 46.4 to 59.8 U/ml, respectively, demonstrating the physiological adjustment to the low-salt diet. In plasma, the levels of bradykinin and plasma kallikrein had significantly decreased from 13.7 to 7.57 pg/ml and 14.4 to 7.13 U/ml, respectively. However, the levels of high-molecular-weight kininogen (HMW kininogen) remain unchanged (101 vs. 112 microg/ml, not significant). Contrary to plasma kallikrein, the plasma levels of tissue kallikrein increased (0.345 vs. 0.500 U/ml; P < 0.01). The plasma kallidin levels, however, did not change (64.7 vs. 68.6 pg/ml, not significant). This can be explained by a simultaneous decrease in the plasma low-molecular-weight kininogen (LMW kininogen) levels (89.9 vs. 44.4 microg/ml; P < 0.05). As in plasma, we find increased urinary concentrations of renal (tissue) kallikrein (23.3 to 42.8 U/24 h; P < 0.05) that contrast with, and are presumably counterbalanced by, urinary LMW kininogen levels (77.0 vs. 51.8 microg/24 h; P < 0.05). Consequently, in urine low-NaCl diet caused no significant change in either bradykinin or kallidin (9.2 vs. 10.8 microg/24 h, and 10.9 vs. 10.3 microg/24 h). It is concluded that the stimulation of the renin-angiotensin system on a low-NaCl diet is associated with a decrease in pKKS (bradykinin and plasma kallikrein) but not in tissue and renal KKS. Although tissue kallikrein is increased, there is no change in kallidin, as LMW kininogen in plasma and urine is decreased. These data suggest a difference in the regulation of pKKS and tKKS by low-salt diet.

The fate of plasma kallikrein in normal and kininogen-deficient rats

The clearance of exogenous plasma kallikrein, its uptake by liver, spleen, kidneys, lungs and its extravasation in the paws were determined in normal Wistar rats, normal and kininogen-deficient Brown Norway rats. Kallikrein was purified from rat plasma and labelled with 125I. After intravenous injection of 125I-kallikrein, the disappearance of acid-precipitable kallikrein from the blood fits a biexponential curve similar in the three groups of rats: a rapid initial clearance (T1/2 around 3 min) followed by a phase of slower elimination (T1/2 around 50 min). Removal of kallikrein from the blood was associated with a large uptake of radioactivity by the liver: 67% of the 125I-kallikrein cleared from the blood at 10 min. The kidneys and the spleen accumulated small amounts of the radioactivity. The uptake of kallikrein by the spleen was slightly reduced in kininogen-deficient rats. The kininogen deficiency in Brown Norway rats from the strain BN/May Pfd was confirmed by the low levels of kinins released by tissue kallikrein and by a prolongation of activated thromboplastin times in the plasma of these animals. We concluded that plasma kallikrein is rapidly cleared from the circulation of the rat. The liver is the main clearing organ of plasma kallikrein. The disappearance of kallikrein from the circulation is not affected by the lack of high molecular weight kininogen, except in the case of the uptake of the enzyme performed by the cells of the spleen, which is reduced.