Genetic and dietary control of plasma tissue kallikrein secretion and urinary kinins exretion in man.

OBJECTIVES: Tissue kallikrein is a major kinin-forming enzyme involved in artery and kidney functions. Urinary tissue kallikrein activity (UKLKa) reflects renal tissue kallikrein activity and depends on Na and K intake, and genetic factors, especially the tissue kallikrein-inactivating polymorphism, R53H. The effect of these factors on the level of kinin peptides is, however, not known. Moreover, a circulating form of tissue kallikrein is present in human plasma but its origin and regulation are unknown. METHODS: We used a crossover study to investigate UKLKa, plasma tissue kallikrein (pTK), and urinary kallidin peptides and metabolites (Uki) in 10 R53H and 30 R53R normotensive male subjects randomly assigned to either a 1-week low Na-high K or a high Na-low K diet. RESULTS: UKLKa was 50-60% lower in R53H than R53R subjects and was increased by the low Na-high K diet. pTK was also 45-55% lower in R53H than R53R subjects and was increased by the low Na-high K diet. Uki was slightly but significantly higher under the low Na-high K than the high Na-low K diet, but did not differ between genotypes. CONCLUSION: These observations indicate that pTK levels are genetically determined and regulated by Na and K diet, in parallel with UKLKa; this suggests that circulating tissue kallikrein originates mainly from the kidney, and can contribute to circulatory adaptation to dietary ions. Uki is influenced by the Na and K diet, suggesting that kinins participate in renal adaptation to ion intake, but do not quantitatively reflect tissue kallikrein activity in urine, or presumably, in the kidney.

Kinin system in lupus nephritis.

There are few studies regarding the evaluation of the kinin system in patients with systemic lupus erythematosus (SLE). In this study, we evaluated the plasma levels of high-molecular weight kininogen (HKg), low-molecular weight kininogen (LKg) and plasma kallikrein; the plasma activity of tissue kallikrein and kininase II, and urinary kallikrein and kininase II activities in patients presenting with active lupus nephritis. A total of 30 patients (29 women) aged 21-62 years (median = 39) and 30 controls matched to the patients for sex and age were studied. Patients presenting with other underlying diseases or using drugs, which could interfere with the kinin system, were excluded. HKg and LKg levels were indirectly evaluated by ELISA. Plasma kallikrein, tissue kallikrein, and kininase II were evaluated by their enzymatic activity on selective substrates. The Mann-Whitney test was used for statistical analysis. HKg, LKg and plasma kallikrein levels were significantly increased in patients (p < 0.001, for each comparison). Similarly, tissue kallikrein and kininase II activities were significantly increased in plasma and urine of patients (p <0.001, for each comparison). In urine, the activities of tissue kallikrein and kininase II were at least seven times higher than those seen in the plasma of patients. These results indicate that the kinin system is involved in the acute manifestations of lupus nephritis. Kinins may facilitate immunecomplex deposition and may induce the release of other pro-inflammatory mediators, including cytokines actively involved in the pathogenesis of lupus nephritis.

Human tissue kallikrein gene delivery attenuates hypertension, renal injury, and cardiac remodeling in chronic renal failure.

BACKGROUND: Tissue kallikrein cleaves kininogen substrate to produce the potent vasodilating peptide kinin, which plays important roles in cardiovascular and renal function. To explore cardiac and renal potential protective effects of kallikrein gene delivery in chronic renal failure, we delivered adenovirus carrying the human tissue kallikrein cDNA (cHK) into rats with 5/6 reduction of renal mass. METHODS: Expression of human tissue kallikrein in rats was assessed by enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR)/Southern blotting. Physiological parameters monitored in rats included systolic blood pressure, heart rate, and urinary excretion of protein, albumin, kinin, cGMP, cAMP, and nitrate/nitrites. Systemic and regional hemodynamics were measured by fluorescent-labeled microspheres. Heart weight and myocyte diameter were used to assess left ventricular hypertrophy. Quantitative and qualitative morphological analyses were used to evaluate histologic changes in kidney and heart sections. RESULTS: Active tissue kallikrein reached a peak serum level of 463 +/- 76 ng/mL following gene delivery and returned to control levels within 21 days. A maximal blood pressure reduction of 37 mm Hg was observed within one week in rats receiving kallikrein gene delivery as compared with control rats receiving adenovirus containing the luciferase gene (159 +/- 5 vs. 196 +/- 6 mm Hg, N = 15, P < 0.001), and a significant blood pressure difference continued for five weeks postgene delivery. Kallikrein gene delivery significantly decreased total urinary protein and albumin excretion and increased levels of urinary kinin, nitrite/nitrate, and cGMP levels. Cardiac output and regional blood flow were also increased, while peripheral vascular resistance decreased. Kallikrein gene transfer reduced glomerular sclerotic lesions, tubular damage, lumenal protein cast accumulation, and interstitial inflammation in the kidney. Myocardial hypertrophy and fibrosis were also attenuated in rats receiving kallikrein gene delivery. CONCLUSIONS: These findings indicated that kallikrein gene delivery attenuates hypertension and protects against renal injury and cardiac remodeling in the rat remnant kidney model of chronic renal failure.

Adenovirus-mediated human tissue kallikrein gene delivery inhibits neointima formation induced by interruption of blood flow in mice.

Tissue kallikrein cleaves kininogen to produce vasoactive kinin peptides. Binding of kinins to bradykinin B(2) receptors on vascular endothelial cells stimulates the release of nitric oxide and prostacyclin, thus activating the cGMP and cAMP pathways. In this study, we evaluated the effects of adenovirus-mediated human tissue kallikrein gene (Ad.CMV-cHK) delivery in a mouse model of arterial remodeling induced by permanent alteration in shear stress conditions. Mice underwent ligature of the left common carotid artery and were injected intravenously with saline or 1.8 x 10(9) plaque-forming units of Ad.CMV-cHK or control virus (Ad.CMV-LacZ). Fourteen days after surgery, morphometric analysis revealed that Ad. CMV-cHK reduced neointima formation by 52% (P<0.05) compared with Ad. CMV-LacZ. Expression of human tissue kallikrein (HK) mRNA was detected in mouse carotid artery, aorta, kidney, heart, and liver, and recombinant HK was present in the urine and plasma of mice receiving HK gene. Kallikrein gene transfer resulted in increases in urinary kinin, cGMP, and cAMP levels. The protective action of Ad. CMV-cHK on neointima formation was significantly reduced (P<0.05) in mice with knockout of the kinin B(2) receptor gene compared with wild-type control mice (J129Sv mice). In contrast, the effect of Ad. CMV-cHK was amplified (P<0.05) in transgenic mice overexpressing human B(2) receptor compared with wild-type control mice (c57/Bl6 mice). Thus, the inhibitory effect of recombinant kallikrein on structural alterations caused by the interruption of blood flow appears to be mediated by the B(2) receptor. These results provide new insight into the role of the tissue kallikrein-kinin system in vascular remodeling and suggest the application of HK gene therapy to treat restenosis and atherosclerosis.

Human tissue kallikrein attenuates hypertension and secretes into circulation and urine after intramuscular gene delivery in hypertensive rats.

Systemic delivery of the human tissue kallikrein transgene has been shown to markedly delay the increase of blood pressure in hypertensive rat models. To demonstrate potential hypotensive effects of kallikrein via local delivery, adenovirus carrying the human tissue kallikrein gene was inoculated into quadriceps of spontaneously hypertensive rats (SHR). A single intramuscular injection of the kallikrein gene caused a significant delay of blood pressure increase for 5 weeks. The expression of human tissue kallikrein and its mRNA was identified solely in injected muscle. Immunoreactive human tissue kallikrein was detected in the muscle as well as in the circulation and urine of adult and newborn rats. Urinary kinin and cGMP levels increased significantly in rats receiving kallikrein gene delivery as compared with rats receiving control virus containing the LacZ gene. The detection of human tissue kallikrein in rat urine after local gene delivery into the muscle provides direct evidence that circulatory kallikrein can be secreted into the urine. These findings indicated that a continuous supply of human tissue kallikrein in the circulation is sufficient to reduce blood pressure and kallikrein gene delivery via the intramuscular route may have significant implications in therapeutic applications.

[The characteristics of the sympathico-adrenal and kinin systems in engineers in the early stages of arterial hypertension]. / Osoblyvosti sympatyko-adrenalovoï i kininovoï system u mashynistiv na rannikh stadiiakh arterial'noï hipertenziï.

Overall seventy-two engine-drivers with borderline arterial hypertension (BAH) and stage I arterial hypertension (AH) were studied for the condition of the sympathoadrenal and kinin systems before and after trip. Both groups exhibited a rise in the activity of the sympathoadrenal system before trip, with still greater rise being recordable after trip. BAH and stage I AH subjects demonstrated an increased activity of the kinin system of the kidneys before trip and decreased one after trip. Suppression of the kinin system of the kidneys with simultaneous progression of pressor effects leads to decline in adaptation to physical and psychoemotional overloads in those engine-drivers presenting with early stages of AH.

Adenovirus-mediated kallikrein gene delivery reduces aortic thickening and stroke-induced death rate in Dahl salt-sensitive rats.

BACKGROUND AND PURPOSE: Kallikrein gene delivery has been shown to attenuate hypertension, cardiac hypertrophy, and renal injury in hypertensive animal models. The aim of this study was to investigate the potential protective effects of kallikrein gene delivery in salt-induced stroke and cerebrovascular disorders. METHODS: Adenovirus harboring the human tissue kallikrein gene (AdCMV-cHK) was delivered intravenously into Dahl salt-sensitive (DS) rats after 4 weeks of high salt loading, and blood pressure was monitored weekly for 9 weeks. RESULTS: A single injection of AdCMV-cHK caused a significant reduction of systolic blood pressure compared with that in control rats, with or without an injection of adenovirus carrying the LacZ (control) gene (AdCMV-LacZ). A maximal blood pressure reduction of 21 mm Hg was observed 2 weeks after gene delivery. The stroke mortality rate of DS rats (AdCMV-LacZ group versus the AdCMV-cHK group) was significantly decreased: 38% versus 9% at 3 weeks and 54% versus 27% at 5 weeks after gene delivery. Kallikrein gene delivery significantly attenuated salt-induced aortic hypertrophy, as evidenced by reduced thickness of the aortic wall. Recombinant human tissue kallikrein was detected in rat serum and urine after gene transfer. Kinin-releasing activities in the brain as well as urinary kinin and cGMP levels were significantly increased in rats receiving the kallikrein gene. CONCLUSIONS: This is the first study to demonstrate the protective effect of kallikrein gene delivery in reducing salt-induced stroke mortality and vascular dysfunction.

Activation of the kallikrein kinin system in interstitial cystitis.

PURPOSE: We investigated whether the kallikrein kinin system is activated in interstitial cystitis by measuring urinary excretion rates of kinin peptides, active and total kallikrein, and the kininase neutral endopeptidase in women with interstitial cystitis. We compared these excretion rates to a control group of women with stress incontinence and normal bladder function. MATERIALS AND METHODS: Catheter urine was collected from subjects during a water diuresis (approximately 10 ml. per minute) before and after distention of the bladder with 100 ml. water. The contribution of the bladder wall to urinary kinins was assessed by measuring the change in kinin levels after 2 minutes of bladder stasis before and after distention. RESULTS: Absolute bradykinin and kallidin excretion rates were similar in women with interstitial cystitis and control subjects. Two minutes of bladder stasis after bladder distention increased urinary bradykinin (p = 0.02) but not kallidin excretion rates. Active and total kallikrein excretion rates were similar in patients with interstitial cystitis and control subjects. Neutral endopeptidase excretion rates were reduced in the initial urine collection from subjects with interstitial cystitis but were similar in both groups during later collection periods. CONCLUSIONS: These data provide evidence for increased bradykinin levels in the bladder wall of subjects with interstitial cystitis, which may be due in part to reduced neutral endopeptidase levels. These increased bradykinin levels may participate in the pathogenesis and symptomatology of interstitial cystitis.

Effect of prolonged administration of a urinary kinase inhibitor, ebelactone B on the development of deoxycorticosterone acetate-salt hypertension in rats.

The effect of prolonged administration of a carboxypeptidase Y-like kininase inhibitor, ebelactone B (EB) (2-ethyl-3, 11-dihydroxy-4, 6, 8, 10, 12-pentamethyl-9-oxo-6-tetradecenoic 1, 3-lactone), on the development of deoxycorticosterone acetate (DOCA)-salt hypertension was tested. The systolic blood pressure (SBP) of non-treated 6-week-old Sprague-Dawley strain rats was gradually increased by DOCA-salt treatment from 137+/-2 mmHg (n=11) to 195+/-7 mmHg at 10 weeks of age. With daily oral administration of lisinopril (5 mg kg(-1), twice a day), which is an inhibitor of angiotensin converting enzyme, a major kininase in plasma, the development of hypertension was not suppressed. By contrast, administration of EB (5 mg kg(-1), twice a day), completely inhibited the development of hypertension (SBP: 146+/-1 mmHg, n=5, 10 weeks old). The reduced SBP at 10 weeks of age was equal to the SBP before any treatment (142+/-1 mmHg, n=5). Direct determination of mean blood pressure (MBP) in conscious, unrestrained rats confirmed that MBP elevation was completely inhibited by EB. Continuous subcutaneous infusion (5 mg kg(-1) day(-1)) of HOE140, a bradykinin B2 receptor antagonist, restored the elevation of SBP, which was suppressed by EB. The weights of left ventricle of DOCA-salt treated rats 10-weeks-old (0.36+/-0.02 g 100 g body weight(-1), n=11) was significantly reduced by EB (0.27+/-0.01, n=5), as were the sodium levels in serum, cerebrospinal fluid and erythrocyte. These findings suggested that EB is effective in preventing salt-related hypertension presumably by eliminating sodium retention.

Potassium supplement upregulates the expression of renal kallikrein and bradykinin B2 receptor in SHR.

High potassium intake is known to attenuate hypertension, glomerular lesion, ischemic damage, and stroke-associated death. Our recent studies showed that expression of recombinant kallikrein by somatic gene delivery reduced high blood pressure, cardiac hypertrophy, and renal injury in hypertensive animal models. The aim of this study is to explore the potential role of the tissue kallikrein-kinin system in blood pressure reduction and renal protection in spontaneously hypertensive rats (SHR) on a high-potassium diet. Young SHR were given drinking water with or without 1% potassium chloride for 6 wk. Systolic blood pressure was significantly reduced beginning at 1 wk, and the effect lasted for 6 wk in the potassium-supplemented group compared with that in the control group. Potassium supplement induced 70 and 40% increases in urinary kallikrein levels and renal bradykinin B2 receptor density, respectively (P < 0.05), but did not change serum kininogen levels. Similarly, Northern blot analysis showed that renal kallikrein mRNA levels increased 2.7-fold, whereas hepatic kininogen mRNA levels remained unchanged in rats with high potassium intake. No difference was observed in beta-actin mRNA levels in the kidney or liver of either group. Competitive RT-PCR showed a 1.7-fold increase in renal bradykinin B2 receptor mRNA levels in rats with high potassium intake. Potassium supplement significantly increased water intake, urine excretion, urinary kinin, cAMP, and cGMP levels. This study suggests that upregulation of the tissue kallikrein-kinin system may be attributed, in part, to blood pressure-lowering and diuretic effects of high potassium intake.

Effects of a neutral endopeptidase inhibitor, BP102, on the development of deoxycorticosterone acetate-salt hypertension in kininogen-deficient Brown Norway Katholiek rats.

The nature of all of the peptides critical to the mechanism(s) of the antihypertensive action of neutral endopeptidase (NEP) inhibitors is still unclear, but bradykinin is thought to be one such peptide. This study was designed to assess the effectiveness of an NEP inhibitor in deoxycorticosterone acetate (DOCA)-salt treated kininogen-deficient Brown Norway Katholiek (BN-Ka) rats. Oral administration of BP102 (10-100 mg/kg), an NEP inhibitor, increased urine volume and urinary sodium excretion in a dose-dependent manner in anesthetized Sprague-Dawley rats. DOCA-salt hypertension was induced in both BN-Ka and Brown Norway Kitasato (BN-Ki) rats after left nephrectomy. The development of DOCA-salt hypertension in normal BN-Ki rats was prevented, and that in BN-Ka rats was also significantly reduced, by an 8-day administration of BP102. When BP102 was administered for 5 weeks, the high blood pressure of DOCA-salt treated BN-Ka rats was markedly lowered, and their heart weights were reduced. These results suggest that kinins play no role in the antihypertensive effect of this inhibitor and that other factors may be involved in this effect.

Enhanced blood pressure sensitivity to deoxycorticosterone in mice with disruption of bradykinin B2 receptor gene.

The renal kallikrein-kinin system is activated under conditions of mineralocorticoid excess. To evaluate whether endogenous kinins exert a protective role against the development of mineralocorticoid-induced hypertension, we studied the cardiovascular effects induced by long-term administration of deoxycorticosterone (DOC; 0.3 micromol/g body wt s.c. once per week for 6 weeks) or vehicle in transgenic mice (Bk2r-/-) lacking the bradykinin B2 receptor gene and in wild-type controls (Bk2r+/+). Under basal conditions, Bk2r-/- mice showed higher systolic blood pressure (tail-cuff plethysmography) than wild-type Bk2r+/+ and heterozygous Bk2r+/- mice (121+/-2 versus 114+/-2 and 115+/-2 mm Hg, respectively; P<0.05 for both comparisons). Heart rate was higher in Bk2r-/- and Bk2r+/- than in Bk2r+/+ (459+/-12 and 418+/-7 versus 390+/-7 bpm; P<0.05 for both comparisons). Systolic blood pressure was increased by DOC in transgenic as well as in wild-type mice, whereas no change was induced by the vehicle. The pressor response to DOC was more rapid and pronounced in Bk2r-/- than in Bk2r+/+ and Bk2r+/- (30+/-5 versus 15+/-4 and 6+/-3 mm Hg, respectively, at 3 weeks; P<0.01 for both comparisons). The difference in systolic blood pressure was consistent with that detected by direct intra-arterial measurements of mean blood pressure. Neither DOC nor its vehicle altered heart rate or gain in body weight over time. Under basal conditions, urinary sodium excretion did not differ between strains. During DOC administration, cumulative urinary sodium excretion was lower in Bk2r-/- than in Bk2r+/+ (2.59+/-0.15 versus 3.31+/-0.22 mmol, respectively, during the first week; P<0.05). Urinary kinin excretion was increased by DOC in both Bk2r-/- (from 0.65+/-0.17 to 4.27+/-0.80 pmol/24 h; P<0.01) and Bk2r+/+ (from 0.55+/-0.09 to 6.27+/-1.48 pmol/24 h; P<0.05). The increase in urinary kinin excretion was similar between strains. These results show that integrity of the bradykinin B2 receptor is essential for regulation of blood pressure and heart rate under basal conditions. In addition, they indicate that activation of the kallikrein-kinin system represents a compensatory response against the development of hypertension induced by mineralocorticoid excess.

Isolation and properties of a new kallikrein inhibitor from Tityus serrulatus venom.

The kallikrein inhibitor-peptide content of Tityus serrulatus scorpion crude venom was purified by Sephadex G-50 and Sephadex G-25 fine gel filtration chromatographies, followed by two steps of reverse-phase column on HPLC. The isolated inhibitor peptide was homogeneous in its N-terminal and partial amino acid sequence, showing a molecular weight of 4.489 Da by mass spectrometry and amino acid analysis. The peptide was tested with rat plasma and urine kallikrein, which resulting in an inhibition with similar affinity to both enzymes, showing an IC50 of 14.3 microM after 13 and 8 min, respectively, using kininogen as substrate on the isolated guinea-pig ileum bioassay. The porcine pancreatic kallikrein showed after 10 min an IC50 value of 12.6 microM with H-D-Val-Leu-Arg-pNA HCl as substrate. In addition, the isolated peptide significantly inhibited porcine pancreatic kallikrein with values in the range of apparent or absolute calculated peptide Ki = 2.5 microM. The inhibitor was heat resistant and stable at pH values less than 5.

Role of kinin and renal ANG II blockade in acute effects of ACE inhibitors in low-renin hypertension.

In conscious deoxycorticosterone acetate (DOCA) salt-hypertensive dogs, the angiotensin-converting enzyme (ACE) inhibitors captopril and imidaprilat significantly decreased mean arterial pressure (MAP) and significantly increased urine flow rate, effective renal plasma flow (ERPF), glomerular filtration rate, and urinary sodium excretion. However, the angiotensin type 1 (AT1) receptor antagonist losartan caused a significant increase only in urinary sodium excretion without significant changes in MAP, urine flow rate, ERPF, and glomerular filtration rate. Simultaneous infusion of a bradykinin receptor antagonist inhibited the ACE inhibitor-induced reduction in MAP and increase in ERPF. DOCA salt treatment markedly suppressed plasma angiotensin II (ANG II) concentration (P < 0.001), although it decreased renal ANG II content only slightly (P < 0.05). Comparison of the expression of renal AT1 receptor mRNA in control kidneys with that in DOCA salt-hypertensive kidneys revealed no significant change. These results suggest that, in low-renin hypertension, inhibition of the relatively maintained ANG II production in the kidney participates in the natriuretic action of ACE inhibitors. However, hypotensive and other renal effects are mainly due to the action of bradykinin.

The mechanisms of the renal effects of neutral endopeptidase inhibitor in rats.

To further investigate the mechanisms of renal effects of neutral endopeptidase 24.11 (NEP) inhibition, we employed a specific NEP inhibitor, UK 73967 (UK), with or without a specific kinin receptor antagonist, Hoe 140 (Hoe), or nitric oxide (NO) synthase inhibitor, N-monomethyl-L-arginine (L-NMMA), in Sprague-Dawley rats, and evaluated the urinary NEP, kinins, cGMP and plasma atrial natriuretic peptide (ANP). None of the variables changed with vehicle injection. After injection of UK, NEP decreased significantly and urinary kinins, cGMP, urine volume (UV) and urinary sodium excretion (UNaV) increased significantly. Injected Hoe canceled the increase in UV and UNaV induced by UK. Plasma ANP did not show any difference between vehicle and UK groups. With a pretreatment of L-NMMA, injected UK decreased NEP and increased kinins, while urinary cGMP, UV and UNaV did not increase. In conclusion, augmented kinins may play an important role in the renal water-sodium metabolism by NEP inhibition, and NO may contribute to the kinins' action on this mechanism, while ANP may not contribute to it, at least in normotensive rats. Moreover, changes in urinary cGMP do not reflect the changes in plasma ANP, but rather, those in NO under this condition.

The role of kinins and atrial natriuretic peptide on the renal effects of neutral endopeptidase inhibitor in normotensive and hypertensive rats.

To further elucidate the renal effects of NEP inhibition, we employed NEP inhibitor UK 73967 (UK), with or without a kinin receptor antagonist Hoe 140 (Hoe), in Sprague-Dawley normotensive rats and DOCA-salt hypertensive rats. In Sprague-Dawley rats: 1) injected UK significantly decreased NEP, and increased kinins, urine volume (UV) and urinary sodium excretion (UNaV), while none of the variables changed with vehicle treatment; 2) no difference was found in plasma ANP between the vehicle and UK groups; and 3) Hoe canceled the increases of UV and UNaV caused by UK. In DOCA-salt rats: 1) infused UK significantly decreased NEP, and increased UV and UNaV, while UV and UNaV were slightly decreased, and NEP did not change with vehicle treatment; 2) plasma ANP was significantly higher in UK group than in the vehicle group; and 3) Hoe could not abolish the increase of UV and UNaV induced by UK. These data indicate that the contributions of renal kinins and plasma ANP to the diuretic and natriuretic mechanisms of NEP inhibition may differ between Sprague-Dawley normotensive rats and DOCA-salt hypertensive rats.

Ebelactone B, an inhibitor of urinary carboxypeptidase Y-like kininase, prevents the development of deoxycorticosterone acetate-salt hypertension in rats.

Kininogen-deficient Brown Norway Katholiek rats (BN-Ka) excrete little urinary kinin, compared with normal rats of the same strain (BN Kitasato rats (BN-Ki)). Deoxycorticosterone acetate-salt treatment increased systolic blood pressure in both rats, but much faster in BN-Ka than in BN-Ki. Daily subcutaneous administration of ebelactone B (15 and 5 mg/kg/day), a rat urinary carboxypeptidase Y-like kininase inhibitor, significantly reduced systolic blood pressure in BN-Ki, but not in BN-Ka. This treatment significantly increased urinary Na+ excretion and reduced Na+ concentration in the erythrocytes in BN-Ki, but not in BN-Ka. An angiotensin-converting enzyme inhibitor, lisinopril (5 mg/kg/day s.c.), did not reduce the systolic blood pressure in either BN-Ki or BN-Ka. These results suggested that ebelactone B has promise as a preventive agent for the development of hypertension acting through the inhibition of urinary kinin degradation.

Oxytocin-induced natriuresis mediated by the renal kallikrein-kinin system in anesthetized male rats.

Intravenous infusion of oxytocin (OT) (10-100 nmol/kg/30 min) to 8-week-old anesthetized male rats resulted in a dose-dependent increase in urine volume, which showed a peak value 30-45 min after the start of OT-infusion. Urinary excretions of sodium, chloride and potassium were also increased by OT, showing peak values at 30-45 min, without any increase in the creatinine level. The natriuresis by OT was accompanied by increased excretion of urinary active kallikrein, which showed a peak value 15 min after the start of OT-infusion. The urinary kinin level was also increased. Intravenous infusion of a kallikrein inhibitor, aprotinin (15 mg/kg/90 min), when started 30 min before the OT-infusion, significantly inhibited the OT-induced increase in urine volume and urinary excretion of sodium, chloride and potassium. Intravenous infusion of a bradykinin B2 antagonist, Hoe 140 (D-Arg[Hyp3,Thi5,D-Tic7,Oic8]BK, 4.5 mg/kg/90 min), when started 30 min before the OT-infusion, significantly inhibited the OT-induced increases in urine volume and urinary excretion of sodium and chloride, but not that of potassium. These results indicate that the OT-infusion induces natriuresis in male rats, and more than half of the natriuresis is mediated by a concomitant increase in excretion of urinary active kallikrein and the kinin generated.

Kinin, a mediator of diabetes-induced glomerular hyperfiltration.

Renal kallikrein is increased in diabetic patients and streptozotocin (STZ)-induced diabetic rats with hyperfiltration. Chronic inhibition of renal kallikrein reduces glomerular filtration rate (GFR) and renal plasma flow (RPF) in hyperfiltering STZ-induced diabetic rats. To investigate whether these actions of kallikrein and its inhibition are kinin-mediated, we used a B2-kinin receptor antagonist (BKA). In STZ-induced diabetic rats with hyperfiltration, renal kallikrein excretion rate was significantly increased (P < or = 0.01), and kinin excretion rate was increased 57%, as compared with control rats. Left kidney GFR and RPF were measured before and during a 40-min infusion of BKA (0.5 micrograms.kg-1.min-1) or vehicle. Infusion of the kinin receptor antagonist reduced the GFR and RPF significantly. GFR was reduced by 18%, from an average baseline value of 2.07 +/- 0.11 to 1.70 +/- 0.06 ml/min, P < or = 0.001 (means +/- SE). RPF was reduced by 25%, from 6.74 +/- 0.38 to 5.06 +/- 0.17 ml/min, P < or = 0.001. Total renal vascular resistance was significantly increased during BKA infusion, P < or = 0.001. Vehicle infusion for the same period had no significant effect on GFR, RPF, or renal vascular resistance. These findings further support the hypothesis that increased renal production of kinins contributes to the renal vasodilation of diabetes.