Early blockade of bradykinin B2-receptors alters the adult cardiovascular phenotype in rats

The temporal dynamic of bradykinin type 2 receptor effects reveals its neuroprotective role in the chronic phase of cerebral and retinal ischemic injury

The activation of the bradykinin type 2 receptor is intricately involved in acute post-ischemic inflammatory responses. However, its precise role in different stages of ischemic injury, especially in the chronic phase, remains unclear. Following simultaneous cerebral and retinal ischemia, bradykinin type 2 receptor knockout mice and their controls were longitudinally monitored for 35 days via magnetic resonance imaging, fundus photography, fluorescein angiography, behavioral assessments, vascular permeability measurements, and immunohistochemistry, as well as glycemic status assessments. Without impacting the lesion size, bradykinin type 2 receptor deficiency reduced acute cerebral vascular permeability preventing the loss of pericytes and tight junctions. In the chronic phase of ischemia, however, it resulted in increased astrogliosis and cortical neuronal loss, as well as higher functional deficits. The retinal findings demonstrated a similar pattern. Bradykinin type 2 receptor deficiency delayed, but exacerbated the development of retinal necrosis, increased subacute vascular permeability, and promoted retinal ganglion cell loss in the chronic phase of ischemia. This investigation sheds light on the temporal dynamic of bradykinin type 2 receptor effects in ischemia, pointing to a therapeutic potential in the subacute and chronic phases of ischemic injury.

Multiple doses of icatibant used during pregnancy

Background:

Hereditary angioedema (HAE) is a life-long disease that often manifests by puberty. Treatment of attacks is essential to improve quality of life and to decrease morbidity and mortality. During pregnancy, treatment is limited because multiple treatment options, including icatibant, are not approved for use during pregnancy.

Objective:

We report the outcomes of three pregnancies during which icatibant was used by a patient with HAE with normal C1-inhibitor for treatment of attacks. We also reviewed the literature for reports of icatibant use during pregnancy for outcomes and adverse events.

Methods:

We report on a patient who treated herself with icatibant during three separate pregnancies. Postpartum follow-up verified the health of the mother and children. We also performed a complete literature search of medical literature data bases on icatibant use during pregnancy.

Results:

The patient in our report administered multiple doses of icatibant during three pregnancies. The child born from the first pregnancy and the child from the third pregnancy were born at term and without congenital anomalies. The child from the second pregnancy was 1-month preterm. All three children were developmentally normal. The literature search identified two case reports and one abstract of limited icatibant use without adverse events during pregnancy in patients with HAE. These pregnancies resulted in the births of healthy infants.

Conclusion:

From a search of the literature, three cases of icatibant use during pregnancy resulted in healthy infants. In addition, we report that from icatibant use in three separate pregnancies, one infant was born prematurely, but there were no birth defects. From follow-up, the children continued meeting developmental milestones. This report adds to the acquisition of knowledge for drug adverse events during postmarketing surveillance for icatibant use during pregnancy.

Mechanisms of Disease: the tissue kallikrein–kinin system in hypertension and vascular remodeling

The pathogenesis of arterial hypertension often involves a rise in systemic vascular resistance (vasoconstriction and vascular remodeling) and impairment of salt excretion in the kidney (inappropriate salt retention despite elevated blood pressure). Experimental and clinical evidence implicate an imbalance between endogenous vasoconstrictor and vasodilator systems in the development and maintenance of hypertension. Kinins (bradykinin and lys-bradykinin) are endogenous vasodilators and natriuretic peptides known best for their ability to antagonize angiotensin-induced vasoconstriction and sodium retention. In humans, angiotensin-converting enzyme inhibitors, a potent class of antihypertensive agents, lower blood pressure at least partially by favoring enhanced kinin accumulation in plasma and target tissues. The beneficial actions of kinins in renal and cardiovascular disease are largely mediated by nitric oxide and prostaglandins, and extend beyond their recognized role in lowering blood pressure to include cardioprotection and nephroprotection. This article is a review of exciting, recently generated genetic, biochemical and clinical data from studies that have examined the importance of the tissue kallikrein-kinin system in protection from hypertension, vascular remodeling and renal fibrosis. Development of novel therapeutic approaches to bolster kinin activity in the vascular wall and in specific compartments in the kidney might be a highly effective strategy for the treatment of hypertension and its complications, including cardiac hypertrophy and renal failure.

Bradykinin release and inactivation in brain of rats submitted to an experimental model of Alzheimer's disease

The kallikrein-kinin system is involved in a variety of physiological and pathological processes. Components of this system, identified in rat and human brains, can be altered in neurodegenerative processes such as Alzheimer's disease. Here, we studied kinin release and its inactivation in rats submitted to chronic cerebroventricular infusion of beta-amyloid (Abeta) peptide. Neurodegeneration was confirmed by histological analysis of brain samples. In cerebrospinal fluid of animals infused with Abeta, bradykinin concentration was increased, as determined by radioimmunoassay. However, in the brain of Abeta group, we only detected the tripeptide Arg-Pro-Pro, purified by reversed-phase chromatography and characterized by liquid chromatography-electrospray ionization mass spectrometry. This fragment of bradykinin indicated the possible participation of kinin-processing enzymes in the brain such as a prolyl oligopeptidase.

Role of bradykinin B1 and B2 receptors in normal blood pressure regulation

With inhibition or absence of the bradykinin B2 receptor (B2R), B1R is upregulated and assumes some of the hemodynamic properties of B2R, indicating that both participate in the maintenance of normal vasoregulation or to development of hypertension. Herein we further evaluate the role of bradykinin in normal blood pressure (BP) regulation and its relationship with other vasoactive factors by selectively blocking its receptors. Six groups of Wistar rats were treated for 3 wk: one control group with vehicle alone, one with concurrent administration of B1R antagonist R-954 (70 microg x kg(-1) x day(-1)) and B2R antagonist HOE-140 (500 microg x kg(-1) x day(-1)), one with R-954 alone, one with HOE 140 alone, one with concurrent administration of both R-954 and HOE-140 plus the angiotensin antagonist losartan (5 mg x kg(-1) x day(-1)), and one with only losartan. BP was measured continuously by radiotelemetry. Only combined administration of B1R and B2R antagonists produced a significant BP increase from a baseline of 107-119 mmHg at end point, which could be partly prevented by losartan and was not associated with change in catecholamines, suggesting no involvement of the sympathoadrenal system. The impact of blockade of bradykinin on other vasoregulating systems was assessed by evaluating gene expression of different vasoactive factors. There was upregulation of the eNOS, AT1 receptor, PGE2 receptor, and tissue kallikrein genes in cardiac and renal tissues, more pronounced when both bradykinin receptors were blocked; significant downregulation of AT2 receptor gene in renal tissues only; and no consistent changes in B1R and B2R genes in either tissue. The results indicate that both B1R and B2R contribute to the maintenance of normal BP, but one can compensate for inhibition of the other, and the chronic inhibition of both leads to significant upregulation in the genes of related vasoactive systems.

Effects of early perturbation of the renin–angiotensin system on cardiovascular remodeling in spontaneously hypertensive rats

RATIONALE

The goal of this study was to analyze cardiovascular (CV) remodeling in early, short-term CAP treated SHR and their offspring.

METHODS

We treated SHR with Captopril (CAP, 100 mg/kg) from in utero to 1 month of age (OCAP). Some of these rats were mated at 3-4 months of age and we used their offspring (2nd G). Controls were untreated SHR, normotensive Wistar Kyoto rats (WKY) and SHR maintained on CAP (SCAP). At 12-14 months of age, rats were cannulated for mean arterial blood pressure (MAP) measurements. An image analysis system was used to quantitate changes in cardiac and vascular (wall-to-lumen ratios, w/l) morphology and fibrosis.

RESULTS

Early, short-term CAP treatment prevented the full expression of hypertension in treated rats and their offspring. MAPs were: SHR (180+/-2.2 mm Hg); WKY 125+/-3 mm Hg); SCAP 112+/-2.5mm Hg; OCAP 138+/-2.3 mm Hg; and 2nd G (145+/-2.0 mm Hg). There were significant decreases in heart weight/body weight ratios, large and small vessel morphology, and interstitial and perivascular fibrosis in CAP-treated animals and their offspring in comparison to untreated SHR.

CONCLUSIONS

The CV protective properties of early, short-term CAP treatment were not solely due to a reduction in MAP. Although MAP was higher in OCAP and 2nd G, CV structure resembled that found in WKY and SCAP. The effects of our early treatment appear to be due to chronic blockade of the renin-angiotensin system and its effects on growth of CV tissues and the development of fibrosis.

The renal kallikrein-kinin system: its role as a safety valve for excess sodium intake, and its attenuation as a possible etiologic factor in salt-sensitive hypertension

The distal tubules of the kidney express the full set of the components of the kallikrein-kinin system, which works independently from the plasma kallikrein-kinin system. Studies on the role of the renal kallikrein-kinin system, using congenitally kininogen-deficient Brown-Norway Katholiek rats and also bradykinin B2 receptor knockout mice, revealed that this system starts to function and to induce natriuresis and diuresis when sodium accumulates in the body as a result of excess sodium intake or aldosterone release, for example, by angiotensin II. Thus, it can be hypothesized that the system works as a safety valve for sodium accumulation. The large numbers of studies on hypertensive animal models and on essential hypertensive patients, particularly those with salt sensitivity, indicate a tendency toward the reduced excretion of urinary kallikrein, although this reduction is modified by potassium intake and impaired renal function. We hypothesize that the reduced excretion of the renal kallikrein may be attributable to a genetic defect of factor(s) in renal kallikrein secretion process and may cause salt-sensitive hypertension after salt intake.

Regulation of the kinin receptors after induction of myocardial infarction: a mini-review

It is well known that the responses to vasoactive kinin peptides are mediated through the activation of two receptors termed bradykinin receptor B1 (B1R) and B2 (B2R). The physiologically prominent B2R subtype has certainly been the subject of more intensive efforts in structure-function studies and physiological investigations. However, the B1R activated by a class of kinin metabolites has emerged as an important subject of investigation within the study of the kallikrein-kinin system (KKS). Its inducible character under stress and tissue injury is therefore a field of major interest. Although the KKS has been associated with cardiovascular regulation since its discovery at the beginning of the last century, less is known about the B1R and B2R regulation in cardiovascular diseases like hypertension, myocardial infarction (MI) and their complications. This mini-review will summarize our findings on B1R and B2R regulation after induction of MI using a rat model. We will develop the hypothesis that differences in the expression of these receptors may be associated with a dual pathway of the KKS in the complex mechanisms of myocardial remodeling.

Altered baroreflex control of heart rate in bradykinin B2-receptor knockout mice

Recently, we have shown that a knockout mouse strain lacking the bradykinin B2-receptor gene exhibits an accelerated heart rate (HR) under basal conditions, this alteration being associated with mildly elevated blood pressure (BP) levels and ultimately with the development of cardiomyopathy. The goal of the present study was to determine whether genetic disruption of the B2-receptor alters autonomic cardiovascular reflexes to acute or chronic changes in BP. The direct mean BP and HR levels of unrestrained B2 knockout mice (B2-/-) were higher than those of wild type (B2+/+) controls (131 +/- 2 vs. 105 +/- 2 mm Hg and 480 +/- 5 vs. 414 +/- 8 beats/min, P < 0.01 for both comparisons). The difference in HR observed between groups under basal conditions was nullified by the acute administration of propranolol and atropine as well as by hexamethonium; it was attenuated by long-term blockade of angiotensin AT1 receptors. In B2-/- mice, the presence of an alteration in baroreceptor regulation of HR was supported by a reduced gain in the HR responses to acute nitroprusside-induced hypotension or phenylephrine-induced hypertension (slope of the regression line: 0.82 +/- 0.07 vs. 5.58 +/- 0.08 beats/min per mmHg in B2+/+, P < 0.01), as well as by an exaggerated tachycardic response to chronic hypertension induced by clipping of the left renal artery (60 +/- 3 vs. 15 +/- 3 beats/min in B2+/+, P < 0.01). Our findings indicate that disruption of the bradykinin B2-receptor gene is associated with an impaired baroreflex control of HR. The combination of chronically elevated resting HR and impaired baroreflex control could contribute to the development of cardiomyopathy in these animals.

Role of the bradykinin B2 receptor in the maturation of blood pressure phenotype: lesson from transgenic and knockout mice

The binding of bradykinin (BK) to its B2 receptor results in a wide spectrum of biological effects including vasodilation, smooth muscle contraction and relaxation, pain, and inflammation. In order to gain a better insight into the physiological function of this potent vasoactive peptide, murine models have been created by the use of gene insertion or deletion. The results of studies using these strategies are revisited in the present article. In transgenic mice harboring the human BK B2 receptor cDNA (cHBKR), expression of the transgene was identified in the aorta, brain, heart, lung, liver, kidney, uterus and prostate gland by RT-PCR Southern blot analysis. These mice displayed an exaggerated hypotensive response to intra-aortic injection of BK, whereas the blood pressure of knockout mice, homozygous for targeted disruption of the endogenous gene, was insensitive to BK. Two transgenic mouse lines expressing the human BK B2 receptor showed a significant reduction of systolic tail-cuff blood pressure (84 +/- 1 mm Hg, n = 28; 80 +/- 1 mm Hg, n = 24; P < 0.001) compared with the control littermates (97 +/- 1 mm Hg, n = 52). Systolic blood pressure was elevated in BK B2 receptor knockout mice (124 +/- 1 mm Hg, n = 38). In heterozygous mice, systolic blood pressure was similar to that of controls until 5 month-old, then it raised to the elevated levels of knockout mice at 7 months of age. Together these data indicate that kinins acting through the B2 receptor play a role in the development of the blood pressure phenotype.

Tissue kallikrein and kinins in renal disease

The renal kallikrein-kinin system is involved in sodium and water homeostasis, blood pressure regulation and inflammation. Tissue kallikrein and kinin levels were measured in the urine of patients with renal disease and in the urine of living related kidney donors prior to uninephrectomy who served as controls. Tissue kallikrein and kinin B1 and B2 receptors were immunolocalised by confocal microscopy in renal biopsy material from patients with renal disease and controls (fresh autopsy material and normal kidney tissue from nephrectomies for malignancy). Urinary tissue kallikrein excretion was significantly decreased in patients with mild renal disease (16.6 +/- 6.7 ng tissue kallikrein (TK)/ng protein; p < 0.05) and more markedly so (1.8 +/- 0.7 ng TK/microg protein; p < 0.01) in patients with severe renal failure requiring dialysis compared to normal controls (78.9 +/- 31.7 ng TK/microg protein). Basal kinin values were unchanged in patients with renal disease (14 +/- 0.8 ng/ml) compared to controls (13.3 +/- 0.56 ng/ml). In control kidney tissue kallikrein was immunolocalised in the distal connecting tubules and collecting ducts whereas decreased immunolabelling was observed with renal disease. Kinin B2 receptor labelling was present in the entire nephron in the normal control kidney but was reduced with renal disease. While kinin B1 receptor immunolabelling was not observed in the control kidneys, labelling of distal tubules and collecting ducts was noted in renal disease, suggesting an upregulation of B1 receptors in renal parenchymal disease.

Ontogenetic aspects of hypertension development: analysis in the rat

In this review, we attempt to outline the age-dependent interactions of principal systems controlling the structure and function of the cardiovascular system in immature rats developing hypertension. We focus our attention on the cardiovascular effects of various pharmacological, nutritional, and behavioral interventions applied at different stages of ontogeny. Several distinct critical periods (developmental windows), in which particular stimuli affect the further development of the cardiovascular phenotype, are specified in the rat. It is evident that short-term transient treatment of genetically hypertensive rats with certain antihypertensive drugs in prepuberty and puberty (at the age of 4-10 wk) has long-term beneficial effects on further development of their cardiovascular apparatus. This juvenile critical period coincides with the period of high susceptibility to the hypertensive effects of increased salt intake. If the hypertensive process develops after this critical period (due to early antihypertensive treatment or late administration of certain hypertensive stimuli, e.g., high salt intake), blood pressure elevation, cardiovascular hypertrophy, connective tissue accumulation, and end-organ damage are considerably attenuated compared with rats developing hypertension during the juvenile critical period. As far as the role of various electrolytes in blood pressure modulation is concerned, prohypertensive effects of dietary Na+ and antihypertensive effects of dietary Ca2+ are enhanced in immature animals, whereas vascular protective and antihypertensive effects of dietary K+ are almost independent of age. At a given level of dietary electrolyte intake, the balance between dietary carbohydrate and fat intake can modify blood pressure even in rats with established hypertension, but dietary protein intake affects the blood pressure development in immature animals only. Dietary protein restriction during gestation, as well as altered mother-offspring interactions in the suckling period, might have important long-term hypertensive consequences. The critical periods (developmental windows) should be respected in the future pharmacological or gene therapy of human hypertension.

Potent antihypertrophic effect of the bradykinin B2 receptor system on the renal vasculature

BACKGROUND

Angiotensin type 1 (AT1) receptor-deficient mice (Agtr1-/-), which selectively lack both AT1A and AT1B receptor genes, are characterized by marked intrarenal vascular thickening. In the present study, we explored the possible involvement of the kinin-kallikrein system in the development of this renal vascular hypertrophy.

METHODS

Wild-type and Agtr1-/- mice were examined for the developmental regulation pattern of the kinin-kallikrein system and treated with aprotinin (a kallikrein inhibitor), AcLys [D-b Nal7, Ile8] des-Arg9-bradykinin (a bradykinin B1 receptor antagonist), or Hoe-140 (a bradykinin B2 receptor antagonist) from 3 to 14 days of age.

RESULTS

The normal postnatal up-regulation of kininase II was organ-specifically suppressed in Agtr1-/- kidneys at 2 and 3 weeks of age. Immunohistochemical staining in Agtr1-/- mice revealed tissue kallikrein staining along the nephron from connecting tubules to cortical collecting tubules in proximity to the hypertrophic vasculature, whereas tissue kallikrein staining was confined to connecting tubules in wild-type mice. Aprotinin and Hoe-140 accelerated the vascular hypertrophy significantly as determined by wall thickness ratio, whereas B1 receptor antagonism had no effect.

CONCLUSION

The kinin-kallikrein system in the Agtr1-/- mouse kidney is functionally activated by local suppression of kininase II and extensive redistribution of kallikrein to perivascular areas. This activation, specific to the kidney, serves to dampen a development of the marked vascular hypertrophy. These results demonstrate, to our knowledge for the first time, the antihypertrophic effect of the bradykinin B2 receptor system on the renal vasculature in vivo.

Pharmacology and cardiovascular implications of the kinin-kallikrein system

Kinins are peptide hormones that can exert a significant influence on the regulation of blood pressure and vascular tone due to their vasodilatatory, natriuretic and growth modulating activity. Their cardiovascular involvement in physiological and pathophysiological situations has been studied intensively since inhibitors for angiotensin I-converting enzyme and selective receptor antagonists have become available for pharmacologically potentiating or inhibiting kinin-mediated reactions. Molecular biological analysis and the establishment of genetically modified animal models have also allowed newer information to be acquired on this subject. In this review, the components and cardiovascularly relevant mechanisms of the kinin-kallikrein system shall be described. Organ-specific effects concerning the kidneys, the vascular system, the heart and nervous tissue shall also be illustrated. On this issue, the physiological functions and pathophysiological implications of the kinin-kallikrein system should be clearly distinguished from the many, mostly endothelium-mediated protective effects which occur during ACE inhibition due to the potentiation of kinin effects. Finally, a view shall also be cast upon newly discovered targets of action, which could be exploited for therapeutically altering the kinin-kallikrein system.

Activation of kininogen expression during distal nephron differentiation

Previous studies have shown that the epithelial precursors of the connecting tubule and collecting duct express tissue kallikrein and bradykinin B2 receptors, respectively, suggesting the presence of a local kinin-producing/responsive system in the maturing distal nephron. However, evidence for the existence of kininogen in the developing nephron is still lacking. This study examined the spatiotemporal relationships between segmental nephron differentiation and the ontogeny of kininogen and kinins in the rat. Kininogen immunoreactivity is detectable in the metanephros as early as embryonic day 15. In the nephrogenic zone, the terminal ureteric bud branches are the main kinin-expressing segments. Kininogen is also observed in the stromal mesenchyme. In contrast, proximal ureteric bud branches, metanephrogenic mesenchyme, and pretubular aggregates express little or no kininogen. After completion of nephrogenesis, kininogen distribution assumes its classic "adult" pattern in the collecting ducts. Peak kininogen mRNA and protein expression occur perinatally, corresponding to the period of active nephrogenesis in the rat, and declines gradually thereafter. Estimations made by RT-PCR, Western blotting, and radioimmunoassays indicate that renal kininogen mRNA and protein levels are at least 20-fold higher in newborn than adult rats. Likewise, immunoreactive tissue kinin levels are 2.3-fold higher in newborn than adult kidneys (P < 0.05). In summary, the present study demonstrates the activation of kininogen gene expression and kinin production in the developing kidney. The terminal ureteric bud branches and their epithelial derivatives are the principal kinin-producing segments in the maturing nephron. The results suggest an autocrine/paracrine role for the kallikrein-kinin system in distal nephron maturation.

Effects of a chronic high-salt diet on large artery structure: role of endogenous bradykinin

Bradykinin activity could explain the blood pressure increase during NaCl loading in hypertensive animals, but its contribution on vascular structure was not evaluated. We determined cardiac mass and large artery structure after a chronic, 4-mo, high-salt diet in combination with bradykinin B2-receptor blockade by Hoe-140. Four-week-old rats were divided into eight groups according to strain [spontaneously hypertensive rats (SHR) vs. Wistar-Kyoto (WKY) rats], diet (0.4 vs. 7% NaCl), and treatment (Hoe-140 vs. placebo). In WKY rats, a high-salt diet significantly increased intra-arterial blood pressure with minor changes in arterial structure independently of Hoe-140. In SHR, blood pressure remained stable but 1) the high-salt diet was significantly associated with cardiovascular hypertrophy and increased arterial elastin and collagen, and 2) Hoe-140 alone induced carotid hypertrophy. A high-salt diet plus Hoe-140 acted synergistically on carotid hypertrophy and elastin content in SHR, suggesting that the role of endogenous bradykinin on arterial structure was amplified in the presence of a high-salt diet.

Effect of chronic bradykinin B2 receptor blockade on blood pressure of conscious Dahl salt-resistant rats

1. In this study 3 protocols were utilized to determine the role of endogenous kinins in the resistance of the inbred Dahl (Rapp) salt-resistant (SR/Jr) rats to high salt diet-induced blood pressure elevation. 2. The bradykinin B2 receptor antagonist, Hoe 140 (D-Arg[Hyp3, Thi5, D-Tic7, Oic8]-bradykinin) at doses of either 10-20 or 20-40 nmol day(-1) (subcutaneously (s.c), via osmotic minipumps, for either 1 or 3 weeks during a high (8%) salt diet) effectively blocked or attenuated the hypotensive responses to 100-1000 ng of bradykinin. 3. In the first protocol, 5 week old SR/Jr rats treated with Hoe 140 (10-20 nmol day(-1), n = 9, s.c., via osmotic minipumps) for 3 weeks and concomitantly fed high (8%) NaCl diet had significantly higher conscious tail cuff blood pressures (BPc) at 1 and 3 weeks when compared with rats treated with vehicle (0.9% NaCl, n = 6). The differences in BPc between the 2 groups were 13 mmHg (P < 0.001) after 1 week and 8 mmHg (P < 0.05) after 3 weeks of treatment. 4. In the second protocol, 5 week old SR/Jr rats were treated with Hoe 140 (20-40 nmol day(-1), n = 8, s.c., via osmotic minipumps) or vehicle (n = 8) for 3 weeks. During the first week of treatment the rats were fed normal (0.8%) NaCl diet. The rats were then switched to 8% NaCl for 2 remaining weeks of the protocol. The mean BPc of Hoe 140-treated rats was not significantly different from that of the vehicle-treated rats when fed 0.8% NaCl diet. In contrast, rats treated with Hoe 140 and concomitantly fed high (8%) NaCl diet had significantly increased BPc (123+/-2 vs 111 +/- 1 mmHg, P < 0.001 for the Hoe 140- and vehicle-treated rats, respectively). 5. In the third protocol, treatment with Hoe 140 (20 40 nmol day(-1), s.c., via osmotic minipumps) during high salt diet did not increase BPc in rats that were pre-exposed to the high salt diet for 2 weeks. 6. At the end of 3 weeks of study, blood pressure was measured via an arterial catheter during pentobarbitone-induced anaesthesia. Rats treated with Hoe 140 for 1 or 3 weeks had significantly lower mean arterial blood pressures than the vehicle-treated rats. 7. Our findings suggest that in SR/Jr rats, kinin activation of bradykinin B2 receptors at least partially contributes to early regulatory mechanisms that resist an increase in blood pressure following exposure to a high salt diet. The mechanism underlying the decreased blood pressure during pentobarbitone anaesthesia of SR/Jr rats chronically treated with Hoe 140 has yet to be elucidated.

Blood pressure responses to acute or chronic captopril in mice with disruption of bradykinin B2-receptor gene

OBJECTIVE

To evaluate the role of kinins in the hypotensive response to angiotensin converting enzyme inhibition, we compared the blood pressure effects induced by acute or chronic captopril administration in a mouse strain (Bk2r-/-) with disruption of the bradykinin B2 receptor gene and in wild-type controls (J129 Sv mice). A second aim was to determine whether Icatibant, a selective bradykinin B2-receptor antagonist, prevented the blood pressure changes induced by acute captopril administration in Swiss, c57/B16, J129 Sv and Bk2r-/- mice.

METHODS AND RESULTS

Under basal conditions, tail-cuff systolic blood pressure (SBP) and intra-arterial mean blood pressure (MBP) were higher in Bk2r-/- than in J129 Sv (SBP: 132+/-2 versus 113+/-3 mmHg; MBP: 144+/-6 versus 122+/-10 mmHg, P< 0.05 for both comparisons). Acute captopril administration (1 mg/kg body weight, intra-arterially) reduced the MBP of Bk2r-/- and J129 Sv by 36+/-8 and 31+/-7 mmHg, respectively. Swiss and c57/B16 mice showed similar decreases in MBP following captopril. Pretreatment with Icatibant (10 nmol/kg body weight, intra-arterially) did not influence the MBP responses to acute captopril in all the strains. Chronic administration of captopril (approximately 120 mg/kg body weight per day for 2 weeks in drinking water) reduced SBP in either Bk2r-/- or J129 Sv. The magnitude of this response was higher in Bk2r-/- than in J129 Sv (65+/-3 versus 47+/-4 mmHg, respectively, P < 0.01).

CONCLUSIONS

Our results suggest that endogenous kinins do not participate in the hypotensive response to angiotensin converting enzyme inhibition in mice; in Bk2r-/-, the exaggerated blood pressure response to chronic captopril appears to be attributable to interference with unbalanced vasoconstrictor action of the renin-angiotensin system.

Kinins and the events influenced by an angiotensin-converting enzyme inhibitor during neointima formation in the rat carotid artery

OBJECTIVE

In balloon-injured rat carotid arteries, angiotensin-converting enzyme inhibitors (ACEI) decrease neointima formation, and a kinin receptor antagonist partially reverses this inhibitory effect. We studied which of the events leading to neointima formation are involved in the effects of ACEI and kinins.

METHODS

We administered 5 mg/kg per day ramipril, either alone or combined with the kinin receptor antagonist icatibant (Hoe 140), on the days each wave occurred and studied the effects on neointima formation 14 days after balloon injury. Ramipril alone or combined with icatibant had no effect on neointima formation when administered from 2 days before to 3 or 5 days after balloon injury. In contrast, ramipril inhibited neointima formation when administered from day 7 to day 14. Treatment with icatibant had a small effect, which was sufficient to abolish the effects of ramipril (control 0.11 +/- 0.01 mm2, ramipril 0.08 +/- 0.01 mm2; P < 0.05; ramipril plus icatibant 0.09 +/- 0.01 mm2; NS, ramipril plus icatibant versus control). Thus ramipril was not effective when treatment was stopped after 3 or 5 days, but was mildly effective when treatment was administered during the second week. The effect on migration was studied by counting the number of neointimal cells in rats treated from 2 days before to 4 days after injury. Ramipril decreased the number of cells by 93% compared with controls (control 65.0 +/- 13.5 cells/slice, ramipril 4.7 +/- 2.0 cells/slice; P < 0.001), and this effect was blunted significantly by icatibant (19.5 +/- 5.7 cells/slice; P < 0.009, versus ramipril; P < 0.007, versus controls). The influence of treatment on the rate of proliferation (the 5'-bromo-2'-deoxyuridine index) was studied in the media 3 days, and in the neointima 7 and 10 days after balloon injury. Although proliferation peaked in the neointima after 7 days, there were no differences among the groups at any time. Thus neither ramipril nor icatibant affected the rate of proliferation at the times sampled. Ramipril increased cell density (cells/mm2) in the neointima, and this effect was abolished by cotreatment with icatibant (P < 0.05).

CONCLUSION

The ACEI needs to be present throughout the experimental period to be most effective. ACEI act on neointima formation in part by inhibiting migration; thus, because ramipril was mildly effective when administered from 7 to 10 days after injury, it is likely that vascular smooth muscle cell migration also occurs continuously. Kinins help mediate roughly 30% of the effect of ACEI on migration. In addition, ACEI, through kinins, affect a process that increases the density of the cells in the neointima, perhaps by decreasing extracellular matrix deposition.

Blood pressure sensitivity to salt in rats with low urinary kallikrein excretion

We evaluated if a rat strain inbred for reduced urinary kallikrein excretion differs from normal-kallikrein Wistar rats regarding blood pressure in basal conditions and during alterations in sodium balance. Low-kallikrein rats showed greater systolic blood pressure values (125 +/- 3 vs. 114 +/- 2 mmHg in controls, P < 0.01) at 9 weeks of age. Systolic blood pressure was increased after 20 days of dietary sodium loading in the low-kallikrein group and remained unchanged in controls (150 +/- 6 vs. 112 +/- 2 mmHg, P < 0.01) and this effect was associated with a reduced cumulative excretion of sodium (23% less in the low-kallikrein group compared with controls, P < 0.01). Urinary creatinine excretion was decreased by sodium loading in both groups, and this effect was more pronounced in the low-kallikrein group. The group-difference in urinary kallikrein excretion found in basal conditions (2.49 +/- 0.10 vs. 7.78 +/- 0.53 Pkat/100 g body weight, P < 0.01) was enhanced by high salt diet (1.05 +/- 0.21 vs. 8.31 +/- 0.70 Pkat/100 g body weight, P < 0.01). The ratio of heart weight to body weight was significantly greater in low-kallikrein rats (331 +/- 7 vs. 275 +/- 4 mg/100 g body weight, P < 0.01), whereas the ratio of kidney weight to body weight was lower (329 +/- 5 vs. 370 +/- 8 mg/100 body weight, P < 0.01). Our results indicate that a genetically-determined defect in urinary kallikrein excretion is associated with a greater blood pressure sensitivity to salt, possibly due to altered renal sodium handling.

Urinary kallikrein: a marker of blood pressure sensitivity to salt

We evaluated if a rat strain inbred for low urinary kallikrein excretion differs from normal-kallikrein Wistar rats regarding blood pressure levels in basal conditions and during alterations in sodium balance. Blood pressure was measured in unanesthetized rats on normal sodium intake. Then, blood pressure sensitivity to salt was evaluated over a period of 20 days of high sodium diet (0.84 mmol per g chow). Low-kallikrein rats showed greater systolic blood pressure levels (125 +/- 3 vs. 114 +/- 2 mm Hg in controls, P < 0.01) at nine weeks of age. Systolic blood pressure was increased after sodium loading in the low-kallikrein group and remained unchanged in controls (150 +/- 6 vs. 112 +/- 2 mm Hg, P < 0.01). This effect was associated with a reduced cumulative urinary excretion of sodium in the low-kallikrein rats. No group difference was found in the clearance of endogenous creatinine in basal conditions. Urinary creatinine excretion decreased during sodium loading, particularly in the low-kallikrein group. The group-difference in urinary kallikrein excretion found in basal conditions (6.85 +/- 0.31 vs. 20.74 +/- 1.71 nkat/24 hr in controls, P < 0.01) was enhanced by high salt diet (2.96 +/- 0.67 vs. 22.07 +/- 2.47 nkat/24 hr in controls, P < 0.01). In addition, renal kallikrein activity and content were reduced in low-kallikrein rats. The latter group showed a greater ratio of heart weight to body wt both in basal conditions and after sodium loading. The ratio of kidney weight to body wt was reduced after sodium loading. These results indicate that a genetically-determined defect in urinary kallikrein excretion is associated with a greater blood pressure sensitivity to salt, possibly due to altered renal sodium handling.

Prevention by blockade of angiotensin subtype1-receptors of the development of genetic hypertension but not its heritability

1. We determined whether early inhibition of angiotensin II subtype1 (AT1) receptors by the newly synthesized nonpeptidic antagonist, A-81988, can attenuate the development of hypertension in spontaneously hypertensive rats (SHR) and if the altered blood pressure phenotype can be passed on to the subsequent generation, not exposed to the antagonist. 2. Pairs of SHR were mated while drinking tap water or A-81988 in tap water, and the progeny was maintained on the parental regimen until 14 weeks of age. At this stage, A-81988-treated rats showed lower systolic blood pressure and body weight values (136 +/- 5 versus 185 +/- 4 mmHg and 247 +/- 4 versus 283 +/- 4 g in controls, P < 0.01); while heart rate was similar. In addition, mean blood pressure was reduced (101 +/- 7 versus 170 +/- 7 mmHg in controls, P < 0.01), and the pressor responses to intravenous or intracerebroventricular angiotensin II were inhibited by 27 and 59%, respectively. Heart/body weight ratio was smaller in A-81988-treated rats (3.2 +/- 0.1 versus 3.8 +/- 0.1 in controls, P < 0.01). 3. The antihypertensive and antihypertrophic effect of A-81988 persisted in rats removed from therapy for 7 weeks (systolic blood pressure: 173 +/- 4 versus 220 +/- 4 mmHg, heart/body weight ratio: 3.4 +/- 0.1 versus 4.1 +/- 0.1 in controls at 21 weeks of age, P < 0.01 for both comparisons), whereas the cardiovascular hypertensive phenotype was fully expressed in the subsequent generation that was maintained without treatment. 4. These results indicate that chronic blockade of angiotensin AT1-receptors attenuates the development of hypertension in SHR but it does not prevent the transmission of hypertension to the following generation. Thus, heritability of the SHR's hypertensive trait is not affected by pharmacological manipulation of the cardiovascular phenotype.