The actions of kinin antagonists on B1 and B2 receptor systems

The newly discovered bradykinin antagonist [Thi5,8,D-Phe7]Bradykinin, supplied by J.-M. Stewart and three other compounds, [D-Phe7]BK, [Thi5,8,D-Phe7]Bradykinin and [Thi6,9,D-Phe8]Kallidin synthesized in our laboratory, were tested for their ability to antagonize bradykinin in four B2 receptor systems, the guinea-pig ileum, the rabbit jugular vein, the dog carotid artery and the dog urinary bladder as well as against desArg9-bradykinin in the rabbit aorta (a B1 receptor system). [D-Phe7]Bradykinin is a partial agonist, while [Thi5,8,D-Phe7]Bradykinin and [Thi6,9,D-Phe8]Kallidin are pure antagonists, the second one showing little BK-like activity on three of the four preparations. The kallidin analogue is more potent in all preparations than the bradykinin one. The two [Thi5,8,D-Phe7]BK (that supplied by J.-M. Stewart and that prepared in our laboratory) show very similar affinities in all preparations. The bradykinin analogue as well as the kallidin one are also active against desArg9-bradykinin in the rabbit aorta, at concentrations similar to those active on B2 receptor systems. The kinin antagonists are however specific for the kinins, since they do not interfere with the myotropic effects of angiotensin or substance P (SP) in the various preparations.     

Comparison of the responses of B1 and B2 kinin receptors to agonist stimulation

The human B2 kinin receptor (B2KR), stably expressed in Chinese hamster ovary cells, responded to bradykinin stimulation with rapid (within minutes) ligand internalization and loss of cell surface receptors (sequestration). By contrast, B1 kinin receptors (B1KR) showed almost no ligand internalization or receptor sequestration upon stimulation with des-Arg10-Kallidin (DAK). The ability of the B2KR to internalize and sequester is conferred by information in the cytoplasmic tail of the receptor. It is normally impossible to determine receptor affinity at 37 degrees C because of internalization and sequestration processes. We created a mutant B2KR, truncated at K315 of the cytoplasmic tail, that was no longer able to internalize or sequester, and compared the affinity of this mutant, and of the B1KR, at 0 degrees C and 37 degrees C. The B1KR receptor showed the same affinity (Kd = 0.4 nM) at both 0 degrees C and 37 degrees C. By contrast, the K315 mutant of the B2KR showed a lower affinity (Kd = 2.9 nM) at 37 degrees C than at 0 degrees C (Kd = 1.4 nM), indicating more rapid ligand dissociation at 37 degrees C. After ligand exposure, clones expressing B1KR exhibited a very slow dissociation of DAK, even at 37 degrees C. Although both kinin receptor subtypes induce the generation of inositol phosphates, functional responses showed clear differences. The response to stimulation of the B2KR comprises a rapid loss of functional responses, receptor sequestration, and ligand dissociation, and, upon long term stimulation, downregulation. By contrast, ligand stimulation of the B1KR, once this receptor is expressed de novo under pathological conditions, results in persistent signaling due to lack of ligand dissociation, desensitization and receptor sequestration. Moreover, long term stimulation of this receptor actually leads to increased expression.     

The effects of cocaine on cardiac electrophysiology in conscious, unsedated dogs.

This study was performed to determine the cardiac electrophysiological effects of cocaine and specifically to determine the time course of these actions. Eighteen chronically instrumented conscious dogs were tested with i.v. cocaine at doses of 1 or 4 mg/kg. The following statistically significant changes were observed 1 min following the 4 mg/kg dose of cocaine: heart rate increased from 135 +/- 8 to 186 +/- 9 beats/min, QRS duration increased from 60 +/- 5 to 74 +/- 5 ms, corrected QT interval increased from 298 +/- 7 to 339 +/- 8 ms, intraatrial conduction time increased from 27 +/- 2 to 31 +/- 3 ms, atrioventricular conduction time increased from 125 +/- 5 to 140 +/- 8 ms, and the atrial effective refractory period (ERP) increased from 101 +/- 6 to 130 +/- 9 ms. All of these parameters had returned to baseline by 10 min after cocaine administration. Corrected sinus node recovery time and the ventricular ERPs were not significantly affected by either cocaine dose. The only significant change produced by the 1 mg/kg cocaine dose was prolongation of the atrial ERP. These results suggest that cocaine causes very transient electrophysiological changes that undoubtedly represent the integrated effects of the adrenergic and local anesthetic actions of this drug.     

Gastric and cardiac H-2 receptor effects of dimaprit and N'(Me),5(Me)histamine in conscious dogs

Two new H-2 agonists 5,N'-dimethyl histamine (DMH), an imidazole analog, and dimaprit, a non-imidazole compound, and histamine (H), a mixed H-1, H-2 agonist, were given to four conscious gastric fistula dogs. Gastric acid was stimulated dose responsively. Dimaprit stimulated a 20% greater maximum output of acid, and more pepsin than the other agents, but inhibited pepsin secretion as doses of greater than 0.63 mumol/kg-h. Heart rate was increased dose responsively by all drugs to approximately 200 beats/min with ED50 of 0.17:0.42:0.80 mumol/kg-h (H:DMH:dimaprit). Normalized dose responses showed that histamine was equipotent on acid and heart rate (ED50 0.15 vs. 0.14 respectively) while DMH (ED50 0.21 vs. 0.40) and dimaprit (ED50 0.27 vs. 0.85) stimulated heart rate less effectively than acid. Histamine was more effective at reducing blood pressure, with approximate ED50 of 0.28:0.60:0.96 for H, DMH and dimaprit respectively. The results indicate considerable heterogeneity of histamine responses for different actions mediated by the H-2 receptors, as well as differences for any one action between H-2 agonists.     

Molecular and pharmacological diversity of the kinin B1 receptor

The pharmacological properties of the kinin B1 receptor in binding the endogenous kinin peptides are known to differ across species. Molecular cloning has revealed that these pharmacological differences arise from the diversity within the BDKRB gene. In this report, the molecular diversity of the human BDKRB1 gene is expanded by the identification of eight single nucleotide polymorphisms (SNPs) in the coding sequence of the receptor, three of which change the amino acid sequence of the receptor. The molecular cloning and pharmacological characterization of two primate B1 receptors, rhesus and African Green monkey, reveals that they exhibit the same high degree of selectivity for des-Arg10 kallidin (Lys-bradykinin) relative to des-Arg9 bradykinin that is observed with the human kinin B1 receptor. Previous mutagenesis studies of the human B1 receptor have implicated extracellular domain (EC) IV in conferring this selectivity for des-Arg10 kallidin, by interacting with the N-terminal Lys residue of the peptide. The pharmacological analysis of chimeric B1 receptors, in which EC-IV of the human B1 receptor is replaced with the corresponding domain of either rat or dog, supports the proposal that EC-IV is an important determinant in conferring ligand selectivity.     

TNF-alpha and IL-1beta mediate inflammatory hypernociception in mice triggered by B1 but not B2 kinin receptor

Kinin receptors are involved in the genesis of inflammatory pain. However, there is controversy concerning the mechanism by which B(1) and B(2) kinin receptors mediate inflammatory hypernociception. In the present study, the role of these receptors on inflammatory hypernociception in mice was addressed. Mechanical hypernociception was detected with an electronic pressure meter paw test in mice and cytokines were measured by ELISA. It was observed that in na?ve mice a B(2) (d-Arg-Hyp(3), d-Phe(7)-bradykinin) but not a B(1) kinin receptor antagonist (des-Arg(9)-[Leu(8)]-bradykinin, DALBK) inhibited bradykinin- and carrageenin-induced hypernociception. Bradykinin-induced hypernociception was inhibited by indomethacin (5 mg/kg) and guanethidine (30 mg/kg), while not affected by IL-1ra (10 mg/kg) or antibody against keratinocyte-derived chemokine (KC/CXCL-1, 500 ng/paw) or in TNFR1 knockout mice. By contrast, in previously lipopolysaccharide (LPS)-primed mouse paw, B(1) but not B(2) kinin receptor antagonist inhibited bradykinin hypernociception. Furthermore, B(1) kinin receptor agonist induced mechanical hypernociception in LPS-primed mice, which was inhibited by indomethacin, guanethidine, antiserum against TNF-alpha or IL-1ra. This was corroborated by the induction of TNF-alpha and IL-1beta release by B(1) kinin receptor agonist in LPS-primed mouse paws. Moreover, B(1) but not B(2) kinin receptor antagonist inhibited carrageenin-induced hypernociception, and TNF-alpha and IL-1beta release as well, in LPS-primed mice. These results suggest that in na?ve mice the B(2) kinin receptor mediates inflammatory hypernociception dependent on prostanoids and sympathetic amines, through a cytokine-independent mechanism. On the other hand, in LPS-primed mice, the B(1) kinin receptor mediates hypernociception by a mechanism dependent on TNF-alpha and IL-1beta, which could stimulate prostanoid and sympathetic amine production.     

Haemodynamic and metabolic effects of xamoterol in exercising dogs

The effects of xamoterol on the haemodynamic adaptation to graded treadmill exercise were evaluated during five subsequent cycles in chronically instrumented dogs. At rest xamoterol, 0.2 mg/kg i.v., preferentially showed a positive inotropic effect, whereas 1 mg/kg i.v. also exhibited a marked chronotropic effect. The cardiac output and left ventricular power increased dose dependently. The mean left atrial pressure and total peripheral resistance decreased concomitantly. Xamoterol did not produce a noteworthy decrease in heart rate or positive dp/dtmax during exercise, even at a dosage of 1 mg/kg. A beta-adrenoceptor blocking effect could only be seen from the diminution of the exercise-induced changes in heart rate, dp/dtmax, cardiac output, left ventricular power and total peripheral resistance. Determination of the blood glucose, lactate and pyruvate levels before the start of each exercise cycle revealed that the drug induced a decrease in blood glucose and an increase in blood pyruvate. Thus, xamoterol exerted a dose-dependent sympathomimetic effect in dogs at rest. However, there was little evidence for a beta-adrenoceptor blocking action even at higher work loads, although preliminary experiments in conscious dogs showed that xamoterol shifted the isoprenaline dose-response curve to the right by a factor of 1.31 (0.2 mg/kg) and 3.05 (1 mg/kg).     

Haemodynamic effects of bromocriptine in the conscious spontaneously hypertensive rat

The systemic haemodynamic effects of 0.3 mg kg-1 bromocriptine s.c. in conscious, chronically instrumented spontaneously hypertensive rats (SHR) has been investigated. Bromocriptine caused a gradual, long-lasting significant fall in mean arterial pressure with a maximum of 26 +/- 3 mmHg (-17%). The fall was related to a significant decrease in stroke volume index (-9 +/- 2 microliters 100 g-1; -10%) and cardiac index (-3.9 +/- 0.8 ml min-1 100 g-1; -12%). No significant changes in heart rate or total peripheral resistance index were observed. These data do not support previous suggestions that the antihypertensive effect of bromocriptine is caused by inhibition of the release of vasopressor substances. It is suggested that bromocriptine causes a reduction of venous return of the blood to the heart, possibly related to intrarenal effects.     

Development of hyperthermia following intracerebroventricular administration of endotoxin in the rat: effect of kinin B1 and B2 receptor antagonists.

1. E. coli lipopolysaccharide (LPS) produced a dose-dependent (dose range: 0.02-150 micrograms) increase in rat core temperature that was maximal 6 h after intracerebroventricular (i.c.v.) administration. LPS (200 ng) increased core temperature by 1.0 +/- 0.2 degrees C, 6 h following administration, as compared to vehicle-treated controls (-0.2 +/- 0.2 degrees C). 2. LPS-induced (200 ng) hyperthermia was prevented by co-administration of the bradykinin (BK) B2 receptor antagonist, Hoe 140 (10 and 30 pmol, i.c.v.) or by indomethacin (10 nmol, i.c.v.). 3. Systemic administration of Hoe 140 at doses up to 1 mumol kg-1, s.c., did not attenuate LPS-induced (200 ng, i.c.v.) hyperthermia. However, LPS hyperthermia was significantly reduced by systemic administration of indomethacin (1 mumol kg-1, i.v.). 4. Co-administration of the selective B1 receptor antagonists, [des-Arg9, Leu8]BK (0.1 - 1 nmol, i.c.v.) or [des-Arg10] Hoe 140 (0.1 - 1 nmol, i.c.v.), did not prevent LPS-induced hyperthermia. 5. It is concluded that the development of hyperthermia following central administration of endotoxin requires activation of central, but not peripheral bradykinin B2 receptors. The formation of kinins within the CNS may be an important initial component of CNS inflammation following infection.     

Effects of beta 2-adrenoceptor stimulation on cardiac metabolism in the conscious dog.

1 The effects of the beta 2-adrenoceptor stimulant, salbutamol, on cardiac metabolism have been studied in conscious mongrel dogs. The potential effects of anaesthesia on the study of cardiac metabolism have been avoided by prior implantation of arterial (A) and coronary sinus (CS) catheters for blood sampling and a central venous catheter for infusion. Extraction of substrates for myocardial energy metabolism (CA-CS) was assessed 3 to 24 days post-operatively. A 100 micrograms bolus of salbutamol was given followed by an infusion of 3 micrograms/min for 1 h. 2 Although heart rate increased significantly from 106 to 165 beats/min, fractional extraction of oxygen tended to fall from 84% to 77%. Thus an increase in coronary blood flow rather than in oxygen extraction must have maintained an oxygen supply commensurate with the salbutamol-induced tachycardia. 3 Neither CA-CS glucose nor fractional glucose extraction altered significantly during salbutamol infusion despite increases in arterial concentration (CA) of glucose and arterial insulin immunoreactivity and a decrease in CA of free fatty acids (FFA). This suggests that an insulin-antagonistic action accompanies the infusion of salbutamol. 4 The fractional extraction of lactate increased during salbutamol infusion. In part, this may have been a reflection of a decreased myocardial extraction of FFA with salbutamol in this model.     

卡维地洛对麻醉犬血流动力学的影响

目的　观察国产卡维地洛（ｃａｒｖｅｄｉｌｏｌ,Ｃａｒ）对动物血流动力学的影响,全面了解该药对心血管系统的作用。方法　杂种家犬麻醉下ｉｖ０－１、０－３、１ｍｇ·ｋｇ－１Ｃａｒ,记录心电、血压、左心室内压、心输出量。结果　Ｃａｒｉｖ给药可引起麻醉犬平均动脉压、心率、左心室内压及其最大变化速率、左心室做功及总外周血管阻力明显下降,给药后１ｍｉｎ即开始起效,给药后１～５ｍｉｎ达最大效能,并具有剂量依赖性,１ｍｇ·ｋｇ－１剂量药效可持续至给药后４５ｍｉｎ,Ｃａｒ对心输出量及左室舒张末压无明显影响。结论　Ｃａｒ具有较广泛的心血管效应,除通过扩张外周阻力血管降低血压外,尚具有降低心率、抑制心肌收缩性能的作用;试验结果同时提示国产Ｃａｒ兼具α肾上腺素受体和β肾上腺素受体拮抗作用,支持该药为具有Ｓ（－）和Ｒ（＋）构型的外消旋化合物。     

In vitro and in vivo effects of kinin B(1) and B(2) receptor agonists and antagonists in inbred control and cardiomyopathic hamsters

The aims of this study were to examine the possible alterations occurring in the effects of kinins on isolated aortae of inbred control (CHF 148) and cardiomyopathic (CHF 146) hamsters of 150 - 175 and 350 - 375 days of age. Bradykinin (BK) and desArg(9)BK contracted isolated aortae (with or without endothelium) of hamsters of both strains and ages. After tissue equilibration (90 min), responses elicited by both kinin agonists were stable over the time of experiments. The patterns of isometric contractions of BK and desArg(9)BK were however found to be different; desArg(9)BK had a slower onset and a longer duration of action than BK. Potencies (pEC(50) values) of BK in all groups of hamsters were significantly increased by preincubating the tissues with captopril (10(-5) M). No differences in the pEC(50) values and the E(max) values for BK or desArg(9)BK were seen between isolated vessels from inbred control and cardiomyopathic hamsters. The myotropic effect of BK was inhibited by the selective non peptide antagonist, FR 173657 (pIC(50) 7.25+/-0.12 at the bradykinin B(2) receptor subtype (B(2) receptor)). Those of desArg(9)BK, at the bradykinin B(1) receptor subtype (B(1) receptor) were abolished by either R 715 (pIC(50) of 7. 55+/-0.05; alpha(E) = 0), Lys[Leu(8)]desArg(9)BK (pIC(50) of 7.21+/-0. 01; alpha(E) = 0.22) or [Leu(8)]desArg(9)BK (pIC(50) of 7.25+/-0.02; alpha(E) = 0.18). FR 173657 had no agonistic activity, exerted a non competitive type of antagonism and was poorly reversible (lasting more than 5 h) from B(2) receptor. In vivo, FR 173657 (given per os at 1 and 5 mg kg(-1), 1 h before the experiment) antagonized the acute hypotensive effect of BK in anaesthetized hamsters. It is concluded that aging and/or the presence of a congenital cardiovascular disorder in hamsters are not associated with changes in the in vitro aortic responses to either BK or desArg(9)BK.     

Evidence for the participation of kinins in Freund's adjuvant-induced inflammatory and nociceptive responses in kinin B1 and B2 receptor knockout mice.

Experiments were designed to investigate the role of kinin B₁ and B₂ receptors in Freund's adjuvant (CFA)-induced inflammation and nociception responses by the use of B₁ and B₂ null mutant mice. Intradermal (i.d.) injection of CFA produced time-dependent and marked hyperalgesic responses in both ipsilateral and contralateral paws of wild-type mice. Gene disruption of the kinin B₂ receptor did not interfere with CFA-induced hyperalgesia, but ablation of the gene of the B₁ receptor reduced the hyperalgesia in both ipsilateral (48±13%, at 12 h) and contralateral (91±22%, at 12 h) paws. Treatment of wild-type mice with the selective B₁ antagonist des-Arg⁹-[Leu⁸]-BK (150 nmol/kg, s.c.) reduced CFA-evoked thermal hyperalgesia, to an extent which was similar to that observed in mice lacking kinin B₁ receptor. I.d. injection of CFA produced a time-related and long-lasting (up to 72 h) increase in paw volume in wild-type mice. A similar effect was observed in B₁ knockout mice. In mice lacking B₂ receptor, the earlier stage of the CFA-induced paw oedema (6 h) was significantly greater compared with the wild-type animals, an effect which was almost completely reversed (76±5%) by des-Arg⁹-[Leu⁸]-BK. This data demonstrates that kinin B₁ receptor, but not B₂ receptor, exerts a critical role in controlling the persistent inflammatory hyperalgesia induced by CFA in mice, while B₂ receptor appears to have only a minor role in the amplification of the earlier stage of CFA-induced paw oedema formation. The results of the present study, taken together with those of previous studies, suggest that B₁ receptor antagonists represent a potential target for the development of new drugs to treat persistent inflammatory pain.     

Swimming training exacerbates pathological cardiac hypertrophy in kinin B2 receptor-deficient mice

Kallikrein-kinin system exerts cardioprotective effects against pathological hypertrophy. These effects are modulated mainly via B2 receptor activation. Chronic physical exercise can induce physiological cardiac hypertrophy characterized by normal organization of cardiac structure. Therefore, the aim of this work was to verify the influence of kinin B2 receptor deletion on physiological hypertrophy to exercise stimulus. Animals were submitted to swimming practice for 5 min or for 60 min, 5 days a week, during 1 month and several cardiac parameters were evaluated. Results showed no significantly difference in heart weight between both groups, however an increased left ventricle weight and myocyte diameter were observed after the 60 min swimming protocol, which was more pronounced in B2(-/-) mice. In addition, sedentary B2(-/-) animals presented higher left ventricle mass when compared to wild-type (WT) mice. An increase in capillary density was observed in exercised animals, however the effect was less pronounced in B2(-/-) mice. Collagen, a marker of pathological hypertrophy, was increased in B2(-/-) mice submitted to swimming protocol, as well as left ventricular thickness, suggesting that these animals do not respond with physiological hypertrophy for this kind of exercise. In conclusion, our data suggest an important role for the kinin B2 receptor in physiological cardiac hypertrophy.     

Comparison of kinin B(1) and B(2) receptor expression in neutrophils of asthmatic and non-asthmatic subjects

Kinins have been implicated in the pathophysiology of asthma and activation of kinin receptors stimulates neutrophil chemotaxis. However, the expression of kinin receptors on neutrophils of asthmatic subjects has not been assessed. The aim of this study was to compare the expression of kinin B(1) and B(2) receptor mRNA and proteins in neutrophils of asthmatic and non-asthmatic subjects, and to assess whether inhaled corticosteroid treatment may influence expression of the kinin receptors. Neutrophils were isolated from peripheral blood of asthmatic (n=27) and non-asthmatic subjects (n=14). The presence of kinin B(1) and B(2) receptor protein on neutrophils was confirmed by immunolabeling with specific antibodies followed by immunoperoxidase, immunofluorescence and FACS detection. Kinin B(1) and B(2) receptor mRNA expression was assessed by RT-PCR. Quantitative image analysis of fluorescence immunolabeled neutrophils showed no differences in kinin B(1) or B(2) receptor protein expression between asthmatic and non-asthmatic subjects. Similarly, quantitative real time RT-PCR analysis demonstrated no differences in expression of mRNA for the kinin B(1) or B(2) receptors between asthmatic and non-asthmatic subjects. However, B(1) receptor mRNA expression was significantly lower in asthmatic subjects using > or =2000 microg of inhaled corticosteroid per day (p<0.05) and B(1) receptor protein levels also tended to be lower in these subjects. Corticosteroids may have a beneficial anti-inflammatory effect in asthma by down-regulating B(1) receptor expression on neutrophils, thereby decreasing the migration of these inflammatory cells into the airways.     

Different effects of mibefradil and amlodipine on coronary vessels and during beta-adrenergic stimulation in conscious dogs

Coronary effects of Ca -channel blockers mibefradil and amlodipine were compared in conscious dogs. Ten dogs were instrumented for measurement of aortic and left ventricular pressures, circumflex coronary blood flow velocity (CBFv), and coronary diameter (CD). A permanent catheter was implanted in the circumflex coronary artery. At doses having no systemic effects (7.5-150 micro g/kg), mibefradil and amlodipine increased CBFv and CD dose dependently. At the same dose, mibefradil increased less CBFv than amlodipine. However, for a similar increase in CBFv induced by amlodipine, mibefradil increased CD more. BAY K8644, an L-type Ca -channel agonist, prevented the CBFv and CD responses to amlodipine, but minimally affected the coronary responses to mibefradil. Intracoronary isoproterenol (6 ng/kg) increased LV dP/dt max, CBFv, and CD. Amlodipine markedly altered these responses, while mibefradil did not affect LV inotropic response and slightly altered CBFv response to isoproterenol. Thus, in conscious dogs, both mibefradil and amlodipine exert coronary vasodilation, with different patterns on coronary conductance and resistance vessels and during beta-adrenergic stimulation. These differences could be related to their actions on different Ca channels.     

Pharmacological and molecular evidence for kinin B1 receptor expression in urinary bladder of cyclophosphamide-treated rats.

1. In the present study, we developed an experimental model of cystitis induced by cyclophosphamide (CYP). In order to characterize des-Arg9-BK-induced contraction on the urinary bladder (UB) during the development of inflammation and to quantify kinin B1 receptor gene expression using a quantitative RT - PCR technique. 2. In the presence of peptidase inhibitors captopril (10 microM), DL-thiorphan (1 microM) and DL-2-mercaptomethyl-3-guanidino-ethylthiopropanoic acid (MERGEPTA 5 microM), bradykinin (BK) (0.3 - 3,000 nM) evoked a concentration-dependent contraction of rat UB which was not different between the CYP- and vehicle-treated groups. Unlike BK, des-Arg9-BK (0.3 - 100,000 nM) did not contract UB from vehicle-treated rats but contracted vigorously bladder strips from CYP-treated rats 14, 24 and 168 h after treatment. In UB of 24 h treated rat, the pD2 value of des-Arg9-BK was 7.3+/-0.1. 3. The cyclo-oxygenase inhibitor indomethacin (3 microM) reduced by 30% the maximal response of des-Arg9-BK. Both the kinin B1 receptor antagonists des-Arg9-[Leu8]BK (10 microM) and des-Arg10-Hoe 140 (10 microM) produced a rightward shift of the concentration-response curve to des-Arg9-BK yielding pKB values of 6.8+/-0.2 and 7.2+/-0.1, respectively, whilst the kinin B2 receptor antagonist Hoe 140 (1 microM) had no effect. 4. After CYP treatment, mRNA coding for the kinin B1 receptor appeared predominantly in UB. In this organ, the induction was progressive, reaching a maximum 48 h after CYP treatment. 5. In conclusion, the present study provides strong evidence for an induction of kinin B1 receptors in UB of CYP-treated rats. This was associated at a molecular level with an increase in mRNA expression of the gene coding for the kinin B1 receptor. This kinin receptor displayed the whole features of a classical rat kinin B1 receptor.     

Comparisons of the depressor, inotropic and renal effects of milrinone and CI-930 to different pure vasodilators and diuretics in conscious instrumented dogs.

The cardiovascular and renal effects of graded i.v. dosages of two low Km cAMP cGMP-inhibitable (cGi) phosphodiesterase (PDE) inhibitors: CI-930 and milrinone (both 10-300 micrograms/kg), and three pure vasodilators: fenoldopam (0.1-3 micrograms/kg), Na nitroprusside (3-100 micrograms/kg) and hydralazine (0.1-3 mg/kg), were compared in conscious dogs. Mean arterial pressure was decreased by CI-930 at 0.3 mg/kg, milrinone at doses greater than or equal to 0.1 mg/kg (both by approximately -17 mmHg [max. change]), nitroprusside at doses greater than or equal to 0.01 mg/kg (-60 +/- 5 mmHg, [mean +/- SEM, max. change]), fenoldopam at doses greater than or equal to 0.001 mg/kg, and hydralazine at all doses (both by approximately -26 mmHg). Heart rate was increased by milrinone and CI-930 at dosages greater than or equal to 0.03 mg/kg (both by approximately 57 beats/min), nitroprusside and hydralazine at all dosages (54 +/- 18 and 91 +/- 18 beats/min, respectively) and fenoldopam at 3 micrograms/kg (21 +/- 2 beats/min). The cGi PDE inhibitors at 0.01-0.3 mg/kg and the pure vasodilators (except fenoldopam) at all dosages increased dP/dt (approximately 1500 and 900 mmHg/s, respectively). Milrinone (greater than or equal to 0.1 mg/kg), CI-930 (greater than or equal to 0.03 mg/kg), nitroprusside (greater than or equal to 0.01 mg/kg) and hydralazine (0.3-1 mg/kg) decreased left ventricular end diastolic pressure (all by approximately -4 mmHg). None of the agents adversely affected urinary volume, Na+ and K+ excretion rates. In conclusion, all agents (except fenoldopam) induced positive inotropic and chronotropic effects, and preload and afterload reduction. The cardiac effects of the pure vasodilators may be reflexly induced, whereas those of the cGi PDE inhibitors may be primarily due to inhibition of cardiac cGi PDE.     

Haemodynamic action of B-type natriuretic peptide substantially outlasts its plasma half-life in conscious dogs

1. The objective of the present study was to determine the plasma half-life of B-type natriuretic peptide (BNP) in conscious dogs after intravenous administration and to compare this with its haemodynamic effects. In six chronically instrumented dogs, plasma BNP concentrations were measured under basal conditions, during a constant infusion of canine BNP-32 (10 pmol/kg per min; 25 min) to steady state and at nominated time points up to 75 min after stopping the infusion. Concomitant, continuous measurements of mean arterial blood pressure (MAP), heart rate (HR), central venous pressure (CVP) and mesenteric blood flow (MBF) were obtained. 2. Baseline plasma BNP levels were 15.0 +/- 2.3 fmol/mL and rose approximately 10-fold to 159 +/- 23 fmol/mL after 20-25 min BNP infusion. When the infusion was turned off, plasma BNP levels declined in a biphasic manner, with an initial half-life of 1.57 +/- 0.14 min and a terminal half-life of 301 +/- 85 min. The metabolic clearance rate of BNP was 2.29 +/- 0.34 L/min. 3. The infusion of BNP reduced MAP (approximately 10%), CVP (approximately 65%) and MBF (approximately 25%), whereas haematocrit (approximately 4%) and mesenteric vascular resistance (MVR) increased (approximately 40%; all P < 0.05). Plasma BNP levels returned to baseline by 20 min after BNP infusion had been stopped, whereas none of the haemodynamic variables returned to normal by this time. Mean arterial pressure returned to resting levels within 10-15 min after plasma BNP returned to normal. However, CVP, haematocrit and MBF remained substantially below baseline values for more than 20 min after circulating BNP levels had returned to pre-infusion levels. Of these, only mesenteric vascular changes were returned to baseline within 60 min of plasma BNP levels normalizing. 4. These results demonstrate that the removal of BNP from the canine circulation is rapid, similar to observations made regarding the metabolism of circulating atrial natriuretic peptide in dogs. The half-life of BNP in dogs was shorter than that in rats, sheep or humans. However, the haemodynamic actions of BNP substantially outlasted its plasma half-life. Whether this disparity in plasma level and haemodynamic activity of BNP reflects long-lasting activation of second messenger systems or slow recovery from the hydraulic changes at the capillary level, reflected in the haematocrit and CVP, remains to be answered.     

MEN16132, a kinin B2 receptor antagonist, prevents the endogenous bradykinin effects in guinea-pig airways

Kinins have been suggested to be involved in human airway diseases such as asthma and rhinitis. MEN16132 is a non-peptide kinin B(2) receptor antagonist able to inhibit the responses produced by intravenous bradykinin into the airways, as bronchoconstriction and microvascular leakage; we tested the effect of MEN16132 on endogenously generated bradykinin through the dextran sulfate-induced contact activation of kinin-kallikrein cascade in guinea-pigs. After dextran sulfate administration (1.5 mg/kg i.v.), the pulmonary insufflation pressure was monitored and the microvascular leakage of upper and lower airways was assessed using Evans blue as tracer of plasma protein extravasation. Our results demonstrated that topical MEN16132 strongly inhibited the dextran sulfate-induced bronchoconstriction (0.3 mM solution aerosol for 5 min) and plasma protein extravasation in both lower airways (3-10 microM solution aerosol for 5 min) and nasal mucosa (0.3 nmol/nostril); Icatibant, the peptide antagonist of kinin B(2) receptor, exerted a 3-30-fold less potent inhibitory effect than MEN16132. We conclude that local application of MEN16132 into the airways abolishes the responses produced by the endogenous generation of bradykinin and it can be useful as new pharmacological tool to check the role of kinins in human diseases.