Brain kinins are responsible for the pressor effect of intracerebroventricular captopril in spontaneously hypertensive rats

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.

Correlation between brain bradykinin receptor binding sites and cardiovascular function in young and adult spontaneously hypertensive rats

Intracerebroventricular (i.c.v.) effects of bradykinin (BK) B(1) and B(2) receptor agonists and antagonists were assessed on mean arterial blood pressure (MAP) and heart rate (HR) in awake unrestrained spontaneously hypertensive rats (SHR, aged of 8 and 16 weeks) and age-matched Wistar Kyoto rats (WKY). Quantitative in vitro autoradiographic studies were also performed on the brain of both strains with specific radioligands for B(2) receptors [(125)I]HPP-Hoe 140 and B(1) receptors [(125)I]HPP-des-Arg(10) and Hoe140. MAP increased linearly with doses of BK (81-8100 pmol) and the amplitudes were significantly greater in SHR, particularly at 16 weeks. While BK evoked a negative linear trend on HR (bradycardia) in WKY, a positive one (tachycardia) was observed in adult SHR. In both strains, BK-induced pressor response was blocked by equimolar doses of B(2) receptor antagonist, D-Arg-[Hyp(3), Thi(5), D-Tic(7), Oic(8)]-BK (Hoe 140), but not by B(1) receptor antagonist, AcLys[D-betaNal(7), Ile(8)]des-Arg(9)-BK (R-715). B(1) receptor agonists (Sar-[D-Phe(8)]-des-Arg(9)-BK, des-Arg(9)-BK, des-Arg(10)-Kallidin) and antagonist (R-715 alone or with Hoe 140) had no or marginal effect on MAP and HR at doses up to 8100 pmol in SHR and WKY. Higher densities of specific [(125)I]HPP-Hoe 140 labelling were found in discrete brain areas of SHR, especially in regions associated with cardiovascular function. Low levels of [(125)I]HPP-[des-Arg(10)]-Hoe140 binding sites were seen in WKY and SHR, yet densities were significantly greater in midbrain and cortical regions of SHR aged of 16 weeks. Contrary to SHR, ageing caused a downregulation of B(2) and B(1) receptor binding sites in specific brain nuclei in WKY. It is concluded that the hypersensitivity of the pressor response to i.c.v. BK in SHR occurs during both the early and established phases of hypertension in parallel with the enhancement of B(2) receptor binding sites in various cardiovascular brain centres. In contrast, brain B(1) receptors do not seem to participate in the central pressor effects of kinins nor in the maintenance of hypertension in SHR.

Kinin B2 receptor localization and expression in the hypothalamo-pituitary-adrenal axis of spontaneously hypertensive rats

OBJECTIVE

An enhanced hypothalamo-pituitary-adrenocortical (HPA) activity has been demonstrated during onset of high blood pressure in spontaneously hypertensive rats (SHR). Furthermore, compared to normotensive Wistar-Kyoto (WKY) rats, SHR show hypersensitivity to bradykinin (BK)-induced pressor responses which may be caused by an upregulation of B(2) receptor expression in the brain.

METHODS

We performed an immunohistochemical localization and measured gene expression of B(2) receptors in the hypothalamus, pituitary and adrenal glands of SHR at three ages corresponding to the development of hypertension, i.e. prehypertensive phase, onset of hypertension and established hypertension. Using reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot technique, B(2) receptor mRNA and protein levels, respectively, were measured.

RESULTS

A specific immunostaining for B(2) receptors was observed in the hypothalamic nuclei paraventricularis (PVN) and supraopticus (SON). In the pituitary and adrenal glands, a strong immunostaining was observed in neurohypophysis (NH) and adrenal medulla, respectively. At all ages tested, B(2) receptor mRNA and protein levels were higher in the hypothalamus and adrenal glands of SHR compared to age-matched WKY rats. Among SHR, the mRNA level was increased in neurohypophysis with age, and no difference was found in the adenohypophysis (AH) between SHR and WKY rats.

CONCLUSION

The data demonstrate a specific localization and an upregulation of B(2) receptor expression in the hypothalamus and adrenal glands of SHR, providing an anatomical and molecular basis for a possible contributory role to bradykinin-induced hypersensitivity of cardiovascular responses. The increased B(2) receptor expression in the hypothalamus and adrenal glands may also play a role in the abnormalities of the HPA axis in SHR during the development of hypertension.

The hypothalamus and hypertension

Most forms of hypertension are associated with a wide variety of functional changes in the hypothalamus. Alterations in the following substances are discussed: catecholamines, acetylcholine, angiotensin II, natriuretic peptides, vasopressin, nitric oxide, serotonin, GABA, ouabain, neuropeptide Y, opioids, bradykinin, thyrotropin-releasing factor, vasoactive intestinal polypeptide, tachykinins, histamine, and corticotropin-releasing factor. Functional changes in these substances occur throughout the hypothalamus but are particularly prominent rostrally; most lead to an increase in sympathetic nervous activity which is responsible for the rise in arterial pressure. A few appear to be depressor compensatory changes. The majority of the hypothalamic changes begin as the pressure rises and are particularly prominent in the young rat; subsequently they tend to fluctuate and overall to diminish with age. It is proposed that, with the possible exception of the Dahl salt-sensitive rat, the hypothalamic changes associated with hypertension are caused by renal and intrathoracic cardiopulmonary afferent stimulation. Renal afferent stimulation occurs as a result of renal ischemia and trauma as in the reduced renal mass rat. It is suggested that afferents from the chest arise, at least in part, from the observed increase in left auricular pressure which, it is submitted, is due to the associated documented impaired ability to excrete sodium. It is proposed, therefore, that the hypothalamic changes in hypertension are a link in an integrated compensatory natriuretic response to the kidney's impaired ability to excrete sodium.

Pharmacological characterization of the cardiovascular responses elicited by kinin B(1) and B(2) receptor agonists in the spinal cord of streptozotocin-diabetic rats

Kinin receptor agonists and antagonists at the B(1) and B(2) receptors were injected intrathecally (i.t., at T-9 spinal cord level) to conscious unrestrained rats and their effects on mean arterial pressure (MAP) and heart rate (HR) were compared in streptozotocin (STZ)-diabetic rats (65 mg kg(-1) STZ, i.p. 3 weeks earlier) and aged-matched control rats. The B(1) receptor agonist, des-Arg(9)-Bradykinin (BK) (3.2 - 32.5 nmol), evoked dose-dependent increases in MAP and tachycardia during the first 10 min post-injection in STZ-diabetic rats only. The cardiovascular response to 6.5 nmol des-Arg(9)-BK was reversibly blocked by the prior i.t. injection of antagonists for the B(1) receptor ([des-Arg(10)]-Hoe 140, 650 pmol or [Leu(8)]-des-Arg(9)-BK, 65 nmol) and B(2) receptor (Hoe 140, 81 pmol or FR173657, 81 pmol) or by indomethacin (5 mg kg(-1), i.a.). The i.t. injection of BK (8.1 - 810 pmol) induced dose-dependent increases in MAP which were accompanied either by tachycardiac (STZ-diabetic rats) or bradycardiac (control rats) responses. The pressor response to BK was significantly greater in STZ-diabetic rats. The cardiovascular response to 81 pmol BK was reversibly blocked by 81 pmol Hoe 140 or 81 pmol FR173657 but not by B(1) receptor antagonists nor by indomethacin in STZ-diabetic rats. The data suggest that the activation of kinin B(1) receptor in the spinal cord of STZ-diabetic rats leads to cardiovascular changes through a prostaglandin mediated mechanism. Thus, this study affords an accessible model for studying the expression, the pharmacology and physiopathology of the B(1) receptor in the central nervous system.

Immunohistochemical localization of kininogen in rat spinal cord and brain

Kininogen localization has been determined by immunocytochemistry in rat spinal cord and brain using a kinin-directed kininogen monoclonal antibody. In the spinal cord, there were immunostained neurons and fibers in laminae I, II, VII, and IX, intensely stained fibers in the superficial layers of the dorsal horn, and immunoreactive glial and endothelial cells. Small neurons, satellite cells, and Schwann cells immunostained distinctly in the dorsal root ganglion. In the brain stem, there were immunoreactive neurons and fibers in the tractus solitarius and nucleus, trigeminal spinal tract and nuclei, periaqueductal gray matter, vestibular nuclei, cochlear nuclei, trapezoid body, medial geniculate nucleus, and red nucleus. Immunostained neurons and fibers were also found in cerebellum (dentate nucleus), cerebral cortex (layers III and V), hippocampus (pyramidal cell layer), and corpus callosum. Glia and endothelial cells stained in all brain regions. The widespread location of kininogen in neurons and their processes, as well as in glial and endothelial cells, indicates more than one functional role, including those proposed as a mediator, a calpain inhibitor, and a kinin precursor, in a variety of neural activities and responses.

Centrally bradykinin B2-receptor-induced hypertensive and positive chronotropic effects are mediated via activation of the sympathetic nervous system

OBJECTIVE

The presence of bradykinin B2 receptors in the cardiovascular regulatory centres of the brain indicates that increase in mean arterial pressure (MAP) and heart rate after intracerebroventricular (i.c.v.) injections of bradykinin is mediated via stimulation of sympathetic nervous system.

METHODS

Adult Wistar- Kyoto (WKY) rats were instrumented chronically with an i.c.v. cannula, and the catheters were placed into the femoral artery and vein. Increasing doses of bradykinin (1 -300 pmol) were given i.c.v. and (i) MAP and heart rate, (ii) plasma dopamine, noradrenaline and adrenaline, and (iii) plasma arginine vasopressin (AVP) levels were determined. In addition, following blockade of peripheral alpha1 -adrenoceptors with prazosin (50 and 250 microg/kg i.v.) beta1-adrenoceptors with atenolol (10 mg/kg i.v.) or V1 -receptors with TMe-AVP (Manning compound) (10 microg/kg i.c.v. and 100 microg/kg i.v.) the effects of bradykinin (100 pmol i.c.v.) on MAP and heart rate were determined.

RESULTS

Bradykinin increased MAP and heart rate dose-dependently. The pressor effects of 100 pmol bradykinin i.c.v. were completely blocked by pretreatment with the specific B2 receptor antagonist Hoe 140 (3 pmol, i.c.v.). There was no change in plasma dopamine, noradrenaline, adrenaline or AVP levels after increasing doses of bradykinin. However, peripheral blockade of alpha1- and beta1-adrenoceptors reduced the bradykinin-induced increase in MAP and heart rate, whereas central and peripheral V1 receptor blockade did not alter the cardiovascular responses to i.c.v. bradykinin.

CONCLUSION

Our data suggest that the hypertensive and positive chronotropic effects induced by i.c.v. bradykinin are due to stimulation of sympathoneuronal rather than sympathoadrenal pathway in vivo.

The bradykinin B1 receptor and the central regulation of blood pressure in spontaneously hypertensive rats

1. We evaluated if the brain bradykinin (BK) B1 receptor is involved in the regulation of blood pressure (BP) in conscious rats. 2. Basal mean BP and HR were 115 +/- 2 and 165 +/- 3 mmHg and 345 +/- 10 and 410 +/- 14 beats min in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR), respectively. Intracerebroventricular (i.c.v.) injection of 1 nmol B1 receptor agonist Lys-desArg9-BK significantly increased the BP of WKY and SHR by 7+/-1 and 19+/-2 mmHg, respectively. One nmol Sar[D-Phe8]-desArg9-BK, a kininase-resistant B1 agonist, increased the BP of WKY and SHR by 19+/-2 and 17+/-2 mmHg, respectively and reduced HR in both strains. 3. I.c.v. injection of 0.01 nmol B1 antagonists, LysLeu8-desArg9-BK or AcLys[D-betaNal7,Ile8]-desArg9-BK (R715), significantly decreased mean BP in SHR (by 9+/-2 mmHg the former and 14+/-3 mmHg the latter compound), but not in WKY. In SHR, the BP response to R715 was associated to tachycardia. 4. I.c.v. Captopril, a kininase inhibitor, increased the BP of SHR, this response being partially prevented by i.c.v. R715 and reversed into a vasodepressor effect by R715 in combination with the B2 antagonist Icatibant. 5. I.c.v. antisense oligodeoxynucleotides (ODNs) targeted to the B1 receptor mRNA decreased BP in SHR, but not in WKY. HR was not altered in either strain. Distribution of fluorescein-conjugated ODNs was detected in brain areas surrounding cerebral ventricles. 6. Our results indicate that the brain B1 receptor participates in the regulation of BP. Activation of the B1 receptor by kinin metabolites could participate in the pathogenesis of hypertension in SHR.

Pathophysiology of the kallikrein-kinin system in mammalian nervous tissue

The nervous system and peripheral tissues in mammals contain a large number of biologically active peptides and proteases that function as neurotransmitters or neuromodulators in the nervous system, as hormones or cellular mediators in peripheral tissue, and play a role in human neurological diseases. The existence and possible functional relevance of bradykinin and kallidin (the peptides), kallikreins (the proteolytic enzymes), and kininases (the peptidases) in neurophysiology and neuropathological states are discussed in this review. Tissue kallikrein, the major cellular kinin-generating enzyme, has been localised in various areas of the mammalian brain. Functionally, it may assist also in the normal turnover of brain proteins and the processing of peptide-hormones, neurotransmitters, and some of the nerve growth factors that are essential for normal neuronal function and synaptic transmission. A specific class of kininases, peptidases responsible for the rapid degradation of kinins, is considered to be identical to enkephalinase A. Additionally, kinins are known to mediate inflammation, a cardinal feature of which is pain, and the clearest evidence for a primary neuronal role exists so far in the activation by kinins of peripherally located nociceptive receptors on C-fibre terminals that transmit and modulate pain perception. Kinins are also important in vascular homeostasis, the release of excitatory amino acid neurotransmitters, and the modulation of cerebral cellular immunity. The two kinin receptors, B2 and B1, that modulate the cellular actions of kinins have been demonstrated in animal neural tissue, neural cells in culture, and various areas of the human brain. Their localisation in glial tissue and neural centres, important in the regulation of cardiovascular homeostasis and nociception, suggests that the kinin system may play a functional role in the nervous system.

Central delivery of human tissue kallikrein gene reduces blood pressure in hypertensive rats

The human tissue kallikrein gene, in the form of naked DNA (CMV-cHK) or an adenoviral vector (Ad.CMV-cHK), was directly delivered by intracerebroventricular injection into spontaneously hypertensive rats. Control rats received the same amount of vector DNA (pcDNA3) or adenoviral vector (Ad.CMV-LacZ) carrying the lacZ gene. A single injection of the human tissue kallikrein gene caused a rapid and prolonged blood pressure-lowering effect that began 1 day post injection and the effect lasted for more than 7 days. The expression of human tissue kallikrein and its mRNA was identified in the cortex, cerebellum, brain stem, hippocampus and hypothalamus. Cellular localization of beta-galactosidase was detected by X-gal staining in the thalamus, hypothalamus and third ventricle in rats injected with Ad.CMV-LacZ. This suggests that the tissue kallikrein-kinin system may function in the central control of blood pressure homeostasis.

Pressor effect mediated by bradykinin in the paratrigeminal nucleus of the rat

1. The participation of the paratrigeminal nucleus (Pa5) in the pressor response produced by bradykinin in the dorsolateral medulla of rats was investigated. The microinjection of 6 pmol of bradykinin directly over the paratrigeminal nucleus of unanaesthetized rats produced a significant increase in arterial pressure and a moderate increase in heart rate. 2. Bradykinin microinjections in different sites surrounding the Pa5 compromising the external cuneate nucleus, the trigeminal nucleus, the lateral and ventral spinal trigeminal tract and the dorsal trigeminal tract rostral and caudal to the Pa5 did not elicit significant pressor responses. In contrast, microinjections in the paratrigeminal nucleus produced pressor effects. Injections in the dorsolateral medulla directly over the paratrigeminal nucleus produced larger responses than when injections were made in the nucleus. Saline injections in the different nuclei did not produce pressor effects. 3. Neurochemical lesioning of the Pa5, with microinjections of ibotenic acid in the Pa5, abolished the pressor response to bradykinin injected over the lesioned nucleus. The effect was present, however, when bradykinin was injected on the contralateral side to the lesion, over the intact nucleus of the same animal. Pretreatment with capsaicin (injected in the lateral cerebral ventricle), which causes selective degeneration of afferent sensory fibres, did not alter the pressor effect of bradykinin injected over the paratrigeminal nucleus. 4. Dose-related responses were produced by different concentrations of bradykinin (0.6-1.8 pmol) microinjected over the nucleus. The bradykinin receptor antagonist HOE 140, injected over the paratrigeminal nucleus 30 min earlier, abolished the pressor response caused by bradykinin. 5. Low doses of bradykinin injected in or directly over the paratrigeminal nucleus increased arterial pressure and caused a small increase in heart rate by stimulating kinin receptors of the paratrigeminal nucleus in the dorsolateral medulla of awake and unrestrained rats. The pattern of the response was consistent with that of sympathetic stimulation. The paratrigeminal nucleus, which receives primary afferents and projects to the nucleus tractus solitarii and the rostral ventral lateral medulla, may be positioned as relay nucleus possibly connecting sensory input to structures that regulate blood pressure.

Distribution of bradykinin B2 receptors in sheep brain and spinal cord visualized by in vitro autoradiography

Bradykinin B2 receptors were localized in the sheep brain and spinal cord by quantitative in vitro autoradiography using a radiolabelled and specific bradykinin B2 receptor antagonist analogue, 3-4-hydroxyphenyl-propionyl-D-Arg0-[Hyp3,Thi5,D-Tic 7,Oic8]bradykinin, (HPP-HOE 140). This radioligand displays high affinity and specificity for bradykinin B2 receptors. The respective K(i) values of 0.32, 1.37 and 156 nM were obtained for bradykinin, HOE140 and D-Arg[Hyp3,D-Phe7,Leu8]bradykinin competing for radioligand binding to lamina II of sheep spinal cord sections. Using this radioligand, we have demonstrated the distribution of bradykinin B2 receptors in many brain regions which have not been previously reported. The highest density of bradykinin B2 receptors occur in the pleoglial periaqueductal gray, oculomotor and trochlear nuclei and the circumventricular organs. Moderate densities of receptors occur in the substantia nigra, particularly the reticular part, the posterior thalamic and subthalamic nuclei, zona incerta, the red and pontine nuclei, some of the pretectal nuclei and in discrete layers of the superior colliculus. In the hindbrain, moderate levels of bradykinin B2 receptor binding occur in the nucleus of the solitary tract, and in spinal trigeminal, inferior olivary, cuneate and vestibular nuclei. Laminae II, X and dorsal root ganglia display the most striking binding densities in the spinal cord, while the remainder of the dorsal and ventral horn display a low and diffuse density of binding. Bradykinin B2 receptors are extensively distributed throughout the sheep brain and spinal cord, not only to sensory areas but also to areas involved in motor activity.

Localization of bradykinin-like immunoreactivity in the rat spinal cord: effects of capsaicin, melittin, dorsal rhizotomy and peripheral axotomy

A putative role for bradykinin has been proposed in the processing of sensory information at the level of the spinal cord. Autoradiographic studies have demonstrated the presence of B2 kinin receptor binding sites in superficial laminae of the dorsal horn and a down-regulation of those receptors in rat models of pain injury. In this study, classical immunocytochemistry and confocal microscopy immunofluorescence were used first to localize bradykinin-like immunoreactivity in all major spinal cord segments of naive rats; second, to assess bradykinin-like immunoreactivity changes that occur in animals subjected to various chemical treatments and surgical lesions. High densities of bradykinin-like immunoreactivity were observed in motoneuron of the ventral horn, deeper laminae and nucleus dorsalis of the dorsal horn. Higher magnification of ventral horn showed strong immunostaining of motoneuron perikaryas and their proximal processes. Two types of bradykinin-like immunoreactivity immunostained cellular bodies were observed in deeper laminae of the dorsal horn. These interneurons, morphologically corresponding to islets and antenna-type cells project dendrites to adjacent laminae. Furthermore, numerous strongly marked dendrites, transversally cut, suggest the presence of projection neurons to higher cervical centres. Following unilateral lumbar dorsal rhizotomy (L1-L6) or peripheral lesion of the sciatic nerve, important increases of bradykinin-like immunoreactivity were found in laminae III and IV of the ipsilateral dorsal horn. In contrast, significant decreases of immunodeposits were observed in both cell bodies and numerous dendrites of motoneuron surrounding neuropil. Specific destructions of sensory afferent fibres with capsaicin or selective activation of kallikreins with melittin caused increases of bradykinin-like immunoreactivity in both the dorsal and ventral horns of the spinal cord. These results which demonstrate the cellular localization of bradykinin-like immunoreactivity in both dorsal and ventral horns of the rat spinal cord, further reveal the plasticity of this non-sensory peptidergic system following various chemical and surgical treatments. Hence, these anatomical findings along with earlier functional and receptor autoradiographic studies reinforce the putative role of bradykinin in sensory function.

Antisense inhibition of the brain kallikrein-kinin system

We used antisense oligodeoxynucleotide (ODN) strategy, based on interference of information flow from gene to protein, to determine the role of kininogen and bradykinin B2 receptor genes in the pathogenesis of genetic hypertension in rats. Mean blood pressure of 9-week-old spontaneously hypertensive rats (SHR) increased 4 hours after acute intracerebroventricular injection of synthetic 18-mer antisense ODNs targeting the translation initiation codon of kininogen mRNA (from 164 +/- 5 to 181 +/- 4 mm Hg, P < .01) or bradykinin B2 receptor mRNA (from 161 +/- 5 to 185 +/- 8 mm Hg, P < .01) and then returned to basal levels within 24 hours. Prolonged vasopressor effects were observed after repeated injections of antisense ODN targeting kininogen mRNA. Antisense ODNs to kininogen and B2 receptor mRNAs increased blood pressure of normotensive Wistar-Kyoto rats only slightly compared with SHR (from 116 +/- 3 to 124 +/- 1 and from 116 +/- 2 to 126 +/- 4 mm Hg, respectively; P < .05). Cardiovascular responses were confirmed by the use of antisense ODNs targeted to bind to different non-overlapping regions of kininogen or B2 receptor mRNA. Microinjection of antisense ODN to B2 receptor mRNA into the nucleus tractus solitarii increased mean blood pressure in SHR and prevented the vasodepressor effect induced by intranuclear microinjection of bradykinin. No significant change in mean blood pressure was induced in either strain by intravenous injection of antisense ODNs or by central injection of sense or scrambled ODNs. A strong fluorescent signal was detected at the level of the hippocampus, thalamus, hypothalamus periventricularis, midbrain, and cerebrum 1 hour after central injection of fluorescein isothiocyanate-conjugated antisense ODNs. Kininogen levels were significantly lower in the brain of rats given intracerebroventricular antisense kininogen ODN compared with controls. Our results indicate that the brain kallikrein-kinin system plays a role in the central regulation of blood pressure and suggest that this system may exert a protective action against further elevations of blood pressure levels in SHR.

Cardiovascular effects produced by bradykinin microinjection into the nucleus tractus solitarii of anesthetized rats

In this study, we characterized the cardiovascular effects produced by microinjection of doses in the femtomole range of bradykinin (BK) into the nucleus tractus solitarii of male Wistar rats (230-280 g, n = 120) anesthetized with urethane (1.2 g/kg, i.p.). Microinjections of BK (1, 10, 100 fmol, and 1 and 10 pmol, in 50 nl) or vehicle (NaCl, 0.9%) were made by using a triple-barreled glass micropipette into the medial nTS (0.4 mm anterior, 0.3 mm lateral to the obex and 0.3 mm deep from the dorsal surface). Microinjection of BK produced a shallow dose-dependent decrease in mean arterial pressure and heart rate reaching -18 +/- 6 mmHg and -21 +/- 5 beats/min, with the dose of 10 pmol. The peripheral mechanism of these effects, tested in animals treated with methylatropine (2 mg/kg, i.v.), or propranolol (2 mg/kg, i.v.) or prazosin (30 micrograms/kg, i.v.), was shown to be mainly dependent on an increase in vagal efferent activity for bradycardia and a decrease in sympathetic activity for hypotension. In order to investigate the receptor subtype involved in these effects, BK was microinjected into the nTS before and after the injection of the B1 receptor antagonist, Des-Arg9-Leu8-BK (DALBK) (11.5 pmol) or before and after the B2 receptor antagonist, HOE-140 (7.7 pmol). The cardiovascular effects of BK were significantly attenuated by the microinjection of HOE-140 and DALBK into the nTS. The effect of BK microinjected into the nTS on the baroreflex modulation was also investigated. While BK produced a significant facilitation of the baroreflex, HOE-140 and DALBK produced a significant attenuation of the baroreceptor control of heart rate. Taken together, the data presented in this study indicate the nTS as a site, in the central nervous system, for the modulatory effect of BK on the central cardiovascular control.

Hypertensive effect of tissue kallikrein in rostral ventrolateral medulla is mediated by brain kinins

Microinjections of kallikrein, 0.5-2.0 units, in the rostral ventrolateral medulla (RVLM) of brain increased arterial pressure in Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). This effect was significantly greater in SHR. The kinin B2 receptor antagonist icatibant (Hoe 140) blocked the hypertensive responses to kallikrein in both groups and caused greater hypotension and bradycardia in SHR. These results suggest that local kinins in the RVLM act to alter cardiovascular function and may be involved in the maintenance of blood pressure in the SHR.

Brain kallikrein-kinin system abnormalities in spontaneously hypertensive rats

The objective of the present study was to determine whether the brain kallikrein-kinin system differs between spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) and if so, whether any detected differences occur before the development of hypertension in SHR. We measured cerebrospinal fluid levels of various components of the system in adult and young prehypertensive SHR and WKY. Cerebrospinal fluid kinin concentration and appearance rate were higher in SHR. Cerebrospinal fluid active kallikrein level and kininogenase activity were also higher in adult SHR. In addition, cerebrospinal fluid kinin concentration and appearance rate were higher in prehypertensive, 5- to 6-week-old SHR compared with age-matched WKY. However, no differences in cerebrospinal fluid kallikrein or kininogenase activity were observed between the two strains of young rats. Cerebrospinal fluid kinin concentration was higher in young versus adult rats of the same strain. In WKY, cerebrospinal fluid kallikrein also decreased with age although cerebrospinal fluid kallikrein concentration did not decrease in young and adult SHR. Together, these data suggest that there is a hyperactive kallikrein-kinin system in the brain of SHR that may contribute to the hypertensive state in this animal model.

Bradykinin modulation of alpha 2-adrenoceptors in the nucleus tractus solitarii of the rat. An in vitro autoradiographical study

The existence of an interaction between bradykinin (Bk) receptors and the alpha 2-adrenoceptors were evaluated by means of quantitative receptor autoradiography in the nucleus tractus solitarii (NTS) of the rat. In competition experiments using L-noradrenaline (0.1 nM to 10 microM) against [3H]p-aminoclonidine ([3H]PAC) (10 nM) it was observed that Bk produced an increase in the IC50 value of L-noradrenaline in a concentration response manner, which reached a maximum of about 100% with 10 nM of the peptide associated with a small decrease in the B0 value (15%). In saturation experiments Bk promoted a significant increase in the KD value of [3H]PAC (60%) and a decrease in the Bmax value (36%). The specific Bk B2 receptor antagonist HOE-140 fully counteracted the effect of Bk on the alpha 2-adrenoceptors as analyzed by the competition experiments. Furthermore, des-Arg9-Bk, a Bk analog which exhibits selective agonist activity to the Bk B1 receptor subtype did not produce any effect on the alpha 2-adrenoceptors, suggesting that the Bk B2 receptor subtype may be mediating the Bk action on the alpha 2-adrenoceptors in the NTS. The effect of Bk (10 nM) was analyzed together with GTP (0.1 nM) in competition experiments and no change in the ability of L-noradrenaline to compete for [3H]PAC binding sites was observed in the presence of GTP, suggesting that the receptor interaction between the Bk B2 receptors and the alpha 2-adrenoceptors may be a G-protein dependent mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinins and kinin receptors in the nervous system

Kinins, including bradykinin and kallidin, are peptides that are produced and act at the site of tissue injury or inflammation. They induce a variety of effects via the activation of specific B1 or B2 receptors that are coupled to a number of biochemical transduction mechanisms. In the periphery the actions of kinins include vasodilatation, increased vascular permeability and the stimulation of immune cells and peptide-containing sensory neurones to induce pain and a number of neuropeptide-induced reflexes. Mechanisms for kinin synthesis are also present in the CNS where kinins are likely to initiate a similar cascade of events, including an increase in blood flow and plasma leakage. Kinins are potent stimulators of neural and neuroglial tissues to induce the synthesis and release of other pro-inflammatory mediators such as prostanoids and cytotoxins (cytokines, free radicals, nitric oxide). These events lead to neural tissue damage as well as long lasting disturbances in blood-brain barrier function. Animal models for CNS trauma and ischaemia show that increases in kinin activity can be reversed either by kinin receptor antagonists or by the inhibition of kinin production. A number of other central actions have been attributed to kinins including an effect on pain signalling, both within the brain (which may be related to vascular headache) and within the spinal dorsal horn where primary afferent nociceptors can be stimulated. Kinins also appear to play a role in cardiovascular regulation especially during chronic spontaneous hypertension. Presently, however, direct evidence is lacking for the release of kinins in pathophysiological conditions of the CNS and it is not known whether spinal or central neurones, other than afferent nerve terminals, are sensitive to kinins. A more detailed examination of the effects of kinins and their central pharmacology is necessary. It is also important to determine whether the inhibition of kinin activity will alleviate CNS inflammation and whether kinin receptor antagonists are useful in pathological conditions of the CNS.

Cardiovascular effects of brain kinin receptor blockade in spontaneously hypertensive rats

We studied the role of brain kinins in the regulation of cardiovascular function. Intracerebroventricular injection of 380 pmol bradykinin increased mean blood pressure by 20 +/- 2 mm Hg (P < .01) in normotensive Wistar-Kyoto (WKY) rats. Complete inhibition of this effect was achieved with intracerebroventricular administration of the newly synthesized, long-acting B2 receptor antagonist D-Arg,[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin (Hoe 140). On a molar basis, Hoe 140 was two orders of magnitude more potent than antagonists of the first generation. Baroreceptor sensitivity, estimated as the heart rate response to blood pressure changes induced by intravenous injection of phenylephrine or sodium nitroprusside, was not altered by Hoe 140 in WKY rats. In spontaneously hypertensive rats (SHR), baroreceptor reflex sensitivity to increments in mean blood pressure was reduced by Hoe 140 (mean slope value: -0.47 +/- 0.07 versus -0.92 +/- 0.13 beats per minute per millimeter of mercury in controls, P < .05). Hoe 140 did not affect the tachycardic component of the baroreceptor reflex. Two-week intracerebroventricular infusion of Hoe 140 did not alter systolic blood pressure or heart rate in WKY rats. In SHR, systolic blood pressure increased (P < .01) similarly during the infusion of Hoe 140 or vehicle (from 174 +/- 6 to 220 +/- 5 mm Hg and 178 +/- 4 to 210 +/- 4 mm Hg at 2 weeks, respectively), whereas heart rate did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

Rostral ventrolateral medulla as a site for the central hypertensive action of kinins

In the present study, we focused on the rostral ventrolateral medulla as a possible site of action for kinins because of its established importance in the central regulation of the cardiovascular system. Unilateral microinjections of 100 pmol to 4 nmol bradykinin into the rostral ventrolateral medulla produced dose-dependent increases in mean arterial pressure in Sprague-Dawley (SD) rats, Wistar-Kyoto (WKY) rats, and spontaneously hypertensive rats (SHR). The dose-response curves for the hypertensive responses to bradykinin in SD and WKY rats were essentially the same, whereas the hypertensive effect of bradykinin was significantly greater in SHR than in either SD or WKY rats. The kinin B2 receptor antagonists D-Arg0,Hyp3,Thi5,8,D-Phe7-bradykinin and Hoe 140 inhibited the hypertensive responses to bradykinin in both SHR and WKY rats. The hypertensive effect of 500 pmol bradykinin was reduced 65 +/- 5% after 4 nmol of D-Arg0, Hyp3,Thi5,8,D-Phe7-bradykinin in SHR and 50 +/- 16% in WKY rats, whereas 1 nmol Hoe 140 abolished the hypertensive effect of 500 pmol bradykinin injected into the rostral ventrolateral medulla. Microinjection of D-Arg0,Hyp3,Thi5,8,D-Phe7-bradykinin produced prolonged dose-dependent decreases in mean arterial pressure and heart rate. Blood pressure decreased 70 +/- 8 mm Hg and heart rate decreased 49 +/- 9 beats per minute in SHR, whereas in WKY rats mean arterial pressure decreased 12 +/- 4 mm Hg, with no change in heart rate. In a similar fashion, Hoe 140 caused a 51 +/- 7 and 17 +/- 3 mm Hg reduction in blood pressure in SHR and WKY rats, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of chronic intracerebroventricular dexamethasone on blood pressure in normotensive rats

We report herein the effects of long-term intracerebroventricular (icv) dexamethasone in normotensive rats. Dexamethasone (0.002, 0.02, 0.2, and 2.0 micrograms/day) or its vehicle (0 microgram/day, n = 8 each group) was infused icv via subcutaneous miniosmotic pumps (Alzet 2002) for 24 days in male conscious Wistar rats (weight range 190-240 g). Eighteen Wistar rats (weight range 200-230 g) received either vehicle or dexamethasone (0.2 and 2 micrograms/day) subcutaneously (sc) for 24 days. Systolic blood pressure (SBP, tail cuff) and body weight were recorded two times a week in the trained conscious rats. Dexamethasone (0.2 micrograms/day icv) exerted a progressive significant decrease in SBP over 24 days compared with both rats receiving vehicle and to pretreatment values (108 +/- 4 vs. 122 +/- 4 and 120 +/- 2 mmHg, P < 0.01). As previously reported, a significant increase in SBP was observed after 6 days in rats given 2 micrograms/day sc dexamethasone compared with both rats receiving vehicle and to pretreatment values (150 +/- 4 vs. 122 +/- 2 and 120 +/- 2 mmHg, P < 0.01 for both). Thereafter, SBP remained at plateau for the entire experiment. A similar significant decrease in body weight gain with age was observed in rats given icv or sc dexamethasone. Our data suggest that the glucocorticoid receptors exert opposite effects on blood pressure when stimulated at the brain level instead of at the peripheral vascular level.

Chronic central administration of enalaprilat lowers blood pressure in stroke-prone spontaneously hypertensive rats

Earlier studies on the cardiovascular effects of intracerebroventricular (i.c.v.) administration of angiotensin converting enzyme (ACE) inhibitors implicate angiotensin II (AII) present in the central nervous system in the pathogenesis of hypertension. We have now examined whether central AII contributes to the maintenance of established hypertension in adult stroke-prone spontaneously hypertensive rats (SHRSP). The ACE inhibitor, enalaprilat, was infused i.c.v. for two weeks at a rate of 5 micrograms/h via osmotic minipumps. Control rats were either untreated or infused with saline. Mean arterial pressure (MAP), measured via an indwelling catheter, fell within 24 h in the enalaprilat-treated rats and remained at least 30 mmHg lower than in controls. This difference persisted after intravenous (i.v.) administration of a vasopressin (AVP) antagonist but was eliminated by subsequent ganglion blockade with i.v. pentolinium. Without prior administration of the AVP antagonist, however, the reductions of MAP after pentolinium were smaller. The reduction was still attenuated in treated rats compared with controls but there was a significant difference in the residual MAP. Circulating catecholamine levels were reduced by central ACE inhibition. However, pressor responsiveness to i.v. phenylephrine was unaffected. The results suggest that, in SHRSP, central ACE inhibition lowers blood pressure by reducing sympathetic outflow, implying that central AII has a tonic sympathoexcitatory effect in this strain.

Cardiovascular responses elicited by intrathecal kinins in the conscious rat

In the conscious, unrestrained rat, intrathecal (i.t.) injection of 0.81 pmol-81 nmol bradykinin (BK), kallidin (KD) and T-kinin at the T-9 spinal cord level produced transient (less than 10 min) increases in mean arterial pressure (MAP) and longer lasting decreases in heart rate (HR). These effects were dose-dependent and similar with respect to intensity and time course for the three kinins. The des-Arg9-BK fragment, a selective agonist for B1 receptors, was active only at 81 nmol. The pressor response induced by BK was enhanced by propranolol and by transection of the cervical spinal cord but was converted to a vasodepressor effect by prazosin. The bradycardia was converted to tachycardia by prazosin, atropine, pentolinium, capsaicin and in spinal transected rats. However, the cardiovascular responses to BK remained unaffected by diphenhydramine plus cimetidine, morphine, indomethacin, adrenal medullectomy, i.t. idazoxan and after bulbospinal noradrenaline deafferentation with 6-hydroxydopamine. These results suggest that the increase in MAP induced by i.t. BK is mediated by the sympathoadrenal system while the decrease in HR is ascribable to a vagal reflex involving sensory C-fibers and a spinobulbar pathway. This pharmacological evidence therefore supports a role for kinins in cardiovascular regulation in the spinal cord.

The kallikrein-kinin system in the rat hypothalamus. Immunohistochemical localization of high molecular weight kininogen and T kininogen in different neuronal systems

High molecular weight kininogen (HKg) and T kininogen (TKg) were detected and localized by immunocytochemistry in adult rat hypothalamus. In addition, kininogens were measured by their direct radioimmunoassay (RIA) or by indirect estimation of kinins released after trypsin hydrolysis and high pressure liquid chromatography (HPLC) separation of bradykinin (BK) and T kinin. A specific HKg immunoreactivity demonstrated with antibodies directed against the light chain (LC) of HKg was colocated with SRIF in neurons of hypothalamic periventricular area (PVA) projecting to external zone (ZE) of median eminence (ME). Heavy chain (HC) immunoreactivity which could be related to HKg or to low molecular weight kininogen (LKg) was detected in some other systems: i) parvocellular neurons of suprachiasmatic (SCN) and arcuate nuclei containing SRIF, ii) magnocellular neurons (mostly oxytocinergic) of paraventricular (PVN) and supraoptic (SON) nuclei, iii) neurons of dorsomedian and lateral hypothalamic areas. TKg immunostaining was restricted to magnocellular neurons of PVN, SON, accessory nuclei (mostly vasopressinergic) and to parvocellular neurons of SCN (vasopressinergic). TKg projections are directed towards the internal zone (ZI) of ME, but very few immunoreactive terminals are detectable in neurohypophysis. TKg staining parallels with vasopressin during water deprivation, and is undetectable in homozygous Brattleboro rats. In some magnocellular neurons, TKg and HC (related to HKg or LKg) are coexpressed. TKg, was also detected in hypothalamus and cerebellum extracts by direct RIA, and BK and T kinin were identified after trypsin hydrolysis. HKg and LKg can act as precursor of BK which can play a physiological role as releasing factor, neuromodulator--neurotransmitter,--or modulator of local microcirculation in hypothalamus. The three kininogens are also potent thiolprotease inhibitors which could modulate both the maturation processes of peptidic hormones and their inactivation and catabolism.