Evidence for a possible role of the brain kallikrein-kinin system in the modulation of the cerebral circulation

Mathematical modelling of blood-brain barrier failure and oedema

Injuries such as traumatic brain injury and stroke can result in increased blood-brain barrier (BBB) permeability. This increase may lead to water accumulation in the brain tissue resulting in vasogenic oedema. Although the initial injury may be localized, the resulting oedema causes mechanical damage and compression of the vasculature beyond the original injury site. We employ a biphasic mixture model to investigate the consequences of BBB permeability changes within a region of brain tissue and the onset of vasogenic oedema. We find that such localized changes can indeed result in brain tissue swelling and suggest that the type of damage that results (stress damage or strain damage) depends on the ability of the brain to clear oedema fluid.

Neuroprotective effects of a postischemic treatment with a bradykinin B2 receptor antagonist in a rat model of temporary focal cerebral ischemia

Bradykinin, an endogenous nonapeptide produced by activation of the kallikrein-kinin system, promotes neuronal tissue damage as well as disturbances in blood-brain barrier function through activation of B2 receptors. In a rat model of focal cerebral ischemia, blockade of B2 receptors before initiation of ischemia with the B2 receptor antagonist, LF 16-0687 Ms, afforded substantial neuroprotection. In order to assess the potential clinical value of this approach, we evaluated the effect of LF 16-0687 Ms given at reperfusion following focal cerebral ischemia on local cerebral blood flow (LCBF), neurological outcome, and infarct size. Sprague-Dawley rats were subjected to MCA occlusion for 90 min by an intraluminal filament. Animals were assigned to one of four treatment arms (n = 7 each): (1) vehicle, (2) LF 16-0687 Ms (1.0 mg/kg/day), (3) LF 16-0687 Ms (3.0 mg/kg/day), or (4) LF 16-0687 Ms (10.0 mg/kg/day) given at reperfusion and repetitively over 2 days. Neurological recovery was examined daily, and infarct volume was assessed histologically on day 7 after ischemia. Physiological parameters and local CBF were not influenced by the treatment. Significant improvement of neurological outcome was observed on postischemic day 3 in animals receiving 1.0 and 3.0 mg/kg/day of LF 16-0687 Ms (P < 0.05). Inhibition of B2 receptors significantly reduced infarct volume in all treated animals predominantly in the cortex. B2 receptor blockade with LF 16-0687 Ms showed neuroprotective effectiveness even when therapy was initiated upon reperfusion, i.e. 90 min after induction of ischemia. Therefore, blockade of B2 receptors seems to be a promising therapeutic approach after focal cerebral ischemia, which deserves further experimental and clinical evaluation.

The effect of n-3 polyunsaturated fatty acid-rich diets on cognitive and cerebrovascular parameters in chronic cerebral hypoperfusion

Western diets consist to a large part of n-6 polyunsaturated fatty acids (PUFAs). These n-6 PUFAs and their conversion products favor immune and inflammatory reactions and compromise vasoregulation, which can contribute to the development of dementia. Recent epidemiological studies associated dementia, particularly the type accompanied by a vascular component, with high, saturated dietary fat intake. Conversely, high fish consumption (a source of long chain n-3 PUFAs) was related to a reduced risk for cognitive decline. Therefore we studied the effects of long chain n-3 PUFAs in rats with bilateral occlusion of the common carotid arteries (2VO), which mimics cerebral hypoperfusion, a risk factor for dementia. Male Wistar rats received experimental diets with a decreased (n-6)/(n-3) ratio from weaning on. At the age of 3 months, the animals underwent 2VO surgery. The rats were tested in the elevated plus maze, an active avoidance paradigm and the Morris water maze (at different survival times). Following behavioral testing, the animals were sacrificed at the age of 7 months. The frontoparietal cortex was analyzed for capillary ultrastructure with electron microscopy. No effects of cerebral hypoperfusion or diet were found on elevated plus maze and active avoidance, while spatial memory in the Morris maze was compromised due to cerebral hypoperfusion under placebo dietary conditions. n-3 PUFA supplementation in combination with extra additives improved the performance of the 2VO animals. The number of endothelial mitochondria, as well as the ratio of microvessels with degenerative pericytes appeared to be lower due to long chain n-3 PUFAs. These results may indicate an improved condition of the blood-brain barrier.

Bradykinin 2 receptor antagonist LF 16-0687Ms reduces posttraumatic brain edema

Activation of the kallikrein-kinin system contributes to traumatic brain edema formation. Inhibition of bradykinin 2 (B2) receptors has been shown to successfully reduce brain edema formation. The purpose of this study was to investigate the protective effect of the novel nonpeptide B2 receptor antagonist LF 16-0687Ms in brain-injured rats. Contusion was produced in forty rats by controlled cortical impact injury. Five minutes after trauma rats received a single dose of 0, 3, or 30 mg/kg of LF 16-0687Ms. After 24 hours brain swelling and hemispheric water content were determined. Brain swelling was significantly decreased by 25% in the low and 27% in the high dose group compared to controls (p < 0.03). Water content of the traumatized hemisphere tended to be decreased (80.2 +/- 0.1 vs. 80.4 +/- 0.1%) while water content of the non-traumatized hemispheres tended to be increased after administering LF 16.0687Ms (79.3 +/- 0.1 vs. 79.0 +/- 0.1%). Single administration of the novel nonpeptide B2 receptor antagonist LF 16-0687Ms significantly reduces brain swelling. The missing significant reduction in water content of the traumatized hemisphere, however, could be related to an unspecific increase in water content due to LF 16.0687Ms as suggested by increased water content in the non-traumatized hemisphere.

Significant reduction in brain swelling by administration of nonpeptide kinin B2 receptor antagonist LF 16-0687Ms after controlled cortical impact injury in rats

OBJECT

Identification of new therapeutic agents aimed at attenuating posttraumatic brain edema formation remains an unresolved challenge. Among others, activation of bradykinin B2 receptors is known to mediate the formation of brain edema. The purpose of this study was to investigate the protective effect of the novel nonpeptide B2 receptor antagonist, LF 16-0687Ms, in brain-injured rats.

METHODS

Focal contusion was produced by controlled cortical impact injury. Five minutes after trauma, the rats received a single dose of no, low- (3 mg/kg body weight), or high- (30 mg/kg) dose LF 16-0687Ms. After 24 hours, the amount of brain swelling and hemispheric water content were determined. Low and high doses of LF 16-0687Ms significantly reduced brain swelling by 25% and 27%, respectively (p < 0.03). Hemispheric water content tended to be increased in the nontraumatized hemisphere. In a subsequent series of 10 rats, cisternal cerebrospinal fluid (CSF) samples were collected to determine whether changes in substances associated with edema formation could clarify why LF 16-0687Ms increases water content. For this, the volume regulator amino acid taurine, the excitatory transmitter glutamate, and the adenosine triphosphate degradation products hypoxanthine and xanthine were measured. In CSF, the levels of taurine, hypoxanthine, and xanthine were significantly decreased following a single administration of LF 16-0687Ms (p < 0.005); the level of glutamate, however, was double that found in control animals (p < 0.05).

CONCLUSIONS

Using the present study design, a single administration of LF 16-0687Ms successfully reduced posttraumatic brain swelling. The decreased levels of taurine, hypoxanthine, and xanthine may reflect reduced posttraumatic brain edema, whereas the increased level of glutamate could account for the elevated water content observed in the nontraumatized hemisphere.

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.

Angiotensin II-stimulated nitric oxide release from porcine pulmonary endothelium is mediated by angiotensin IV

In this study, a nitric oxide (NO) sensor was used to examine the ability of angiotensin II (AngII), AngIV, and bradykinin (Bk) to stimulate NO release from porcine pulmonary artery (PPAE) and porcine aortic endothelial (PAE) cells and to explore the mechanism of the AngII-stimulated NO release. Physiologic concentrations of AngII, but not Bk, caused release of NO from PPAE cells. In contrast, Bk, but not AngII, stimulated NO release from PAE cells. AngIII-stimulated NO release from PPAE cells required extracellular L-arginine and was inhibited by L-nitro-arginine methyl ester. AT1 and AT2 receptor inhibition had no affect on AngII-mediated NO release or activation of NO synthase (NOS). AngIV, an AngII metabolite with binding sites that are pharmacologically distinct from the classic AngII receptors, stimulated considerably greater NO release and greater endothelial-type constitutive NOS activity than the same amount of AngII. The AngIV receptor antagonist, divalinal AngIV, blocked both AngII- and AngIV-mediated NO release as well as NOS activation. The results demonstrate that AngIV and the AngIV receptor are responsible, at least in part, for AngII-stimulated NO release and the associated endothelium-dependent vasorelaxation. Furthermore, these results suggest that differences exist in both AngII- and Bk-mediated NO release between PPAE and PAE cells, which may reflect important differences in response to these hormones between vascular beds.

Peptide aldehyde inhibitors of the kallikreins: an investigation of subsite interactions with tripeptides containing structural variations at the amino terminus

A series of tripeptide aldehyde derivatives containing variations at the P3 subsite and the amino terminus has been prepared and evaluated for trypsin-like serine protease inhibition. These compounds exhibit strong in vitro inhibition of human plasma kallikrein (HPK), porcine pancreatic kallikrein (PPK) and human plasmin (HP). As suspected from an examination of a related crystal structure, the presence of a hydrophobic residue (adamantyl) at the amino terminus dramatically improves the binding to PPK. The adamantyl group, however, represents a peak in binding; larger residues cause the binding to be reduced, and thus are less well accommodated in this subsite. Although both HP and HPK also can accept large molecular volume at the amino terminus, they do not exhibit the same preference for large residues at this subsite that is demonstrated by PPK. Selectivity differences also are observed with P3 subsite substitution; with PPK preferring a bulky, but compact side-chain (t-butyl) and HP and HPK preferring a more extended (e.g. benzyl) group.

Distribution of tonin- and kallikrein-like activities in rat brain

Tonin- and kallikrein-like activities were investigated in different regions of the rat brain. The highest values of specific tonin activity, expressed as picomoles of angiotensin II liberated per minute per milligram of protein, were found in the neurohypophysis (359 +/- 190) and in the archicerebellum (200 +/- 68). The highest level of total tonin activity (picomoles of angiotensin II liberated per minute) was observed in the archicerebellum (902 +/- 308) which retained 97% of total tonin activity of whole cerebellum. Tonin activity was not detected in the cortex of cerebellum and in the choroid plexus. Low to intermediate values of specific (1.09 +/- 0.33 to 5.32 +/- 2.37) and total (1.38 +/- 0.55 to 93.00 +/- 49.30) tonin activity were observed in adenohypophysis, cerebellar nuclei, hypothalamus, thalamus, midbrain, pons, medulla and neurohypophysis. The lowest values of specific (0.11 +/- 0.05) and total (0.69 +/- 0.31) activities were observed in the hippocampus. Kallikrein-like activity was expressed as picomoles of p-nitroaniline liberated per minute per milligram of protein. No activity was detected in the neurohypophysis. For other regions, the values of the specific activity ranged between 72 +/- 18 and 282 +/- 14 except for the choroid plexus which was 5 +/- 2. The total kallikrein activity was also homogeneous ranging from 330 +/- 100 to 1870 +/- 112. For the choroid plexus and adenohypophysis the total kallikrein activity was 2.0 +/- 0.8 and 27 +/- 11, respectively.

The inflammatory response and extracorporeal circulation

Defining the cause of organ and tissue dysfunction associated with the use of perfusion systems will produce methods of prevention or treatment and improve patient outcome. The problem is the plethora of triggers, effectors, and mediators in this process, which can now be measured. Each new measureable compound becomes another biochemical "smoking gun" without physiological data to show any relevance to the human problem. This review critically compares and contrasts the role of certain, largely novel, initiation, amplification, and cytotoxic mechanisms in the inflammatory response of the myocardium and pulmonary systems after a period of cardiopulmonary bypass. The available evidence strongly points to the process being different for each of these tissue beds. These data suggest that ensuring normal lung and heart functions after surgery will require separate therapeutic strategies.

Role of activation of bradykinin B2 receptors in disruption of the blood-brain barrier during acute hypertension

Cellular mechanisms which account for disruption the blood-brain barrier during acute hypertension are not clear. The goal of this study was to determine the role of synthesis/release of bradykinin to activate B2 receptors in disruption of the blood-brain barrier during acute hypertension. Permeability of the blood-brain barrier was quantitated by clearance of fluorescent-labeled dextran before and during phenylephrine-induced acute hypertension in rats treated with vehicle and Hoe-140 (0.1 microM). Phenylephrine infusion increased arterial pressure, arteriolar diameter and clearance of fluorescent dextran by a similar magnitude in both groups. These findings suggest that disruption of the blood-brain barrier during acute hypertension is not related to the synthesis/release of bradykinin to activate B2 receptors.

Vasomotor and permeability effects of bradykinin in the cerebral microcirculation

All components of an intracerebral kallikrein-kinin system have been described. Thus, bradykinin (BK) acting from the parenchymal site as well as from the blood site may influence cerebral microcirculation. BK is a potent dilator of extra- and intraparenchymal cerebral arteries when acting from the perivascular site. The vasomotor effect of BK is mediated by B2 receptors which appear to be located at the abluminal membrane of the endothelial cell. The effect of BK is mediated by NO. prostanoids, free radicals, H2O2 or leukotrienes depending on the animal species and on the location of the artery. Selective opening of the blood-brain barrier for small tracers (Na(+)-fluorescein; MW, 376) has been found in cats during cortical superfusion or intraarterial application of BK. This leakage is mediated by B2 receptors located at the luminal and abluminal membrane of the endothelial cells. Formation of brain edema has been found after ventriculo-cisternal perfusion or interstitial infusion of BK. This can be explained by increase of vascular permeability and cerebral blood flow due to arterial dilation thus enhancing driving forces for the extravasation. An increase of the BK concentration in the interstitial space of the brain up to concentrations which induce extravasation, dilatation and oedema formation has been found under several pathological conditions. Thus, BK may be involved in oedema formation after cold lesion, concussive brain injury, traumatic spinal cord and ischemic brain injury. The mediator role of BK in brain edema is further supported by therapeutic results. Brain swelling due to cold lesion or ischemia could be diminished by treatment with kallikrein-inhibitors. Similarly, dilatation of cerebral arterioles after concussive brain injury was reduced by blockade of B2 receptors. Thus, all criteria favour BK as one mediator of vasogenic oedema.

Bradykinin dilates rat middle cerebral artery and its large branches via endothelial B2 receptors and release of nitric oxide

Ring segments of rat middle cerebral artery (MCA) were prepared for measurement of isometric force and precontracted with 10(-4) M uridine triphosphate (UTP). Concentration-effect curves (CEC) were constructed for bradykinin (BK, 10(-8)(-10)(-1) M) in segments with functionally intact (E+) or denuded (E-) endothelium. E- segments did not dilate to BK. The BK receptor was characterized by application of specific B1 or B2 antagonists [des-Arg4-Leu8] BK (10(-5) M) and [D-Arg4-Hyp3-Thi5-D-Tic7-Oic8] BK (HOE140, 3 x 10(-7) M), respectively, or B2 agonist [des-Arg9] BK (10(-8)-10(-4) M). Involvement of nitric oxide (NO) was tested with NG-nitro-L-arginine (LNNA, 10(-4) M). BK induced concentration-dependent relaxation with a maximal effect (Emax) of 40.86 +/- 1.50% at 10(-4) M and a pD2 (-log10 EC50) of 6.818 +/- 0.044. This relaxation could be prevented with HOE140 or LNNA, but was not influenced by [des-Arg(9)-Leu] BK. [des-Arg9] BK did not induce any effect. These results demonstrate that BK induced relaxation via endothelial B2 receptors and release of NO in isolated rat MCA.

Traumatic optic neuropathy

Knowledge concerning the pathophysiologic mechanisms of traumatic optic neuropathy is limited. The optic nerve is a tract of the brain. Therefore, the cellular and biochemical pathophysiology of brain and spinal cord trauma and ischemia provide insight into mechanisms that may operate in traumatic optic neuropathy. The dosage of methylprednisolone (30 mg/kg/6 hours) which was successful in the National Acute Spinal Cord Injury Study 2 (NASCIS 2) evolved from the unique pharmacology of corticosteroids as antioxidants. The management of traumatic optic neuropathy rests on an accurate diagnosis which begins with a comprehensive clinical assessment and appropriate neuroimaging. The results of medical and surgical strategies for treating this injury have not been demonstrated to be better than those achieved without treatment. The spinal cord is a mixed grey and white matter tract of the brain in contrast to the optic nerve which is a pure white matter tract. The treatment success seen with methylprednisolone in the NASCIS 2 study may not generalize to the treatment of traumatic optic neuropathy. Conversely, if the treatment does generalize to the optic nerve, NASCIS 2 data suggests that treatment must be started within eight hours of injury, making traumatic optic neuropathy one of the true ophthalmic emergencies. Given the uncertainties in the treatment, ophthalmologists involved in the management of traumatic optic neuropathy are encouraged to participate in the collaborative study of traumatic optic neuropathy.

Mediators of vascular and parenchymal mechanisms in secondary brain damage

Several putative mediators of vasogenic brain edema will be considered with respect to the following criteria: 1) their effect on blood-brain barrier (BBB) permeability, 2) their vasomotor actions which may increase driving forces for transmural bulk flow, 3) their influence on edema formation, 4) their actual tissue concentration in pathological states, and 5) the therapeutic results after specific treatment. Bradykinin (BK) can induce brain edema by increasing BBB permeability to small solutes and enhancing blood pressure in the microcirculation due to arterial dilatation and venous constriction. Its interstitial concentration is enhanced after experimental trauma. Since kallikrein inhibitors reduce brain swelling all criteria favour BK as a mediator of vasogenic edema. Arachidonic acid (AA) opens BBB also for large tracers but exerts only small vasomotor effects. The edema formation is associated with an increase of the AA concentration in the interstitial space. However, convincing therapeutic results on inhibition of AA are still lacking. In addition to the formation of vasogenic edema AA has been found to induce cytotoxic edema. From experiments dealing with the vasomotor effects Ellis et al. (Am J Physiol 255: H397-H400, 1988) concluded an interaction of BK and AA in brain injury. However, our own results do not favour this hypothesis since we found divergent vasomotor and permeability effects of BK and AA. Histamine (HA) opens BBB unspecifically and dilates cerebral vessels, mechanisms by which edema formation can be explained.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of contractile responses to bradykinin in canine basilar arteries

This study was undertaken to investigate the role of endothelium in the modulation of vascular responses to bradykinin and to elucidate the receptor types and mechanism of action of bradykinin in isolated basilar artery. The results showed a contractile response to bradykinin in basilar artery. This contractile response to bradykinin was partially modulated by endothelium in a dose-dependent manner. In addition, both des-Arg9-[Leu8]bradykinin and [d-Arg0,Hyp3,Thi5,8,D-Phe7]bradykinin significantly antagonized the responses to bradykinin. However, the blocking effect and the apparent affinity of [d-Arg0,Hyp3,Thi5,8,D-Phe7]bradykinin (pA2 = 9.6 +/- 0.4) were greater than those with des-Arg9-[Leu8]bradykinin (pA.2 = 7.8 +/- 0.3). These results suggest that two apparently distinct types of BK receptors may exist in basilar arteries. Furthermore, the contractile response to bradykinin in basilar artery was significantly inhibited by 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (10(-5) M), H-7 (10(-5) M) and TMB-8 (10(-5) M), but not by indomethacin (10(-5) M) or nordihydroquariaretic acid (10(-5) M). On the other hand, nifedipine, Ca(2+)-free medium, EGTA and Ca(2+)-free medium/EGTA significantly reduced the bradykinin-induced contraction, indicating that part of the contractile response of basilar artery to bradykinin is dependent on extracellular Ca2+. In conclusion, the mechanism of the contractile responses to bradykinin in basilar artery may involve increased intracellular Ca2+ levels acting on the BK1 and BK2 receptor, followed by activation of the phosphoinositide pathway and receptor-mediated Ca2+ channel.

Brain synthesis and cerebrovascular action of epoxygenase metabolites of arachidonic acid

The purpose of this study was to determine if whole brain makes epoxygenase metabolites of arachidonic acid and, if so, whether they are vasoactive on the cerebral microcirculation. Blood-free mouse brain slices were incubated with exogenous radiolabeled arachidonic acid, and the extracted metabolites were resolved by HPLC. Metabolite structures were confirmed by gas chromatography/mass spectrometry. In addition to prostaglandins, leukotriene B4, and hydroxyeicosatetraenoic acids, mouse brain metabolized arachidonic acid into several other compounds. Among them, we identified 5,6- and 14,15-epoxyeicosatrienoic acid. Next, we tested the effect of topical application of brain-synthesized 5,6-epoxyeicosatrienoic acid and synthetic epoxyeicosatrienoic acids on in vivo rabbit cerebral arteriolar diameter using the cranial window technique and in vivo microscopy. Brain-synthesized 5,6-epoxyeicosatrienoic acid caused a transient 28% arteriolar dilation, similar to that produced by 5 micrograms/ml of synthetic 5,6-epoxyeicosatrienoic acid. A concentration of synthetic 14,15- and 11,12-epoxyeicosatrienoic acid of 5 micrograms/ml CSF had little or no effect on diameter, whereas 8,9-epoxyeicosatrienoic acid caused a maximum dilation of 8%. These studies suggest that brain-synthesized 5,6-epoxyeicosatrienoic acid may play a role in the normal or pathophysiological regulation of the cerebral microcirculation.

Restoration of cerebrovascular responsiveness to hyperventilation by the oxygen radical scavenger n-acetylcysteine following experimental traumatic brain injury

Previous experiments have shown that, following experimental fluid-percussion brain injury, cyclo-oxygenase-dependent formation of oxygen radicals prevents arteriolar vasoconstriction in response to hyperventilation. The oxygen radical scavengers superoxide dismutase and catalase restore normal reactivity; however, they are not routinely available for clinical use. The present study tested whether n-acetylcysteine (Mucomyst), an agent currently available for acetaminophen toxicity, could be used as a radical scavenger to restore reactivity after brain injury. N-acetylcysteine (163 mg/kg) was given intraperitoneally prior to or 30 minutes after fluid-percussion brain injury (2.6 atm) in cats, and reactivity to hyperventilation was tested 1 hour after injury. The authors found either that pre- or postinjury administration led to normal reactivity. Additional experiments supported the hypothesis that n-acetylcysteine is an oxygen radical scavenger, since it reduced or prevented the free radical-dependent cerebral arteriolar dilation normally induced by the topical application of arachidonic acid or bradykinin. The mechanism by which n-acetylcysteine is effective in trauma may involve direct scavenging of radicals or stimulation of glutathione peroxidase activity. The results suggest that n-acetylcysteine may be useful for treatment of oxygen free radical-mediated brain injury.

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.

Endothelium-dependent responses of cerebral blood vessels during chronic hypertension

Acetylcholine produces less dilatation of pial arterioles in stroke-prone spontaneously hypertensive rats (SHRSP) than in normotensive (WKY) rats. Responses of cerebral vessels to acetylcholine and bradykinin appear to involve different mechanisms. Our first goal was to determine whether responses of pial arterioles to bradykinin are impaired in SHRSP. Diameter of pial arterioles (20-60 microns) was measured using intravital microscopy in WKY rats and SHRSP (9-12 months old). Superfusion of bradykinin (3 x 10(-7) M) dilated pial arterioles by 35 +/- 6% (mean +/- SEM) in WKY rats, but only 21 +/- 3% in SHRSP (p less than 0.05 versus WKY rats). Both nitric oxide (5 x 10(-7) M) and nitroglycerin (10(-5) M) produced similar vasodilatation in WKY rats and SHRSP. Our second goal was to determine whether alteration of postreceptor mechanisms contributes to impairment of endothelium-dependent cerebral vasodilatation in SHRSP. Calcium ionophore A23187 (10(-5) M) produced more vasodilatation in WKY rats than in SHRSP (32 +/- 8% versus 9 +/- 4%, p less than 0.05). Responses to A23187 (10(-5) M) were inhibited by indomethacin (46 +/- 13% versus 15 +/- 5%, p less than 0.05) in WKY rats, whereas responses to A23187 (10(-6) M) were potentiated modestly by indomethacin (-3 +/- 2% versus 4 +/- 2%, p less than 0.05) in SHRSP.(ABSTRACT TRUNCATED AT 250 WORDS)

Participation of the kallikrein-kinin-receptor system in reflexes arising from neural afferents in the dog epicardium

1. Reflexogenic effects of bradykinin, lysyl-bradykinin and endogenously formed kinins on neural afferents of the left ventricular epicardium were studied in anaesthetized, open-chest dogs. 2. Epicardial application of either bradykinin (0.01-10 micrograms), lysyl-bradykinin (0.01-10 micrograms) or tissue kallikrein (0.003-1 U) consistently resulted in dose-related increases in blood pressure and heart rate. The pressor and heart rate responses to epicardial kallikrein were slower in onset and longer lasting than those evoked by bradykinin or lysyl-bradykinin. The effects of kallikrein, but not those of exogenous kinins, were subject to tachyphylaxis. The application of higher doses of kallikrein (0.1 or 1 U) also resulted in long-lasting desensitization of the epicardium to the effects of bradykinin. 3. Treatment of the epicardium with a proteinase inhibitor, aprotinin, prevented the reflexogenic effects of kallikrein but not those of bradykinin or lysyl-bradykinin. Treatment with aprotinin also counteracted post-kallikrein desensitization of sensory receptors of the ventricular epicardium to the reflexogenic effect of bradykinin. 4. Superfusion of the epicardium with a selective B2 receptor antagonist, D-Arg[Hyp3,Thi5,8,D-Phe7]-bradykinin, was equally effective in antagonizing the reflexogenic effects of kallikrein, bradykinin and lysyl-bradykinin. 5. We conclude that the response to epicardial application of kallikrein indicates an ample presence of endogenous substrate for local formation of bradykinin and/or related kinins. These then initiate reflex activation of the cardiovascular system by interacting with specific B2 receptors associated with sympathetic afferent neurones in the dog epicardium. We suggest that the kallikrein-kinin-receptor system has a role in the reflex function of the cardiac sympathetic afferents in both physiological and pathological conditions.

Brain kininogen following experimental brain injury: evidence for a secondary event

Previous studies have shown that following experimental brain injury cerebral arterioles dilate and display endothelial lesions and reduced responsiveness to hypocapnia. These abnormalities are caused by cyclo-oxygenase-dependent free radical generation. There is evidence that the kallikrein-kinin system may in part stimulate the cyclooxygenase-dependent damage since bradykinin is a powerful stimulator of prostaglandin formation and it has recently been shown that a specific kinin receptor blocker decreases the arteriolar abnormalities caused by injury. In order to further examine the hypothesis that the kallikrein-kinin system is important in inducing damage, rat brain tissue was examined for kininogen, the precursor of kinins, at 10 minutes and 1, 3, 6, 15, 24, 48, and 72 hours after injury. A fluid-percussion brain injury device was attached over the right cerebral cortex of rats and a 1.6-atmosphere pressure injury was administered. The kininogen content was determined by a radioimmunoassay procedure in tissues which were free of intravascular blood. After injury, bleeding was confined mainly to the right hemisphere. The kininogen content in the right hemisphere was significantly elevated by one hour after injury, continued to rise until 15 hours after injury, then was significantly decreased by 2 days after injury. In the left hemisphere, kininogen was significantly elevated at 1 hour postinjury, returned toward control levels over the 3- to 6-hour period after injury, then was again elevated at 15 hours after injury. These studies also show that brain water and cerebrovascular permeability were greater at 15 hours postinjury than at earlier time points. The data further support a role for the kallikrein-kinin system in brain injury and, when considered with the results of other studies, suggest that a secondary event is occurring in the 12- to 24-hour period after neural injury. The authors hypothesize that this secondary event is related to endothelial and vascular repair and may be important for the return of normal cerebrovascular function.

Oxygen radicals in CNS damage

The products of univalent reduction of oxygen, superoxide anion radical, hydrogen peroxide, and the hydroxyl radical, are capable of causing cellular damage and death. They are, therefore, logical candidates as mediators of vascular and parenchymal injury in the central nervous system (CNS). This paper reviews the sources of oxygen radicals in the CNS, their effects on cerebral vessels and on brain and spinal cord parenchyma, and the evidence which implicates oxygen radicals in various pathological conditions of the CNS.

Blood-brain barrier permeability and vascular reactivity to bradykinin after pretreatment with dexamethasone

The role of kinins as mediator substances is increasingly recognized in cerebral ischemia and trauma. It has previously been shown that cerebral exposure to bradykinin, which causes brain edema, is associated with arteriolar dilatation and selective opening of the blood-brain barrier (BBB) to small molecular weight indicators, such as Na+-fluorescein. Since the evidence suggests that these effects results from an activation of the arachidonic acid cascade, particularly from formation of E- and I-type prostaglandins, therapeutical inhibition of the cerebral effect of bradykinin has been attempted by pretreatment of experimental animals with dexamethasone. The BBB function and changes of the pial vessel diameters were studied by fluorescence microscopy in cats in alpha-chloralose anesthesia during superfusion of the exposed cerebral cortex. After a control phase bradykinin was added to a cerebral superfusate in concentrations of 4 x 10(-8) M to 4 x 10(-3) M. Two additional groups of animals received dexamethasone in a dose of 1, or 5 mg/kg body wt., respectively, 5 h prior to the cerebral superfusion with bradykinin. Na+-fluorescein (mol wt.: 376) was infused intravenously as a BBB indicator. The BBB marker remained strictly confined to the intravascular compartment under control conditions. Pretreatment with dexamethasone did not prevent opening of the BBB by bradykinin, either at the low, or high dose. However, the low dose of dexamethasone blunted the vasodilatory response to bradykinin, whereas the high dose (5 mg/kg) was found to enhance the dilatory properties of bradykinin at concentrations of 4 x 10(-3) M.(ABSTRACT TRUNCATED AT 250 WORDS)

Diversity of rat brain cysteine proteinase inhibitors: isolation of low-molecular-weight cystatins and a higher-molecular weight T-kininogen-like glycoprotein

Conditions for extraction of rat brain soluble and particulate cysteine proteinase inhibitors (CPIs) were compared and an optimal one was selected to isolate low- and high-molecular-weight forms active toward papain or brain cathepsins B/L. The different forms were purified by affinity chromatography on alkylated papain, and identified on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels by use of Schiff's reagent, or by immunoblots using antisera to monomer or polymeric forms of human urinary cystatin c, to a human plasma histidine-rich glycoprotein (HRG), or to rat plasma T-kininogen. In particulates containing nuclei (P1) or synaptosomes (P2) the predominant CPI was an 80-kDa glycoprotein cross-reacting to anti-HRG and shown to be a T-kininogen by treatment with TPCK-trypsin, and subsequent bioassay of the released kinins. The levels found in rat brain were approximately 0.5 nmol/g wet weight. The higher-molecular-weight CPI potently inhibited cathepsin L hydrolysis of Leu-enkephalin at the Gly2-Gly3 bond with a Ki 10(-10) M. In contrast the low-molecular-weight CPIs were present in postmicrosomal fractions (S3) and cross-reacted with anti-cystatin c, but not with anti-HRG, anti-lysozyme, anti-beta protein amyloid peptide, or anti-T-kininogen. The low-molecular-weight forms were present at approximately 1-1.5 nmol/g wet weight and resembled "cerebrocystatin" purified previously from rat brain cytosol by M. Kopitar, F. Stern, and N. Marks [1983) Biochem. Biophys. Res. Commun. 112, 1000-1006.).

Kallidin and bradykinin metabolism by isolated cerebral microvessels

Although kinins have been reported to affect cerebral vascular tone and permeability, their actions are not potentiated by angiotensin converting enzyme inhibitors. To investigate cerebral vascular kinin metabolism, porcine cerebral microvessels were isolated by differential sieving and centrifugation and characterized by microscopic examination and marker enzyme enrichment. Purified microvessels contained a membrane-bound carboxypeptidase which hydrolyzed the C-terminal Phe-Arg bond of both kallidin and bradykinin. Hydrolysis was optimal at pH 7.0, was activated more than 300% by 0.1 mM CoCl2, and was inhibited by o-phenanthroline and the carboxypeptidase N (EC 3.4.17.3) inhibitor DL-2-mercaptomethyl-3-guanidino-ethylthiopropanoic acid (MERGETPA) (IC50 = 2 microM). Conversely, inhibitors of angiotensin I converting enzyme (captopril), neutral endopeptidase (phosphoramidon), post proline cleaving enzyme (Z-Pro-prolinal), dipeptidyl(amino)peptidase IV (diprotin A) and amino-peptidase M (amastatin) had no effect. When the rates of C-terminal hydrolysis of kallidin by detergent-solubilized cerebral microvasculature were determined over a range of substrate concentrations (16.6 to 250 microM), the Km and Vmax values obtained were 26.0 +/- 3.0 microM and 14.7 +/- 1.3 nmol/min/ml (N = 4) respectively. These data suggest that a cerebral microvascular carboxypeptidase may play a role in vivo in modulating the effects of kinins on cerebral blood flow and permeability and in preventing circulating kinins from crossing the blood-brain barrier.

Vasomotor responses of rat intracerebral arterioles to vasoactive intestinal peptide, substance P, neuropeptide Y, and bradykinin

The effect of vasoactive peptides on vascular smooth muscle in the cerebral microcirculation was examined using an isolated intracerebral arteriole preparation. Extraluminally applied vasoactive intestinal peptide (VIP) dilated the spontaneous tone of intracerebral arterioles to 118.9 +/- 3.1% of control diameter at pH 7.30, with an EC50 of 7.27 X 10(-8) M. Similar degrees of dilation to VIP were seen in vessels preconstricted by changing bath solution to pH 7.60. Substance P had no effect on vessel diameter at pH 7.30. However, in vessels precontracted by pH 7.60, significant dose-dependent dilation was observed with an EC50 of 2.55 x 10(-10) M. Neuropeptide Y constricted intracerebral arterioles to 81.22 +/- 2.7% of control diameter, with an EC50 of 6.23 x 10(-10) M. Bradykinin dilated intracerebral arterioles at pH 7.30 and pH 7.60 to 130 +/- 3.0% of control diameter. VIP and bradykinin are potent vasodilators of intracerebral arterioles. Neuropeptide Y is a vasoconstrictor. The effect of substance P appeared to be either pH-dependent or dependent on some degree of precontraction by another agonist, but no effect on vessel diameter was seen at pH 7.30.

Analysis of the mechanism of action of bradykinin on human basilar artery in vitro

Bradykinin (BK) initially produced concentration-related relaxations of human basilar artery in vitro. Concentration-effect curves constructed at 2 h intervals to BK over an 8 h period were reproducible. The rank order of potency of three kinins on the human basilar artery was found to be BK greater than methionyl-lysyl-BK greater than des-Arg9-BK. The B2-receptor antagonist Thi5,8, D-Phe7-BK but not the B1-receptor antagonist des-Arg9-Leu8-BK selectively blocked BK-induced relaxations of the human basilar artery. The relaxant effects of bradykinin and acetylcholine but not papaverine were attenuated after removal of the endothelium or treating the tissues with BW755C. Indomethacin was without effect. Concentration-effect curves to angiotensin I were markedly attenuated by captopril at a concentration which had no effect on BK, angiotensin II or 5-hydroxytryptamine responses. It is concluded that BK induced relaxations of the human basilar artery are mediated via activation of a B2 receptor and the response is dependent upon the release of a factor present in the endothelium. Angiotensin converting enzyme is present in the human basilar artery and is important for the conversion of angiotensin I to angiotensin II but apparently not for the degradation of BK. It is likely that other kininases are present and active in the tissue.

Oxygen radicals in brain injury

Experimental fluid percussion brain injury in anesthetized cats causes vascular injury characterized by sustained arteriolar dilation, abnormal reactivity to vasoconstrictor and vasodilator interventions, focal endothelial lesions, and reduction of the oxygen consumption of the vessel wall. These abnormalities are minimized or completely inhibited by pretreatment with cyclooxygenase inhibitors or with oxygen radical scavengers. They were therefore ascribed to oxygen radicals generated in the course of accelerated arachidonate metabolism via cyclooxygenase. Following this type of brain injury, there is an increase in the activity of phospholipase c in the brain and a transient increase in brain concentration of prostaglandins. Superoxide anion radical was detected in the extracellular space of the brain both immediately following brain injury as well as one hour afterwards as the superoxide dismutase inhibitable portion of nitroblue tetrazolium reduction. The sustained dilation and abnormal reactivity of cerebral arterioles following brain injury were also reversed by superoxide dismutase and catalase applied on the brain surface 30 minutes after injury. These results suggest that treatment with oxygen radical scavengers might be effective in inhibiting or reversing some of the effects of brain injury, even though the intervention with the therapeutic agents occurs sometime after the injury has taken place.