Relationship between central actions of bradykinin and prostaglandins in the conscious rat

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.

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.

Brain prostaglandins mediate the bombesin-induced increase in plasma levels of catecholamines

Intracerebroventricular (i.c.v.) administration of bombesin (0.1, 1.0, 10.0 nmol/animal) in urethane-anesthetized rats induced long-lasting and dose dependent increases in plasma levels of adrenaline and noradrenaline. These effects of bombesin were inhibited by i.c.v. pretreatment with indomethacin (50-500 micrograms/animal), while the same dose of indomethacin by the intravenous route was without effect. The bombesin-induced increases in plasma levels of catecholamines were also inhibited by i.c.v. pretreatment with diclofenac (100-500 micrograms/animal), a cyclooxygenase inhibitor other than indomethacin. I.c.v. administration of thyrotropin releasing hormone (TRH) (10 nmol/animal) also induced increases in plasma levels of adrenaline and noradrenaline, however, these increases were not modified by i.c.v. pretreatment with indomethacin. The present results suggest that the bombesin-induced increases in plasma levels of catecholamines are probably due to prostaglandins synthetized in the brain with this neuropeptide. Furthermore, it is likely that prostaglandins are not always involved in central activation of sympatho-adrenomedullary system by other brain neuropeptides.

Anxiogenic activity of intraventricularly administered bradykinin in rats

The anxiogenic action of bradykinin was investigated in rats and compared with that of yohimbine, a known anxiogenic agent. Bradykinin (0.5, 1 and 2 μg/rat) was administered intracerebroventricularly (i.c.v.), whereas yohimbine (2 mg/kg) was administered i.p. The experimental methods used were the open- field, elevated plus-maze, social interaction and novelty suppressed feeding latency tests, and estimation of brain tribulin activity in terms of endogenous monoamine oxidase (MAO) A and MAO B inhibition. The behavioural and biochemical effects induced by bradykinin were qualitatively similar to those of yohimbine. Thus, both the drugs reduced ambulation and rears, and increased immobility and defecation, in the open-field test. They decreased the number of entries and time spent on the open arms of the elevated plus-maze, reduced social interaction in paired rats and increased the feeding latency in an unfamiliar environment in 48 h food-deprived rats. These effects are known to be associated with anxiety in animals. Bradykinin and yohimbine increased rat brain tribulin activity, the effect on the MAO A inhibitor component being more marked than that on the MAO B inhibitor component. The MAO A inhibitor component has been postulated to be the major anxiogenic moiety of tribulin. Lorazepam, a well known benzodiazepine anxiolytic agent, attenuated the anxiogenic effects of bradykinin and yohimbine, which may not be a functional effect. The investigation indicates that, like cholecystokinin (CCK), bradykinin may function as an endogenous anxiogenic peptide.

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.

The role of bradykinin in mediating ischemic brain edema in rats

BACKGROUND AND PURPOSE

We investigated the hypothesis that bradykinin generation may induce ischemic brain edema in spontaneously hypertensive rats.

METHODS

Cerebral ischemia lasting 3 hours was produced by bilateral common carotid artery occlusion in 67 rats. After the ischemic period, the rats were reperfused. Cerebral water content and energy metabolites (adenosine triphosphate, lactate, and pyruvate), as well as plasma and tissue bradykinin, were measured. Additionally, using the same experimental paradigm, bradykinin synthesis inhibitors (aprotinin [n = 7] and soybean trypsin inhibitor [n = 7]) were administered immediately after ischemia induction to determine the relation of bradykinin generation to the progression of ischemic brain edema.

RESULTS

Cerebral water content increased during the 3-hour ischemic period, peaked at 30 minutes of reperfusion, and declined thereafter. Bradykinin levels in plasma and tissue rose markedly 30 minutes after reperfusion and fell thereafter. The progressive loss of adenosine triphosphate was mirrored by the rise in lactate. In the treated groups, aprotinin and soybean trypsin inhibitor administration significantly attenuated cerebral edema (p < 0.01 and p < 0.05, respectively). The treated groups also showed less lactate accumulation and more adenosine triphosphate preservation than did the controls.

CONCLUSIONS

These results demonstrate that bradykinin levels in plasma and tissue corresponded to cerebral edema progression and that bradykinin suppression decreased edema formation. These novel findings indicate that bradykinin activation augments the progression of ischemic brain edema.

Inhibitory effect of inaperisone hydrochloride (inaperisone), a new centrally acting muscle relaxant, on the micturition reflex

We examined the effects of inaperisone hydrochloride (inaperisone), a new centrally acting muscle relaxant, on bladder function in anesthetized rats and isolated rat tissues. We also investigated its mechanism of action. When a balloon inserted into the bladder was expanded, rhythmic bladder contractions were observed; inaperisone (4 mg/kg i.v.) abolished these contractions, in both normal and decerebrated rats. The bladder tonus or bladder contraction induced by peripheral stimulation of the pelvic nerve was barely inhibited by inaperisone (4 mg/kg i.v.), but this dose of inaperisone abolished the efferent discharge from the pelvic nerve that accompanied the rhythmic bladder contractions. The doses of intracerebroventricularly (i.c.v.) and intrathecally injected inaperisone which abolished the rhythmic bladder contractions were 10 and 100 micrograms, respectively. The inhibitory effects of inaperisone (4 mg/kg i.v.) were not diminished by naloxone (1 mg/kg i.v.) or by bicuculline (0.5 mg/kg i.v.), but were diminished by phaclofen (30 mg/kg i.v. or 300 micrograms i.c.v.). The specific binding of [3H]baclofen to rat brain synaptosomal membranes was barely inhibited by inaperisone (up to 1 mM). From these results, it is speculated that, among other possible mechanisms, inaperisone inhibits the micturition reflex by acting indirectly on GABAB receptors in the brainstem.

Role of endogenous brain kinins in the cardiovascular response to intracerebroventricular melittin

Intracerebroventricular infusion of the peptide melittin increases immunoreactive kinins in the cerebrospinal fluid of anesthetized dogs, probably secondary to activation of brain or cerebrospinal fluid kininogenases. Intracerebroventricular melittin also increases blood pressure and heart rate, possibly mediated by brain kinins, since intracerebroventricular bradykinin also increases blood pressure and heart rate. We tested whether the effects of centrally administered melittin on blood pressure and heart rate could be blocked by simultaneous infusion of a kinin receptor antagonist, [DArg0]Hyp3-Thi5,8[DPhe7]bradykinin, in normotensive awake rats. In the controls, intracerebroventricular infusion of kinin receptor antagonist given for 1 hour at a rate of 10 micrograms/hr blocked bradykinin-induced increases in blood pressure and heart rate by 80%. Basal blood pressure and heart rate were not affected by the kinin receptor antagonist alone. After a 30-minute infusion of melittin (8 micrograms/30 min), cerebrospinal fluid kininogenase activity (n = 17) rose from 0.13 +/- 0.05 to 0.43 +/- 0.1 ng/ml/min (p less than 0.02). Although cerebrospinal fluid kinins increased from below sensitivity (0.02 ng/ml, n = 12) to 0.19 +/- 0.1 ng/ml (n = 17), this change was due to drastic increases in three rats, whereas in 12 of them kinins were below sensitivity. Incubation of bradykinin (10 ng) with 0.1 ml rat cerebrospinal fluid for 5 minutes destroyed 70% of kinins, suggesting that rapid destruction may have made detection of increased CSF kinins difficult.(ABSTRACT TRUNCATED AT 250 WORDS)

Central effect of aprotinin, a serine protease inhibitor, on blood pressure in spontaneously hypertensive and Wistar-Kyoto rats

We examined the effect of centrally administered aprotinin, a serine protease inhibitor, on blood pressure (BP) in conscious spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Twenty-two gauge needles and polyethylene catheters were implanted into lateral cerebroventricle and femoral artery, respectively, at 48 hours before the experiments. In Group 1 (8 SHR, 6 WKY), rats received a bolus intracerebroventricular injection (i.c.v.) of aprotinin (1,000 KIU/kg/10 microliters). A prompt increase of BP was observed in SHR after aprotinin and this elevation of BP was persisted for over 30 minutes (mean BP: 158.8 +/- 2.9 mmHg at control to 168.7 +/- 3.2 at 15 min., p less than 0.01; to 168.3 +/- 3.4 at 30 min., p less than 0.01). On the other hand, BP of WKY decreased gradually after aprotinin (mean BP: 143.0 +/- 3.3 at control to 136.8 +/- 2.7 at 15 min., n.s.; to 134.2 +/- 5.1 at 30 min., p less than 0.05). The intravenous injection (i.v.) of aprotinin (Group 2: 7 SHR, 5 WKY) and the i.c.v. of artificial cerebrospinal fluid (CSF) (Group 3: 5 SHR, 6 WKY) did not affect BP in both SHR and WKY except for the minor transient increase of BP in WKY immediately after artificial CSF i.c.v.. We performed additional experiments to study the contributions of sympathetic nervous system and vasopressin to these changes in BP.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the mechanism of the sedational state; "tranquilization" evoked by bradykinin or kallikrein in rats

The mechanism of the sedative state "tranquilization" evoked by bradykinin(BK) or kallikrein(Kal), was studied. The drugs were injected intracerebroventricularly(icv) into the lateral ventricle, according to Yaksh's procedure. The behavior of a rat was estimated comparatively by the spontaneous movement. Two groups of animals were examined; one group was pretreated with prostaglandin (PG)-synthesis inhibitors, and the other group was not pretreated. The tranquilization was observed at the period of 12 to 16 min after BK or Kal injection. Almost of the PG-synthesis inhibitors reduced the tranquilization. On the contrary, eugenol or guaiacol, elongated the tranquilization. The levels of monoamines and PGs in the rat brain at the tranquilization, 15 min after BK injection detected with HPLC (high performance liquid chromatography). The levels of almost monoamines in the rat brain were decreased, however, PGE2 was increased considerably. Those results suggest that PGs is greatly involved in tranquilization evoked by BK or Kal.

Intracerebroventricularly administered bradykinin augments carrageenan-induced paw oedema in rats

Intracerebroventricular (i.c.v.) administered bradykinin (2.5 and 5.0 micrograms/rat) was found to augment carrageenan-induced acute paw oedema throughout the 4 h post-carrageenan observation period. The effect was statistically significant with the higher dose. The pro-inflammatory effect of i.c.v. bradykinin was antagonized following pretreatment with hemicholinium and atropine ethoiodide administered i.c.v., drugs that reduce central cholinergic activity. Similarly, central administration of drugs that inhibit the synthesis of eicosanoids, hydrocortisone, diclofenac and paracetamol, also attenuated the pro-inflammatory effect of bradykinin. The findings indicate that the inflammation-promoting effect of centrally administered bradykinin involves the central prostaglandin and cholinergic neurotransmitter systems.

Hyperthermic effect of centrally administered bradykinin in the rat: role of prostaglandins and serotonin

Intracerebroventricularly administered bradykinin (2.5, 5 and 10 micrograms/rat) produced a dose-related increase in the rectal temperature of adult Wistar strain albino rats. The bradykinin-induced hyperthermia was significantly attenuated following pretreatment of the animals with pharmacological agents which selectively reduce rat brain serotonin or prostaglandin (PG) activity. These findings, and those of earlier reports emanating from this laboratory which indicate that centrally administered bradykinin augments rat brain serotonin and PGE2 activity, suggest the involvement of PGs and serotonin in the hyperthermic action of bradykinin in this species.

The involvement of the sympathetic nervous system in the centrogenic pressor and tachycardiac effects of prostaglandins E2 and F2 alpha in anaesthetised cats

The intracerebroventricular (i.c.v.) administration of prostaglandin E2 (PGE2, 1 micrograms) and prostaglandin F2 alpha (PGF2 alpha, 10 micrograms) produced prolonged pressor and tachycardiac responses in chloralose-anaesthetised cats. Phenoxybenzamine-pretreatment completely prevented the pressor response without altering the tachycardiac response, whereas propranolol intervention completely inhibited the tachycardiac response and also attenuated the pressor response. The pretreatment with pentolinium completely antagonised both the pressor and tachycardiac responses to i.c.v. PGE2 and PGF2 alpha. The results suggest that the centrally administered PGE2 and PGF2 alpha augment sympathetic outflow to the heart and vascular system and thereby cause excitatory cardiovascular responses in anaesthetised cats.

Interrelationship between central bradykinin and vasopressin in conscious rats

Intracerebroventricular administration of bradykinin (1, 5 and 20 micrograms) into conscious rats resulted in significant dose-dependent increases in the plasma vasopressin concentration, mean arterial blood pressure and heart rate. Peripheral blockade of the pressor action of vasopressin with a vasopressin pressor antagonist (10 micrograms/kg, i.v.) did not cause an attenuation but rather a potentiation and prolongation of the pressor effects of central bradykinin (20 micrograms). Central administration of the vasopressin antagonist (150 ng) caused no peripheral blockade of the pressor effects of exogenous i.v. vasopressin but almost abolished the bradykinin-induced tachycardia, with little effect on the pressor effects of central bradykinin (20 micrograms). The results indicate that centrally administered bradykinin stimulates vasopressin release into the plasma and that central vasopressin may modulate the cardiovascular actions of central bradykinin.

Regional distribution and characterization of kinin in the CNS of the rat

The distribution of kinin in the CNS of the rat, which was extracted with n-butanol from an acidified homogenate, was determined using a bradykinin (BK) radioimmunoassay system. The immunoreactive kinin was widely distributed throughout the brain. The highest content was found in the pituitary gland (4,135 fmol BK Eq/g), followed by the medulla oblongata (912 fmol/g), cerebellum (549 fmol/g), and cortex (512 fmol/g). The kinin in the posterior pituitary was concentrated 4.5 times as much as in the anterior lobe. Serial dilution of brain extracts produced binding curves parallel to the standard radioimmunoassay curve. The purified brain kinin comigrated with authentic BK during CM-cellulose chromatography and Sephadex LH-20 gel chromatography. Its molecular weight was estimated to be 1,127 +/- 45 by gel filtration, which coincides well with that of BK. Chymotrypsin degraded the extracted kinin and authentic BK, but trypsin did not. These data demonstrate that a peptide indistinguishable from BK exists in the rat brain. Furthermore, pituitary kinin was separated into BK (87%), Lys-BK (10%), and Met-Lys-BK (3%), using reverse phase HPLC.

Bradykinin and related peptides in central control of the cardiovascular system

The evidence for a brain kallikrein-kinin system and for the possible role for kinins in brain control of the cardiovascular system are reviewed. All components of the kallikrein-kinin system are present in brain and kinins have a variety of cardiovascular actions of central origin following peripheral, intracerebroventricular or brain parenchymal administration. How components of the brain kallikrein-kinin system are regulated or even whether they function as a system remains to be established. However, bradykinin does fulfill several of the criteria necessary for establishing a substance as a neurotransmitter and these are discussed.

Identification of bradykinin in mammalian brain

Bradykinin-like activity was purified from acetic acid extracts of saline-perfused rat brains by gel filtration chromatography and two reverse-phase HPLC systems capable of resolving bradykinin from lysyl-bradykinin and other bradykinin analogs and fragments. Addition of [3H]bradykinin to extracts permitted calculation of recoveries and monitoring of chromatographic fractions. Fractions were examined by radioimmunoassay using a potent and highly specific antiserum raised against bradykinin-human albumin conjugates in rabbits. Bradykinin receptor-active material was also measured by radioreceptor assay using guinea pig ileum, as well as by a bioassay with the estrous rat uterus. Active material chromatographed as authentic bradykinin in all systems. Levels of 0.6 pmol/g whole rat brain were detected, with eight times higher levels in the hypothalamus. Activity increased up to 10-fold following treatment with trypsin; treatment with alpha-chymotrypsin or angiotensin-converting enzyme substantially reduced activity. Similar levels and distribution of bradykinin-like activity were also detected in guinea pig brain extracts. These data substantiate the existence of authentic bradykinin in mammalian brain.

The kallikrein-kinin system as mediator in vasogenic brain edema

✓ Vasogenic edema was induced in mongrel cats by cold injury to study uptake and activation of the plasma-kallikrein-kinin system in central nervous system (CNS) tissue. A method was developed for quantitative assessment of kinin formation in affected brain tissue areas. Gross disruption of the blood-brain barrier by focal trauma causes marked penetration of plasma kininogens into necrotic and edematous brain tissue. Moreover, the kallikrein-kinin (KK) system was activated in both necrotic and perifocal edematous areas, and was markedly enhanced by additional cerebral ischemia. Formation of kinins in necrotic brain tissue led to consumption of approximately 60% to 80% of the amount of kininogens being taken up. In perifocal edematous tissue, formation of kinins was less pronounced, or even absent. However, if cerebral ischemia evolved after severe intracranial hypertension, kinins were also formed in the perifocal edematous brain. The intravascular origin of kininogens found in pathological tissue areas secondary to injury was deduced from the observation that cerebral tissue of the contralateral hemisphere with an intact blood-brain barrier had no measurable quantities of kininogens. Consumption of plasma kininogens or formation of kinins were assessed as the difference of the total amount of plasma kininogens taken up into the tissue minus the amount of kininogens found in the brain at postmortem examination.

The data indicate that uptake and activation of the plasma-KK system might occur under all pathological conditions in which blood-brain barrier damage permits cerebral penetration of plasma proteins, such as with cerebral contusion, focal ischemia, and tumors. The potent pathophysiological mechanisms induced by kinins in CNS tissue, such as formation of brain edema, microcirculatory dysfunction, and enhancement of blood-brain barrier permeability, together with their formation in focal and perifocal pathological brain tissue, provide further support for a mediator function of the KK system. Methods that specifically interfere with the formation of kinins in damaged brain should therefore be expected to attenuate vasogenic edema.

Cardiovascular effects of discrete intrahypothalamic and preoptic injections of bradykinin

Blood pressure and heart rate were monitored during discrete injections of bradykinin (5 nmol; 100-300 nl) in the hypothalamus and preoptic area of halothane anesthetized rats. In the paraventricular nucleus, bradykinin produced bradycardia without effecting blood pressure. The decrease in heart rate was abolished by pretreatment with methylatropine (IP), suggesting that the parasympathetic nervous system mediates this response. In contrast, in the dorsomedial and posterior hypothalamic nuclei, bradykinin increased both heart rate and blood pressure; methylatropine pretreatment (but not adrenalectomy) blocked these responses, suggesting that inhibition of the parasympathetic nervous system is responsible for the actions of bradykinin in these nuclei. In the preoptic suprachiasmatic nucleus, bradykinin produced an increase in heart rate only, which was attenuated by either methylatropine or adrenalectomy, indicating that both inhibition of the parasympathetic nervous system and adrenal catecholamine release contribute to the actions of bradykinin at this site. The increase in heart rate observed with bradykinin in the medial preoptic and anterior hypothalamic (A6400-6001 region) nuclei was not effected by either methylatropine or adrenalectomy, therefore activation of the sympathetic nervous system may be involved in responses in these regions. Finally, a 5 nmol dose of bradykinin potentiating factor (converting enzyme inhibitor; CEI) had effects similar to bradykinin when injected into the posterior hypothalamus, but no effect at any other brain site. CEI administration into brain sites 15 min prior to bradykinin injections failed to alter the bradykinin response. In summary, the central cardiovascular responses to bradykinin depend upon the specific site of injection and these sites correspond with the localization of bradykinin-like immunoreactivity previously reported by others.

Cardiovascular responses of conscious DOCA-salt hypertensive rats to acute intracerebroventricular and intravenous administration of captopril

The effect on blood pressure and heart rate, following administration of the same intracerebroventricular (ivt) and intravenous (iv) doses of captopril, was compared in freely moving DOCA-salt hypertensive rats, with chronically implanted ivt, iv and intraarterial cannulae. Ivt captopril (500 micrograms) in DOCA-salt rats showed an initial pressor response followed by a long lasting hypotensive effect. The ivt effect was greater than that following iv administration. No effect was observed in normotensive controls either ivt or iv. ASA or naloxone pretreatments significantly lowered the captopril hypotensive effect, thus suggesting an involvement of prostaglandin and opioid systems in blood pressure elevation in "non renin dependent" hypertension.