Tissue kallikrein in rat brain and pituitary: regional distribution and estrogen induction in the anterior pituitary

Sex-specific Regulation of Prolactin Secretion by Pituitary Bradykinin Receptors

Sex differences in the control of prolactin secretion are well documented. Sex-related differences in intrapituitary factors regulating lactotroph function have recently attracted attention. Sex differences in prolactinoma development are well documented in clinic, prolactinomas being more frequent in women but more aggressive in men, for poorly understood reasons. Kallikrein, the enzyme releasing kinins has been found in the pituitary, but there is no information on pituitary kinin receptors and their function. In the present work, we characterized pituitary bradykinin receptors (BRs) at the messenger RNA and protein levels in 2 mouse models of prolactinoma, Drd2 receptor gene inactivation and hCGβ gene overexpression, in both males and females, wild type or genomically altered. BR B2 (B2R) accounted for 97% or more of total pituitary BRs in both models, regardless of genotype, and was present in lactotrophs, somatotrophs, and gonadotrophs. Male pituitaries displayed higher level of B2R than females, regardless of genotype. Pituitary B2R gene expression was downregulated by estrogen in both males and females but only in females by dopamine. Activation of B1R or B2R by selective pharmacological agonists induced prolactin release in male pituitaries but inhibited prolactin secretion in female pituitaries. Increased B2R content was observed in pituitaries of mutated animals developing prolactinomas, compared to their respective wild-type controls. The present study documents a novel sex-related difference in the control of prolactin secretion and suggests that kinins are involved, through B2R activation, in lactotroph function and prolactinoma development.

Role of Kinins in Hypertension and Heart Failure

The kallikrein-kinin system (KKS) is proposed to act as a counter regulatory system against the vasopressor hormonal systems such as the renin-angiotensin system (RAS), aldosterone, and catecholamines. Evidence exists that supports the idea that the KKS is not only critical to blood pressure but may also oppose target organ damage. Kinins are generated from kininogens by tissue and plasma kallikreins. The putative role of kinins in the pathogenesis of hypertension is discussed based on human mutation cases on the KKS or rats with spontaneous mutation in the kininogen gene sequence and mouse models in which the gene expressing only one of the components of the KKS has been deleted or over-expressed. Some of the effects of kinins are mediated via activation of the B2 and/or B1 receptor and downstream signaling such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and/or tissue plasminogen activator (T-PA). The role of kinins in blood pressure regulation at normal or under hypertension conditions remains debatable due to contradictory reports from various laboratories. Nevertheless, published reports are consistent on the protective and mediating roles of kinins against ischemia and cardiac preconditioning; reports also demonstrate the roles of kinins in the cardiovascular protective effects of the angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARBs).

Implication of the Kallikrein-Kinin system in neurological disorders: Quest for potential biomarkers and mechanisms

Neurological disorders represent major health concerns in terms of comorbidity and mortality worldwide. Despite a tremendous increase in our understanding of the pathophysiological processes involved in disease progression and prevention, the accumulated knowledge so far resulted in relatively moderate translational benefits in terms of therapeutic interventions and enhanced clinical outcomes. Aiming at specific neural molecular pathways, different strategies have been geared to target the development and progression of such disorders. The kallikrein-kinin system (KKS) is among the most delineated candidate systems due to its ubiquitous roles mediating several of the pathophysiological features of these neurological disorders as well as being implicated in regulating various brain functions. Several experimental KKS models revealed that the inhibition or stimulation of the two receptors of the KKS system (B1R and B2R) can exhibit neuroprotective and/or adverse pathological outcomes. This updated review provides background details of the KKS components and their functions in different neurological disorders including temporal lobe epilepsy, traumatic brain injury, stroke, spinal cord injury, Alzheimer's disease, multiple sclerosis and glioma. Finally, this work will highlight the putative roles of the KKS components as potential neurotherapeutic targets and provide future perspectives on the possibility of translating these findings into potential clinical biomarkers in neurological disease.

Characterization of the renal renin-angiotensin system in transgenic mice that express rat tonin

INTRODUCTION

Tonin is an enzyme that is able to generate angiotensin II (Ang II) from angiotensin I (Ang I) or directly from angiotensinogen. Our goal was to characterize the renal renin-angiotensin system in transgenic mice that express rat tonin (TGM`(rTon)).

MATERIALS AND METHODS

Mice were euthanized and the kidneys removed for analysis. Tonin activity was evaluated by radioimmunoassay and angiotensin I-converting enzyme (ACE) activity by HPLC. Tonin, ACE and angiotensin II-converting enzyme (ACE2) expression was analyzed by Western blotting.

RESULTS

Tonin activity was significantly increased in TGM`(rTon) compared to their respective wild-type (WT) littermates (1.7 ± 0.21 vs 0.11 ± 0.02 nmol of Ang II/min/mg of protein). Tonin activity had a strong positive correlation with tonin expression in both TGM`(rTon) and their respective wild-type littermates. The ACE activity and expression levels of 65-kDa N-domain angiotensin I-converting enzyme isoform were significantly increased in the TGM`(rTon) when compared with WT. ACE2 expression levels were statistically significantly higher in the TGM`(rTon) when compared with WT. Angiotensin 1-7 (Ang(1-7)) and Ang I levels were significantly lower in the TGM`(rTon).

CONCLUSIONS

We suggest that the environment of tonin abundance may increase N-domain ACE activity liberated by a secretase able to cleave somatic ACE.

Neuropeptides: metabolism to bioactive fragments and the pharmacology of their receptors

The proteolytic processing of neuropeptides has an important regulatory function and the peptide fragments resulting from the enzymatic degradation often exert essential physiological roles. The proteolytic processing generates, not only biologically inactive fragments, but also bioactive fragments that modulate or even counteract the response of their parent peptides. Frequently, these peptide fragments interact with receptors that are not recognized by the parent peptides. This review discusses tachykinins, opioid peptides, angiotensins, bradykinins, and neuropeptide Y that are present in the central nervous system and their processing to bioactive degradation products. These well-known neuropeptide systems have been selected since they provide illustrative examples that proteolytic degradation of parent peptides can lead to bioactive metabolites with different biological activities as compared to their parent peptides. For example, substance P, dynorphin A, angiotensin I and II, bradykinin, and neuropeptide Y are all degraded to bioactive fragments with pharmacological profiles that differ considerably from those of the parent peptides. The review discusses a selection of the large number of drug-like molecules that act as agonists or antagonists at receptors of neuropeptides. It focuses in particular on the efforts to identify selective drug-like agonists and antagonists mimicking the effects of the endogenous peptide fragments formed. As exemplified in this review, many common neuropeptides are degraded to a variety of smaller fragments but many of the fragments generated have not yet been examined in detail with regard to their potential biological activities. Since these bioactive fragments contain a small number of amino acid residues, they provide an ideal starting point for the development of drug-like substances with ability to mimic the effects of the degradation products. Thus, these substances could provide a rich source of new pharmaceuticals. However, as discussed herein relatively few examples have so far been disclosed of successful attempts to create bioavailable, drug-like agonists or antagonists, starting from the structure of endogenous peptide fragments and applying procedures relying on stepwise manipulations and simplifications of the peptide structures.

Roles of kinins in the nervous system

The kallikrein-kinin system (KKS) is an endogenous pathway involved in many biological processes. Although primarily related to blood pressure control and inflammation, its activation goes beyond these effects. Neurogenesis and neuroprotection might be stimulated by bradykinin being of great interest for clinical applications following brain injury. This peptide is also an important player in spinal cord injury pathophysiology and recovery, in which bradykinin receptor blockers represent substantial therapeutic potential. Here, we highlight the participation of kinin receptors and especially bradykinin in mediating ischemia pathophysiology in the central and peripheral nervous systems. Moreover, we explore the recent advances on mechanistic and therapeutic targets for biological, pathological, and neural repair processes involving kinins.

The kallikrein-kinin system as a regulator of cardiovascular and renal function

Autocrine, paracrine, endocrine, and neuroendocrine hormonal systems help regulate cardio-vascular and renal function. Any change in the balance among these systems may result in hypertension and target organ damage, whether the cause is genetic, environmental or a combination of the two. Endocrine and neuroendocrine vasopressor hormones such as the renin-angiotensin system (RAS), aldosterone, and catecholamines are important for regulation of blood pressure and pathogenesis of hypertension and target organ damage. While the role of vasodepressor autacoids such as kinins is not as well defined, there is increasing evidence that they are not only critical to blood pressure and renal function but may also oppose remodeling of the cardiovascular system. Here we will primarily be concerned with kinins, which are oligopeptides containing the aminoacid sequence of bradykinin. They are generated from precursors known as kininogens by enzymes such as tissue (glandular) and plasma kallikrein. Some of the effects of kinins are mediated via autacoids such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF), and/or tissue plasminogen activator (tPA). Kinins help protect against cardiac ischemia and play an important part in preconditioning as well as the cardiovascular and renal protective effects of angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARB). But the role of kinins in the pathogenesis of hypertension remains controversial. A study of Utah families revealed that a dominant kallikrein gene expressed as high urinary kallikrein excretion was associated with a decreased risk of essential hypertension. Moreover, researchers have identified a restriction fragment length polymorphism (RFLP) that distinguishes the kallikrein gene family found in one strain of spontaneously hypertensive rats (SHR) from a homologous gene in normotensive Brown Norway rats, and in recombinant inbred substrains derived from these SHR and Brown Norway rats this RFLP cosegregated with an increase in blood pressure. However, humans, rats and mice with a deficiency in one or more components of the kallikrein-kinin-system (KKS) or chronic KKS blockade do not have hypertension. In the kidney, kinins are essential for proper regulation of papillary blood flow and water and sodium excretion. B2-KO mice appear to be more sensitive to the hypertensinogenic effect of salt. Kinins are involved in the acute antihypertensive effects of ACE inhibitors but not their chronic effects (save for mineralocorticoid-salt-induced hypertension). Kinins appear to play a role in the pathogenesis of inflammatory diseases such as arthritis and skin inflammation; they act on innate immunity as mediators of inflammation by promoting maturation of dendritic cells, which activate the body's adaptive immune system and thereby stimulate mechanisms that promote inflammation. On the other hand, kinins acting via NO contribute to the vascular protective effect of ACE inhibitors during neointima formation. In myocardial infarction produced by ischemia/reperfusion, kinins help reduce infarct size following preconditioning or treatment with ACE inhibitors. In heart failure secondary to infarction, the therapeutic effects of ACE inhibitors are partially mediated by kinins via release of NO, while drugs that activate the angiotensin type 2 receptor act in part via kinins and NO. Thus kinins play an important role in regulation of cardiovascular and renal function as well as many of the beneficial effects of ACE inhibitors and ARBs on target organ damage in hypertension.

Ischemic stroke and traumatic brain injury: the role of the kallikrein-kinin system

Acute ischemic stroke and traumatic brain injury are a major cause of mortality and morbidity. Due to the paucity of therapies, there is a pressing clinical demand for new treatment options. Successful therapeutic strategies for these conditions must target multiple pathophysiological mechanisms occurring at different stages of brain injury. In this respect, the kallikrein-kinin system is an ideal target linking key pathological hallmarks of ischemic and traumatic brain damage such as edema formation, inflammation, and thrombosis. In particular, the kinin receptors, plasma kallikrein, and coagulation factor XIIa are highly attractive candidates for pharmacological development, as kinin receptor antagonists or inhibitors of plasma kallikrein and coagulation factor XIIa are neuroprotective in animal models of stroke and traumatic brain injury. Nevertheless, conflicting preclinical evaluation as well as limited and inconclusive data from clinical trials suggest caution when transferring observations made in animals into the human situation. This review summarizes current evidence on the pathological significance of the kallikrein-kinin system during ischemic and traumatic brain damage, with a particular focus on experimental data derived from animal models. Experimental findings are also compared with human data if available, and potential therapeutic implications are discussed.

Kallikreins on steroids: structure, function, and hormonal regulation of prostate-specific antigen and the extended kallikrein locus

The 15 members of the kallikrein-related serine peptidase (KLK) family have diverse tissue-specific expression profiles and putative proteolytic functions. The kallikrein family is also emerging as a rich source of disease biomarkers with KLK3, commonly known as prostate-specific antigen, being the current serum biomarker for prostate cancer. The kallikrein locus is also notable because it is extraordinarily responsive to steroids and other hormones. Indeed, at least 14 functional hormone response elements have been identified in the kallikrein locus. A more comprehensive understanding of the transcriptional regulation of kallikreins may help the field make more informed hypotheses about the physiological functions of kallikreins and their effectiveness as biomarkers. In this review, we describe the organization of the kallikrein locus and the structure of kallikrein genes and proteins. We also focus on the transcriptional regulation of kallikreins by androgens, progestins, glucocorticoids, mineralocorticoids, estrogens, and other hormones in animal models and human prostate, breast, and reproductive tract tissues. The interaction of the androgen receptor with androgen response elements in the promoter and enhancer of KLK2 and KLK3 is also summarized in detail. There is evidence that all kallikreins are regulated by multiple nuclear receptors. Yet, apart from KLK2 and KLK3, it is not clear whether all kallikreins are direct transcriptional targets. Therefore, we argue that gaining more detailed information about the mechanisms that regulate kallikrein expression should be a priority of future studies and that the kallikrein locus will continue to be an important model in the era of genome-wide analyses.

Bradykinin into amygdala induces thermal hyperalgesia in rats

Bradykinin is one of the most potent endogenous algesic substances and its role in pain transmission has been intensively studied in the periphery. However, the action of this peptide in central structures involved in pain transmission remains unclear. Administration of bradykinin (0.25 nmol/site) into the right amygdala of adult male Wistar rats induced thermal hyperalgesia, evaluated in the paw-flick test. Bradykinin-induced hyperalgesia was abolished by co-administration with the B(2) receptor antagonist Hoe 140 (5 pmol/site), the NMDA antagonist MK-801 (5 nmol/site), the cyclooxygenase inhibitor indomethacin (10 nmol/site) and the glial metabolic inhibitor fluorocitrate (1 nmol/site). Since the intra-amygdala administration of bradykinin did not alter spontaneous locomotion in the open-field test, it is unlikely that the current described hyperalgesic effect of bradykinin is due to an unspecific action on motor activity. These findings provide evidence that bradykinin, through activation of amygdalar B(2) receptors induces hyperalgesia and that glutamatergic- and prostanoid-mediated mechanisms are involved in such effect.

Multifunctional effects of bradykinin on glial cells in relation to potential anti-inflammatory effects

Kinins have been reported to be produced and act at the site of injury and inflammation. Despite many reports that they are likely to initiate a particular cascade of inflammatory events, bradykinin (BK) has anti-inflammatory effects in the brain mediated by glial cells. In the present review, we have attempted to describe the complex responses and immediate reaction of glial cells to BK. Glial cells express BK receptors and induce Ca(2+)-dependent signal cascades. Among them, production of prostaglandin E(2) (PGE(2)), via B(1) receptors in primary cultured microglia, has a negative feedback effect on lipopolysaccharide (LPS)-induced release of tumor necrosis factor-alpha (TNF-alpha) via increasing intracellular cyclic adenosine monophosphate (cAMP). In addition, BK up-regulates the production of neurotrophic factors such as nerve growth factor (NGF) via B(2) receptors in astrocytes. These results suggest that BK may have anti-inflammatory and neuroprotective effects in the brain through multiple functions on glial cells. These observations may help to understand the paradox on the role of kinins in the central nervous system and may be useful for therapeutic strategy.

Neuroprotective role of bradykinin because of the attenuation of pro-inflammatory cytokine release from activated microglia

Bradykinin (BK) has been reported to be a mediator of brain damage in acute insults. Receptors for BK have been identified on microglia, the pathologic sensors of the brain. Here, we report that BK attenuated lipopolysaccharide (LPS)-induced release of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta from microglial cells, thus acting as an anti-inflammatory mediator in the brain. This effect was mimicked by raising intracellular cAMP or stimulating the prostanoid receptors EP2 and EP4, while it was abolished by a cAMP antagonist, a prostanoid receptor antagonist, or by an inhibitor of the inducible cyclooxygenase (cyclooxygenase-2). BK also enhanced formation of prostaglandin E(2) and expression of microsomal prostaglandin E synthase. Expression of BK receptors and EP2/EP4 receptors were also enhanced. Using physiological techniques, we identified functional BK receptors not only in culture, but also in microglia from acute brain slices. BK reduced LPS-induced neuronal death in neuron-microglia co-cultures. This was probably mediated via microglia as it did not affect TNF-alpha-induced neuronal death in pure neuronal cultures. Our data imply that BK has anti-inflammatory and neuroprotective effects in the central nervous system by modulating microglial function.

Anti-inflammatory effects of kinins via microglia in the central nervous system

Kinins are important biologically active peptides that are up-regulated after lesions in both the peripheral and central (CNS) nervous systems. Microglia are immune cells in the CNS and play an important role in the defense of the neuronal parenchyma. In cultured murine microglia, bradykinin (BK) induces mobilization of intracellular Ca2+, microglial migration, and increases the release of nitric oxide and prostaglandin E2. On the other hand, BK attenuates lipopolysaccharide-activated TNF-α and IL-1β release. These results suggest that BK functions as a signal in brain trauma and may have an anti-inflammatory role in the CNS.

The tissue kallikrein-kinin system protects against cardiovascular and renal diseases and ischemic stroke independently of blood pressure reduction

Tissue kallikrein (hK1) cleaves low-molecular-weight kininogen to produce kinin peptide, which binds to kinin receptors and triggers a wide spectrum of biological effects. Tissue kallikrein levels are reduced in humans and in animal models with hypertension, cardiovascular and renal diseases. Transgenic mice or rats over-expressing human tissue kallikrein or kinin B2 receptor are permanently hypotensive, and somatic kallikrein gene delivery reduces blood pressure in several hypertensive rat models. Moreover, kallikrein gene delivery or kallikrein protein infusion can directly improve cardiac, renal and neurological function without blood pressure reduction. Kallikrein has pleiotropic effects in inhibiting apoptosis, inflammation, proliferation, hypertrophy and fibrosis, and promoting angiogenesis and neurogenesis in different experimental animal models. Kallikrein's effects can be blocked by kinin B2 receptor antagonists. Mechanistically, tissue kallikrein/kinin leads to increased nitric oxide levels and Akt activation, and reduced reactive oxygen species formation, TGF-beta1 expression, MAPK and nuclear factor-kappaB activation. Our studies indicate that tissue kallikrein, through the kinin B2 receptor and nitric oxide formation, can protect against oxidative damage in cardiovascular and renal diseases and ischemic stroke. These novel findings suggest that kallikrein/kinin may serve as new drug targets for the prevention and treatment of heart failure, renal disease and stroke in humans.

Rhythmic expression of adenylyl cyclase VI contributes to the differential regulation of serotonin N-acetyltransferase by bradykinin in rat pineal glands

The rhythmic nocturnal production of melatonin in pineal glands is controlled by the periodic release of norepinephrine from the superior cervical ganglion. Norepinephrine binds to the beta-adrenergic receptor and stimulates an increase in intracellular cAMP levels, leading to the transcriptional activation of serotonin N-acetyltransferase, which in turn promotes melatonin production. In the present study, we report that bradykinin inhibits basal- and forskolin-stimulated adenylyl cyclase activity, norepinephrine-induced cAMP generation, and N-acetyltransferase expression in a calcium-dependent manner. These effects were blocked by pretreatment with U73122 (a selective phospholipase C inhibitor), and 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (a Ca(2+) chelator), but not pertussis toxin. The calcium ionophore, ionomycin, inhibited isoproterenol-mediated cAMP generation, similar to bradykinin. Interestingly, the inhibitory effect of bradykinin was evident only during the daytime. At midday, bradykinin inhibited the cAMP level by approximately 50% but markedly stimulated cAMP production (by approximately 50%) at night. Northern blotting and immunoblotting data disclosed circadian expression of calcium-inhibitable adenylyl cyclase type 6. Expression of adenylyl cyclase type 6 was maximal at Zeitgeber Time (ZT) 01 and very low at ZT 13. Our results suggest that bradykinin-induced calcium inhibits melatonin synthesis through the mediation of adenylyl cyclase type 6 expression.

Actions of insulin-like growth factor binding protein-5 (IGFBP-5) are potentially regulated by tissue kallikrein in rat brains

Tissue kallikrein (EC 3.4.21.35) that hydrolyzes kininogen and releases a physiologically active peptide, kinin, is found in rat brains. Insulin-like growth factor binding proteins (IGFBPs) that modulate IGF actions are also expressed in a variety of tissues including rat brains, and one of the major IGFBPs expressed in brain is known to be IGFBP-5, which is reported to be hydrolyzed in vitro by prostate-specific antigen (PSA) and gamma-nerve growth factor (gamma-NGF), both of which belong to the member of the kallikrein gene family. This study was designed to determine whether or not kallikrein has a potential to hydrolyze IGFBP-5 and their topographic proximity was investigated in rat brain using double immunohistochemical staining method. Immunohistochemically, IGFBP-5 positive cells were numerous and widespread in the cerebral cortex and belonged to neurons in the cell configuration. IGFBP-5 positive cells were negative for S-100 protein and were positive for betaIII tubulin, confirming them to be neurons. In addition, kallikrein positive cells were virtually all IGFBP-5 positive cells. IGFBP-5 was clearly hydrolyzed by kallikrein with cleavage sites of Arg188-Met189 and Arg136-Arg137 of IGFBP-5. Therefore, there is a possibility that kallikrein plays an important role in brain physiology, specifically in the neurons by regulating the actions of IGFBP-5 and IGF.

Lipopolysaccharide injection into the cerebral ventricle evokes kininogen induction in the rat brain

Kinins, such as bradykinin and Lys-bradykinin, are important mediators in peripheral inflammation. Although the existence of the components necessary for generating kinins has been demonstrated in the brain, a functional role of the kinin-generating system in cerebral inflammation remains to be defined. The aim of the present study was to elucidate whether inflammatory stimuli alter the mRNA levels of components for the kallikrein-kinin system, including kallikreins, kininogens and bradykinin type 2 (B(2)-) receptor in rat brain using the reverse transcription polymerase chain reaction. The intracerebroventricular (i.c.v.) injection of lipopolysaccharide (LPS; 0.25 microg/animal) resulted in the elevation of T-kininogen and high-molecular-weight (H-) kininogen mRNAs in various brain regions within 24 h, prominently in the choroid plexus. The appearance of immunoreactive T-kininogen was demonstrated in the epithelium of the choroid plexus, but not in the matrix and vessels, after i.c.v. injection of LPS. The mRNA levels of kallikreins, such as tissue kallikrein, T-kininogenase and plasma kallikrein, and B(2)-receptor did not change in any brain region following i.c.v. injection of LPS. The levels of cyclooxygenase-2 mRNA in the choroid plexus were increased within 2 h after i.c.v. injection of LPS, and pretreatment with indomethacin (3 microg/animal, i.c.v.) abolished the LPS-induced elevation of T- and H-kininogen mRNAs in the choroid plexus. The i.c.v. injection of prostaglandin E(2) (100 ng/animal) also caused increases in the mRNA levels of T- and H-kininogens in various brain regions, including the choroid plexus. These results suggest that LPS stimulates the induction of kininogens in the brain, especially the choroid plexus, by stimulating the production of arachidonic metabolites such as prostaglandin E(2).

Tonin in rat heart with experimental hypertrophy

The present study was undertaken to determine tonin expression and activity in rat heart presenting isoproterenol-induced hypertrophy. Renin, angiotensin-converting enzyme (ACE), and angiotensinogen (AG) expression were also determined. Wistar rats were treated with isoproterenol for 7 days (5 mg x kg(-1) x day(-1) sc). For untreated animals, the levels of tonin-specific activity in the atrium were 2.6- and 5.5-fold higher than those of the left and right ventricle, respectively. After treatment, the levels of tonin-specific activity increased twofold in the atrium but did not change in the ventricles. Renin expression was not detectable in these structures, and ACE expression levels did not change with treatment. AG expression was detected in the left ventricle at very low levels compared with the atrium and increased significantly only in the hypertrophied atrium (1.8-fold). Tonin mRNA was not detected in the ventricle but was found at low levels in the atrium, which increased after isoproterenol treatment. Our results permit us to conclude that tonin may play a role in the process of heart hypertrophy in the rat.

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.

Detection of tissue kallikrein and kinin B1 and B2 receptor mRNAs in human brain by in situ RT-PCR

Tissue kallikrein (TK) and kinin receptors have been immuno-localized in various areas of the human nervous system, suggesting that the kallikrein-kinin system (KKS) may be functionally active in the brain. The aim of this study was to determine the cellular expression of TK and kinin B1 and B2 receptor mRNAs in specific regions of the human brain by in situ reverse transcriptase polymerase chain reaction. Autopsy samples of the brain, spinal cord, kidney and salivary gland were embedded in paraffin. Sections (5 microm), adhered onto silane coated glass slides, were treated with Proteinase K and DNase, followed by reverse transcription polymerase chain reaction with specific KKS primers and digoxigenin-dUTP. Detection of the digoxigenin-label demonstrated localization of TK, B1 and B2 mRNAs in the cytoplasm of some neuronal cell bodies in the hypothalamus, thalamus, frontal cortex and spinal cord. TK mRNA was also observed in the ependymal cells lining the cerebral ventricles and epithelial cells of the choroid plexus. In the choroid plexus, only B1 gene expression was observed in some choroidal epithelial cells while no B2 labeling was detected. The identification of mRNAs to TK, B1 and B2 kinin receptors in human nervous tissue supports previous evidence for the presence of the KKS in the brain and confirms localized protein synthesis.

Biochemical and immunohistochemical demonstration of tissue kallikrein in the neuronal nuclei of the developing rat brains

Kallikrein content and cellular localization in the prenatal, newborn and adult rat brains were determined by the enzyme-linked immunosorbent assay and immunohistochemistry. The content was the highest in the prenatal rats and highly predominant in the neuronal nuclei during the prenatal to newborn periods, whereas the immunoreactive kallikrein was mainly located around neuronal cell bodies and their processes in the adult rats. The preferential nuclear localization in the prenatal rat brains was further confirmed by the immunoblotting technique after the SDS-polyacrylamide gel electrophoresis of the lysate of the nuclei fractionated from the prenatal rat brains. The meaning(s) of this kallikrein localization in the neuronal nuclei at the prenatal and newborn stages is unknown. However, we would like to conclude that this enzyme plays an important role in the morphogenesis of brain by acting on the substance(s) in the neuronal nuclei at the developing stage.

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.

Brain sites involved in the antinociceptive effect of bradykinin in rats

The localization of brain sites where bradykinin (BK) induces its antinociceptive effect in rats, was studied using as index the threshold for the jaw-opening reflex elicited by the dental pulp electrical stimulation test (DPEST). The microinjection of BK into the lateral or fourth cerebral ventricles induced an antinociceptive effect, with Index of Antinociception (IA) of 0.51+/-0.03 and 0.68+/-0.05, respectively. However, microinjections of the peptide into the third ventricle induced a less marked antinociception (IA = 0.28+/-0.08). The brain sites where the microinjection of BK caused an antinociceptive effect were: locus coeruleus, principal nucleus, oral part of the spinal sensorial trigeminal nucleus, and the sensory root of the trigeminal nerve. The antinociceptive effect was more intense when BK (4-16 nmol) was injected into the locus coeruleus. Microinjection of BK (4 nmol) into the fourth ventricle, but not into the locus coeruleus, induced an increase in blood pressure. The microinjection of the peptide into the nucleus tractus solitarius, a site that is also involved in the pressor effect of BK, did not induce an antinociceptive effect. These results indicate that the antinociceptive effect of BK is not related to blood pressure changes. The microinjection of BK into some of the sites involved in the mechanisms of analgaesia, including the periaqueductal gray matter (dorsal, lateral and ventrolateral) and the dorsal raphe nucleus did not induce an antinociceptive effect. The results suggest that the most likely brain sites involved in the antinociceptive effect of BK are the locus coeruleus and the principal sensory trigeminal nucleus. The present results did not exclude the involvement of other brain sites surrounding the lateral and the third ventricles.

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.

Potential role of kallikrein in diurnal rhythms and perivascular distribution in rat pineal glands

Kallikrein hydrolyzes various biologically active peptides, other than kininogens, such as vasoactive intestinal polypeptide (VIP), in vitro. Since kallikrein and VIP have been immunohistochemically shown to be present in the perivascular areas of the pineal gland, this study was designed to determine their topographic proximity in these glands, using immunohistochemical and immunoelectron microscopic double staining methods. Furthermore, since this gland is well-known to have a circadian rhythm, the kallikrein content was measured every 4 h, using a synthetic substrate, Pro-Phe-Arg-MCA, and an enzyme-linked immunosorbent assay (ELISA) to determine whether kallikrein has a circadian rhythm. The immunoreactivities of kallikrein and VIP were highly localized in the perivascular extracellular spaces and were virtually identical in distribution. The kallikrein content changed every 4 h and was high under light and low under dark conditions. The change was more evident when the synthetic substrate was used, and this rhythm was subtle on ELISA. VIP is also said to have a circadian rhythm in the pineal glands, being low under light and high under dark conditions, i.e., opposite to that of kallikrein. Since kallikrein degrades VIP in vitro, it is reasonable to speculate that pineal gland kallikrein is involved in the processing of VIP and possibly other biologically active peptides in the perivascular areas with a discernible circadian rhythm.

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.

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.

Distribution of tissue kallikreins in lower vertebrates: potential physiological roles for fish kallikreins

Fish skeletal muscle prokallikrein was purified from black sea bass, Centropritis striata, and used for the production of polyclonal antiserum. Tissue proteins from primitive fish and teleosts, an alligator, and an insectivore were resolved by sodium dodecylsulfate-polyacrylamide gel electrophoresis, Western blotted, and probed with fish muscle prokallikrein antiserum. A recurring theme was the presence of approximately 36 and 72 kDa kallikrein-like proteins in skeletal muscle, heart, gill, kidney, and spleen of higher teleosts and in selected tissues of sturgeon, shark, alligator, and mole. The presence of immunoreactive kallikreins in osmoregulatory organs such as the gills of teleosts and the rectal gland of sharks signifies a potential role for these proteins in osmoregulation. Black sea bass, rock bass, and sturgeon contained many immunoreactive kallikreins in their swimbladders, which implicates a role for kallikreins in the regulation of blood flow and vascular permeability to facilitate gas exchange within the bladder. Kallikreins were consistently identified in skeletal muscle and heart of all the species evaluated and may regulate local blood flow, muscle contraction or relaxation, or participate in various transport processes. The antiserum to fish prokallikrein recognized immunoreactive kallikreins from pancreatic tissues from fish and lower vertebrates, but not from the pyloric caecum of sea bass. The wide distribution of tissue kallikrein in lower vertebrates suggests that it may participate in a variety of physiological functions.

Kinin receptors on human neurones

Knowledge of the distribution of kinin receptors in the human brain will aid our understanding of the role of kinins in neurophysiology. Furthermore, induction of the kinin B1 receptor may be important in the pathogenesis of neural diseases. Using polyclonal antibodies directed to specific regions of the B1 and B2 kinin receptors and standard immunolabelling techniques, we report on the localisation of these receptors on neurones in specific areas of the human brain. B2 bradykinin receptors are present in neurones of the brain stem, basal nuclei, cerebral cortex, thalamus and hypothalamus. B2 immunolabelling was also observed in the endothelial lining of the superior sagittal dural sinus and ependyma of the lateral and third ventricles. B1 kinin receptors have been localised on neurones of the thalamus, spinal cord and hypothalamus. Although binding of labelled bradykinin to neuronal membranes has been demonstrated, this is the first conclusive evidence for the existence of immunoreactive B1, and further confirmation of B2 receptors on human neurones.

Tissue-specific expression and promoter analyses of the human tissue kallikrein gene in transgenic mice

The expression of the tissue kallikrein gene is tissue-specific and exhibits a complex pattern of transcriptional and post-translational regulation. Information concerning the mechanism of its tissue-specific expression has been limited owing to the lack of suitable cell lines for the expression study. We approached this problem by introducing human tissue kallikrein gene constructs into mouse embryos, creating transgenic lines carrying its coding sequence with varying lengths of the promoter region. One construct (PHK) contained 801 bp in the 5'-flanking region and two deletion constructs contained either 302 bp (D300) or 202 bp (D200) of the promoter region. The expression of human tissue kallikrein in these transgenic mice was monitored by Northern blot, reverse transcriptase-PCR followed by Southern blot, and radioimmunoassay. In all three lines, human tissue kallikrein was expressed predominantly in the pancreas and at lower levels in other tissues, including salivary gland, kidney and spleen. This pattern was similar to that of tissue kallikrein expression in human tissues. The D300 line has higher levels of transgene expression than the D200 and PHK lines. The results indicate that the 202 bp segment immediately upstream of the translation starting site is sufficient to direct a tissue-specific expression pattern of the human tissue kallikrein gene, and that regulatory elements might exist between -801 and -202.

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.

Central B2 receptor involvement in the antinociceptive effect of bradykinin in rats

1. The effect of intracerebroventricular (i.c.v.) injection of bradykinin (BK) and related peptides was tested on the dental pulp electrical stimulation threshold (DPEST) in rats. 2. BK (4, 8 and 16 nmol) induced a dose-dependent increase of DPEST, indicative of an antinociceptive effect. 3. I.c.v. injection of equimolar doses of BK-related peptides, Lys-BK and Met-Lys-BK, also induced an increase of DPEST, but the magnitude of the effect was not as intensive as that induced by BK, when the maximum increase of DPEST was considered. The peptide T-kinin induced a short lasting and weak antinociceptive effect. 4. The B1 agonist, des-Arg9-BK (8 nmol) induced a significant antinociceptive effect, but this was not as intensive as that induced by BK. 5. The B2 antagonist D-Arg0-Hyp3-Thi5,8-D-Phe7-BK (D-Arg0) competitively antagonized the BK-induced antinociception. Likewise, Hyp3-Thi5,8-D-Phe7-BK (Hyp) also antagonized BK effect. However, the compound Thi5,8-D-Phe7-BK (Thi), initially considered a pure BK antagonist, induced an antinociceptive effect, supporting previous observations that this peptide can also act as a partial agonist. 6. It is concluded that the dose-dependent antinociceptive effect induced by i.c.v. injection of BK is mediated by the stimulation of brain B2 receptors.

Intragranular prolactin phosphorylation and kallikrein cleavage are regulated by zinc and other divalent cations

Rat prolactin (PRL) secretory granules contain enzymes for proteolytic cleavage and serial phosphorylation, but hormone cleavage products and phosphorylated PRL are not detected until just prior to exocytosis. Similarly, although PRL is stored in granules, in part, as high-mol-wt oligomers, PRL is primarily monomeric in the circulation. PRL secretory granules contain zinc, calcium, and magnesium, which inhibit depolymerization and dissolution of granules. Divalent cations also protect cysteine free thiol residues in the carboxy-terminal region of the intragranular hormone. The present studies examined the effect of removal and replacement of divalent cations on kallikrein cleavage and phosphorylation of secretory granule PRL.Kallikrein cleavage was assessed utilizing two experimental protocols. First, granules were treated with or without 3 mM EDTA, free hormone thiols were alkylated, the PRL was cleaved by kallikrein, and the small kallikrein-cleavage peptides were assessed by reversephase HPLC. No differences in hormone cleavage owing to removal of divalent cations were observed at this concentration of EDTA. Second, divalent cations in granules were reduced/removed by 10 mM EDTA/ 3 mM o-phenanthroline (OP), followed by addition of either 5 mM zinc, magnesium, calcium, or additional EDTA. Kallikrein cleavage was then initiated. In this instance, the extent of proteolysis was analyzed by two-dimensional polyacrylamide gel electrophoresis (PAGE) of the larger remnant PRL pieces. After treatment with 10 mM EDTA/3 mM OP, results indicated that cleavage between R174 and R175 (site 1) was unaffected by added cations or additional EDTA. Recovery of site 2 cleaved PRL (L1-K185) and site 3 cleaved PRL (L1-R188) was∼40% reduced by zinc, but unaffected by calcium or magnesium. Additional EDTA resulted in increased recovery of site 2 cleaved PRL, but no change in site 3 recovery, suggesting the presence of tightly bound intragranular zinc around site 2, even after the initial EDTA/OP treatment.Phosphorylation of PRL at S177 was studied using the same protocols. Phosphorylation was increased by added EDTA, even at 3 mM, and decreased by divalent cations, with no marked specificity for zinc observed. An additional experiment studied phosphorylation without exposure to kallikrein. Comparisons between the plus and minus kallikrein experiments showed kallikrein to have no apparent preference for unmodified or phosphorylated PRL.From the kallikrein cleavage and phosphorylation studies and modeling of PRL, we suggest D181 as a likely site for intragranular zinc coordination. When C189 and C197 are present as free thiols in intragranular PRL, these may also contribute to binding. Zinc coordination in this region of the molecule apparently regulates proteolytic processing by kallikrein, as well as contributing to the stability of the hormone storage forms.

Regional distribution of tissue kallikrein in the human brain

Except for the localisation of tissue kallikrein (TK) in human prolactin secreting adenomas, its apparent deficiency in Alzheimer's disease and presence in human cerebrospinal fluid (CSF), the regional distribution of TK in human brain has not been defined. In this study on human brains collected within 24 h of death, we report on the regional distribution of TK in 24 different brain areas. The presence of TK was determined by its amidase and kininogenase activities, and the cellular localisation by immunocytochemistry. The highest amidolytic activity using the substrate D-ValLeuArg-pNA was recorded with extracts of the choroid plexus and hypothalamus, whereas extracts of the cerebral cortex (5 areas), cerebellum (3 areas), brain stem and thalamus possessed moderate amidolytic activity which correlated with the kininogenase assay. Immunoreactive TK has thus far been visualised in neurones of the hypothalamus, thalamus and reticular areas of the brain stem, as well as in cells of the anterior pituitary and choroid plexus by light and confocal microscopy. The cellular distribution of TK in specific areas suggests a role for TK in the neurones and epithelial cells of the brain. The question whether the functional importance of TK may relate to a particular cell type remains to be elucidated.

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.

Immunohistochemical demonstration of tissue kallikrein in the neurons of rat brain

The distribution of tissue kallikrein (EC.3.4.21.35) in the rat brain was investigated by an enzyme-linked immunosorbent assay (ELISA) and immunohistochemical technique using antiserum against rat urinary kallikrein. More than 75% of the total amount of kallikrein in the extracts of the cerebral cortex and brain stem was determined by the ELISA to be in the form of prokallikrein, suggesting that the greater part of the enzyme exists in the form of pro-enzyme in the central nervous system. Furthermore, immunohistochemical examination revealed that, although the kallikrein-positive cells were widespread and scattered in the brain, the immunoreactive substances preferentially locate in the neuronal cell bodies and their processes in both the cerebral cortex and brainstem.

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)

Cellular mechanisms of estrogen- and dopamine-induced control of glandular kallikrein in the anterior pituitary of the rat

Glandular kallikrein (GK, a trypsin-like serine protease) exhibits estrogen induction and dopamine repression in rat pituitary lactotrophs. Steroid induction may reflect primary actions to increase selectively the synthesis of specific proteins, or may be part of broad cellular responses secondary to steroid-induced phenotype transitions. This study examined the cellular mechanisms underlying estrogen and dopaminergic control of lactotroph GK using a quantified immunocytochemical approach. Pituitaries from ovariectomized rats exhibited little GK staining. Estradiol treatment for 10 days produced dose-dependent increases in pituitary mass, the percentage of lactotrophs (indicating lactotroph proliferation) and the percentage of GK-positive cells. Also, GK staining intensity was dependent upon estradiol dose, increasing 4-fold between 5 micrograms and 50 micrograms/48 h. Dopamine receptor blockade with haloperidol (2.5 mg/kg/24 h) elicited weak GK immunostaining in 46% of the lactotrophs in the absence of estradiol, and markedly potentiated GK staining intensity elicited with low but not high doses of estradiol. The results suggest that GK induction is a primary estrogen effect, and is not secondary to a phenotype transition: the induction is enhanced by estrogen-induced lactotroph proliferation. Dopaminergic systems strongly inhibit GK induction by low estradiol levels. This dopaminergic modulation may shift the induction of lactotroph GK to physiological events associated with high estradiol levels or low dopaminergic tone.

Molecular aspects of kallikrein and kininogen in the maturing kidney

Kinins are vasoactive paracrine peptides which participate in a wide range of functions, including the regulation of local organ blood flow, systemic blood pressure, transepithelial water and electrolyte transport, cellular growth, capillary permeability and inflammatory response, and pain. The recent introduction of specific bradykinin receptor subtype antagonists has greatly advanced our understanding of the role of the kallikrein-kinin system (KKS) in various physiological and disease states. However, a major gap remains in our knowledge of the role of kinins in early development. In this review, evidence is presented that the developing nephron expresses both tissue kallikrein and kininogen, and that the genes encoding the components of the KKS are subject to considerable developmental regulation. The activity of the intrarenal kinin-generating system is lowest in the developing kidney and increases with age. Completion of nephrogenesis is characterized by a marked surge in intrarenal kallikrein synthesis and gene transcription. Maturation is associated with redistribution of intrarenal kallikrein and its messenger RNA from the inner to outer cortical nephrons following the centrifugal pattern of nephron development. Challenges for the future include delineation of the direct role of kinins in the maturation of renal functions and elucidation of the molecular mechanisms underlying the developmental expression of the KKS.

Adrenal kallikrein

Kallikrein was identified in the adrenal glands of the rat. The enzyme was present in active and inactive forms (n = 9), since preincubation with trypsin increased kininogenase activity from 54.8 +/- 11.8 to 230 +/- 23 pg bradykinin per milligram protein per minute. Adrenal kininogenase activity was inhibited by 91% by phenylmethylsulfonyl fluoride (2 mM), 81% by D-Phe-Phe-Arg-chloromethyl ketone (1 microM), 88% by aprotinin (1,000 KIU), and only 16% by soybean trypsin inhibitor (50 microM). Preincubation with antibodies against rat urinary kallikrein resulted in over 90% inhibition of kininogenase activity. Immunoreactive glandular kallikrein was 30.7 +/- 4.8 ng/mg protein (n = 11). The apparent molecular weight of the adrenal kininogenase on gel filtration chromatography was 33,000 +/- 500 D. Both the adrenal enzyme and the purified submandibular gland kallikrein used as a control had the same mobility on alkaline polyacrylamide gel electrophoresis. To determine whether messenger RNA (mRNA) for glandular kallikrein is present in adrenal gland RNA, we used the polymerase chain reaction employing oligonucleotide primers and glandular kallikrein 32P complementary DNA (cDNA) as a probe, which should give a cDNA fragment of 370 bp. Southern blots of the amplified products revealed a fragment of the predicted size. In conclusion, glandular kallikrein has been identified in the adrenal glands. The presence of mRNA for glandular kallikrein suggests that kallikrein is synthesized locally in this tissue. This provides an anatomic basis for possible participation of a local kallikrein-kinin pathway in the regulation of adrenal function.

Tissue kallikrein in the rat pineal gland: an immunocytochemical study

Tissue kallikrein in the rat pineal gland was immunocytochemically investigated with the aid of specific antiserum against rat urinary kallikrein. We also compared the tissue kallikrein immunoreactivity of the pineal gland with that of the submandibular gland and kidney, which have been well established as tissue kallikrein-synthesizing organs. The cytoplasm of pinealocytes from both the superficial and the deep portion of the gland exhibited specific immunolabeling for tissue kallikrein, but the immunoreaction was weaker than that observed in exocrine organs. Two types of tissue kallikrein-immunoreactive pinealocytes were distinguished; the first predominant type displayed moderate immunostaining, whereas a small number of cells, the second type, were so intensely labeled that their cytoplasmic processes were clearly outlined. The results of the present study suggest the existence of different types of pinealocytes and a potential physiological role of tissue kallikrein in the rat pineal gland.