Action of bradykinin at the cyclooxygenase step in prostanoid synthesis through the arachidonic acid cascade

Airway hyperresponsiveness in anaesthetised guinea-pigs 18-24 hours after antigen inhalation does not occur with all intravenously administered spasmogens

Actively sensitised guinea-pigs were exposed to inhalation challenges with ovalbumin aerosol (macro- and microshock) and airway responsiveness to six intravenously administered spasmogens was evaluated 18 to 24 hr later in the anaesthetised animal. An increase in airway sensitivity was defined as a significant leftward shift of the dose-response curve when compared with saline-challenged control sensitized animals. After ovalbumin-macroshock (1% ovalbumin for 2 min. with mepyramine cover against fatal anaphylaxis), airway hyperresponsiveness was seen to 5-HT, the thromboxane A2-mimetic, U-46619, and bradykinin but not to methacholine, histamine or substance P. A similar pattern was seen after ovalbumin-microshock (0.010% ovalbumin for 60 min.), with induction of airway hyperreactivity to 5-HT and U-46619 but not methacholine or histamine. When the U-46619 dose-response curve was constructed following treatment of the animals with atropine (1 mg/kg, intravenously), airway hyperresponsiveness was no longer significant. As an index of airway inflammation, lung weights were significantly heavier in ovalbumin-challenged animals, than in saline-challenged controls. The results of this study with intravenously administered spasmogens does not support claims that ovalbumin-induced airway hyperreactivity in the guinea-pig is a 'non-specific' phenomenon.

Differential regulation of bradykinin receptor density, intracellular Ca2+, and prostanoid release in skin and foreskin fibroblasts. Effects of cell density and interleukin-1alpha

1. Bradykinin (BK) receptors, cytosolic Ca2+, and prostanoids were studied in human skin and foreskin fibroblasts. 2. Bmax values of BK receptors were higher in foreskin than in skin fibroblasts, increasing with cell densities in both cell types. IL-1alpha-dependent receptor induction was blocked by cycloheximide. 3. BK-stimulated cytosolic Ca2+ elevation was higher in confluent than in non-confluent cultures and larger in foreskin than in skin fibroblasts. Responses were not enhanced after IL-1-alpha-induced up-regulation of BK receptors. 4. Intrinsic prostanoid production was higher in foreskin than in skin fibroblasts at comparable cell densities. In foreskin, but not in skin fibroblasts, BK stimulation increased the release of PGE2 10 fold and that of 6-oxo-PGF1alpha 6-7 fold. 5. Preincubation with IL-1alpha had a marked effect on prostanoid release in foreskin fibroblasts only. Subsequent BK stimulation increased the release of PGE2 and 6-oxo-PGF1alpha 7-10 fold in skin fibroblasts while this increase was only 30% in foreskin fibroblasts. Release of TXA2 reached values up to one third of the other prostanoids. The IL-1alpha induced rise in BK-stimulated PGE2 synthesis was fully abolished by specific inhibition of cyclo-oxygenase 2. 6. IL-1alpha sensitized BK-stimulated prostanoid synthesis and modulated prostanoid patterns differently in fibroblasts from skin and foreskin. The IL-1alpha effects on prostanoid release were not related to BK receptor numbers nor to the BK-stimulated Ca2+ signal but appear to be due to induction of prostanoid synthesizing enzymes. Foreskin fibroblasts seem to be unique and significantly different from fibroblasts of other skin locations in respect to their response to inflammation-associated kinins and cytokines.

Bradykinin-induced reductions in collagen gene expression involve prostacyclin

Cardiac fibrosis after myocardial infarction and in chronic hypertension involves an increase in the synthesis and deposition of collagen within the myocardium. Angiotensin-converting enzyme (ACE) inhibitors limit hypertrophy and fibrosis; their mechanism of action remains controversial, although kinins have been implicated to play a role. Because both bradykinin and prostaglandins (PG) have been shown to reduce collagen gene expression in cardiac fibroblasts, the goal of this study was to determine whether the bradykinin effect was mediated through enhanced prostaglandin formation by cardiac fibroblasts. Bradykinin increased [3H]arachidonic acid metabolite release 2.3-fold over control and stimulated a dose-dependent increase in 6-keto PGF1alpha (the stable metabolite of PGI2) release from these cells, in which 1 nmol/L bradykinin produced a 4-fold increase in 6-keto PGF1alpha release. Beraprost (a PGI2 analogue) reduced steady-state proalpha1(I) and proalpha1(III) collagen mRNA levels by 35.6+/-6.6% and 34.2+/-10.0%, respectively. Bradykinin-induced reductions in collagen type I and III gene expression were reversed by pretreatment with indomethacin. Our results indicate that one mechanism by which bradykinin modulates collagen biosynthesis via the rabbit cardiac fibroblast involves formation of arachidonic acid metabolites, particularly PGI2. The results of the present study argue that stabilization of endogenous kinins (as by ACE inhibitors) would enhance prostacyclin production and result in the attenuation of collagen gene expression, with potential implications for collagen synthesis and deposition within the myocardium.

Prostacyclin release by rat cardiac fibroblasts: inhibition of collagen expression

Cardiac fibroblasts, as the source of extracellular matrix for the left ventricle, subserve important functions to cardiac remodeling and fibrotic development following myocardial infarction or with pressure-overload cardiac hypertrophy. The fibroblast may be the target cell for angiotensin-converting enzyme inhibitors (ACEI) that are cardioprotective and reverse collagen deposition and remodeling but whose mechanisms of action remain controversial. Because we previously documented phenotypic differences between cardiac fibroblasts from the spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) left ventricle, the present study evaluated whether phenotypic differences also exist in the release of endogenous arachidonic acid metabolites or in the activation of phospholipase D, and the importance of observed differences to the formation of collagen and the mechanism of action of ACEI. The experimental design compared endogenous sources of arachidonic acid with exogenous prelabeling of cells. Angiotensin II stimulated greater arachidonic acid release than bradykinin, and WKY cells were more responsive than SHR. The major prostanoid formed by cardiac fibroblasts was prostaglandin I2 (PGI2), with more prostacyclin production by WKY cells than SHR cells both under nonstimulated conditions and in response to angiotensin II or bradykinin. Beraprost, a PGI2 analogue, was shown to decrease growth rate and DNA synthesis of fibroblasts and to inhibit mRNA expression for collagen types I and III, with SHR cells being less responsive to beraprost than WKY cells. These results potentially implicate eicosanoid metabolism, particularly PGI2, in collagen formation, fibrotic development, and cardiac remodeling, and they imply that the SHR genetic hypertension model may be predisposed to excess cardiac fibrosis.

Prostacyclin and thromboxane production of rat and cat arterial tissue is altered independently by several vasoactive substances

The modulation of the production of prostacyclin and thromboxane from cat and cat aortic tissue slices by different vasoactive agents has been studied in order to reveal whether the release of these main two vasoactive prostanoids goes in parallel or may be controlled independently. Norepinephrine, isoproterenol, phentolamine, propranolol, angiotensin II, vasopressin, bradykinin, thrombin, verapamil, gallopamil, dopamine or methionin enkephalin were added to the incubation medium and 6-keto-PGF1 alpha (the stable metabolite of prostacyclin) and TxB2 (the stable metabolite of thromboxane) were determined in the supernatant by radioimmunoassay. The ratio of the release of prostacyclin and thromboxane was computed. Norepinephrine increased both prostacyclin and thromboxane release. Isoproterenol increased the ratio of prostacyclin and thromboxane released in cat aortic tissue slices. Phentolamine and propranolol had no effects. Angiotensin II induced a slight but statistically insignificant increase in the ratio of the two prostanoids released. Vasopressin increased thromboxane release only. Bradykinin stimulated the prostacyclin while thrombin stimulated the thromboxane release. Verapamil decreased both prostacyclin and thromboxane production. Gallopamil decreased prostacyclin release and increased thromboxane release from vessel wall slices in a certain concentration range causing a characteristic dose dependent minimum in the ratio of prostacyclin and thromboxane release. Dopamine separately increased prostacyclin release while enkephalin had no significant effect. The data obtained show that in vascular tissue some unidentified yet cytophysiological mechanisms might exist which specifically control the activities of the prostacyclin synthase and thromboxane synthase enzymes.

Role of thromboxane A2 in bradykinin-induced human isolated small bronchi contraction

We previously demonstrated that the bradykinin-induced contraction of human isolated small bronchi is inhibited by indomethacin, capsaicin (N-methyl-N-6-nonenamide) and ruthenium red but not by tachykinin receptor antagonists. The thromboxane A2 receptor (TP receptor) antagonist GR32191 ((1R-(1 alpha(Z),2 beta,3 beta,5 alpha))-(+)-7-(5-(((1,1'-biphenyl)-4-yl)- methoxy)-3-hydroxy-2-(1-piperidinyl)cyclopentyl)-4-heptenoic acid, hydrochloride) (10(-10) to 10(-8) M) dose dependently inhibited the effect of bradykinin, suggesting the mediation of the TP receptor in the action of bradykinin. With higher concentrations of GR32191 (10(-7) and 10(-6) M) bradykinin induced a relaxation which was inhibited by indomethacin and by the bradykinin B2 receptor antagonist Hoe 140 (D-Arg0[Hyp3,Thi-5,D-Tic7,Oic8]bradykinin). The thromboxane A2 synthase inhibitor dazoxiben (4-(-2-(1H-imidazol-1-yl)ethoxy) benzoic acid hydrochloride) 10(-6) M inhibited the bradykinin-induced contraction, suggesting that thromboxane A2 was involved in TP receptor stimulation. The thromboxane A2 mimetic U-46619 (9,11-dideoxy-11 alpha,9 alpha-epoxy-methano-prostaglandin F2 alpha)-induced contraction of human distal bronchi was not inhibited by capsaicin and ruthenium red. Our data suggest that bradykinin contracts human isolated small bronchi through thromboxane A2 release. The inhibitory effect of ruthenium red and capsaicin on the bradykinin response may be due to inhibition of thromboxane A2 release or arachidonic mobilisation.

Responsiveness of slowly conducting articular afferents to bradykinin: effects of an experimental arthritis

Bradykinin (BK), an important inflammatory mediator and potent algogenic substance, is supposed to contribute to the generation of arthritic hyperalgesia and pain. The present study was undertaken to examine if an experimental kaolin/carrageenan arthritis sensitizes articular afferents to BK in the cat's knee joint using two different approaches. First, the proportion of afferent units activated by BK was assessed in fully inflamed joints and compared with corresponding data of normal knee joints. BK (injected i.a. as a bolus close to the joint) at the dose of 2.6 micrograms activated 60% of the units of groups II-IV in the inflamed state, compared to 71% in normal joints. The proportions of low- and high-threshold afferents activated by BK were similar, but more spontaneously active units than units without ongoing activity responded to BK both in inflamed and normal knee joints. Second, the responsiveness of individual afferent units to BK was examined during the development of inflammation. Units not activated by BK remained unresponsive after inflammation. From 11 units activated by BK, 3 units lost their responsiveness and in 4 other units the response to BK was reduced within 2-6 h after the onset of inflammation. Only in 4 units was the BK response increased in the inflamed joint. It is concluded that desensitizing rather than sensitizing processes are involved to change the response behavior of articular afferents to BK during acute experimental inflammation.

Sensitization of peripheral afferent fibres in the in vitro neonatal rat spinal cord-tail by bradykinin and prostaglandins

The sensitization of peripheral nociceptors by different prostaglandins was studied in an in vitro preparation of the neonatal spinal cord with functionally attached tail. Nociceptors in the rat tail were activated by chemical (bradykinin, capsaicin) and thermal (heated saline) stimuli and responses were recorded as a depolarization of a ventral root in the lumbar region of the spinal cord (L3-L5). Responses evoked by bradykinin, capsaicin or submaximal thermal stimulation were enhanced in the presence of prostaglandin E1, prostaglandin E2, prostaglandin F2 alpha, prostaglandin I2 and the stable prostaglandin I2 analogue cicaprost, but not by prostaglandin D2. Cyclic AMP and threshold concentrations of bradykinin also induced an enhancement of responses to chemical and thermal stimuli. Responses evoked by small concentrations of bradykinin on unsensitized preparations were reduced by indomethacin or aspirin, whereas responses to maximal concentrations of bradykinin were not affected. Immunocytochemical localization of protein gene product 9.5 and growth associated protein 43 indicated that the neuronal innervation of subepidermal skin layers was preserved in the tail following removal of the most superficial skin layers which was performed in order to facilitate drug access to peripheral nerve endings. These results indicate that different prostaglandins and cyclic AMP sensitize peripheral nerve endings to noxious stimulation without directly activating nociceptors. The stimulation of nociceptors by bradykinin was only partially mediated via arachidonic acid metabolites whereas bradykinin-induced sensitization was independent of cyclo-oxygenase activity.

Interactions between the monocyte/macrophage and the vascular smooth muscle cell. Stimulation of mitogenesis by a soluble factor and of prostanoid synthesis by cell-cell contact

The effect of soluble factors from the monocyte/macrophage (M phi) on cell proliferation and the functional effects of cell-cell contact on the arachidonic acid (AA) cascade were studied with vascular smooth muscle cells (SMCs). Peripheral blood M phi s were isolated by adherence or in a Percoll gradient, and alveolar M phi s were obtained by lavage. Conditioned medium (CM) was prepared by preincubating M phi s with medium alone or by separating SMC and M phi cocultures by a membrane insert. Cell proliferation (image analysis) and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha, radioimmunoassay) were measured in SMCs. Labeled prostanoids and other eicosanoid metabolites were isolated by high-performance liquid chromatography from SMCs prelabeled with 14C-AA. M phi s did not synthesize 6-keto-PGF1 alpha. The CM enhanced proliferation but did not stimulate 6-keto-PGF1 alpha synthesis in SMCs. However, cell-cell contact in cocultures of SMCs with the same concentration of M phi s used to generate CM resulted in increased 6-keto-PGF1 alpha synthesis by SMCs. Since the stimulatory effect of cell contact was not blocked by butylated hydroxytoluene, it could not be attributed to an oxidative burst from M phi s. Functional studies showed that the stimulatory effect of cell contact was enhanced by exogenous free AA and by endogenous AA release through A23187. Release of total radioactivity from prelabeled SMCs was enhanced by cell contact, and this effect was blocked by indomethacin (IM). Cell contact did not increase the release of free AA from prelabeled SMCs, even in the presence of IM. Finally, cell contact only stimulated the formation of prostanoids (IM-sensitive eicosanoid metabolites) from prelabeled SMCs. Lipoxygenase and other products of AA were not formed through cell-cell contact. These data showed that M phi s express a soluble factor that enhances SMC proliferation without affecting prostanoid synthesis. Subsequent cell contact between SMCs and M phi s stimulates prostanoid synthesis, which may possibly serve as a local and focal homeostatic mechanism for the regulation of uncontrolled SMC proliferation in atherogenesis.