Bradykinin action in the rat duodenum through the cyclic AMP system

Effects of methylprednisolone on exercise-induced increases of plasma levels of polymorphonuclear elastase and myeloperoxidase in man. Preliminary results

The aim of the present study was to verify whether a single oral dose of methylprednisolone could modulate the exercise-induced release of polymorphonuclear neutrophil (PMN) elastase and myeloperoxidase. Four healthy, male subjects were submitted to a 20 min downhill run (-20%) at 60% VO(2) max, 3 h after oral absorption of a placebo or a single dose of 32 mg methylprednisolone. A marked neutrophilia (+103% of basal PMN count; p < 0.02) was observed 3 h after methylprednisolone ingestion. During both exercise trials, placebo and methylprednisolone, PMN counts were increased by 46% and 19% (p < 0.05), respectively. The running test caused marked and significant (p < 0.05) increases in plasma myeloperoxidase concentration (MPO). The magnitude of MPO changes was the same in the two trials (+110%). Exercise also resulted in significant changes in plasma elastase concentration (EL) in both experimental conditions (placebo: +104%, p < 0.05; methylprednisolone: +338%, p < 0.005). Plasma elastase levels reached at the end of exercise on methylprednisolone were significantly higher than after placebo (p < 0.05). A significant relationship was found between EL and PMN in methylprednisolone trial only (r = 0.72; l0 < 0.005). These results showed that the transient exercise-induced release of elastase and myeloperoxidase were not decreased by methylprednisolone.

Bradykinin modulates the ouabain-insensitive Na+-ATPase activity from basolateral membrane of the proximal tubule

This paper studies the modulation by bradykinin of the ouabain-insensitive Na+-ATPase activity in both renal cortex homogenate and basolateral membrane from proximal tubule. The increase in bradykinin concentration from 10-14 to 10-10 M stimulated the ouabain-insensitive Na+-ATPase activity in cortex homogenates about 2.2-fold, but inhibited the enzyme activity of basolateral membrane preparations by 60%. In both preparations, the maximal effect was obtained with 10-10 M bradykinin. Further increase in the concentration of bradykinin completely abolished these effects. The antagonist of the B2 receptor, Hyp3, completely abolished the effect of 10-10 M bradykinin on the Na+-ATPase activity in the basolateral membrane preparation in a dose-dependent manner, but had no effect on the bradykinin stimulated enzyme activity of the cortex homogenate. Furthermore, in the presence of 10-7 M Hyp3, 10-10 M bradykinin stimulated the Na+-ATPase activity by 45% in the basolateral membrane preparations. The increase in des-Arg9-bradykinin concentration from 10-12 to 10-7 M, an agonist of the B1 receptor, stimulated the Na+-ATPase activity of the cortex homogenates and of the basolateral membrane preparations by 105 and 148%, respectively. In the presence of 25 microM mergetpa, an inhibitor of kininase I, the increase in bradykinin concentration from 10-12 to 10-10 M promoted similar inhibition of the Na+-ATPase activity of both cortex homogenates and basolateral membrane preparations. These results suggest that bradykinin stimulated the Na+-ATPase activity of proximal tubule through the interaction with B1 receptors and inhibited the enzyme through the interaction with B2 receptors. Furthermore, the cortex homogenate expresses a kininase I activity that cleaves bradykinin to des-Arg9-bradykinin.

Mechanisms of the relaxant and contractile responses to bradykinin in rat duodenum

The signal pathway for bradykinin-induced relaxation followed by contraction in the isolated rat duodenum was investigated by comparing the effect of blocking agents on the response to bradykinin and acetylcholine. The phospholipase C inhibitor U-73122 inhibited the relaxation induced by bradykinin, but had no effect on the contraction to either bradykinin or acetylcholine. The same response pattern was observed when the tissues were pre-treated with thapsigargin, a selective inhibitor of microsomal Ca2+ pumps. An inhibitor of non-voltage-dependent Ca2+ influx, SK&F 96365, inhibited the relaxant response to bradykinin and the contraction induced by acetylcholine, but not the contraction induced by bradykinin. In Ca2+-free Krebs-Henseleit buffer, the tissues failed to respond when they were exposed to either bradykinin or acetylcholine. When the tissues were partly depolarized (30 mM KCI), both bradykinin and acetylcholine induced contraction, while the relaxant response to bradykinin was almost completely abolished. Apamin (an antagonist of low-conductance calcium-activated K+ channel) together with charybdotoxin (CTX, an antagonist of large-conductance calcium-activated K+ channel) and CTX alone inhibited the relaxant but not the contractile response to bradykinin. We conclude that the biphasic response in isolated rat duodenum to bradykinin involves two distinct pathways. We propose that the relaxant component is induced indirectly via inositol-mediated increase in cytosolic Ca2+ in non-muscle cells with subsequent signals to the smooth muscle cells, whereas the contractile response is induced by direct effect on the smooth muscle cells.

Bradykinin elevates cytosolic Ca2+ concentration in smooth muscle cells isolated from rat duodenum

The effect of bradykinin on the cytosolic Ca2+ concentration were measured in single, Fura-2 loaded, smooth muscle cells isolated from rat duodenum. All cells responded with a Ca2+ signal when exposed to bradykinin. The bradykinin response consisted of an initial Ca2+ spike followed by a plateau. Pre-treatment of single muscle cells with either the phospholipase C blocker U-73122 or thapsigargin, which is a potent inhibitor of the endoplasmic reticulum Ca2+-ATPase, inhibited the response to bradykinin. Pre-treatment of the cells with EGTA or La3+ to inhibit the Ca2+ influx, abolished the response induced by bradykinin. We conclude that bradykinin applied to single smooth muscle cells from rat duodenum, increases cytosolic Ca2+ by emptying intracellular Ca2+ stores, and by contribution from extracellular Ca2+. In contrast to bradykinin-induced response in isolated rat duodenum (a relaxation followed by a contraction), we did not observe a biphasic effect of bradykinin on cytosolic Ca2+ in single muscle cells. Bradykinin may thus cause relaxation of duodenal smooth muscle indirectly through an effect on neighbouring cells as dilatation is brought about by this agent in blood vessels.

Effects of the agents affecting cyclic nucleotide metabolism on the bradykinin- and des-Arg9-bradykinin-induced relaxations and contractions in isolated rat duodenum

1. Bradykinin and related kinins possess two different types of action (consisting of relaxation and contraction) in the isolated rat duodenum via their specific receptors. However, the mechanisms of these actions have not been fully elucidated. The present study was undertaken to investigate the effects of the agents affecting cyclic nucleotide metabolism on bradykinin-induced relaxations and on bradykinin- and des-Arg9-bradykinin-induced contractions. 2. Des-Arg9-bradykinin, B1 receptor agonist, and high concentrations of bradykinin elicited dose-dependent contractile responses in the rat duodenum, while low concentrations of bradykinin caused a dose-dependent relaxation in this tissue. 3. Nicotinic acid, an inhibitor of adenylate cyclase, inhibited the relaxation of rat duodenum induced by bradykinin at low concentrations in a non-competitive manner. However, the inhibitory efficacy of nicotinic acid against bradykinin was limited by 39.9% and this inhibition was not further increased by higher concentrations of nicotinic acid up to 10(-3) M. 4. Imidazole, an activator of cyclic nucleotide phosphodiesterase, caused a slight inhibition of the relaxant responses to low concentrations of bradykinin and of the contractile responses to des-Arg9-bradykinin and high concentrations of bradykinin in isolated rat duodenum. These inhibitions were also limited in efficacies and not increased by higher concentrations of imidazole. 5. Methylene blue, an agent that inhibits soluble guanylate cyclase, suppressed the contractions of rat duodenum induced by des-Arg9-bradykinin and high concentrations of bradykinin in a non-competitive manner. Again, these inhibitions were limited and further increase in the inhibitory efficacy was not observed in spite of increasing the methylene blue concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Bradykinin receptors in intestinal smooth muscles and their post-receptor events related to calcium

The effects of trifluoperazine and verapamil on bradykinin- and des-Arg⁹-bradykinin induced responses of isolated rat duodenum and guinea-pig ileum were investigated to elucidate post-bradykinin receptor events. Verapamil and trifluoperazine inhibited bradykinin induced relaxations and contractions and des-Arg⁹- bradykinin induced contractions in rat duodenum. Bradykinin induced contractions of ileum were also inhibited by trifluoperazine and. verapamil. Since non-competitive affinity constants of trifluoperazine and verapamil for the relaxant responses to bradykinin in duodenum and for the contractile responses to bradykinin in ileum are different, post-bradykinin receptor events related to calcium may be different in ileum and duodenum. In addition, affinity constants of bradykinin in guinea-pig ileum and rat duodenum are also disparate suggesting the presence of different types of bradykinin B₂ receptors in these two organs.

Bradykinin receptors: pharmacological properties and biological roles

Kinins contribute to the acute inflammatory response and are implicated in the pathophysiology of inflammatory disease. The development of therapeutically viable agents that counteract the effects of kinins is, therefore, potentially very rewarding. Since kinin actions are generally mediated via an interaction with cell-surface receptors, one approach is the development of site-specific receptor antagonists. The emphasis in this review is to outline our current understanding of the properties of bradykinin receptors and the potential therapeutic applications for drugs acting at these sites. As a result of the recent introduction of potent bradykinin receptor antagonists and the cloning of bradykinin receptor genes, considerable advances in kinin research can now be confidently anticipated.

Bradykinin receptors in isolated rat duodenum

Pharmacological properties of the bradykinin receptors in the isolated rat duodenum were investigated by examining the relaxant and contractile responses to bradykinin and [des-Arg9]-bradykinin, an agonist of B1 receptors. A specific desensitization and de novo formation for B1 receptors were observed. Changes in medium pH caused a decrease in the responses to bradykinin and [des-Arg9]-bradykinin of rat duodenum. Urea incubation in test tube inhibited the responses to bradykinin and [des-Arg9]-bradykinin of rat duodenum, while urea in bathing medium was ineffective. These findings strongly suggested that (a) ionic bonds are important in the interaction between bradykinin and its receptors, and (b) B2 receptors in rat duodenum are different from those in guinea pig ileum.

Bradykinin-induced cyclic AMP accumulation in mouse fibrosarcoma independent of prostaglandin E2 formation

The relationship between bradykinin (BK)-induced prostaglandin E2 (PGE2) and cyclic AMP syntheses in mouse fibrosarcoma cells (HSDM1C1) was investigated. Maximal BK-induced increases in cyclic AMP preceded increases in PGE2 production. PGE2 synthesis reached maximum at a much lower concentration of BK than cyclic AMP synthesis. Indomethacin completely inhibited BK-induced PGE2 production, but did not influence the cyclic AMP levels. Arachidonic acid in the medium induced PGE2 production in large quantities, but increased cyclic AMP accumulation only slightly. A high PGE2 concentration increased cyclic AMP levels only slightly. Theophylline increased basal and BK-mediated cyclic AMP levels, but did not affect PGE2 production at all. These results indicate that BK-evoked PGE2 and cyclic AMP syntheses in HSDM1C1 are not dependent upon each other.