Role of ACE and NEP in bradykinin-induced relaxation and contraction response of isolated porcine basilar artery

The aim of the present study was to clarify the role of angiotensin converting enzyme (ACE) and neutral endopeptidase (NEP) in bradykinin (BK)-induced relaxation and contraction of isolated porcine basilar artery by measuring isometric tension, ACE and NEP activities and their localization. BK induced endothelium-dependent relaxation followed by contraction; however, in the presence of indomethacin BK induced relaxation but not contraction, in contrast, in the presence of L-nitro-arginine BK induced contraction but not relaxation. Captopril and thiorphan increased the p D(2) value for BK-induced relaxation from 8.11 to 9.55 and the p A(2) value for [Thi(5,8), D-Phe(7)]-BK (a B(2)-receptor antagonist) from 6.95 to 7.59. The same treatment increased the p D(2) value for BK-induced contraction from 7.93 to 8.97 and the p A(2) value for [Thi(5,8), D-Phe(7)]-BK from 6.86 to 7.50. Captopril inhibited ACE activity with an IC(50) of 38.0 nM, and thiorphan inhibited NEP and ACE activities with an IC(50) of 1.4 nM and 295.0 nM, respectively. Endothelial denudation decreased the ACE and NEP activities by 76.7% and 15.9%, respectively, and ACE mRNA level by 59.4%, but had no significant effect on NEP mRNA level. These results suggest that BK-induced relaxation and contraction in the porcine basilar artery are enhanced by captopril and thiorphan which predominantly inhibit ACE activity localized on endothelial cells.     

Converting enzyme inhibition in isolated porcine resistance artery potentiates bradykinin relaxation

The purpose of this study was to determine the effects of converting enzyme inhibition on the contractile reactivity of porcine femoral and intramuscular resistance arteries. The arteries were dissected free of hind limb skeletal muscle from anaesthetized pigs (Micro-pig Yucatan, Charles River), and were mounted in organ chambers and in a myograph system for tension recording. Bradykinin induced an endothelium-dependent relaxation in both vessels which was potentiated by S 10211, a converting enzyme inhibitor, only in resistance arteries. Under basal conditions angiotensin II and angiotensin I did not contract resistance arteries although contraction could be obtained with other agents such as KCl, noradrenaline or vasopressin. If the tone was increased with noradrenaline, angiotensin II and angiotensin I produced an increase in tension. S 10211 inhibited the increase in tension induced by angiotensin I but not by angiotensin II in vessels with and without endothelium. These results suggest that (1) converting enzyme is present in the vascular wall of porcine resistance arteries, (2) this enzyme is not necessarily located on the endothelial cells and, (3) converting enzyme could influence the responsiveness to angiotensin I and bradykinin.     

过氧化氢酶和内皮素对缺氧引起的猪基底动脉收缩的体外影响

AIM: To study whether anoxia-induced vasoconstriction was related to the release of endothelin (ET). METHODS: Acute anoxia was induced by gassing the organ chamber with 95% N2 + 5% CO2. Changes in tension of porcine basilar arterial ring was recorded. RESULTS: Anoxia-induced increases in tension were 0.21 g +/- 0.08 g and 0.24 g +/- 0.09 g under basal tension and during ET 3 nmol.L-1-induced contractions, respectively. In the rings tension did not further augment following the increase of ET from 100 to 300 nmol.L-1, acute anoxia did cause further increase in tension of 0.16 g +/- 0.10 g (n = 4). Catalase 800 and 2400 kU.L-1 decreased the anoxia-induced contraction, with inhibitory rate of 33% +/- 7% and 47% +/- 9%, respectively. CONCLUSION: Anoxia-induced vasoconstriction was related to release of hydrogen peroxide from endothelial cells.     

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

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

Lovastatin induces relaxation and inhibits L-type Ca(2+) current in the rat basilar artery

Statins inhibit cholesterol biosynthesis and protect against ischaemic stroke. It has become increasingly apparent that the beneficial effects of statin therapy may extend beyond lowering of serum cholesterol. The present study was done to explore possible pleiotropic statin effects at the level of the cerebral vascular smooth muscle. Lovastatin, lovastatin acid, simvastatin and pravastatin, were added to segments of the rat basilar artery and effects on contraction and Ca2+ handling were examined. Pravastatin had no effect on contraction. Simvastatin, lovastatin, and, to a lesser degree, lovastatin acid, caused relaxation (IC50=0.8, 1.9 and 22 micromol/l) of both intact and denuded arteries precontracted with 5-HT or high-K+. This effect was not reversed by mevalonate, suggesting that it was not related to cholesterol or isoprenoid metabolism. Relaxation was associated with a reduction of the intracellular Ca2+ concentration measured with Fura 2 and with a reduced Mn2+ quench rate, suggesting a direct effect on ion channels in the smooth muscle cell membrane. Current measurements in isolated and voltage clamped basilar artery muscle cells demonstrated that both lovastatin and lovastatin acid inhibit L-type Ca2+ current. We propose that lipophilicity is an important factor behind the effects of statins on vascular tone and that Ca2+ current inhibition is the likely mechanism of action.     

Progesterone induces endothelium-independent relaxation of rabbit coronary artery in vitro.

The effect of progesterone on isolated rabbit coronary arteries and its possible mechanism was investigated by measuring changes of isometric tension. Progesterone (1, 3, 10 and 30 microM) induced significant coronary relaxation in K+ (30 mM)-, prostaglandin F2 alpha (3 microM)- or Bay K 8644 (1 microM plus 15 mM K+)- precontracted arteries. There was no difference between endothelium-intact and -denuded coronary arteries from both male and female rabbits, precontracted with these three agents. Haemoglobin, indomethacin, methylene blue, glibenclamide or barium chloride did not affect the relaxation. In endothelium-denuded rabbit coronary arteries, progesterone shifted calcium concentration-dependent constrictor-response curves to the right, the maximal contraction was also reduced. The -log ED50s were 3.6 in control, and 3.3 and 2.9 after incubation with progesterone (3 and 30 microM), respectively. Similar results were obtained in rat aorta. We conclude that progesterone induces significant endothelium-independent relaxation in rabbit coronary arteries in vitro, possibly by affecting calcium influx.     

The mechanism of bradykinin-induced endothelium-dependent contraction and relaxation in the porcine interlobar renal artery

The mechanism of endothelium-dependent regulation of vascular tone of bradykinin was investigated by simultaneously monitoring the changes in the cytosolic Ca(2+) concentration and the force of smooth muscle in fura-2-loaded strips of the porcine renal artery with endothelium. During phenylephrine-induced sustained contraction, bradykinin (>3x10(-9) M) caused endothelium-dependent triphasic changes in the force of the strips, composed of an initial relaxation, a subsequent transient contraction and a late sustained relaxation. At low concentrations (10(-10) - 10(-9) M), bradykinin caused an endothelium-dependent biphasic relaxation with no contraction. A thromboxane A(2) (TXA(2))/prostaglandin H(2) (PGH(2)) receptor antagonist (10(-5) M ONO-3708) completely inhibited, while a TXA(2) synthase inhibitor (10(-5) M OKY-046) only partially inhibited, the transient contraction induced by bradykinin. Under conditions where the bradykinin-induced contraction was inhibited by ONO-3708 during the phenylephrine-induced contraction, bradykinin induced only a transient relaxation in the presence of N(Omega)-nitro-L-arginine methyl ester (L-NAME). This transient relaxation was inhibited when the precontraction was initiated by phenylephrine plus 40 mM extracellular K(+). The removal of L-NAME from this condition caused a partial reappearance of the initial relaxation and a complete reappearance of the sustained relaxation. In conclusion, bradykinin caused the endothelium-dependent triphasic regulation of vascular tone in the porcine renal artery. The concentrations of bradykinin required to induce a contraction was higher than that required to induce relaxation. Both TXA(2) and PGH(2) were involved in the bradykinin-induced contraction. The initial relaxation was mediated by nitric oxide and hyperpolarizing factors while the sustained relaxation depended on nitric oxide.     

Ibuprofen or ozagrel increases NO release and l-nitro arginine induces TXA(2) release from cultured porcine basilar arterial endothelial cells

The vascular resting tone of the porcine basilar artery appears to be mostly maintained by a balance between spontaneously released nitric oxide (NO) from endothelial cells and thromboxane (TX) A(2) from endothelial and smooth muscle cells. However the precise role of the interaction between the above two substances in the control of vascular tone is unclear. We attempted to clarify the interaction between NO and TXA(2) using cultured porcine basilar arterial endothelial cells. The cultured endothelial cells produced NO spontaneously, while TXB(2) (a stable metabolite of TXA(2)) production remained below the detection limit. Ibuprofen (a COX inhibitor) and ozagrel (a TXA(2) synthetase inhibitor) significantly increased the spontaneous production of NO, which was not affected by 1400W (an iNOS inhibitor). l-Nitro arginine (a NOS inhibitor) significantly induced TXB(2) production. These results suggest that NO may inhibit COX or TXA(2) synthetase, and that therefore inhibition of NOS might disinhibit COX or TXA(2) synthetase, subsequently inducing TXA(2) production. On the other hand, as TXA(2) and other contractility-related prostaglandin(s) may inhibit NOS, therefore the inhibition of COX or TXA(2) synthetase might disinhibit NOS, and then increase the spontaneous production of NO in porcine basilar arterial endothelial cells.     

Role of endothelium in hypoxic contraction of canine basilar artery.

1. Reversible contraction of canine basilar artery, produced by hypoxia, persisted after mechanical and chemical removal of the endothelium. The removal of endothelium was confirmed by scanning electron microscopy as well as by the abolition or reversal of the relaxant response to acetylcholine or arginine8-vasopressin. 2. Hydroquinone, believed to block selectively endothelium-mediated relaxation, also preferentially attenuated hypoxic contractions even in the absence of endothelium but did not reduce responses to 5-hydroxytryptamine (5-HT) or high external potassium. 3. Contractions induced by red blood cell haemolysate, which occur independently of the endothelium, were also selectively attenuated by hydroquinone. 4. Contractions caused by hypoxia were inhibited by pretreatment with adenosine or by its application after contraction had developed. 5. Hypoxic contraction in canine basilar artery may result partly from a direct effect on smooth muscle as well as through the endothelium. 6. Hydroquinone may have an additional locus of action in smooth muscle cells besides its well known effect on the endothelium.     

Effects of catalase and endothelin on anoxia induced vasoconstriction of porcine basilar artery in vitro 1

目的：研究缺氧引起的血管收缩是否与血管内皮细胞释放内皮素（ＥＴ）有关．方法：９５％Ｏ２＋５％ＣＯ２混合气体换成９５％Ｎ２＋５％ＣＯ２引起急性缺氧,描记猪基底动脉环的张力变化．结果：在基础张力条件下和由ＥＴ３ｎｍｏｌ·Ｌ－１引起收缩时,缺氧分别使基底动脉张力增加０２１ｇ±００８ｇ和０２４ｇ±００９ｇ．当ＥＴ浓度从１００ｎｍｏｌ·Ｌ－１增加到３００ｎｍｏｌ·Ｌ－１时,动脉的张力不进一步增加,此时急性缺氧仍使张力进一步增加０１６ｇ±０１０ｇ．过氧化氢酶８００,２４００ｋＵ·Ｌ－１明显降低缺氧引起的收缩,抑制率分别为３３％±７％和４７％±９％．结论：缺氧引起的血管收缩与内皮细胞释放过氧化氢有关     

High-affinity bradykinin B2 binding sites sensitive to guanine nucleotides in bovine aortic endothelial cells.

Bradykinin (BK) binding sites were studied in membranes from bovine aorta. [3H]BK specifically bound to one high-affinity binding site (KD = 152 pM; Bmax = 4.6 fmol.mg-1) and was displaced by unlabeled BK (Ki = 121 pM). The B2-agonist kallidin and B2-antagonists D-Arg0[Hyp3,Leu5,8,Gly6,D-Phe7]BK, D-Arg0[Hyp3,D-Phe7]BK, [D-Phe7]BK, and [Thi5,8,D-Phe7]BK inhibited [3H]BK binding with respective Ki values of 101, 282, 678, 2000 and 6000 pM. The B1-antagonist des-Arg9[Leu8]BK had no effect. GTP, GTP gamma S, GDP, and GDP beta S but not 5'-GMP, guanosine, cyclic 3',5'-GMP, ATP, ADP, 5'-AMP, nor adenosine, inhibited [3H]BK binding with an IC50 of 1-3 microM for GTP and GDP and an IC50 of 0.1-0.3 microM for GTP gamma S and GDP beta S. GTP and GDP at 3 microM decreased the Bmax value by 30-70%. Millimolar concentrations of Ca2+ and Mg2+ ions increased [3H]BK binding and counteracted the effect of guanine nucleotides. This study demonstrates the existence of a specific high-affinity B2 BK binding site in bovine aortic endothelial cells. It suggests that this site is located on a G protein-interacting receptor.     

Protamine induces elevation of cytosolic free Ca2+ in cultured porcine aortic endothelial cells.

To test the hypothesis that protamine influences calcium movement in endothelial cells, we measured the concentration of intracellular free calcium ([Ca2+]i) in cultured porcine aortic endothelial (PAE) cells in Krebs solution (2.5mM Ca2+, pH 7.4) at 37 degrees C, by fura-2 fluorimetry. The basal [Ca2+]i of PAE cells was 113+/-18 nM (n=6). Protamine increased [Ca2+]i in a concentration-dependent manner (EC50, the concentration having 50% of the maximum effect, 1.4+/-0.3 microg mL(-1), n=6). The response of PAE cells to 100 microg mL(-1) protamine (330+/-80 nM, n=6) was blocked by a Ca2+ chelator, 5 mM glycoletherdiaminetetraacetic acid (EGTA; 131+/-16 nM, n=6), and by a non-selective Ca2+ channel blocker, 3 mM Co2+ (134+/-14 nM, n=6). These results suggest that Ca2+ influx through cell-membrane Ca2+ channels is mainly responsible for the protamine-induced Ca2+ elevation.     

Ostreolysin induces sustained contraction of porcine coronary arteries and endothelial dysfunction in middle- and large-sized vessels

Ostreolysin (Oly), a cytolytic and cardiotoxic protein from the oyster mushroom (Pleurotus ostreatus), is lethal for mice with an LD₅₀ of 1170 μg/kg following intravenous application. Its cardiotoxicity is associated with hyperkalemia, which is probably a consequence of potassium released from the lysed cells. Moreover, sub-micromolar concentrations of Oly induce a concentration-dependent increase in rat aortic ring tension, suggesting that ischaemia, and consequent hypoxic injury of cardiomyocytes, could also derive from vasospasm induced by this toxic protein.The purpose of the present study was to demonstrate histopathological lesions caused by Oly after parenteral application to rats, and to define the mechanisms of Oly-induced vasoconstriction using inhibitors verapamil, lanthanum chloride, and selective endothelin receptor antagonist TBC3214, which have different molecular targets, in vitro on porcine coronary artery rings. We found that Oly causes endothelial injury with perivascular oedema in the heart and lungs, as well as myocardial haemorrhages in rats. Treatment of porcine coronary artery rings with Oly causes concentration-dependent vasoconstriction and prevents endothelium-mediated relaxation. Using TBC3214 as a selective blocker of the endothelin A receptor, we showed that vasoconstriction induced by Oly was independent of endothelin release and its effects. Verapamil (1 μM) greatly reduced Oly-evoked contractions of porcine coronary artery rings, while lanthanum abolished them completely. These results provide evidence that the contraction of coronary arteries by Oly is due mainly to the increased influx of Ca²⁺ from the extracellular space through voltage-dependent L-type Ca²⁺ channels and cation non-selective channels. Experiments suggest that Oly damages endothelial cells both in vitro and in vivo, and probably exhibits direct contractile effects on coronary smooth muscle cells.     

Sustained contraction and endothelial dysfunction induced by reactive oxygen species in porcine coronary artery

A combination of purine and xanthine oxidase (XOD) dose-dependently elicited sustained contraction of porcine coronary arterial rings and resulted in increased concentrations of superoxide anions and hydrogen peroxide. These contractile responses appeared, with a delay, after the application of purine and XOD, used as a reactive oxygen species (ROS)-generating system. Coronary arteries precontracted with prostaglandin F(2alpha) failed to relax in response to substance P after exposing the arterial preparation to this ROS-generating system. The contractile response of the coronary artery to the ROS-generating system was almost completely inhibited by catalase (130 U/ml), and was partially inhibited by superoxide dismutase (60 U/ml), or mannitol (30 mM). A voltage-dependent L-type Ca(2+) channel antagonist, nicardipine, had no effect on contraction. Dysfunction of endothelial cells was completely prevented by catalase, but not by superoxide dismutase or mannitol. These results suggest that superoxide anions, hydrogen peroxide and hydroxyl radicals might be involved in eliciting sustained, delayed-onset coronary artery contraction, which is not related to L-type Ca(2+) channels. They also suggest that hydrogen peroxide might play a major role in endothelial dysfunction of the porcine coronary artery.     

Prostanoid involvement in the relaxation of in vitro mesenteric artery by bradykinin and des-Arg9-bradykinin

Bradykinin (BK), des-Arg9-BK, prostaglandin E2, prostacyclin and angiotensin II all produced concentration-related relaxation of rabbit in vitro de-endothelialized superior mesenteric arterial ring preparations precontracted with phenylephrine. Responses were reproducible at time 1 h and 4 h after setting up the preparations. The cyclo-oxygenase inhibitor indomethacin (2.8 x 10(-6) M) and the protein synthesis inhibitor cycloheximide (7.2 x 10(-5) M) introduced at t = 0 h inhibited relaxant responses to BK, des-Arg9-BK and angiotensin II, but not prostaglandin E2 or prostacyclin at t = 1 h and t = 4 h. Cycloheximide and indomethacin applied to the tissues at t = 3 h inhibited relaxant responses to BK, des-Arg9-BK and angiotensin II (but not prostaglandin E2 or prostacyclin) at t = 4 h. It is concluded that BK, des-Arg9-BK and angiotensin II (but not prostaglandin E2 or prostacyclin) induced relaxant responses of the in vitro rabbit mesenteric artery are dependent upon the generation of a relaxant prostanoid from the tissue and that cycloheximide produces its effect in this tissue by a mechanism similar to that seen with indomethacin.     

Involvement of K+ channels in adenosine A2A and A2B receptor-mediated hyperpolarization of porcine coronary artery endothelial cells

This study investigated the effects of the following adenosine agonists: 5;-ethylcarboxamidoadenosine (NECA), N6-cyclopentyadenosine (CPA) 2-[p-(2-carboxyethyl)]phenylamino-5;N-ethylcarboxamidoadenosine (CGS-21680), and 2-chloroadenosine (CAD) and its antagonist, 4-(2-[7-amino-2-[2-furyl]]1,2,4-triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM-241385), a selective A2A adenosine receptor antagonist, and the involvement of the K+ATP and KCa channels on the resting membrane potential (RMP) of confluent monolayers of cultured porcine coronary artery endothelial cells (PCAECs). Adenosine agonists and K+ATP channel openers (pinacidil, cromakalim) hyperpolarized cultured PCAECs. The average RMP was -32.31 +/- 1.2 mV. Adenosine agonists at 10-5 M caused a significant increase in RMP to -65.0 +/- 1.5 mV for CAD (a nonselective adenosine receptor agonist) to -75.9 +/- 1.6 mV for CGS-21680 (a selective A2A receptor agonist) and to -87.0 +/- 3.5 mV for NECA (a nonselective A1/A2A/A2B receptor agonist). Pinacidil and cromakalim at 10 microM increased the membrane potential to -76.2 +/- 1.2 mV and -75.22 +/- 0.12 mV, respectively. The hyperpolarization induced by adenosine receptor agonists and KATP openers was inhibited by an application of the K+ATP channel blocker glibenclamide (10 microM), indicating the involvement of the K+ATP channel in the adenosine-mediated hyperpolarization of PCAECs. Moreover, 1-EB10, a selective opener of the maxi-KCa channel, hyperpolarized PCAECs, and the effect of 1-EB10 was completely blocked by a selective, irreversible blocker of the high conductance KCa (maxi-K) channels (penitrem A), but it only partially blocked the effect of NECA. ZM-241385 has no effect on hyperpolarization elicited by K+ATP and KCa channel openers. However, ZM-241385 significantly blocked the hyperpolarization effect of CAD and CGS-21680. ZM-241385 partially blocked the hyperpolarizing effect of NECA, and a combination of ZM-241385 and penitrem A further blocked the hyperpolarizing effect of NECA. These results further support the involvement of K+ channels in adenosine A2A and A2B receptor-mediated hyperpolarization of PCAECs.     

Involvement of bradykinin B1 and B2 receptors in relaxation of mouse isolated trachea

1. The aim of the present study was to investigate the effects of bradykinin and [des-Arg⁹]-bradykinin and their relaxant mechanisms in the mouse isolated trachea.
2. In the resting tracheal preparations with intact epithelium, bradykinin and [des-Arg⁹]-bradykinin (each drug, 0.01–10 μM) induced neither contraction nor relaxation. In contrast, bradykinin (0.01–10 μM) induced concentration-dependent relaxation when the tracheal preparations were precontracted with methacholine (1 μM). The relaxation induced by bradykinin was inhibited by the B₂ receptor antagonist, D-Arg⁰-[Hyp³,Thi⁵,D-Tic⁷,Oic⁸]-bradykinin (Hoe 140, 0.01–1 μM) in a concentration-dependent manner whereas the B₁ receptor antagonist, [des-Arg⁹,Leu⁸]-bradykinin (0.01–1 μM), had no inhibitory effect on bradykinin-induced relaxation. [des-Arg⁹]-bradykinin (0.01–10 μM) also caused concentration-dependent relaxation after precontraction with methacholine. The relaxation induced by [des-Arg⁹]-bradykinin was concentration-dependently inhibited by the B₁ receptor antagonist, [des-Arg⁹,Leu⁸]-bradykinin (0.01–1 μM), whereas the B₂ receptor antagonist, Hoe 140 (0.01–1 μM) was without effect.
3. In the presence of the cyclo-oxygenase inhibitor, indomethacin (0.01–1 μM), the relaxations induced by bradykinin and [des-Arg⁹]-bradykinin were inhibited concentration-dependently.
4. Two nitric oxide (NO) biosynthesis inhibitors N^G-nitro-L-arginine methyl ester (L-NAME, 100 μM) and N^G-nitro-L-arginine (L-NOARG, 100 μM) had no inhibitory effects on the relaxations induced by bradykinin and [des-Arg⁹]-bradykinin. Neither did the selective inhibitor of the soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 μM) inhibit the relaxations induced by bradykinin and [des-Arg⁹]-bradykinin.
5. Prostaglandin E₂ (PGE₂, 0.01–33 μM) caused concentration-dependent relaxation of the tracheal preparations precontracted with methacholine. Indomethacin (1 μM) and ODQ (10 μM) exerted no inhibitory effects on the relaxation induced by PGE₂.
6. The NO-donor, sodium nitroprusside (SNP; 0.01–100 μM) also caused concentration-dependent relaxation of the tracheal preparations precontracted with methacholine. ODQ (0.1–1 μM) concentration-dependently inhibited the relaxation induced by SNP.
7. These data demonstrate that bradykinin and [des-Arg⁹]-bradykinin relax the mouse trachea precontracted with methacholine by the activation of bradykinin B₂-receptors and B₁-receptors, respectively. The stimulation of bradykinin receptors induces activation of the cyclo-oxygenase pathway, leading to the production of relaxing prostaglandins. The NO pathway is not involved in the bradykinin-induced relaxation. The relaxation caused by NO-donors in the mouse trachea is likely to be mediated via activation of soluble guanylate cyclase.

     

Stimulation of in vitro angiogenesis by tetrahydrobiopterin in bovine aortic endothelial cells.

This study examined whether tetrahydrobiopterin (BH4) stimulates angiogenesis by measuring the formation of tube-like structures in vascular endothelial cells. Bovine aortic endothelial cells that were cultured between two layers of collagen type I gel formed tube-like networks. Addition of BH4 or sepiapterin, a precursor of BH4 synthesis, stimulated the formation of tube-like structures. The sepiapterin-stimulated tube formation was completely inhibited by co-treatment with N-acetylserotonin, an inhibitor of sepiapterin reductase. These findings show that BH4 stimulates in vitro angiogenesis in vascular endothelial cells.