Effects of bradykinin on prostaglandin synthesis and cytosolic calcium in rabbit subcultured renal cortical smooth muscle cells.

Smooth muscle cells were cultured from an arteriole-rich fraction of the rabbit renal cortex and characterized by their ultrastructural and immunohistochemical features, their high content in creatine kinase (60-times that of the initial preparation) and their ability to synthesize renin. Cells, studied between passages 2 and 5, produced mainly PGE2 and, to a lesser extent, PGF2 alpha. Bradykinin (BK) (0.1 nM-1 microM) induced a concentration-dependent increase in PGE2 (28-40-times basal value at 1 microM after a 5 min incubation period) and stimulated also the free cytosolic calcium concentration [( Ca2+]i) with a 2-fold maximal rise to its basal value. Both effects, inhibited by the anti-B2 receptor [Thi5.8D-Phe7] BK, were not reproduced by DesArg9 BK. A decrease in the extracellular calcium concentration and incubation in the presence of a calcium-channel blocker (lanthanum chloride) inhibited the BK-dependent rise of [Ca2+]i but not that of PGE2. Preincubation with phorbol myristate acetate increased basal and BK-induced PGE2 synthesis but prevented the effect of BK on [Ca2+]i. These results demonstrate the ability of BK to increase [Ca2+]i and PGE2 production in cultured vascular cells from the rabbit renal cortex and suggest that kinins might act on the cortical microcirculation via their direct effects on arteriolar smooth muscle cells.

Antagonist effect of a receptor-mimicking peptide encoded by human angiotensin II complementary RNA.

This article reports on the binding and the angiotensin II (Ang II) antagonistic properties of a peptide, referred to as hIIA, encoded by an RNA strand complementary to the human Ang II messenger RNA. Although Ang II and hIIA (H2N-Glu-Gly-Val-Tyr-Val-His-Pro-Val-COOH) share four amino acids, the iodinated and tritiated forms of hIIA were unreactive with seven monoclonal antibodies defining four distinct epitopes on the Ang II molecule and failed to bind to Ang II hepatic and mesangial receptors. However, hIIA did inhibit binding of 125I-Ang II to rat hepatocyte membranes (IC50, 2 x 10(-7) M) and to the various monoclonal antibodies. The lowest IC50 (5 x 10(-7) M) was measured with the monoclonal antibody specific for the Ang II sequence generally considered as implicated in receptor recognition. As predicted from the binding studies, hIIA was further shown to antagonize some biological properties of Ang II. On mesangial cells, hIIA alone had no effect on intracellular calcium concentration ([Ca2+]i) and prostaglandin E2 synthesis but did abolish the transient increase in [Ca2+]i in response to 100 nM Ang II and did induce a specific dose-dependent inhibition of the Ang II-stimulated prostaglandin E2 release. Furthermore, intravenous infusion of hIIA (200 micrograms.kg-1.min-1) inhibited by 66 +/- 3% the rat hypertensive response to 100 ng.kg-1 Ang II but had no effect on the pressor activity of agents such as alpha 1-adrenergic and HT2 serotonin agonists. Our data suggest that the "complementary" peptide hIIA interacts directly with Ang II by mimicking the Ang II complementary site on the receptor and can inhibit the physiological effects of Ang II. This type of Ang II complementary peptide may serve as a model for a new class of antihypertensive drugs.

Lack of importance of NO in beta-adrenoceptor-mediated relaxation of large epicardial canine coronary arteries.

This study was designed to test the role of endothelium and the L-arginine/NO pathway in the relaxation of canine large coronary arteries to the beta-adrenoceptor agonist, isoprenaline. Relaxation of left circumflex (LCX) and left anterior descending (LAD) coronary arteries were measured in organ baths after contraction with the thromboxane analogue, U46619, either in absence or in presence of endothelium and in LCX arteries after pretreatment with NG-nitro-L-arginine-methyl-ester (L-NAME). LAD arteries with and without endothelium relaxed identically to isoprenaline but their maximal relaxation was smaller than corresponding LCX arteries with endothelium. A slight but non significant difference was observed in LCX arteries with endothelium as compared to rings without endothelium or pretreated with L-NAME. No difference was observed in the relaxation of LCX arteries to forskolin in arteries with or without endothelium. These results suggest that endothelium is not essential and that NO is not directly involved in the relaxation of large coronary arteries induced by isoprenaline.

Modulation of renin synthesis by lipoxygenase products in cultured human mesangial cells.

Modulation of renin synthesis by lipoxygenase products has been studied in cultured human mesangial cells under basal conditions and in the presence of prostaglandin (PG) E2. Total renin and cyclic AMP productions were stimulated in a dose-dependent manner (0.1-10 microM) by PGE2. The stimulatory effect of PGE2 on renin production was inhibited by 12-hydroxyeicosatetraenoic acid (12-HETE) between 0.1 and 100 nM. Extracellular and intracellular renin were affected similarly. Neither basal and PGE2-dependent cyclic AMP nor basal cyclic GMP productions were modified. 15-Hydroxyeicosatetraenoic acid (15-HPETE), 12-hydroperoxyeicosatetraenoic acid (12-HPETE) and 15-hydroperoxyeicosatetraenoic acid (15-HPETE) had the same effects as 12-HETE. Intracellular calcium concentration was not modified in the presence of 12-HETE. Since oleyl-2-acetylglycerol (OAG), an analog of diacylglycerol, also inhibited PGE2-stimulated renin production, it is hypothesized that the effect of the lipoxygenase products is mediated via protein kinase C stimulation.

Chronic inhibition of NO synthase enhances the production of prostacyclin in coronary arteries through upregulation of the cyclooxygenase type 1 isoform.

We previously reported that chronic inhibition of NO synthase (NOS) in dogs leads to an upregulation of the cyclooxygenase (COX) pathway in the endothelium of the coronary artery after stimulation by bradykinin (BK) in vitro. The present experiments were designed to identify the nature of the COX isoform involved in this phenomenon. Rings of circumflex (LCX) and left anterior descending (LAD) coronary arteries were isolated from six control dogs and six dogs treated with the NOS-inhibitor, N omega-nitro-L-arginine (L-NNA, 30 mg/kg/d, i.v., during 7 days). Concentration-response curves to BK in U46619-contracted rings from LCX coronary arteries were constructed in the presence and absence of another NOS inhibitor (NG-monomethyl-L-arginine, L-NMMA), of selective inhibitors of the inducible isoform of COX (NS-398 and L-745,337) and of a non selective inhibitor of the inducible and constitutive isoforms of COX (indomethacin). Finally, measurements of 6-keto-prostaglandin F1 alpha, the stable metabolite of prostacyclin, were performed in the incubation medium by enzymo-immuno-assay on rings of isolated LAD coronary arteries in the presence and absence of the same inhibitors of COX, before and after stimulation by BK. In rings taken from control dogs, BK evoked a concentration-dependent relaxation (Emax: 115 +/- 10%; EC50: 8 +/- 4 nM). In the presence of L-NMMA, the concentration-relaxation curve to BK was significantly shifted to the right (Emax: 77 +/- 8%; EC50: 43 +/- 22 nM, P < 0.05). Addition of NS-398, L-745,337 and indomethacin to L-NMMA did not further modify the concentration-relaxation curve to BK. After chronic inhibition of NOS, the concentration-relaxation curve to BK was similar to that observed in rings taken from control dogs in the presence of L-NMMA (Emax: 75 +/- 5%; EC50: 69 +/- 36 nM). Addition of L-NMMA, alone or in combination with NS-398 or L-745,337 did not significantly modify this concentration-relaxation curve to BK. In contrast, the L-NMMA-indomethacin combination blunted the BK-induced relaxation of the coronary artery (Emax: 28 +/- 10%, P < 0.01). Basal release of prostacyclin was not different in rings taken from control and L-NNA treated dogs (56 +/- 16 vs 58 +/- 15 pg.mm-2). BK significantly increased this release but the increment was twofold greater in rings taken from L-NNA treated dogs than in rings taken from control dogs (P < 0.05). In rings taken from control and L-NNA treated dogs, the BK-stimulated production of prostacyclin observed in the presence of the solvent was not significantly modified by L-NMMA or the L-NMMA-L-745,337 combination. In contrast, the L-NMMA-indomethacin combination as well as endothelium removal completely suppressed the BK-stimulated production of prostacyclin. These findings demonstrate that in dogs submitted to chronic inhibition of NO synthesis (1) the residual relaxation to BK of canine isolated coronary arteries is mainly due to production of prostacyclin of endothelial origin, and (2) the enhancement of prostacyclin production by these vessels is mainly due to an upregulation of the endothelial constitutive isoform of COX.

[Hemodynamic effects of sub-chronic NO synthase inhibition in conscious dogs: role of EDRF/NO in muscular exertion]. / Effets hémodynamiques résultant du blocage sub-chronique de la NO-synthétase chez le chien éveillé: rôle de l'EDRF/NO dans l'exercice musculaire.

Acute and chronic administration of nitric oxide (NO) synthase (NOS) inhibitors increase mean arterial blood pressure (MAP) in rats but their hemodynamic effects in other species remain unknown. Moreover, the role of NO in the control of exercise-induced vasodilation is still debated. To answer these questions, six dogs were instrumented for the continuous measurement of cardiac output (CO, electromagnetic flow probe on the aorta), MAP (aortic catheter) and left ventricular pressure (Konigsberg gauge). Total peripheral resistance (TPR) was calculated as MAP/CO ratio and dP/dt was used as an index of cardiac inotropism. The dogs were treated from day 0 (D0) to 7 (D7) by the NOS inhibitor, N omega-nitro-L-arginine (L-NNA), 20 mg/kg/day (IV). Such a dose regimen resulted in NOS inhibition evidenced (a) in vivo by a reduction of the hypotensive responses to graded doses of acetylcholine and bradykinin, (b) ex vivo by a decrease in the relaxation of the femoral artery to acetylcholine (EC 50 = 2.2 +/- 0.6 10(-7) M after L-NNA vs 2.2 +/- 0.8 10(-8) M in controls). One month after instrumentation, the dogs being conscious, MAP measured at rest remained unchanged following one week L-NNA treatment (from 90 +/- 2 at D0 to 91 +/- 5 mmHg at D7). However, TPR increased (from 3,600 +/- 290 at D0 to 6,300 +/- 510 dyn.s.cm-5 at D7) and CO decreased (from 2.1 +/- 0.2 at D0 to 1.2 +/- 0.1 l/min at D7) (all p < 0.01), partly as the result of a marked bradycardia (from 100 +/- 7 at D0 to 60 +/- 7 beats/min at D7). L-NNA induced-increase in TPR was completely reversed by a bolus injection of nitroglycerin (10 micrograms/kg). During treadmill exercise (12 km/h), heart rate (251 +/- 9 at D0 vs 226 +/- 11 beats/min at D7), CO (6.3 +/- 0.9 at D0 vs 4.3 +/- 0.7 l/min at D7) and stroke volume remained significantly lower, and TPR significantly higher (1,662 +/- 278 at D0 vs 2,621 +/- 489 dyn.s.cm-5 at D7) after L-NNA than in the control state. Thus, NOS inhibition in resting conscious dogs by L-NNA markedly increases peripheral resistance but does not increase arterial pressure. In addition, L-NNA blunts both exercise-induced peripheral vasodilation and increase in cardiac output, despite metabolic vasodilation.

Characterization of ANF receptors in cultured renal cortical vascular smooth muscle cells.

Because atrial natriuretic factor (ANF) has been demonstrated to decrease resistances in cortical renal vessels in vivo, we studied 125I-ANF binding and ANF-dependent guanosine 3',5'-cyclic monophosphate (cGMP) production in subcultured vascular smooth muscle cells (VSMC) prepared from the rabbit renal cortex. 125I-ANF specific binding at 4 degrees C represented 70% of total binding and reached a plateau at 30-60 min. Equilibrium saturation binding curves suggested one group of high-affinity receptor sites (KD = 78 +/- 16 pM, Bmax = 45 +/- 11 fmol/mg) but were compatible with several groups exhibiting close binding parameters. ANF, [Ala7,Ala23]ANF (a linear analogue), and C-ANF-(4-23) (a ligand of C receptors) inhibited 125I-ANF binding at 37 degrees C with nearly similar potencies. In contrast, at 4 degrees C, complete or nearly complete inhibition of binding was obtained with ANF and linear ANF, the latter exhibiting the weakest potency, whereas C-ANF-(4-23) displaced only 35% of the tracer. ANF markedly stimulated cGMP accumulation, with a threshold concentration of 10 pM and a stimulation of 115 times basal value at 0.1 microM. Linear ANF was also stimulatory with a much weaker potency. Around 25% of 125I-ANF bound to cell surface was internalized at 37 degrees C. Phenylarsine oxide partially inhibited internalization as well as the inhibitory potency of C-ANF-(4-23) on 125I-ANF binding. As shown by high-performance liquid chromatography extracellular 125I-ANF was rapidly degraded at 37 degrees C into its 125I-COOH-terminal tripeptide and 125I-Tyr.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary and systemic hemodynamic effects of sustained inhibition of nitric oxide synthesis in conscious dogs. Evidence for cross talk between nitric oxide and cyclooxygenase in coronary vessels.

Sustained inhibition of NO synthesis (N omega-nitro-L-arginine [L-NNA], 20 mg.kg-1.d-1, 7 days) was investigated at rest and during exercise in conscious dogs. At rest, L-NNA did not alter mean arterial blood pressure but markedly increased total peripheral resistance (+73 +/- 14%, P < .01). Exaggerated hypertension was observed during exercise (+132 +/- 5 mm Hg after L-NNA versus +113 +/- 5 mm Hg before L-NNA, P < .01). L-NNA decreased the resting coronary artery diameter by 6 +/- 1% and suppressed its exercise-induced dilation but had no effect on coronary blood flow and resistance. L-NNA decreased flow repayment volumes during reactive hyperemia, but corresponding flow debt volumes remained unchanged. The cyclooxygenase inhibitor diclofenac (10 mg/kg) had no effect on reactive hyperemia parameters before L-NNA but reduced flow repayment volumes, durations, and corresponding debt-to-repayment ratios in L-NNA-treated dogs (all P < .05). In vitro, indomethacin blunted the residual relaxation to bradykinin of large coronary arteries taken from L-NNA-treated, but not from control, dogs. Bradykinin-induced increase in 6-ketoprostaglandin F1 alpha production was greater in coronary arteries taken from L-NNA-treated dogs (+ 179 +/- 41 pg/mm2) than from control dogs (+ 66 +/- 18 pg/mm2) (P < .05). These results indicate that (1) NO is of major importance in the control of systemic but not coronary resistance vessels at rest and during exercise, and (2) after L-NNA, the cyclooxygenase pathway is involved in myocardial reactive hyperemia and in the residual relaxation to bradykinin of isolated coronary arteries. Thus, in conscious dogs, the cyclooxygenase pathway might act as a protective mechanism of the coronary circulation when endothelial nitric oxide synthesis is altered.

Characterization of neutral endopeptidase in vascular smooth muscle cells of rabbit renal cortex.

In addition to biological and clearance receptors for atrial natriuretic factor (ANF), cultured vascular smooth muscle cells (VSMC) from the rabbit renal cortex possess ectoenzymes degrading this hormone. We examined whether neutral endopeptidase (NEP) was implicated in this process. The presence of NEP in VSMC was demonstrated as follows. 1) NEP activity measured from the hydrolysis of a synthetic substrate by intact cells cultured in a medium containing 10% fetal calf serum was 1,609 +/- 65 pmol.min-1 x mg-1 [surface localization of the enzyme was confirmed by low activity (4% of total) in the cytosol; release of NEP activity in the medium was negligible]; 2) a monoclonal antibody directed against rabbit NEP specifically stained VSMC membranes; and 3) mRNA from VSMC hybridized a NEP cDNA probe with a single band as shown by Northern blot analysis. The role of NEP in ANF catabolism was demonstrated by incubating 125I-ANF or unlabeled ANF for increasing periods of time with VSMC in the presence of thiorphan (1-100 microM). Intact hormone estimated by trichloroacetic acid precipitation or radio-immunoassay, respectively, increased markedly compared with control in the presence of this specific inhibitor of NEP. NEP activity was stimulated (x1.6) in quiescent VSMC deprived from serum during 3 days. This effect was dose dependent and was not observed with creatine kinase activity measured as control. NEP expression at the cell surface estimated by sorting of immunostained cells was also increased in the absence of serum. Northern blot analysis showed increases in the mRNA band of NEP with increasing periods of serum deprivation.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelium-dependent hyperpolarization in isolated arteries taken from animals treated with NO-synthase inhibitors.

To study the effects of chronic in vivo inhibition of NO synthase on endothelium-dependent hyperpolarization, cell-membrane potential (in individual vascular smooth-muscle cells) and changes in tension (in isolated rings) were recorded from isolated canine coronary arteries and guinea-pig carotid arteries and aortas. In coronary arteries taken from control dogs and contracted with U46619, acetylcholine- and bradykinin-induced endothelium-dependent relaxations, which were unaffected by short-term in vitro exposure to indomethacin but were inhibited partially by L-nitro-arginine (LNA). In coronary arteries taken from dogs treated over the long term in vivo with LNA (30 mg/kg on the first day and 20 mg/kg the 7 following days, i.v.), the response to acetylcholine and bradykinin was inhibited when compared with arteries from control dogs. Short-term in vitro exposure to LNA or indomethacin or both did not influence the effects of either agonist. In these arteries, the hyperpolarizing response to acetylcholine, observed in the presence of LNA and indomethacin, was enhanced, whereas that to bradykinin was partially inhibited. In the guinea pig isolated aorta, the relaxation to bradykinin was abolished by long-term in vivo treatment with L-nitro-arginine-methyl-ester (L-NAME; 1.5 mg/ml, in the drinking water for > or =4 days). In the isolated guinea pig carotid artery studied in the presence of LNA and indomethacin, acetylcholine induced a hyperpolarization that was not significantly affected by long-term in vivo treatment with L-NAME. These findings indicate that endothelium-dependent hyperpolarizations are maintained during long-term inhibition of NO synthase and probably act as a back-up mechanism to elicit endothelium-dependent relaxations.

Oxidized low density lipoproteins induce mRNA expression and release of endothelin from human and porcine endothelium.

Experiments were designed to examine the effect of oxidized low density lipoproteins (Ox-LDLs) on the expression and the release of endothelin from cultured endothelial cells and intact blood vessels. Ox-LDLs (30-300 micrograms/ml), but not native low density lipoproteins (200 micrograms/ml), stimulated the expression of preproendothelin mRNA in porcine and human endothelial cells, leading to a time- and concentration-dependent release of the peptide into the culture medium. The Ox-LDL-stimulated release of endothelin was mimicked by acetylated low density lipoprotein and abolished by downregulation of protein kinase C by phorbol ester. In the intact porcine aorta, Ox-LDLs, but not native low density lipoproteins, also increased the release of peptide in an endothelium- and concentration-dependent manner. The maximal effect was observed at a concentration of 100 micrograms/ml. Incubation of the intact porcine aorta with the scavenger receptor antagonist dextran sulfate decreased the formation of endothelium evoked by Ox-LDLs. The Ox-LDL-stimulated production of the peptide was further augmented in the presence of thrombin (4 units/ml) and was unaffected by nitric oxide-generating compound 3-morpholinosydnonimine (10(-5) M). These results suggest that Ox-LDL may be an endogenous mediator of the augmented release of endothelin observed in hyperlipidemia and atherosclerosis. The increased production of the peptide could contribute to vasospastic events and may promote vascular smooth muscle proliferation and progression of atherosclerotic vascular disease.

Endothelial modulation of beta-adrenergic dilation of large coronary arteries in conscious dogs.

BACKGROUND: Endothelium-derived relaxing factors have been described as important intermediates in beta-adrenergic vasodilation of resistance coronary vessels, but their involvement at the level of large epicardial coronary arteries remains controversial. Therefore, we examined the role of vascular endothelium in the beta-adrenergic-mediated vasodilation of large epicardial coronary arteries in conscious dogs. METHODS AND RESULTS: Nine dogs were instrumented for measurement of left circumflex coronary artery diameter (CD) by sonomicrometry and coronary blood flow velocity (CBFv) with a Doppler technique in response to graded doses of isoproterenol (0.001 to 0.1 microgram/kg IV bolus). Under control conditions, isoproterenol induced dose-dependent increases in CD and CBFv. When CBFv was kept constant at its baseline value by inflation of a cuff occluder, isoproterenol still induced dose-dependent increases in CD, but the latter were of lesser magnitude than those observed under normal CBFv conditions (110 +/- 20 versus 170 +/- 30 microns, respectively, ie, a reduction of 33% of the dilatory response at 0.1 microgram/kg, P < .01). In the same dogs, the coronary endothelium was then mechanically removed at the site of CD measurement by a balloon angioplasty technique. After this procedure, the dose-dependent increases in CD induced by isoproterenol under either normal or controlled CBFv conditions were overimposable, and their magnitude was similar to that of the increases observed in the presence of an intact endothelium when CBFv was kept constant. After beta 1-adrenergic receptor blockade by atenolol (1 mg/kg), isoproterenol-induced increases in CD were abolished either when CBFv was kept constant or after endothelium removal. CONCLUSIONS: In conscious dogs, the direct stimulating effect of isoproterenol on beta 1-adrenergic receptors is endothelium-independent at the level of large coronary arteries. The endothelium reinforces the dilatory response to isoproterenol through an indirect, flow-dependent mechanism.