Profibrotic Effects of Endothelin-1 via the ETA Receptor in Cultured Human Cardiac Fibroblasts

BACKGROUND/AIMS

Endothelin-1 (ET-1) has been implicated in pathologic remodelling and tissue repair processes in the heart. We investigated the effects of ET-1 on growth and collagen synthesis responses in cardiac fibroblasts isolated from human hearts. We also studied the receptor subtype(s) mediating such responses and the factors regulating their expression.

METHODS

Fibroblasts were isolated from cardiac transplant recipient hearts and characterised by immunocytochemistry. Serum-starved cells were exposed to ET-1 and incorporation of [3H]proline and thymidine were measured as indexes of collagen and DNA synthesis respectively. Blocking experiments utilised the selective ETA receptor antagonist BQ123 and the ETB antagonist BQ788.

RESULTS

ET-1 elicited a potent collagen synthesis response in cardiac fibroblasts, with a maximum 29+/-5% increase that was abolished by BQ123. Cardiac fibroblasts responded to ET-1 with a concentration-dependent decrease in DNA synthesis rate. The effects of ET-1 were similar to those of TGF-beta. Radioligand binding studies revealed the presence of high-affinity ET-1 binding sites on these cells, which were upregulated by treatment with the growth factors PDGF and EGF but downregulated by TGF-beta.

CONCLUSIONS

These results therefore implicate ET-1 as a trophic agent in the human heart with the ability to influence the development of cardiac fibrosis.

In-vitro contraction of the equine aortic valve

BACKGROUND AND AIM OF THE STUDY

The equine aortic valve is subject to non-inflammatory degenerative changes, associated with aortic valvular regurgitation (AR). This disease shares pathological and epidemiological features with AR in humans, and may serve as a useful model to study in-vitro functional responses associated with aging and disease. The study aim was to determine the contractile properties of the normal equine aortic valve.

METHODS

The contractile responses of equine aortic valves to angiotensin II, the thromboxane-mimetic U44069, endothelin-1, 5-hydroxytryptamine and the alpha-adrenoceptor agonists medetomidine, norepinephrine and phenylephrine were studied in vitro in organ baths. Selective antagonists were used to confirm the receptors involved.

RESULTS

The order of potency of the agents causing contraction of equine aortic valve segments was angiotensin II > endothelin-1 > U44069 > medetomidine norepinephrine phenylephrine. 5-Hydroxytryptamine did not cause contraction of the equine aortic valve. The contractile response to angiotensin II was abolished by the AT1 receptor antagonist Sar1-Ile8-Angiotensin II, and that of U44069 by the thromboxane TXA2 receptor (TP) antagonist SQ29548. The contractile effects of endothelin-1 were blocked by the ET(A) receptor antagonist BQ123, but not by the ET(B) receptor antagonist BQ788. Yohimbine inhibited the contractile effects of phenylephrine, suggesting an alpha-2 adrenoceptor-mediated response.

CONCLUSION

Equine aortic valves contract in response to a number of physiologically important endocrine, paracrine and neuronal mediators. Regulation of valvular tone could therefore be important in the normal functioning of the valve, and further understanding of these mechanisms may lead to insights into the pathophysiology of naturally occurring equine aortic insufficiency. In this respect, the horse should be considered as a model of the human condition.

Differential response of human cardiac fibroblasts to angiotensin I and angiotensin II

The vasoactive peptide angiotensin II (Ang II) has been implicated as a mediator of myocardial fibrosis. We carried out a comparative investigation of the effects of Ang II and its precursor Ang I on collagen metabolism and proliferation in cultured human cardiac fibroblasts. Cardiac fibroblasts responded to both Ang I and Ang II with concentration-dependent increases in collagen synthesis but no proliferation. The stimulatory effect of Ang II was abolished by the AT(1) receptor antagonist losartan but not the AT(2) receptor antagonist PD123319. The response to Ang I was not affected by either antagonist, nor by the angiotensin-converting enzyme (ACE) inhibitor captopril. In conclusion, Both Ang I and Ang II stimulate collagen synthesis of human cardiac fibroblasts, the effect of Ang II occurring via the AT(1) receptor whilst Ang I appears to exert a direct effect through non-Ang II-dependent mechanisms. These results suggest distinct roles for angiotensin peptides in the development of cardiac fibrosis.

Differential effects of rapamycin, cyclosporine A, and FK506 on human coronary artery smooth muscle cell proliferation and signalling

BACKGROUND

Immunosuppressive agents are at the forefront of preventing organ rejection after transplantation. However, their effects on vascular smooth muscle cell-mediated intimal hyperplasia that occurs in post-transplant coronary artery disease are less well known.

METHODS AND RESULTS

We investigated the in vitro effects of three immunosuppressive agents cyclosporine A (CsA), FK506 (tacrolimus), and rapamycin (sirolimus, Rapa) on cultured human coronary artery smooth muscle cells (cSMC). CsA inhibited both platelet-derived growth factor (PDGF)-stimulated DNA synthesis and serum-induced proliferation at high concentrations (> or =1000 ng/ml). The growth-inhibitory effect of CsA was not altered by anti-TGF-beta neutralising antibodies nor was autocrine TGF-beta release detected in CsA-treated culture medium. At inhibitory doses, CsA inhibited ERK kinase activation by PDGF, although cytotoxicity was also apparent. Most notably, CsA visibly prevented PDGF-induced altered cell morphology. Rapa was a highly potent and effective inhibitor of cSMC proliferation (reduction in DNA synthesis by >50% from 0.01 ng/ml), acting through inhibition of 70-kDa S6 kinase (p70S6k). FK506 (1-1000 ng/ml) did not affect cSMC proliferation alone, although a > or =250-fold excess of FK506 over Rapa completely reversed the inhibitory effect of Rapa, confirming that these two agents share a common intracellular receptor, the FK506-binding protein (FKBP).

CONCLUSION

Rapa is a powerful inhibitor of cSMC proliferation, while CsA slighly inhibits cSMC proliferation, although only at higher concentrations that may be toxic. These results indicate that therapeutic immunosuppression with Rapa may be additionally useful in prevention or delay of posttransplant coronary artery disease.

Clinical and haemodynamic effects of sildenafil in pulmonary hypertension: acute and mid-term effects

AIM

The treatment of patients with pulmonary arterial hypertension remains a challenge. We set out to investigate the use of sildenafil, a selective inhibitor of phosphodiesterase type 5, in patients with this disease.

METHODS AND RESULTS

Ten patients (8 females, mean age 34.5+/-3.3 years) with pulmonary hypertension underwent right heart catheterisation with vasodilator testing using incremental doses of intravenous sildenafil without adverse events. All patients were subsequently commenced on oral sildenafil 50 mg t.d.s. Nine patients had repeat right heart catheterisation 3 months after the commencement of oral therapy. There was a significant reduction in mean pulmonary artery pressure (from 55.8+/-5.9 to 50.4+/-6.1 mmHg, p=0.038 ) and pulmonary vascular resistance (from 10.1+/-1.7 to 8.6+/-1.5 Wood units, p=0.009 ), and an increase in cardiac output (from 4.7+/-0.3 to 5.0+/-0.4 l/min, p=0.15 ). Furthermore, there was a significant increase in the 6-minute walk test, a mean of 112 m. In response to a quality-of-life questionnaire, patients indicated marked clinical improvement on sildenafil. Sildenafil was discontinued in 1 patient due to a transient visual disturbance. The only patient previously awaiting transplantation was removed from the active transplantation list.

CONCLUSIONS

Sildenafil is well tolerated in its intravenous and oral forms and appears to improve both pulmonary haemodynamics and the clinical status of patients with pulmonary hypertension after 3 months of oral therapy.

Differential in vitro response of the human radial artery versus left internal thoracic artery to cerivastatin: implications to bypass grafting

BACKGROUND

This study investigated acute (in vitro) and long-term (in vivo) effects of statins on the vascular function of human radial artery (RA) and left internal thoracic artery (LITA).

METHODS

RA and LITA specimens were divided into vascular rings, which were incubated in the absence or presence of 10(-6) mol/L Cerivastatin for 2 or 24 hours. In terms of preoperative statin treatment, four groups included: group 1 [preop statin(-)/in vitro cerivastatin(-)]; group 2 [preop(-)/in vitro(+)]; group 3 [preop(+)/in vitro(-)]; and group 4 [preop(+)/in vitro(+)]. Endothelial function was assessed with acetylcholine (10(-9) to 10(-5) mol/L) following contraction by 3 x 10(-8) mol/L endothelin-1.

RESULTS

Although endothelium-dependent vasodilatation was higher in RA (57.7% +/- 3.5%) than in LITA (46.5% +/- 3.8%, p = 0.046), there was no significant evidence that it depended on the preoperative use of statins or incubation period. In vitro incubation with cerivastatin significantly increased endothelium-dependent vasodilatation by 14.2% +/- 2.4% (p < 0.0001) independent of artery types (RA/LITA). There was no significant evidence that endothelium-dependent vasodilatation depended on the preoperative use of statins or incubation period.

CONCLUSIONS

In vitro incubation with cerivastatin preserved endothelial function more effectively than preoperative use of statins. This could have implications to perioperative use of statins for patients undergoing coronary surgery.

Age-related changes in the protective effect of chronic administration of L-arginine on post-ischemic recovery of endothelial function

OBJECTIVE

The aim of this study was to assess the effect of chronic administration of L-arginine (LA) on vascular functions as well as its age-related changes.

METHODS

Male Sprague-Dawley rats aged 1, 4, 8 and 16 months were divided into control and LA groups, which were administered LA (4 mg/ml) for 6 weeks. Isolated heart perfusion was performed, followed by cardioplegic arrest for 4h at 4 degrees C and reperfusion. Vascular functions were assessed through observations of pre-/post-ischemic coronary flow response to 5-hydroxytryptamine (5-HT) and glyceryl trinitrate (GTN). Ultrastructure was studied after the same ischemia-reperfusion.

RESULTS

A significant improvement of percentage recovery (post-/pre-ischemic value) of response to 5-HT were seen in 4 and 8 months LA group when compared to the control (84.2+/-14.0 vs. 33.9+/-12.5 (P<0.05) and 97.0+/-23.2 vs. 21.5+/-9.7 (P<0.05), respectively). Furthermore, 8 months LA group had better percentage recovery of response to GTN (124.5+/-41.6 vs. 47.7+/-6.3, P<0.05). Ultrastructural study showed no significant differences between the groups in any age.

CONCLUSIONS

Chronic oral administration of LA enhanced the post-ischemic recovery of vascular function in the young adult and adult hearts, but not in the infant and elderly.

Up-regulation of endothelin-converting-enzyme mRNA expression following cardioplegic arrest

Endothelin-1 (ET-1) is believed to play an important role in cardiac ischaemia/reperfusion injury. ET-1 is synthesized from preproET-1 by the action of ET-converting enzyme (ECE). It is unclear to what extent the ET system is activated following prolonged ischaemia. In this study we used a model mimicking the conditions of the donor heart during transplantation. Isolated rat hearts perfused with Krebs-Henseleit buffer were subjected to 30 min of normothermic perfusion, then 4 h of cardioplegic arrest at 4 degrees C with St Thomas' Hospital solution, followed by reperfusion for 2 h. Hearts were freeze-clamped at different time points during the protocol. Using quantitative reverse transcription-PCR, relative levels of ET-1 and ECE mRNA expression were measured and compared with a housekeeping gene (ribosomal protein L32). During reperfusion there was a consistent decrease in coronary flow to approx. 85-90% of pre-ischaemic flow. There was no significant alteration in preproET-1 mRNA expression during 2 h of reperfusion. However, ECE mRNA expression was increased by 77.5% at 1 h and by 74.6% at 2 h following ischaemia compared with pre-ischaemic values (P<0.05). Thus we conclude that ECE mRNA expression is increased following prolonged hypothermic cardioplegic arrest. Elevations in the expression of this enzyme may help to explain the role of the ET system in the pathogenesis of ischaemia/reperfusion injury following cardiac surgery and transplantation.

Biological mechanisms influencing the function of the aortic root

Optimal function of the aortic root relies upon the ability of its component structures to move in a coordinated fashion. Some of the cells that make up the structures of the aortic root have been shown to contain nerves, receptors, and contractile elements. The ability to contract or relax may contribute to the successful function of the valve by allowing it to move in a coordinated manner in response to biological stimuli. It is known that cusp tissue receives primary, sensory, and autonomic nerves, suggesting a role for neuronal regulation of cusp function. In addition, cusp tissue has been shown to express a wide variety of receptors and to contract to a range of common vasoactive agents. The cells that constitute the valve have also shown secretory and proliferative responses. The biological signals that mediate the cross-talk between the different parts of the root have not been established. This review will examine the mechanisms that have been documented to be present and to assess their potential contribution in affecting aortic valve function.

Localization of immunoreactive endothelin and characterization of its receptors in aortic cusps

BACKGROUND AND AIM OF THE STUDY

Aortic valve cusp tissue has been shown to have contractile properties in response to a range of common vasoactive agents. Of these, endothelin (ET) is both the most potent and efficacious.

METHODS

In an attempt to define the mechanism of action and localization of ET, the response of porcine aortic valve cusps to ET and the selective ET(B) receptor agonist sarafotoxin 6c (S6c) was examined, in the presence and absence of ET(A) and ET(B) receptor antagonists. An attempt was made, using immunocytochemical techniques, to localize ET in cusp tissue.

RESULTS

Addition of 90 mM KCl produced a mean contractile response of 1.02+/-0.09 mN (n = 27). ET (10- to 10(-7)M) produced a concentration-dependent contraction of aortic valve cusps, with a maximum response of 116.7+/-12.7% (n = 6) of that obtained with 90 mM KCl. In a similar manner, 10(-5)M of the selective ET(A) receptor antagonist BQ123 (n = 4) and 10(-5)M of the selective ET(B) receptor antagonist BQ788 (n = 4) each partially inhibited the effect of ET. The ET(B)-selective agonist S6c (10(-9) to 10(-7)M) also induced a concentration-dependent contraction of valve cusps (n = 4), with a maximum response of 99.1+/-11.1%. This response was completely inhibited by 10(-5)M BQ788 (n = 4). Immunoreactive ET was localized to the endothelial cells that lined both the ventricular and aortic side of the cusps.

CONCLUSION

These results show that aortic valve cusps contract to ET via an action at both ET(A) and ET(B) receptors. The presence of immunoreactive ET in the endothelial cells of the cusps also suggests that it might play a role in valve function. Further studies are required to elucidate the role of these receptors in the physiology and pathophysiology of the aortic valve.

Effects of cerivastatin on vascular function of human radial and left internal thoracic arteries

BACKGROUND

Statins may enhance vascular function independently of effects on cholesterol. This study investigated the ability of statins to modulate the vascular recovery of arteries used as coronary bypass grafts.

METHODS

Specimens of radial artery and left internal thoracic artery were obtained during coronary artery bypass grafting. The specimens were divided into vascular rings, which were incubated in the absence or presence of cerivastatin (10(-6) mol/L) for either 2 or 24 hours. Using an organ bath technique, endothelial function was examined using acetylcholine (10(-9) to 10(-5) mol/L) after contraction by 3x10(-8) mol/L of endothelin-1.

RESULTS

Time-related endothelial dysfunction was shown in the control group of radial artery but not in the cerivastatin group: maximal endothelium-dependent vasodilation in the control and cerivastatin groups were 56.8% +/- 10.2% and 65.9% +/- 10.1% at 2 hours and 39.4% +/- 4.7% and 68.4% +/- 5.0% (p < 0.01, vs control) at 24 hours, respectively. On the other hand, in the left internal thoracic artery, those in the control and cerivastatin groups were 38.3% +/- 8.2% and 45.0% +/- 5.5% at 2 hours and 38.1% +/- 8.2% and 56.5% +/- 8.8% at 24 hours, respectively (NS).

CONCLUSIONS

In radial artery, cerivastatin significantly preserved endothelium-dependent vasodilation, which diminished with time in the control group. This could have very important implications in the clinical practice of coronary artery bypass grafting.

In vivo early and mid-term flow-mediated endothelial function of the radial artery used as a coronary bypass graft

OBJECTIVES

We sought to evaluate the in vivo endothelial function of the radial artery (RA) used as a coronary graft.

BACKGROUND

The RA is becoming a recognized alternative coronary bypass conduit. In vivo endothelial function is a possible predictor of long-term performance.

METHODS

Sixty consecutive patients underwent coronary artery bypass graft surgery (CABG); all received RA and left internal mammary artery (LIMA) grafts. Three weeks after CABG, 36 patients underwent angiography under basal conditions, during pacing and after intragraft injection of glyceryl trinitrate (GTN). Angiography was repeated at six months in 20 patients.

RESULTS

The estimated mean difference of 66 segments of the radial graft on the first QCA study was 0.170 mm (95% confidence interval [CI] 0.101 to 0.258, p < 0.001) between baseline and pacing, and 0.310 mm (CI 0.225 to 0.401, p < 0.001) between baseline and GTN. At six months, the differences between baseline and pacing and baseline and GTN were 0.112 mm (CI 0.062 to 0.162, p < 0.001) and 0.274 (CI 0.192 to 0.353, p < 0.001), respectively. The difference between baseline values at three weeks and six months was 0.416 mm (CI 0.236 to 0.603, p < 0.001). In the LIMA segments, the difference between baseline and pacing and baseline and GTN were 0.206 mm (CI 0.136 to 0.278, p < 0.001) and 0.304 mm (CI 0.213 to 0.396, p < 0.001), respectively. At six months, the differences between baseline and pacing and baseline and GTN were 0.098 mm (CI 0.014 to 0.173, p < 0.001) and 0.218 mm (CI 0.130 to 0.298, p < 0.001). The difference between baseline values at three weeks and six months was 0.061 mm (CI 0.064 to 0.176, p > 0.05).

CONCLUSIONS

In vivo flow-mediated dilation of the RA is comparable to that of pedicled LIMA. The increased dilation both at baseline and after pacing at six months represents a time-related improvement in the vasomotor function of the RA, which could have implications for its performance as a coronary conduit.

Regulation of NF-kappaB and ICAM-1 expression in human airway epithelial cells

The aim of this study was to elucidate the redox regulation of cytokine-induced NF-kappaB activation and NF-kappaB mediated gene induction in A549 cells and primary cultures of human airway epithelial cells. In A549 cells, Western blot analysis showed transient depletion of IkappaBalpha after 15 min IL-1beta treatment followed by its reappearance after 60 min, indicating efficient NF-kappaB-driven gene induction. A similar pattern was observed in primary epithelial cells however, the kinetics were slower and depletion was less. In primary airway epithelial cells IkappaBalpha levels were 59.8+/-8.5% of control following 30 min treatment with IL-1beta and in A549 cells 29.1+/-8.5% of control following 15 min IL-1beta treatment. Cytokine-induced IkappaBalpha depletion was associated with NF-kappaB nuclear accumulation and subsequent resynthesis of IkappaBalpha and upregulation of ICAM-1 in both cell types. The antioxidant, NAC (20 mM) had no effect on the kinetics of cytokine-induced IkappaBalpha depletion or NF-kappaB p65 nuclear translocation in either cell type and failed to influence kappaB dependent IkappaBalpha resynthesis. H2O2 treatment alone or in combination with cytokines had no significant effects on IkappaBalpha depletion, NF-kappaB p65 nuclear translocation or ICAM-1 expression in either cell type but did cause significant activation of p38 MAPK. These results suggest that cytokine-induced NF-kappaB activation in cultured human airway epithelial cells does not involve an NAC-sensitive oxidant stress and that H2O2-induced oxidant stress does not result in effective NF-kappaB activation and NF-kappaB mediated gene induction.

Influence of 5-hydroxytryptamine on aortic valve competence in vitro

BACKGROUND AND AIM OF THE STUDY

The contraction of cusp tissue has been implicated to play a role in aortic valve function. The effect of the contractile agent 5-hydroxytryptamine (5-HT) on the competence of isolated aortic roots has been assessed, and the vasomotor properties of 5-HT on aortic root tissue examined.

METHODS

Isolated porcine aortic roots were pressurized with Kreb's solution through the aortic arch. 5-HT was added in increasing concentrations (10(-7) to 10(-5) M) and the degree of leakage measured over time. In additional experiments, portions of sinotubular junction, sinus, annular and cusp tissue were set up in organ baths, placed under tension, and challenged with 5-HT (10(-9) to 10(-5) M). Viability of each valve structure was assessed by addition of KCl (90 mM).

RESULTS

The rate of leakage from intact aortic roots increased when 10(-6) and 10(-5) M 5-HT was added. The maximum effect, observed at 10(-5) M 5-HT, was equal to an increase of 61.8+/-23.0% above control (p <0.05). The perfusion pressure at each concentration of 5-HT was unchanged. This response was inhibited by the 5-HT2A receptor antagonist ketanserin. Addition of KCl to isolated valve structures gave a mean contractile response of 0.8+/-0.1mN for cusp, 19+/-11.0 mN for annular, 29+/-8.0 mN for sinus, and 23+/-8.0 mN for sinotubular junction tissue (each n = 4). Only cusp tissue contracted when treated with 5-HT, with a maximum 105.5+/-17.2% (n = 4) of the response to KCl. The response to 5-HT was blocked by the 5-HT2A-receptor antagonist ketanserin at 10(-6) M (n = 4). None of the other aortic root structures responded to 5-HT.

CONCLUSION

These results show that 5-HT influences the competence of isolated porcine aortic valves. This effect is contributed by contraction of the cusp tissue, and is mediated by 5-HT2A receptors. These effects may contribute to the association between valve dysfunction, 5-HT and certain appetite suppressants.

The effects of diaspirin cross-linked hemoglobin on the tone of human saphenous vein

Diaspirin cross-linked hemoglobin (DCL-Hb), when infused into animals, causes vasoconstriction thought to be caused by nitric oxide (NO) binding by the hemoglobin molecule. The purpose of this study was to ascertain whether DCL-Hb causes vasoconstriction in human saphenous vein taken from patients undergoing myocardial revascularization and whether NO scavenging is the mechanism. The direct effect of DCL-Hb on saphenous vein tone was tested by adding increasing concentrations (10(-8) to 10(-5)M) of the drug. In an additional series of experiments, the influence of DCL-Hb on the dilator response to endothelial dependent and independent vasodilators was tested. This was achieved by attempting either to reverse the effects of acetylcholine, sodium nitroprusside, or S-nitrosylglutathione with prior incubation with DCL-Hb or to inhibit the dilator response in vessels preconstricted with 10(-6)M norepinephrine. There was no effect of DCL-Hb alone on saphenous vein tone. DCL-Hb significantly reduced vasodilatation with all vasodilators (P < 0.05). After maximal relaxation with sodium nitroprusside and s-nitrosylglutathione, there was significant vasoconstriction with DCL-Hb at concentrations larger than 10(-6)M, (P < 0.05). The authors conclude that DCL-Hb does not constrict human saphenous vein but can affect vessel tone by reversal of the effect of endogenously or exogenously released NO.

Expression and function of angiotensin converting enzyme, chymase, and angiotensin II in the human radial artery and internal thoracic artery

BACKGROUND

The potential role of the local renin-angiotensin system to differentially affect radial artery and internal thoracic artery graft performance has not been examined.

METHODS

Contractile responses to angiotensin I and II in the radial artery and the internal thoracic artery were examined in vitro. The expression function, and localization of angiotensin receptors, angiotensin converting enzyme, and chymase were studied in radial artery and internal thoracic artery segments.

RESULTS

Angiotensin I and II contractions were significantly greater (p < 0.05) in the radial artery compared to the internal thoracic artery. In both arteries, angiotensin II responses were mediated via the AT1 receptor. Messenger RNA transcripts for angiotensin-converting enzyme and chymase were detected in both arteries. Angiotensin-converting enzyme was localized to luminal and vaso vasorum endothelial cells and smooth muscle cells in both vessels, while chymase was colocalized with mast cells in adventitial and medial layers. An angiotensin converting enzyme or a chymase inhibitor singularly had no effect on angiotensin I contractions, however, when combined, a marked inhibition of the angiotensin I response was observed in both vessels.

CONCLUSIONS

Our results illustrate the complexities which exist within the local renin angiotensin system and suggest that clinical trials which may modulate the system are warranted.

The renin angiotensin system in bypass graft surgery

The renin angiotensin system is implicated in the development of vein graft disease after coronary artery bypass surgery. Components of this system have been shown to play important roles in determining the short-term and long-term performance of coronary artery bypass grafts. Significant differences exist in the commonly used arterial and venous grafts in angiotensin converting enzyme activity and angiotensin responses. The existence of a dual enzyme pathway in angiotensin II formation has also been demonstrated. Such findings have implications for the use of AT1-receptor antagonists over enzyme inhibitors to improve graft performance and prevent the development of coronary artery bypass graft disease.

Interaction between thromboxane A2 and 5-hydroxytryptamine in the radial artery compared to the internal thoracic artery

The aim of the present study was to investigate if the function of 5-hydroxytryptamine-1B/1D (5-HT1B/1D) receptors in human radial artery (RA) and internal thoracic artery (ITA) can be modified by thromboxane A2 (TXA2) released from the vessel wall in these two arteries that are commonly used in coronary artery bypass grafts. The 5-HT1B/1D agonist sumatriptan contracted the RA with a maximum response of 23.5+/-6.8 mN and a pD2 value of 6.6+/-0.1. The effect of sumatriptan was significantly reduced in the ITA with a maximum of 5.8+/-2.7 mN (P<.05) and a pD2 value of 6.4+/-0.2. The TXA2 receptor antagonist SQ30741 inhibited contractions to sumatriptan in the RA but not in the ITA. It is concluded that the effect mediated by 5-HT1B/1D is augmented by endogenous TXA2 in the RA.

Mitogenic and secretory responses of human valve interstitial cells to vasoactive agents

BACKGROUND AND AIM OF THE STUDY

The vasoactive agent 5-hydroxytryptamine (5-HT) has been implicated in valve disease due to possible trophic effects on valve interstitial cells (IC). The present study was aimed at characterizing the responses of cultured human heart valve IC to 5-HT in terms of intracellular calcium concentration ([Ca2+]i), mitogenesis and collagen synthesis. The effects of angiotensin II (Ang II) were also studied in parallel.

METHODS

IC were obtained by collagenase digestion of valve leaflets isolated from transplant recipient hearts. Changes in [Ca2+]i were measured from fluorescence of the ratiometric calcium dye, fura 2. Mitogenic and collagen synthetic responses of valve IC were measured by 3H-thymidine incorporation (DNA synthesis) and 3H-proline incorporation assays respectively, in quiescent cells.

RESULTS

Human valve IC responded to 5-HT and Ang II with mean maximal increases in [Ca2+]i of 249 +/- 47 nM and 397 +/- 159 nM, respectively. 5-HT stimulated DNA synthesis in quiescent IC, although to varying degrees among different isolations, with a maximum 43.4 +/- 20.1% increase by 10(-7) M 5-HT (p <0.05). Ang II did not stimulate IC DNA synthesis. Valve IC also responded to 5-HT with a maximum increase in collagen synthesis of 15.7 +/- 2.0% by 10(-6) M 5-HT (p <0.05). Ang II provoked a more powerful collagen synthesis response (maximum 50.5 +/- 15.1% increase by 10(-5) M Ang II; p <0.05).

CONCLUSION

We have shown that 5-HT and Ang II promote the prolonged processes of growth and collagen synthesis in cultured human valve IC. Thus, these vasoactive agents may play a role in the development of heart valve disease.

A redox-based mechanism for nitric oxide-induced inhibition of DNA synthesis in human vascular smooth muscle cells

1. The current study explored potential redox mechanisms of nitric oxide (NO)-induced inhibition of DNA synthesis in cultured human and rat aortic smooth muscle cells. 2. Exposure to S-nitrosothiols, DETA-NONOate and NO itself inhibited ongoing DNA synthesis and S phase progression in a concentration-dependent manner, as measured by thymidine incorporation and flow cytometry. Inhibition by NO donors occurred by release of NO, as detected by chemiluminescence and judged by the effects of NO scavengers, haemoglobin and cPTIO. 3. Co-incubation with redox compounds, N-acetyl-L-cysteine, glutathione and L-ascorbic acid prevented NO inhibition of DNA synthesis. These observations suggest that redox agents may alternatively attenuate NO bioactivity extracellularly, interfere with intracellular actions of NO on the DNA synthesis machinery or restore DNA synthesis after established inhibition by NO. 4. Recovery of DNA synthesis after inhibition by NO was similar with and without redox agents suggesting that augmented restoration of DNA synthesis is an unlikely mechanism to explain redox regulation. 5. Study of extracellula interactions revealed that all redox agents potentiated S-nitrosothiol decomposition and NO release. 6. Examination of intracellular NO bioactivity showed that as opposed to attenuation of NO inhibition of DNA synthesis by redox agents, there was no inhibition (potentiation in the presence of ascorbic acid) of soluble guanylate cyclase (sGC) activation judged by cyclic GMP accumulation in rat cells. 7. These data provide evidence that NO-induced inhibition of ongoing DNA synthesis is sensitive to redox environment. Redox processes might protect the DNA synthesis machinery from inhibition by NO, in the setting of augmented liberation of biologically active NO from NO donors.

Receptor-mediated contraction of aortic valve leaflets

BACKGROUND AND AIM OF THE STUDY

The mechanisms that regulate the function of the aortic valve are not fully understood. Cusp tissue has been shown to have contractile properties, but little is known as to which receptors mediate these effects.

METHODS

We have examined, using isolated organ baths, the response of porcine aortic valve leaflets to a range of vasoactive agents including endothelin-1, noradrenaline, adrenaline, the thromboxane (TX) A2 mimetic U46619, 5-hydroxytryptamine (5-HT), histamine and angiotensin II. The viability of each individual leaflet was tested by the addition of 90 mM KCl.

RESULTS

All agents tested, with the exception of angiotensin II, were capable of inducing concentration-dependent contractions of the valve leaflets. The responses to endothelin-1 and U46619 were significantly greater than those of all the other agents tested. Responses to endothelin-1 could be inhibited by 10(-5) M of the mixed ET(A/B) receptor antagonist bosantan. The response to both catecholamines was blocked by 10(-6) M yohimbine, but not by 3 x 10(-7) M prazosin, indicating the presence of alpha2-adrenoceptors. The response to histamine was mediated exclusively by H1-receptors, as judged by the antagonistic effect of 10(-6) M of the H1-receptor antagonist mepyramine. The response to 5-HT could be blocked by 10(-6) M of the 5-HT2A-receptor antagonist ketanserin, and that of U46619 by 10(-6) M of the TXA2-receptor antagonist SQ30741.

CONCLUSION

These results demonstrate the range of receptor systems that can mediate contraction of aortic valve leaflets. Further studies are required to elucidate the role of these receptors in the physiology and pathophysiology of the aortic valve.