Balloon catheter injury to rabbit carotid artery. II. Selective increase in reactivity to some vasoconstrictor drugs

Phenotypic Reversion of Smooth Muscle Cells in Hybrid Vascular Prostheses

Our purpose was to evaluate whether or not and when phenotypic modulation of smooth muscle cells (SMCs) in hybrid vascular prostheses preincorporated with SMCs occurs upon implantation. Two types of hybrid vascular grafts incorporated with vascular cells derived from canine jugular veins were prepared: grafts containing a collagen gel layer covered with an endothelial monolayer at the luminal surface (Model I graft) and those containing an endothelial monolayer and SMC multilayer (Model II graft). They were bilaterally implanted into carotid arteries of the same dogs from which the cells had been harvested for 2 wk (n = 3) and 12 wk (n = 3). The time-dependent changes in populations of three SMC phenotypes (synthetic, intermediate, and contractile) in the neoarterial layers were quantified by morphometric evaluation using a transmission electron microscope in hybrid vascular grafts. Before implantation, all the SMCs were of the synthetic phenotype. In Model II grafts at 2 wk, synthetic and intermediate SMCs were dominant especially in the luminal layer. On the other hand, neoarterial layers at 12 wk were dominated by contractile SMCs, which were evenly distributed throughout the entire neoarterial tissues. A markedly delayed phenotypic reversion was noted for the Model I grafts at 12 wk. In the hybrid grafts, during about 3 mo of implantation, neoarterial SMCs transformed from the synthetic to the contractile phenotypes, which was promoted by SMC incorporation.

Loss of Tachyphylaxis and Increased Sensitivity to Angiotensin II in Experimental Vein Grants

Intimal hyperplasia and atherosclerosis have been implicated in the pathophysiology of vein graft failure. Several recent studies have also reported alterations in the vasoreactivity of vein grafts. These alterations in vasoreactivity could contribute to vein graft spasm and lead to graft occlusion. This study examined the vasomotor responses of experimental vein grafts to angiotensin II, the most potent natural vasoconstrictor known. The right carotid artery was divided and bypassed in 12 rabbits with use of the right external jugular vein. The left external jugular vein was used as a control.

Eight vein grafts and jugular veins were harvested after fourteen days and 4 vein grafts after twenty-eight days. Segments of vein graft and control vein were mounted under isometric tension in an organ bath, and the dose response curves to angiotensin II obtained. On day 14, the response of the jugular veins was triphasic, while the respnse of the vein grafts was sigmoidal. The vein grafts were hypersensitive to angiotensin II. The ED50 was reduced from 8.4 ± 2.5 x 10-6 M in the jugular veins to 1.62 ± 0.24 x 10-8 M in the vein grafts (p < 0.005). The maximal response to angiotensin II was also increased from 342 ± 24 mg in the jugular veins to 558 ± 108 mg in the vein grafts on day 14 (p < 0.05). There was no significant difference in either the ED50 or the maximal response of the vein grafts on day 14 or 28. Tachyphylaxis (desensitization with repeated doses of agonist) was observed in the jugular veins but not in the vein grafts. The results show that experimental vein grafts are hypersensitive to angiotensin II, with either single or repeated exposure. This increased vasoreactivity to angiotensin II may have important clinical implications, particularly when vein grafts are used in patients with renovascular hypertension.

Aging and total stenosis triggers differential responses of carotid and basilar arteries to endothelin-1 and phenylephrine

Our aim was to investigate the effects of ageing on the vascular contractility of carotid and basilar arteries from guinea-pigs, in a model of total stenosis. Moreover, we attempted to identify whether total stenosis of the left common carotid (stenosed) in adult guinea-pigs, would affect the contractions of contralateral carotid (intact) and basilar arteries to different vasoconstrictors. With this purpose, the left carotid was occluded with a silk thread at a position close to its origin. Vascular reactivity experiments using standard muscle bath were performed 7, 15, 30, and 90 days after carotid occlusion. Reactivity of carotid and basilar arteries to endothelin-1, phenylephrine and KCl was reduced with ageing in naive guinea-pigs. The endothelin-1 and KCl-induced contractions were unaltered in arteries from SHAM-operated animals. Moreover, phenylephrine-induced contractions were reduced in both carotids from 7 days SHAM-operated guinea-pigs, when compared to naive group. Stenosis induced progressive reduction in the contraction induced by endothelin-1, phenylephrine and KCl in the stenosed carotid, when compared to their respective age-matched naive and SHAM groups. Interestingly, an increased contractile-response to vasoconstrictor agents in all the contralateral carotids was observed. Stenosis (30 and 90 days) also induced an increase in the contractions induced by endothelin-1 in the basilar artery. Conversely, phenylephrine and KCl-induced contractions were reduced in basilar arteries 7, 15, 30 and 90 days after stenosis. These results showed that stenosis in adult guinea-pigs induce alterations of vascular reactivity in arteries distant from the site of injury. Thus, in spite of the common use of contralateral carotid as control, it must be aware of the potential alteration induced by stenosis in the vascular motility of such vessels. Additionally, it was verified a relationship between the period of stenosis and the alterations in the vascular reactivity to these vasoconstrictors.

Locally administered antiproliferative drugs inhibit hypercontractility to serotonin in balloon-injured pig coronary artery

Although drugs such as sirolimus and paclitaxel are effective in reducing restenosis, their effects on vascular function are often overlooked. In this study, we have examined the effects of local delivery of several anti-restenotic drugs given in vivo after balloon injury on in vitro vascular contraction and relaxation 28 days after injury. Paclitaxel (50 microM), the farnesyl protein transferase inhibitor L744 (25 microM), sirolimus (25 microM) and Van 10/4 (decahydro-1,1,4,7-tetramethyl-1H-cycloprop[e]azulen-4-o-[2-(3-methylpent-2-enoyl)-fucopyranoside]; 25 microM) were delivered to porcine coronary arteries in vivo and the arteries removed 28 days later. Contractions to KCl and 5-hydroxytryptamine (5-HT) and relaxations to calcimycin and 3-morpholinosydnonimine (SIN-1) were measured in control (LCx) and balloon-injured (LAD) rings. In vehicle-infused coronary arteries, contraction to KCl and 5-HT was significantly enhanced 28 days after balloon injury, while the response to calcimycin had recovered fully, indicating endothelial regrowth. The response to SIN-1 was unchanged. None of the four drugs tested had any effect on the enhanced response to KCl 28 days after injury or on recovery of the calcimycin response. The hyper-responsiveness to 5-HT was eliminated by sirolimus, Van 10/4 and L744, but not paclitaxel. This study demonstrates that local drug infusion with structurally different antiproliferative drugs at the time of balloon angioplasty does not affect endothelial recovery and may in some cases prevent hyper-responsiveness to constrictor agents.

Coronary vasospasm associated with uncontrolled carcinoid tumour

We report on a 74-year-old carcinoid patient who, following acute myocardial infarction (MI) and percutaneous transluminal coronary angioplasty, suffered recurrent episodes of chest pain and ST-segment elevation on ECG. This was accompanied by elevation of urinary 5-hydroxy-indole acetic acid. A review of the patient's file revealed that during the 3 weeks prior to the MI, she had been treated inadvertently with a fivefold lower dosage of octreotide. Following the correction of octreotide dosage, episodes of chest pain resolved immediately. We therefore suggest that this patient suffered from recurrent coronary vasospasm due to uncontrolled carcinoid tumour.

Early phase alterations in endothelium dependent vasorelaxation responses due to aneurysm clip application and related manipulations

Mechanically induced vasoconstriction observed throughout surgery and in the immediate postoperative period was investigated to assess the effects of various microsurgical manipulations. Factors such as the type of aneurysm clip, duration of temporary clipping and peri-adventitial tissue stripping were the variables in this study. Microsurgical clips were applied on guinea pig "cervical carotid arteries" in which peri-adventitia had been removed microsurgically. Arterial rings were removed immediately after surgery. Endothelium dependent relaxations were measured and morphological investigations were performed using light microscopy. It was observed that as the clip application period increased, relaxation responses decreased. Peri-adventitial tissue stripping caused a marked decrease in the relaxation responses in all types of the clips. Microvascular clips, in spite of their lower closing forces, had the greatest deleterious effect on relaxation responses of the vessel, in both normal and peri-adventitial tissue stripped. When the peri-adventitial tissue of the vessel had been stripped, convolutions of the lamina elastica interna were found to be lost in parallel with the decreased tonus of the artery. In the vessels subjected to clipping endothelial denudation and cracking took place. As a conclusion it can be stated that both peri-adventitial tissue stripping and microvascular clip application have deleterious effects in the early postoperative period. While choosing clips from minimal occlusion force tables, care must be taken to choose clips with less width; and while performing microvascular anastomosis, temporary clips with a lesser width must be used in place of microvascular clips. Adventitial stripping must not be unnecessarily generous during microvascular anastomosis.

alpha 1-Adrenoceptors on rabbit aortic smooth muscle cells in culture and in experimental intimal thickening

1. This study has defined alpha 1-adrenoceptors and their reactivity in rabbit aorta, following removal of the endothelium and formation of a myointimal thickening, and also in smooth muscle cells (SMC) in cell culture which had undergone serial passaging and changes in phenotype. 2. [3H]-prazosin binding to SMC from control aorta, vessels 2 weeks after endothelial denudation and sub-cultured SMC (passage 3-6) was specific (displaceable with 10 mumol/L phentolamine), and of high affinity to a single class of sites (KD range: 71-114 pmol/L). The maximum binding density (Bmax) of alpha 1-adrenoceptors on SMC from the neointima (11,105 +/- 771 sites/cell) was not significantly different to that of control medial SMC (14,014 +/- 2472 sites/cell). However, SMC cultured to passage 6, showed a 2-fold increase in Bmax (30,227 +/- 4349 sites/cell). 3. The production of inositol phosphates (IP1, IP2 and IP3) by SMC following 10 mumol/L phenylephrine was assayed. Both freshly-dispersed aortic SMC and sub-cultured SMC were stimulated to produce increased inositol phosphates by the addition of phenylephrine which was completely inhibited by pre-incubation with 10 mumol/L phentolamine, suggesting that the stimulation was via alpha 1-adrenoceptors. 4. Maximal contractile responses of isolated thoracic and abdominal aortic rings to KCl (100 mmol/L), 5-HT and phenylephrine were unchanged two weeks after endothelial denudation. However, phenylephrine was significantly less potent (2.7-fold) in both areas of the aorta, while the potency of 5-HT was significantly enhanced (2.7-fold) after endothelial denudation only in the abdominal aorta. 5. The decreased sensitivity of the rabbit aorta to alpha 1-adrenoceptor agonists following endothelial denudation and the formation of a myointimal thickening is not due to changes in affinity or density of alpha 1-adrenoceptors. However multiple passaging of SMC in culture leads to an increase in alpha 1-adrenoceptor density. This change can be related to the altered cytodifferentiation of irreversible synthetic state SMC which are similar to those in atherosclerotic lesions.

Influence of chronic treatment with a nitric oxide donor on fatty streak development and reactivity of the rabbit aorta

1. The influence of chronic treatment with molsidomine, pro-drug of the nitric oxide (NO) donor, 3-morpholino-sydnonimine (SIN-1), on fatty streak development and release of NO and prostacyclin (PGI2) was studied in the aorta of normal and cholesterol-fed rabbits. 2. Groups of 10 rabbits received standard diet (150 g day-1), or diets with 0.3% cholesterol, with 0.02% molsidomine or with the combination of cholesterol and molsidomine for 16 weeks. Lesion area and thickness, maximum change in isometric force (Emax) and sensitivity (-log EC50 or pD2) to constricting and relaxing agonists were assessed in segments of arch, thoracic and abdominal aorta. Bioassay was used to assess NO release. 3. Cholesterol-induced fatty streaks tapered off towards the abdominal aorta. Area, thickness, weight and cholesterylester content of the lesions were augmented by the NO donor, whereas the hypercholesterolaemia remained unchanged. The exacerbation was attributed to co-release of superoxide anion from the sydnonimine. 4. As fatty streaks progressed, amplitude and pD2 of acetylcholine (ACh)-induced relaxations decreased, whereas cyclic GMP and cyclic AMP second messenger systems were not influenced, since Emax and sensitivity to SIN-1 and forskolin remained unchanged. However, extensive lesions apparently trapped some NO, as the pD2 of authentic NO decreased. 5. The fatty streaks curtailed the biosynthesis of PGI2 and the overflow of NO from the perfused thoracic aorta. The latter defect was not restored by L-arginine and appears to be consistent with a functional change of the endothelial muscarinic receptors. 6. The NO donor desensitized the aorta to cyclic GMP-mediated relaxations (ACh, SIN-1 and NO), without affecting cyclic AMP-mediated relaxation to forskolin or constrictor responses to phenylephrine and 5-hydroxytryptamine. 7. The drug also suppressed the ACh-induced overflow of NO, without changing PGI2 release. This selective reduction of endothelial NO release and the desensitization of cyclic GMP-mediated relaxations occurred independently of fatty streak formation. 8. The results indicate that chronic exposure to exogenous NO downregulates endothelial NO release and cyclic GMP-mediated relaxations, and provide evidence for the existence of negative feed-back regulations of the L-arginine NO pathway under in vivo conditions.

Vasoconstrictor responses after neo-intima formation and endothelial removal in the rabbit carotid artery

1. The present study examined the responses of the rabbit carotid artery to five vasoconstrictors after neo-intima formation induced by perivascular collar treatment and evaluated the role of constitutive and inducible nitric oxide (NO) synthase and endothelial cells (ECs). 2. Ring segments of the rabbit carotid artery were mounted in organ chambers for isometric tension recording. Neo-intima-bearing vessels developed less force (Emax) in response to KCl, the thromboxane-mimetic U-46619 and 5-hydroxytryptamine (5-HT), but not to angiotensin I and II. 3. The collar-treatment increased the sensitivity to 5-HT, and decreased the sensitivity to angiotensin II. The sensitivity to U-46619 and angiotensin I remained unchanged. 4. Mechanical removal of ECs and inhibition of NO biosynthesis by NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine (L-NOARG) increased the sensitivity to 5-HT in sham and collar-treated segments to the same extent. The effects of collar-treatment and endothelial removal or treatment with inhibitors of NO biosynthesis were additive. Inhibition of NO biosynthesis failed to augment sensitivity to 5-HT after endothelial denudation. L-NOARG increased the force development to KCl in sham and collar-treated segments to the same extent. However, L-NMMA and L-NOARG failed to augment the contractile responses of neo-intima-bearing vessels to 5-HT and KCl after endothelial removal. 5. The responses to angiotensin I were not altered, either by the neo-intima or by endothelial removal. In arteries with a neo-intima the sensitivity to angiotensin II was decreased. Removal of the endothelium or incubation with L-NOARG counteracted this rightward shift and increased Emax.6. Our results demonstrate that contractions to 5-HT, angiotensin II and KCl are modulated by NO in both sham and neo-intima-bearing vessels. Inhibition of NO biosynthesis and collar treatment resulted in additive effects on the EC50 values, suggesting that the 5-HT and angiotension (AT) receptors on the smooth muscle cells are also modified by the formation of a neo-intima. Furthermore, the reduced contractile responses of segments with a neo-intima are not due to NO formed by an inducible NO synthase in those vessels.

Reduced contractile function after balloon denudation of rat carotid arteries

In rat carotid arteries isolated 2 weeks after balloon denudation, a significant neointima developed with little change in medial size. Associated with this neointimal hyperplasia was a marked decrease in contraction to various agents including angiotensins I and II, big endothelin-1, endothelin-1, norepinephrine, phenylephrine, and serotonin. Vasodilator responses to acetylcholine were significantly reduced. In contrast, vasodilator responses to nitroglycerin were unaffected. It is suggested that modulation of the neointimal cells to a more non-contractile phenotype may be responsible for the loss in contractile ability.

Spirapril and cilazapril inhibit neointimal lesion development but cause no detectable inhibition of lumen narrowing after carotid artery balloon catheter injury in the rat

Five groups of 12 rats were subject to balloon lesion of the left carotid artery and neointimal thickening was measured histologically 2 weeks after injury. Rat groups received either spirapril (3, 10 or 30 mg/kg/day, administered throughout the study in the food), cilazapril (10 mg/kg/day) or placebo. Spirapril caused a dose-dependent inhibition of the neointimal thickening of the rat carotid artery. The degree of inhibition with 10 mg/kg/d spirapril and cilazapril was similar (-44% and -42% respectively). The carotid lumen area was measured in vivo by nuclear magnetic resonance (NMR) imaging both before and 2 weeks after balloon injury and also postmortem by histological techniques. Two weeks after injury, the lumen area of the left carotid artery was significantly reduced following balloon injury, as measured by both techniques. Treatment did not detectably modify this stenosis process despite the use of two independent methods for assessing lumen size, even though neointimal thickening was strongly attenuated by both angiotensin converting enzyme inhibitors. This dissociation between inhibition of neointimal lesion development and decrease of lumen size provides a new view of the role of angiotensin converting enzyme inhibitors in vascular damage situations. Our results suggest that the focus, particularly in clinical studies, on lumen size, may mean that potentially beneficial effects of these drugs on other parts of the vascular wall be overlooked.

Response of human coronary arteries to serotonin after injury by coronary angioplasty

BACKGROUND

Atherosclerotic stenoses that have exaggerated vasomotor responses are especially prone to restenosis after coronary angioplasty. Experimental studies show that vasomotor responses in normal vessels are altered by acute mechanical injury, an alteration that in part reflects changes in the functional characteristics of endothelium that has regenerated after injury.

METHODS AND RESULTS

We examined, by quantitative coronary arteriography, the response of dilated and control coronary segments to intracoronary infusions of graded doses of serotonin, an endothelium-dependent vasoactive agent, and to intracoronary injection of isosorbide dinitrate, an endothelium-independent smooth muscle dilator in 15 patients who had undergone a single percutaneous transluminal coronary angioplasty procedure and who had no clinical features of variant angina. Dose-dependent constriction to serotonin occurred at all measured sites. The mean +/- SEM diameter reductions, expressed as percent reduction in baseline diameter that was observed at proximal (18.1 +/- 2.9, 18.8 +/- 2.2) and distal (30.9 +/- 4.4, 35.4 +/- 5.3) control sites in the dilated and nondilated vessels, respectively, at the highest dose, were similar. The degree of constriction in distal segments was significantly (P < .01) greater than that in proximal segments. Total or subtotal occlusion occurred at the angioplasty site in 4 patients at the highest infused dose (10(-4) mol/L). The mean percent reduction in baseline diameter at previously dilated sites (53.8 +/- 5.9) at this dose was significantly (P < .05) greater than that observed at the adjacent proximal control sites and similar to that observed at distal control sites. All segments dilated significantly after intracoronary injection of isosorbide dinitrate.

CONCLUSIONS

In dilated and nondilated vessels, serotonin caused significantly more marked constriction in distal than in proximal vessel segments. In dilated vessels, the vessel segments that had been subjected to angioplasty had a constrictor response to serotonin that was more marked than at adjacent proximal control sites and equivalent to that in the distal vessel segments. This enhanced constrictor response could be related to changes in endothelial cell function after regeneration or to hyperreactivity of smooth muscle cells at the angioplasty site.

Characterization of the responses of isolated rings of rabbit left carotid artery. A potential protocol for the assessment of pathologically induced functional changes

Studies on such injury processes as atherosclerosis, angioplasty, and restenosis, have shown an impairment of relaxations mediated by endothelium-derived relaxing factor (EDRF). Increasingly, the rabbit carotid artery is being used as the vessel of choice in such studies, but a definite protocol for the assessment of endothelial dysfunction or denudation has not been developed. Using isolated carotid artery rings, we have obtained reproducible dose-response curves in endothelially intact and denuded vessels from normally fed rabbits to a variety of vasoconstrictors and endothelium-dependent and -independent vasodilators. Endothelium-dependent vasodilators (acetylcholine (1 x 10(-8)-1 x 10(-6) M), carbachol (1 x 10(-8)-5 x 10(-6) M), substance P (0.01-100 nM), and A23187 (1 x 10(-8)-1 x 10(-7) M) relaxed the arteries in a concentration-dependent manner but produced no relaxation in denuded vessels. Endothelium-independent nitric oxide (NO) donors [Sin-1 (1 x 10(-8)-1 x 10(-6) M)] and sodium nitroprusside (1 x 10(-8)-1 x 10(-6) M)) relaxed both intact and denuded vessels to a similar degree (slight augmentation of the relaxation induced in denuded vessels was not significant), demonstrating that denuded vessels did not have an impaired reactivity to NO. Concentration response curves to the vasoconstrictors [5-HT (1 x 10(-7)-1 x 10(-4) M) and KCl (15-60 mM)] were produced in intact vessels and it was shown that similar contraction was produced by 1 x 10(-6) M 5-HT in intact and denuded vessels. This indicated that the vessels retained contractile ability following denudation.(ABSTRACT TRUNCATED AT 250 WORDS)

Arterial response to mechanical injury: balloon catheter de-endothelialization

Coronary angioplasty has been used clinically for over a decade. Its initial promise as an alternative to coronary bypass surgery has only partially been fulfilled because of the high rate of post-operative restenosis. A number of animal models have been devised to study this phenomenon and although none is entirely satisfactory, they have, together with recent advances in molecular biology provided an insight into the cellular mechanisms that may contribute to this complication. This knowledge may ultimately lead to a means of therapeutic intervention. This review summarises our present understanding of the pathology of post-angioplasty re-stenosis as revealed by studies using the balloon catheter de-endothelialization model, and discusses some of the intervention strategies that have been attempted.

Coronary artery spasm and vascular biology. Cholinergic constriction

Coronary artery spasm is undoubtedly one of the causative factors of ischemic heart disease, particularly variant-type angina pectoris and myocardial infarction, but the disease mechanisms involved are still unclear. The present review describes the clinical background of coronary artery spasm in relation to ischemic heart disease, including a brief history of studies in this field, and also suggests future guidelines for experimental investigations based on the characteristics of coronary artery spasm, focusing particularly on data we have obtained in our laboratory from studies of cholinergic constriction. The pig may be a suitable animal in which coronary artery spasm could be provoked with cholinergic agents following endothelial denudation. The use of such large animals would allow the study of spastic arterial segments by various methods with angiographic confirmation. After endothelial denudation it is possible that phenotypic changes in cholinergic receptors might occur in smooth muscle cells, and that such changes might remain even after endothelial repair.

Endothelium-derived relaxing factor: basic review and clinical implications

EDRF is a potent, endogenous vasodilator that is produced and released from endothelial cells and subsequently causes the relaxation of VSM through the activation of soluble guanylate cyclase and an increase in VSM cyclic GMP. Structurally, EDRF is likely to be NO or a related nitrogen oxide-containing compound. It is synthesized in endothelial and other cell types from L-arginine by a calcium-calmodulin and NADPH-dependent enzyme. Its action is very similar to the nitrovasodilators that act directly on VSM. EDRF is present in all vascular beds, large and small vessels, and in a wide range of species. Its role in human vascular physiology and pathophysiology is just beginning to be understood. EDRF is a potent endogenous vasodilator and inhibitor of platelet aggregation and adhesion. Its activity is impaired in hypertension and atherosclerosis, and its absence due to endothelial damage may play a role in cerebral and coronary vasospasm. It is a mediator of flow-dependent vasodilation, and its inhibition by hypoxia may contribute to the hypoxic pulmonary vasoconstrictor response. Endothelial cell damage and impairment of EDRF production may also contribute to acute and chronic pulmonary hypertension. A further understanding of the chemical nature and synthetic pathways of EDRF should lead to the production of analogs and antagonists, which may play an important role in future treatments for atherosclerosis, myocardial infarction, angina, hypertension, and other vascular diseases. The recent realization that EDRF serves as the second messenger for guanylate cyclase activation and cyclic GMP production in a variety of cell types outside of the cardiovascular system, including renal and respiratory epithelium, cerebellar neurons, macrophages, and adrenocytes, suggests even broader implications. The importance of EDRF to the anesthesiologist may go beyond an understanding of its role in cardiovascular physiological and pathophysiological states. Initial studies have shown that the endothelium may play a role in mediating the vascular actions of anesthetics, and that anesthetics can inhibit the production, release, or action of EDRF. How are these interactions mediated? Are there significant differences between anesthetics with regard to their effects on EDRF? Is there a clinically significant effect of anesthetics on basal activity of EDRF, or only in response to exogenous stimulation? Conversely, it is important to determine if alterations in endothelial cell function by various disease states such as hypertension, atherosclerosis, adult respiratory distress syndrome, cerebral vasospasm, and others cause changes in the vascular actions of anesthetics. The potential interactions of anesthetics with EDRF production and action in cell types other than the endothelium have not yet been explored.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of basic fibroblast growth factor in vascular lesion formation

In the present study we investigated whether basic fibroblast growth factor (bFGF) plays a role in the proliferative response of smooth muscle cells (SMCs) to denuding injury. Rat carotid smooth muscle was found to express the mRNA for bFGF, and bFGF protein was found to be present in rat aorta by immunoblot analysis. Systemically administered bFGF was a potent mitogen for vascular SMCs in arteries denuded with a balloon catheter, increasing replication from 11.5% in controls to 54.8%. Denudation with a device (filament loop), which causes only minimal damage to medial SMCs, showed a similar increase in replication (1.3% versus 43.3%) after bFGF infusion. In unmanipulated vessels, however, SMCs were unresponsive to infused bFGF. Infusion of a "mitotoxin" (bFGF conjugated to saporin) caused a greater than 50% decrease in the number of viable SMCs in the arterial wall after balloon injury. Prolonged administration of bFGF (12 micrograms/day for 2 weeks) after balloon injury caused an approximately twofold increase in intimal thickening. These results show that bFGF, which is synthesized by the arterial wall, could be a potent mitogen for SMCs in vivo and suggest that any release of endogenous bFGF may be capable of stimulating SMC proliferation, which may subsequently lead to intimal lesion formation.