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Biomedical subjects

F Dagenais

Publications and source records attributed to F Dagenais.

At least 19 recordsLinked to original sources
PubMed2006

Distribution of SPARC during neovascularisation of degenerative aortic stenosis.

OBJECTIVE: To examine the hypothesis that degenerative aortic stenosis (AS) is associated with the development of blood vessels and the expression of the secreted protein, acidic and rich in cysteine/osteonectin (SPARC), a matricellular protein that is involved in ossification, the modulation of angiogenesis and the production of metalloproteinases. METHODS: 30 surgically excised AS valves and 20 normal aortic valves were studied. RESULTS: Blood vessels were detected in the aortic valves from patients with degenerative AS, whereas normal valves were avascular structures. Blood vessels in AS valves expressed endothelial nitric oxide synthase, CD34 and von Willebrand factor (vWF). Blood vessels were located in three distinct regions: near calcified nodules, under the leaflet border and in rich cellular areas forming cell islands. Blood vessels were predominantly present in early and intermediate grades of calcification. Cell islands were densely populated by CD45-positive cells where endothelial cells (CD34+, vWF+) forming cord-like structures were present. Immunoblotting detected SPARC only in AS valves and immunohistological analysis located SPARC in mature blood vessels. The proportion of blood vessels positive for SPARC was higher in valves with a lower grade of calcification. In cell islands, SPARC was distributed to mature blood vessels and to macrophages, where it co-located with matrix metalloproteinase-9, whereas no expression was detected in endothelial cells forming cord-like structures. CONCLUSION: The localisation of SPARC to mature blood vessels and its predominant expression in AS valves with a lower calcification grade suggest that the spatial and temporal distribution of this matricellular protein is tightly controlled to participate in the neovascularisation of AS valves.

Aged↗
PubMed2006

Expression of bone-regulatory proteins in human valve allografts.

OBJECTIVE: To test the hypothesis that valve allograft (VA) calcification results from an ossification process in which bone-regulatory proteins are expressed. METHODS: 15 VA that were explanted at the time of surgery for dysfunction were studied. VA were analysed and compared with normal aortic valves (n = 20). RESULTS: All the VA (5 aortic, 10 pulmonary) exhibited heavy calcification and important fibrosis. Immunohistochemistry studies showed that the bone-specific transcription factor Cbfa-1 was expressed by stromal cells. Bone alkaline phosphatase was expressed in calcified regions. Immunostaining for alpha smooth muscle (alpha-SM) actin was increased in VA compared with normal valves and in 6 of the 15 valves formed cellular clusters close to the calcified nodules. In VA osteopontin and osteonectin were expressed by stromal cells, whereas osteocalcin was closely associated with the calcified regions. Furthermore, analysis of the bone-regulatory proteins that control bone resorption showed that receptor activator of nuclear factor kappaB ligand (RANKL), receptor activator of nuclear factor kappaB (RANK) and osteoprotegerin (OPG) were differentially expressed in calcified VA and normal valves. Normal valve leaflets expressed OPG, whereas OPG expression was absent or faint in calcified VA. RANKL and RANK were not detected in normal valves, whereas calcified VA expressed RANKL and RANK. CONCLUSION: These data suggest that calcification of VA results from an ossification process, which relies on tight control of bone-regulatory protein expression. The expression pattern of the RANKL/RANK/OPG system suggests that it may have a regulatory role not only in osteoclastogenesis but also in the calcification of human VA.

Actins↗
PubMed2005

Which biologic valve should we select for the 45- to 65-year-old age group requiring aortic valve replacement?

OBJECTIVE: The diversity of biologic valves available to replace the aortic valve renders selection difficult for the 45- to 65-year-old patient. To evaluate and compare the results of biologic valves in the 45- to 65-year-old patient, we reviewed our experience (1991-2004). METHODS: Three hundred thirty-two patients between 45 and 65 years old with isolated aortic valve disease had a biologic valve implanted: Freestyle valve in 140 patients, a homograft in 54 patients, a stented Mosaic or Perimount valve (stented xenograft) in 62 patients, and a Ross procedure in 76 patients. RESULTS: Perioperative mortality was comparable for all groups (Freestyle, 2.1%; homograft, 3.7%; stented xenograft, 3.2%; Ross procedure, 1.3%; P = .8). Echocardiographically determined valve performance at discharge was significantly enhanced in the Ross procedure and homograft groups (indexed effective orifice area: Freestyle, 0.9 +/- 0.3 cm 2 /m 2 ; homograft, 1.3 +/- 0.3 cm 2 /m 2 ; stented xenograft, 0.8 +/- 0.2 cm 2 /m 2 ; Ross procedure, 1.4 +/- 0.4; P < .0001; mean gradient: Freestyle, 12.0 +/- 6.6 mm Hg; homograft, 7.4 +/- 4.0 mm Hg; stented xenograft, 15.4 +/- 5.4 mm Hg; Ross procedure, 4.6 +/- 3.2 mm Hg; P < .0001). For all yearly follow-up, freedom from New York Heart Association class III or IV was comparable and greater than 95% for all groups. At 7 years, cardiac survival (homograft, 96.3% +/- 3.7%; Ross procedure, 90.6% +/- 6.3%; stented xenograft, 86.0% +/- 10.3%; Freestyle, 89.2% +/- 10.8%; P = .7) and freedom from reoperation (Ross procedure, 98.5% +/- 1.4%; homograft, 90.6% +/- 5.7%; Freestyle, 88.0% +/- 4.9%; stented xenograft, 90.0% +/- 8.0%; P = .4) were comparable. Freedoms from significant bleeding events, valve-related neurologic events, or endocarditis were comparable and greater than 95% for all groups. CONCLUSION: Type of aortic biologic valve for the 45- to 65-year-old patient does not affect midterm survival or valve-related morbidity. Thus the choice of biologic valve for the 45- to 65-year-old patient should be dictated by patient-surgeon preference, ease of implantation, and reoperation until longer comparative studies are available.

Age Factors↗
PubMed2003

Cartilaginous metaplasia and calcification in aortic allograft is associated with transforming growth factor beta 1 expression.

BACKGROUND: Calcification of homografts and vascular conduits is poorly understood. Mechanisms leading to calcification were studied in a rat model of aortic allografts. METHODS: Rat aortas from Lew1W (RT1(u)) were transplanted into Lew1A (RT1(a)). Animals were killed at 30 days and 180 days, and aortic grafts were removed and analyzed for histologic and immunohistologic studies. RESULTS: Intimal surface increased progressively over 6 months and was the site of important modifications. Intimal cellular population changed from a leukocyte (CD45, OX1-OX30)- and macrophage (CD68, ED-1)-based population at 30 days to predominantly alpha-smooth muscle actin-expressing cells at 180 days. At 180 days, allografts were characterized by an abundant extracellular matrix composed of collagen and elastic fibers associated with extensive calcification (von Kossa staining) located in the intima and media. Osteoblastic activity was present in calcified lesion as shown by alkaline phosphatase activity. At 180 days, numerous chondrocytes (protein S100-positive and alpha-smooth muscle actin-negative) were present focally in the media. However, double immunostaining revealed that a cellular population within the media with a chondrocyte-like morphology was alpha-smooth muscle actin-positive and S100-negative. Active form of transforming growth factor beta1 was expressed from 30 to 80 days in the medial and intimal layers. CONCLUSIONS: These observations suggest that alpha-smooth muscle actin-positive cells within aortic allografts are eventually transformed to a chondrocyte-like structure, leading to vascular cartilaginous metaplasia associated with the expression of transforming growth factor beta1 and could be a potential pathway leading to extensive vascular wall calcification in allografts through endochondral ossification.

Animals↗
PubMed2003

Does moderate mitral regurgitation impact early or mid-term clinical outcome in patients undergoing isolated aortic valve replacement for aortic stenosis?

OBJECTIVE: The early and mid-term impact of functional mitral regurgitation (MR) in patients undergoing isolated aortic valve replacement (AVR) for aortic stenosis remains unresolved. METHOD: Through our institutional databank, using a case-match study, we identified 58 patients with MR grades 0-1 and 58 patients with MR grades 2-3 (patients matched for sex, age, ejection fraction (EF), NYHA, diabetes, and CVA). Data were collected prospectively (mean duration of follow-up: 3.2 +/- 2.4 years). RESULTS: Perioperative morbidity (re-operation for bleeding, low cardiac output, CVA, renal failure) was comparable among groups. Difference in mortality between the two groups was non-significant (7.0 vs. 3.5%, P = 0.67 in groups MR 2-3 vs. 0-1, respectively). At early echocardiographic follow-up, 7/58 patients (12.1%) within group MR grades 0-1 increased their MR to grades 2-3; among which only two remained with MR grades 2-3 at mid-term follow-up. Within MR group 2-3, 18/58 (31.0%) remained with MR grades 2-3 among which 7/18 (38.9%) decreased of at least one grade at follow-up. Eight year actuarial survival was comparable in both groups: MR grades 0-1 = 60.9% vs. MR grades 2-3 = 55.0%; P = 0.1. Actuarial survival of patients with MR grades 2-3 postoperatively was similar to patients with MR grades 0-1 (MR grades 0-1 = 59.0%, MR grades 2-3 = 58.9%, P = NS). CONCLUSIONS: Presence of preoperative moderate functional MR (grades 2-3) in patients undergoing isolated AVR for aortic stenosis regresses in the majority of patients postoperatively and has no significant impact on perioperative morbidity or mortality, nor mid-term survival. Thus, moderate functional MR should be treated conservatively in the majority of patients especially in the elderly subjected to isolated AVR for aortic stenosis.

Aged↗
PubMed2001

The Novacor left ventricular assist system: clinical experience from the Novacor registry.

The electrically powered Novacor left ventricular assist (LVAS) system was first used clinically as a bridge to transplant in 1984. The configuration has evolved to the current wearable model used clinically for the first time in 1993. In 1998, the inflow conduit was modified, reducing embolic events by 50%. Over 1100 implants have been performed worldwide with cumulative support greater than 300 patient years, and only 0.7% requiring replacement. The Novacor is a safe and effective device for bridge to transplant, bridge to recovery, or potentially permanent implant with reliable long-term support for periods as long as 4 years.

Adolescent↗
PubMed2001

A single center experience with the freestyle bioprosthesis: midterm results at the Québec Heart Institute.

Stentless bioprostheses show excellent early hemodynamic performance. However, longevity still remains unknown. This study reports midterm follow-up in 419 patients in which a Freestyle bioprosthesis (Medtronic Heart Valves, Minneapolis, MN) was inserted between January 1993 and January 2000 at the Quebec Heart Institute (Ste-Foy, Québec, Canada). Mean age at implantation was 68.0 +/- 8.2 years. Implantation was subcoronary in 81.9% of the patients, as a root replacement in 16.5%, and as a root inclusion in 1.7%. Mortality at 30 days was 6.2% for the whole cohort (2.8% for isolated subcoronary aortic valve replacement). Female gender, root implantation, valve sizes 19 to 21 mm, previous surgery, a history of stroke and diabetes were identified as predictors of 30-day mortality. Actuarial freedom from all death causes was 81.5% at 7 years; freedom from valve-related deaths 97.0%, and freedom from cardiac deaths 92.7%. Freedom from thromboembolic events was 86.1% at 7 years (55.1% of events were < 30 days). Freedom from endocarditis and hemorrhagic complications were respectively 98.5% and 95.6% at 7 years. Six patients required reoperations for valve explantation: 2 for endocarditis, 2 for structural dysfunction, and 2 for nonstructural dysfunction. Incidence of moderate or severe valve insufficiency at annual echocardiographic follow-up was: discharge: 0.6%; year 1: 0.7%; year 2: 1.3%; year 3: 3.3%; year 4: 3.7%; year 5: 2.6%; year 6: 0%. At 6 years after implantation, mean transvalvular gradient and effective valve orifice area were comparable to the year 1 values. This single center experience with the Medtronic Freestyle prosthesis shows preserved hemodynamic performance and low valve-related complications at midterm.

Actuarial Analysis↗
PubMed2000

Systematic off-pump coronary artery revascularization in multivessel disease: experience of three hundred cases.

OBJECTIVE: We sought to report our recent experience with off-pump coronary artery revascularization in multivessel disease. METHODS: Between October 1996 and December 1998, 300 off-pump beating heart operations were performed at the Montreal Heart Institute by a single surgeon, representing 94% of all procedures undertaken during this same time frame (97% for 1998). This cohort of patients was compared with 1870 patients operated on with cardiopulmonary bypass from 1995 to 1996. RESULTS: Mean age, sex distribution, and preoperative risk factors were comparable for the two groups. On average, 2.92 +/- 0.8 and 2.84 +/- 0.6 grafts per patient were completed in the beating heart and cardiopulmonary bypass groups, respectively. A majority of patients (70%) had either a triple or quadruple bypass. Coronary anastomoses were achieved with myocardial mechanical stabilization and heart "verticalization." Ischemic time was shorter in the beating heart group (29.8 +/- 0.9 vs 45 +/- 0.4 minutes, P <.05). Similarly, the need for transfusion was significantly less in the beating heart group (beating heart operations, 34%; cardiopulmonary bypass, 66%; P <.005). Reduced use of postoperative intra-aortic counterpulsation, as well as a lower rise in creatine kinase MB isoenzyme, was observed in the beating heart group. Operative mortality rates (beating heart operations, 1. 3%; cardiopulmonary bypass, 2%) and perioperative myocardial infarction (beating heart operations, 3.6%; cardiopulmonary bypass, 4.2%) were comparable for the two groups. CONCLUSION: In a majority of patients, off-pump complete coronary artery revascularization is an acceptable alternative to conventional operations, yielding good results given progressive experience, rigorous technique, and adequate coronary artery stabilization.

Cardiopulmonary Bypass↗
PubMed1999

Antegrade/retrograde cardioplegia for valve replacement: a prospective study.

BACKGROUND: From 1994 to 1996, 75 patients undergoing valve replacement were randomized to antegrade (36 patients, group 1) or antegrade/retrograde (39 patients, group 2) administration of cold blood cardioplegia. METHODS: Groups were comparable for age, sex, valve disease, and ventricular dysfunction. The aortic valve was replaced in 27 patients from group 1 and 24 patients from group 2, the mitral valve in 8 and 15 patients, and 1 patient in group 1 underwent double valve replacement (p = not significant). RESULTS: Lengths of cardiopulmonary bypass and aortic cross-clamp averaged, respectively, 10 minutes (p = not significant) and 12 minutes (p = < 0.05) shorter in group 2. Total amount of cardioplegia solution infused averaged 1,279 +/- 406 mL and 1,341 +/- 379 mL (p = not significant), respectively, in groups 1 and 2, and the period of infusion averaged 44% and 72% (p = < 0.01) of the total period of aortic cross-clamping. No death occurred in group 1 compared to two in group 2 (p = not significant). The perioperative myocardial infarction and stroke rates were comparable in both groups. Peak enzyme release at 24 hours was similar both for creatine kinase-MB fraction (26 versus 37 IU/L) and for troponin T (2.1 versus 2.5 IU/L). CONCLUSIONS: Our study shows no significant advantage of the antegrade/retrograde administration of cardioplegia over the antegrade route in routine valvular replacement, other than a slightly shorter aortic cross-clamping time.

Aged↗
PubMed1999

Beating heart coronary artery bypass grafting: technical aspects and results in 200 patients.

OBJECTIVE: To describe the initial experience of the first 200 patients who underwent coronary artery bypass grafting (CABG) on beating hearts at the Montreal Heart Institute, Montreal. DESIGN: A prospective cohort of 200 patients was analyzed to study immediate and short term (two-year follow-up) results. SETTING: Patients underwent CABG at the Montreal Heart Institute from February 1996 to June 1998. The first 30 patients underwent CABG without the use of a myocardial wall stabilizer (group 1), and a myocardial wall stabilizer was used in the following 170 patients (group 2). PATIENTS: Group 1 patients averaged 60+/-10 years of age compared with 66+/-10 years in group 2 (P=0.002). Twelve patients (40%) in group 1 had unstable angina compared with 107 patients (63%) in group 2 (P=0.03). INTERVENTIONS: Group 1 patients underwent 1.7+/-0.7 CABG per patient compared with 2.4+/-0.8 grafts per patient in group 2 (P=0.001). Sixty-seven patients (39%) in group 2 had an obtuse marginal coronary artery grafted, and 145 patients (73%) of both groups had a complete myocardial revascularization. RESULTS: Ten patients (5%) in both groups were converted to cardiopulmonary bypass during surgery. Seven patients (3.5%) died postoperatively: five from myocardial infarction, one from aortic dissection and rupture, and one from arrhythmia. Seventeen patients (8.5%) suffered a perioperative myocardial infarction. In groups 1 and 2, respectively, actuarial survival was 100% and 95+/-2%, and freedom rate from reoperation, percutaneous balloon dilation and recurrent myocardial infarction averaged 93+/-4% and 97+/-2% 18 months following CABG. CONCLUSION: CABG on beating hearts appears to be an alternative approach to the use of cardiopulmonary bypass in selected patients.

Aged↗
PubMed1999

Videoassisted thrombectomy of mechanical prosthetic heart valves.

BACKGROUND AND AIM OF THE STUDY: Thrombosis of a bileaflet mechanical heart valve is a life-threatening clinical event. Surgical thrombectomy of bileaflet mechanical prostheses remains an appropriate treatment in selected patients. METHODS: Between 1996 and 1998, five patients (three men, two women; average age 56 +/- 1 years; range: 56 to 66 years) with thrombosis of left-sided bileaflet mechanical valves were treated with videoassisted thrombectomy of the prosthesis. Four patients had thrombosis of a bileaflet mitral mechanical valve, and one patient had thrombosis of an aortic valve prosthesis. Preoperatively, patients were in either NYHA functional class IV (n = 4) or class I (n = 1). Surgery was performed through a right anterior thoracotomy or a median sternotomy. A rigid 30 degrees thoracoscope was inserted into the left atrium or aorta to visualize the thrombosed valve. The thrombus was extracted and the prosthesis under-surface examined and cleaned. Leaflet mobility, assessed with transesophageal echocardiography, was normal following surgical thrombectomy. RESULTS: Mean cardiopulmonary bypass time was 102 +/- 30 min; mean aortic cross-clamping time was 47 +/- 25 min. There was no hospital mortality; mean hospital stay was 9 +/- 1 days (range: 6 to 11 days). Anticoagulation with intravenous heparin was resumed 24 h after surgery. Three patients were discharged on coumarin treatment alone; two patients received aspirin plus coumarin. Mean postoperative follow up was 7 +/- 8 months (range: 1 to 21 months). One patient died 21 months after thrombectomy of a mitral prosthesis, with an unconfirmed diagnosis of recurrent mitral valve dysfunction. At 1-15 months after surgery, four patients are in NYHA class I, without evidence of prosthesis dysfunction. CONCLUSION: Videoassisted thrombectomy of a bileaflet mechanical heart valve is a treatment option in patients with acute thrombosis of the prosthesis.

Anticoagulants↗
PubMed1998

Coronary endarterectomy revisited: mid-term angiographic results.

OBJECTIVES: To evaluate the value of concomitant coronary endarterectomy (CE) in the modern era of coronary revascularization. METHODS: Retrospective study. Twenty-eight patients (five women; 23 men) who underwent coronary endarterectomy were angiographically studied 24 +/- 22 months after the procedure. Necessity CE (vessel completely occluded or with lumen less than 1 mm) was performed on the left anterior descending (LAD) artery in 12 patients, the right coronary artery (RCA) in nine, the obtuse marginal artery (OM) in five and a diagonal branch in two patients. Conduits used for revascularization were the internal thoracic artery (ITA) in 11 (all anastomosed to the LAD; combined with saphenous vein patch in four) and a saphenous vein graft in 17 patients. Mean atherosclerotic core length was 3.3 +/- 1.8 cm. An average of 3.1 +/- 0.7 distal anastomoses per patient were constructed, with mean aortic cross-clamp and cardiopulmonary bypass times of 61.2 +/- 20.2 mins and 94.0 +/- 23.5 mins, respectively. RESULTS: Overall, angiographic patency rate was 71% (20 of 28) for the endarterectomized vessels (12 of 12 LAD, six of nine RCA, two of five OM and none of two diagonal arteries) and 93% (57 of 61) for the nonendarterectomized vessels. Among the eight patients with occluded CE vessels, two sustained a perioperative myocardial infarction, five developed angina during follow-up, and one patient remained asymptomatic. CONCLUSION: Necessity CE demonstrates acceptable mid-term patency. In addition, this study showed excellent patency following CE of the LAD revascularized with the ITA, with or without only a saphenous vein patch.

Aged↗
PubMed1998

[Cardiac surgery in renal transplant patients. Apropos of 24 cases].

UNLABELLED: Results of cardiac surgery in renal transplant patients are not well documented. Immunosuppression as well as associated conditions in these patients, and the increased susceptibility of the renal allograft to the extracorporeal circulation (ECC) may alter the prognosis of renal transplant patients submitted to cardiac surgery. To evaluate this hypothesis, we reviewed the files of 24 patients (18 Male, 6 Female; age: 49 +/- 12 years) operated under ECC between 1978 and 1997. Twenty patients underwent coronary artery bypass surgery, 5 patients a valve replacement procedure (aortic and/or mitral), and one patient necessitated a Cabrol procedure for an ascending aorta aneurysm. Preoperatively, the majority of patients were in functional class (NYHA) IV (16 patients), and ejection fraction was > 50% in 18 patients. Two operative deaths secondary to cardiogenic shock were encountered. Five patients (23%) were reoperated for bleeding; 5 patients (23%) sustained a major infection (2 pneumonias, 2 mediastinitis and one wound infection) resulting in death in one patient; 5 patients (23%) were treated for arythmia; and 2 patients (9%) suffered a perioperative myocardial infarction. Serum creatinine levels did not increase significantly during hospitalization (p = 0.41 between extreme values). Mean follow-up (41 +/- 28 months) of the 20 survivors revealed recurrent angina in 5 patients and late death in 4 patients, cardiac-related in 3 cases. CONCLUSION: Cardiac surgery in renal transplant patients is subjected to a high morbidity and mortality. Mid-term prognosis is reserved especially in presence of associated conditions.

Angina Pectoris↗
PubMed1997

Calcium-channel blockers preserve coronary endothelial reactivity after ischemia-reperfusion.

BACKGROUND: Calcium-channel blockers have been reported to improve myocardial recovery after ischemia-reperfusion, but their effects on coronary blood flow regulation remain to be defined. Experiments were designed to evaluate the effects of calcium antagonists on coronary artery vasoregulation exposed to ischemia-reperfusion. METHODS: Three groups of hearts (n = 6) were pretreated with a 10-minute infusion of either diltiazem, verapamil, or nifedipine at concentrations of 10(-9) mol/L to 10(-6) mol/L and exposed to 30 minutes of no-flow ischemia and 45 minutes of reperfusion. Another group (n = 6) received no pretreatment and was used as control. Endothelium-dependent and -independent relaxations were tested by assessing coronary flow increase to 5-hydroxytryptamine (10(-6) mol/L) and sodium nitroprusside (10(-5) mol/L) infusion, respectively. Left ventricular pressure, its first derivative, and coronary basal flow were recorded before and after ischemia as well as during calcium antagonist infusion. RESULTS: Endothelium-dependent relaxation after ischemia was significantly improved with all three drugs in a dose-dependent fashion; nifedipine was found to be the more potent. Endothelium-independent relaxation was also significantly preserved with calcium antagonists regardless of the type, whereas left ventricular hemodynamics were not. During perfusion, nifedipine was found to have the most negative inotropic effect and to be the most potent vasodilator on the coronary circulation. Diltiazem was the less effective drug on both left ventricular hemodynamics and coronary circulation. CONCLUSIONS: This study indicates that preischemic infusion of calcium antagonists enhance endothelium-dependent and -independent coronary artery relaxation in the isolated rat heart model in a dose- and drug-dependent fashion. This can be achieved at low doses without affecting left ventricular hemodynamics and should contribute to preserve coronary artery autoregulation.

Animals↗
PubMed1997

[Effects of chronic administration of captopril on vascular reactivity of the rat aorta].

UNLABELLED: The vascular endothelial function is altered in certain vascular pathology such as arterial hypertension. However, the endothelial effect of the pharmacologic treatment of this pathology with angiotensin converting enzyme (ACE) inhibitor is poorly understood. To evaluate the effects of long-term treatment of captopril on the rat aortic vascular reactivity, 2 groups of spontaneously hypertensive rats (SHR) (n = 6) were studied for 12 weeks: the first group was treated with captopril (CAP) (2 g/l of water) while group 2 (OCAP) received no treatment. A third group without hypertension was considered as control group (CTL). At the end of the experiments, isolated aortic rings were studied in organ chambers for endothelial and smooth muscle vascular reactivity. The endothelial-dependent relaxations (EDR) to cumulative doses of acetylcholine, histamine or adenosine diphosphate were significantly decreased in the aortic segments of CTL compared to CAP (p < 0.05). Aortic segments from OCAP group demonstrated intermediate EDR responses between CAP and CTL groups. Smooth muscle relaxation to sodium nitroprusside was comparable among the 3 groups. Maximal smooth muscle contraction to progressive doses of norepinephrine was significantly higher in the CTL group compared to the hypertensive groups. CONCLUSION: Spontaneously hypertensive rats have an increased basal vascular tone. The increased EDR observed with hypertension partially compensates this hypercontractility. Chronic hypertension treatment with captopril partially normalizes EDR responses in the rat aorta suggesting the lost of the endothelial compensatory mechanism by ACE inhibitors.

Angiotensin-Converting Enzyme Inhibitors↗