Pathogenic mechanisms of atherosclerosis: effect of lipid lowering on the biology of atherosclerosis

Numerous trials have demonstrated that cholesterol-lowering therapy leads to marked reductions in cardiovascular and overall mortality and in the need for coronary revascularization. Angiographic regression trials have shown that cholesterol lowering can reduce progression and, in some instances, achieve regression of coronary atherosclerotic lesions. However, recent studies have contradicted the traditional view that the clinical course of coronary artery disease is closely linked to the severity of coronary artery stenosis. It is now apparent that stenoses responsible for myocardial infarction or unstable angina are typically mild rather than severe. These observations suggest that regression may not be the principal mechanism by which cholesterol lowering affects cardiovascular risk. Two mechanisms---plaque stabilization and improved endothelial function-have been examined in this regard. Basic studies suggest that cholesterol lowering favorably alters those features of atherosclerosis that promote plaque stability. Recent clinical studies have clearly established that aggressive lipid-lowering therapy improves endothelial function and reduces myocardial ischemia in patients with hypercholesterolemia.

Pathogenic mechanisms of atherosclerosis: effect of lipid lowering on the biology of atherosclerosis

Numerous trials have demonstrated that cholesterol-lowering therapy leads to marked reductions in cardiovascular and overall mortality and in the need for coronary revascularization. Angiographic regression trials have shown that cholesterol lowering can reduce progression and, in some instances, achieve regression of coronary atherosclerotic lesions. However, recent studies have contradicted the traditional view that the clinical course of coronary artery disease is closely linked to the severity of coronary artery stenosis. It is now apparent that stenoses responsible for myocardial infarction or unstable angina are typically mild rather than severe. These observations suggest that regression may not be the principal mechanism by which cholesterol lowering affects cardiovascular risk. Two mechanisms---plaque stabilization and improved endothelial function-have been examined in this regard. Basic studies suggest that cholesterol lowering favorably alters those features of atherosclerosis that promote plaque stability. Recent clinical studies have clearly established that aggressive lipid-lowering therapy improves endothelial function and reduces myocardial ischemia in patients with hypercholesterolemia.

Activation of ATP-sensitive potassium channels contributes to reactive hyperemia in humans

Activation of ATP-sensitive potassium (KATP) channels present on vascular smooth muscle cells causes membrane hyperpolarization and vasodilation. The purpose of this study was to determine whether KATP channels contribute to reactive hyperemia in humans. Accordingly, we studied the effect of tolbutamide, a KATP channel inhibitor, on reactive hyperemic forearm blood flow. Forearm blood flow was measured by venous occlusion plethysmography. Forearm ischemia was produced by inflating a sphygmomanometric cuff on the arm to suprasystolic pressures for 5 min. After cuff release, forearm blood flow was measured during the reactive hyperemic phase for 5 min. Tolbutamide (1 mM blood concentration, n = 6) did not affect basal (2.4 +/- 0.2 to 2.2 +/- 0.1 ml.100 ml-1.min-1) or peak reactive hyperemic forearm blood flow (21.9 +/- 3.8 to 22.6 +/- 2.9 ml.100 ml-1.min-1, each P = NS), but it significantly attenuated total hyperemic volume (12.6 +/- 1.7 vs. 9.2 +/- 1.8 ml/100 ml, P < 0.02). Vehicle (n = 6) did not affect basal flow, peak reactive hyperemic flow, or total hyperemia. To determine whether adenosine or endothelium-derived nitric oxide contribute to reactive hyperemia via KATP channels, adenosine (1.5-500 micro grams/min, n = 6) and acetylcholine (30 micrograms/min, n = 6) were infused before and during tolbutamide coinfusion. Tolbutamide did not significantly alter the forearm blood flow response to either adenosine or acetylcholine. In conclusion, KATP channels contribute to vasodilation during reactive hyperemia in humans.

Nitroglycerin-induced coronary vasodilation is not enhanced in patients with impaired endothelium-dependent dilation

OBJECTIVES

This study was designed to determine whether enhanced sensitivity to exogenous nitrovasodilators is present in the coronary arteries of patients with impaired endothelium-dependent dilation.

BACKGROUND

Animal studies have demonstrated that the dilator response to exogenous nitrovasodilators is exaggerated in the setting of endothelial dysfunction (diminished nitric oxide activity). Whether such relative hyperresponsiveness to exogenous nitrates occurs and is important in humans is unknown.

METHODS

We assessed coronary vasomotion in 110 patients (mean [+/- SD] age 56 +/- 10 years) by serial intracoronary infusions of acetylcholine (10(-8) to 10(-6) mol/liter) to test endogenous nitric oxide and nitroglycerin (40 micrograms) to test responses to exogenous nitrovasodilators.

RESULTS

The vasomotor response to 10(-6) mol/liter of acetylcholine differed between patients with (n = 95) and those without (n = 15) normal endothelial dysfunction (-21 +/- 14% vs. 12 +/- 8%, respectively, p < 0.001). However, neither the dilator response to nitroglycerin (21 +/- 14% vs. 18 +/- 13%) nor the baseline diameter differed between those with endothelial dysfunction and normal function, respectively. There was no correlation between the magnitude of the dilator response to nitroglycerin and acetylcholine. The response to nitroglycerin was decreased with increasing age (r = -0.21, p = 0.03) but was not related to any other demographic factors or to the angiographic appearance of the vessel.

CONCLUSIONS

The coronary vasodilator response to nitroglycerin is not significantly enhanced in patients with impaired endothelium-dependent dilation but decreases with increasing age. This finding provides indirect evidence that basal coronary tone is not increased in patients with endothelial dysfunction and that supersensitivity to exogenous nitrates is not clinically important in humans.

Endothelium-dependent coronary vasomotion relates to the susceptibility of LDL to oxidation in humans

BACKGROUND

Oxidatively modified LDL has been shown to markedly impair endothelium-dependent dilation in experimental studies. The aim of the present study was to determine the relationship between the coronary vasomotor response to the endothelium-dependent agonist acetylcholine and the in vitro susceptibility of LDL to oxidation in patients.

METHODS AND RESULTS

Endothelium-dependent coronary vasomotion in response to acetylcholine (10(-8) to 10(-6) mol/L) was assessed in 23 patients with hypercholesterolemia (mean age, 56 +/- 9 years) after 1 year of therapy with either an American Heart Association Step 1 diet (seven patients), lovastatin and cholestyramine (seven patients), or lovastatin and probucol (nine patients). The susceptibility of LDL to oxidation was determined by measuring the lag phase of conjugated diene formation induced by Cu2+. Patients treated with lovastatin and probucol had prolongation of the lag phase (263 +/- 64 minutes) compared with diet- (91 +/- 22 minutes) or lovastatin and cholestyramine-(118 +/- 57 minutes) treated patients (P<.0001). By univariate analysis, the coronary vasomotor response to acetylcholine was significantly related to the lag phase of conjugated diene formation (P=.002), cholesterol-lowering therapy (P=.002), and serum cholesterol (P=.02). By multivariate analysis, the lag phase remained a significant predictor of the acetylcholine vasomotor response, independent of the effect of cholesterol-lowering treatment.

CONCLUSIONS

In patients treated with lipid-lowering agents, the vasodilator response to acetylcholine is related to the susceptibility of LDL to oxidation. These findings suggest that oxidative stress is an important determinant of the coronary endothelial dysfunction observed in patients with atherosclerosis and hypercholesterolemia.

Postischemic vasodilation in human forearm is dependent on endothelium-derived nitric oxide

Although endothelium-derived nitric oxide contributes to basal vascular tone, little is known about its role in regulating blood flow during changes in metabolic supply and demand. We examined the contribution of endothelium-derived nitric oxide to reactive hyperemia in the forearm of 20 normal subjects (12 women, 8 men) aged 27 +/- 4 yr (means +/- SD), using the nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA). Forearm ischemia was induced by suprasystolic blood pressure cuff inflation for 5 min, and the subsequent hyperemic flow was recorded for 5 min using venous occlusion strain-gauge plethysmography. The efficacy of nitric oxide blockade was tested by comparing the dose-response relationship to the endothelium-dependent agonist, acetylcholine (3, 10, and 30 mg/min), before and after intra-arterial infusion of up to 2,000 mg/min of L-NMMA. L-NMMA produced a significant downward and rightward shift in the dose-response relationship to acetylcholine and a 39% reduction in response to the maximum dose (P < 0.001). In the presence of L-NMMA, peak hyperemic flow was reduced 16% (26.5 +/- 2.1 to 22.3 +/- 1.5 ml.min-1.100 ml of forearm-1, P < 0.03), and the minimum forearm vascular resistance was increased 22.8% (3.5 +/- 0.3 to 4.3 +/- 0.4 mmHg.ml-1.min.100 ml, P < 0.02). Total hyperemia, calculated from the area under the flow vs. time curve, at 1 and 5 min after cuff release was 17 and 23% less, respectively (13.6 +/- 1.2 vs. 11.3 +/- 1.1 and 31.8 +/- 2.7 vs. 24.6 +/- 1.8 ml/100 ml, P < 0.002), following L-NMMA. These data suggest that endothelium-derived nitric oxide plays a role in both reactive hyperemia and in the maintenance of the hyperemic response following ischemia in the forearm.

Early endothelial dysfunction predicts the development of transplant coronary artery disease at 1 year posttransplant

BACKGROUND

Accelerated coronary arteriosclerosis is the major obstacle to long-term survival after cardiac transplantation. Endothelial dysfunction is common early posttransplant. The relationship between early endothelial dysfunction and the development of allograft arteriosclerosis has not been analyzed serially with intravascular ultrasound in the same patients. We hypothesized that an early constrictor response to acetylcholine, indicative of endothelial dysfunction, may predict the development of transplant coronary arteriosclerosis.

METHODS AND RESULTS

Endothelium-dependent vasomotion was assessed early posttransplant in 20 patients by serial intracoronary acetylcholine infusion, and the percent change in diameter was measured by quantitative angiography. The development of arteriosclerosis was studied by use of intravascular ultrasound in the same 20 patients by quantifying the changes in intimal index (delta Ii) and maximal intimal thickness [delta Mt] of 46 matched coronary segments between initial and 1-year follow-up studies. Coronary segments with endothelial dysfunction (constriction > or = 5%; n = 23) demonstrated a significantly greater increase in mean Ii and Mt by 1 year posttransplant compared with segments with normal endothelial function (n = 23) (delta Ii = 7 +/- 2% versus 2 +/- 1% [P < .05] and delta Mt = 140 +/- 40 versus 50 +/- 20 microns [P < .05]). No other parameters examined predicted the development of allograft arteriosclerosis in the initial year posttransplant.

CONCLUSIONS

Paired studies that used intravascular ultrasound showed that early endothelial dysfunction predicts the development of allograft arteriosclerosis during the initial year posttransplant. This early pathophysiological feature is likely an important marker that could be useful in therapeutic trials.

Atherosclerosis: risk factors and the vascular endothelium

The endothelium can respond to a local environment by releasing a variety of substances that regulate the level of vascular tone. One of the most important of these vasoregulatory substances is EDRF. The function of the endothelium is altered in a variety of pathologic and physiologic conditions. This review focused on the role of risk factors for atherosclerosis as it relates to EDRF. Atherosclerotic blood vessels respond abnormally on exposure to stimuli that release EDRF. It is now also apparent that this abnormal vascular response may precede the development of significant atherosclerosis and that normalization of the EDRF response with treatment is possible. Thus abnormal endothelium-dependent relaxation has been demonstrated in hypercholesterolemic patients with little or no evidence of coronary angiographic disease and in patients with hypertension before the development of atherosclerosis. The interaction between risk factors and the function of the vascular endothelium with development of atherosclerosis may become a useful focus for therapies that benefit patient outcomes.

Role of nitric oxide in the local regulation of pulmonary vascular resistance in humans

BACKGROUND

Endothelium-derived nitric oxide (NO) may be an important mediator of vascular resistance in the pulmonary circulation. We tested the hypotheses that in conscious adults the endothelium, through NO production, is important in maintaining basal pulmonary vascular resistance and that it can increase NO production further in response to receptor-mediated stimulation, leading to further vasodilation.

METHODS AND RESULTS

Pulmonary arterial resistance vessel function was studied within the distribution of a segmental lower lobe pulmonary artery in eight conscious adults 37 to 76 years old who were undergoing cardiac catheterization. Segmental blood flow was determined with use of a Doppler-tip guide wire and quantitative angiography. Drugs were administered locally within the segmental artery through an infusion catheter. NG-Monomethyl-L-arginine (L-NMMA) was used as a specific inhibitor of NO production, whereas acetylcholine (ACh) was used to test receptor-mediated vasodilation. To demonstrate that vasodilation to ACh was NO dependent, ACh response was tested alone, in the presence of L-NMMA, and in the presence of a control constrictor phenylephrine. Basal pulmonary vascular resistance was NO dependent because L-NMMA infusion resulted in a dose-dependent decrease in local flow velocity (P < .005), with flow decreasing 33% at the highest dose of L-NMMA. ACh infusion resulted in a dose-dependent increase in flow velocity (P = .001). The ACh response was at least in part NO dependent because it was diminished by the presence of L-NMMA (P < .05). The effect of L-NMMA on the ACh response was not due to nonspecific preconstriction because L-NMMA diminished the ACh response significantly more than did the endothelium-independent constrictor phenylephrine (P < .05) despite comparable preconstriction.

CONCLUSIONS

In healthy conscious adults, (1) normal basal pulmonary resistance is maintained in part by continuous local production of NO and (2) the local NO production is responsive to receptor-mediated stimulation, leading to further vasodilation, and can be tested with ACh.

Vitamin C improves endothelium-dependent vasodilation in patients with non-insulin-dependent diabetes mellitus

Endothelium-dependent vasodilation is impaired in humans with diabetes mellitus. Inactivation of endothelium-derived nitric oxide by oxygen-derived free radicals contributes to abnormal vascular reactivity in experimental models of diabetes. To determine whether this observation is relevant to humans, we tested the hypothesis that the antioxidant, vitamin C, could improve endothelium-dependent vasodilation in forearm resistance vessels of patients with non-insulin-dependent diabetes mellitus. We studied 10 diabetic subjects and 10 age-matched, nondiabetic control subjects. Forearm blood flow was determined by venous occlusion plethysmography. Endothelium-dependent vasodilation was assessed by intraarterial infusion of methacholine (0.3-10 micrograms/min). Endothelium-independent vasodilation was measured by intraarterial infusion of nitroprusside (0.3-10 micrograms/min) and verapamil (10-300 micrograms/min). Forearm blood flow dose-response curves were determined for each drug before and during concomitant intraarterial administration of vitamin C (24 mg/min). In diabetic subjects, endothelium-dependent vasodilation to methacholine was augmented by simultaneous infusion of vitamin C (P = 0.002); in contrast, endothelium-independent vasodilation to nitroprusside and to verapamil were not affected by concomitant infusion of vitamin C (P = 0.9 and P = 0.4, respectively). In nondiabetic subjects, vitamin C administration did not alter endothelium-dependent vasodilation (P = 0.8). We conclude that endothelial dysfunction in forearm resistance vessels of patients with non-insulin-dependent diabetes mellitus can be improved by administration of the antioxidant, vitamin C. These findings support the hypothesis that nitric oxide inactivation by oxygen-derived free radicals contributes to abnormal vascular reactivity in diabetes.

Identification of anomalous coronary arteries and their anatomic course by magnetic resonance coronary angiography

BACKGROUND

Anomalous coronary arteries are a rare but recognized cause of myocardial ischemia and sudden death. Identification currently requires x-ray angiography, which may have difficulty defining the three-dimensional course of the anomalous vessel. Magnetic resonance coronary angiography (MRCA) has been shown to image coronary artery anatomy noninvasively. We hypothesize that MRCA may be useful in the identification of anomalous coronary arteries and their anatomic course.

METHODS AND RESULTS

Sixteen patients (9 men, 7 women, age 44 to 81 years) with anomalous aortic origins of the coronary arteries by conventional x-ray angiography underwent MRCA. Multiple images of the major epicardial coronary arteries were obtained by use of a breathhold, fat-suppressed, segmented-k space, gradient-echo technique by investigators blinded to all patient data. Anomalous coronary artery pathology, by x-ray angiography, included right-sided left main coronary artery (n = 3), right-sided left circumflex artery (n = 6), separate left-sided left anterior descending and left circumflex arteries (n = 2), left-sided right coronary artery (n = 4), and an anteriorly displaced right coronary artery (n = 1). MRCA correctly identified the anomalous coronary vessel(s) in 14 of 15 patients. In 1 patient, the anomalous vessel was incorrectly identified, and in 2 patients the course of the anomalous vessel was not clearly seen; one of these was a nondominant, anomalous right coronary artery.

CONCLUSIONS

MRCA is a useful technique for the noninvasive identification of anomalous coronary arteries and their anatomic course.

Close relation of endothelial function in the human coronary and peripheral circulations

OBJECTIVES

The relation between endothelium-dependent vasodilator function in the brachial and coronary arteries was determined in the same subjects.

BACKGROUND

Coronary artery endothelial dysfunction precedes the development of overt atherosclerosis and is important in its pathogenesis. A noninvasive assessment of endothelial function in a peripheral conduit vessel, the brachial artery, was recently described, but the relation between brachial artery function and coronary artery vasodilator function has not been explored.

METHODS

In 50 patients referred to the catheterization laboratory for the evaluation of coronary artery disease (mean age +/- SD 56 +/- 10 years), the coronary vasomotor response to serial intracoronary infusions of the endothelium-dependent agonist acetylcholine (10(-8) to 10(-6) mol/liter), was studied. Endothelium-dependent vasodilation was also assessed in the brachial artery by measuring the change in brachial artery diameter in response to reactive hyperemia.

RESULTS

Patients with coronary artery endothelial dysfunction manifested as vasoconstriction in response to acetylcholine had significantly impaired flow-mediated vasodilation in the brachial artery compared with that of patients with normal coronary endothelial function (4.8 +/- 5.5% vs. 10.8 +/- 7.6%, p < 0.01). Patients with coronary artery disease also had an attenuated brachial artery vasodilator response compared with that of patients with angiographically smooth coronary arteries (4.5 +/- 4.6% vs. 9.7 +/- 8.1%, p < 0.02). By multivariate analysis, the strongest predictors of reduced brachial dilator responses to flow were baseline brachial artery diameter (p < 0.001), coronary endothelial dysfunction (p = 0.003), the presence of coronary artery disease (p = 0.007) and cigarette smoking (p = 0.016). The brachial artery vasodilator response to sublingual nitroglycerin was independent of coronary endothelial responses or the presence of coronary artery disease. The positive predictive value of abnormal brachial dilation ( < 3%) in predicting coronary endothelial dysfunction is 95%.

CONCLUSIONS

This study demonstrated a close relation between coronary artery endothelium-dependent vasomotor responses to acetylcholine and flow-mediated vasodilation in the brachial artery. This noninvasive method may become a useful surrogate in assessing the predisposition to atherosclerosis in patients with cardiac risk factors.

The overexpression of proliferating cell nuclear antigen in biliary cirrhosis in the rat and its relationship with epidermal growth factor receptor

Chronic bile duct obstruction in the rat leads to biliary cirrhosis but maintained hepatocellular mass. We have previously demonstrated translocation of epidermal growth factor receptor to nuclei. It remained unclear, however, whether this was due to hepatocyte proliferation and/or altered handling of epidermal growth factor receptor. Therefore, in the present investigation we stereologically estimated expression of proliferating cell nuclear antigen, a marker of the S phase of teh cell cycle at 1, 2, 3, 7, 14, 21 and 28 days after bile duct ligation. Proliferating cell nuclear antigen positive hepatocytes averaged 2.1 +/- 3.6% in sham-operated control animals. This increased to 20.7 +/- 6.4, 26.8 +/- 18.7, 31.3 +/- 23.9, 42.3 +/- 16.6 and 24.7 +/- 28.0% 3, 7, 14, 21 and 28 days after bile duct ligation, respectively (p<0.005 by ANOVA). This was correlated with the number of epidermal growth factor receptor positive nuclei (rs = 0.737) and inversely with the maximal binding capacity of epidermal growth factor to a crude plasma membrane fraction (rs = 0.697) reported previously. We conclude that bile duct ligation in the rat induces a significant hepatocellular proliferation as assessed by proliferating cell nuclear antigen expression and that this process could, at least in part, be related to increased nuclear expression of the epidermal growth factor receptor.

The effect of cholesterol-lowering and antioxidant therapy on endothelium-dependent coronary vasomotion

BACKGROUND

Patients with coronary artery disease and abnormalities of serum lipids often have endothelial vasodilator dysfunction, which may contribute to ischemic cardiac events. Whether cholesterol-lowering or antioxidant therapy can restore endothelium-dependent coronary vasodilation is unknown.

METHODS

We randomly assigned 49 patients (mean serum cholesterol level, 209 +/- 33 mg per deciliter [5.40 +/- 0.85 mmol per liter]) to receive one of three treatments: an American Heart Association Step 1 diet (the diet group, 11 patients); lovastatin and cholestyramine (the low-density lipoprotein [LDL]-lowering group, 21 patients); or lovastatin and probucol (the LDL-lowering-antioxidant group, 17 patients). Endothelium-dependent coronary-artery vasomotion in response to an intracoronary infusion of acetylcholine (10(-8) to 10(-6) M) was assessed at base line and after one year of therapy. Vasoconstrictor responses to these doses of acetylcholine are considered to be abnormal.

RESULTS

Treatment resulted in significant reductions in LDL cholesterol levels of 41 +/- 22 percent in the LDL-lowering-antioxidant group and 38 +/- 20 percent in the LDL-lowering group (P < 0.001 vs. the diet group). The maximal changes in coronary-artery diameter with acetylcholine at base line and at follow-up were -19 and -2 percent, respectively, in the LDL-lowering-antioxidant group, -15 and -6 percent in the LDL-lowering group, and -14 and -19 percent in the diet group (P < 0.01 for the LDL-lowering-antioxidant group vs. the diet group; P = 0.08 for the LDL-lowering group vs. the diet group). (The negative numbers indicate vasoconstriction). Thus, the greatest improvement in the vasoconstrictor response was seen in the LDL-lowering-antioxidant group.

CONCLUSIONS

The improvement in endothelium-dependent vasomotion with cholesterol-lowering and antioxidant therapy may have important implications for the activity of myocardial ischemia and may explain in part the reduced incidence of adverse coronary events that is known to result from cholesterol-lowering therapy.

Systemic nature of endothelial dysfunction in atherosclerosis

Vascular endothelium plays a pivotal role in the maintenance of vasodilation and the inhibition of platelet aggregation and smooth muscle cell proliferation through the release of nitric oxide and other factors. Extensive data have demonstrated abnormalities in coronary endothelial function in the epicardial coronary arteries in patients with atherosclerosis or risk factors for atherosclerosis. This dysfunction leads to abnormal vasoconstriction and platelet aggregation, which likely play a role in producing ischemia in patients with coronary artery disease. Invasive techniques have been available to assess endothelium-dependent vasodilator responses in the coronary arteries. However, until recently little has been known about endothelial responses in the peripheral vasculature, as methods to assess this have not been readily available. The hypothesis that endothelial dysfunction is a systemic process is explored, and new noninvasive methods of assessing endothelial function are discussed.

Predictive value of inducible endothelial cell adhesion molecule expression for acute rejection of human cardiac allografts

We conducted a prospective longitudinal study to determine the clinical significance of endothelial adhesion molecule expression in endomyocardial biopsies from human cardiac allografts. Ten to 18 (mean 13) consecutive allograft biopsies were obtained from 20 serial human transplant recipients over a one-year period. A total of 267 biopsies was examined. The expression of endothelial adhesion molecules intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin, as well as the presence of CD3+ T cell infiltrates was assessed by immunocytochemical staining of frozen sections. Separate specimens taken at the same time were analyzed histologically for ischemic injury or rejection. ICAM-1--and, to a lesser extent VCAM-1--was expressed at low levels in normal biopsies. E-selectin was only expressed in 15% of histologically normal biopsy specimens. Ischemic injury noted in the immediate posttransplant period was associated with increased expression of all three adhesion molecules. VCAM-1 expression increased both with the degree of CD3+ T cell infiltrates (P < 0.001) and with the degree of rejection (P < 0.05). ICAM-1 increased over constitutive levels in association with diffuse CD3+ infiltrates (P < 0.001) and with rejection (P < 0.05). E-selectin was increased on occasional vessels in association with CD3+ infiltrates (P < 0.001), but was not associated with active rejection. Increases in E-selectin were most likely to occur in biopsies just prior to rejection episodes (odds ratio 3.3), and were least likely to occur in biopsies following rejection (odds ratio 0.3). ICAM-1, but not VCAM-1, was also elevated in prerejection specimens. VCAM-1 and ICAM-1 declined in postrejection specimens. These data suggest a dynamic pattern in the expression of endothelial cell adhesion molecules during the course of cardiac allograft rejection. This study also suggests that endothelial E-selectin expression may be a useful clinical marker of impending rejection. Finally, inducible VCAM-1 expression may be a helpful adjunct in the diagnosis of ongoing acute rejection, and decreases in its expression may be indicative of successful antirejection therapy.

Estrogen improves endothelium-dependent, flow-mediated vasodilation in postmenopausal women

OBJECTIVE

To assess the effect of estrogen replacement therapy on endothelium-dependent vasodilation in postmenopausal women.

DESIGN

Double-blind, placebo-controlled, crossover trial.

SETTING

University medical center.

PATIENTS

13 postmenopausal women aged 44 to 69 years (average age, 55 +/- 7 years).

INTERVENTION

Patients were randomly assigned to receive placebo, oral estradiol at a dose of 1 mg/d, and oral estradiol at a dose of 2 mg/d. Each treatment phase lasted 9 weeks.

MEASUREMENTS

High-resolution ultrasonography was used to measure vascular reactivity in a peripheral conduit vessel, the brachial artery. Endothelium-dependent vasodilation was determined by measuring the change in brachial artery diameter during increases in flow induced by reactive hyperemia. Endothelium-independent vasodilation was measured after sublingual nitroglycerin was administered.

RESULTS

Flow-mediated, endothelium-dependent vasodilation of the brachial artery was greater when patients received estradiol (13.5% and 11.6% for 1-mg and 2-mg doses, respectively) than when patients received placebo (6.8%; P < 0.05 for each dose compared with placebo). In contrast, estrogen administration had no effect on endothelium-independent vasodilation as assessed by sublingual nitroglycerin.

CONCLUSION

Short-term estrogen replacement therapy improves flow-mediated endothelium-dependent vasodilation in postmenopausal women. This improvement may be mediated by a direct effect of estrogen on vascular function or may be induced through modification of lipoprotein metabolism.

Nitric oxide and nitrovasodilators: similarities, differences and potential interactions

Many similarities exist between the exogenous nitrates and endothelium-derived relaxing factor, which is nitric oxide or a thiol derivative. Both act by way of guanylate cyclase, which increases intracellular concentrations of cyclic guanosine monophosphate, resulting in smooth muscle cell relaxation and antiplatelet effects. Thiols may be important in the biotransformation of exogenous nitrates and other intracellular processes involving nitric oxide. As such, important interactions might be expected between nitrates and endothelium-dependent processes that involve nitric oxide. This review explores the mechanisms of action, biologic effects and potential interactions between nitrates and endothelium-derived relaxing factor.

Relation of restenosis after excimer laser angioplasty to fasting insulin levels

Several studies have shown that diabetes mellitus increases the risk of restenosis after coronary intervention, but the role of insulin in restenosis has not been defined. The relation between fasting insulin levels and restenosis was evaluated prospectively at 6-month angiographic follow-up in 70 patients undergoing excimer laser coronary angioplasty of 75 lesions. Restenosis (> 50% diameter narrowing on quantitative angiography) was observed at 37 of 75 treated sites (49%). Although patients with glucose intolerance and noninsulin-dependent diabetes mellitus showed a trend toward increased restenosis (restenosis rate 69%; odds ratio for restenosis 2.7 [95% confidence interval 0.76, 9.82]; p = 0.124), those with increased fasting insulin levels > 15 muU/ml had reduced restenosis (restenosis rate 24%; odds ratio 0.22 [0.07, 0.67]; p = 0.008). Other factors including fasting serum glucose, glycated hemoglobin and lipoprotein fraction were not predictive of restenosis. The relation between insulin levels and restenosis after excimer laser angioplasty may provide insights into the biology of vascular injury and repair after coronary intervention.

Sustained activation of vascular cells and leukocytes in the rabbit aorta after balloon injury

BACKGROUND

To improve understanding of the cellular basis of the arterial response to injury, we tested whether balloon withdrawal can induce certain inflammatory functions of vascular cells and leukocytes and whether such "activation" persists even after the acute phase of injury.

METHODS AND RESULTS

We examined the expression of several inducible cell surface molecules in the rabbit aorta at 2, 5, 10, and 30 days after balloon injury. Longitudinal sections encompassing parts of the uninjured, border, and injured zones were examined for expression of vascular adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), class II major histocompatibility (MHC) antigens, and markers for smooth muscle cells (SMCs), macrophages, endothelial cells, and T-lymphocytes. Endothelial cell healing involved true endothelial regeneration as well as migration, as shown by nuclear incorporation of bromodeoxyuridine. Luminal endothelial cells at the leading edge of repopulation at each time point expressed VCAM-1. As healing progressed, VCAM-1 expression decreased in the regenerated endothelial cells. The neointimal endothelium also expressed high levels of ICAM-1 that persisted longer than the elevation of VCAM-1. SMCs in the neointima also showed increased levels of ICAM-1. Some neointimal endothelial cells, SMCs, and macrophages also expressed high levels of class II MHC antigens during 30 days after injury.

CONCLUSIONS

Local inflammatory activation of endothelial cells, SMCs, and leukocytes occurs in a predictable sequence and persists up to 30 days after balloon injury to the rabbit aorta. Our findings suggest that ongoing local signals persisting after the original balloon injury may contribute to later phases of intimal thickening.

Accuracy of electronic digital calipers compared with quantitative angiography in measuring coronary arterial diameter

BACKGROUND

Quantitative angiography is the accepted method for measuring coronary luminal diameter. Electronic digital calipers have been used to assess arterial diameters in vasomotor function studies and after interventional procedures. However, careful validation of calipers against quantitative angiography has not been described.

METHODS AND RESULTS

We used digital calipers and quantitative angiography to measure 517 arterial diameters (88 nonstenotic segments) in 24 transplant patients undergoing vasomotor function studies with acetylcholine and nitroglycerin, 20 stenoses in 14 patients with coronary artery disease, and 15 stenoses in 15 patients before and after excimer laser-facilitated coronary angioplasty and at 6 months' follow-up. In nonstenotic arterial segments ranging in size from 0.6 to 3.5 mm, calipers overestimated diameters measured by quantitative angiography by 0.29 +/- 0.21 mm (mean +/- SD) (limits of agreement, -0.13 to 0.71 mm). However, when the vasomotor responses were expressed as percent diameter change, the two methods did not differ significantly (-1 +/- 10%; limits of agreement, -21% to 19%). In the 35 stenoses measured before intervention and 30 stenoses measured after intervention, calipers and quantitative angiography differed by 3 +/- 9% (limits of agreement, -15% to 21%) across a range of stenosis severity (11% to 80%). Repeat caliper measurements by the same observer of the percent diameter change in the transplant patients and the percent stenosis in the coronary artery disease patients led to standard deviations of the differences of 9.3% and 7.6%, respectively. Two different observers recorded percent diameter change and percent stenosis that differed with standard deviations of 9.6% and 7.8%, respectively.

CONCLUSIONS

Quantitative angiography and electronic digital calipers produce similar relative changes in arterial diameters and percent stenosis in a broad range of severities. Digital calipers thus are a rapid and convenient alternative to computerized quantitative angiography in certain research studies and clinical practice of assessing stenosis severity.

Electrostatic and nonpolar peptide-membrane interactions. Lipid binding and functional properties of somatostatin analogues of charge z = +1 to z = +3

The interaction of four structurally related somatostatin analogues (effective electric charge +0.4 < or = < or = +3) with lipid membranes was studied with titration calorimetry and was compared with the functional activity of the peptides. Surface activity measurements provided average cross-sections of 70 or 135 A2, indicating that the cyclic molecules orient at the air-water interface with their ring system either parallel (z = +3) or perpendicular (z = +1) to the surface or switching between the two orientations according to the surface density (z = +2). The nonspecific binding of the peptides to sonified lipid vesicles was enthalpy-driven with a delta H of -4 to -7.5 kcal/mol. A consistent quantitative analysis of the binding isotherms was achieved by combining electrostatic attractions, calculated via the Gouy-Chapman theory, with a nonspecific surface partition equilibrium for the nonpolar interactions. The electrostatic attraction of the cationic peptides varied strongly according to the peptide charge. Due to the flat ring structure of the cyclic peptides, their true physical charge was sensed at the membrane surface, and no "charge screening" was observed. Peptide binding to the negative charged membrane was accompanied by a proton-uptake of the N-terminal amino group of 0.23-0.38 H+/peptide. Deviations from the theoretical prediction of 0.39 H+/peptide can be explained by a preferential binding of the nonprotonated species. The nonpolar interactions, as described by the surface partition coefficients of the four peptides, fell into a narrow range of K congruent to 50-230 M-1 whereas the apparent overall binding constants were between 200 and 5000 M-1.(ABSTRACT TRUNCATED AT 250 WORDS)