Tissue Plasminogen Activator Antigen and D-Dimer as Markers for Atherothrombotic Risk Among Healthy Postmenopausal Women
Background— Plasma markers of fibrinolytic function are associated with incident coronary events among several, but not all, prospective epidemiologic investigations of healthy individuals. Few studies have evaluated this relationship in women. In addition, although menopausal hormone therapy (HT) may alter markers of fibrinolytic function, the relevance of this effect for coronary risk assessment has not been studied.
Methods and Results— In a prospective, nested case-control study among 75 343 postmenopausal women without prior cardiovascular disease or cancer, we evaluated the relationships of elevated tissue plasminogen activator (tPA) antigen and D-dimer with subsequent first coronary heart disease events over a median period of 2.9 years. Baseline levels of both biomarkers were higher among 304 cases compared with 304 controls matched on age, smoking status, ethnicity, and length of follow-up; median values were 9.0 versus 7.4 ng/mL (P<0.001) for tPA antigen and 27.6 versus 23.4 ng/mL (P=0.001) for D-dimer. In matched-pairs analyses, the odds ratio in the highest versus lowest quartile of tPA antigen was 3.5 (95% CI, 2.1 to 5.8; P trend <0.001) and for D-dimer was 2.0 (95% CI, 1.2 to 3.2; P trend=0.005). After adjustment for lipid and nonlipid risk factors, including C-reactive protein, tPA antigen remained a significant predictor. Multivariable-adjusted associations for D-dimer, although attenuated, largely remained statistically significant. When stratified by HT, the relationship between tPA antigen and incident coronary heart disease was similar among nonusers, estrogen-only users, and current users of any HT.
Conclusions— Elevated tPA antigen and, to a lesser extent, D-dimer are independently associated with incident coronary events among postmenopausal women. In analyses stratified by HT, tPA antigen remained a consistent marker of increased coronary risk.
Received September 27, 2003; revision received March 25, 2004; accepted March 26, 2004.
Thrombosis and atherosclerosis are closely related phenomena. Changes in vessel wall architecture and composition during atheroma formation ultimately lead to plaque rupture,1 with most coronary occlusive events occurring in the setting of fulminant intraluminal thrombosis. It has been hypothesized that relative abnormalities in hemostatic systems are common on a population basis and that endogenous markers of fibrinolytic function may identify certain otherwise healthy individuals predisposed to clinically pathologic thrombosis.
Endogenous fibrinolysis is regulated predominantly by tissue plasminogen activator (tPA) through enzymatic conversion of plasminogen to plasmin. Plasma levels of active tPA are determined by the combined effects of synthesis from vascular endothelium,2 binding to plasminogen activator inhibitor-1 (PAI-1) and other inhibitors,3 and hepatic clearance.4 Elevated tPA antigen levels, which reflect both active free tPA and inert tPA bound in activator/inhibitor complexes, may therefore be indicative of coagulation activation and either enhanced or impaired fibrinolytic function. D-dimer is the primary degradation product of cross-linked fibrin and as such is a more direct measure of ongoing fibrin turnover, because levels are dependent not only on the presence of fibrin and plasmin but active fibrinolysis.
Among healthy individuals, increased tPA antigen and D-dimer have been shown to predict future cardiovascular events in several prospective epidemiologic investigations.5–11 However, these studies were predominantly comprised of middle-aged men. In addition, some studies did not find associations to be independent of other cardiovascular risk factors. Data pertaining to this issue are sparse among women, in particular postmenopausal women, among whom the absolute number of coronary events continues to rise despite more widespread adoption of primary preventive measures.12 In addition, although hormone therapy (HT) impacts on levels of both biomarkers, with most studies demonstrating a lowering of tPA antigen levels and no effect or modest increase in D-dimer, the clinical relevance of these effects is uncertain. We examined these issues in a large diverse cohort of postmenopausal women.
The objectives and design of the WHI Observational Study (WHI-OS) have been described elsewhere.13 Between 1994 and 1998, 93 724 women aged 50 to 79 years were recruited from 40 clinical centers throughout the United States. Of these participants, 75 343 having no prior history of cardiovascular disease or cancer represented the source population for cases and controls. At enrollment, women completed screening visits, during which demographic information, medical history, personal habits, and medication inventories were reviewed and anthropometric measurements, blood pressure, and fasting blood specimens were obtained. Most baseline blood specimens in the case-control study population were collected in the morning (96.5%) after a 12-hour fast (99.7%). All specimens were immediately processed for long-term storage at −70°C.
History of hypertension was defined as self-reported history of treated or untreated diagnosed high blood pressure. If report of diagnosed hypertension was missing (n=22), hypertension was coded for subjects with a measured baseline systolic blood pressure of 140 mm Hg or higher or diastolic blood pressure of 90 mm Hg or higher. History of diabetes was defined as self-report of diagnosed diabetes mellitus. Family history of premature coronary artery disease was defined by self-report of myocardial infarction (MI) in a first-degree male relative before age 55 years or first-degree female relative before age 65 years. Unknown family history was coded for those participants unsure of family history of MI or age at presentation (n=33).
Hormone therapy status was classified as never, past, or current use of unopposed estrogen (E) or estrogen plus progestin (EP) from pills or patches. Most current HT users were undergoing treatment with conventional doses of conjugated equine estrogens (CEE) with or without medroxyprogesterone acetate. Specifically, 82% of current E users were on oral CEE, of whom 74% were treated with a dose of 0.625 mg per day. Among current EP users, 70% were taking oral CEE, most of whom (75%) were treated with a daily dose of 0.625 mg. Eighty-seven percent of current EP users were undergoing treatment with medroxyprogesterone acetate.
Participants were monitored over an average follow-up of 2.9 years for incident health outcomes, including the coronary heart disease (CHD) events MI and death from CHD. Clinical events were classified after medical record review by centrally trained local physician adjudicators. Confirmation of self-reported nonfatal MI was based on documentation of new chest pain syndromes accompanied by characteristic electrocardiographic changes or clear evidence of myocyte damage, as demonstrated by elevated creatine kinase-MB or troponin values. CHD deaths were confirmed on the basis of death certificates, autopsy reports, circumstances of death, ECG, laboratory test results, and reports from all relevant procedures. In addition, we included cases of sudden cardiac death in which death occurred within 1 hour of symptom onset in the absence of other potentially lethal noncardiac disease processes.
Case subjects were matched in a 1:1 ratio to control subjects by the following factors: age (±2 years), smoking status (nonsmoker, former smoker, or current smoker), ethnicity (white not of Hispanic origin, African American, Hispanic, American Indian or Alaskan Native, Asian or Pacific Islander, or unknown), and follow-up time (±6 months). As of February 2000, 315 case-control pairs meeting these criteria were identified for analysis. Eleven case-control pairs were eliminated due to inadequate blood specimen. Of the 304 events analyzed, 219 were nonfatal MIs and 85 were deaths attributable to CHD.
The study was reviewed and approved by human subjects review committees at each participating institution. Signed informed consent was obtained from all women enrolled.
Baseline EDTA-plasma specimens were thawed and assayed for tPA antigen, D-dimer, lipids, and C-reactive protein (CRP). Total tPA antigen and D-dimer were measured by ELISA using the Imubind tPA antigen and Dimer test Gold EIA reagent kits purchased from American Diagnostica. Coefficients of variation for tPA and D-dimer derived from a 5% sample of simultaneously analyzed blinded quality control specimens were 7.6% and 20.4%. Median tPA antigen and D-dimer levels in these quality-control samples were 7.2 and 15.2 ng/mL, respectively. CRP and lipids were measured as previously described.14 Samples were analyzed in randomly ordered, blinded case-control pairs so as to minimize systematic bias and interassay variation.
We used the paired t test and matched χ2 statistic to evaluate differences in means and proportions respectively in the matched case-control populations. Because several variables were skewed, differences in medians were assessed using the signed-rank test. Conditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) after the population was divided into groups based on quartile cutpoints for the control distribution of each biomarker. Tests for linear trends were computed using an ordinal variable for biomarker quartiles. Adjusted models were based on case-control pairs for whom complete data were available on all covariates of interest.
To further assess independent effects, we conducted analyses among 8 subgroups of women characterized by absence of either hypertension, diabetes, family history of premature coronary artery disease, current smoking, or low body mass index, waist-to-hip ratio, ratio of total cholesterol to HDL cholesterol, and triglyceride levels. Each of the latter lower-risk categories of continuous variables was defined by a value below the upper tertile cutpoint among controls. In these exploratory analyses, P values for linear trend across quartiles of each biomarker were calculated without adjustment for multiple comparisons. To evaluate the joint role of tPA antigen and D-dimer, we estimated ORs among 4 groups defined by levels of each biomarker dichotomized at the median cutpoint for controls.
Median values of tPA antigen and D-dimer were determined according to nonuse or use of estrogen-only or estrogen-plus-progestin preparations. Stratified analyses were then performed, in which comparisons were made within HT subgroups. Owing to small numbers of women and limited statistical power, stratum-specific ORs were not estimated for EP users separately. Quartiles were redefined based on control distributions of tPA antigen and D-dimer among nonusers, all current users combined, and estrogen-only users of HT. To retain all available cases and controls, quartile-specific ORs and trend tests were derived from unconditional (ordinary) logistic regression models, which included the matching variables.
The mean age of participants was 69.0 years (Table 1). Case subjects had a higher prevalence of traditional cardiovascular risk factors than controls. Overall, 36.5% of women reported current use of HT, most being long-term users on treatment for more than 4 years. HT initiation within 6 months of enrollment was infrequent (4 case and 3 control subjects). Duration of treatment among current users appeared somewhat shorter in cases, but this difference was not statistically significant. In addition, there were no case-control differences in the proportion of women taking unopposed estrogen versus combined estrogen plus progestin formulations. Baseline use of aspirin, lipid-lowering medications, and warfarin was similar between groups.
Median tPA antigen and D-dimer levels were higher among cases than controls; 9.0 versus 7.4 ng/mL (P<0.001) for tPA antigen and 27.6 versus 23.4 ng/mL (P=0.001) for D-dimer (Table 1). Baseline tPA antigen and D-dimer were not significantly correlated (Spearman age-adjusted partial correlation: R=0.07, P=0.07). In matched-pairs analyses, higher levels of both biomarkers were associated with increased CHD risk (Tables 2 and 3⇓). Adjustment for ratio of total cholesterol to HDL cholesterol slightly attenuated these results. In models additionally adjusting for nonlipid cardiovascular risk factors, we found a strong association for tPA antigen with a weaker but persistent trend according to D-dimer. In these latter models, the per-quartile linear increase in CHD odds was 40% (95% CI, 14.5 to 71.9; P=0.001) for tPA antigen and 19% (95% CI, 0.1 to 41.4; P=0.048) for D-dimer.
Additional adjustment for alcohol consumption, physical activity, and baseline use of aspirin or lipid-lowering medications did not materially alter these results (P trend <0.001 for tPA antigen, 0.046 for D-dimer). There was no evidence of interaction according to baseline use or nonuse of aspirin (P interaction 0.34 for tPA antigen and 0.37 for D-dimer). Exclusion of women reporting warfarin use at enrollment (5 case and 2 control subjects) or with a history of deep vein thrombosis within 6 months of entry into the study (2 case subjects) did not change our results; the fully-adjusted ORs in the highest quartile of tPA antigen and D-dimer were 3.5 (95% CI, 1.8 to 6.9; P trend=0.001) and 1.8 (95% CI, 1.0 to 3.1; P trend=0.032), respectively. Among subgroups of women defined by the absence of each of several known cardiovascular risk factors (Table 4), tPA antigen remained strongly associated with CHD risk, whereas with the exception of nonhypertensive and nondiabetic women, elevated D-dimer was not. In analyses of potential joint effects (Figure 1), the OR for women with baseline elevations in both tPA antigen and D-dimer was greater than for those with low levels of both biomarkers or with elevations of either marker alone. There was no evidence for multiplicative interaction (P=0.83).
Because we found moderate correlations between baseline concentrations of CRP with tPA antigen (R=0.20, P<0.001) and D-dimer (R=0.30, P<0.001) and CRP is a known predictor of CHD incidence in this population,14 we examined to what extent elevations in fibrinolytic parameters and associated risk relationships may be accounted for by concurrent elevations in this marker of subclinical inflammation. In regression models adjusting for baseline CRP in quartiles as well as lipid and nonlipid risk factors, we found a nearly identical increase in CHD odds across quartiles of tPA antigen (ORs, 1.0, 2.1, 1.9, and 3.1; P trend=0.002) and D-dimer (ORs, 1.0, 1.3, 1.6, 1.6; P trend=0.09).
In crude analyses of biomarker levels according to HT status at baseline, current users of E or EP had generally lower levels of tPA antigen than nonusers within both case and control groups. Median tPA antigen among control subjects was 8.5, 6.3, and 5.9 ng/mL for nonusers and current users of E and EP, respectively. Corresponding values among case subjects were 9.8, 7.7, and 9.0 ng/mL. Similar trends in D-dimer level according to HT were not observed. Median D-dimer among control subjects was 22.5, 27.0, and 19.5 ng/mL for nonusers and current users of E and EP, respectively. Values among case subjects were generally higher than among controls (28.1, 24.9, and 34.2 ng/mL for nonusers and current users of E and EP, respectively). However, within case and control groups, no consistent difference in D-dimer levels in relation to HT was apparent.
Because our findings concur with prior studies showing lower tPA antigen and equivalent or slightly raised levels of D-dimer15–19 in association with HT use, we evaluated the possibility that risk gradients associated with elevated fibrinolytic markers might differ according to baseline HT status (Figure 2). In analyses stratified by HT (nonusers, all current users, and estrogen-only users), among all groups we observed a consistent rise in relative odds with increasing tPA antigen. Elevated D-dimer was associated with increasing relative odds among nonusers, and a nonsignificant trend was suggested by our results for all current users combined. This latter finding appeared to be driven mainly by users of EP (Figure 2B).
In this nationwide prospective study of 2 markers of fibrinolytic function among apparently healthy postmenopausal women, elevated plasma levels of tPA antigen and D-dimer predicted incident CHD events. In particular, tPA antigen was a powerful independent predictor after adjustment for both lipid and nonlipid cardiovascular risk factors, including CRP, in stratified analyses conducted among selective risk groups and according to baseline HT. Similar associations were observed for D-dimer, although lower in magnitude and of borderline statistical significance after multivariate adjustments. Elevations of both markers increased risk to a greater extent than elevations of either marker alone.
Prior prospective studies have found tPA antigen and D-dimer to be univariate risk predictors; however, the independence of these effects has been uncertain.5–11 Although these studies generally support an association between intrinsic fibrinolytic activity and subsequent coronary events, these data derive from cohorts exclusively or predominantly comprised of men. Although limited, in 2 studies that did examine gender differences in prothrombotic risk, the observed associations were stronger in women than in men. Specifically, among 16 women included in a population-based nested case-control study,7 elevated tPA antigen level as defined by a value above the median level (8.1 ng/mL) was associated with an OR for first MI of 8.4 (95% CI, 1.1 to 67.1). In the Atherosclerosis Risk in Communities (ARIC) study,10 women in the highest versus lowest D-dimer quintile had a 3-fold greater multivariate-adjusted odds of first CHD events (MI, CHD death, or coronary revascularization) compared with men. No study inclusive of middle-aged or older women adjusted for postmenopausal status or HT use, an important issue, because these factors in addition to female gender itself may influence the normal distribution of both biomarkers.
The main finding of the current analysis is that among postmenopausal women, as previously shown in men, activation of endogenous coagulation and fibrinolytic systems occurs in advance of acute coronary occlusion. With regard to our findings pertaining to tPA antigen, the extent to which elevations in this biomarker reflect an ongoing fibrinolytic response to chronic, clinically silent, low-grade intravascular thrombosis depends on complex interactions involving thrombin-mediated fibrin clot formation, vascular endothelial function, other noncellular components of the coagulation and fibrinolytic cascade, and hepatic uptake and clearance. Although elevated tPA levels may indicate a normal physiological response to ongoing prothrombotic activity, laboratory assessment of tPA antigen may give limited information about bioavailability. Because only a small fraction of circulating tPA antigen is active in the presence of PAI-1 and hepatic clearance of tPA bound in tPA/PAI-1 complexes may be delayed,20 measured levels of tPA antigen may reflect a prolonged plasma half-life attributable to elevated PAI-1, which was not measured in this study. It is therefore possible that rather than reflecting a normal fibrinolytic response to procoagulant stimuli, relative increases in tPA antigen may signal impaired fibrinolysis among susceptible individuals. In addition, PAI-1 is an acute-phase reactant, and to the extent that circulating total tPA concentrations rise in proportion to PAI-1, endogenous tPA levels may also reflect subclinical inflammation.
Because the accurate assessment of tPA and PAI-1 activity requires the use of nonstandard anticoagulants in the collection process, broad-based epidemiologic studies like ours are unable to comprehensively evaluate these issues. However, our results do address some concerns. Our observation that D-dimer is also a relevant, albeit weaker, CHD risk marker supports the hypothesis that upstream tPA activity, plasminogen conversion, and ongoing fibrinolysis are operative mechanisms among individuals at risk for developing subsequent coronary events. Our findings in subgroups of women with low levels of traditional atherogenic risk factors also suggest a possible novel role for tPA antigen as a marker of altered fibrinolytic function. Finally, the lack of attenuation of risk associations in CRP-adjusted analyses suggests that these results are independent of concurrent subclinical inflammation.
Several cross-sectional studies and short-term randomized trials have found that menopausal hormone therapy alters plasma-based markers of coagulation and fibrinolytic balance, with most studies demonstrating a lowering of tPA antigen levels and no effect or modest increase in D-dimer.15–19 However, longer-term associations may not resemble short-term effects both because of the potential physiological consequences of long-term HT use and selection bias in retention of women who do not develop early thrombotic complications. Because our results derive from observations among women who were undergoing long-term HT, our data cannot distinguish whether reductions in tPA antigen on HT initiation favorably impact subsequent cardiac risk. However, our results do suggest that any beneficial lowering of tPA antigen levels among long-term estrogen users does not abolish CHD risk gradients within groups (Figure 2A). In contrast, no significant association between D-dimer and incident CHD was evident among either current users of estrogen-only preparations or users of any formulation combined (Figure 2B), a result that may in part be explained by lack of consistent effects of E and EP regimens on this biomarker.
There are several limitations of the current investigation that require discussion. First, we relied on a single baseline blood sample and thus cannot account for variations in fibrinolytic biomarker levels that may arise over time. Although diurnal variation may occur, our specimens were generally obtained in the morning. Nonetheless, random misclassification, if present, would tend to bias our estimates for both markers toward the null. In addition, greater measurement error in the assessment of D-dimer levels may have resulted in further attenuation in risk associations based on this marker. Second, because of variability in average D-dimer levels related to choice of biologic assay used, the cutpoint value for elevated D-dimer in this report may differ from those in studies using other assay systems. Third, because fasting glucose levels were not available for all subjects on enrollment, the baseline prevalence of diabetes was assessed by self-report, and therefore cases of undiagnosed diabetes may have been missed. Fourth, we did not adjust for changes in HT status, which may have occurred during the observation period. However, because most current users were on long-term therapy, the influence of this factor is likely to be small. Lastly, our data are observational; therefore, as WHI-OS participants chose whether or not to undergo HT, users and nonusers of HT likely differ in characteristics that may affect levels of tPA antigen and D-dimer. Although a clear strength of the WHI-OS cohort is the uniformly high quality of covariate assessment, uncontrolled confounding cannot be excluded.
In conclusion, in this prospective study of fibrinolytic markers among postmenopausal women, tPA antigen emerged as a powerful independent predictor of coronary risk. These data suggest that among otherwise healthy postmenopausal women, altered fibrinolytic function may predispose to subsequent ischemic events. We also demonstrate persistence of this association among both nonusers and current users of HT. D-dimer was a less important predictor in this study, an observation that may in part be attributable to the heterogeneous effects of exogenous menopausal hormone therapy.
National Heart, Lung, and Blood Institute, Bethesda, Md: Barbara Alving, Jacques Rossouw, Linda Pottern, Shari Ludlam, Joan McGowan.
Clinical Coordinating Center
Fred Hutchinson Cancer Research Center, Seattle, Wash: Ross Prentice, Garnet Anderson, Andrea LaCroix, Ruth Patterson, Anne McTiernan, Barbara Cochrane, Julie Hunt, Lesley Tinker, Charles Kooperberg, Martin McIntosh, C.Y. Wang, Chu Chen, Deborah Bowen, Alan Kristal, Janet Stanford, Nicole Urban, Noel Weiss, Emily White; Wake Forest University School of Medicine, Winston-Salem, NC: Sally Shumaker, Pentti Rautaharju, Ronald Prineas, Michelle Naughton; Medical Research Labs, Highland Heights, Ky: Evan Stein, Peter Laskarzewski; University of California at San Francisco, San Francisco, Calif: Steven Cummings, Michael Nevitt, Maurice Dockrell; University of Minnesota, Minneapolis, Minn: Lisa Harnack; McKesson BioServices, Rockville, Md: Frank Cammarata, Steve Lindenfelser; University of Washington, Seattle, Wash: Bruce Psaty, Susan Heckbert.
Albert Einstein College of Medicine, Bronx, NY: Sylvia Wassertheil-Smoller, William Frishman, Judith Wylie-Rosett, David Barad, Ruth Freeman; Baylor College of Medicine, Houston, Tex: Jennifer Hays, Ronald Young, Jill Anderson, Sandy Lithgow, Paul Bray; Brigham and Women’s Hospital, Harvard Medical School, Boston, Mass: JoAnn Manson, Julie Buring, J. Michael Gaziano, Kathryn Rexrode, Claudia Chae; Brown University, Providence, RI: Annlouise R. Assaf, Richard Carleton (deceased), Carol Wheeler, Charles Eaton, Michelle Cyr; Emory University, Atlanta, Ga: Lawrence Phillips, Margaret Pedersen, Ora Strickland, Margaret Huber, Vivian Porter; Fred Hutchinson Cancer Research Center, Seattle, Wash: Shirley A.A. Beresford, Vicky M. Taylor, Nancy F. Woods, Maureen Henderson, Mark Kestin; George Washington University, Washington, DC: Judith Hsia, Nancy Gaba, Joao Ascensao, Somchia Laowattana; Harbor-UCLA Research and Education Institute, Torrance, Calif: Rowan Chlebowski, Robert Detrano, Anita Nelson, James Heiner, John Marshall; Kaiser Permanente Center for Health Research, Portland, Ore: Cheryl Ritenbaugh, Barbara Valanis, Patricia Elmer, Victor Stevens, Njeri Karanja; Kaiser Permanente Division of Research, Oakland, Calif: Bette Caan, Stephen Sidney, Geri Bailey Jane Hirata; Medical College of Wisconsin, Milwaukee, Wis: Jane Morley Kotchen, Vanessa Barnabei, Theodore A. Kotchen, Mary Ann C. Gilligan, Joan Neuner; MedStar Research Institute/Howard University, Washington, DC: Barbara V. Howard, Lucile Adams-Campbell, Maureen Passaro, Monique Rainford, Tanya Agurs-Collins; Northwestern University, Chicago/Evanston, Ill: Linda Van Horn, Philip Greenland, Janardan Khandekar, Kiang Liu, Carol Rosenberg; Rush-Presbyterian St Luke’s Medical Center, Chicago, Ill: Henry Black, Lynda Powell, Ellen Mason; Stanford Center for Research in Disease Prevention, Stanford University, Stanford, Calif: Marcia L. Stefanick, Mark A. Hlatky, Bertha Chen, Randall S. Stafford, Linda C. Giudice; State University of New York at Stony Brook, Stony Brook, NY: Dorothy Lane, Iris Granek, William Lawson, Gabriel San Roman, Catherine Messina; Ohio State University, Columbus, Ohio: Rebecca Jackson, Randall Harris, Electra Paskett, W. Jerry Mysiw, Michael Blumenfeld; University of Alabama at Birmingham, Birmingham, Ala: Cora E. Lewis, Albert Oberman, Mona N. Fouad, James M. Shikany, Delia Smith West; University of Arizona, Tucson/Phoenix, Ariz: Tamsen Bassford, John Mattox, Marcia Ko, Timothy Lohman; University at Buffalo, Buffalo, NY: Maurizio Trevisan, Jean Wactawski-Wende, Susan Graham, June Chang, Ellen Smit; University of California at Davis, Sacramento, Calif: John Robbins, S. Yasmeen, Karen Lindfors, Judith Stern; University of California at Irvine, Orange, Calif: Allan Hubbell, Gail Frank, Nathan Wong, Nancy Greep, Bradley Monk; University of California at Los Angeles, Los Angeles, Calif: Howard Judd, David Heber, Robert Elashoff; University of California at San Diego, La Jolla/Chula Vista, Calif: Robert D. Langer, Michael H. Criqui, Gregory T. Talavera, Cedric F. Garland, R. Elaine Hanson; University of Cincinnati, Cincinnati, Ohio: Margery Gass, Suzanne Wernke, Nelson Watts; University of Florida, Gainesville/Jacksonville, Fla: Marian Limacher, Michael Perri, Andrew Kaunitz, R. Stan Williams, Yvonne Brinson; University of Hawaii, Honolulu, Hawaii: David Curb, Helen Petrovitch, Beatriz Rodriguez, Kamal Masaki, Santosh Sharma; University of Iowa, Iowa City/Davenport, Iowa: Robert Wallace, James Torner, Susan Johnson, Linda Snetselaar, Bradley VanVoorhis; University of Massachusetts/Fallon Clinic, Worcester, Mass: Judith Ockene, Milagros Rosal, Ira Ockene, Robert Yood, Patricia Aronson; University of Medicine and Dentistry of New Jersey, Newark, NJ: Norman Lasser, Norman Hymowitz, Vera Lasser, Monika Safford John Kostis; University of Miami, Miami, Fla: Mary Jo O’Sullivan, Linda Parker, R. Estape, Diann Fernandez; University of Minnesota, Minneapolis, Minn: Karen L, Margolis, Richard H. Grimm, Donald B. Hunninghake, June LaValleur, Kathleen M. Hall; University of Nevada, Reno, Nev: Robert Brunner, Sachiko St. Jeor, William Graettinger, Vicki Oujevolk; University of North Carolina, Chapel Hill, NC: Gerardo Heiss, Pamela Haines, David Ontjes, Carla Sueta, Ellen Wells; University of Pittsburgh, Pittsburgh, Pa: Lewis Kuller, Arlene Caggiula, Jane Cauley, Sarah Berga, N. Carole Milas; University of Tennessee, Memphis, Tenn: Karen C. Johnson, Suzanne Satterfield, Raymond W. Ke, Jere Vile, Fran Tylavsky; University of Texas Health Science Center, San Antonio, Tex: Robert Brzyski, Robert Schenken, Jose Trabal, Mercedes Rodriguez-Sifuentes, Charles Mouton; University of Wisconsin, Madison, Wis: Catherine Allen (deceased), Douglas Laube, Patrick McBride, Julie Mares-Perlman, Barbara Loevinger; Wake Forest University School of Medicine, Winston-Salem, NC: Greg Burke, Robin Crouse, Lynne Parsons, Mara Vitolins; Wayne State University School of Medicine/Hutzel Hospital, Detroit, Mich: Susan Hendrix, Michael Simon, Gene McNeeley, Pamela Gordon, Paul Makela.
Supported by grants from the National Heart, Lung, and Blood Institute (HL 63293 and HL 07575) and pursuant to contract No. N01-WH-3-2109 with the National Heart, Lung, and Blood Institute, Department of Health and Human Services.
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