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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1997;17:217-221.)
© 1997 American Heart Association, Inc.

Articles

Medroxyprogesterone Acetate Antagonizes Inhibitory Effects of Conjugated Equine Estrogens on Coronary Artery Atherosclerosis

Michael R. Adams; Thomas C. Register; Deborah L. Golden; Janice D. Wagner; J. Koudy Williams

the Comparative Medicine Clinical Research Center, Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, NC.

Correspondence to Michael R. Adams, DVM, Dept of Comparative Medicine, Bowman Gray School of Medicine, Medical Center Blvd, Winston-Salem, NC 27157-1040. E-mail madams@cpm.bgsm.edu.

	Abstract

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Although estrogen replacement therapy is associated with reduced risk of coronary heart disease and reduced extent of coronary artery atherosclerosis, the effects of combined (estrogen plus progestin) hormone-replacement therapy are uncertain. Some observational data indicate that users of combined hormone replacement consisting of continuously administered oral conjugated equine estrogens (CEE) and oral sequentially administered (7 to 14 days per month) medroxyprogesterone acetate (MPA) experience a reduction in risk similar to that of users of CEE alone. However, the effects of combined, continuously administered CEE plus MPA (a prescribing pattern that has gained favor) on the risk of coronary heart disease or atherosclerosis are not known. We studied the effects of CEE (monkey equivalent of 0.625 mg/d) and MPA (monkey equivalent of 2.5 mg/d), administered separately or in combination, on the extent of coronary artery atherosclerosis (average plaque size) in surgically postmenopausal cynomolgus monkeys fed atherogenic diets and treated with these hormones for 30 months. Treatment with CEE alone resulted in atherosclerosis extent that was reduced 72% relative to untreated (estrogen-deficient) controls (P<.004). Atherosclerosis extent in animals treated with CEE plus MPA or MPA alone did not differ from that of untreated controls. Although treatment had marked effects on plasma lipoprotein patterns, statistical adjustment for variation in plasma lipoproteins did not alter the between-group relationships in atherosclerotic plaque size, suggesting that these factors do not explain substantially the atheroprotective effect of estrogen or the MPA-associated antagonism. Although the mechanism(s) remains unclear, we conclude that oral CEE inhibits the initiation and progression of coronary artery atherosclerosis and that continuously administered oral MPA antagonizes this atheroprotective effect.

Key Words: coronary artery atherosclerosis • cynomolgus monkeys • estrogen • medroxyprogesterone acetate • women's health

	Introduction

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Coronary heart disease is the leading cause of death and a major cause of disability among postmenopausal women in most western societies. Although a causal relationship has not been demonstrated, it is well established that CHD risk is reduced by 50% in postmenopausal women who take 0.625 mg of CEE daily.^{1 2} Furthermore, among women with preexisting CHD, estrogen use is associated with a similar reduction in the risk of myocardial infarction.³ Also, observational studies of postmenopausal women undergoing coronary angiography for the diagnosis of chest pain have shown that coronary occlusions are markedly fewer among estrogen users than nonusers,^{4 5 6 7} suggesting that the inhibitory effects of estrogen on atherosclerosis progression may be involved in its apparently cardioprotective effects.

Although estrogen use is associated with reduced risk of CHD, its long-term use is associated with a marked increase in the risk of endometrial cancer. It is recommended that a progestin be taken with the estrogen to offset this effect. However, the impact of the coadministration of progestin on the cardioprotective effects of estrogen is unclear. Combined estrogen-progestin replacement has been in widespread use for a relatively short time, and convincing data on its cardiovascular effects are limited. Two studies with relevance to US prescribing practices (Reference 7 and M.J. Stampfer, MD, unpublished data, 1996) indicate that users of continuous CEE and sequential (7 to 14 days per month) MPA have a similar reduction in CHD risk compared with users of CEE alone. However, there are no data regarding the effects of combined, continuously administered replacement with CEE and MPA, a prescribing practice that has become widespread recently because of its inhibition of menstrual bleeding.

The progression of coronary artery atherosclerosis and its association with CHD risk variables are exceedingly difficult to study prospectively in human subjects. For this reason, we used a nonhuman primate model of atherosclerosis, the cynomolgus macaque (Macaca fascicularis), to address questions regarding the effects of sex hormones on atherosclerosis. A series of studies has established the usefulness of the monkey model for this purpose. Relevant to the current report, we have found that surgically induced menopause (ovariectomy) results in accelerated progression of atherosclerosis.⁸ Furthermore, physiological estrogen replacement (17ß-estradiol administered by subcutaneous implant) of ovariectomized monkeys markedly inhibited atherosclerosis progression, whereas added physiological (cyclic) replacement of natural progesterone by subcutaneous implant had a neutral influence.⁹

We report here the effects of continuously administered CEE and MPA on the progression of diet-induced atherosclerosis in female cynomolgus monkeys.

	Methods

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Experimental Design
The subjects of the study were 91 female cynomolgus monkeys imported directly from Indonesia (Institut Pertanian Bogor, Bogor, Indonesia). For a total of 34 months, all animals were fed a moderately atherogenic diet (40% of calories as fat and 0.28 mg cholesterol/kcal).⁹ Monkeys lived in social groups consisting of 4 to 6 animals. All procedures involving animals were conducted in compliance with Institutional Animal Care and Use Committee policies.

Monkeys were ovariectomized and consumed the atherogenic diet for a 4-month preexperimental period. They were then assigned, by use of a stratified randomization scheme with pretreatment TPC and HDL cholesterol concentrations as stratification variables, to one of four experimental groups: untreated (surgically postmenopausal controls) (n=21); treated with CEE (Wyeth-Ayerst, Princeton, NJ) (n=25); treated with MPA (Cycrin; Wyeth-Ayerst) (n=19); or treated with CEE and MPA (n=26). Hormones were administered in the diet continuously for 30 months. As in previous studies, the difference in caloric intake between monkeys and human beings was used to calculate the appropriate dose for the monkeys, adjusted for differences in both body size and metabolic rate.¹⁰ On this basis, a 4-kg monkey received 0.17 mg CEE and/or 0.65 mg MPA. Plasma concentrations of estradiol, estrone, and MPA were measured by radioimmunoassay of samples collected 2 hours after administration to verify that dosing resulted in plasma concentrations similar to those of women taking these compounds.

Risk Variables
TPC,¹¹ triglycerides,¹² and HDL cholesterol¹³ were determined at 3-month intervals. One month before treatment and at months 12 and 24, plasma lipoprotein patterns were assessed. Lipoprotein fractions were separated by ultracentrifugation and high-performance liquid chromatography,¹⁴ and the cholesterol content of each fraction was measured.¹⁵ In macaques, four major fractions are obtained. In addition to VLDL, LDL, and HDL, a fourth peak, IDL, intermediate in density to LDL and VLDL, is seen. Average LDL molecular weight was determined for each sample by including a trace amount of iodinated LDL of known molecular weight.¹⁶

Polyacrylamide gradient gel electrophoresis (4% to 30% gels; Pharmacia) was used 1 month before treatment and at months 12 and 24 to assess HDL subfraction size heterogeneity.¹⁷ Plasma concentrations of apo B¹⁸ and apo A-I¹⁹ were determined by enzyme-linked immunosorbent assay 1 month before treatment and at months 12 and 24.

Fasting blood glucose²⁰ and insulin²¹ were determined at months 12 and 24. Body weight was determined at 3-month intervals. Blood pressure was determined with the use of a Dinamap model 1245 Ultrasound Research Monitor (Critikon) and a pediatric cuff according to previously published methods²² at 6-month intervals.

Necropsy and Measurement of Atherosclerosis
At 30 months after randomization, the monkeys were anesthetized deeply with pentobarbital (30 mg/kg IV), and the cardiovascular system was flushed with normal saline. The heart was excised after ligation of the vena cava and pulmonary arteries and was perfusion fixed via the aorta with 4% paraformaldehyde at a pressure of 100 mm Hg. The heart was then immersed in 4% paraformaldehyde. After fixation, five serial tissue blocks were cut from each of the left circumflex, left anterior descending, and right coronary arteries. One section from each block was stained with Verhoeff–van Gieson's stain, sections were projected, and the cross-sectional area occupied by intimal lesion (plaque size), the area encompassed by the internal elastic lamina (artery size), and the lumen area were measured by use of a digitizer. Plaque size, artery size, and lumen area were expressed as the mean of the 15 sections of coronary arteries.

Statistical Analysis
To satisfy the linearity, homogeneity, and normality assumptions of the parametric statistical methods used, reduce skewness, and equalize group variances, all atherosclerosis data underwent square-root transformation before analysis. ANOVA, repeated-measures ANOVA, ANCOVA, multiple regression, and Pearson's product-moment correlation were used for the statistical analyses. Duncan's new multiple range test was used for post hoc comparisons. To increase the precision of the analyses, risk variable data for the treatment period were analyzed by use of ANCOVA with pretreatment values as the independent variable. The adjusted means produced by these analyses are reported in Tables 2 and 3. Statistical analyses were made with the use of BMDP statistical software (University of California).

View this table: [in this window] [in a new window]   Table 2. TPC, HDL Cholesterol, Triglyceride, and Apo Concentrations in Ovariectomized Monkeys

View this table: [in this window] [in a new window]   Table 3. Cholesterol Content of Plasma Lipoprotein Fractions and Average Plasma LDL Molecular Weight in Ovariectomized Monkeys

	Results

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Plasma Steroid Concentrations
These data are summarized in Table 1.

View this table: [in this window] [in a new window]   Table 1. Plasma Estradiol, Estrone, and MPA Concentrations in Ovariectomized Monkeys

TPC, HDL Cholesterol, and Triglycerides
Lipid data appear in Table 2. These represent adjusted means, ie, means of all values for each animal for the 30-month treatment period adjusted for baseline (pretreatment) values in an ANCOVA. TPC was highest in the animals receiving MPA, although this group differed statistically only from animals in the CEE and CEE plus MPA groups. HDL cholesterol concentrations were reduced in all treatment groups. Total plasma triglyceride concentrations were increased an average of 135% in animals receiving CEE alone or combined with MPA.

Plasma Apolipoproteins
Plasma apo B concentrations were increased 45% in animals treated with CEE plus MPA relative to untreated controls and increased 22% relative to animals in the other two groups (Table 2). Plasma apo A-I concentrations were reduced 22% and 28% in animals treated with MPA alone and CEE plus MPA, respectively, and were 21% lower in animals treated with CEE plus MPA relative to animals treated with CEE alone (Table 2).

Plasma Lipoprotein Patterns
These data are summarized in Table 3. Changes in plasma LDL cholesterol paralleled changes in TPC, although none were significant statistically. However, average LDL molecular weight was reduced 10% in animals receiving CEE plus MPA and 14% in animals receiving CEE alone. Changes in plasma HDL cholesterol, as assessed by high-performance liquid chromatography, were similar to those shown in Table 2. Plasma VLDL plus IDL cholesterol was reduced 53% in animals treated with CEE alone relative to untreated controls. In animals treated with CEE plus MPA, VLDL plus IDL cholesterol was reduced 37% relative to animals treated with MPA alone.

Treatment with CEE plus MPA resulted in marked changes in heterogeneity of HDL subfraction sizes. HDL_2a and HDL_2b subfractions were reduced 22% and 49%, respectively, whereas HDL_3b and HDL_3c subfractions were increased 118% and 50% relative to untreated controls (all P<.05). Treatment with CEE alone resulted in qualitatively similar changes in heterogeneity of HDL subfraction sizes, although the magnitude of effect was less marked. In these animals, HDL_2b was reduced 30% whereas HDL_3b was increased 63% (for both, P<.05 versus controls).

Blood Pressure and Carbohydrate Metabolism
Blood pressure was not affected by treatment. Effects of treatment on fasting plasma glucose and insulin concentrations were apparent in animals treated with MPA alone. In these animals, plasma glucose was increased 19% (P<.05) and plasma insulin was increased 68% (P<.05) relative to untreated controls at month 12. This effect was not apparent at month 24.

Coronary Artery Atherosclerosis
Treatment with CEE alone resulted in a marked decrease in the extent of coronary artery atherosclerosis (F_3,87=4.86, P<.004) (Figure). Average plaque size was reduced by 72% relative to untreated controls, 74% relative to monkeys treated with MPA, and 63% relative to animals treated with CEE and MPA (for all, P<.05 versus controls). These three treatment groups (control, MPA, and CEE plus MPA) did not differ from one another.

View larger version (22K): [in this window] [in a new window]   Figure 1. Extent of diet-induced atherosclerotic plaque in coronary arteries of ovariectomized cynomolgus macaques either untreated (CTL) or treated with CEE, MPA, or combined CEE plus MPA. Data are either unadjusted or adjusted for significant plasma lipoprotein risk variables (described in text). *P<.05 versus other three groups.

Risk Variables as Predictors of Atherosclerosis Extent
Using multiple regression analysis, we determined that TPC was a significant predictor of coronary artery atherosclerosis and accounted for 44% of the variability in lesion size. Therefore, TPC was used as a covariate in an ANCOVA to determine if it accounted for effects of treatment on atherosclerosis. Adjusted values are shown in the Figure. A significant effect of treatment persisted (F_3,87=2.67, P<.05), and relationships among groups were unchanged; atherosclerosis extent was decreased 47% to 56% in CEE-treated monkeys relative to the other three groups (all P<.05), which, in turn, did not differ from each other. Thus, effects of treatment on atherosclerosis progression are unexplained by effects on risk variables measured in this study.

	Discussion

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Although it is clear that estrogen-replacement therapy is associated with a marked reduction in risk of CHD, the mechanisms involved are not certain. Yet there is extensive evidence that estrogen replacement inhibits the initiation and progression of coronary artery atherosclerosis. Data presented herein show that orally administered CEE caused a 72% reduction in coronary artery plaque size relative to untreated, estrogen-deficient controls. Furthermore, data from a previous study⁹ show that parenterally administered 17ß-estradiol caused a 50% reduction in coronary plaque size. In agreement with these findings are those of several studies of the effects of exogenous estrogen on diet-induced atherosclerosis in rabbits.^{23 24 25 26} Furthermore, results of several studies of women undergoing angiography for diagnosis of chest pain reveal a markedly lower prevalence of coronary stenoses in estrogen users relative to nonusers.^{4 5 6}

Although the atheroprotective effects of estrogens are well established, the influence of the coadministration of a progestin, necessary for the prevention of endometrial cancer, is unclear. Limited observational data indicate that CHD risk in users of combined CEE and sequentially administered MPA (7 to 14 days per month) is similar to that of users of CEE alone.^{7 27} However, there are no observational data for users of combined, continuously administered CEE and MPA. The experimental data described herein indicate that MPA administered continuously antagonizes the atheroprotective effect of CEE alone. This is in contrast to the results of a previous study in which the parenteral administration of progesterone sequentially (alternating months) had no influence on the atheroinhibitory effect of parenterally administered estradiol.⁹ The reasons for these contrasting results are not clear; however, we speculate that they may relate to differences between the two progestins in potency, route of administration (oral versus parenteral), or pattern of administration (continuous versus sequential). Among other physiological functions, progestins act as antiestrogens. Thus, it is perhaps not surprising that MPA (a potent synthetic progestin) given orally and continuously for 30 months had substantial antiestrogenic effects, whereas a natural progestin, progesterone, administered parenterally and sequentially did not.

Although plasma lipoprotein patterns were substantially affected by CEE, with and without MPA, these effects did not appear to explain substantially the effects of hormone-replacement therapy on CHD risk²⁸ or coronary artery atherosclerosis.⁹ Similarly, the antagonistic effect of MPA on atherosclerosis remains unaccounted for statistically by plasma lipoproteins. Nonetheless, it remains possible that aspects of plasma lipoproteins not assessed in the present study (eg, effects on the metabolism or compositional heterogeneity of lipoprotein fractions) may play a role.

Evidence continues to accumulate regarding the existence of atheroprotective effects of estrogen mediated at the level of the artery wall. Using the macaque model, we have found that certain estrogens (ie, esterified estrogens; Solvay Pharmaceuticals) and estrogen-progestin combinations (ie, estradiol-progesterone, ethinyl estradiol–levonorgestrel) inhibit the arterial uptake and catabolism of plasma LDL.^{29 30} This represents a means by which estrogen may directly inhibit arterial cholesterol accumulation as well as atherosclerosis initiation and/or progression. These data also suggest that some progestins do not antagonize the inhibitory effects of estrogen on arterial uptake and catabolism of LDL. The effects of MPA on this process remain unclear.

Sex hormones may influence other cellular or molecular processes occurring in arterial intima implicated in the initiation and progression of atherosclerosis. There is plentiful evidence that sex hormones are modulators of immune and inflammatory processes, localized variations of which have been implicated in the initiation and progression of atherosclerosis.^{31 32} Evidence supporting direct effects on these localized inflammatory/proliferative processes of the artery wall is somewhat limited and largely confined to results from studies of cultured cells. Nonetheless, several studies have implicated estrogens as modulators of the expression of inflammatory mediators and growth factors.^{33 34 35 36 37 38} Although the effects of progestins on these atherogenic processes remain unknown, it seems likely that antiestrogenic effects of some progestins or forms of administration of progestins may antagonize directly the antiatherogenic effects of estrogen.

Sex hormones also may influence the initiation or progression of atherosclerosis by modulating arterial vasomotor responsiveness. It is now clear that estrogen can reverse the atherosclerosis-related impairment of coronary artery vasodilator function in both monkeys^{39 40} and women.^{41 42} Although the mechanisms involved in this vasodilator effect are uncertain, the available evidence suggests that estrogen acts by augmenting the production, release, or viability of nitric oxide.^{43 44 45 46} Progestins antagonize estrogen-induced increases in blood flow and vasodilation in normal (nonatherosclerotic) animals.⁴⁷ Recently, we⁴⁸ have shown that MPA, administered either cyclically or continuously, causes partial antagonism of the CEE-induced augmentation of coronary vasodilator responsiveness and complete antagonism of the estrogen-induced augmentation of coronary flow reserve in female monkeys with diet-induced atherosclerosis. Atherosclerosis-related coronary vasospasm, which represents impairment of vasodilator responses or augmentation of vasoconstrictor responses, can lead to accelerated progression of atherosclerosis, plaque instability or rupture, thrombosis, and myocardial infarction.^{49 50 51} Although estrogen treatment preserves vasodilator function and may thereby retard atherosclerosis progression and reduce the risk of clinical ischemic events, experimental evidence indicates that MPA antagonizes this cardioprotective effect of estrogen⁴⁸ and thus may counteract the benefits of estrogen.

Regardless of mechanism, we conclude that CEE and other estrogens inhibit the initiation and progression of atherosclerosis. However, in the current study, the coadministration of continuously administered MPA completely antagonized the antiatherosclerotic effect of CEE. This result contrasts with the findings of a previous study⁹ in which progesterone administered parenterally and sequentially had a neutral influence on the antiatherosclerotic effects of parenterally administered estradiol. The results indicate that some progestins have antiestrogenic influences on the cardiovascular system that may depend on potency, dose, route (oral versus parenteral), or pattern (continuous versus sequential) of administration. Furthermore, some forms of progestin coadministration may antagonize the favorable cardiovascular effects of estrogen.

	Selected Abbreviations and Acronyms

 

apo = apolipoprotein CEE = conjugated equine estrogens CHD = coronary heart disease MPA = medroxyprogesterone acetate TPC = total plasma cholesterol

	Acknowledgments

 
This study was supported in part by grant HL-P0145666, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Md. The authors gratefully acknowledge the editorial assistance of Karen Potvin Klein and thank Wyeth-Ayerst Research (Princeton, NJ) for providing Premarin and Cycrin.

Received February 22, 1996; revision received May 22, 1996;

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Bush TL. Noncontraceptive estrogen use and risk of cardiovascular disease: an overview and critique of the literature. In: Korenman SG, ed. The Menopause: Biological and Clinical Consequences of Ovarian Failure; Evolution and Management. Norwell, Mass: Serono Symposia; 1990:211-224.
2. Stampfer MJ, Colditz GA. Estrogen replacement and coronary heart disease: a quantitative assessment of the epidemiologic evidence. Prev Med. 1991;20:47-63.[Medline] [Order article via Infotrieve]
3. Sullivan JM. Hormone replacement in the secondary prevention of cardiovascular disease. In: Wenger NK, Speroff L, Packard B, eds. Cardiovascular Health and Disease in Women: Proceedings of an NHLBI Conference. Greenwich, Conn: LeJacq Communications, Inc; 1993:189-194.
4. Gruchow HW, Anderson AJ, Barboriak J, Sobocinski VA. Postmenopausal use of estrogen and occlusion of coronary arteries. Am Heart J. 1988;115:954-963.[Medline] [Order article via Infotrieve]
5. Sullivan JM, Vander Zwaag R, Lemp GF, Hughes JP, Maddock V, Kroetz FW, Ramanathan KB, Mirvis DM. Postmenopausal estrogen use and coronary atherosclerosis. Ann Intern Med. 1988;108:358-363.
6. Hong MK, Romm PA, Reagan K, Green CE, Rackley CE. Effects of estrogen replacement therapy on serum lipid values and angiographically defined coronary artery disease in postmenopausal women. Am J Cardiol. 1992;69:176-178.[Medline] [Order article via Infotrieve]
7. Psaty B, Heckbert S, Atkins D, Lemaitre R, Koepsell TD, Wahl PW, Siscovick DS, Wagner EH. The risk of myocardial infarction associated with the combined use of estrogens and progestins in postmenopausal women. Arch Intern Med. 1994;154:1333-1339.[Abstract]
8. Adams MR, Kaplan JR, Koritnik DR, Clarkson TB. Ovariectomy, social status, and atherosclerosis in cynomolgus monkeys. Arteriosclerosis. 1985;5:192-200.[Abstract/Free Full Text]
9. Adams MR, Kaplan JR, Manuck SB, Koritnik DR, Parks JS, Wolfe MS, Clarkson TB. Inhibition of coronary artery atherosclerosis by 17-beta estradiol in ovariectomized monkeys: lack of an effect of added progesterone. Arteriosclerosis. 1990;10:1051-1057.[Abstract/Free Full Text]
10. Clarkson TB, Shively CA, Morgan TM, Koritnik DR, Adams MR, Kaplan JR. Oral contraceptives and coronary artery atherosclerosis of cynomolgus monkeys. Obstet Gynecol. 1990;75:217-222.[Abstract/Free Full Text]
11. Allain CC, Poon LS, Chan CSG, Richmond W, Fu PC. Enzymatic determination of total serum cholesterol. Clin Chem. 1974;20:470-475.[Abstract]
12. Fossati P, Principe L. Serum triglycerides determined colorimetrically with an enzyme that produces hydrogen peroxide. Clin Chem. 1982;28:2077-2080.[Abstract/Free Full Text]
13. Lipid Research Clinics Program. Manual of Laboratory Operations: Lipid and Lipoprotein Analysis. Bethesda, Md: National Institutes of Health; 1984. US Dept of Health, Education, and Welfare publication NIH 75-628 [revised 1982].
14. Carroll RM, Rudel LL. Lipoprotein separation and low density lipoprotein molecular weight determination using high performance gel-filtration chromatography. J Lipid Res. 1983;24:200-207.[Abstract]
15. Auerbach BJ, Parks JS, Applebaum-Bowden D. A rapid and sensitive micro-assay for the enzymatic determination of plasma and lipoprotein cholesterol. J Lipid Res. 1990;31:738-742.[Abstract]
16. Rudel LL, Pitts LL II, Nelson CA. Characterization of plasma low density lipoproteins of nonhuman primates fed dietary cholesterol. J Lipid Res. 1977;18:211-222.[Abstract]
17. Verdery RB, Benham DF, Baldwin HL, Goldberg AP, Nichols AV. Measurement of normative HDL cholesterol levels by gaussian summation analysis of gradient gels. J Lipid Res. 1989;30:1085-1095.[Abstract]
18. Sorci-Thomas M, Wilson MD, Johnson FL, Williams DL, Rudel LL. Studies on the expression of genes encoding apolipoproteins B100 and B48 and the low density lipoprotein receptor in nonhuman primates. J Biol Chem. 1989;264:9039-9045.[Abstract/Free Full Text]
19. Koritnik DL, Rudel LL. Measurement of apolipoprotein A-I concentration in nonhuman primate serum by enzyme-linked immunosorbent assay (ELISA). J Lipid Res. 1983;24:1639-1645.[Abstract]
20. Alpert NL. Glucose analyzer and BUN analyzer. Lab World. 1973;24:40.
21. Meis PJ, Kaplan JR, Koritnik DR, Rose JC. Effects of gestation on glucose tolerance and plasma insulin in cynomolgus monkeys (Macaca fascicularis). Am J Obstet Gynecol. 1982;144:543-545.[Medline] [Order article via Infotrieve]
22. Corbett WT, Schey HM, Lehner NDM, Greene AW. Standardized methods for recording blood pressure in anesthetized Macaca fascicularis. Lab Anim. 1981;15:37-40.[Abstract/Free Full Text]
23. Kushwaha RS, Hazzard WR. Exogenous estrogens attenuate dietary hypercholesterolemia and atherosclerosis in the rabbit. Metabolism. 1981;30:359-366.[Medline] [Order article via Infotrieve]
24. Hough JL, Zilversmit DB. Effect of 17-beta estradiol on aortic cholesterol content and metabolism in cholesterol-fed rabbits. Arteriosclerosis. 1986;6:57-63.[Abstract/Free Full Text]
25. Haarbo J, Leth-Espensen P, Stender S, Christiansen C. Estrogen monotherapy and combined estrogen-progestogen replacement therapy attenuate aortic accumulation of cholesterol in ovariectomized cholesterol-fed rabbits. J Clin Invest. 1991;87:1274-1279.
26. Haarbo J, Svendsen OL, Christiansen C. Progestogens do not affect aortic accumulation of cholesterol in ovariectomized cholesterol-fed rabbits. Circ Res. 1992;70:1198-1202.[Abstract/Free Full Text]
27. Walsh B, Schiff I, Rosner B, Greenberg L, Ravnikar V, Sacks F. Effects of hormonal replacement on the concentrations and metabolism of plasma lipoproteins. N Engl J Med. 1991;73:925-930.
28. Barrett-Connor E, Bush TL. Estrogen and coronary heart disease in women. JAMA. 1991;265:1861-1867.[Abstract]
29. Wagner JD, Clarkson TB, St. Clair RW, Schwenke DC, Shively CA, Adams MR. Estrogen and progesterone replacement therapy reduces LDL accumulation in the coronary arteries of surgically postmenopausal cynomolgus monkeys. J Clin Invest. 1991;88:1995-2002.
30. Wagner JD, Adams MR, Schwenke DC, Clarkson TB. Oral contraceptive treatment decreases arterial LDL degradation in female cynomolgus monkeys. Arterioscler Thromb. 1992;12:716-723.
31. Libby P, Hansson GK. Involvement of the immune system in human atherogenesis: current knowledge and unanswered questions. Lab Invest. 1991;64:5-15.[Medline] [Order article via Infotrieve]
32. Ross R. The pathogenesis of atherosclerosis: a perspective for the 1990s. Nature. 1993;362:801-809.[Medline] [Order article via Infotrieve]
33. Shanker G, Sorci-Thomas M, Register TC, Adams MR. The inducible expression of THP-1 cell interleukin-1 mRNA: effects of estrogen on differential response to phorbol ester and lipopolysaccharide. Lymphokine Cytokine Res. 1994;13:1-7.[Medline] [Order article via Infotrieve]
34. Stock JL, Coderre JA, McDonald B, Rosenwasser J. Effect of estrogen in vitro and in vivo on spontaneous interleukin-1 release by monocytes from postmenopausal women. J Clin Endocrinol Metab. 1989;68:364-368.[Abstract]
35. Shanker G, Sorci-Thomas M, Adams MR. Estrogen modulates the inducible expression of platelet-derived growth factor mRNA by monocyte/macrophages. Life Sci. 1995;56:499-507.[Medline] [Order article via Infotrieve]
36. Shanker G, Sorci-Thomas M, Adams MR. Estrogen modulates the expression of tumor necrosis factor-alpha mRNA in phorbol ester- and lipopolysaccharide-stimulated human monocytic THP-1 cells. Lymphokine Cytokine Res. 1994;13:377-382.[Medline] [Order article via Infotrieve]
37. Frazier-Jessen MR, Kovacs EJ. Estrogen modulation of JE/monocyte chemoattractant protein-1 expression in murine macrophages. J Immunol. 1995;154:1838-1845.[Abstract]
38. Jilka RL, Hangoc G, Girasole G, Passeri G, Williams DC, Abrams JS, Boyce B, Broxmeyer H, Manolagas S. Increased osteoclast development after estrogen loss: mediation by interleukin-6. Science. 1992;257:88-91.[Abstract/Free Full Text]
39. Williams JK, Adams MR, Klopfenstein HS. Estrogen modulates responses of atherosclerotic coronary arteries. Circulation. 1990;75:217-222.
40. Williams JK, Adams MR, Herrington DM, Clarkson TB. Short-term administration of estrogen and vascular responses of atherosclerotic coronary arteries. J Am Coll Cardiol. 1992;20:452-457.[Abstract]
41. Herrington DM, Braden GA, Downes TR, Williams JK. Estrogen modulates coronary vasomotor responses in postmenopausal women with early atherosclerosis. Am J Cardiol. 1994;73:951-952.[Medline] [Order article via Infotrieve]
42. Reis SE, Gloth ST, Blumenthal RS, Resar JR, Zacur HA, Gestenblith G, Brinker JA. Ethinyl estradiol acutely attenuates abnormal coronary vasomotor responses to acetylcholine in postmenopausal women. Circulation. 1994;89:52-60.[Abstract/Free Full Text]
43. Gisclard V, Miller VM, Vanhoutte PM. Effect of 17-beta estradiol on endothelium-dependent responses in the rabbit. J Pharmacol Exp Ther. 1988;244:19-22.[Abstract/Free Full Text]
44. Miller VM, Gisclard V, Vanhoutte PM. Modulation of endothelium-dependent and vascular smooth muscle responses by oestrogens. Phlebology. 1988;3(suppl 1):63-69.
45. Schray-Utz B, Zeiher AM, Busse R. Expression of constitutive NO synthase in cultured endothelial cells is enhanced by 17-beta estradiol. Circulation. 1993;88(suppl I):I-80. Abstract.
46. Keaney JF, Schwaery GT, Yu A, Nicolosi RJ, Foxall TL, Vita JA. 17-Beta estradiol preserves endothelial vasodilator function and limits low-density lipoprotein oxidation in hypercholesterolemic swine. Circulation. 1994;89:2251-2259.[Abstract/Free Full Text]
47. Sarrel PM. Blood flow and ovarian secretions. In: Naftolin F, DeCherney AH, Gutmann JN, Sarrel PM, eds. Ovarian Secretions and Cardiovascular and Neurovascular Function. New York, NY: Raven Press; 1990:81-89.
48. Williams JK, Honore EK, Washburn SA, Clarkson TB. Effects of hormone replacement therapy on reactivity of atherosclerotic coronary arteries in cynomolgus monkeys. J Am Coll Cardiol. 1994;24:1757-1761.[Abstract]
49. Maseri A, Severi S, DeNes M, L'Abbate A, Chierchia S, Marzilli M, Ballestra AM, Paradi O, Biagini A, Distante A. `Variant' angina: one aspect of a continuous spectrum of vasospastic myocardial ischemia—pathogenetic mechanisms, estimated incidence and clinical and coronary arteriographic findings in 138 patients. Am J Cardiol. 1978;42:1019-1035.[Medline] [Order article via Infotrieve]
50. Maseri A, Severi S, DeNes M, L'Abbate A, Chierchia S, Marzilli M, Ballestra AM, Pardoli O. Coronary vasospasm as a possible cause of myocardial infarction: a conclusion derived from the study of `preinfarction' angina. N Engl J Med. 1978;299:1271-1277.[Abstract]
51. Roberts WC, Durry RC, Isner JM. Sudden death in Prinzmetal's angina with coronary spasm documented by angiography: analysis of three necropsy patients. Am J Cardiol. 1982;50:203-210.[Medline] [Order article via Infotrieve]

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