Post-menopausal hormone replacement therapy: effects of progestogens on serum lipids and lipoproteins. A review

Maturiras, Elsevier

8 (1986) 7-17

MAT 00368

Review

Post-menopausal hormone replacement therapy: effects of progestogens on serum lipids and lipoproteins. A review M.J. Tikkanen, T. Kuusi, E.A. Nikkib and S. Sipinen Third Department of Medicine, University of Helsinki, Finland (Received

28 January

1985; revision received 17 June 1985; accepted

30 July 1985)

Introduction

Until a few years ago, post-menopausal hormone replacement therapy was based on oestrogen alone. There was a general feeling that oestrogen, if it had any effect at all on the risk of coronary heart disease (CHD), was probably beneficial as long as conventional doses of natural oestrogen were used [1,2]. Some studies indicated quite convincingly that the menopause was associated with an increased risk of coronary heart disease [3,4]. Moreover, published data suggested that this risk could be diminished by oestrogen substitution [5,6], although this was not confirmed by all studies [7,8]. Post-menopausal oestrogen replacement therapy was found to be associated with ‘beneficial’ effects on at least two major CHD risk factors: high-density lipoprotein (HDL) cholesterol was increased and low-density lipoprotein (LDL) cholesterol was decreased by oestrogen treatment [9-111. The magnitude of the fall in LDL cholesterol was directly proportional to the initial LDL cholesterol level, suggesting that oestrogen could be the drug of choice in the treatment of postmenopausal hypercholesterolaemia lipid disorder [ 121. The recent recommendation (for review, see [13]) that sequential progestogen should be added to cyclic oestrogen therapy in order to reduce the risk of endometrial cancer has greatly increased the use of progestational agents ‘by postmenopausal women. Since many of the effects of oestrogen, including changes in lipoproteins, are opposed by some progestogens, great interest has been focused on the potential merits and demerits of combining progestogens with oestrogen. In this review we attempt to summarise current knowledge concerning the effects on serum lipids and lipoproteins of progestogens used either alone or as a supplement to post-menopausal oestrogen replacement therapy. Correspondence to: Matti J. Tikkanen, MD, Third Department Haartmanink 4, 00290 Helsinki, Finland.

037%5122/86/$03.50

0 1986 Elsevier Science Publishers

of Medicine,

B.V. (Biomedical

Central

Division)

University

Hospital,

8

Serum lipoproteins

and lipid transport

Lipoproteins serve as vehicles in the transport of dietary and tissue lipids (cholesterol, triglycerides, phospholipids) in the blood. There are four major classes of lipoprotein in human serum: chylomicrons; very low-density lipoprotein (VLDL); low-density lipoprotein (LDL); and high-density lipoprotein (HDL). Elevated serum LDL cholesterol levels correlate positively with the risk of coronary heart disease [14] and elevated serum and VLDL triglycerides also increase this risk. HDL cholesterol is inversely related to CHD risk, i.e. it constitutes a protective factor [15]. Chylomicrons are the major carriers of dietary triglycerides from the intestine to the peripheral tissues. VLDL transports endogenously-produced triglycerides to peripheral tissues for consumption or storage. Triglycerides are released from chylomicrons and VLDL in a stepwise lipolytic process catalysed by lipoprotein lipase. During this process, VLDL gives rise to smaller particles that are slowly converted to LDL, which is the principal carrier of cholesterol to the peripheral tissues in man. LDL is removed from the circulation by a receptor-mediated process; both peripheral cells and hepatocytes carry specific membrane receptors that recognise LDL apoprotein B [16]. The formation of HDL, another cholesterol-rich lipoprotein, involves the action of two enzymes, lipoprotein lipase (LPL) and lecithin cholesterol acyltransferase (LCAT). ‘Nascent’ HDL particles containing apoprotein A are produced in the splanchnic area and supplied with material (phospholipids, free cholesterol and apoproteins) derived from the surface of chylomicrons and VLDL during Iipolysis of the triglycerides by LPL. The free cholesterol is esterified by LCAT, and the HDL particles acquire their mature spherical form as esterified cholesterol is accommodated in their hydrophobic cores. HDL also receives free cholesterol from peripheral tissues and is thus involved in the ‘reverse’ transport of cholesterol (for review, see

P71). Two distinct subpopulations of HDL, namely HDL2 and HDL3, are found in plasma. The larger HDL2 particles contain about four times as much esterified cholesterol as does HDL3, as well as twice the amount of triglycerides and phospholipids. There is evidence to suggest that on receiving surface material from lipolysed VLDL and chylomicrons, HDL3 is converted to HDL2 in the circulation [18], this being followed by LCAT-mediated cholesterol esterification. Hepatic lipase, a lipolytic enzyme with triglyceride lipase and phospholipase activity, is located in the endothelial cells of liver sinusoids. It participates in the catabolism of HDL. Lipid constituents can be released from HDL2 in a process catalysed by this enzyme, with resultant regeneration of HDL3 [19].

Progestational

agents

Since oestrogen administration is associated with an increased incidence of endometrial hyperplasia and adenocarcinoma, a combination of sequential pro-

9

gestogen and oestrogen has been recommended to protect the endometrium [13]. This has resulted in a remarkable increase in the use of progestational agents as components of post-menopausal replacement therapy. Basically, two types of progestogen are currently used [20,21]. The 19-nortestosterone-derived progestogens, such as levo-norgestrel (D-norgestrel), norethindrone (norethisterone) and norethindrone acetate are relatively strongly androgenic. The C-21 progestogens, derived from 17-hydroxyprogesterone, including the acetates of medroxyprogesterone, megestrol and cyproterone, are significantly less androgenic than the 1Pnortestosterones [20,21]. Desogestrel, despite its structural relation to norgestrel, resembles the C-21 progestogens in having a very low androgenicity [22,23]. Good as the oestrogen-progestogen combination may be for preventing malignancy, concern has been expressed regarding the CHD risk, since the effects of oestrogen on serum lipoproteins, especially HDL, may be nullified or even reversed by the addition of certain progestogens [24-291. Effects of progestogens on serum triglycerides and VLDL Most of the available data on the effects of progestogens on VLDL and triglyceride (TG) metabolism have been derived from studies in fertile women treated with small doses of contraceptive progestogens administered alone (for review, see [30]). The 19-nortestosterone derivatives lower VLDL and TG, whereas 17-hydroxyprogesterone derivatives do not alter serum TG or VLDL levels. In contrast to the voluminous literature on contraceptive progestogens, relatively few trials have been documented that have attempted to elucidate the effects of progestogens administered alone in peri-menopausal and post-menopausal women. Some of the progestogens used in the latter case are listed in Table I. The 17-hydroxyprogesterone derivatives given alone or in combination with oestrogen did not reduce serum or VLDL TG levels. On the other hand, Farish et al. [31] reported a significant reduction in serum TG in pet-i-menopausal women treated with norethindrone. Studies with levo-norgestrel and norethindrone acetate also showed minor reductions, but these were not statistically significant [25,27]. The addition of levo-norgestrel to an oestrogen regimen in short-term trials invariably resulted in a reduction in serum and VLDL TG concentrations [26,27,32]. Other 19-nortestosterone derivatives, such as norethindrone and its acetate, did not decrease serum TG significantly when combined with natural oestrogen (oestradiol valerate) [26,33], but did so when administered to women on a synthetic oestrogen (ethinyl oestradiol) [24,33]. Ethinyl oestradiol, but not oestradiol valerate, is known to raise serum TG levels in post-menopausal women [35,36]. The TG-elevating effect of synthetic and equine oestrogens is due to increased production of VLDL and TG [37-391. Norethindrone and norethindrone acetate are effective in lowering serum TG levels in subjects with increased VLDL and TG production due to ethinyl oestradiol administration (Table I) or primary hypertriglyceridaemia [40]. Accordingly, progestogens with androgenic properties have a TG-lowering effect that may manifest itself only under circumstances where increased VLDL and TG production has already been stimulated.

10 TABLE

I

EFFECT OF PROGESTOGENS ADMINISTERED ALONE OR IN ADDITION a TO OESTROGEN ON SERUM TRIGLYCERIDE (TG) AND LOW-DENSITY LIPOPROTEIN (LDL) CHOLESTEROL LEVELS IN MENOPAUSAL OR POST-MENOPAUSAL WOMEN. Oestrogen

Dose

Progestogen

Dose mg/day

Serum TG

LDL Chol

Reference

Levo-norgestrel Levo-norgestrel Levo-norgestrel Norethindrone acetate Norethindrone Medroxyprog. acetate Desogestrel Cyproterone acetate Norgestrel a Levo-norgestrel Levo-norgestrel Norethindrone acetate Norethindrone acetate Norethindrone Medroxyprog. acetate Progesterone

1.8 0.25 0.125 10.0 10.0 10.0 0.125 5.0 0.5 0.25 0.12 10.0 10.0 10.0 10.0 300.0

NS NS D NS D NS D NS D D D NS D D NS NS

NS NS D I I NS NS NS ND NS NS I I Ie ND NS

25,29 27 23 25.29 31 25,29 23 34b 26 27 32 33 33 24 26 32

mg/day _ _ _ _ _ _ E, valerate E, valerate Cutaneous d E, E, valerate Ethinyl E2 Ethinyl Ez E, valerate Cutaneous d E,

2.0 2.0 3.0 2.0 0.02 0.02 2.0 3.0

a Sequential progestogen was added to cyclic oestrogen for 10 days at the end of the oestrogen cycle. b Study carried out in menstruating women. ’ Equivalent to 0.25 mg levo-norgestrel; d cutaneous administration; ’ statistically significant increase in total cholesterol. ND = not determined, statistically significant changes: I = increase. D = decrease, NS = not significant.

The TG-lowering action of 19-nortestosterone derivatives may in principle be based on increased removal or decreased production of VLDL and TG. There are in fact indications that both mechanisms may be involved [30,41]. Thus the nortestosterone-derived progestogens may share the properties of another androgenic steroid, oxandrolone, which enhances the clearance of plasma TG [42]. The accelerated removal of plasma TG during contraception with oestrogen-protestogen pills has also been attributed to the progestogen components [37]. In animal studies, norethindrone acetate was shown to inhibit TG synthesis and secretion [43,44]. The fact that androgenic progestogens tend to lower serum and VLDL TG levels seems to have been established, at least in short-term treatment trials in postmenopausal women. However, the persistence of the effect has not been explored sufficiently. Farish and coworkers [31] observed a significant reduction in serum TG during continuous administration of norethindrone alone, which still persisted after 12 mth of therapy. On the other hand, during continuous treatment with norethindrone acetate in combination with oestrogen, the reduction in serum TG achieved during the first 3 mth ceased after 12 mth on the drug [45]. We studied the long-term effects of adding sequential levo-norgestrel to an oestrogen regimen in post-menopausal women who had been on cyclic oestradiol valerate for l-2 yr (Table II). After 12 mth on combined oestrogen-progestogen, the average VLDL TG

11 TABLE

II

LONG-TERM EFFECT ON SERUM LIPOPROTEIN LIPIDS OF THE ADDITION OF SEQUENTIAL LEVO-NORGESTREL (LN) TO AN OESTRADIOL VALERATE (E2) REGIMEN IN 12 POST-MENOPAUSAL WOMEN a Lipid (mmol/l)

VLDL

LDL

HDL

E2

E,/LN

‘52

E,/LN

E2

E2/‘-N

Cholesterol Triglyceride

0.49 0.90

0.35 0.75

4.59 0.43

4.33 0.40

1.84 0.23

1.34 * 0.22

* P < 0.05, paired t-test. a The subjects had been on cyclic E, 2 mg/day (21-day cycles separated by 7-day intervals) for 1-2 years. Levo-norgestrel 250 pg/day was added on days 11-21 and the estrogen-progestogen combination was administered for 12 months. Lipoprotein determinations were effected on oestrogen alone (day 21) and after 12 months of combination therapy (day 21). (Previously unpublished data).

and VLDL cholesterol levels were lower, but the change was not significant, suggesting that short-term effects may not persist over longer periods of time. Effect of progestogens on serum cholesterol and LDL

The LDL cholesterol-lowering effect of oestrogen replacement in oestrogen-deficient states is well documented. This has been demonstrated in men [lo] and post-menopausal women 146,471,with conjugated oestrogens [47], synthetic alkylated oestrogens [36] and oestradiol valerate [12]. Women with initially elevated LDL cholesterol levels responded best to oestradiol valerate, whereas initially normal LDL cholesterol levels were little affected [12]. On the other hand, most progestogens, including levo-norgestrel and desogestrel as well as hydroxyprogesterone derivatives, did not cause significant alterations in LDL cholesterol (Table I). However, during continuous administration of norethindrone to per&menopausal women, LDL cholesterol increased slowly with time, this change becoming statistically significant after 12 mth [31]. Moreover, LDL cholesterol lowered by previous oestrogen therapy was raised on addition of norethindrone to the oestrogen regimen (Table I). This effect has been interpreted as a consequence of increased VLDL turnover, resulting in increased formation of LDL due to the androgenic properties of norethindrone [29,33]. It is not clear why levo-norgestrel, another androgenic steroid with even greater TG-lowering activity (Table I), does not share this property. Our long-term trial (Table II) indicated that sequential combination of levo-norgestrel to cyclic oestradiol valerate treatment did not have any influence on LDL cholesterol or triglycerides, even after 12 mth of treatment. Thus, most oestrogen-progestogen combinations do not affect LDL cholesterol concentrations in any adverse way. In the case of norethindrone, it may be taken that most of the LDL cholesterol increases that have been reported were in fact reversals of oestrogen-induced reductions. Moreover, the timing of the lipoprotein determinations in the treatment trials (last day of the progestogen period) coincided with maximum progestogen effect and the results consequently do not reflect an

12

average effect. It is therefore unlikely that any of the progestogens a significant negative effect on LDL cholesterol when combined gen. Effect of progestogens

on high-density

in current use has with cyclic oestro-

lipoproteins

The most consistent lipid effect of post-menopausal progestogen therapy is a reduction in HDL cholesterol by 19-nortestosterone-derived progestogens given either alone or in combination with oestrogen [19,41]. During long-term therapy with oestradiol valerate and levo-norgestrel, the reduction in HDL cholesterol persisted even after 12 mth (Table II). Almost all of the progestogen-induced fall in total HDL cholesterol was due to a reduction in the HDL2 subfraction [27,28,48,49], HDL3 being decreased only slightly. Relatively non-androgenic progestogens, such as medroxyprogesterone acetate [49] and desogestrel [23], do not affect HDL (HDL2) lipid concentrations significantly when used in conventional replacementtherapy doses. However, in larger doses, they too may cause significant decreases in HDL cholesterol [50]. The mechanisms underlying the sex-steroid regulation of HDL2 levels have recently begun to emerge. The formation of HDL2 particles is promoted by two major enzymes, lipoprotein lipase and LCAT. The catabolism of HDL2 appears to depend on the activity of hepatic lipase. The activities of these three enzymes have been studied in subjects treated with a variety of hormonal steroids. The major finding in all these studies was that hepatic lipase activity is suppressed by equine [51], synthetic [52] and natural oestrogen [53], but increased by androgenic progestogens [48,54] and anabolic steroids [55,56]. However, lipoprotein lipase [28,48,51-53,551 and LCAT [23,28] activity is not influenced by these hormones in human subjects. Moreover, a striking reciprocal relationship is invariably present between the changes in HDL (HDL2) levels and the changes in hepatic lipase activity: HDL (HDL2) levels rise during hepatic lipase suppression and fall during its stimulation [19,23,27,28,41,48,49,53,56]. This has been corroborated in studies employing a large number of oestrogenic, androgenic, progestational and anabolic steroids (Table III). In addition a highly significant correlation has been found to exist between the magnitude of the change in hepatic lipase activity and the magnitude of the change in HDL2 cholesterol [19]. On the other hand, progestogens with low androgenicity, such as medroxyprogesterone acetate [49], cyproterone acetate [34] and desogestrel [23], have much less effect on both hepatic lipase and HDL. On the basis of these findings it has been suggested that HDL2 may be degraded by hepatic lipase [57,58] and that sex-steroid effects on HDL2 are caused by steroid-induced changes in hepatic lipase activity [28,48]. Reductions in the levels of plasma phospholipids (lecithin, cephalin) during androgenic progestogen administration and, conversely, the increases in these levels during oestrogen therapy, are also explained by sex-steroid-induced alterations in the phospholipase activity of hepatic lipase [59]. The hypothesis is compatible with the data so far accumulated but does not exclude the possibility that other factors may also be involved in the regulation of serum HDL2 levels by sex steroids. Thus, oestrogen-induced enhance-

13 TABLE EFFECT (HDLZ)

III OF STEROIDS

ON POSTHEPARIN

PLASMA

HEPATIC

LIPASE

ACTIVITY

AND

HDL

CHOLESTEROL

Steroid

Hepatic lipase

HDL (HDL2) cholesterol

Reference

Levo-norgestrel Norethindrone acetate Norethindrone acetate Oxandrolone Oxandrolone Stan020101 Medroxyprogesterone acetate Desogestrel Cyproterone acetate Equine oestrogens Equine oestrogens Ethinyl oestradiol Ethinyl oestradiol Oestradiol valerate

I I ND I ND I NS NS NS D ND D ND D

D ND D ND D D NS NS NS ND I ND I I

48 54 25 55 63 56 49 23 34 51 47 52 36 53

ND = not determined.

statistically

significant

changes:

D = decrease;

I = increase;

NS = not signficant.

ment of apoprotein A synthesis [60] may contribute to the increase in HDL2 cholesterol during oestrogen treatment and, conversely, steroids with androgenic properties may suppress apoprotein A synthesis [61,62], with a consequent reduction in HDL2 production.

Progestogen-induced alterations in HDL metabolism and their relation to the risk of coronary heart disease in post-menopausal women When used in combination with oestrogen the only significant adverse effect of a 19-nortestosterone-derived progestogen appears to be the reduction in HDL2 cholesterol (and total HDL cholesterol) which persists during prolonged administration. The lowering of VLDL lipids by progestogens is evidently beneficial. The LDL cholesterol levels are not affected to any major degree. However, most trials, such as that reported in Table II, were designed to detect progestogen effects. The reported HDL levels therefore reflect not average, but minimum concentrations. An assessment of the clinical significance of this progestogen effect is clearly necessary. It is relevant here to consider the implications of alterations in HDL cholesterol levels due to hormonal agents with regard to the risk of coronary heart disease. The central question is whether a low HDL concentration induced by androgenic progestational agents reflects an impaired reverse transport of cholesterol and a consequent increase in atherogenesis. Low levels of HDL, if caused by enhanced hepatic lipase-mediated lipolysis of HDLZ, could in fact reflect an

14

accelerated reverse transport of cholesterol. On the other hand, decreased production of HDL2 due to androgen-induced inhibition of apoprotein A synthesis might result in insufficient amounts of apolipoprotein being available for reverse cholesterol transport. The fact that low HDL levels may under some circumstances reflect an enhanced transport of cholesterol through HDL makes it difficult to know whether lPnortestosterone-derived progestogens are atherogenic. Firstly, it would be necessary to determine whether or not the low HDL level is associated with an impaired turnover of cholesterol, i.e. an impeded reverse cholesterol transport. Conventional determination of HDL protein turnover is not useful for this purpose, since each HDL constituent, including free and esterified cholesterol, turns over in HDL with a different half-life. It is beyond the scope of this review to discuss the possible merits of androgenic progestogens other than in regard to the lipoprotein field. Theoretically, nortestosterone-derived progestogens could be beneficial in reducing the levels of some coagulation factors elevated by oestrogen. Although there is no evidence that the lowering of HDL cholesterol by progestational agents or other drugs really increases the risk of CHD, physicians and patients may, in order to be on the safe side, prefer to use a progestogen that does not reduce HDL levels.

Acknowledgements This work was supported Nordisk Insulinfond.

by the Sigrid Juselius

Foundation

(Helsinki)

and The

References 1 Gambrel1 Jr RD. The menopause: benefits and risks of estrogen-progestogen replacement therapy. Fertil Steril 1982; 37: 457-474. 2 Henderson BE. Arteriosclerotic heart disease. In: Judd HL, moderator. Estrogen replacement therapy: indications and complications. Ann Int Med 1983; 98: 195-205. 3 Bengtsson C. Ischemic heart disease in women. Acta Med Stand 1973; 549: 75-81. 4 Kannel WB, Hjortland MC, McNamara PM, Gordon T. Menopause and risk of cardiovascular disease. The Framingham study. Ann Int Med 1976; 85: 447-452. 5 Ross RK, Paganini-Hill A, Mack TM, Arthur M, Henderson BE. Menopausal oestrogen therapy and protection from death from ischaemic heart disease. Lancet 1981; 1: 858-860. 6 Bain C. Willett W, Hennekens CH, Rosner B, Belanger C, Speizer FE. Use of postmenopausal hormones and risk of myocardial infarction. Circulation 1981; 64: 42-46. 7 Rosenberg L, Armstrong B, Hershel J. Myocardial infarction and estrogen therapy in post-menopausal women. N Engl J Med 1976; 294: 1256-1259. 8 Pfeffer RI, Whipple GA, Kurosak TT, Chapman JM. Coronary risk and estrogen use in postmenopausal women. Am J Epidemiol 1978; 107: 479-87. 9 Barr DP. Some chemical factors in the pathogenesis of atherosclerosis. Circulation 1953; 8: 641-654. 10 Russ EM, Eder HA, Barr DP. Influence of gonadal hormones on protein-lipid relationships in human plasma. Am J Med 1955; 15: 4-24.

15 11 Furman steroids

RH, Howard RP, Norcia LN, Keaty EC. The influence of androgens, estrogens and related on serum lipids and lipoproteins. Observations in hypogonadal and normal human subjects.

Am J Med 1958; 24: 80-97. E. Natural oestrogen as an effective treatment for type-II 12 Tikkanen MJ, Nikkila EA. Vartiainen hyperlipoproteinaemia in post-menopausal women. Lancet 1978; 2: 490-492. RB. Role of estrogens and progesterone in the etiology and 13 Gambrel1 Jr RD, Bagnell CA, Greenblatt prevention of endometrial cancer: Review. Am J Obstet Gynecol 1983; 146: 696-707. 14 Castelli WB, Doyle JT, Gordon T, Humes CG, Hjortland MC, Halley SB. Kagan A, Zukel WJ. HDL cholesterol and other lipids in coronary heart disease: the cooperative lipoprotein phenotyping study. Circulation 1977; 55: 767. MC, Kannel WB, Dawber TR. High density lipoprotein as a 15 Gordon T. Castelli WP, Hjortland protective factor against coronary heart disease: the Framingham study. Am J Med 1977; 62: 707-714. In: Have1 RJ, ed. 16 Goldstein JL, Brown MS. LDL receptor defect in familial hypercholesterolemia. Lipid disorders. Med Clin North Am 1982; 66: 335-362. 17 Eisenberg S. High density lipoprotein metabolism. J Lipid Res 1984; 25: 1017-1058. 18 N&kill EA. Kuusi T, Taskinen M-R. Role of lipoprotein lipase and hepatic endothelial lipase in the metabolism of high density lipoproteins: a novel concept on cholesterol transport in HDL cycle. In: Carlson LA, Pemow B, eds. Metabolic risk factors in ischemic cardiovascular disease. New York: Raven Press, 1982: 205-215. 19 Kuusi T. Niklcila EA, Tikkanen MJ, Taskinen M-R. Ehnholm C. Function of hepatic endothelial lipase in lipoprotein metabolism. In: Atherosclerosis VI. New York, Heidelberg, Berlin: SpringerVerlag, 1983; 628-632. of progestogens. J Reprod Med 1982; 27: 490-497. 20 Brenner PF. The pharmacology action of progesterone and the pharmacological effects of progesto21 Neumann F. The physiological gens - a short review. Postgrad Med J 1978; 54 (Suppl 2): 11-24. combinations containing levo22 Bergink EW, Holma P, Pyorala T. Effects of oral contraceptive norgestrel or desogestrel on serum proteins and androgen binding. Stand J Clin Lab Invest 1981; 41: 663-668. 23 Kuusi T, Nikkila EA. Tikkanen MJ, Sipinen S. Effects of two progestins properties on hepatic endothelial lipase and high density lipoprotein-2.

with different Atherosclerosis

androgenic 1985; 54:

251-262. 24 Gustafson A, Svanborg A. Gonadal steroid effects on plasma lipoproteins and individual phospholipids. J Clin Endocrinol Metab 1972; 35: 203-207. 25 Silfverstolue G, Gustafson A, Samsioe G, Svanborg A. Lipid metabolic studies in oophorectomized women. Effects of three different progestogens. Acta Obstet Gynecol Stand 1979: (Suppl) 88: 89-95. V. Effects of different progestogens on lipoproteins during 26 Hirvonen E, Malkiinen M, Manninen postmenopausal replacement therapy. N Engl J Med 1981; 304: 560-563. on lipoprotein 27 Tikkanen MJ, Nikkila EA, Kuusi T, Sipinen S. Effects of oestradiol and levonorgestrel lipids and postheparin plasma lipase activities in normolipoproteinaemic women. Acta Endocrinol 1982; 99: 630-635. MJ, Nikkil’a EA. Kuusi T. Sipinen S. High density lipoprotein-2 and hepatic lipase: 28 Tikkanen reciprocal changes produced by estrogen and norgestrel. J Clin Endocrinol Metab 1982: 54: 1113-1117. A, Samsioe G, Svanborg A. Lipid metabolic studies in oophorectomized 29 Silfverstolpe G, Gustafson women: effects on serum lipids and lipoproteins of three synthetic progestogens. Maturitas 1982; 4: 103-111. and plasma lipoproteins. Submitted for 30 Tikkanen MJ. Nikkila EA. Kuusi T. Oral contraceptives publication. 31 Farish E, Fletcher CD, Hart DM, Kitchener H, Sharpe GLM. A long-term study of the effects of norethisterone on lipoprotein metabolism in menopausal women. Clin Chim Acta 1983; 132: 193-198. U, Wallentin L. r_-norgestrel and progesterone have different influences on 32 F&hraeus L, Larsson-Cohn plasma lipoproteins. Eur J Clin Invest 1983; 13: 447-453. Gustafson A, Samsioe G, Svanborg A. Lipid and carbohydrate metabolism studies in 33 Silfverstolpe.G, oophorectomized women: effects produced by the addition of norethisterone acetate to two estrogen preparations. Arch Gynecol 1982; 231: 279-287.

16 34 Kuusi T, Tikkanen MJ, Nikkila EA, Sipinen S. Lipid metabolic studies with cyproterone acetate. Submitted for publication. 35 Pyorala T. The effect of synthetic and natural estrogens on glucose tolerance, plasma insulin and lipid metabolism in postmenopausal women. In: Campbell S, ed. The management of the menopause and post-menopausal years. Lancaster: MTP Press 1976; 195-210. 36 Wallentin L, Larsson-Cohn U. Metabolic and hormonal effects of post-menopausal oestrogen replacement treatment, II. Plasma lipids. Acta Endocrinol 1977; 86: 597-607. 37 Kekki M, Nikkila EA. Plasma triglyceride turnover during use of oral contraceptives. Metabolism 1971; 20: 878-889. 38 Kissebah AH, Harrigan P, Wynn V. Mechanism of hypertriglyceridemia associated with contraceptive steroids. Horm Metab Res 1973; 5: 184-190. 39 Glueck CJ. Fallat RW, Scheel D. Effects of estrogenic compounds on triglyceride kinetics. Metabolism 1975; 24: 537-545. 40 Glueck CJ, Levy RI. Fredrickson DS. Norethindrone acetate, postheparin lipolytic activity, and plasma triglycerides in familial types I, II, IV and V hyperlipoproteinemia. Ann Int Med 1971; 75: 345-352. 41 Nikkila EA, Tikkanen MJ, Kuusi T. Effects of progestins on plasma lipoproteins and heparin-releasable lipases. In: Bardin CW, Milgrom E, Mauvais-Jarvis P. eds. Progesterone and progestins. New York: Raven Press, 1983; 415-424. 42 Glueck CJ, Ford S, Steiner P, Fallat R. Triglyceride removal efficiency and lipoprotein lipases: effects of oxandrolone. Metabolism 1973; 22: 807-814. 43 Wolfe BM, Grace DM. Norethindrone acetate inhibition of splanchnic triglyceride secretion in conscious glucose-fed swine. J Lipid Res 1979; 20: 175-182. 44 Cheng DCH, Wolfe BM. Norethindrone acetate inhibition of triglyceride synthesis and release by rat hepatocytes. Atherosclerosis 1983; 46: 41-48. 45 Mattsson L-A. Cullberg G, Samsioe G. A continuous estrogen-progestin regimen for climacteric complaints. Effects on lipid and lipoprotein metabolism. Acta Obstet Gynecol Stand 1984. 46 Furman RH. Alaupovic P, Howard RP. Effects of androgens and estrogens on serum lipids and the composition and concentration of serum lipoproteins in normolipidemic and hyperhpidemic states. Prog Biochem Pharmacol 1967; 2: 215-249. 47 Robinson RW, Lebeau RJ. Effect of conjugated equine estrogens on serum lipids and the clotting mechanism. J Atheroscler Res 1965; 5: 120-124. 48 Tikkanen MJ, Nikkila EA, Kuusi T, Sipinen S. Reduction of plasma high-density lipoprotein-2 cholesterol and increase of postheparin plasma hepatic lipase activity during progestin treatment. Clin Chim Acta 1981; 115: 63-71. 49 Tikkanen MJ, Nikkill EA, Kuusi T, Sipinen S. Different effects of two progestins on plasma high density lipoprotein (HDLZ) and postheparin plasma hepatic lipase activity. Atherosclerosis 1981; 40: 365-369. 50 Gronroos M, Lehtonen A. Effect of high dose progestin on serum lipids. Atherosclerosis 1983; 47: 101-105. 51 Glueck CJ, Gartside P, Fallat RW, Mendoza S. Effect of sex hormones on protamine inactivated and resistant postheparin plasma lipases. Metabolism 1976; 25: 625-632. 52 Applebaum DM, Goldberg AP, Pykahsto OJ, Brunzell JD, Hazzard WR. Effect of estrogen on post-heparin lipolytic activity. Selective decline in hepatic triglyceride hpase. J Clin Invest 1977; 59: 601-608. 53 Tikkanen MJ. Kuusi T, Vartiainen E. Nikkila EA. Treatment of post-menopausal hypercholestrerolaemia with estradiol. Acta Obstet Gynecol Stand 1979; (Suppl.) 88: 83-88. 54 Krauss RM, Levy RI, Fredrickson DS. Selective measurement of lipoprotein lipase and hepatic hpase in post-heparin plasma. In: Schettler G, Weizel A, eds. Atherosclerosis III. New York: Springer-Verlag 1973; 561-564. 55 Ehnholm C. Huttunen JK, Kinnunen PJ, Miettinen TA, Nikkila EA. Effect of oxandrolone treatment on the activity of lipoprotein lipase, hepatic lipase and phospholipase Al of human postheparin plasma. N Engl J Med 1975; 292: 1314-1317.

17 56 Taggart HM, Applebaum-Bowden D, Haffner S, Wamick GR, Cbeung MC, Albers JJ, Chestnut Ill CH, Hazzard WR. Reduction in high density lipoproteins by anabolic steroid (stanozolol) therapy for postmenopausal osteoporosis. Metabolism 1982; 31: 1147-1152. 57 Kuusi T, Saarinen P, Nikkill EA. Evidence for the role of hepatic endothelial lipase in the metabolism of plasma high density lipoprotein-2 in man. Atherosclerosis 1980; 36: 589-593. 58 Jansen H, van To1 A, Htilsmann WC. On the metabolic function of heparin-releasable liver lipase. Biochem Biophys Res Commun 1980; 92: 53-59. 59 Silfverstolpe G, Johnson P, Samsioe G, Svanborg A, Gustafson A. Lipid metabolic studies in oophorectomized women. Effects induced by the addition of norethisterone acetate to two different oestrogens on serum individual phospholipids and serum lecithin fatty acid composition. Acta Endocrinoll981; 96: 527-533. 60 Shaefer ET, Foster DM, Zech LA, Lindgren FT, Brewer Jr HB, Levy RI. The effects of estrogen administration on plasma lipoprotein metabolism in premenopausal females. J Clin Endocrinol Metab 1983; 57: 262-267. 61 Solyom A. Effect of androgens on serum lipids and lipoproteins. Lipids 1972; 7: 100-105. 62 Haffner SM, Kushwaha S, Foster DM, Applebaum-Bowden D, Hazzard WR. Studies on the metabolic mechanisms of reduced high density lipoproteins during anabolic steroid therapy. Metabolism 1983; 32: 413-420. 63 Tamai T, Nakai T, Yamada S. Kobayashi T, Hayashi T, Kutsumi Y. Takeda R. Effects of oxandrolone on plasma lipoproteins in patients with type lla, llb and IV hyperlipoproteinemia: occurrence of hypo-high density lipoproteinemia. Artery 1979; 5: 125-143.