0021-972X/82/5406-1113$02.00/0 Journal of Clinical Endocrinology and Metabolism Copyright © 1982 by The Endocrine Society

Vol. 54, No. 6 Printed in U.S.A.

High Density Lipoprotein-2 and Hepatic Lipase: Reciprocal Changes Produced by Estrogen and Norgestrel* MATTI J. TIKKANEN, ESKO A. NIKKILA, TIMO KUUSI, AND SEPPO SIPINEN Third Department of Medicine, University of Helsinki (M.J.T., E.A.N., T.K.), and the State Maternity Hospital (S.S), Helsinki, Finland

ABSTRACT. The concentrations of plasma high density lipoprotein (HDL) and its subtraction HDL2 are influenced by endogenous and exogenous sex hormones. The catabolism of HDL2 is mediated by a lipolytic enzyme, hepatic lipase, which is present in endothelial cells covering the liver sinusoids. Since the activity of this enzyme is also regulated by gonadal and anabolic steroids, we examined whether the effect of sex steroids on plasma HDL is related to changes in hepatic lipase. In postmenopausal women, estradiol valerate (2 mg/day, orally) increased the HDL2 cholesterol and phospholipid concentrations by 20% (P < 0.05). Simultaneously, the hepatic lipase activity of

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postheparin plasma decreased by 25% (P < 0.05). The addition of levonorgestrel (250 /xg/day, orally) to the treatment reversed both effects of estrogen, so that HDL2 cholesterol and phospholipid levels fell below and hepatic lipase activity rose above the respective pretreatment values. The hormones did not influence the HDL3 lipid concentrations or the lipoprotein lipase and lecithinxholesterol acyltransferase activities. The results are compatible with the hypothesis that the effects of sex steroids on plasma HDL (HDL2) are mediated by changes in hepatic lipase activity. (J Clin Endocrinol Metab 54: 1113,1982)

the degradation of plasma HDL, particularly HDL2 (1216). The purpose of the present study was to examine the concentration and composition of HDL2 and HDL3 and the HL activity during the administration of estradiol valerate and norgestrel. In addition, the postheparin plasma lipoprotein lipase (LPL) activity and the plasma lecithinxholesterol acyl transfer (LCAT) rate were determined.

NDROGENS (1), androgen-derived anabolic steroids (2), and progestational steroids (3,4) decrease the plasma high density lipoprotein (HDL)1 concentration, whereas synthetic alkylated (5) and nonalkylated estrogens (6, 7) as well as conjugated equine estrogens have the opposite effect. The basis for this remarkable sex steroid sensitivity exhibited by plasma HDL is not known with certainty. We have previously suggested that hepatic lipase (HL), a heparin-releasable enzyme located on the endothelium of liver sinusoids (8), could be the mediator of the sex hormone effects on plasma HDL and on its subtraction HDL2 (9, 10). The estradiol-induced increase in HDL lipids is accompanied by a decrease in postheparin plasma HL activity (9, 11), and conversely, the levonorgestrel-induced decrease in HDL lipids is associated with an increase in postheparin plasma HL activity (9,10). The reciprocal behavior of these changes lends support to the suggestion that HL participates in

Subjects and Methods

Received September 18,1981. Address all correspondence and requests for reprints to: Esko A. Nikkila, M.D., Third Department of Medicine, 00290 Helsinki 29, Finland. * This work was supported by grants from the Sigrid Juselius Foundation, the University of Helsinki (to T.K.), and the Finnish State Medical Research Council. 1 The following abbreviations and definitions are used: HDL (density range, 1.063-1.21 g/ml); HDL2 (density range, 1.063-1.125 g/ml); HDL3 (density range, 1.125-1.21 g/ml); LDL (density range, 1.006-1.063 g/ ml); VLDL (density range < 1.006 g/ml).

Sixteen postmenopausal women (aged 42-61 yr) volunteered for the study. Except for vasomotor symptoms, all were in good health, and none had received any regular drug treatment for at least 1 month before the study. The subjects had normal serum triglyceride (TG; 0.59 to 1.77 mmol/liter) and very low density lipoprotein (VLDL) TG concentrations (0.05 >0.05

ment. The magnitude of change in HDL2 Choi during estradiol treatment was inversely correlated with the change in HL activity during the same period (Fig. 4). LCAT activity The activity of LCAT was not significantly changed during either period of hormone administration. This statement applies equally to values expressed as the fractional esteriflcation rate or the molar fatty acyl transfer rate (Table 3). Discussion A series of studies during the last 25 yr have established that plasma HDL levels are influenced by endogenous and exogenous sex steroids. Estrogenic hormones increase and androgenic or anabolic steroids decrease HDL Choi and PL (1, 2, 5-7). A similar difference is present between the HDL values of normal females and males (23). The sex difference is expressed mainly in the less dense HDL2 subtraction, being greatest in the most lipidrich particles (HDL2b) of the HDL spectrum (23). Exogenous estrogens also cause an increase in the HDL2a and HDL2b subtractions (24), but observations of their effects on HDL3 are somewhat contradictory (24, 25). The influence of exogenous androgens on HDL subtractions has not been described so far. The effects of progestational steroids on plasma HDL are variable (3, 4, 26). The progestins with androgenic activity, such as levonorgestrel (3, 10, 27) and norethindrone (24), decrease the HDL Choi levels, while the less androgenic medroxyprogesterone has only a slight effect on the lipoprotein concentrations (4, 26). The reduction is limited to the HDL2 subtraction, with no change in HDL3. In contraceptive pills, the progestins may completely abolish the increase in HDL caused by the estrogenic component (28). Our present results show that levonorgestrel reduces selectively the HDL2 concentration, leaving the HDL3 levels unchanged. Moreover, at a dose level of 250 jug levonorgestrel prevented the effect of estradiol on HDL2 and caused a significant drop of HDL2 Choi and PL to even lower levels than those present before any hormonal treatment. The hepatic endothelial lipase has recently turned out

JCE & M • 1982 Vol 54 • No 6

to be a target of gonadal hormones. That this enzyme is regulated by endogenous sex hormones is shown by the significantly lower postheparin plasma HL activity in women compared to men (29). Elevations in postheparin plasma HL activity have been reported during the administration of several steroids with androgenic activity, including oxandrolone (30), norethindrone (31), and levonorgestrel (10). Conversely, conjugated equine estrogens (32), alkylated synthetic estrogens (33), and the nonalkylated estradiol (11) all suppress HL activity. On the other hand, medroxyprogesterone acetate, a progestational steroid with little androgenic or estrogenic activity, does not significantly influence HL activity (26). In the present study, estradiol suppressed HL, but the simultaneous administration of levonorgestrel reversed this effect, resulting in markedly higher HL activity than that observed before any hormonal treatment. On the basis of the above studies it is evident that androgenic and estrogenic steroids have reciprocal effects on plasma HDL2 levels and HL activity. An increase in HL is accompanied by a decrease in HDL2 Choi, while a decrease in HL activity is associated with an increase in HDL2. Furthermore, when the HL activity is not changed by a steroid such as medroxyprogesterone, the HDL2 also remains unaffected. These changes suggest that the sex steroid-induced alterations of plasma HDL2 levels may be secondary to the effect of the hormones on the steroidsensitive HL. A series of recent observations has led to the conclusion that hepatic endothelial lipase has a major physiological role in the uptake and catabolism of HDL2 lipids in the liver. The lipase is located on the luminal surface of the hepatic endothelial cells (8), and inhibition of its activity by a specific antiserum in rats leads to an increase in HDL Choi and PL (12, 13). In normal human subjects, the HDL2 Choi and PL concentrations show a significant inverse correlation with postheparin plasma HL activity, whereas no association is present between HDL3 and HL (14). HL binds to HDL (34) and hydrolyzes the PL in HDL2 in preference to those in HDL3 or LDL (15, 16). All of this evidence indicates that hepatic endothelial lipase is a relatively specific HDL2 phospholipase and that it may act in the hepatic uptake of Choi and in the conversion of HDL2 to HDL3 (14-16). The precise mechanism by which gonadal steroids regulate the activity of HL remains unknown. Probably, they induce or repress the synthesis of the enzyme protein. On the other hand, they could bind to the enzyme and cause conformational changes, which either increase or decrease the enzyme activity. In addition to HL, the HDL2 concentration is regulated by LPL, which stimulates the formation of HDL2 from surface constituents of VLDL and chylomicrons (27, 35, 36). Since neither estrogen nor progestin caused any

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FEMALE SEX STEROIDS, PLASMA HDLa AND HEPATIC LIPASE

change in the activity of LPL, the alterations of the HDL2 level induced by these hormones could not be accounted for by this mechanism. It is remarkable, however, that the HDL2 levels showed a significant correlation with LPL activity during suppression of the HL activity by estrogen, but not when the HL activity was elevated by norgestrel. This finding is in good accordance with the hypothesis of a dual regulation of the HDL2 concentration by the two enzymes (27).

Acknowledgments The skillful technical assistance of Miss Paula Teravainen, Mrs. Sirkka-Liisa Runeberg, and Mrs. Sirkka Mannelin is gratefully acknowledged.

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