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Changes in serum high density lipoproteins in women on oral contraceptive drugs
465
Clinica Chimico Acta, 80 (1977) 465-470 @ Elsevier/North-Holland Biomedical Press
CCA 8860
CHANGES IN SERUM HIGH DENSITY ON ORAL CONTRACEPTIVE DRUGS
LIPOPROTEINS
IN WOMEN
RONALD M. KRAUSS ‘q*, FRANK T. LINDGREN *, ABRAHAM SILVERS b***, RAJENDRA JUTAGIR band DOUGLAS D. BRADLEY b a Donner Laboratory of Medical Physics and Biophysics, Biomedical Division, Lawrence Berkeley Laboratory, University of California, Berkeley, CA 94720, and b Kaiser Medical Center, Walnut Creek, CA 94596 (U.S.A.) (Received April 13th, 1977)
Summary Serum lipids, lipoproteins, and lipoprotein subfractions were measured in a group of 18 women aged 20 through 39 who were users of oral contraceptive drugs, and in 19 age-matched controls. Concentrations of the major lipid and lipoprotein classes were higher in the users, but the elevation was statistically significant only in the case of the high density lipoproteins. This increase was shown to be due to a highly significant increase (275 f 9 vs. 223 + 9 mg/lOO ml, p < 0.005) in the denser high density lipoprotein subfraction (HDL3). Levels of the other subfraction (HDL2) were similar in users and controls. Thus, anovulatory steroids have selective effects on individual types of high density lipoproteins. Studies of such specific effects may help to further define the functional properties of the high density lipoproteins such as their apparent protective role in atherosclerosis.
Introduction Oral contraceptive use has been associated with changes in serum lipids and lipoproteins. Triglyceride concentrations increase, along with levels of very low density lipoproteins [l-9]. Concentrations of cholesterol and low density and high density lipoproteins may also increase [l-5], but the changes are variable [ 6-91, and may depend on the relative amounts of estrogen and progestin in the preparation [ 8,9]. * Address all correspondence and reprint requests to: Dr. Ronald M. Krause. Donna Laboratory. University of California, Berkeley. CA 94720. U.S.A. ** Dr. Silvers’ present address is the Department of Epidemiology, Mayo Clinic, Rochester. MN MN 55901. U.S.A.
466
Recent studies have shown that oral contraceptive use is associated with an increased incidence of premature coronary disease [lO,ll]. It has been suggested that this may be due, in part, to the effects of these drugs on serum lipids and lipoproteins, and particularly to the increase in triglycerides and very low density lipoproteins [ 121. It is not known, however, whether such an increase contributes significantly to coronary risk [13]. Other reports have focused on the inverse relationship between high density lipoprotein concentrations and coronary disease, and this has been proposed as a major independent coronary risk factor [ 14-181. In this study, serum lipoprotein concentrations in women using combined estrogen-progestin contraceptive agents were compared with those in an agematched control group. Special attention was given to possible changes in levels of the high density lipoprotein fractions. Materials and methods Subjects were females, 20-39 years of age, enrolled in the Kaiser Health Plan, Walnut Creek, California. Informed consent was obtained, and the research was carried out according to the Declaration of Helsinki. Blood samples were obtained after a 12-h fast from 18 women currently taking combination oral contraceptive agents, and from 19 age-matched women who had never used these drugs. Mean body weight, blood pressure, and smoking habits were similar in the two groups. Table I shows the oral contraceptive agents being used by the subjects; none were of the sequential type. The minimum duration of continuous oral contraceptive use was 11.5 months. Blood samples were taken on random days of the drug cycle. All subjects were consuming normal American diets, and were found to be free of diabetes, cardiac, renal, or hepatic disease as judged by a detailed multiphasic examination [ 191. Serum cholesterol and triglyceride concentrations were determined by AutoAnalyzer (AA II) techniques [ 201. Serum lipoproteins were measured by analytic ultracentrifugation (Beckman, Model E) with computerized quantitation as previously described [21]. The high density lipoproteins were measured after division of the Schlieren pattern into two density classes (FF.,,, O-3.5 and 3.5-9) which approximate the HDL3 and HDLz subfractions separable in the preparative ultracentrifuge (Fig. 1). The concentrations of cholesterol and tri-
TABLE
I
TYPES
OF
ORAL
CONTRACEPTIVE
DRUGS
USED Progestin
Estrogen
Number subjects
Mestranol
0.05
mg
Norethindrone
1.0
mg
Mestranol
0.08
mg
Norethindrone
1.0
mg
1
Mestranol
0.10
mg
Ethynodiol
1.0
mg
3 1
Mestranol
diacetate
5
0.10
mg
Norethindrone
2.0
mg
Ethinyl
estradiol
0.035
mg
Norethindrone
0.5
mg
1
Ethinyl
estradiol
0.05
mg
Norgestrel
0.5
mg
5
Etbinyl
estradiol
0.05
mg
Norethindrone
1.0
mg
2
acetate
of
467 High 1.05
density
I
L
lipoprotein
I
I
Ultracentrifuge 9
spectrum 1.10
I
I
f lototion
1.20g/ml
I111111111
analysis 3.5
Fig. 1. Density and ultracentrifugal flotation sents the rate of flotation of the lipoproteins tional to the density of the lipoprotein.
( FtzO rote) 0
characteristics in a solution
of the high density lipoproteins. Fy.29 repreof density 1.20 at 26°C. This rate is propor-
glyceride in serum high density lipoproteins were measured of serum with heparin and manganese chloride [ 201.
after precipitation
Results
Serum lipid concentrations Mean values for total serum cholesterol and triglyceride concentrations, and the concentrations of these lipids in high density lipoproteins for both oral contraceptive users and controls are presented in Table II. The mean values were all higher in users, but the differences were not significant (p > 0.05).
Serum lipoprotein concentrations The analytic ultracentrifuge was used to measure concentrations of serum lipoproteins in various density classes (Table III). Levels of very low density lipoproteins (Sf” 20-400) and two subclasses (SF 20-100, 100-400) did not differ significantly between the users and controls. There was a tendency TABLE
II
SERUM AND HIGH DENSITY TIVE USERS AND CONTROLS
LIPOPROTEIN
LIPID
mg/dl (mean Non-users (n = 19) Cholesterol Total serum High density Triglycerides Total swum High density
lipoproteins
208.1 56.8
lipoproteins
99.4 19.8
?: f
CONCENTRATIONS
? S.E.) Users (n = 18)
7.9 3.8
219.5 62.8
+ ?:
9.0 3.5
f 10.4 + 1.3
117.9 24.4
f 11.1 f 1.9
IN ORAL
CONTRACEP-
468 TABLE
III
SERUM
LIPOPROTEIN
CONCENTRATIONS
IN
ORAL
CONTRACEPTIVE
USERS
AND
CONTROLS
Lipoprotein
mg/dI
(mean
t S.E.)
fraction
Very
low
20-100
s’: Low
50.5
+ 10.8
64.9
43.4
+
8.9
55.7
_c
2.2
9.2
100-400
7.1
+ 13.0 f 11.2 i
2.3
density Total S1
o-
12
SF
lZ--
20
High
338.3
C 23.0
371.1
+ 28.3
318.1
t 18.7
353.6
+_ 26.3
20.2
+
17.5
5.4
*
4.1
density
Total -3.5
G.20
0
FT.20
3.6-9.0
*p< **
Users (n = 18)
density
Total Sf
Non-users (n = 19)
328.3
? 19.2
*
386.4
223.3
+
**
275.2?
105.0
+ 14.3
8.6
? 19.4
111.2
*
8.9
**
f 14.3
0.05.
p < 0.005.
toward higher concentrations of the major low density lipoprotein subfraction Sfo O-12 in users, but the variation was large and the difference not statistically significant (p > 0.05). SF 12-20 lipoprotein levels were nearly identical in the two groups. Analysis of the high density lipoproteins revealed a significantly (p < 0.05) higher level in oral contraceptive users (Table III). This increase was almost totally accounted for by an elevation of the denser (Ff_,, O-3.5) subfraction.
Fig.
2.
and
controls
trols).
Serum The
high (solid
shaded
density line).
lipoprotein The
curves
area represents
distributions represent
the difference
the
in women means
between
on
oral
of
the
values
the
two
curves.
contraceptive for
each
group
drugs (18
(dashed users,
line)
19 con-
469
Levels of the other major component, FFszO 3.5-9, were similar in the two groups. The mean high density lipoprotein distributions are shown in Fig. 2. Because of the variation in type and dose of contraceptive drug being used, relationships between these variables and the lipoprotein fractions could not be determined. Discussion Sex steroid hormones appear to have a major influence on serum lipoprotein distributions. For example, premenopausal females have lower concentrations of very low density lipoproteins and higher concentrations of HDLII than males in similar age groups [ 221. Furthermore, exogenous gonadal steroids and their analogs can cause substantial changes in serum lipid and lipoprotein levels [l-9,23,24]. The present study was undertaken to define the effects of combined estrogen-progestin contraceptive drugs on the high density lipoproteins in normal menstruating women. Analytic ultracentrifugation revealed a significantly higher concentration of total high density lipoproteins in the group of contraceptive users than in controls. Levels of high density lipoprotein cholesterol and triglyceride, measured after precipitation of serum with heparin and manganese chloride [20], did not discriminate between the two groups. This result may have been due to small sample size, or nonspecific precipitation [25], but it raises the possibility that constituents other than cholesterol (i.e., phospholipids and/or proteins) may account for a large proportion of the increase in total high density lipoprotein mass in the oral contraceptive users. It has previously been reported that estrogen administration results in a significant increase in the protein concentration of high density lipoproteins [ 241, With the analytic ultracentrifuge, measurements were made of two major high density lipoprotein subfractions, FF.,, O-3.5 and FP,, 3.5-9. These density classes correspond approximately to the HDL3 and HbL2 subfractions previously defined by preparative ultracentrifugation [ 21,221. The results showed that the elevation of total high density lipoprote~ was due to a selective and highly significant increase in the denser subfraction (FP,, O-3.5). Given the variation in type and amount of component estrogens and progestins in oral contraceptive preparations, it is not possible to identify the separate contributions of these steroids to the lipoprotein changes observed in this study. Estrogens and androgens have been shown to exert opposing effects on serum ~iglyceride and low and high density lipopro~in concentrations with the effects of combinations dependent on the amounts of each [ 241. Studies of various synthetic progestins have shown that nortestosterone derivatives tend to counteract the hypertriglyceridemic effect of estrogens [ 8,9] much as do the more androgenic testosterone derivatives [24]. This may help to explain the relatively small elevation of serum triglycerides observed in the group of oral contraceptive users in the present study, since most of the subjects were using preparations containing nortestosterone analogs (Table I). It is likely that the progestational components of the oral contraceptives also modify the increase in high density lipoproteins known to occur with estrogen treatment [24]. Preliminary studies from this laboratory [26] have shown that estrogen treatment results in higher levels of both HDLz and HDLJ lipoproteins in contrast to the
470
isolated increase in HDL3 shown here for estrogen-progestin combinations. A number of groups have reported that increased levels of high density lipoprotein cholesterol are associated with reduced risk of coronary artery disease [ 13-171. The consequences of an increase in HDL3 lipoproteins without a proportional increase in high density lipoprotein cholesterol are not known. Oral contraceptive drug users appear to have a higher incidence of coronary events than non-users [ 9,101. This suggests that if HDL3 elevation does have a protective role, it is not sufficient to overcome the effects of oral contraceptives which may predispose to coronary disease. Acknowledgements This work was supported in part by Contract NOl-HD-3-2710, Center for Population Research, National Institutes of Child Health and Development, National Institutes of Health Grant l-OPl-HL-18574-01, and the United States Energy Research and Development Administration. We thank Dr. S. Ramcharan for her enthusiasm and support of this project. We also thank Suzanne Pan for able computer analysis of data. References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
20 21 22 23 24 25 26
Wynn. V.. Dear. J.W.H. and Mills. G.L. (1966) Lancet ii, 720-723 AureII. M., Cramer, K. and Rybo. G. (1966) Lancet i, 291-293 Sach, B.A., W&man, L. and Herzig, H. (1969) Obstet. Gynecol. 34. 530-535 Wynn. V., Dear. J.W.H.. MilIs, G.L. and Stokes, T. (1969) Lancet ii, 756-760 Barton. G.M.G.. Freeman, P.R. and Lawson, J.P. (1970) J. Obstet. Gynaecol. Br. Commons. 77, 551-554 Corredor, D.G.. Mendelsohn, L.V.. Sabeh, G., Sunder, J.H. and Danowski, T.S. (1970) CIm. Pharmacol. Ther. 11.188-193 Schenker, J.B.. Pinson, A. and Polishuk. W.Z. (1971) FertiI. Steril. 22.604-608 Stokes, T., Wynn. V. (1971) Lancet ii, 677-680 Beck, P. (1973) Metabolism 22, 841-855 Mann. J.I., Vessey. M.P., Thorogood, M. and Doll. R. (1975) Br. Med. J. 2. 241-245 Mann. J.I. and Inman, W.H.W. (1975) Br. Med. J. 2.245-248 Stern, M.P.. Brown, Jr., B.W.. HaskeII, W.L.. Farquhar, J.W.. Wehrle. C.L. and Wood. P.D. (1976) J. Am. Med. Assoc. 235.811-815 Kannel. W.B., CasteIli, W.P.. Gordon, T. and McNamara, P.M. (1971) Ann. Intern. Med. 74, l-12 Barr, D.P.. Russ, E.M. and Eder, H.A. (1951) Am. J. Med. 11.480-493 Seamy, R.L. and Bergquist. L.M. (1962) in Lipoprotein Chemistry in Health and Disease, P. 162. Charles C. Thomas, Springfield, IL, U.S.A. Miller. G.H. and Miller, N.E. (1975) Lancet i, 16-19 CasteIli, W.P., Doyle, J.T., Gordon, T.. Hames. C., HuIIey, S.B., Kagan, A., McGee, D.. Vici, W.J. and Zukel, W.J. (1975) Circulation 51 & 52 (Suppl. II), II-97 Rhoads. G.G.. Gulbrandsen, C.L. and Kagan. A. (1976) N. Eng. J. Med. 294.293-298 Ramcharan, S. (ed.) (1974) The Walnut Creek Contraceptive Drug Study. A Prospective Study of the Side Effects of Oral Contraceptives. Vol. 1, DHEW Publication No. (NIH) 74-562. U.S. Government Printing Office, Washington, D.C. Manual of Laboratory Operations, Lipid Research Clinics Program, Vol. 1. Lipid and Lipoprotein Analysis. DHEW Publication No. (NIH) 75-628, U.S. Government Printing Office. Washington, D.C. Ewing, A.M., Freeman. N.K. and Lindgren, F.T. (1965) in Advances in Lipid Research (Paoletti. R. and Kritchevsky. D.. eds.), Vol. III, pp. 25-61, Academic Press, New York Nichols, A.V. (1967) in Advances in Biological and Medical Physics (Lawrence, J.H. and Gofman, J.W., eds.), Vol. 11, pp. 109-158, Academic Press, New York Barr, D.P. (1955) J. Chronic Dis. 1,63-85 Furman, R.H.. Alaupovic. P. and Howard. R.P. (1967) in Progress in Biochemical Pharmacology (Kritchevsky, D., Paoletti, R. and Steinberg, D., eds.). Vol. 2, PP. 215-249, Karger, Base1 and New York Srinivasan, S.. Radhakrishnamurthy. B. and Berenson, G.S. (1975) Arch. Biochem. Biophys. 170. 334-340 Krauss, R.M.. Lindgren. F.T., Wood, P.D.S. and Von der Groeben, J.. in preparation
Clinica Chimico Acta, 80 (1977) 465-470 @ Elsevier/North-Holland Biomedical Press
CCA 8860
CHANGES IN SERUM HIGH DENSITY ON ORAL CONTRACEPTIVE DRUGS
LIPOPROTEINS
IN WOMEN
RONALD M. KRAUSS ‘q*, FRANK T. LINDGREN *, ABRAHAM SILVERS b***, RAJENDRA JUTAGIR band DOUGLAS D. BRADLEY b a Donner Laboratory of Medical Physics and Biophysics, Biomedical Division, Lawrence Berkeley Laboratory, University of California, Berkeley, CA 94720, and b Kaiser Medical Center, Walnut Creek, CA 94596 (U.S.A.) (Received April 13th, 1977)
Summary Serum lipids, lipoproteins, and lipoprotein subfractions were measured in a group of 18 women aged 20 through 39 who were users of oral contraceptive drugs, and in 19 age-matched controls. Concentrations of the major lipid and lipoprotein classes were higher in the users, but the elevation was statistically significant only in the case of the high density lipoproteins. This increase was shown to be due to a highly significant increase (275 f 9 vs. 223 + 9 mg/lOO ml, p < 0.005) in the denser high density lipoprotein subfraction (HDL3). Levels of the other subfraction (HDL2) were similar in users and controls. Thus, anovulatory steroids have selective effects on individual types of high density lipoproteins. Studies of such specific effects may help to further define the functional properties of the high density lipoproteins such as their apparent protective role in atherosclerosis.
Introduction Oral contraceptive use has been associated with changes in serum lipids and lipoproteins. Triglyceride concentrations increase, along with levels of very low density lipoproteins [l-9]. Concentrations of cholesterol and low density and high density lipoproteins may also increase [l-5], but the changes are variable [ 6-91, and may depend on the relative amounts of estrogen and progestin in the preparation [ 8,9]. * Address all correspondence and reprint requests to: Dr. Ronald M. Krause. Donna Laboratory. University of California, Berkeley. CA 94720. U.S.A. ** Dr. Silvers’ present address is the Department of Epidemiology, Mayo Clinic, Rochester. MN MN 55901. U.S.A.
466
Recent studies have shown that oral contraceptive use is associated with an increased incidence of premature coronary disease [lO,ll]. It has been suggested that this may be due, in part, to the effects of these drugs on serum lipids and lipoproteins, and particularly to the increase in triglycerides and very low density lipoproteins [ 121. It is not known, however, whether such an increase contributes significantly to coronary risk [13]. Other reports have focused on the inverse relationship between high density lipoprotein concentrations and coronary disease, and this has been proposed as a major independent coronary risk factor [ 14-181. In this study, serum lipoprotein concentrations in women using combined estrogen-progestin contraceptive agents were compared with those in an agematched control group. Special attention was given to possible changes in levels of the high density lipoprotein fractions. Materials and methods Subjects were females, 20-39 years of age, enrolled in the Kaiser Health Plan, Walnut Creek, California. Informed consent was obtained, and the research was carried out according to the Declaration of Helsinki. Blood samples were obtained after a 12-h fast from 18 women currently taking combination oral contraceptive agents, and from 19 age-matched women who had never used these drugs. Mean body weight, blood pressure, and smoking habits were similar in the two groups. Table I shows the oral contraceptive agents being used by the subjects; none were of the sequential type. The minimum duration of continuous oral contraceptive use was 11.5 months. Blood samples were taken on random days of the drug cycle. All subjects were consuming normal American diets, and were found to be free of diabetes, cardiac, renal, or hepatic disease as judged by a detailed multiphasic examination [ 191. Serum cholesterol and triglyceride concentrations were determined by AutoAnalyzer (AA II) techniques [ 201. Serum lipoproteins were measured by analytic ultracentrifugation (Beckman, Model E) with computerized quantitation as previously described [21]. The high density lipoproteins were measured after division of the Schlieren pattern into two density classes (FF.,,, O-3.5 and 3.5-9) which approximate the HDL3 and HDLz subfractions separable in the preparative ultracentrifuge (Fig. 1). The concentrations of cholesterol and tri-
TABLE
I
TYPES
OF
ORAL
CONTRACEPTIVE
DRUGS
USED Progestin
Estrogen
Number subjects
Mestranol
0.05
mg
Norethindrone
1.0
mg
Mestranol
0.08
mg
Norethindrone
1.0
mg
1
Mestranol
0.10
mg
Ethynodiol
1.0
mg
3 1
Mestranol
diacetate
5
0.10
mg
Norethindrone
2.0
mg
Ethinyl
estradiol
0.035
mg
Norethindrone
0.5
mg
1
Ethinyl
estradiol
0.05
mg
Norgestrel
0.5
mg
5
Etbinyl
estradiol
0.05
mg
Norethindrone
1.0
mg
2
acetate
of
467 High 1.05
density
I
L
lipoprotein
I
I
Ultracentrifuge 9
spectrum 1.10
I
I
f lototion
1.20g/ml
I111111111
analysis 3.5
Fig. 1. Density and ultracentrifugal flotation sents the rate of flotation of the lipoproteins tional to the density of the lipoprotein.
( FtzO rote) 0
characteristics in a solution
of the high density lipoproteins. Fy.29 repreof density 1.20 at 26°C. This rate is propor-
glyceride in serum high density lipoproteins were measured of serum with heparin and manganese chloride [ 201.
after precipitation
Results
Serum lipid concentrations Mean values for total serum cholesterol and triglyceride concentrations, and the concentrations of these lipids in high density lipoproteins for both oral contraceptive users and controls are presented in Table II. The mean values were all higher in users, but the differences were not significant (p > 0.05).
Serum lipoprotein concentrations The analytic ultracentrifuge was used to measure concentrations of serum lipoproteins in various density classes (Table III). Levels of very low density lipoproteins (Sf” 20-400) and two subclasses (SF 20-100, 100-400) did not differ significantly between the users and controls. There was a tendency TABLE
II
SERUM AND HIGH DENSITY TIVE USERS AND CONTROLS
LIPOPROTEIN
LIPID
mg/dl (mean Non-users (n = 19) Cholesterol Total serum High density Triglycerides Total swum High density
lipoproteins
208.1 56.8
lipoproteins
99.4 19.8
?: f
CONCENTRATIONS
? S.E.) Users (n = 18)
7.9 3.8
219.5 62.8
+ ?:
9.0 3.5
f 10.4 + 1.3
117.9 24.4
f 11.1 f 1.9
IN ORAL
CONTRACEP-
468 TABLE
III
SERUM
LIPOPROTEIN
CONCENTRATIONS
IN
ORAL
CONTRACEPTIVE
USERS
AND
CONTROLS
Lipoprotein
mg/dI
(mean
t S.E.)
fraction
Very
low
20-100
s’: Low
50.5
+ 10.8
64.9
43.4
+
8.9
55.7
_c
2.2
9.2
100-400
7.1
+ 13.0 f 11.2 i
2.3
density Total S1
o-
12
SF
lZ--
20
High
338.3
C 23.0
371.1
+ 28.3
318.1
t 18.7
353.6
+_ 26.3
20.2
+
17.5
5.4
*
4.1
density
Total -3.5
G.20
0
FT.20
3.6-9.0
*p< **
Users (n = 18)
density
Total Sf
Non-users (n = 19)
328.3
? 19.2
*
386.4
223.3
+
**
275.2?
105.0
+ 14.3
8.6
? 19.4
111.2
*
8.9
**
f 14.3
0.05.
p < 0.005.
toward higher concentrations of the major low density lipoprotein subfraction Sfo O-12 in users, but the variation was large and the difference not statistically significant (p > 0.05). SF 12-20 lipoprotein levels were nearly identical in the two groups. Analysis of the high density lipoproteins revealed a significantly (p < 0.05) higher level in oral contraceptive users (Table III). This increase was almost totally accounted for by an elevation of the denser (Ff_,, O-3.5) subfraction.
Fig.
2.
and
controls
trols).
Serum The
high (solid
shaded
density line).
lipoprotein The
curves
area represents
distributions represent
the difference
the
in women means
between
on
oral
of
the
values
the
two
curves.
contraceptive for
each
group
drugs (18
(dashed users,
line)
19 con-
469
Levels of the other major component, FFszO 3.5-9, were similar in the two groups. The mean high density lipoprotein distributions are shown in Fig. 2. Because of the variation in type and dose of contraceptive drug being used, relationships between these variables and the lipoprotein fractions could not be determined. Discussion Sex steroid hormones appear to have a major influence on serum lipoprotein distributions. For example, premenopausal females have lower concentrations of very low density lipoproteins and higher concentrations of HDLII than males in similar age groups [ 221. Furthermore, exogenous gonadal steroids and their analogs can cause substantial changes in serum lipid and lipoprotein levels [l-9,23,24]. The present study was undertaken to define the effects of combined estrogen-progestin contraceptive drugs on the high density lipoproteins in normal menstruating women. Analytic ultracentrifugation revealed a significantly higher concentration of total high density lipoproteins in the group of contraceptive users than in controls. Levels of high density lipoprotein cholesterol and triglyceride, measured after precipitation of serum with heparin and manganese chloride [20], did not discriminate between the two groups. This result may have been due to small sample size, or nonspecific precipitation [25], but it raises the possibility that constituents other than cholesterol (i.e., phospholipids and/or proteins) may account for a large proportion of the increase in total high density lipoprotein mass in the oral contraceptive users. It has previously been reported that estrogen administration results in a significant increase in the protein concentration of high density lipoproteins [ 241, With the analytic ultracentrifuge, measurements were made of two major high density lipoprotein subfractions, FF.,, O-3.5 and FP,, 3.5-9. These density classes correspond approximately to the HDL3 and HbL2 subfractions previously defined by preparative ultracentrifugation [ 21,221. The results showed that the elevation of total high density lipoprote~ was due to a selective and highly significant increase in the denser subfraction (FP,, O-3.5). Given the variation in type and amount of component estrogens and progestins in oral contraceptive preparations, it is not possible to identify the separate contributions of these steroids to the lipoprotein changes observed in this study. Estrogens and androgens have been shown to exert opposing effects on serum ~iglyceride and low and high density lipopro~in concentrations with the effects of combinations dependent on the amounts of each [ 241. Studies of various synthetic progestins have shown that nortestosterone derivatives tend to counteract the hypertriglyceridemic effect of estrogens [ 8,9] much as do the more androgenic testosterone derivatives [24]. This may help to explain the relatively small elevation of serum triglycerides observed in the group of oral contraceptive users in the present study, since most of the subjects were using preparations containing nortestosterone analogs (Table I). It is likely that the progestational components of the oral contraceptives also modify the increase in high density lipoproteins known to occur with estrogen treatment [24]. Preliminary studies from this laboratory [26] have shown that estrogen treatment results in higher levels of both HDLz and HDLJ lipoproteins in contrast to the
470
isolated increase in HDL3 shown here for estrogen-progestin combinations. A number of groups have reported that increased levels of high density lipoprotein cholesterol are associated with reduced risk of coronary artery disease [ 13-171. The consequences of an increase in HDL3 lipoproteins without a proportional increase in high density lipoprotein cholesterol are not known. Oral contraceptive drug users appear to have a higher incidence of coronary events than non-users [ 9,101. This suggests that if HDL3 elevation does have a protective role, it is not sufficient to overcome the effects of oral contraceptives which may predispose to coronary disease. Acknowledgements This work was supported in part by Contract NOl-HD-3-2710, Center for Population Research, National Institutes of Child Health and Development, National Institutes of Health Grant l-OPl-HL-18574-01, and the United States Energy Research and Development Administration. We thank Dr. S. Ramcharan for her enthusiasm and support of this project. We also thank Suzanne Pan for able computer analysis of data. References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
20 21 22 23 24 25 26
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