Comparison of the metabolic effects of two hormonal contraceptive methods: an oral formulation and a vaginal ring. II. Serum lipoproteins and apolipoproteins

Advances in contraceptive vaginal rings: what does the future hold?

INTRODUCTION

Contraceptive vaginal rings (CVRs) are good contraceptive options because they do not require skilled providers, are self-administered, and show a higher stability of drug diffusion.

AREAS COVERED

This article provides a review of the developments made with CVRs over the past number of years, while giving focus to the latest CVRs that have gone through clinical development. The author of the article also provides an expert perspective on the future of these useful therapeutic options.

EXPERT OPINION

Pharmacokinetic studies have shown that segesterone, an absorbable progestin that is used alone or in combination with ethinyl estradiol (EE) or E_2, is the CVR of choice at this present time. Indeed, segesterone has demonstrated safety and efficacy as a CVR and is also an appropriate option for lactating women, as they are not absorbed orally. However, good cycle control is important for improved CVR adherence. CVRs that allow the combination of more than one drug may unravel another multi-purpose use when combined with microbicides and could provide combined protection to women who wish to protect themselves from pregnancy and sexually transmitted infection.

Lipid profile in women over 35 years old using triphasic combined oral contraceptives

Twenty-nine women aged 35 years old or more, using triphasic combined oral contraceptive (COC) were evaluated during six cycles for the following parameters: total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and its subfraction HDL2, triglycerides, apoproteins A and B, Castelli risk index I and II (cholesterol/HDL-C and LDL-C/HDL-C) and apoprotein ratio (apoprotein B/apoprotein A). The same laboratory measurements were done in a control group of 49 non-COC-user women. The results showed that there were no differences on most of the studied parameters between user and nonuser women. There was a significant reduction of HDL-C and HDL2-C, although within the normal range. In addition, it was observed a significant increment of triglycerides and apoprotein B at 6 months of follow-up only in user group (p < 0.05), although within the normal range. It is concluded that the use of levonorgestrel triphasic COC appeared to have no additional adverse impact when used by women aged over 35 years. Further studies are needed to obtain conclusive data.

Dose-finding study of a contraceptive ring releasing norethindrone acetate/ethinyl estradiol

A core design contraceptive vaginal ring (CVR) with average daily release of 650 mcg of norethindrone acetate (NA) and 30 mcg of ethinyl estradiol (EE) inhibited ovulation and controlled vaginal bleeding well, but caused some nausea. This study was designed to minimally alter the dose of steroid to see if nausea could be reduced without loss of contraceptive efficacy. This 30/650 CVR was compared to a CVR releasing 20 mcg of EE and 1000 mcg of NA (20/1000) and another releasing 25 mcg of EE and 650 mcg of NA (25/650) in 69 subjects. Twenty-three subjects using an oral contraceptive containing NA/EE served as controls. Ovulation inhibition was excellent and comparable to the OC for all formulations. The CVR provided better control of vaginal bleeding than did the OC. Side effects were equivalent to the OC with the exception of a slight increase in nausea in CVR users. Lipid changes and globulin increases were comparable to oral contraceptive users. The 20/1000 CVR increased sex hormone binding globulin-binding capacity less than the other two CVRs. The performance of the three CVRs was not significantly different, but the 25/650 showed a trend of reduced performance relative to the other two formulations.

A contraceptive vaginal ring releasing norethindrone acetate and ethinyl estradiol

A core design contraceptive vaginal ring (CVR) releasing 650 mcg of norethindrone acetate (NA) and 10, 20, 30 or 65 mcg of ethinyl estradiol (EE) daily was developed and tested in 99 women. The CVR inhibited ovulation well with 30 or 65 mcg EE. Vaginal bleeding was better controlled than in 23 control women using NA/EE oral contraceptives. Side effects were comparable to controls for the 20 and 30 mcg EE CVR. The 65 mcg EE CVR resulted in an unacceptably high level of nausea. The 20 and 30 mcg EE CVR caused an increase in serum HDL cholesterol and triglycerides. Total cholesterol was unchanged. Angiotensinogen and sex hormone binding globulin-binding capacity were increased in a subgroup of the 20 and 30 mcg EE CVR subjects, similar to that of 20 controls using EE/gestodene oral contraceptives. This new CVR offers an excellent contraceptive alternative with the best performance provided by the 30 mcg EE dose.

Vaginal contraceptive rings

Steroids diffuse through polysiloxone at a constant rate, and steroids placed in the vagina rapidly pass through the vaginal epithelium into the circulation. Combining these principles led to the development of contraceptive vaginal rings (CVR) consisting of various progestins, with and without oestrogen, placed in flexible polysiloxone, doughnut-shaped devices. As occurs with oral contraceptives, the CVRs containing progestin plus oestrogen are left in the vagina for 3 weeks and removed for 1 week to allow withdrawal bleeding, while CVRs releasing a small dose of progestins without oestrogen are left in the vagina continuously for several months. Large-scale, clinical trials were performed with a low dose levonorgestrel-releasing-only CVR by the WHO. At 1 year, continuation rates were about 50 per 100 women with 17.2 per 100 discontinuing for menstrual problems and 4.5 for pregnancy. Two sizes of a CVR containing levonorgestrel and oestradiol were studied in a multinational trial organized by the Population Council. At the end of 1 year, about half the women were continuing with the method, one-quarter had discontinued because of bleeding problems, and pregnancy rates were between 1 and 2 per 100 women. The CVR was well accepted by women and their partners, but because of lowered HDL-cholesterol levels and accelerated atherosclerosis in female monkeys, further development of this formulation was discontinued. Recently, phase II clinical trials with CVRs containing combinations of NET-acetate plus ethinyloestradiol and 3-ketodesogestrel plus ethinyloestradiol have been undertaken. These CVRs provide good bleeding control, inhibit ovulation consistently and do not have an adverse effect on serum lipids. Phase III trials with these two types of CVRs will be initiated shortly.

Evaluation of four different contraceptive vaginal rings: steroid serum levels, luteal activity, bleeding control and lipid profiles

Four different models of contraceptive vaginal rings were tested during three cycles for luteal activity, bleeding control, plasma lipoproteins and serum levels of the contraceptive steroids. Two progestins, levonorgestrel acetate (LNGA) and ST 1435, alone or in combination with ethynyl-estradiol (EE) were tested. The rings released 100 ug/day of the progestins and 30 ug/day of EE. Luteal activity was detected among users of the progestin-only rings: 4 of 8 cycles with ST 1435 and 2 of 10 with LNGA. Only one of the 18 cycles studied with the two combined rings showed luteal activity, but the measurement of contraceptive steroid in plasma suggested that this subject delayed reinsertion of the ring for about one week in that particular cycle. Breakthrough bleeding was observed in 12 of 30 cycles of use of the progestin-only rings, and in only 2 of 27 cycles with the combined models. No significant changes in total cholesterol or its HDL-fraction were observed. However, the only reduction observed in HDL-cholesterol was among users of the LNGA-only ring. It is concluded that the two combined CVR models offer good possibilities of high effectiveness and bleeding control and merit further development.

Progestagen-only oral contraceptives: comparison of the metabolic effects of levonorgestrel and norethisterone

A 6-month single-blind study compared the use of a progestagen-only oral contraceptive containing norethisterone 350 micrograms/day (NE 350) with one containing levonorgestrel 30 micrograms (LN 30), to assess the metabolic effects. At the end of 6 months, there were no significant differences between the two groups with respect to plasma cholesterol, lipoproteins including HDL subfractions, triglycerides or glucose concentration. Levels of fibrinogen, plasminogen, Factor VII, Factor X and antithrombin III were also similar. Women changing from a combined oral contraceptive to LN 30 showed a significant fall in Factor X. Mean blood pressure fell on LN 30 by 7/9 mmHg, but the 6-month reading did not differ significantly from that in women on NE 350. Acceptability, and the metabolic effects of the two preparations were similar in this study. Further larger studies are warranted.

A comparative study of the effects of a monophasic and a triphasic oral contraceptive containing ethinyl estradiol and levonorgestrel on lipid and lipoprotein metabolism

A comparative study of the effects of a monophasic and a triphasic oral contraceptive containing ethinylestradiol (EE) and levonorgestrel (LNG) on lipid and lipoprotein metabolism was conducted on 45 Singapore women under the WHO Special Programme of Research in Human Reproduction. The women were randomly allocated to one of the two pill groups--a triphasic preparation containing low doses of LNG and EE in various proportions and a monophasic preparation of 150 micrograms LNG and 30 micrograms EE, and an additional 18 women, choosing to use IUDs, were recruited as controls. Blood samples were taken at admission, 3 and 12 months thereafter. For both pill groups, total cholesterol decreased with duration of use, while HDL cholesterol decreased slightly at 3 months and thereafter increased. LDL cholesterol decreased slightly at 3 months, returning to baseline at 12 months for the monophasic group, while remaining unchanged at 12 months for the triphasic group. The monophasic preparation appeared to lower total, LDL and HDL cholesterols to a greater extent at 3 months than the triphasic preparation. Compared with IUD users, for the monophasic group, both total and HDL cholesterols were significantly lower at 3 months and HDL and LDL cholesterols were lower at 12 months. In addition, ratios of HDL cholesterol/LDL cholesterol and HDL cholesterol/total cholesterol were significantly lower at 12 months. Changes in triglycerides were minimal for both pill groups. However, at 3 months, triglycerides for the triphasic group were significantly higher than the IUD users, but this observation was not of any clinical importance since comparison of changes with their respective pretreatment values were not statistically significant. These results indicate that these changes are related to the dosage and estrogen-progestogen ratio of the preparation. Furthermore, the monophasic preparation may have a disadvantage over the triphasic preparation since it appears to cause more disturbance in lipid metabolism. However, it is noted that these changes in lipids and lipoproteins were minimal and did not appear to be of any clinical significance.

Time-dependent alterations in lipid metabolism during treatment with low-dose oral contraceptives

The effect of sex steroids on lipid metabolism depends on the type and dose of the compounds, the route of administration, and the duration of treatment. Therefore the composition of an oral contraceptive determines the resultant effect on lipids and lipoproteins. During 12 months of treatment, the effects of two oral contraceptives containing 30 micrograms of ethinyl estradiol and 150 micrograms of desogestrel (EE/DG) or 75 micrograms of gestodene (EE/GSD) on 19 serum parameters of lipid metabolism were followed in 11 women each. There was no change in total cholesterol and phospholipids. Total triglyceride levels were significantly elevated only by EE/GSD. After 3 and 6 months of intake of both preparations, a transitory increase in the triglyceride content of very low-density lipoprotein and low-density lipoprotein and a decrease in low-density lipoprotein-phospholipids was observed. After 12 months, very low-density lipoprotein cholesterol, very low-density lipoprotein phospholipids, and apolipoprotein B were significantly elevated, whereas very low-density lipoprotein triglycerides and all components of low-density lipoprotein were unchanged. Most of the components of high-density lipoprotein (HDL) were increased as a result of a rise in HDL3 and apolipoprotein A2, whereas HDL2 and apolipoprotein A1 were not altered. There was no significant difference between the effects of the two preparations, although those of EE/GSD were mostly more pronounced. The increase in high-density lipoprotein, very low-density lipoprotein, and total triglycerides reflects a slight preponderance of the effect of the estrogen component. Because low-density lipoprotein cholesterol and total cholesterol were not changed, treatment with both formulations is in all probability not associated with an elevated risk of atherosclerosis.

Changes in lipid metabolism during 12 months of treatment with two oral contraceptives containing 30 micrograms ethinylestradiol and 75 micrograms gestodene or 150 micrograms desogestrel

The effect of two oral contraceptives containing 30 micrograms ethinylestradiol + 75 micrograms gestodene (EE/GSD) or 30 micrograms ethinylestradiol + 150 micrograms desogestrel (EE/DG) upon serum lipids and lipoproteins were measured in 11 women each on days 1, 10, and 21 of the first, third, sixth, and twelfth treatment cycle and compared to the levels on days 1, 10, and 21 of the preceding control cycle. There was no change in total cholesterol (CH) and phospholipids (PL), while total triglycerides (TG) were significantly elevated only during treatment with EE/GSD. After 3 and 6 months of intake of both oral contraceptives, a transitory increase in the TG content of very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL), and a decrease in LDL-PL was observed. After 12 months, VLDL-CH, VLDL-PL, and apolipoprotein B were significantly elevated, while VLDL-TG and all components of LDL were unchanged. Most of the components of high-density lipoprotein (HDL) were increased due to a rise in HDL3 and apolipoprotein A-II, while HDL2 and apolipoprotein A-I were not altered. There was no significant difference between the effects of the two preparations, although those of EE/GSD were mostly more pronounced. The time-dependent change in the effects of the oral contraceptives on various parameters of lipid metabolism demonstrates that the relevance of results of short-time studies may be questionable. There was also a significant alteration in some parameters between day 1 and 10 of the treatment cycles and a tendency to return to the pretreatment levels during the pill-free week, e.g., in total TG and in the PL component of VLDL, LDL and HDL. The increase in HDL, VLDL, and total TG reflects a slight preponderance of the effect of ethinylestradiol on lipid metabolism. The unchanged total CH and LDL-CH and the elevated HDL levels indicate that the risk of the development of atherosclerosis is in all probability not increased during treatment with both preparations.

Metabolic effects of oral contraceptives

Combination oral contraceptives (OCs) are probably not an independent risk factor for cardiovascular disease but through their metabolic actions, may partly amplify the effects of known risk factors for cardiovascular disease. This review of the literature and our own data indicate that use of high-dose, progestogen-dominant OCs induces a potentially atherogenic lipoprotein profile (high low-density lipoprotein-cholesterol:high-density lipoprotein-cholesterol ratio), mostly attributable to the antiestrogenic action of the progestogen content of these OCs. In contrast, lower-dose combination OCs with reduced amounts of progestogens and slight estrogen dominance, either monophasic or multiphasic, produce strikingly fewer adverse effects on lipoproteins. Moreover, use of low-dose, as opposed to high-dose, OCs results in almost unchanged glucose tolerance, marginally increased or unchanged insulin and glucagon responses to glucose, and probably unchanged levels and activity of peripheral insulin receptors. Further in-depth studies of low-dose OC formulations are mandatory to ascertain reduced metabolic risk of these OCs.

Cholesterol and HDL-cholesterol values in women during use of subdermal implants releasing levonorgestrel

Plasma concentrations of cholesterol, HDL-cholesterol, and levonorgestrel were determined in two groups of women using levonorgestrel-releasing subdermal implants. One group used six capsules (NORPLANT)*; the other six covered rods. Plasma concentrations of levonorgestrel among NORPLANT users averaged 700 pg/ml in the first two weeks of use, decreased to 300 pg/ml at 8 weeks, and to about 230 pg/ml by 50 weeks. Concentrations among covered rod users were 1.4 to 1.7 times higher at comparable time periods. Total serum cholesterol and HDL-cholesterol were decreased as compared with controls at all sampling intervals during the 114 weeks of the trial, although the differences did not meet tests of significance at all time periods. Decreases during the test period were of the order of 10 percent, except for total cholesterol among covered rod users where the decrease was less. Cholesterol to HDL-cholesterol ratios did not differ significantly from control values at any sampling period.

Oral contraceptives, lipids and cardiovascular disease

Evidence for the involvement of changes in lipid metabolism and oral contraceptive use in the development of cardiovascular disease is briefly reviewed with particular reference to the main object of the article, to assess the effect of different oral contraceptive formulations on serum lipid levels. The preferred formulations should contain a low dose of ethynyloestradiol and should not increase serum levels of cholesterol and LDL-C or reduce those of HDL-C. Such formulations appear to be the triphasic one containing ethynyloestradiol and levonorgestrel and the ethynyloestradiol-desogestrel combination, which appears to be unique in that it may actually increase HDL-C. However other determinants in addition to effects on lipid metabolism will be important in deciding the choice of an oral contraceptive. Any changes which do occur in serum lipid concentrations with OC use appear within the first three months and do not appear to be progressive with continued use after this time.

The progestagen releasing vaginal ring

The results of the Manchester study and its reinforcement from data from the multicenter study indicate that the ring is a well-tolerated delivery system for low-dose progestagens. The expulsion rate is low and vaginal tolerance satisfactory. The pregnancy rate and bleeding pattern is of the same order as oral low-dose progestagens. Indeed, there is an indication that the pregnancy rate and abnormal bleeding rate may be even lower. Data from other more extensive phase 3 studies will be required to confirm this impression. The subjective assessment is that the majority of patients are enthusiastic about this method of contraception, bearing in mind that many of them had become disenchanted with existing marketed contraceptive methods. Because of its high level of acceptability, the gap between theoretical and use-effectiveness in narrowed and once inserted, a high degree of motivation is not required since the existing ring only needs to be reinserted after 90 days of use. The acceptability of vaginal methods of contraception as evidenced by the rapid uptake of the vaginal sponge suggests that there is considerable potential for increased use of vaginal methods. In the present state of knowledge, it would appear that the woman for whom the progestagen only conception is particularly appropriate is the one who is lactating or for the older woman whose fertility is on the wane. For the woman who wishes to space her family, the progestagen only contraceptive is also appropriate. With increased refinements and experience of this method, there is a likelihood that the ring may extend the use and application of progestagen only contraception to a wider range of potential patients.

Effect of low-dose oral contraceptives on lipoproteins and lipolytic enzymes: differences between two commonly used preparations

Changes in circulating lipoproteins, which may be related to the risk for atherosclerotic vascular disease, were studied in a control group and in two groups of 24 or 26 women using different preparations of low-dose oral contraceptives for 3 months. One preparation contained 150 micrograms levo-norgestrel and 30 micrograms ethinylestradiol (Stediril-d 150/30); the other contained 750 micrograms lynestrenol and 37.5 micrograms ethinylestradiol (Ministat). No significant changes were found with either of the preparations in serum cholesterol or high density lipoprotein cholesterol (HDL-C) levels. Apolipoprotein A-II levels increased during Ministat treatment from 50.4 to 61.4 mg/dL and during Stediril-d 150/30 treatment from 52.7 to 58.9 mg/dL (both P less than 0.001). These changes differed significantly from each other (P less than 0.01). Apolipoprotein A-I levels increased significantly during use of Ministat only. Apolipoprotein B in low density lipoprotein increased by about 20% (P less than 0.001) in both groups. Post-heparin lipoprotein lipase activity did not change, but hepatic lipase activity decreased to the same extent in both groups (P less than 0.001). Reductions in post-heparin lipase activity were not correlated with increases in HLD-C.

Effects of levonorgestrel and desogestrel in low-dose oral contraceptive combinations on serum lipids, apolipoproteins A-I and B and glycosylated proteins

Fasting serum lipids, apolipoproteins and glycosylated serum proteins were studied in 20 women before, after three months of treatment and two months after termination of treatment with oral contraceptives containing 30 micrograms ethinyloestradiol (EE) plus 150 micrograms levonorgestrel or desogestrel. Levonorgestrel + EE induced significant increases in total triglycerides (48%), apoB (19%) and the ratio apoB/apoA-I (18%) and no significant changes in HDL-cholesterol (8% decrease), apoA-I, % HDL-cholesterol, total cholesterol and serum glycosylated proteins. Desogestrel + EE induced significant increases in HDL-cholesterol (12%), % HDL-cholesterol (15%), triglycerides (35%) and apoA-I (20%), no changes in total cholesterol, apoB and glycosylated serum proteins and a significant decrease in the ratio apoB/apoA-I (17%). Two months after termination of treatment the values for all parameters for both preparations were similar to those observed before treatment. The differences between the effects of the two preparations on the parameters HDL-cholesterol, % HDL-cholesterol, apoA-I, apoB and the ratio apoB/apoA-I were statistically significant and can be explained by a difference in the intrinsic androgenicity of the two progestagens.

Long-term reversible contraception with levonorgestrel-releasing Silastic rods

Subcutaneously placed Silastic capsules containing levonorgestrel are effective for 5 years and have a higher continuation rate than other methods of reversible contraception. Six 3 cm capsules are required to achieve satisfactory circulating levels of levonorgestrel. Two 4 cm covered Silastic rods containing levonorgestrel, which are easier to manufacture, insert, and remove than the capsules, produce similar in vitro release rates. This study compared clinical and metabolic effects as well as bleeding patterns in 23 women using either six capsules (n = 11) or two covered rods (n = 12). Serum levels of levonorgestrel, lipids, and lipoproteins as well as frequency of elevated progesterone levels were compared in serum samples obtained before treatment and 1, 6, 12, 18, and 24 months after insertion with the two systems. While bleeding patterns were similar for users of the two systems, rod users had slightly higher serum levels of levonorgestrel and a lower incidence of cycles with elevated progesterone levels. Therefore, rods could replace capsules as a long-term, reversible contraceptive method.

Changes in serum apo-lipoprotein AI and sex-hormone-binding globulin levels after treatment with two different progestins administered alone and in combination with ethinyl estradiol

Twenty women, oophorectomized as part of the surgical treatment for cervical carcinoma in either clinical stage IB or IIA but otherwise healthy, participated in the study. After a period of six weeks without hormonal treatment, ten of them were given 150 micrograms desogestrel (DG) daily for three weeks followed by 150 micrograms DG + 30 micrograms ethinyl estradiol (EE) for six weeks and, finally, 30 micrograms EE alone for three weeks. The remaining ten women were given 150 micrograms levonorgestrel (NORG) and EE in a similar regimen. Before treatment and after each period of treatment, apo-lipoprotein AI and sex-hormone-binding globulin (SHBG) were assayed in serum. Both progestins decreased apo-AI and SHBG when given alone, thereby indicating an "androgenic" influence. In combination with EE, however, DG seems to be less "anti-oestrogenic" than NORG, as judged from the higher apo-AI and SHBG values after the combination DG + EE compared to those after NORG + EE.

Unaltered lipoprotein and carbohydrate metabolism during treatment with contraceptive subdermal implants containing ST-1435

Nine healthy, fertile women were treated for six months with subdermal contraceptive implants of two different sizes containing a potent progestogen, ST-1435. Lipoprotein cholesterol and triglyceride concentrations were not influenced by the treatment. Similarly, the main apolipoproteins in low- and high-density lipoproteins were not changed, which further supports the interpretation that the lipoprotein metabolism is not affected by this type of treatment. An oral glucose tolerance test (OGTT) including insulin determinations was performed in five of the volunteers with the largest implants. Blood glucose and insulin concentrations during the OGTT remained unchanged during treatment, indicating that the treatment with ST-1435 did not affect carbohydrate metabolism.

Pharmacodynamics of a contraceptive vaginal ring releasing norethindrone and estradiol: ovarian function, bleeding control and lipoprotein patterns

A new contraceptive vaginal ring (CVR), releasing approximately 700 micrograms of norethindrone (NET) and approximately 140 micrograms of estradiol (E2) daily, was studied in eleven women for a total of 61 21-day cycles. Ovarian function, as judged by plasma progesterone (P) and E2 levels, and plasma NET levels were studied by weekly blood samples in 30 cycles. The lipoprotein pattern was studied before, after two and six months of treatment and one month after completed treatment. The CVR gave rise to stable plasma NET levels which however varied considerably between individuals. Signs of luteal activity/ovulation were encountered in 4/30 cycles, all in subjects with the lowest NET plasma levels. E2 levels above 250 pmol/l, indicating follicular activity, were encountered in 22/30 cycles. Breakthrough bleeding and spotting appeared in 40/61 cycles and in 12 per cent of the treatment days. Bleeding control was significantly better in the same subjects when using a CVR releasing levo-Norgestrel and E2. Serum and HDL cholesterol concentrations decreased significantly by 10-12 per cent during treatment. The ratios between apolipoproteins A-I and A-II on one hand and HDL cholesterol on the other increased significantly and the ratio apolipoprotein A-I:A-II decreased significantly, indicating a change in the lipoprotein composition. These changes are qualitatively similar but quantitatively not as pronounced as with the more extensively studied 1-Ng/E2 CVR. The difference in clinical performance and in the effects on the lipoprotein pattern between the presently studied CVR and the 1-Ng/E2 CVR is most likely the result of not using equipment doses of gestagen in the CVRs.

Influence of a levonorgestrel-containing contraceptive vaginal ring on plasma lipids and lipoproteins in cynomolgus monkeys

The effect of a contraceptive vaginal ring (CVR) containing levonorgestrel on plasma lipid and lipoprotein concentrations and characteristics was assessed in ten cynomolgus monkeys. The animals were fed a diet similar to the average American diet in fat (40% of calories) and cholesterol (0.2 mg/kcal) content. The objective of this study was to determine if changes in lipids and lipoproteins caused by progestogen administration parallel those seen in human females. A parallel pattern would recommend the cynomolgus monkey as a model for studying the effects of progestogens on the atherosclerotic process. Treatment with the CVR resulted in significant decreases in total plasma, VLDL + ILDL + LDL, and HDL cholesterol concentrations and a decrease in the percentage of HDL2 in total HDL. Plasma triglyceride concentrations were low throughout the study and consistent effects of the CVR were not seen. CVR treatment resulted in increases in TPC:HDL-C ratios and in the flotation rate of the LDL particle. The patterns of effects on HDL cholesterol, total plasma cholesterol, and HDL2 concentrations were similar to the progestogen-induced changes observed in human plasma lipids and lipoproteins. Based on these effects, the cynomolgus monkey appears to be a suitable model for the study of progestogen-induced changes in plasma lipids and lipoproteins and their consequent influences on coronary artery atherosclerosis.

Effects of continuous levonorgestrel treatment (subcutaneous capsules) on the lipoprotein and carbohydrate metabolism in fertile women

The lipoprotein and carbohydrate metabolism was studied during contraceptive treatment with levonorgestrel, released at a low rate (70 micrograms/day) from subcutaneous capsules, in five women who were treated for 180-403 days. The serum cholesterol concentration decreased slightly but significantly during treatment. This was attributable to a tendency to a reduction of cholesterol in high-density lipoproteins. The treatment did not affect the lipoprotein lipase activity in adipose tissue. The elimination rates of intravenously injected fat and glucose were unchanged, as were the serum insulin concentrations. Thus, in this pilot study the concentration and composition of the serum lipoproteins altered to only a minor extent during treatment with levonorgestrel in a dose of 70 micrograms/day.