Evidence that smoking alters prostacyclin formation and platelet aggregation in women who use oral contraceptives

Occlusive vascular diseases in oral contraceptive users. Epidemiology, pathology and mechanisms

Despite being an unprecedented departure from normal physiology, the combined oral contraceptive is not only highly effective, but it also has a remarkably good safety record. Concerns over safety persist, though, particularly with regard to venous thromboembolism (VTE), stroke and myocardial infarction (MI). Epidemiological studies consistently show an increase in risk of VTE, but the results are more contentious with regard to arterial diseases. Despite 40 years of research, the mechanisms behind these adverse effects are not understood. In this review, we integrate information from published studies of the epidemiology and pathology of the occlusive vascular diseases and their risk factors to identify likely explanations for pathogenesis in oral contraceptive users. Oral contraceptives induce both prothrombotic and fibrinolytic changes in haemostatic factors and an imbalance in haemostasis is likely to be important in oral contraceptive-induced VTE. The complexity of the changes involved and the difficulty of ascribing clinical significance has meant that uncertainty persists. A seriously under-researched area concerns vascular changes in oral contraceptive users. Histologically, endothelial and intimal proliferation have been identified in women exposed to high plasma estrogen concentrations and these lesions are associated with thrombotic occlusion. Other structural changes may result in increased vascular permeability, loss of vascular tone and venous stasis. With regard to arterial disease risk, epidemiological information relating to dose effects and joint effects with other risk factors, and studies of pathology and changes in risk factors, suggests that oral contraceptive use per se does not cause arterial disease. It can, nevertheless, synergise very powerfully with subclinical endothelial damage to promote arterial occlusion. Accordingly, the prothrombotic effects of the oral contraceptive estrogen intervene in a cycle of endothelial damage and repair which would otherwise remain clinically silent or would ultimately progress - in, for example, the presence of cigarette smoking or hypertension - to atherosclerosis. Future work in this area should focus on modification of the effects of established risk factors by oral contraceptive use rather than modification of the supposed risk of oral contraceptive use by established risk factors. Attempts to understand vascular occlusion in oral contraceptive users in terms of the general features of VTE or with reference to atherosclerosis may be limiting, and future work needs to acknowledge that such occlusions may have unique features. Unequivocal identification of the mechanisms involved would contribute considerably to the alleviation of fears over vascular disease and to the development of even safer formulations.

Smoking and cardiovascular disease

Mainstream and ETS exposure are strong risk factors for cardiovascular disease in men and women. The relationships between smoking and cardiovascular disease result from multiple mechanisms that interact to contribute to atherosclerosis, vascular injury, thrombosis, and vascular dysfunction. We are only now beginning to understand how smoking contributes to the genesis and progression of cardiovascular disease. Because of the complexity of the interactions between nicotine and the components of MSS, ETS, and sidestream smoke with the vasculature, it will take a great deal of time and effort to fully unravel the mechanisms by which smoking contributes to cardiovascular disease. In addition, cardiovascular risk in female smokers is complicated by hormonal variables that may contribute to greater relative risk. It is important that health care providers, educators, and policy makers recognize the changing patterns of smoking and the impact of smoking on cardiovascular disease, and continue campaigns aimed at enhancing smoking cessation in the general population and in teens. Rigorous research is needed on the changing cultural, psychosocial, and environmental factors that influence tobacco use to improve our understanding of racial/ethnic smoking patterns, and identify strategic tobacco control opportunities. The capacity of tobacco control efforts to keep pace with patterns of tobacco use and cessation depends on timely recognition of emerging prevalence and cessation patterns and the resulting development of appropriate community-based programs to address the factors involved. Smoking trends today will determine how heavy the health burden of cardiovascular disease and others will be among communities tomorrow. Programs that aim at early intervention and reflect cultural diversity will be the cornerstone in the battle against tobacco use. Continued interest in research, educational, and prevention efforts are needed to help curb the risk of cardiovascular disease from smoking in men and women.

Cardiovascular disease: pathogenesis, epidemiology, and risk among users of oral contraceptives who smoke

Smoking increases the risk of lung cancer and cardiovascular disease among persons of both sexes. The risk of cardiovascular disease is further increased among users of oral contraceptives who smoke, particularly those who are >/=35 years old or carry the coagulation factor V Leiden mutation. Other important cardiovascular disease risk factors in women include waist/hip girth ratio >0.8, high concentration of low-density lipoprotein cholesterol (>115 mg/dL), high triglyceride level (>/=150 mg/dL) with low concentration of high-density lipoprotein cholesterol (</=45 mg/dL), high ratio of total cholesterol/high-density lipoprotein (4.0), high ratio of low-density lipoprotein/high-density lipoprotein (3.0), glucose values >/=100 mg/dL, hypertension, lack of physical activity, and high-fat diet. Most excess cardiovascular disease among users of oral contraceptives is due to thrombosis (not atherosclerosis); studies indicate that the lower the oral contraceptive estrogen dose is, the lower is this risk. Oral contraceptives containing the third-generation progestins desogestrel and gestodene have been associated with greater risks of venous thromboembolism than are associated with older progestins, although there is some controversy surrounding these findings.

Effects of smoking on prostacyclin formation and platelet aggregation in users of oral contraceptives

OBJECTIVE

The aim of this review was to determine which subgroups within the population of smokers and oral contraceptive users are at especially elevated risk for thromboembolic events.

STUDY DESIGN

This review covers 10 articles published between 1981 and 1996 that examined the effects of smoking and oral contraceptive use, in conjunction or independently, on factors affecting the coagulation pathway, particularly the expressions of prostacyclin and thromboxane.

RESULTS

Heavy, prolonged, or current nicotine use was associated with a reduction in the urinary metabolite of prostacyclin (prostaglandin I2) in oral contraceptive users. Smoking and increased excretion of thromboxane were also linked, and in 1 study the effect was dose related. These changes were associated with increased platelet aggregation. Oral contraceptive use and concurrent smoking increased the risk of acute myocardial infarction by a ratio of 10.1. Although most of this risk was seen among smokers who used second-generation oral contraceptives (odds ratio 11.1), with a much reduced odds ratio for smokers who used third-generation oral contraceptives (odds ratio 3.1), the study was not controlled for estrogen dose. A reduction in myocardial infarction risk compared with that in the 1970s was seen for all oral contraceptive users, probably because of the reduced hormonal doses in current preparations.

CONCLUSION

Smoking, not oral contraceptive use, constitutes the greater cardiovascular risk. However, cigarette smoking and oral contraceptive use act synergistically to increase the risk of thromboembolic events. Differences in oral contraceptive formulations may mitigate the increased risk resulting from concurrent smoking and use of oral contraceptives, but whether the progestin component or the lowered estrogen dose is responsible is unclear.

Effect of oral contraceptives containing 20 and 35 micrograms ethinyl estradiol on urinary prostacyclin and thromboxane metabolite levels in smokers and nonsmokers

The interaction between smoking and oral contraceptive (OC) use with respect to thrombogenesis was investigated by studying the effects of OC and smoking on urinary prostacyclin (PGI2) and thromboxane A2 (TxA2) metabolite levels in smokers and nonsmokers. Sixty healthy women, aged 19-32 years, who were not taking any hormonal treatment for at least 3 months before initiating the study, were divided into three equal groups: OC users who smoked (N = 20), OC users who did not smoke (N = 20), and a control group of 10 smokers and 10 nonsmokers. Each OC treatment group was randomized to receive either norethindrone (NET) acetate (1 mg)/ethinyl estradiol (EE2) (35 micrograms) (N = 10) or NET acetate (1 mg)/EE2 (20 micrograms) (N = 10) daily for 3 months. Overnight urine collections and fasting blood samples were obtained at baseline and at the end of the 3-month study. Serum levels of NET and EE2, as well as urinary levels of cotinine and the stable metabolites of PGI2 and TxA2, namely 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane (TxB2), respectively, were measured by specific immunoassays. Analysis of pre- to posttreatment changes in mean urinary 6-keto-PGF1 alpha and TxB2 levels for each subgroup, as determined by smoking status and EE2 dose, showed no statistically significant differences. Also, no significant differences were found in each subgroup with respect to changes in the 6-keto-PGF1 alpha/TxB2 ratios. Large intersubject variability in urinary 6-keto-PGF1 alpha and TxB2 levels were observed in all subgroups. The results of this study indicate that both low-estrogen-dose compounds, when used by smokers or nonsmokers, did not significantly alter the ratio of PGI2 to TXA2 metabolites, compared with pretreatment. However, the small number of subjects and the large intersubject variability in this study make it difficult to determine if there is a significant difference between the 20- and 30-microgram EE2 doses.

Haemostatic changes and the oral contraceptive pill

Oral contraceptives have been linked to an increased incidence of thrombovascular disease. This may be mediated by their effects on the haemostatic system. An increase in the activity of coagulation Factors VII, X and fibrinogen occur with pill usage. Increased Factor VII levels are dependent on both the oestrogen and progestogen component of the oral contraceptive. A reduction in antithrombin III levels has also been observed in some but not all studies. Increased fibrinolysis has also been shown in oral contraceptive users which should balance the changes in the coagulation pathway. The increase in fibrinolytic potential is thought to be due to a decrease in the levels of plasminogen activator inhibitor I combined with an increase in the levels of plasminogen; tissue plasminogen activator antigen is decreased in most studies. The increased levels of endpoints of coagulation and fibrinolysis in pill users indicate that enhanced activity of both systems is occurring in vivo. The increased coagulation activity appears to be balanced by the rise in fibrinolytic activity, so preserving haemostatic balance. Enhanced platelet activity has also been shown in women taking oral contraceptives. Thrombus formation can result, however, when local vascular wall damage exists, or when other risk factors for thrombo-embolism, such as older age and smoking, coexist and create a local activation resulting in a thrombus. In these situations, the small differences in levels of coagulation factors in women taking different oral contraceptive formulations may be important. Pills containing the lowest doses of oestrogen (20 micrograms ethinyloestradiol) have shown the least changes in haemostatic factors. The progestogen component of the pill modifies the effect of oestrogen on the haemostatic system.

Menorrhagia--a search for epidemiological risk markers

OBJECTIVE

To isolate epidemiological risk factors for menorrhagia.

METHODS

Menstrual blood loss (MBL) of one bleeding episode of 182 healthy women was measured with the alkaline hematin method and the results were related to age, parity, body mass index and smoking habits. Multiple and logistic regression analysis was performed to isolate the variables that most influence MBL. Two consecutive menstrual episodes were measured in 117 women, to determine individual constancy.

RESULTS

MBL increased significantly with age (Kruskal-Wallis, P < 0.03) and the percentage of women with menorrhagia was significantly higher above 40 years of age (Mann-Whitney's ranks sum test, P < 0.05). The odds ratio of parous:nulliparous women for menorrhagia was 2.27:1, but after adjustment for age this influence disappeared. Body mass index and smoking habits were not significantly related to menorrhagia. The mean difference between the MBL of two consecutive menstruations is 2.1 ml (S.E.: 1.7, 95% CI: -1.3 to 5.5 ml).

CONCLUSIONS

Only age could be indicated as a risk marker for menorrhagia. Parity, body mass index and smoking habits appear to have no significant effect on MBL, when adjusted for age. The individual constancy in MBL between two consecutive cycles is very high and therefore one single measurement suffices in studies of MBL.

Cigarette smoke-modified low density lipoprotein impairs endothelium-dependent relaxation in isolated rabbit arteries

1. We investigated the effects of cigarette smoke-modified low-density lipoprotein (CS-LDL) on endothelium-dependent relaxations in various isolated rabbit arteries, and compared them with those of oxidized LDL (Ox-LDL). 2. In aorta rings, acetylcholine-induced endothelium-dependent relaxations were attenuated by preincubation with CS-LDL and Ox-LDL. Endothelium-independent relaxations induced by sodium nitroprusside were not modified. Similar changes were observed in rings of coronary and basilar arteries. 3. These findings indicate that CS-LDL, as well as Ox-LDL, may decrease the release or activity of endothelium-derived relaxing factor in vascular endothelial cells.

The role of thromboxane A2 in increased whole blood platelet aggregation in oral contraceptive users

Epidemiological studies have shown that oral contraceptives increase the risk of thromboembolic disease in susceptible women however the mechanisms involved are unclear. We investigated whole blood platelet aggregation in 44 women randomly allocated to 6 cycles of treatment with either gestodene (75ug) or desogestrel (150ug) combined with 30ug ethinyloestradiol (EE). The in vitro effects of aspirin and a thromboxane synthetase inhibitor, dazmegrel (UK38485) were also investigated. Oral contraceptive treatment caused a significant increase in collagen, arachidonic acid (AA) and ADP induced whole blood platelet aggregation. PAF induced aggregation was unchanged. There were no significant differences in the levels of platelet aggregation between the desogestrel/30ugEE and gestodene/30ugEE groups. In vitro incubation of platelets with aspirin and dazmegrel prevented the oral contraceptive induced increase in platelet aggregation. Dazmegrel caused an on treatment decrease in PAF induced aggregation in the desogestrel/30ugEE but not the gestodene/30ugEE group. The results of this study indicate that the use of oral contraceptives is associated with an increase in platelet aggregation that is mediated by changes in thromboxane/prostacyclin ratio(TXA2/PGI2). Although no significant differences were found between the two different progestogen combinations, the effects of dazmegrel on PAF induced aggregation suggest a possible difference in the progestogen modifying effects of desogestrel and gestodene which is unmasked when thromboxane synthetase is inhibited.

Interrelationship of magnesium and estrogen in cardiovascular and bone disorders, eclampsia, migraine and premenstrual syndrome

The anticonvulsive and antihypertensive values of magnesium (Mg) in eclampsia, and its antiarrhythmic applications in a variety of cardiac diseases, have caused Mg to be considered only for parenteral administration by many physicians. In contrast, nutritionists have long recognized Mg as an essential nutrient, because severe deficiencies elicit neuromuscular manifestations similar to those justifying its use in eclampsia. More recently, this element has been used to favorably influence latent tetany with and without thrombotic complications, to delay preterm birth, to influence premenstrual syndrome, and to ameliorate migraine headaches. Most of these disorders exclusively or largely afflict women. The lesions of arteries and heart caused by experimental Mg deficiency have been well documented and may contribute to human cardiovascular disease. Estrogen's enhancement of Mg utilization and uptake by soft tissues and bone may explain resistance of young women to heart disease and osteoporosis, as well as increased prevalence of these diseases when estrogen secretion ceases. However, estrogen-induced shifts of Mg can be deleterious when estrogen levels are high and Mg intake is suboptimal. The resultant lowering of blood Mg can increase the Ca/Mg ratio, thus favoring coagulation. With Ca supplementation in the face of commonly low Mg intake, risk of thrombosis increases.

Considerations for contraception in women with cardiovascular disorders

Women with hypertension, angina pectoris, or mitral valve prolapse require special considerations when selecting an appropriate method of contraception. All three effective, reversible options (oral contraceptives, intrauterine devices, or progestin implants) carry some degree of added risk for these patient populations. However, pregnancy itself presents certain risks and, in the event of contraceptive failure, certain women with these disorders are at increased risk of developing serious cardiovascular sequelae that affect both mother and fetus. These negative effects can carry far into the neonatal period. This article describes the risk/benefit profiles of the currently available contraceptive options relative to their potential impact in these compromised women.

Norgestimate: a clinical overview of a new progestin

The efficacy and safety of a new monophasic oral contraceptive, norgestimate/ethinyl estradiol, containing the third-generation progestin, norgestimate (250 micrograms), and ethinyl estradiol (35 micrograms), are reviewed. Norgestimate/ethinyl estradiol demonstrates excellent contraceptive efficacy, with a Pearl index of 0.25. Cycle control is reliable, with a low incidence of breakthrough bleeding and spotting. Because of the minimal androgenicity of norgestimate, norgestimate/ethinyl estradiol has a low impact on carbohydrate and lipid metabolism. It neither reduces the vasodilatory and antiaggregatory prostacyclin nor increases its endogenous antagonist, thromboxane. Norgestimate/ethinyl estradiol has no significant effect on blood coagulation factors. All these characteristics suggest that norgestimate/ethinyl estradiol may be associated with a lower risk of cardiovascular disease than other oral contraceptives currently available. Epidemiologic data, however, are not available, and physicians should be reluctant to prescribe it or any oral contraceptive to patients who have a history of vascular or thrombotic disorders.

The effect of low-dose oral contraceptives on lipids and lipoproteins in two at-risk populations: young female smokers and older premenopausal women

Young women who smoke and women over age 35 are considered to be at high risk for cardiovascular complications associated with oral contraceptive use. This study evaluated the effects of low-dose oral contraceptives on lipid and lipoprotein concentrations in 45 high-risk patients before, during, and after 6 months of treatment. Neither group showed a significant change from baseline in cholesterol, HDL cholesterol, LDL cholesterol or cholesterol ratios. Triglycerides increased and HDL2a levels decreased significantly in both groups but returned to baseline after treatment was discontinued, with the largest changes in both triglycerides and HDL2a levels occurring at 1 month. The change in triglyceride and HDL2a blood levels were within the laboratories' reference range. The lipid profile of these patients, therefore, was not worsened significantly through 6 months of oral contraceptive use. The young women who smoked did have consistently lowered levels of HDL cholesterol and its HDL2a subfraction when compared to their elder non-smoking cohort.