Effects of oral contraceptives containing different ... - Nature

Journal of Human Hypertension (1998) 12, 235–238  1998 Stockton Press. All rights reserved 0950-9240/98 $12.00

ORIGINAL ARTICLE

Effects of oral contraceptives containing different progestogens on sodium-lithium countertransport in normal females GI Adebayo1, L Norris2, M Devitt2, J Bonnar2 and J Feely1 Departments of 1Therapeutics and 2Obstetrics & Gynaecology, TCD Medical School, Trinity Centre for Health Science, St James’s Hospital, Dublin 8, Eire

In view of the lack of unanimity on the effect of longterm intake of combined oral contraceptives (OC) on external sodium-dependent lithium efflux, otherwise known as sodium-lithium countertransport (SLC), we undertook a double-blind study to investigate the possible interaction between SLC and OC in healthy women with regular menstrual cycles. In a group of 17 volunteers, aged 27.0 ± 1.1 years (mean ± s.e.m.) and weighing 61.4 ± 2.0 kg, ingestion of ethinyloestradiol + 150 ␮g desogestrel for 30 ␮g 3 months caused an increase in SLC activity from a baseline value of 0.254 ± 0.017 mmol/lcell.h to 0.274 ± 0.017 mmol/lcell.h (P = 0.05). The activity of the transport system after 6 months treatment remained higher than at baseline (0.280 ± 0.016 mmol/lcell.h, P ⬍ 0.025) but was comparable to that at 3 months.

Blood pressure and weight remained unaltered during the study period. In a comparable group of 16 volunteers of age 26.1 ± 1.3 years and weight 63.5 ± 2.1 kg, control SLC activity (0.218 ± 0.012 mmol/lcell.h) was comparable to that after 3 months (0.215 ± 0.011 mmol/lcell.h) and 6 months (0.216 ± 0.011 mmol/lcell.h) intake of 35 ␮g ethinyloestradiol + 2 mg cyproterone acetate. Body weight and blood pressure remained similarly unchanged. These results not only confirm that long-term intake of OC may cause increased SLC activity, but also suggest that the type of the progesterone in the medication used could be an important determinant of such interaction.

Keywords: combined oral contraceptives; sodium-lithium countertransport; blood pressure

Introduction A recognised complication of oral contraceptives is the development of hypertension.1 Abnormalities in cellular cations transport have been incriminated in the pathogenesis of essential hypertension.2–4 Evidence that similar aberrations might be involved in hypertension associated with long-term use of combined oral contraceptives (OC) is provided by the reported increase in the activities of both sodiumpotassium co-transport and sodium-lithium countertransport (SLC) in individuals on such medications.5,6 However, not all are agreed on the issue of increased SLC activity following intake of OC, the observation by Beuckelmann and Erdmann6 has been confirmed by some workers,7,8 but others have reported that such medication is not associated with any alteration in the activity of the transport system.9 The cause of this lack of unanimity is not clear, but differences in the formulations of OC is, conceivably, a possibility. Whatever the cause, it is noteworthy that none of the studies that have so far Correspondence: Professor J Feely, Department of Therapeutics, TCD Medical School, Trinity Centre for Health Science, St James’s Hospital, Dublin 8, Eire Received 1 June 1997; revised 9 September 1997; accepted 5 November 1997

addressed the possible OC/SLC interaction was blinded in any way. The aim of this study was to look, serially, at the effects of two OCs on SLC using a double-blind design.

Materials and methods Thirty-five healthy females with regular menstrual cycles (28 ± 5 days), aged 18–35 years (26.9 ± 0.8 years; mean ± s.e.m.) and weighing 43.5–73.0 kg (62.7 ± 1.4 kg) were recruited. All volunteers gave full and informed consent; and the study had the approval of the hospital ethics committee. Each volunteer was randomly given either 30 ␮g ethinyloestradiol/150 ␮g desogestrel combination or 35 ␮g ethinyloestradiol/2 mg cyproterone acetate in a double-blind fashion. For each volunteer, blood was taken in the morning of days 15–18 of their menstrual cycle for biochemistry and SLC assay before treatment, and at the same stage of the cycle, after 3 and 6 months of medication. At each study point, blood pressure was determined, by the same person, as the average of two readings made in the sitting position after a 15-min period of rest. Their weights were also recorded at each visit. All patients had at least two normal periods since childbirth, miscarriage or previous OC use. Some descriptive

Effects of oral contraceptives on Naⴙ/Liⴙ countertransport GI Adebayo et al

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statistics of those who completed the study are presented in Table 1. Inclusion criteria These were as follows: (i) healthy women of 18–35 years and not on any medication; (ii) regular cycle pattern (28 ± 5 days); (iii) normal blood pressure, defined as systolic and diastolic less than 140 mm Hg and 90 mm Hg, respectively; (iv) negative family history of hypertension and/or cardiovascular diseases established from computer records in the maternity (Coombe) hospital where available, and/or by direct questioning; (v) at least two normal, biphasic cycle after childbirth (or miscarriage); and (vi) willingness to undergo regular check-ups pre-, intra-, and post-treatment. Exclusion criteria These included: (i) likelihood of pregnancy; (ii) lactation; (iii) liver disease; (iv) hypertension requiring treatment (diastolic ⬎90 mm Hg, systolic ⬎140 mm Hg after repeated measurements); (v) past, and/or family history of hypertension, thromboembolism or thrombophlebitis, diabetes, haemoglobinopathies, systemic lupus erythematosis, and dyslipidaemia; (vi) history of chorea, migraine, herpes gestationalis, endometriosis, uterine myoma, multiple sclerosis, and epilepsy; (vii) smoking in women over 30 years and/or more than 10 cigarettes per day; and (viii) obesity. SLC assay SLC activity was quantified by a modification of the method reported by Canessa et al.10 After the removal of the plasma and buffy coat, erythrocytes were washed five times with a washing solution of the following composition: 140 mM choline chloride, 10 mM glucose, 4 mM magnesium chloride, and 10 mM Tris-MOPS (pH 7.4, 4°C). The washed cells were then loaded with lithium by incubating them Table 1 Baseline descriptive statistics of women on combined oral contraceptives Parameter

Medication Ethinyloestradiol Ethinyloestradiol (35 ␮g) + (30 ␮g) + Desogestrel Cyproterone acetate (2 mg) (150 ␮g)

Number Age (years) Weight (kg) Blood pressure (mm Hg) Systolic Diastolic Plasma sodium (mmol/l) Plasma potassium (mmol/l) Plasma chloride (mmol/l) Plasma creatinine (␮mol/l) Plasma uric acid (␮mol/l) Plasma calcium (mmol/l)

17 27.0 ± 1.1 61.4 ± 2.0

16 26.1 ± 1.3 63.5 ± 2.1

109.7 ± 1.5 68.5 ± 1.2 140.4 ± 0.4 4.1 ± 0.1 102.7 ± 0.8 74.1 ± 3.1 206.6 ± 9.3 2.45 ± 0.02

110.9 ± 1.5 68.4 ± 1.6 140.1 ± 0.4 4.2 ± 0.1 103.1 ± 0.8 69.2 ± 2.4 226.8 ± 14.5 2.47 ± 0.02

for 2 h in a solution of 140 mM lithium chloride, 10 mM lithium carbonate, 10 mM glucose, and 10 mM Tris-MOPS (pH 8.0, 37°C); and washed thereafter as before. Subsequently, SLC was determined at 37°C as previously reported.11 For this study, the sodium-free medium, used to quantify passive lithium efflux, was of the same composition as the washing solution. Additionally, it contained 0.1 mM ouabain and was of pH 7.4 at 37°C. The sodium-rich medium contained 140 mM sodium chloride, 0.1 mM ouabain, and the same amount of glucose, magnesium chloride, and Tris-MOPS as the washing solution; and was of pH 7.4 at 37°C. All solutions were of 290–300 mosmol/kg. Statistical analyses Data are given as mean ± s.e.m.; and statistical evaluation made with one-way analysis of variance and Bonferroni’s correction for multiple analyses. In all cases, P ⬍ 0.05 was taken as the minimum level of significance.

Results Two volunteers withdrew from the study after 1 month — one because of headache and the other just did not report for follow-up. Of the remaining 33, 17 volunteers aged 20.0–34.0 years (27.0 ± 1.1 years) and weighing 43.5–73.0 kg (61.4 ± 2.0 kg), took the ethinyloestradiol/ desogestrel combination. Their baseline SLC activity was 0.254 ± 0.017 mmol/lcell.h; and was not significantly different from that of 0.218 ± 0.012 mmol/ lcell.h in the ethinyloestradiol/cyproterone acetate-treated group (t = 1.745, df = 31, P = 0.091, unpaired t-test). It rose after 3 months of medication to 0.274 ± 0.017 mmol/lcell.h (P = 0.05); and remained higher after 6 months treatment (0.280 ± 0.016 mmol/lcell.h; P ⬍ 0.025). The activities of the transport system after 3 and 6 months of medication were comparable (Figure 1a). Weight and blood pressure were unaltered (Table 2). Sixteen volunteers took the ethinyloestradiol/ cyproterone acetate combination. They were 26.1 ± 1.3 years (range: 18.0–35.0 years), and weighed 63.5 ± 2.1 kg (range: 52.5–82.0 kg) (Table 1). In this group, the baseline SLC activity was 0.218 ± 0.012 mmol/lcell.h; and was comparable to that after 3 months (0.215 ± 0.011 mmol/lcell.h) and 6 months (0.216 ± 0.011 mmol/lcell.h) medication (Figure 1b). Weight and blood pressure also remained unaltered during the experimental period (Table 2).

Discussion This study shows different effects of two different OC preparations in two groups of otherwise comparable volunteers (Table 1). Ingestion of ethinyloestradiol/cyproterone acetate combination for 6 months was not associated with alteration in any of the parameters measured. However, SLC activity increased after 3 (P = 0.05) and 6 months (P ⬍ 0.025) of ethinyloestradiol/desogestrel medication (Figure 1a).


Figure 1 Effects of oral intake of ethinyloestradiol combined with desogestrel (a) or cyproterone acetate (b) on SLC activity in healthy female volunteers. *P = 0.05; **P ⬍ 0.025 compared with control. Table 2 Effect of combined oral contraceptives on weight and blood pressure in healthy subjects Parameters

Control

3-months

6-months

Ethinyloestradiol (35 ␮g) + Cyproterone acetate (2 mg) (n = 16) Weight (kg) 63.5 ± 2.1 63.0 ± 2.0 62.8 ± 2.5 Blood pressure (mm Hg) Systolic 110.9 ± 1.5 114.1 ± 2.4 111.9 ± 1.8 Diastolic 68.4 ± 1.6 67.5 ± 1.6 68.1 ± 1.4 Ethinyloestradiol (30 ␮g) + Desogestrel (150 ␮g) (n = 17) Weight (kg) 61.4 ± 2.0 60.9 ± 2.1 61.3 ± 2.0 Blood pressure (mm Hg) Systolic 109.7 ± 1.5 112.6 ± 1.6 114.7 ± 2.0 Diastolic 68.5 ± 1.2 68.8 ± 1.3 70.0 ± 1.7

Opinions are divided on the effect of OCs on SLC. Some believe the drugs increase the activity of the transport system;6–8 but others affirm, albeit in a smaller number of subjects, that they do not.9 The results of this study suggest that possibly part of the discrepancy could be the different type(s) of medication used by the subjects studied. The design of this study does not allow for the identification of what the cause(s) of the observed different effects of the medications used might be. Desogestrel belongs to the gonane group of 19-nortestosterone derivatives, known to reduce hepatic elimination of triglyceride. Indeed, there are at least 13 reports of elevation of plasma triglyceride resulting from medication with ethinyloestradiol/desogestrel combination.12 Such increase in plasma triglyceride

could be expected to increase SLC activity.13–16 Fasting plasma lipids were not measured in this study, but even so elevated plasma triglyceride is unlikely to be mainly responsible for the increased SLC activity in the ethinyloestradiol/desogestrel-treated group in view of the fact that the ethinyloestradiol/cyproterone acetate combination, taken by the other group, has been reported to similarly alter plasma lipids.17 There are reports that increased plasma renin activity, resulting from increased level of the hormone, is associated with increased SLC activity.18,19 Given the well recognised capacity of oestrogen-progesterone combinations to induce increase in plasma renin activity,20 it could be argued that the latter is a possible mechanism for the increase in SLC activity observed in those on ethinyloestradiol/desogestrel combination in the present study. However, such argument is flawed by the fact that the oestrogen-progesterone combination-induced increase in plasma renin activity is due more to an increase in plasma level of renin substrate than that of the hormone renin itself.21 Furthermore, ethinyloestradiol, which induces synthesis of renin substrate,22 is a component of both medications used in the present study. It seems more likely that the different effects of the two medications used in this study is related to their different progestogen contents. A suggestion has been made that the generally higher levels of activity of cation transport systems in males, compared to females, is due mainly to testosterone; and that such effect(s) could be accomplished to varying extents by progestogens depending on how closely related each of the latter is to testosterone structurally and/or functionally.5 In this regard, it is interesting to note that the cyproterone acetate is a 17␣-hydroxyprogesterone derivative which, though has progestational activity, is primarily an antiandrogen. On the other hand, desogestrel is a 19-nortestosterone-derived progesterone with some residual androgenic activity.12 Consistent with this reasoning is the observation that the oestrane norethisterone, also a 19-nortestosterone derivative with residual androgenic activity, similarly increased Na+/Na+ countertransport (a mode of operation of Na+/Li+ countertransport) after 3 to 6 months intake in healthy volunteers.8 The increase in SLC, unaccompanied by similar change in blood pressure in the ethinyloestradiol/desogestrel-treated group, is not supportive of a direct link between the stimulation of the transport system and the development of hypertension resulting from OC intake. Doubt over such a link has similarly been expressed by others.8 However, it need be emphasized that SLC is but one of the many transport systems involved in the homeostatic control of intracellular cations. Alteration(s) in the activity of other cation transport systems may well be involved in the pathogenesis of oral contraceptive-induced hypertension; and it is possible that in this situation, and as has been suggested in essential hypertension, increased SLC activity is simply an epiphenomenon. There are other possible alternative explanations.

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SLC activity is mainly genetically determined.23 However, the encoding gene, far from being a disease one, is a susceptibility gene. Development of hypertension is, therefore, not an inevitable consequence of inheriting a high activity of the transport system in the absence of an environmental trigger. Attesting to this is the fact that much higher activities than those in individuals who developed hypertension have been observed in subjects who are normotensive but are nevertheless predisposed to hypertension, given their family history.24 None of the volunteers in this study had hypertension or a family history of same. They are, therefore, unlikely to have the major recessive susceptibility gene.23 This lack of the requisite genetic make-up may have rendered the environmental trigger by ethinyloestradiol/desogestrel medication ineffective in causing an increase in blood pressure. It is possible that susceptible women, treated similarly, may show an increase in blood pressure in association with an increase in SLC. Secondly, there has been a report that hypertension associated with OC medication could develop over a period of 3 years.1 It could, therefore, be argued that the relatively short period of the present study was, at least, partly responsible for the lack of a significant increase in blood pressures of the volunteers. There is yet another possible reason for the observed lack of significant increase in blood pressure. It relates to the size of the study. Given the relatively small number of observations, a type II error cannot be outrightly discounted. Results of this study not only support the observations by other workers that intake of combined oral contraceptives is associated with increased SLC activity, but also suggest that the progestogen component of the preparation used could be an important determinant of such alteration in the activity of the transport system.

Acknowledgement This work was supported by the Health Research Board of Ireland.

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