Effect of four different oral contraceptives on various sex hormones and serum-binding globulins

1. Introduction 

For many years, the so-called estrogenicity of oral contraceptives (OCs) has often been used as a marker of possible side effects. It has been suggested, e.g., that formulations which reduce serum parameters such as high-density lipoprotein cholesterol levels, due to a preponderance of the androgenic properties of the progestogen component, may increase cardiovascular risk [1]. Therefore, OCs have been developed that are regarded as being estrogen-dominant, although in nonsmokers OCs containing “androgenic” progestogens do not increase the risk of myocardial infarction [2]. A simple method for the evaluation of the “estrogenicity” of OCs was the measurement of the serum levels of corticosteroid-binding globulin (CBG), which were increased dose-dependently by ethinylestradiol (EE) irrespective of the progestogen component [3]. On the other hand, the response of sex hormone-binding globulin (SHBG) appears to reflect the resultant estrogen-stimulated rise and the counteraction by progestogens with androgenic properties [4]. Therefore, the composition of the respective formulation determines the effect on SHBG, but does not necessarily reflect their action on extra-hepatic parameters or tissues.

During the last decades, the development of OCs was focused on the reduction of the EE dose and the use of progestogens with minor androgenic activities in order to reduce their effect on various metabolic systems. The use of estradiol as an estrogen component in ovulation inhibitors, which could be expected to exert less impact on hepatic metabolism, was not successful because of a high rate of intermenstrual bleeding. As this side effect can be explained by a progestogen-induced enhancement of inactivation of estradiol in the endometrial cells, particularly by 17β-hydroxysteroid dehydrogenase [5], a sufficient local estrogenic efficacy and, hence, an acceptable cycle control can be achieved by the addition of a small dose of EE to estradiol [6], [7]. On the other hand, the profound reduction of the dose of EE, the ovulation-inhibitory action of which cannot be substituted adequately by estradiol, is only practicable if the progestogen component ensures a sufficient contraceptive efficacy [8]. This was the case for all preparations used in this study, as the ovulation inhibition dose of dienogest (DNG) is 1 mg and of levonorgestrel (LNG) 0.06 mg per day in the absence of EE [9].

In order to investigate whether a further reduction of the EE dose and a partial substitution by estradiol valerate (EV) in DNG-containing OCs will result in formulations with acceptable pharmacodynamics, we compared the effects on serum-binding globulins and some hormonal parameters of new preparations containing either 20 μg EE or a combination of 10 μg EE and 2 mg EV with those of two OCs containing 30 μg EE.

2. Methods 

3. Results 

Screening was carried out with 110 subjects, 100 of whom were randomized and received medication. Eight subjects discontinued the study prematurely, and no data were available from the treatment phase of one subject. Ninety-one subjects completed the study. The reasons for discontinuation were: bleeding anomalies (n = 1); withdrawal of consent (n = 1); inclusion criteria not met (n = 1); did not appear for final examination (n = 1); adverse events (n = 2); pregnancy (n = 1); other (n = 1).

The statistical analysis was carried out with the data of all 99 subjects who received any study medication and those from whom data from the treatment phase were available (full-analysis set). The four treatment groups were comparable in terms of baseline data for age and body mass index, which did not change significantly during treatment. No significant change in blood pressure or pulse rate was observed throughout the study.

During the treatment period of 6 months, the bleeding intensity was shifted to a lighter bleeding in all four groups, whereas the duration of bleeding remained unaltered. Absence of withdrawal bleeding was most frequently recorded in women using EE/EV/DNG (10%), while the lowest rate was observed with 30EE/DNG (1.4%).

As compared to the control cycle, the frequency of intracyclic bleeding was elevated in the first cycle of treatment with all preparations, but decreased during the following cycles. In the majority of the cases, intracyclic bleeding occurred only once (Table 1). During cycles 2–6, the proportion of women with at least one intracyclic bleeding was significantly higher in the groups with EE/EV/DNG and 20EE/DNG (Table 2).

Table 1. Number of episodes of intracyclic bleeding in treatment cycles 1–6 under treatment with 30EE/DNG, 20EE/DNG, EE/EV/DNG or EE/LNG (%)

		30EE/DNG	20EE/DNG	EE/EV/DNG	EE/LNG
	Cycles 1 to 6
	One episode	83.3	84.3	85.3	85.7
	Two episodes	16.7	13.7	14.7	14.3
	Four episodes	0	2.0	0	0

Table 2. Number of subjects with at least one intracyclic bleeding in treatment cycles 2–6 under treatment with 30EE/DNG, 20EE/DNG, EE/EV/DNG or EE/LNG (%)

		30EE/DNG	20EE/DNG	EE/EV/DNG	EE/LNG
	No	65.2	33.3	40.0	72.0
	Yes	34.8	66.7*	60.0*	28.0

* p < 0.05 vs. 30 EE/DNG and EE/LNG.

3.1. Sex hormones 

In all four treatment groups, the mean levels of free testosterone were profoundly reduced by 40–60% throughout the study (Table 3). The suppressive effect of 30EE/DNG was significantly more pronounced than that of EE/LNG only during cycle 1 (p < 0.05).

Table 3. Serum concentration of free testosterone (pg/mL), DHEAS (μg/mL), and prolactin (μIU/mL) in the control cycle and in the first, third and sixth cycle of treatment with 30EE/DNG, 20EE/DNG, EE/EV/DNG or EE/LNG

	Formulation	Control cycle	Cycle 1	Cycle 3	Cycle 6
	Free testosterone
	30EE/DNG	1.40 ± 0.87	0.45 ± 0.35**	0.38 ± 0.29**	0.56 ± 0.52**
	20EE/DNG	1.83 ± 1.20	0.68 ± 0.45**	0.52 ± 0.32**	0.59 ± 0.45**
	EE/EV/DNG	1.90 ± 1.80	0.89 ± 0.64**	0.74 ± 0.50**	0.86 ± 0.66**
	EE/LNG	1.56 ± 0.79	0.82 ± 0.60**	0.59 ± 0.42**	0.63 ± 0.47**
	DHEAS
	30EE/DNG	1.69 ± 1.06	1.25 ± 0.59**	1.19 ± 0.69**	1.06 ± 0.51**
	20EE/DNG	2.22 ± 1.10	1.75 ± 0.99**	1.63 ± 0.83**	1.57 ± 0.76**
	EE/EV/DNG	2.03 ± 0.99	1.78 ± 1.00**	1.70 ± 1.04**	1.52 ± 0.96**
	EE/LNG	2.01 ± 0.92	1.81 ± 0.85**	1.76 ± 0.85**	1.53 ± 0.86**
	Prolactin
	30EE/DNG	275 ± 149	316 ± 189	328 ± 207	339 ± 169
	20EE/DNG	331 ± 257	274 ± 135	315 ± 159	311 ± 137
	EE/EV/DNG	310 ± 177	369 ± 264	361 ± 192*	438 ± 276**
	EE/LNG	363 ± 261	392 ± 245	356 ± 209	380 ± 252

Values are mean ± SD. Within-group differences refer to relative changes.

* p < 0.05 vs. control cycle. ** p < 0.01 vs. control cycle.

During the first cycle of treatment with all preparations, the mean serum level of DHEAS was significantly reduced by 10–20% (Table 3). The suppressive effect appeared to be enhanced time-dependently and, at the end of the sixth cycle, the decline was in the range of 25–30%. There were, however, no significant inter-group differences concerning DHEAS.

During treatment with EE/EV/DNG, a rise in the mean prolactin levels occurred, which became significant in the third cycle and was highest in the sixth cycle (+75%). In contrast, the slight changes observed in the other groups were not significant (Table 3). There were, however, no inter-group differences at any time during the study. In the control cycle, only a few women showed elevated prolactin levels. While these findings did not change during treatment with 20EE/DNG, 30EE/DNG and EE/LNG, the number of hyperprolactinemic women increased from two to seven during treatment with EE/EV/DNG.

3.2. Serum-binding globulins 

The four preparations caused a progressive rise in the serum levels of SHBG, which reached the highest values at the end of the sixth cycle (Fig. 1). During the treatment period, the degree and time course of the effects differed significantly among the groups, showing much larger increases with the DNG-containing OCs than with EE/LNG. The mean changes observed in the sixth cycle were +320% with 30EE/DNG, +270% with 20EE/DNG, +260% with EE/EV/DNG and +80% with EE/LNG.

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Fig. 1. Effect of three dienogest-containing oral contraceptives (30EE/DNG, 20EE/DNG, EE/EV/DNG) and EE/LNG on the serum concentration of SHBG (mean ± SD).

The CBG concentrations increased rapidly during the first cycle of treatment with all preparations, and the values remained elevated at this level until the end of the study (Fig. 2). The degree and the time course of the effects differed significantly among the four groups. The effect correlated with the EE dose, while the influence of the progestogen component appeared to be less pronounced. The lower increase in CBG (+55%) observed during treatment with EE/EV/DNG as compared to that with 20 EE/DNG and EE/LNG (+85%) indicates that the addition of 2 mg EV does not compensate for the 10 μg difference in the EE dose (Fig. 2).

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Fig. 2. Effect of three dienogest-containing oral contraceptives (30EE/DNG, 20EE/DNG, EE/EV/DNG) and EE/LNG on the serum concentration of CBG (mean ± SD).

There was a significant increase in serum TBG already in the first cycle of treatment with all formulations which remained at this level until the end of the study (Fig. 3). The effect was significantly more pronounced with the DNG-containing OCs (+50–60%) than with EE/LNG (+30%).

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Fig. 3. Effect of the three dienogest-containing oral contraceptives (30EE/DNG, 20EE/DNG, EE/EV/DNG) and EE/LNG on the serum concentration of TBG (mean ± SD).

4. Discussion 

The present study demonstrates that the reduction in the EE dose of DNG-containing OCs from 30 to 20 μg leads to a slight increase in the rate of intermenstrual bleeding, and a further increase could be expected for OCs containing only 10 μg EE. The results suggest that the combination of 10 μg EE with 2 mg EV results in an acceptable bleeding pattern which is in agreement with previous findings [6]. It must, however, be kept in mind that due to the low number of volunteers, the data must not necessarily be representative for a large population. Previous investigations revealed that the use of 2–4 mg estradiol or EV only, as an estrogen component in combination with a potent progestogen, is associated with a high incidence of irregular bleeding [11], [12], [13]. Obviously, an acceptable cycle control can be achieved by the addition of a small dose of EE to natural estrogens. These observations correspond to the supposition that in the presence of potent progestogens, a sufficient estrogenic activity must be maintained within the endometrial cells and the endometrial vessel walls in order to achieve a stable bleeding pattern [5], [14].

Serum-binding globulins, which are synthesized in the liver, are elevated under oral treatment with estrogens; as during the first liver passage, the local estrogen concentrations are considerably higher than those measured peripherally. The effect, which depends on the dose and type of the estrogen, can be counteracted by progestogens with androgenic activity, at least in the case of SHBG and TBG. Previous investigations demonstrated a 200–300% rise in SHBG levels under treatment with estrogen-dominant OCs [15], [16], [17], [18], [19]. The present study revealed that all formulations containing DNG, which has no androgenic but antiandrogenic properties, caused a much stronger rise in SHBG than EE/LNG. As previously shown with desogestrel-containing formulations [20], the effect on SHBG of the DNG-containing OCs were dependent on the EE dose, and the comparison between 20EE/DNG and EE/EV/DNG suggests that the addition of 2 mg estradiol can compensate for the reduction of the EE dose by 10 μg. The progressive rise in SHBG in the course of the six treatment cycles can be explained by the observation that during the hormone-free interval of 7 days, the SHBG levels decline, but do not reach baseline values [18], [21].

In contrast to SHBG, the estrogen-stimulated elevation of CBG, which is also dose-dependent [3], [19], [20], [22], is not attenuated by progestogens to an appreciable degree [17], [18], [23], [24]. In the present study, the CBG levels measured during treatment with 20EE/DNG were only slightly less than with 30EE/DNG. The significantly lower levels in the EE/EV/DNG group indicate, however, that in contrast to SHBG, the effect of 2 mg EV on CBG is considerably less than that of 10 μg EE. Moreover, the lower rise in CBG observed with 30EE/LNG than with 30EE/DNG suggests that progestogens with androgenic activity may moderately counteract the estrogen-dependent effect on CBG. A similar tendency was observed in another study, which revealed a higher increase in CBG with an OC containing the antiandrogenic progestogen cyproterone acetate than with formulations containing nortestosterone derivatives [17].

The moderate rise in the TBG levels during treatment with the DNG-containing OCs, which did not differ significantly, suggests a lesser effect of EE on hepatic synthesis of TBG and a lack of dose-dependency. On the other hand, the significantly lower serum concentrations of TBG in the EE/LNG group indicates an antagonistic effect of progestogens with androgenic activity. The increase in TBG, which was also observed with other estrogen-dominant OCs [25], is, in all probability, caused by reduced degradation and clearance due to a higher sialic acid content [26].

The 40–60% reduction in the serum concentrations of free testosterone was observed with the four formulations in the first cycle of intake and remained in this range during further treatment. The effect is similar to that reported for various OCs irrespective of their composition [17], [18], [21]. The level of free testosterone, which is suggested to be the biologically active fraction of circulating testosterone, is influenced by the concentration of total testosterone and SHBG, which binds a large proportion of the androgen with high affinity [27]. The suppression of total testosterone by 30–40%, which has been observed during treatment with many OCs [15], [16], [17], [18], [19], [28], [29], [30], was suggested to be caused by both a reduction of gonadotropin release and a rapid direct inhibitory effect of sex steroids on ovarian and adrenal steroid synthesis [31], [32], [33]. The corresponding reduction of free testosterone levels is enhanced by the EE-induced rise in SHBG [27]. It must, however, be emphasized that the free-testosterone concentrations measured with solid-phase RIA, do not reflect the “true” values. They are considerably lower than those measured with validated methods like the ultrafiltration technique, and are dependent on the endocrine status [10].

The present study revealed a significant reduction of DHEAS throughout the study in all treatment groups, which appeared to be enhanced with increasing duration of treatment. A similar effect has been reported previously, at least during a period of up to six cycles of treatment with various OCs [16], [18], [21], [34]. During longer treatment, the suppressive effect on DHEAS might also be attenuated [21]. The underlying mechanism of the reduction of this adrenal androgen precursor is not clarified, but might be caused by a direct inhibitory action of OCs on adrenal steroid synthesis [33].

It is known that treatment with low-dose OCs mostly generally does not influence prolactin levels [16], [25], [28], [32], [34], [35], [36], except sporadic and transitory hyperprolactinemias in predisposed women [21], [37]. In contrast, a significant rise in prolactin has been measured in women treated with high-dose OCs [38], [39]. In the present study, no changes in prolactin levels were observed with 20EE/DNG, 30EE/DNG and EE/LNG, while using EE/EV/DNG caused a time-dependent significant rise that was 40% higher after six treatment cycles. This suggests that estradiol exerts a more pronounced effect on prolactin release than ethinylestradiol.

The present results demonstrate that the four OCs with differing composition exert a marked reduction of the serum concentration of free testosterone, which is brought about by a suppression of total testosterone and androgen precursors and an increase in SHBG. The substitution of a proportion of the EE dose by 2 mg EV may lead to a lesser influence on some, but not all, serum hepatic parameters, while the effects on other tissues, e.g., release of prolactin from the pituitary, might even be enhanced. Therefore, with respect to clinical efficacy and adverse effects, a possible benefit of replacement of EE by natural estrogens in OCs remains to be proven.