Blood serotonin levels in postmenopausal women: Effects of age and serum oestradiol levels

Maturitas, 17 (1993) 23-29 Elsevier Scientific Publishers Ireland Ltd.

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MAT 00733

Blood serotonin levels in postmenopausal women: effects of age and serum oestradiol levels Gustav0 F. Gonzales and Carlos Carrillo Institute de Investigaciones de la Altura and Department of Physiological Sciences, Faculty of Sciences, Universidad Peruana Cayetano Heredia, Lima (Peru)

(Received January 29, 1992; revision received July 7, 1992; accepted November 20, 1992)

This study investigated the effect of agcing and reduction in ovarian function on whole blood scrotonin levels and the effect of the oestrogen replacement in postmenopausal women on blood serotonin levels. Amenorrheic, natural postmenopausal and ovariectomised women had lower blood serotonin levels than regularly menstruating women. Blood serotonin levels increased after oestrogen replacement in postmenopausal women to values similar to those observed in regularly menstruating women. In ovaricctom&d women, the blood serotonin levels were inversely correlated with age (P < 0.01). In women with different serum oestradiol levels ranging 30-1335 pg/ml, a direct relationship was observed between serum oestradiol levels and whole blood serotonin levels (P < 0.001). It was concluded that whole blood serotonin concentration is reduced during menopause by suppression of ovarian function but may also be an effect of ageing.

Key work:

postmenopausal; serotonin; ovariectomy; oestrogen; age

Introduction Menopausal syndrome may be characterised mainly by hot flushes, depression and decreased libido [ 11;however, little is known about the pathophysiology of these symptoms. There are clinical and experimental data suggesting that serotonin may be implicated in these symptoms [2-61. Blood serotonin levels are lower in postmenopausal women than in normal menstruating women [2]. Low blood serotonin level has been related with depressive mood symptoms observed during peri- and postmenopause [3]. The reduced blood serotonin levels during postmenopause may be an effect of the reduction in ovarian function [2,4] but may also be an effect of ageing. Peripheral serotonin concentration is mostly bound to platelets but is also found free in plasma in low concentrations [7]. Oestradiol stimulates serotonin uptake by human blood platelets, in vitro [8], then, under normal circumstances estradiol may Correspondence to: Gustav0 F. Gonzales, Instituto de Investigaciones de la Altura, Universidad Peruana Cayetano Heredia, P.O. 1843, Lima-Peru. 03785122/93/$06.00 0 1993 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland

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increase blood serotonin levels thus increasing its uptake by the platelets, bringing the values to higher than those in men [2]. In order to investigate the role of ovarian hormones and age in the regulation of blood serotonin levels, we studied the whole blood serotonin concentrations in regularly menstruating women, postmenopausal women, ovariectomised women and in those with secondary amenorrhoea by ovarian failure. In addition, the response of blood serotonin levels in postmenopausal and ovariectomised women after oestrogen administration was also assessed. Materials and Methods

Blood serotonin in menstruating women and menopausal women Regularly menstruating women. Thirty-one regularly menstruating women aged 25-35 years were studied. In these women we have obtained 44 samples during follicular phase and 12 samples during luteal phase. Premature ovarian failure. Ten women aged 20-38 years with secondary amenorrhea by primary ovarian failure with or without presence of follicles determined by biopsy, but with serum FSH levels above 50 mU/ml were studied. No differences in blood serotonin levels were found between both groups, then, data were pooled. Postmenopausal women. Thirteen women aged 50-70 years with absence of menses by at least 12 months and serum FSH levels above 50 mu/ml were studied. Bilateral ovariectomised women. Twenty women aged 30-50 years who had undergone a surgical procedure for ovarian removal due to medical reasons (abortion, cystic tumours) were studied. At the time of the study, the post ovariectomy length ranged from 1 day to 6 months. Relationship between serum oestradiol level and blood serotonin Eighteen women attending our laboratory for serum oestradiol measurement were also studied for blood serotonin determination. One of the women was in a protocol of induction of ovulation with gonadotropins, three were attending the laboratory due to secondary amenorrhoea and fourteen were normal menstruating women. Effect of treatment with oestrogens on blood serotonin levels Nine oophorectomized women were treated with oral oestriol succinate at dose of 6 mg per day during 3 weeks and six women with natural menopause were treated with oral ethinyl oestradiol(30 &day) during 2 weeks. Blood serotonin concentration was measured before and at the end of the treatment. In all the cases, blood samples were obtained after fasting. One fraction of the sample was collected in a vial containing 15% EDTA in 3% ascorbic acid and the other fraction was centrifuged at 3000 rev./mm to obtain serum. The fraction for serotonin measurement was immediately frozen and assessed within a week. Hormone assays Serotonin levels were determined in whole blood (platelet fraction plus free frac-

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tion) by the spectrofluorometric method described by Geeraerts et al. [9] with the following modifications: HC104 (4N) was used instead of zinc sulphate (10%) and NaOH (1 N). The fluorescence of the sample was measured with an AmincoBowman spectrophoto-fluorometer at 540 nm after excitation at 295 nm. The intra-assay coefficient of variation was 4% and the interassay CV was 6% and the normal range of values for our laboratory was 1lo-250 rig/ml in regularly menstruating women [2]. Serum oestradiol was determined without extraction by radioimmunoassay, using [ “‘I]oestradiol as a radioactive marker. The assay was done using commercial kits (Diagnostic Products Co, Los Angeles, CA). The intra- and interassay variations were 4% (50-500 pg/ml) and 4.7%. The sensitivity of the method was 1.4%. The antiserum is highly specific for oestradiol with very low crossreactivity to other naturally occurring steroids. Statistics The comparison between normal regularly menstruating women, premature ovari-

an failure, natural and surgical menopausal women were analyzed by one-way analysis of variance (ANOVA). The significance between two means was determined by Tukey’s test. The paired f-test was used to assess the significance of the differences after treatment. The association between age and blood serotonin levels in oophorectomized women and between serum oestradiol and blood serotonin levels were assessed by linear regression analysis. A P value below 0.05 was considered as significant. Results

Blood serotonin levels were similar in regularly menstruating women during the follicular and the luteal phase (Table I).

TABLE 1 BLOOD SEROTONIN LEVELS IN ADULT WOMEN WITH OR WITHOUT NORMAL OVARIAN FUNCTION Group

N

Blood serotonin ng/ml

Regularly menstruating women Follicular phase Luteal phase Postmenopausal women Secondary amenorrhoca Bilateral ovariectomised women

44 12 13 10 20

167.9 ?? 10.0’ 187.9 f 18.4’ 89.2 f 8.1 90.7 f 7.3 89.8 f 6.0

Data are mean ?? S.E.M. N = number of data. *P < 0.05 with respect to adult men, postmenopausal women, secondary amenorrhoca and bilateral ovariectomised women.

26 TABLE II BLOOD SEROTONIN LEVELS IN POSTMENOPAUSAL (NATURAL OR SURGICAL) WOMEN BEFORE AND DURING TREATMENT WITH OESTROGENS

Pretreatment Treatment

Surgical menopause (oestriol treated)

Natural menopause (oestradiol treated)

9 9

6 6

76.0 f 6.8 153.9 f 29.4’

83.0 * 5.9 168.9 zt 40.1*

Data are mean & S.E.M. N = Number of data. *P c 0.01 with respect to values obtained before treatment.

In premature ovarian failure, natural postmenopausal and ovariectomized women, the blood serotonin levels were lower than in regularly menstruating women (Table I). Table II shows data on blood serotonin levels in natural and surgical postmenopausal women before and after oestrogen therapy. As observed in the table, the blood serotonin levels increased after 3 weeks of treatment with oestriol succinate or after 2 weeks with oestradiol treatment obtaining values similar to that observed in regularly menstruating women. Ovariectomized women aged 19-59 years were analysed for the relationship between whole blood serotonin level and age using regression analyses. Blood serotonin levels were inversely correlated with chronological age in these women (r = -0.73; P < 0.01; Y = 137.2-1.06X) (Fig. 1). In eighteen women having serum oestradiol levels ranging 30 to 1335 pg/ml, the relationship between whole blood serotonin level and serum oestradiol level was analysed using regression analyses (Fig. 2). A direct relationship was observed between serum oestradiol and blood serotonin levels (r = 0.92; Y = 77.2 + 0.22X; P < 0.001). A best-tit curve was observed using the following equation Y = 2.29 + 9.35 fi with a coefficient of correlation of 0.96, P < 0.001. Discussion The present study showed that whole blood serotonin levels were lower in women without ovarian function than in regularly menstruating women. This is in accordance with previous reports showing that whole blood serotonin [2] or platelet serotonin content [3] were lower in natural menopause. The levels of blood serotonin during postmenopause (natural or surgical) were similar to those reported in men [2] suggesting that oestrogens may play a role in determining the blood serotonin levels. In fact, our study also demonstrates that serum oestradiol correlated significantly with blood serotonin levels and that treatment of menopausal women with oestrogens increased the blood serotonin levels to values observed in regularly menstruating women; thus, suggesting a cause-effect relationship between blood serotonin and oestrogens.

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This effect of oestrogen on blood serotonin has been previously demonstrated under in vitro conditions [8]. In fact, human platelet serotonin uptake is increased in vitro by addition of oestradiol [8]. Reduced platelet serotonin content has been demonstrated in depression [lo] and

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in postmenopausal women showing depression [3]. Thus, it seems that serotonin may play a role in the etiopathogeny of the menopause syndrome. Although our results demonstrated a direct relationship between ovarian function and whole blood serotonin levels, they also showed that reduction in blood serotonin

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concentration may also be as a result of aging. This effect was observed by analysing women with surgical menopause but with different chronological ages. From this analysis, it was observed that the younger women had higher blood serotonin levels than the older ones, but in both cases the serotonin levels were lower than in regularly menstruating women. This means that reduction of blood serotonin by effect of ovarian removal is more dramatic than that in natural menopause where blood serotonin has been reduced gradually by an effect of ageing. The above observation may be in relation to the higher symptomatology observed in ovariectomised women than in natural menopausal women [12,13]. In summary, the present study demonstrated that blood serotonin is reduced during menopause as a result of suppression of ovarian function and also by the ageing process. Further studies will be required to determine whether these changes in blood serotonin are related to the menopausal syndrome. Acknowledgement

This work was supported by the WHO Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organization and by CONCYTEC (Lima-Per6). We acknowledge Dr Arturo Villena for his critical review of the manuscript. References 1 2 3

4 5 6

11 12 13

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