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Diurnal Rhythm of Free Estradiol During the Menstrual Cycle

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Diurnal Rhythm of Free Estradiol During the Menstrual Cycle European Journal of Endocrinology (2003) 148 227–232 ISSN 0804-4643 CLINICAL STUDY Diurnal rhythm of free estradiol during the menstrual cycle Ai-Min Bao1,2, Rong-Yu Liu2, Eus J W van Someren3,5, Michel A Hofman3, Yun-Xia Cao4 and Jiang-Ning Zhou1,2 1Department of Neurobiology, School of Life Science, University of Science and Technology of China, Hefei 230032, Anhui, People’s Republic of China, 2Anhui Geriatrics Institute, The First Affiliated Hospital of Anhui Medical University, Hefei 230022, Anhui, People’s Republic of China, 3Netherlands Institute for Brain Research, 1105 AZ Amsterdam ZO, The Netherlands, 4Department of Obstetrics and Gynecology, The First Affiliated Hospital of Anhui Medical University, Hefei 230022, Anhui, People’s Republic of China and 5Netherlands Institute for Clinical and Experimental Neuroscience, VU University Medical Centre, 1105 AZ Amsterdam ZO, The Netherlands (Correspondence should be addressed to Jiang-Ning Zhou, Anhui Geriatrics Institute, The First Affiliated Hospital of Anhui Medical University, Hefei 230022, Anhui, People’s Republic of China; Email: [email protected]) Abstract Objective: To investigate the diurnal rhythm of estrogens in normally cyclic women during reproduc- tive life. Design: Multiple saliva sampling in normally cyclic healthy women during reproductive life at different phases of their menstrual cycles was carried out. Methods: Salivary estradiol was measured by radioimmunoassay in samples collected every 2 h for 24 h from 15 normally cyclic healthy women during reproductive life during the menstrual phase, the late follicular/peri-ovulation phase, the early to mid luteal phase and the late luteal phase, respectively, of their menstrual cycles. The levels of salivary estradiol were analyzed by means of periodic regression. Results: A daily biological rhythm of free estradiol was found after quantification with a nonlinear periodic regression model. The observed diurnal free estradiol rhythm consists of two major com- ponents: an asymmetrically peaked diurnal cycle and ultradian harmonics in the range of 6 to 12 h. The diurnal and ultradian rhythms were remarkably consistent throughout the menstrual cycle in terms of mesor (24 h mean level), peak width and amplitude. There was a tendency for the 24-h rhythm acrophases to converge in the early morning, while the acrophase of the menstrual phase occurred significantly later than in the late follicular/peri-ovulation phase. Conclusions: The diurnal rhythm of estradiol has a similar complex temporal organization for different menstrual phases. The menstrual cycle mainly modulates the acrophase of the diurnal rhythm. European Journal of Endocrinology 148 227–232 Introduction rhythm (11–15), little is known about the fluctuation of estrogens in normally cyclic women over the 24-h It is known that estrogens are more than just ‘sex hor- period, i.e. its daily biological rhythm. Knowledge of mones’ that play a principal role in regulating beha- the daily secretion profiles of estrogen will contribute vioral and physiological events essential for successful not only to our understanding of its function but also procreation (1). Estrogens are also important for the offer useful reference data for further study on the roles protection of the cardiovascular system (2) and for of rhythms in estrogen secretion in various diseases. the maintenance of bone (3, 4). Estrogens play an It is known that both the hypothalamic gonadotropin- important role in the sexual differentiation of the releasing hormone (GnRH), and the pituitary luteinizing brain (5) and in modulating the regulation of the auto- nomic and reproductive neuroendocrine system, mood, and follicle-stimulating hormones have pulsatile and cognition (5–7). Changes in estrogen level in secretion profiles (11–16) and that these hormones different physiological and pathological situations are affect the secretion of estrogens within the human hypo- a topic of considerable research interest. Previous thalamic–pituitary–gonadal axis. It is suggested in studies on estrogen levels mainly focused on their fluc- studies with both animal and human material that the tuation during the menstrual cycle, postpartum and hypothalamic suprachiasmatic nucleus (SCN), the menopause, using single or multiple time-point samples endogenous circadian pacemaker in the brain, is sex (8–10). Although studies on estrogen secretion in early hormone sensitive and is involved in the generation puberty, gestation and breast cancer have assumed for a and regulation of the female reproductive cycle long time that estrogen levels in humans have a diurnal (17, 18). Based on the observations mentioned above, q 2003 Society of the European Journal of Endocrinology Online version via http://www.eje.org Downloaded from Bioscientifica.com at 10/02/2021 03:41:51AM via free access 228 A Bao and others EUROPEAN JOURNAL OF ENDOCRINOLOGY (2003) 148 it is reasonable to hypothesize that the biological rhythm the subject’s pillow at night until the end of each of estrogens is composed of a complex of cycles including 24-h period. The samples were centrifuged for 10 min not only the monthly cycle but also circadian rhythms at 3000 g and frozen at 220 8C until assayed. The and ultradian pulses. The recent development of non- subjects were non-heavy exercisers, non-alcohol/non- invasive saliva measurements of steroid hormones (19) caffeine drinkers and non-smokers. Subjects were allowed us to investigate the diurnal and ultradian studied in their habitual environment with their habit- rhythms of salivary free estradiol, i.e. the biologically ual occupations. They were advized to brush their teeth active form of estrogen, in women of reproductive age without toothpaste, to drink plenty of water but to in their natural environment. We further explored avoid eating and to rinse their mouths thoroughly whether circadian and ultradian rhythms of free estra- with water 30 min before sampling during the daytime. diol are modulated by the menstrual cycle. They were also asked to avoid sexual intercourse during the sampling day. A total of 57 sets of data points were gathered in the present study (no data were available Materials and methods for phase I of subject #10 and phases I and IV of subject Participants #8 because of the lack of sufficient saliva at some time- points). Please note that we did a pilot study before the Fifteen healthy Chinese women (mean age 32.8 years, formal study with two subjects for two days, every range 25–40 years) entered the study between 25 other day of phase II (late follicular, peri-ovulation March and 20 June 2001. They all took part on a phase) respectively, in which the saliva sampling inter- voluntary basis, and had regular menstrual cycles val was set at 1 h between 0800 h and 2200 h and at with periods from 27 to 30 days. Exclusion criteria 2 h between 2200 h and 0600 h the next morning. were as follows: abnormal body mass index (BMI The study of the secretion pattern of estradiol in the #18 or $25), medication for chronic illnesses, oral pilot study suggested that a 2-h sampling interval contraceptives within the last 6 months, lactating throughout the day (which is more convenient for par- within the last 12 months, evidence of infertility, or ticipants) would not affect the deduced diurnal rhythm presence of sexually transmitted diseases. All subjects pattern, which is the main topic of our study. signed a consent form and the study was approved by the Anhui Medical University review board. Salivary estradiol assay Procedures Salivary estradiol (E2) concentrations were measured with the use of a double-antibody radioimmunoassay 125 Subjects participated in the study for a total of four days (RIA) with I-labeled E2. Antibody and tracers were over a period of one month, based upon their self- derived from DSL-39100 estradiol (third generation; reported menstrual cycle day-count: phase I, one day Diagnostic Systems Laboratories, Inc., Webster, TX, from day 2–3 (menstrual phase); phase II, one day USA). The estradiol antibody is rabbit anti-estradiol in from day 12–14 (late follicular, peri-ovulation phase); a protein-based buffer with sodium azide. The antibody phase III, one day from day 18–23 (early to mid cross-reacts 6.9% with estrone and less than 1.0% with luteal phase); phase IV, one day from day 25–28 (late 17b-estradiol-3-glucuronide. The protocol used was luteal phase). In phase II, ovulation was determined that according to Shirtcliff et al. (22). The standard by changes in body basal temperature and every sub- curve of the salivary estradiol assay was highly repro- ject had an ovary ultrasonic examination in the B ducible, with an average correlation coefficient of mode to help ensure the phase according to the dimen- 0.9969 in this study. The average intra- and interassay sion of the dominant follicle and to ensure the presence coefficients of variation were 7.2 and 9.9% respectively. of a normal genital system (20). At the entrance time of Analytical recovery was on average 100.7%. Linearity each day, they were given a package containing 12 was assessed (1:2 to 1:12 dilutions) across the range Salivettes (Sarstedt, Nu¨mbrecht, Germany) (21) and of measurements with an average recovery of 89% were asked to collect saliva every 2 h from 0800 h to (range 76%–103%). The range of standards was 0600 h the next morning. Between 2200 h and 0.375–7.500 pg/ml. The analytic sensitivity was 0600 h the next morning the subjects went to 0.250 pg/ml. bed/got up with the light(s) turned off/on respectively. This schedule was not significantly different from Statistical analysis their work and rest routine. Saliva samples were collected with small polyester tampons held in the Examination of the raw data indicated that both ultra- mouth for about 5 min to soak up the saliva and dian and diurnal components were clearly present, were then placed in the Salivette container.
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