Adipocyte insulin action during the normal menstrual cycle

The relationship between the menstrual cycle and insulin sensitivityis unclear. The aim of this study was to investigate insulinsensitivity during the normal menstrual cycle using the physiologicalinsulin target organ adipose tissue. A total of 23 normal healthyvolunteers were studied, nine of whom were in the follicularphase, and 14 of whom were age and body mass index-matched andin the luteal phase of the menstrual cycle. Adipocyte insulinreceptor binding was measured and adipocyte insulin action wasassessed by measuring initial rates of 3–0-methylglucoseuptake and by inhibition of lipolysis. The maximum specificinsulin receptor binding was significantly higher in subjectsstudied during the follicular phase of the menstrual cycle comparedto subjects studied during the luteal phase (1.81 ± 0.13versus 136 ± 0.15% per 10 cm2 cell surface, P < 0.05).Maximum rates of 3–0-methylglucose transport were 1.70± 0.22 versus 1.75 ± 0.22 pmol/10 cm2/5 s in thefollicular and luteal phase respectively and were not significantlydifferent between the two groups. The maximum percentage lipolysisinhibition observed was 42.5 ± 7.5% in the follicularphase and 39.9 ± 7.4% in the luteal phase (not significant).This study demonstrated that there is a reduction in insulinreceptor binding in the luteal phase of the normal ovulatorymenstrual cycle. The post-receptor action of insulin is notaffected between the two phases of the menstrual cycle.     

Response to activated protein C during normal menstrual cycle and ovarian stimulation

Oestrogen has been pointed out as a pre-thrombotic factor. Protein C is a key enzyme in the down-regulation of blood coagulation. Recent data suggest that activated protein C (APC) resistance which is not due to the factor V:Q 506 Leiden mutation and appears to be acquired, is also a risk factor for thrombosis. In this study, we evaluated the endogenous oestradiol production and its possible influence on APC. Eighteen normally menstruating women were studied during one ovulatory cycle. Furthermore, 20 women undergoing controlled ovarian stimulation, and achieving extremely high oestradiol concentrations, were investigated. Normalized APC (nAPC) ratio (clotting time of tested sample/clotting time of pooled control plasma) was measured. Samples collected on menstrual cycle days 1-3, 6-8, 13-14, 20-24 corresponded to nAPC ratios 1.02 +/- 0.19 (mean +/- SD), 1.05 +/- 0. 15, 1.02 +/- 0.16 and 1.03 +/- 0.21 respectively. During ovarian stimulation, the nAPC ratios were 0.99 +/- 0.12, 1.03 +/- 0.18, 1.01 +/- 0.16 and 0.97 +/- 0.13 at oestradiol minimum, days 5-8 pre-oocyte retrieval, oestradiol maximum and at oocyte retrieval respectively. In spite of the great difference in the concentrations of oestradiol between women in normal menstrual cycle and women undergoing ovarian stimulation, no difference in nAPC ratios was observed.     

Human endometrial proteins with cyclic changes in the expression during the normal menstrual cycle: characterization by protein sequence analysis

Endometrial proteins showing cyclic expression during the normalmenstrual cycle were localized on twodimensional (2-D) electrophoresisgels separating proteins with isoelectric points (pi) rangingfrom 3.5 to 7 and relative molecular weights ranging from 10to 300 kDa. Menstrual cycle-related proteins were excised fromseveral 2-D gels, concentrated by one-dimensional (1-D) sodiumdodecyl sulphate (SDS)-polyacrylamide gel electrophoresis, andcleaved in situ by trypsin. The tryptic fragments were extractedand separated by reverse phase high performance liquid chromatography(RP-HPLC). Finally, the partial amino-terminal amino acid sequenceof selected tryptic fragments were determined for each protein.We aimed at characterizing the 21 menstrual cycle-related proteinsthat were visible on silver-stained 2-D electrophoresis gels.Of the proteins being maximally synthesized in the proliferativephase endometrium, we identified proteins associated mainlywith the cytoskeleton: vimentins, keratin, tropomyosin and tubulin,but also proteins such as proliferating cell nuclear antigenand -galactoside binding lectin. The partial amino acid sequencesfor another two proteins did not match any protein sequencein the Protein Identification Resource (PIR) and Swissprot databases.In the group of proteins having maximal synthesis in the secretoryphase endometrium, we identified creatine kinase chain B andan isocitrate dehydrogenase-homologous protein, both of whichare involved in energy metabolism. However, we also identifiedthe annexin IV precursor, the 14-3-3 protein homologue alsocalled stratifin or the epithelial cell marker protein 1 andthe 21K tumour protein. Finally, four of the proteins were presentin too low amounts to allow characterization. Interestingly,most of the identified proteins have not previously been describedas having a menstrual cycle-related synthesis in the human endometrium.It may be considered that the concentration of some of the cycle-relatedproteins may be used in clinical situations to reflect specificendometrial phases.     

Two-dimensional gel analysis of human endometrial proteins: cyclic changes in the expression of specific proteins during the normal menstrual cycle

High resolution two-dimensional (2-D) gel electrophoresis wasused to compare the patterns of [³⁵S]methionine-labelled cellularproteins in endometrial tissue from healthy, normally menstruatingwomen. Samples of endometrial tissue were incubated with [³⁵S]methioninefor 20 h, and total cell lysates were processed for 2-D gelelectrophoresis. Using this technique it was possible to studyproteins with iso-electric points (pI) ranging from 3.5 to 11and relative molecular weights (M_r) ranging from 10 000 to 300000 Da. The fluorograms were compared by computer-aided analysiswhereby a total of 1095 [³⁵S]-labelled proteins were resolvedon the iso-electric focusing gels (IEF, pI 3.5–7) and488 on the non-equilibrium pH gradient electrophoresis (NEPHGE)gels (pI 6.5–11). Of the proteins on the IEF gels, 125showed differential expression during the menstrual cycle. Ofthese, 36 were maximally expressed in proliferative phase endometrium,26 in the interval phase and 63 in secretory and/or late secretoryphase endometrium. Correspondingly, on the NEPHGE gels a totalof 61 proteins exhibited cyclical variation, of which 30 weremore prominent in proliferative phase, 13 in interval phaseand 18 in secretory phase endometrium. This study shows that2-D gel electrophoresis is eminently suited to the identificationof proteins whose expression varies in a cyclical manner duringthe menstrual cycle. Further investigations should be carriedout to isolate and characterize these proteins with the aimof establishing useful markers for specific endometrial phasesof the menstrual cycle.     

The endometrial capillaries during the normal menstrual cycle: a morphometric study.

The areas of the capillary lumen, the entire capillary, the endothelial cells and the adventitia, as well as the thickness of the endothelial cell layer and the adventitia were studied using morphometric methods in endometrial samples from 34 fertile women who had a hormonal profile compatible with normal ovarian function. The biopsies were grouped around the luteinizing hormone surge. The results were calculated as mean values of 72-h periods and related to the mean levels of oestradiol and progesterone circulating in plasma 72 h prior to the biopsy. The results indicated that the sub-epithelial capillary plexus of the human endometrium undergoes dynamic changes during the normal menstrual cycle with a significant dilatation of the vessels during the post-ovulatory phase. A significant correlation was found between the area of the capillary lumen and the mean level of progesterone circulating in the plasma 72 h prior to the biopsy (P = 0.037). We conclude that the ovarian steroids produced during the normal menstrual cycle are likely to influence sub-epithelial vascularization causing dilatation in the post-ovulatory phase. This dilatation of the sub-epithelial capillaries may be related to the development of oedema appearing in the stroma at the time of the expected implantation. The possible functional significance of the capillary dilatation in terms of implantation, however, needs to be further investigated.     

Assessment of changes in volume and vascularity of the ovaries during the normal menstrual cycle using three-dimensional power Doppler ultrasound

BACKGROUND: Our aim was to describe changes in the volume and vascularization of both ovaries, the dominant follicle and the corpus luteum during the normal menstrual cycle using three-dimensional (3D) power Doppler ultrasound. METHODS: Fourteen healthy volunteers underwent serial transvaginal 3D ultrasound examinations of both ovaries on cycle day 2, 3 or 4, then daily from cycle day 9 until follicular rupture and 1, 2, 5, 7 and 12 days after follicular rupture. The volume and vascular indices of the ovaries, the dominant follicle and the corpus luteum were calculated off-line using virtual organ computer-aided analysis (VOCAL) software. RESULTS: The volume of the dominant ovary increased during the follicular phase, decreased after follicular rupture and then increased again during the luteal phase. Vascular indices in the dominant ovary and the dominant follicle/corpus luteum increased during the follicular phase, the vascular flow index (VFI) in the dominant follicle being on average (median) 1.7 times higher on the day before ovulation than 4 days before ovulation (P=0.003). The vascular indices continued to rise after follicular rupture so that VFI in the corpus luteum was on average (median) 3.1 times higher 7 days after ovulation than in the follicle on the day before ovulation (P=0.0002). The volume and vascular indices in the non-dominant ovary manifested no unequivocal changes during the menstrual cycle. CONCLUSIONS: Substantial changes occur in volume and vascularization of the dominant ovary during the normal menstrual cycle. 3D power Doppler ultrasound may become a useful tool for assessing pathological changes in the ovaries, for example, in subfertile patients.     

Cyclic changes of granulocyte colony-stimulating factor (G-CSF) mRNA in the human follicle during the normal menstrual cycle and immunolocalization of G-CSF protein

BACKGROUND: Ovulation has several similarities with inflammation and is closely connected to the activity of leukocytes and inflammatory cytokines. Since granulocytes are one of the major leukocytes, we focused our attention on the presence and local production of granulocyte colony-stimulating factor (G-CSF) in the human ovary. METHODS: The presence of G-CSF protein in the follicular fluid and perifollicular tissues was examined by Western blot analysis (n = 5) and immunohistochemical staining (n = 10). The relative expression levels of G-CSF mRNA in relation to GAPDH in granulosa, theca and luteal cells during the menstrual cycle were measured by quantitative RT-PCR using TaqMan technology (n = 15). RESULTS: G-CSF protein was detected in all follicular fluid and located mainly in granulosa cells of the follicle and luteal cells. The expression level of G-CSF mRNA in the late follicular phase was 137.6 +/- 18.5, which was approximately 10-fold greater than other phases during the menstrual cycle (P < 0.05). CONCLUSIONS: These results demonstrate that G-CSF is produced in the human follicle shortly before the ovulatory phase and may play an important role in the mechanism of ovulation.     

Expression of the epidermal growth factor system in human endometrium during the menstrual cycle

The epidermal growth factor (EGF) system is ubiquitous in humans and plays fundamental roles in embryogenesis, development, proliferation and differentiation. As the endometrium of fertile women is characterized by proliferation and differentiation, we hypothesize a role for the EGF system. Fourteen premenopausal women had endometrial samples removed on day 6 +/- 1 and day 6 +/- 1 and 12 +/- 1 after ovulation during one menstrual cycle. RNA was extracted and analysed by real-time PCR, and immunohistochemistry was performed to localize the components of the EGF system. Human EGF Receptor 1 (HER1) showed highest expression during the proliferative phase, HER2 and HER4 during the early and HER3 during the late secretory phase. Amphiregulin (AR) and transforming growth factor alpha (TGFalpha) expression is highest in proliferative phase. Heparin binding (HB)-EGF and betacellulin (BCL) show no variation. Epiregulin (EP) is detectable in some samples. EGF is undetectable. HER1, HER2, HER3 and HER4 were localized to the epithelium and glands HER3 and HER4 solely in the secretory phase. Amphiregulin was seen in leucocytes and stromal cells, TGFalpha and betacellulin in the epithelial lining, epiregulin in stromal cells whereas HB-EGF and EGF are undetectable. In conclusions, we observed cyclical expression of the four EGF receptors and two ligands and localized all four receptors and four ligands in endometrial biopsies. This suggests a role for the EGF system in growth of the endometrium.     

Effects of human menstrual cycle on thermoregulatory vasodilation during exercise

Summary To investigate the effects of the menstrual cycle and of exercise intensity on the relationship between finger blood flow (FBF) and esophageal temperature (T_es), we studied four women, aged 20–32 years. Subjects exercised at 40% and 70% in the semi-supine posture at an ambient temperature of 20 C. Resting T_es was higher during the luteal phase than the follicular phase (P<0.01). There were no significant differences between the two phases in FBF, oxygen consumption, carbon dioxide production, heart rate or minute ventilation at rest and during exercise, respectively. Each regression line of the FBF-T_es relationship consists of two distinct segments of FBF change to T_es (slope 1 and 2). FBF increased at a threshold T_es for vasodilation ([T_{es 0}]) and the rate of FBF rise became greater at another T_es above this threshold ([T_{es 0}']). For both levels of exercise, [T_{es 0}] and [T_{es 0}'] were shifted upward during the luteal phase, but the slopes of the FBF-T_es relationship were almost the same in the two phases of the menstrual cycle. Increasing exercise intensity induced a significant decrease in slope 1 of the FBF-T_es relationship during the follicular (P<0.01) and the luteal phases (P<0.02), respectively. These results show that the set-point temperature may be shifted towards a higher level during the luteal phase of the menstrual cycle during exercise and that, as in males, the thermoregulatory vasodilator response is attenuated by increasing exercise-induced vasoconstrictor tone in proportion to exercise intensity during both phases of the menstrual cycle when heat storage is insufficient in women.Supported in part by Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (grant no. 57770137)     

The onset of the initial rise in follicle-stimulating hormone during the human menstrual cycle

BACKGROUND: The rise in FSH (FSHr) that leads to the recruitment of a cohort of follicles during the menstrual cycle occurs during the luteal-follicular transition, however, it is unclear whether it consistently occurs on one particular day, or is subjected to reproductive ageing. METHODS: We determined the FSHr in 836 complete menstrual cycles from 102 women with regular menses using an algorithm, and additionally compared the relative variation in FSH during the last 14 days of the cycle. Possible effects of reproductive ageing on the onset of FSHr were also investigated. RESULTS: The day of FSHr follows a normal distribution with a median value of -4 (relative to first day of menses), mean -4.1 and SD 2.1. Analysis of the relative changes in FSH during the last 14 days of the cycle revealed the first significant rise on day -4 (P=0.0033), coinciding with the first significant drop in estrogens (P=0.0002). No effect of chronological age, or initial FSH levels, on FSHr was found, however, there was an inverse relationship between total follicular phase length (from day of FSHr to LH peak) and initial FSH levels (P<0.0001). CONCLUSIONS: The initial FSH rise in the cycle occurs consistently 4 days before menses, is related to a drop in estrogen levels, and is not affected by reproductive ageing.     

Effects of breastfeeding chemosignals on the human menstrual cycle

BACKGROUND: To date, there has not been an investigation to determine whether lactating women and their infants influence the ovarian function of other women with whom they interact. METHODS: In a randomized, double-blind, placebo-controlled study of 47 nulliparous women, we utilized both within- and between-subjects controls to assess the effects of sustained exposure to breastfeeding compounds on menstrual cycle length, as well as characteristics of each phase of the ovarian cycle. RESULTS: Breastfeeding compounds modulated ovarian cycle length in comparison with the carrier control (0.01 < or = all P values < or = 0.05), disrupting the normal homeostatic regulation of cycle length and tripling its variance. Hence, women with long cycles stayed long and did not regress to the mode of 29 days and women with short cycles maintained short cycles. This effect was driven by changes in both the follicular and luteal phases of the cycle (0.01 < or = all P values < or = 0.04) and changed the timing of the pre-ovulatory surge of LH. CONCLUSIONS: Because compounds from lactating women and their infants modulated the ovarian cycles of women, as is seen in other mammals, they have the potential to function as pheromones, regulating fertility within groups of women.     

Quantifying the changes in endometrial vascularity throughout the normal menstrual cycle with three-dimensional power Doppler angiography

BACKGROUND: We used three-dimensional power Doppler angiography (3D-PDA) to examine the periodic changes in endometrial and subendometrial vascularity during the normal menstrual cycle in 27 women without obvious menstrual dysfunction or subfertility. METHODS: 3D-PDA was performed on alternate days from day 3 of the cycle until ovulation and then every 4 days until menses. Virtual organ computer-aided analysis and shell-imaging were used to define and to quantify the power Doppler signal within the endometrial and subendometrial regions producing indices of their relative vascularity. RESULTS: Both the endometrial and subendometrial vascularization index (VI) and vascularization flow index (VFI) increased during the proliferative phase, peaking approximately 3 days prior to ovulation (P < 0.001) before decreasing to a nadir 5 days post-ovulation (P < 0.001). Thereafter, both vascular indices gradually increased during the transition from early to mid-secretory phase. The flow index (FI) showed a similar pattern but with a longer nadir post-ovulation. Smoking was associated with a significantly lower VI and VFI. The FI was significantly lower in women aged > or = 31 years and significantly higher in parous patients. CONCLUSIONS: Endometrial vascularity, as assessed by 3D-PDA, varies significantly during the menstrual cycle and is characterized by a pre-ovulatory peak and post-ovulatory nadir during the peri-implantation window.     

Uterine glandular area during the menstrual cycle and the effects of different in-vitro fertilization related hormonal treatments

The human uterine glandular epithelium undergoes a sequenceof well characterized changes during the menstrual cycle thatpresumably play an important role in preparation for blastocystimplantation. The aim of this study was to measure objectivelyglandular volume over the entire menstrual cycle and comparethe results with eight different clinical superovulation orhormone replacement therapy (HRT) subject groups. Endometrialbiopsies were taken from control normal menstrual cycle subjects(n = 96), and eight other smaller groups of women who had receiveddifferent in-vitro fertilization (TVF) related treatments. Thetotal area of glandular epithelium was objectively measuredfrom routine histological slides using computerized image analysis.Control menstrual cycle results showed a significantly greatergland area in the early secretory stage of the cycle than atany time between the early proliferative through to the mid-lateproliferative stages (P < 0.05). FVF patients receiving clomiphenecitrate and human menopausal gonadotrophin had a significantlysmaller glandular area than those in the control groups at equivalentstages of the menstrual cycle. The use of progesterone supplementationremoved this significant difference. Patients on the ‘Flare"regime had the highest gland area, although this was not significantlydifferent from controls. Buserelin down-regulation gave a glandarea that was closest to the normal cycle controls. The threeHRT groups showed high variability in gland volume between patients.The results from this study demonstrate that superovulationcan cause significant alterations in endometrial gland volume,but that these do not necessarily preclude implantation.     

Large scale validation of human N-myc downstream-regulated gene (NDRG)-1 expression in endometrium during the menstrual cycle

A major challenge in the comprehension of the endometrial transformations leading to the completion of each menstrual cycle in humans is in the identification of specific molecular pathways underlying these monthly turnovers. Towards this goal we compared, by the differential display technique, the relative expression of mRNA in endometrial biopsies harvested in individuals (n = 48) either at the proliferative or the secretory phase of the menstrual cycle. We isolated a cDNA fragment homologous to NDRG1 (N-myc Downstream-Regulated Gene-1) that is present in markedly higher amounts in the secretory phase. Northern blot analysis and quantitative real time PCR experiments confirmed this result in distinct cohorts of individuals (44 and 560 respectively). A closer examination of data showed that the highest mRNA levels were found during the range of 25-28 days of the uterine cycle. Consistent with the mRNA data, the temporal profile of the NDRG1 protein showed a 15-fold increase during the secretory phase, as demonstrated by using semi-quantitative dot blot analyses (n = 92). Immunohistochemical localization revealed that NDRG1 was expressed both in epithelial and stromal cells. This large scale validation of the NDRG1 mRNA and protein increase in endometrium during the secretory phase is consistent with its differentiation-related function described in other tissues and its potential involvement in the window of implantation of the human endometrium, as suggested by previous chip-based evidence.     

Reactions of dysmenorrheic and nondysmenorrheic women to experimentally induced pain throughout the menstrual cycle

It has been proposed that dysmenorrheic women have a heightened pain sensitivity compared to nondysmenorrheic women, although previous studies investigating this hypothesis have yielded conflicting results. This study investigated the pain sensitivity of nondysmenorrheic women and of women suffering from spasmodic, congestive, and combined dysmenorrhea, across three phases of the menstrual cycle: premenstrual, menstrual, and intermenstrual. No interaction between type of dysmenorrhea and menstrual phase was found for either pain threshold or pain tolerance, using three procedures of experimentally induced pain. On a self-report measure of pain, however, the congestive and combined dysmenorrheics reported the highest degree of pain and distress, especially during the premenstrual and menstrual phases; nonsufferers reported the lowest degree and were stable across phases.Portions of this paper were presented at the meeting of the Association for Advancement of Behavior Therapy, Houston, Texas, November 1985.     

Fallopian tube ciliary beat frequency in relation to the stage of menstrual cycle and anatomical site

BACKGROUND: The cyclical changes in ciliary structure and motion within the human Fallopian tube are well documented. Previous investigators have studied ciliary beat frequency (CBF) in relation to menstrual cycle and anatomical site, but with conflicting results. METHODS: Using a technique that records variations in light intensity, we have studied the changes in CBF in relation to the menstrual cycle and anatomical site. Fallopian tubes were collected from 26 women who underwent hysterectomy for benign conditions. Menstrual history, hormone profile and endometrial biopsy results were used to determine the stage of the cycle. Fourteen women were in the proliferative phase, and 12 women in the secretory phase. RESULTS: Mean CBF for all subjects was 5.3 plus minus 0.2 Hz. There was no significant difference in CBF in relation to anatomical site. In the fimbrial region the ciliary beat was faster in the secretory (5.8 plus minus 0.3 Hz) as compared with the proliferative phase (4.9 plus minus 0.2 Hz), P < 0.02. CONCLUSIONS: It is possible that this increase in fimbrial CBF may contribute to ovum retrieval and transport after ovulation. However, the reproductive significance of the changes in CBF in relation to the menstrual cycle needs further investigation.     

Endocrinology: Vasopressin and atrial natriuretic hormone response to hypertonic saline during the follicular and luteal phases of the menstrual cycle

We studied the hormonal responses to hypertonic saline duringthe follicular (days 2–9) and luteal (days 21–28)phases of the menstrual cycle in nine healthy young women, aged19–25 years. On both study days, each woman was infusedwith 5% hypertonic saline for 1 h at the rate of 0.1 ml/kg/min.Serum progesterone and oestradiol concentrations confirmed thereported stage of the menstrual cycle. No difference in weightor haematocrit was observed between the two stages of the studyfor each woman. Baseline blood pressure, serum sodium, plasmaosmolality, plasma vasopressin and thirst levels were almostidentical for both stages, and changed to the same degree duringinfusion of hypertonic saline. Baseline atrial natriuretic hormoneconcentrations were higher during the follicular phase and becamesignificantly higher than during the luteal phase followinginfusion of hypertonic saline. We concluded that the intravascularvolume during the luteal phase may be effectively decreasedin comparison to the follicular phase.     

Levels of interleukin-2 receptor in serum of patients during the menstrual cycle and following embryo/gamete transfer

In an attempt to establish whether nidation elicits a measureable systemic immunologic response in vivo, levels of interleukin-2 receptor (IL-2R) have been determined in serum drawn from 34 pregnant patients (IUP) immediately before embryo/gamete transfer, and 7 and 14 days later. For comparison, these same values were determined for 41 subjects who did not conceive, and for 18 who spontaneously aborted (SAB) during the first trimester of gestation. Serum IL-2R values were near 320 U/ml and did not differ between days within outcomes, or within days between outcomes. Furthermore, levels of IL-2R and beta-hCG in serum were not interrelated on days 7 or 14 of pregnancy (SAB or IUP). Serum IL-2R levels did not change during the menstrual cycle. The present results appear to traverse presumptive elements of existing hypotheses of "placental immunotropism."     

Immunohistochemical staining of von Willebrand factor in human endometrium during normal menstrual cycle

Endometrial biopsies were obtained from 73 normal women throughoutthe menstrual cycle. Using a polyclonal antibody and a streptavidin–biotin–peroxidasemethod, formalinfixed paraffin sections of the tissue were stainedfor von Willebrand factor (vWF). Both subjective scoring andobjective quantitative colour image analysis were used to assessthe staining intensity, and the results obtained by the twomethods were in concordance with each other. Positive stainingwas observed at all stages of the menstrual cycle. Specificstaining was confined to the vascular endothelium and showedcyclical changes. The staining intensity was the weakest duringthe menstrual phase and was significantly (P < 0.02) reducedfrom all other stages of the cycle, except late secretory phase.This was followed by a rapid increase in the early proliferativephase to reach a peak in the mid cycle before gradually fallingoff towards the end of the cycle. The staining intensity inthe late secretory phase was significantly reduced (P < 0.05)from other stages except menstrual, early proliferative andmid secretory phase. Vascular staining for vWF was heterogeneouswith some vessels devoid of any positive staining.     

Plasma levels of oxytocin during the menstrual cycle, pregnancy and following treatment with HMG.

In 15 women investigated during the follicular, ovulatory and luteal phases of the menstrual cycle, only small variations in plasma levels of oxytocin were found. There was no mid-cycle surge in oxytocin levels. A parallel variation in oxytocin and oestradiol levels was found in five of the women. In 10 women examined every 4th week during gestation starting at week 12, a small but significant increase in oxytocin levels was found. Pronounced fluctuations in oxytocin levels were observed in four of the pregnant women. These fluctuations were independent of the stage of gestation and were also observed in three of the menstruating women. Seven out of 12 women treated with human menopausal gonadotrophin exhibited a marked elevation of oestradiol levels; oxytocin levels also increased and were significantly elevated when the oestradiol level exceeded 2 pmol/ml. Oxytocin levels were higher in the pregnant and human menopausal gonadotrophin-treated women than in the menstruating women. The oxytocin levels appeared to be only partly related to the oestradiol level. It is possible that the stimulatory effect of oestradiol is antagonized by a concomitantly high progesterone level. Alternatively, there may not be a linear dose-effect relationship between oestradiol and the release of oxytocin.