Direct evidence of estrogen modulation of pituitary sensitivity to luteinizing hormone-releasing factor during the menstrual cycle

Dydrogesterone: pharmacological profile and mechanism of action as luteal phase support in assisted reproduction

The pharmacological and physiological profiles of progestogens used for luteal phase support during assisted reproductive technology are likely to be important in guiding clinical choice towards the most appropriate treatment option. Various micronized progesterone formulations with differing pharmacological profiles have been investigated for several purposes. Dydrogesterone, a stereoisomer of progesterone, is available in an oral form with high oral bioavailability; it has been used to treat a variety of conditions related to progesterone deficiency since the 1960s and has recently been approved for luteal phase support as part of an assisted reproductive technology treatment. The primary objective of this review is to critically analyse the clinical implications of the pharmacological and physiological properties of dydrogesterone for its uses in luteal phase support and in early pregnancy.

Kisspeptin administration to women: a window into endogenous kisspeptin secretion and GnRH responsiveness across the menstrual cycle

CONTEXT

Kisspeptin is the most powerful known stimulus of GnRH-induced LH secretion across mammalian species. However, the effects of kisspeptin are just being explored, and the dynamics of kisspeptin responsiveness across the menstrual cycle are incompletely understood.

OBJECTIVE

The objective of the study was to characterize the effects of kisspeptin on GnRH secretion in healthy women in different phases of the menstrual cycle.

PARTICIPANTS AND INTERVENTION

Ten women in the early follicular phase, three women in the late follicular (preovulatory) phase, and 14 women in the midluteal phase received a bolus of kisspeptin 112-121 0.24 nmol/kg iv. An additional four women in the early to midfollicular phase received kisspeptin 112-121 0.72 nmol/kg iv.

RESULTS

The response to kisspeptin varied depending on the phase of the menstrual cycle. LH pulses were observed immediately after kisspeptin administration in all luteal and preovulatory women. However, only half the women in the early follicular phase had unambiguous kisspeptin responses. Increasing the kisspeptin dose did not increase the LH response in early to midfollicular phase women. Kisspeptin did not appear to reset the GnRH pulse generator in women as it does in men.

CONCLUSIONS

Differences in responses to exogenous kisspeptin across the menstrual cycle suggest that kisspeptin tone is higher in the early follicular phase compared with other cycle phases. The mechanisms that determine the timing of GnRH pulse generation in men and women appear to be distinct.

Novel independent and synergistic regulation of gonadotropin-alpha subunit gene by luteinizing hormone/human choriogonadotropin and gonadotropin releasing hormone in the alphaT3-1 gonadotrope cells

The alphaT3-1 cells are immortalized anterior pituitary gonadotropes which express gonadotropin-alpha subunit gene. These cells contain receptors for gonadotropin releasing hormone (GnRH) as well as for luteinizing hormone (LH) which can also bind human choriogonadotropin (hCG). Like GnRH, LH and hCG can upregulate the expression of gonadotropin-alpha subunit gene. While 0.1-1.0 ng/ml hCG can upregulate, higher concentrations have no effect. However, these higher hCG concentrations can act in a synergistic manner with GnRH to increase the steady state mRNA and protein levels of gonadotropin-alpha subunit. The synergism between hCG and GnRH was mimicked by LH but not by other hormones in the glycoprotein hormone family or alpha or beta subunits of hCG, suggesting that the synergism is hormone specific and requires the conformation of native hormone. The hCG induced increase in gonadotropin-alpha subunit mRNA levels was due to a significant increase in the half-life of gonadotropin-alpha subunit transcripts from 7.8 +/- 1.0 h in the controls to 16.5 +/- 3.8 h after treatment with hCG. The GnRH induced increase in gonadotropin-alpha subunit mRNA levels was due to both a significant increase in the half-life to 26.2 +/- 3.0 h as well as a significant increase in the transcription rate of the gene (159.0 +/- 7.7% of the control). A greater increase in gonadotropin-alpha subunit mRNA levels following a combined treatment with GnRH and hCG was due to a further increase in half-life to 37.6 +/- 3.1 h as well as a greater increase in the transcription rate of the gene (295.1 +/- 24.2% of the control) as compared to the treatment with GnRH alone. In summary, we conclude that LH and hCG can independently and synergistically act with GnRH to increase the expression of gonadotropin-alpha subunit gene by transcriptional as well as by post-transcriptional mechanisms in alphaT3-1 cells. These effects may be important for the increase of LH levels during the preovulatory surge.

Decreased release of gonadotropin-releasing hormone during the preovulatory midcycle luteinizing hormone surge in normal women

To investigate the contribution of hypothalamic gonadotropin-releasing hormone (GnRH) secretion to the midcycle gonadotropin surge in the human, the response of luteinizing hormone (LH) to competitive GnRH receptor blockade achieved by administration of a range of doses of a pure GnRH antagonist was used to provide a semiquantitative estimate of endogenous GnRH secretion. The LH response to 5, 15, 50, and 150 micrograms/kg s.c. of the NAL-GLU GnRH antagonist ([Ac-D-2Nal1,D-4ClPhe2,-D-Pal3,Arg5,D-4-p-met hoxybenzoyl-2-aminobutyric acid6,D-Ala10]GnRH, where 2Nal is 2-naphthylalanine, 4ClPhe is 4-chlorophenylalanine, and 3Pal is 3-pyridylalanine) was measured in normal women in the early and late follicular phases of the menstrual cycle, at the time of the midcycle LH surge and in the early luteal phase. LH decreased in a dose-response fashion after administration of the GnRH antagonist in all cycle phases (P < 0.0001). When this suppression was expressed as maximum percent inhibition, there was no difference in response during the early and late follicular and early luteal phases. However, at the midcycle surge, there was a leftward shift of the dose-response curve with significantly greater suppression of LH at the lower antagonist doses in comparison to the other cycle phases (P < 0.005), but no difference at the highest dose. Thus, we draw the following conclusions. (i) There is a consistently greater degree of LH inhibition by GnRH antagonism at the midcycle surge at submaximal degrees of GnRH receptor blockade than at other phases of the menstrual cycle in normal women. (ii) This leftward shift of the dose-response relationship to GnRH receptor blockade suggests that the overall amount of GnRH secreted at the midcycle surge is less than at other cycle stages. (iii) These data confirm the importance of pituitary augmentation of the GnRH signal at the time of the midcycle gonadotropin surge in the human.

Inhibitory effects of treatment with an LHRH antagonist on the ovulatory cycle are reduced when administered during the late follicular phase

To compare the effects of transitory suppression of pituitary gonadotropin secretion by an LHRH antagonist at the mid or late follicular phase of the menstrual cycle, adult macaques with normal menstrual cycles were treated with an LHRH antagonist (N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Trp3,D-hArg(Et2)6,D-Ala10 ]LHRH (detirelix) administered subcutaneously at a dose of 300 micrograms/kg, daily for 3 days beginning either during the mid or late follicular phase. In all eight animals treated during the mid follicular phase, serum concentrations of LH and FSH declined and remained suppressed for 4 days. This caused a fall in serum concentrations of estradiol and the expected ovulation failed to occur. During the recovery period a marked rise in serum FSH occurred followed by normal follicular development and ovulation 14.8 +/- 0.6 days after the last injection of antagonist. Of the 9 macaques given the same treatment during the late follicular phase, only in two was the expected rise in serum progesterone prevented. In 4 of the animals a transitory suppression in LH and estradiol was observed but this was followed by a recovery and occurrence of an LH surge and rise in serum progesterone indicating ovulation during the course of treatment. In the remaining 3 macaques treatment commenced on the day of the initiation of the LH surge and was associated with a progesterone rise of normal duration but lower than normal magnitude during the early luteal phase. These results show that LHRH antagonist treatment causes rapid inhibition of pituitary-ovarian function when administered up to the mid follicular phase of the cycle and is effective in blocking ovulation. The suppressive effects of the antagonist are reduced when administered during the late follicular phase. This may be due to decreased dependence of the pituitary gonadotrope on LHRH at this time and on decreased dependence of the dominant follicle on the gonadotropins.

Influence of oestradiol and progesterone on pulsatile LH secretion in postmenopausal women

Pulsatile LH secretion was studied in six healthy postmenopausal women. Blood samples were obtained every 10 min during an 8-h saline infusion performed before and during the administration of transdermal oestradiol alone (E2; 50 micrograms/day) and in combination with vaginal progesterone (P; 100 mg twice daily). Plasma E2 and P levels reached values similar to those found in the early follicular phase and in the luteal phase of the menstrual cycle, respectively. The mean plasma LH levels significantly decreased (P less than 0.01) during transdermal E2 with and without vaginal P. A significant increase in the frequency (P less than 0.025) and the amplitude (P less than 0.05) of LH pulses was observed during transdermal E2. The administration of vaginal P to oestrongenized women significantly blunted the frequency (P less than 0.05) and enhanced the amplitude (P less than 0.05) of LH pulses. In all experimental conditions, the mean plasma LH levels showed a positive linear correlation with the amplitude of LH pulses. The present results show that peripheral levels of E2, similar to those of the early follicular phase of the menstrual cycle, can influence the pulsatile pattern of LH secretion, enhancing the frequency and the amplitude of LH pulses. In oestrogenized patients, the increase of peripheral P plasma levels to postovulatory values restored a pulsatile pattern of LH secretion similar to that of the early luteal phase of menstrual cycle.

Clomiphene citrate can mimic the augmentative (positive) but not the depressing (negative) effect of estradiol on the LHRH-stimulated release of LH and FSH by the pituitary gland of the long-term ovariectomized rat

In the long-term ovariectomized rat, both estradiol benzoate (EB) and clomiphene citrate enhance the release of LH induced by luteinizing hormone-releasing hormone (LHRH). EB also enhances the release of FSH. In rats pretreated with LHRH, EB strongly depresses the LHRH-induced LH/FSH release, but clomiphene enhances this release, regardless of the presence of EB.

Clinical and hormonal studies in hyperthecosis of the ovaries

Endocrine studies were performed in five women with ovarian hyperthecosis. Measurement of testosterone (T), dihydrotestosterone (DHT), androstenedione (A), 17 alpha-hydroxyprogesterone (17-OHP), progesterone (P), estradiol (E2), and estrone (E1) in the peripheral and ovarian vein serum obtained simultaneously at the time of surgery indicated that the hyperthecotic ovaries secreted large amounts of potent androgens T and DHT. There was a less marked increase in A secretion. Peripheral P and 17-OHP levels were elevated, with a significant peripheral ovarian gradient. E1 comes entirely from peripheral conversion, while at least a portion of E2 comes from direct secretion from the ovaries. Circulating FSH and LH levels were low or normal. The gonadotropin response to LH-RH was in the normal range. No patient ovulated with Clomid treatment. The hirsutism did not improve with ovarian suppression with birth control pills, possibly because of the absence of tonic elevation of LH. The hypothalamic pituitary physiology in hyperthecosis is different from that in polycystic ovarian disease.

Inter-relationship between changing patterns of LHRH and gonadotrophins in the menstrual cycle

Optimum conditions for a sensitive and highly precise radioimmunoassay of LHRH were established. Precipitation and removal of interfering substances and concentration of the resultant LHRH extracts from peripheral plasma were also achieved. Using these methods, daily plasma LHRH levels in females with normal menstrual cycles were measured and correlated with the corresponding LH and FSH levels. The levels of LHRH in the peripheral plasma of postmenopausal females, as well as eugonadal males, were also determined. The LHRH profile in normal cycling women was found to be cyclic but the peak LHRH levels were observed at the beginning of the rise in LH and FSH levels and preceded the midcycle surge of gonadotrophins. The LHRH levels in the luteal phase (19.8 +/- 1.1 pg/ml, mean +/- SEM) were significantly (P less than 0.01) higher than those in the follicular phase (16.5 +/- 0.5 pg/ml) of the menstrual cycle. A high degree of correlation (r = 0.91) was seen between the immunoreactivity and biological activity of the extracted LHRH.

Endocrine consequences of continuous antiestrogen therapy with tamoxifen in premenopausal women

Daily administration of estrogen antagonists to premenopausal women has been incorporated into the adjuvant treatment of breast cancer. We have studied the changes in reproductive hormones, pituitary responses to hypothalamic-releasing hormones, and endometrial histology during treatment with the antiestrogen tamoxifen in five healthy, premenopausal women. These studies were carried out during one menstrual cycle before and during two cycles of antiestrogen treatment. All subjects continued to have regular menses with biphasic basal body temperature records. During treatment, estradiol (E2) levels were increased but followed the usual pattern reflecting follicular maturation and corpus luteum formation. The mean E2 concentration at the midcycle peak and during the luteal phase was twice that observed during the non-treatment cycle. By contrast, the concentrations and secretory patterns of luteinizing hormone and follicle-stimulating hormone were not greatly changed, and the gonadotropin responses to gonadotropin-releasing hormone were not suppressed. Endometrial biopsies obtained during the follicular phase of control and tamoxifen treatment cycles showed no differences whereas biopsies obtained during the luteal phase of tamoxifen cycles uniformly showed a lack of changes attributed to progesterone action with no progression of histologic changes beyond those expected on day 7-8 of the luteal phase. These observations are consistent with maturation of multiple ovarian follicles, a surprising finding considering the normal gonadotropin concentrations. The retarded development of the endometrium in the presence of supranormal serum E2 and progesterone concentrations is a morphologic demonstration of the antiprogestational effect of antiestrogens. The lack of gonadotropin suppression in the presence of hyperestrogenemia suggests a major antiestrogen action on the hypothalmus and pituitary gland.

Effect of epimestrol on gonadotropin and prolactin plasma levels and response to luteinizing hormone-releasing hormone/thyrotropin-releasing hormone in secondary amenorrhea and oligomenorrhea

The effects of epimestrol (5 mg every 6 hours for 5 days) on basal levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (Prl), estradiol, progesterone, and dehydroepiandrosterone sulfate, and on the response to LH-releasing hormone (LH-RH) and thyrotropin-releasing hormone (TRH) stimulation, were studied in 18 cases of secondary amenorrhea and oligomenorrhea of hypothalamic-pituitary origin, in three cases of anorexia nervosa, in two cases of long-lasting progestin-induced amenorrhea, and in one case of precocious menopause. The results in the first 18 patients indicate that epimestrol treatment induces a significant increase in LH and Prl levels after 24 hours, while the FSH increase becomes significant only after 4 days of therapy. Twelve hours after discontinuation of treatment, all three hormone levels decreased significantly to values similar to the basal levels, while the pituitary response to LH-RH indicated a much more marked LH secretion than before treatment. A second test, performed 36 hours after the last drug administration, again showed a significantly higher LH response than that found under basal conditions. No significant variations were observed in the FSH response to LH-RH, nor in the Prl response to TRH. These data suggest that epimestrol interferes at the level of the centers responsible for Prl and gonadotropin secretion in the manner of a weak estrogen.

Hormonal correlates of normal and abnormal follicle growth after puberty in humans and other primates

After the menarche, changing levels of gonadotrophins, prolactin and sex steroid hormones in peripheral blood are accompanied by ovulation and corpus luteum formation in one follicle, and atresia in the remaining follicles maturing during each menstrual cycle. Available evidence suggests that blood levels of steroid hormones reflect in large part the secretory activity of the ovary containing a pre-ovulatory follicle and most probably of that follicle itself (see Chapter 6). These steroid secretions and those of the corpus luteum coordinate hypothalamic-pituitary-ovarian function. Within the ovary, sex steroid hormones mediate effects of gonadotrophins and prolactin on follicle maturation and participate in determining the fate of individual follicles.

Dynamic testing of hypothalamic-pituitary function in abnormalities of ovulation

A review of 26 unusual patients indicates that a combined luteinizing hormone-releasing hormone (LRH)-clomiphene test in conjunction with an estrogen provocation test not only was helpful in identifying underlying pathophysiology of anovulation but also proved useful in the clinical management of the patients. Dynamic testing per se does not establish a diagnosis but, in conjunction with history and other laboratory findings, it does make possible further subdivisions of groups of patients who otherwise appear similar, both clinically and from routine laboratory evaluations. It, therefore, tends to pinpoint a lesion and establish the area in which further tests should be made. It is concluded that the value of such investigations will be more evident as gynecologic endocrinology moves into investigation of the supratentorial control of hypothalamic function and as hypothalamic LRH becomes available as a therapeutic agent.

Assessment of the negative and positive feedback effects of administered oestrogen on gonadotrophin release in patients with anorexia nervosa

The capacity of the hypothalamic–pituitary axis to respond with changes in LH release to the negative and positive feedback effects of oestrogen was assessed in 19 patients with anorexia nervosa at different stages of the illness. Ethinyl oestradiol, 200 μg daily for 3 days, was administered and serial estimations of serum LH were carried out during and after the course of oestrogen.

In patients with anorexia nervosa tested when markedly underweight, negative feedback effects of oestrogen were demonstrated in those patients with detectable levels of LH. None of the patients demonstrated positive feedback release of LH to the oestrogen stimulus.

After the resumption of a more normal weight, basal LH levels were higher and negative feedback effects of oestrogen were observed in 11 out of 12 patients. The complete response to oestrogen with a subsequent positive release of LH to the oestrogen stimulus was shown by only 3 patients. Two of these 3 patients maintained a normal weight during the subsequent 6 months and both resumed regular menstruation shortly after the test. Three additional patients who had shown only negative feedback effects of oestrogen on LH release similarly maintained a normal weight and only 1 of them resumed menstruation, starting 3 months after the oestrogen test.

It was concluded that in recovery from anorexia nervosa there is a return of normal hypothalamicpituitary–gonadal activity in a definite sequence with recovery of the hypothalamus to respond normally to the negative feedback effects of oestrogen followed by return of the positive feedback capacity between oestrogen and LH which allows menstruation to resume. The resumption of normal hypothalamic–pituitary function is clearly dependent in part upon correction of the malnutrition. However, after correction of the malnutrition some patients fail to menstruate, and this appears to be determined by a continuing impairment of the hypothalamus to respond normally to the feedback effects of oestrogen upon gonadotrophin release.

The apparent paradox of the negative and positive feedback control system on gonadotropin secretion

The separate and interactive effects of estradiol (E2) and luteinizing hormone-releasing factor (LRF) on the dynamics of LH storage and release were studied. Measurements were made of the serum gonadotropin responses to submaximal doses of LRF, given as brief pulses or infused over an extended period to normal women at various stages of the follicular phase of their menstrual cycles and to hypogonadal women with and without estrogen treatment. The two-pool concept of pituitary gonadotropin was verified; the dynamic responses of the two pools to the inputs of LRF and E2 were investigated and related to pituitary properties of sensitivity and reserve. Our results indicate that LRF appears to serve as a primary drive on the gonadotrophs, stimulating gonadotropin synthesis and storage (second pool), as well as release (first). E2 for the most part, amplifies the action of LRF except that it impedes LRF-induced release of gonadotropin. E2 augments the second pool activity (reserve) preferentially, and the relative activity of the first pool appears to be influenced by the E2-dependent self-priming effect of LRF. The interactions of the various elements of the system, when combined, provide a U-shaped curve to describe the over-all capacity of the gonadotrophs as a function of a broad range of E2 inputs. Negative and possitive feedback of E2 are revealed to operate by different mechanisms and to represent different segments of a single U-shaped curve rather than paradoxically disparate actions.

Characterization of the inappropriate gonadotropin secretion in polycystic ovary syndrome

To evaluate gonadotropin release in polycystic ovary syndrome (PCO), one or more of the following hypothalamic-pituitary function tests were performed on 24 patients with the syndrome. These tests included (a) the pulsatile pattern and day-to-day fluctuation of gonadotropin release; (b) effects of exogenous estrogen and antiestrogen (clomiphene) administration on gonadotropin release; and (c) pituitary responsiveness to maximal (150 mug) and submaximal (10 mug) luteinizing hormone-releasing factor (LRF) injections. In 10 of the 14 patients sampled frequently (15 min) for 6 h, luteinizing hormone (LH) levels were elevated above the concentration seen in normal cycling women (except the LH surge). These high LH concentrations appeared to be maintained by and temporally related to the presence of exaggerated pulsatile LH release, either in the form of enhanced amplitude or increased frequency. In all subjects, levels of follicle-stimulating hormone (FSH) were low or low normal, and a pulsatile pattern was not discernible. In four patients, daily sampling revealed marked day-to-day fluctuation of LH but not FSH. That the elevated LH levels were not related to a defect in the negative-feedback effect of estrogen was suggested by the appropriate fall of LH in four patients given an acute intravenous infusion of 17beta-estradiol. This infusion had no effect on FSH levels. In addition, clomiphene elicited rises of both LH and FSH that were comparable to the ones observed in normal women given the same treatment. The clomiphene study also suggested that the positive-feed-back mechanism of estrogen on LH release was intact when the preovulatory rises of 17beta-estradiol induced appropriate LH surges. The elevated LH levels appeared to be related to a heightened pituitary responsiveness to the LRF. This was found in the 11 and 2 patients given maximal (150 mug) and submaximal (10 mug) doses of LRF, respectively. The augmented pituitary sensitivity for LH release correlated with the basal levels of both estrone (P less than 0.025) and 17beta-estradiol (P less than 0.02). The net increase in FSH was significantly greater (P less than 0.001) in the PCO patients than the normal women with maximal doses of LRF. With the smaller dose study none of the injections had a discernible effect on FSH concentrations in either subject. The disparity between LH and FSH secretion could be explained by the preferential inhibitory action of estrogen on FSH release, coupled with a relative insensitivity of FSH release. These data indicate that in these PCO patients the abnormalities of the hypothalamic-pituitary regulation of gonadotropin secretion was not an inherent defect but represented a functional derangement consequent to inappropriate estrogen feedback, which led to a vicious cycle of chronic anovulation and inappropriate gonadotropin secretion.

Modulation of pituitary responsiveness to exogenous LHRH by an oestrogenic and an anti-oestrogenic compound in the normal male

The effect of clomiphene (100 mg daily for 10 days) and ethinyl oestradiol (100 mug daily for 10 days) on the gonadotrophin response to synthetic LHRH has been investigated in two groups of five normal males. A third group of five men served as control group. LHRH, 25 mug, was injected intravenously on days 0, 4, 7 and 10 and the response of serum LH and FSH was monitored by radioimmunoassay. In contrast to the wide inter-individual variation of the response pattern, the intra-individual variation of the response to LHRH in the control group was small. Clomiphene induced a significant elevation of the baseline levels of LH and FSH after a few days of treatment; the pituitary responsiveness to LHRH, however, was significantly reduced. Oestrogen treatment resulted in a uniform suppression of both basal gonadotrophin levels and pituitary responsiveness. The decreased gonadotrophin response to LHRH during clomiphene treatment is thought to be caused by a relative and temporary pituitary depletion of the releasable gonadotrophin content. Although the suppression of LH and FSH response during oestrogen treatment may point to a direct inhibitory effect of oestrogen on pituitary gonadotrophin release, an indirect hypothalamic pathway, through suppression of endogenous LHRH, cannot be ruled out.

Hormonal changes of adolescence

Pubescence is characterized by many physical, emotional, and hormonal changes. The hypothalamic-pituitary-gonadal system is maintained in a dormant state (with a low level of activity) during prepubertal years by higher central nervous system inhibition. With the onset of adolescence, the reproductive endocrine system becomes increasingly active. The attainment of sexual maturity in terms of secondary sexual characteristics, the production of spermatozoa in the male, and the cyclical female pattern with release of ova are end-points of the developmental process.