Rise In Estrogen Research Articles

Steroid hormones modulate the production of nitric oxide and cGMP in the rat uterus.

Previously, we demonstrated the presence of an L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway in the rat uterus and that NO inhibits contractility during pregnancy but not during delivery. In the present study, we investigated the possible role of sex steroid hormones in the regulation of NO synthesis and cGMP generation. NO, measured as nitrite production, and cGMP were determined in full thickness uterine tissues from either pregnant rats on different gestational days or nonpregnant animals after treatment with steroid hormones. NO formation was low in tissues from nonpregnant rats, substantially increased during pregnancy and decreased during labor and immediately postpartum. The cGMP content in the same tissues followed a similar trend. Uterine nitrite production and cGMP levels from animals treated with estradiol and estradiol + progesterone were significantly lower compared to those treated with vehicle or progesterone. These data provide strong evidence that the NO-cGMP system is upregulated during pregnancy to maintain uterine quiescence and a rise in estrogen at term could inhibit this system and thus initiate labor.

The adverse influence of pregnancy upon sulphation: a clue to the pathogenesis of intrahepatic cholestasis of pregnancy?

Sulphation of oestrogens and monohydroxy bile acids is important in attenuating their cholestatic potential. Thus, impairment of sulphation could lead to retention of cholestatic compounds and precipitate intrahepatic cholestasis in susceptible individuals. We tested the hypothesis that such a mechanism may be involved in the pathogenesis of intrahepatic cholestasis of pregnancy. In vivo and in vitro assessment of sulphation capacity was performed in patients with cholestasis of pregnancy, compared with control females on and off the oestrogen-containing oral contraceptive pill and control individuals during normal pregnancy and post partum, to assess the influence of high oestrogen states upon this metabolic pathway. During in vivo studies utilising paracetamol as a metabolic probe, the proportion of paracetamol sulphate and sulphate: glucuronide ratio were decreased in those with elevated oestrogens, whether the rise in oestrogens was endogenous, in pregnancy (paracetamol sulphate p < 0.05; paracetamol sulphate:glucuronide ratio p < 0.01), or exogenous, with the contraceptive pill (paracetamol sulphate p = 0.2; paracetamol sulphate:glucuronide ratio p < 0.001). In vitro, platelet sulphotransferase activity was measured, utilising phenol as substrate. Sulphotransferase activity decreased during pregnancy compared with repeat measurements post partum (p < 0.005) and compared with non-pregnant individuals (p < 0.05). In conclusion, we have shown that elevated oestrogens are associated with significant impairment in sulphation capacity. An imbalance of sulphation with glucuronidation provoked by high circulating oestrogen levels may be contributory in the pathogenesis of cholestasis of pregnancy.

Hormonal correlates of 'masculinization' in female spotted hyaenas (Crocuta crocuta). 1. Infancy to sexual maturity.

This report is concerned with hormone concentrations accompanying sexual maturation in a highly 'masculinized' female mammal, the spotted hyaena, Crocuta crocuta. Plasma concentrations of testosterone, androstenedione and oestrogen were determined by radioimmunoassay in a longitudinal study of 12 female and eight male hyaenas 2.5-62.5 months old. Concentrations of testosterone were significantly higher in males than in females after 26.5 months of age, but earlier measurements did not differ between sexes. Mean testosterone concentrations in adult female hyaenas (0.4-0.5 ng ml-1) were similar to those in several other female mammals that do not display a 'masculine' profile, but mean concentrations of androstenedione (2.5-5.5 ng ml-1) in female hyaenas were significantly higher than in males (1.0-2.0 ng ml-1), at most ages. Oestrogen could not be detected (less than 0.03 ng ml-1) in females until about 14 months of age and then increased (to approximately 0.13 ng ml-1) between 18 and 30 months; oestrogen remained undetectable in males. This rise in oestrogen in females corresponded to nipple enlargement and to changes in the size and elasticity of the urogenital meatus, permitting copulation and parturition through the clitoris. Gonadectomy (two males and four females) at 4-7 months resulted in nondetectable concentrations of testosterone and oestrogen and a marked attenuation in androstenedione (to approximately 0.39 ng ml-1), indicating that the gonads are the major source of these three steroids. Gonadectomy also eliminated sex differences in weight, nipple development and elasticity of the urogenital meatus.

Prolonged follicle stimulation decreases pregnancy rates after in vitro fertilization

Ovarian stimulation with a GnRH-a and hMG for IVF treatment offers the potential to extend the period of follicle recruitment and growth free of the restriction imposed by a spontaneous midcycle LH surge. A randomized trial investigating the impact of extending follicle growth by 1 day resulted in a significantly reduced PR, despite an increase in the number of larger follicles (greater than or equal to 17 mm) at the time of hCG. The reason for a reduced PR was not related to the number of ova recovered or embryo quality. This suggests that follicular aging or the duration of estrogen rise may be important.

Pattern of sex steroids secretion and their relationship with embryo yield in Jersey cows superovulated with PMSG

The levels of progesterone and estrogen secretion were studied in relationship to the superovulatory response in Jersey cows. Progesterone and estrogen concentrations were measured in superovulated Jersey cows with the objective of correlating the patterns of steroid secretion with embryo yield and quality. Pregnant mare serum gonadotropin (PMSG) was used in combination with prostaglandin F 2 alpha analogue to induce superovulation in 18 multiparous, cyclic cows. Serum progesterone and estradiol levels from cows which exhibited estrus within 24 to 48 h after prostaglandin administration (n=13) were used to estimate the superovulatory response. Sex steroid concentrations at the day of estrus (Day 0) was a strong indicator of embryo yield. Progesterone was negatively (r=−0.56) and estrogen positively (r=0.80) correlated to the number of embryos collected. Dramatic increase in progesterone from Day 0 to Day 7 was a significant indicator of embryo yield. A higher rise of estrogen in the follicular phase was an indicator of a larger number of growing follicles and, consequently, better superovulatory response. Nonresponding animals did not show any significant change in the hormonal profile from the day of PMSG treatment to the day of embryo collection. The estimation of progesterone and estradiol concentrations, simultaneously, gave a more objective prediction of embryo yield.

Embryo transfer technology as a tool to establish bovine genetic resources

The levels of progesterone and estrogen secretion were studied in relationship to the superovulatory response in Jersey cows. Progesterone and estrogen concentrations were measured in superovulated Jersey cows with the objective of correlating the patterns of steroid secretion with embryo yield and quality. Pregnant mare serum gonadotropin (PMSG) was used in combination with prostaglandin F2 alpha analogue to induce superovulation in 18 multiparous, cyclic cows. Serum progesterone and estradiol levels from cows which exhibited estrus within 24 to 48 h after prostaglandin administration (n=13) were used to estimate the superovulatory response. Sex steroid concentrations at the day of estrus (Day 0) was a strong indicator of embryo yield. Progesterone was negatively (r=−0.56) and estrogen positively (r=0.80) correlated to the number of embryos collected. Dramatic increase in progesterone from Day 0 to Day 7 was a significant indicator of embryo yield. A higher rise of estrogen in the follicular phase was an indicator of a larger number of growing follicles and, consequently, better superovulatory response. Nonresponding animals did not show any significant change in the hormonal profile from the day of PMSG treatment to the day of embryo collection. The estimation of progesterone and estradiol concentrations, simultaneously, gave a more objective prediction of embryo yield.

Effect of a 48-hour intravenous Δ 4-androstenedione infusion on the pregnant rhesus monkey in the last third of gestation: Changes in maternal plasma estradiol concentrations and myometrial contractility

Increased myometrial activity in the pregnant rhesus monkey occurs in situations in which plasma estrogen concentrations are elevated. Examples of such situations are after laparotomy, with or without hysterotomy, and before delivery. The increased activity occurs primarily in the hours of darkness. To investigate the possibility of a causal relationship between the rise in estrogens and myometrial activity, we infused androstenedione intravenously for 48 hours to the rhesus monkey in the last third of gestation. Myometrial activity was quantified either as an increase in the number of individual contraction events or as a change in the power spectrum at high frequencies characteristic of contractions. Androstenedione infusion was followed by increased myometrial activity. Maternal plasma 17 beta-estradiol concentration was significantly elevated at 10 AM on the second day of androstenedione infusion. We conclude that, in the rhesus monkey late in gestation, estradiol may play a role in the regulation of the contraction activity observed during the hours of darkness in several different situations.

The role of endogenous estrogens in the maturation process of the bovine placenta

The plasma estrogen and progesterone concentrations of 19 pregnant cows (average duration of pregnancy 266.0 ± 2.3 d at the start of the study) were determined daily from Day 6 pre partum to Day 1 post partum. Parturition was induced in all cows by administration of 10 mg i.m. flumethasone. Values were centered around the delivery date (Day 0) following either induced normal calving (n = 3) or surgical delivery (n = 16). In animals showing spontaneous expulsion of the fetal membranes (Group 1, n = 6) the average total estrogen concentration increased significantly from Day 6 until Day 1 before parturition (1329.2 ± 317.9 to 3719.8 ± 951.2 pg/ml in total estrogens). A marked decrease was observed on Day 1 post partum (459.4 ± 344.2 pg/ml). In comparison with Group 1, animals showing either a delayed or partial expulsion of the fetal membranes, or in which the placenta could be withdrawn 16 h after calving (Group 2, n = 5), had consistently lower total estrogen concentrations between Day 6 (595.4 ± 174.8 pg/ml) and Day 1 (1884.3 ± 565.1 pg/ml) before parturition. The estrogen values of the cows with retained placenta (Group 3, n = 8) from Days 6 to 0 pre partum were significantly lower than those of Group 2. Total estrogen concentrations of the three groups 1 d post partum did not differ significantly. It is generally recognized that estrogens play an important role in the maturation process of the placentomes. Our investigation demonstrates that not only is the magnitude of the prepartum rise in estrogens of great influence of the maturation process but the duration of this rise is likewise important. These two factors are vital for a normal expulsion of the fetal membranes.

Down-Regulation of Testicular Aromatization in the Horse

A single i.m. injection of testosterone (750 mg of testosterone bexahydrobenzoate) or i.v. injection of human chorionic gonadotrophin (hCG) (10,000 IU) was given to geldings and stallions. Levels of unconjugated and conjugated (after solvolysis) androgens and estrogens were measured in blood and urine samples taken daily from the day of injection (D0) to the tenth day post-injection (D10). In the stallion, both treatments resulted in a sharp increase of plasma estrogens, which peaked one day before the androgen levels. Our results confirmed the testicular localization of a potent aromatase, which is able to aromatize androgens from endogenous as well as exogenous origin into conjugated estrogens. The very similar patterns of estrogen increase following testosterone or hCG administration suggest that the estrogen rise induced by hCG results at least partly from increased availability of testosterone. The abrupt drop in plasma estrogen levels cannot be explained by a lack of substrate, since two successive androgen injections did not succeed in maintaining the high estrogen levels. Since estrogens were unable to inhibit the aromatase activity in vitro, the drop in estrogen levels suggests a down-regulation of the aromatase synthesis.

Factors affecting fetal loss in induction of ovulation with gonadotropins: Increased abortion rates related to hormonal profiles in conceptual cycles

Thirty-six first-trimester abortions (9.7%), 16 second-trimester abortions (4.3%), 11 ectopic pregnancies (2.9%), and 10 stillbirths (2.7%) occurred in 373 conceptual cycles after gonadotropin induction of ovulation. Fetal wastage was higher in spontaneous pregnancies that occurred before therapy (54.3%, p less than 0.0001) and lower with subsequent spontaneous pregnancies (10.1%, p less than 0.05). Significant risk factors for overall fetal loss during induced ovulation were a continuous rise of estrogen excretion until ovulation (p less than 0.01) and previous abortion (p less than 0.05). For first-trimester abortion, the risk factor was continuous estrogen rise (p less than 0.01); for second-trimester abortion, the risk factors were a low luteal pregnanediol-to-estrogen excretion ratio (p less than 0.002), increased age at conception (p less than 0.02), and high baseline estrogen excretion (p less than 0.05). Multiple pregnancy was not significant. The continuous rising estrogen pattern may serve as a marker of abnormal oocyte maturation. We propose that future studies on infertility treatment should report on pregnancy outcome.

Urinary concentrations of ovarian steroid hormone metabolites and bioactive follicle-stimulating hormone in killer whales (Orcinus orchus) during ovarian cycles and pregnancy.

Reproductive hormone profiles of six captive killer whales (Orcinu orcus) from three Sea World aquaria were studied for intervals up to 2 yr. Daily urine samples and bimonthly blood samples were collected and analyzed for hormone concentration. Immunoreactive estrone conjugates, pregnanediol-3-glucoruonide, 20-alpha-hydroxyprogesterone as well as bioactive follicle-stimulating hormone (FSH) were measured in urine samples and indexed by creatinine concentrations of the same sample. In selected cases, serum progesterone concentrations were also measured. Three of the animals in the study became pregnant during the study period and two of these animals were evaluated during the time of conception and throughout most of gestation. From the data of the three animals that conceived, hormone profiles of the complete ovarian cycle, early pregnancy, and mid- to late gestation are described. The remaining three animals did not conceive and only one of these demonstrated hormone changes that indicated regular ovarian activity. The female reproductive pattern of the killer whale is characterized by a gestation of 17 mo and an ovarian cycle of 6-7 wk in duration. The hormone changes associated with the ovarian cycle of the killer whale are similar to those of most other mammalian species. A bimodal pattern of bioactive FSH with a pronounced rise of estrogen predominates the preovulatory hormone profile. After ovulation, increased progesterone production is observed for approximately 4 wk in the nonconceptive ovarian cycle. During the luteal phase and early pregnancy, when progesterone metabolites are elevated, estrogen metabolite excretion remains low. These data extend the application of urine collections for longitudinal studies involving hormone changes, particularly those involving nondomesticated species.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct measurements of urinary estrone conjugates during the normal menstrual cycle of the gorilla (Gorilla gorilla).

A direct immunoassay for urinary estrone conjugates (estrone sulfate and estrone glucuronide) was used to assess the preovulatory estrogen rise in normal gorilla menstrual cycles. Immunoreactive estrone conjugates in samples concomitantly assessed for total estrogen immunoreactivity reflected similar profiles throughout the cycle; however, the speed and resolution of the direct assay for conjugates indicate this method to be more accurate in monitoring ovulation than the measurement of total immunoreactive estrogens. In a single conceptive ovarian cycle, urinary estrone conjugate continued to rise in the luteal phase, indicating that this test may also be useful for detecting early pregnancy. The application of this technique provides clear profile of ovarian function in gorillas as well as in other primate species.

Temporal changes in steroids, prolactin and growth hormone in pregnant and pseudopregnant gilts during mammogenesis and lactogenesis

Estrogen, progesterone and prolactin are involved in control of mammary growth in all species studied to date. The primary hormonal change temporally related to mammary development in swine is the estrogen rise which begins on day 60 of pregnancy. However, hormonal regulation of mammary development in swine is poorly understood. Plasma was obtained at 15-day intervals (days 15–112) throughout pregnancy, day of parturition and day 4 of lactation to determine relationships between hormonal profiles and mammary development in swine. Fetal plasma was also obtained from day 60 until parturition. Additional gilts were made pseudopregnant and sampled on days 60, 90 and 112. Plasma samples were assayed for estrogens, progesterone, prolactin and growth hormone. Maternal profiles of estrone- and estradiol-sulfate, increased to 2.6 and 0.6 ng/ml, repectively on day 30 of pregnancy, with return to basal concentrations by day 45. Periparturient concentrations of estrone and estradiol did reach 13 and 2.6 ng/ml, respectively. Free estrogen concentrations (estrone and estradiol) did not change significantly at day 30, but were elevated to 6 and 0.7 pg/ml at parturition. Progesterone concentration fluctuated only slightly from a mean concentration of 25 ng/ml until the preparturient decline, resulting in concentrations of <5 ng/ml through day 4 of lactation. Prolactin and growth hormone concentrations remained at basal values (13 and 12 ng/ml, respectively) until the periparturient rise to 68 and 28 ng/ml. Total fetal estrogen concentrations rose steadily throughout the sampling period; progesterone declined through day 105, but rose significantly by day 112 of gestation. Fetal prolactin concentration rose slowly throughout the sampling period to reach 12 ng/ml by day 105 of gestation. The profile for fetal growth hormone differed from that of other fetal hormones, in that concentrations were above maternal values for the entire sampling period, and the profile was best fitted by a second order curve with the peak at day 90 (> 150 ng/ml). With the exception of estrone, hormonal concentrations in estrogen-treated pseudopregnant gilts did not differ from pregnant counterparts, demonstrating that pseudopregnant gilts are an excellent in vivo model to study estrogen effects on mammary development in swine.

Growth rate of follicular estrogen secretion in relation to the outcome of in vitro fertilization and embryo replacement

Estradiol growth rate (EGR) during active follicular development was calculated for 89 stimulated in vitro fertilization cycles by exponential curve fit (r = 0.83). Cycles could be divided into four groups with very low, low, moderate, and high EGR values. Cases without oocyte fertilization and/or embryo replacement did not occur in the moderate EGR range, which also corresponded to a significantly better ratio of replaceable embryos versus oocytes recovered. This group was also endowed with a pregnancy rate amounting to 28.5% per laparoscopy and per replacement, i.e., about three times higher than in the three other groups. Very low or high EGR entailed significantly higher percentages of missed oocyte recovery and/or fertilization failure. The frequency of occurrence of a spontaneous luteinizing hormone peak was negatively correlated with EGR. The data indicate that a better outcome of in vitro fertilization may be expected when the estrogen rise starts early in the cycle and adopts a moderate growth rate (0.3 to 0.4).

Delayed termination of third-trimester gestations in dairy cows after treatment with the PGF 2αanalog Tiaprost

Six dairy cows of the German Black Pied breed were treated between days 190 and 266 of gestation with 0.75 mg of the PGF 2α analog Tiaprost (Iliren R-Hoechst). Luteolysis occurred within 24 hours, with progesterone blood levels dropping to baseline values of about 3.18 nmol/l (l ng/ml), but pregnancies were terminated by spontaneous abortions or premature parturitions only after an average of 24.2 days (range 5 to 50 days) after treatments. Four of six deliveries were premature and all deliveries were preceded by a rise in blood estrogen levels which commenced 1 to 12 days prepartum and peaked intrapartum. Unsuccessful attempts were made to induce this estrogen rise earlier by using treatments with Tiaprost, PGF 2α-THAM or estradiol benzoate; treatments with a progesterone-releasing intravaginal device did not prevent the estrogen rise. Abortions and parturitions were spontaneous or by slight pulling. The placenta was retained in all six animals. Two immature fetuses were stillborn, and one immature born calf died three hours after birth.

Periovulatory glycoprotein secretion in the macaque fallopian tube

Anatomic demonstration of a specific midcycle fallopian tube secretion has been sought by transmission electron microscopy in the Macaca mulatta fascicularis with a method of in vivo perfusion-fixation that includes the polycation alcian blue (plus glutaraldehyde) to precipitate and stabilize anionic extracellular secreted glycoproteins. Of nine monkeys entered into the study, six ovulated regularly. With the help of daily plasma total estrogen radioimmunoassays and serial laparoscopies, these six monkeys were killed and the pelvic organs were perfused at specific times in the menstrual cycle: the midfollicular phase (one), during the midcycle estrogen peak immediately before ovulation (one), 24 hours after ovulation (one), 2 to 4 days after ovulation (two), and premenstrually (one). The other three monkeys were oophorectomized and were treated with estradiol benzoate, 10 μg/kg/day for 7 days (two), or with estradiol benzoate, 10 μg/kg/day for 7 days, and progesterone in oil, 1 mg/kg/day from day 3 to day 7. Evenly distributed, granular, precipitated material was found in the isthmic lumen both immediately before and 24 hours after ovulation (and in the two oophorectomized, estrogen-treated monkeys, both of which had plasma total estrogen levels that exceeded those of preovulatory monkeys); this would coincide with times of sperm ascent through the isthmus, ovulation, and fertilization and with the time of temporary impedance of the ovum's normal transport to the uterus, known to occur at the ampullary-isthmic junction. No substantial precipitable secretion was found in the ampulla at any stage of the cycle, in the isthmus before the midcycle estrogen rise, or 48 hours or more after either ovulation or initiation of progesterone treatment. These observations indicate that, in the primate fallopian tube, the unique ability of the isthmus to transport spermatozoa and ova in opposite directions sequentially is related temporally (and perhaps causally) to the presence and absence, respectively, of specific isthmic luminal secretions. The biochemical basis for this isthmic property may lie in the expected highly expanded state of acid mucus glycoproteins in the secretions.

The effect of exogenous acth and pen-confinement on estrous cycle length, plasma steroid levels and ovarian function of beef heifers

Each of 24 pasture-reared crossbred beef heifers were herded from a large pasture on day 14 of the estrous cycle and assigned randomly to one of four treatment groups as follows: Field Control (FC), Field ACTH (FA), Pen Control (PC) and Pen ACTH (PA). Field groups were maintained in a small field, and pen groups were confined in a pen in a pole barn. ACTH groups received 200 IU of ACTH IM daily for days 17 through 21 of the cycle and control groups received only the gelatin carrier IM on the same cycle days. Average cycle lengths for FA and PA heifers were 25 and 24.3 days with an average period from plasma progesterone decline below 1 ng/ml to estrus of 5.5 days. During the ACTH injection period, follicular growth was suppressed and the proestrus plasma estrogen rise was delayed. Average cycle lengths for FC and PC heifers were 20.8 and 22.8 days respectively. All control group heifers exhibited estrus within 2 days of the plasma progesterone decline below 1 ng/ml. In addition, pen confinement heifers showed a trend for extended luteal function and consequent extended estrous cycle length.

Changes in ovarian oestrogens and in plasma gonadotrophins in female rabbits from birth to adulthood.

Plasma oestrogens (E1, E2) and gonadotrophins, and ovarian oestrogens, were determined in female rabbits from birth to 6 months. Increases in ovarian weight followed a curvilinear pattern, with a phase of slow growth (from 1 to 60 days) preceding a phase of rapid growth (from 60 to 90 days). At birth, E2 was already quantifiable in ovaries; it remained at very low levels up to 50 days. Ovarian E2 content increased until 6 months with two sharp rises between 50 days (46 +/- 4 pg/2 ovaries) and 60 days (365 +/- 53 pg/2 ovaries) and between 80 days (326 +/- 77 pg/2 ovaries) and 90 days (1118 +/- 307 pg/2 ovaries). E1 appeared in ovaries at 50 days and then followed a pattern similar to that of E2. Oestrogens were never detected in plasma. At birth FSH and LH levels were similar to those measured in adult females but from 10 days the secretion of both gonadotrophins showed a clear dissociation. LH concentrations varied little during the period studied (between 1077 +/- 106 pg/ml to 2030 +/- 466 pg/ml). Plasma FSH levels were considerably higher between 10 and 50 days than those measured thereafter, particularly in adulthood. The decline in FSH levels occurred simultaneously with the rise in ovarian oestrogens.

A Bayesian Change Point Problem with an Application to the Prediction and Detection of Ovulation in Women

For most normally menstruating women the sequence of hormonal events leading up to and following occurrence of ovulation is the same. Rise in estrogen induces a midcycle surge of luteinizing hormone (LH) to a peak followed by ovulation and then a sharp rise in plasma progesterone which in turn increases basal body temperature (BBT) to a higher level. Therefore detection of change-points in estrogen and BBT can help predict and detect ovulation. This paper presents sequential Bayesian solutions to the problems of detecting changes in both estrogen and BBT under assumptions of independent normally distributed and sequentially observed responses. The Bayesian solutions are applied to an aggregate of women who were observed throughout their menstrual cycles. In 33 women ovulation was predicted in advance of the LH peak and thus in advance of the actual ovulation. Ovulation was predicted an average of 3.55 days prior to the LH peak with a standard deviation of 1.46 days. In another 41 women BBT observations were taken during 1 menstrual cycle; in 38 of these women BBT shift was detected after it had occurred the detection occurring at an average of 2.58 days after the change point with a standard deviation of 1.31 days where the change point is the day prior to the rise in BBT. In 24 women for whom change points in both estrogen and BBT were detected a midcycle fertile period can be marked off; average length of the fertile period was 7.38 days with a standard deviation of 1.81 days. All women had length <or= to 11 days. A method is proposed by which the accumulation of information for a specific woman can be incorporated into the aggregate prior information.

Serum levels of prolactin, TSH and gonadotrophins following LRH/TRH--double stimulation tests during the menstrual cycle.

Abstract. The objective of this study was to re-investigate the capacity of pituitary prolactin (Prl) and thyrotrophin (TSH) secretion throughout the normal menstrual cycle to respond to repeated thyrotrophin releasing hormone (TRH) stimulation analogous to the double luteinizing hormone-releasing hormone (LRH) stimulation test. This test has been shown to be a sensitive parameter for oestrogenic effects on the gonadotrophs. In addition, the volunteers were selected carefully on the basis of ovulatory cycles and otherwise normal endocrine function. In 9 women a combined LRH/TRH double stimulation test was performed during the early follicular, periovulatory and mid-luteal phases. TRH (200 μg) and LRH (25 μg) each were given iv twice, 2 h apart. Basal and LRH stimulated luteinizing hormone (LH) and follicle stimulating hormone (FSH) were found to follow characteristic cyclic response patterns. The LH responses after both LRH stimulations were greatest in the periovulatory phase; Δ1 and Δ2 were higher in the mid-luteal phase than in the follicular phase. Maximum FSH response to LRH was found during the periovulatory phase, but the FSH response in the early follicular phase was greater than that found in the mid-luteal phase. In contrast, basal and TRH stimulated serum concentrations of TSH and Prl remained constant throughout the cycle. The gonadotrophin ratios Δ2:Δ1 were generally greater than 1. They increased from 1.4 in the early follicular phase to 3.0 in the late follicular phase, concomitant with the rise in oestrogens. The Δ2: Δ1 ratios for TSH and Prl were less than 1, ranging from 0.66 to 0.98 for TSH and from 0.26 to 0.99 for Prl. They did not show any cyclic changes. Thus, this study shows that after LRH/TRH double stimulation, the gonadotrophin but not the Prl and TSH responses vary with the physiological changes in oestrogens during the menstrual cycle. The supposed mechanism of oestrogen effects on pituitary hormone secretion and their possible clinical significance are discussed.