Abnormal 24-hour urinary excretory pattern of 6-sulphatoxymelatonin in both phases of cluster headache

The typical cyclic occurrence of cluster headache suggests the involvement of hypothalamic rhythm regulating centers in the pathogenesis of this primary headache. In previous studies, reduced 24-h plasma melatonin levels during the cluster period, loss of circadian melatonin secretion in remission, as well as permanently reduced excretion of urinary melatonin in both illness phases have been reported, supporting the hypothesis of a hypothalamic derangement. In this study, the 24-h urinary excretion of the main melatonin metabolite, 6-sulphatoxymelatonin, was evaluated in 20 cluster period cluster headache patients. Thirteen were retested 12 months later, in the same period of the year, during remission. Fourteen age- and sex-matched healthy subjects were the controls. As expected, significantly higher levels of 6-sulphatoxymelatonin were present in nocturnal urine than in day-time urine in controls, while in both cluster headache groups urinary levels of this metabolite did not differ between day and night. Nocturnal levels of 6-sulphatoxymelatonin were significantly lower in both cluster headache groups than controls. Day-time levels did not differ significantly between the groups. Altered excretion of urinary 6-sulphatoxymelatonin even during remission indicates that at least some of these anomalies are independent of the pain, and provides further evidence of involvement of the hypothalamic rhythm regulating centers in cluster headache.     

Polycystic ovary syndrome: evidence for reduced sensitivity of the gonadotropin-releasing hormone pulse generator to inhibition by estradiol and progesterone

Plasma LH is commonly elevated in women with the polycystic ovary syndrome (PCOS), but the underlying mechanisms are uncertain. We tested the hypothesis that the elevated LH in part reflects a reduced sensitivity of the hypothalamic GnRH pulse generator to suppression by estradiol (E2) and progesterone (P). In an initial protocol, normal controls (beginning on cycle days 8-10) and women with PCOS were given E2 transdermally and P by vaginal suppository (three times daily), to achieve plasma concentrations similar to those in the midluteal phase of an ovulatory cycle, for 21 days. Blood was obtained at 10-min intervals for 12 h before and on days 5, 10, 20, and 28 (7 days after E2 and P were discontinued). LH pulse amplitude and LH pulse frequency were suppressed in both PCOS and normal controls, but LH pulse frequency fell more rapidly in controls and was lower by day 10 (P < 0.05). Based on this time course a dose-response study was performed, in which E2 in constant dosage and varying concentrations of P were administered for 7 days. Pulsatile LH release was appraised on days 1 and 7. The frequency of LH pulse secretion was reduced in controls and was lower than that in patients with PCOS on day 7 (P < 0.0001). Plasma P concentrations of 13-15 ng/mL suppressed LH pulse frequency to a similar degree in PCOS and controls. In contrast, lower concentrations (P < 10 ng/mL) were more effective in suppressing GnRH/LH pulse frequency in controls (by > 45% of basal) than in PCOS (< 40%; P < 0.01). The data indicate that E2 and P can inhibit the activity of the hypothalamic GnRH pulse generator in women with PCOS. However, higher plasma concentrations of P were required to reduce GnRH/LH pulse frequency in PCOS compared to controls, suggesting an insensitivity of the GnRH pulse generator to suppression by E2 and P. These results suggest that an abnormality in the regulation of hypothalamic GnRH secretion is present in PCOS and may be a factor in the etiology of the disorder in adolescence.     

Brain opioid receptor measurements by positron emission tomography in normal cycling women: relationship to luteinizing hormone pulsatility and gonadal steroid hormones

The regulation of central mu-opioid receptors in women during the menstrual cycle was explored with positron emission tomography and the selective radiotracer [11C]carfentanil. Ten healthy women were studied twice, during their follicular and luteal phases. Plasma concentrations of estradiol, progesterone, testosterone, and beta-endorphin were determined immediately before scanning. LH pulsatility was measured over the 9 h preceding each of the two positron emission tomography scans. No significant differences in the binding potential of mu-opioid receptors (binding capacity/Kd) were observed between phases of the menstrual cycle. However, significant negative correlations were observed between circulating levels of estradiol during the follicular phase and mu-receptor binding measures in the amygdala and hypothalamus, two regions thought to be involved in the regulation of GnRH pulsatility. LH pulse amplitude was positively correlated with mu binding in the amygdala, whereas LH pulse number was negatively correlated with binding in this same region. No significant associations were noted between LH pulse measures and the hypothalamus for this sample. These results suggest that amygdalar mu-opioid receptors exert a modulatory effect on GnRH pulsatility, and that circulating levels of estradiol also regulate central mu-opioid function.     

Neuroendocrine aspects of primary endogenous depression--XIV. Gonadotropin secretion in female patients and their matched controls

To determine the extent of dysregulation of gonadotropin secretion in depressed women, we measured nocturnal and diurnal serum luteinizing hormone (LH) and follicle stimulating hormone (FSH) concentrations and the responses of these hormones to gonadotropin releasing hormone (LHRH) in 20 Research Diagnostic Criteria primary, definite endogenous female depressives and in 20 individually matched female normal controls. Fourteen patients and 14 controls were premenopausal, and six patients and six controls were peri/postmenopausal or panhysterectomized. None of the latter was receiving estrogen replacement therapy. The premenopausal patients showed no significant differences in basal nocturnal or diurnal gonadotropin concentrations and no significant differences in hormone concentrations post-LHRH compared to their premenopausal matched controls. In contrast, in the postmenopausal subjects there were (1) significantly increased diurnal vs. nocturnal serum FSH concentrations in the depressives; (2) marginally increased nocturnal, diurnal, and LHRH-stimulated LH concentrations and highly significantly increased LHRH-stimulated FSH concentrations in the depressives compared to their controls; and (3) positive correlations between the LH measures and ratings of depression severity in the patients. These results suggest a dysregulation of the HPG axis in peri/postmenopausal and panhysterectomized female endogenous depressives.     

The hypothalamic-pituitary-luteal axis in women: effects of long-term orally active opioid antagonist (naltrexone) administration

Aim of our study is to assess the effect of a long-term oral opiate antagonist treatment during the luteal phase on the hypothalamic-pituitary-ovarian axis. Fourteen normovulatory women participated to the study. Immediately after the ovulation, the patients were randomly divided in two groups: in the first one women received naltrexone 50 mg/die orally (Antaxone Zambon Italy) from day 1 of the luteal phase for 7 days. In the second patients were treated with placebo for the same period and served as control group. On day 7, patients were hospitalized for a pulse pattern study followed by a GnRH test. LH, FSH, Estradiol, Progesterone were assayed. The naltrexone administration strongly increased the number as well as the amplitude of the gonadotropin pulses. The circulating P levels were also significantly higher in treated patients. The GnRH injection significantly increases the gonadotropin secretion in all patients. The stimulated LH and FSH secretion was significantly greater in treated patients when compared to controls. Such discharge of LH determined a significant increase of progesterone production in controls, but failed to stimulate the corpus luteum in treated patients. In conclusion the present paper strengthen an important role of the opioidergic system in the regulation of GnRH pulsatility in luteal phase. Moreover, our findings confirms the sensibility of the corpus luteum to LH and the possibility to stimulate the P secretion during the luteal phase.     

Daytime plasma melatonin levels in male hypogonadism

It has previously been shown that increased nocturnal melatonin (MT) secretion exists in male patients with hypogonadotropic hypogonadism. However, little is known about the effects of gonadotropin and testosterone (T) treatment on early morning plasma MT levels in male hypogonadism. Also, the impact of gonadal steroids on plasma MT levels is an open question. We, therefore, determined early morning plasma MT levels at the same hour before and 3 months after treatment in 21 patients with idiopathic hypogonadotropic hypogonadism (IHH), 10 patients with primary hypogonadism, and 11 male controls. Plasma FSH, LH, PRL, T, and estradiol levels were also determined before and 3 months after treatment. Patients with IHH were treated with hCG/human menopausal gonadotropin, whereas patients with primary hypogonadism received T treatment. Short term treatments did not achieve normal T levels, although significant increases in T were observed in both groups. Plasma MT levels were measured by a RIA with a sensitivity of 10.7 pmol/L. Mean plasma MT levels before treatment were significantly higher in IHH (41.8 +/- 24.4 pmol/L) compared with those in the controls (21.7 +/- 10.8 pmol/L; P < 0.05). However, a slight, but not significant, increase in MT (34.2 +/- 21.1 pmol/L) was found in primary hypogonadism. Mean MT levels did not change significantly 3 months after the initiation of gonadotropin (41.7 +/- 22.8 pmol/L) or T (28.4 +/- 12.6 pmol/L) treatment in either IHH or primary hypogonadism, although a tendency for MT to decrease was observed in both groups. No correlation was found between MT and circulating FSH, LH, PRL, and gonadal steroids either before or after therapy. We conclude that male patients with IHH have increased early morning MT levels, although the pathophysiological mechanism is not clear. Furthermore, our study demonstrated that mean plasma MT levels are not influenced by short term gonadotropin or T treatment in male hypogonadism, although a longer time effect of gonadotropins or T treatment may not be excluded. The lack of correlation between plasma MT and circulating gonadal steroids before and after treatment suggests that there is no classic feedback regulation between the pineal gland and the testes.     

Pseudo-precocious puberty in a male patient and the melatonin-testosterone relationship

We describe a 14 year-old boy with a pineal germ cell tumor which secreted beta HCG. Serum testosterone levels were markedly elevated with concomitant decreased LH secretion. 24-h serum melatonin levels were suppressed and lacked the normal nocturnal rise. Pineal radiation therapy was followed by tumor regression and the diminution of beta HCG stimulated testosterone, which in turn inhibited melatonin and LH. When beta HCG and testosterone were normalized after tumor radiation, a recovery of normal melatonin and LH secretory pattern occurred. These results indicate that circulating testosterone down-regulates pineal melatonin.     

Mid-follicular phase pulses of inhibin B are absent in polycystic ovarian syndrome and are initiated by successful laparoscopic ovarian diathermy: a possible mechanism regulating emergence of the dominant follicle

The hypothalamic pulse generator of GnRH is recognized to be central to ovulatory function as evidenced by the anovulation of women with hypogonadotrophic hypogonadism due to Kallmann's syndrome or severe anorexia nervosa. LH is released from the anterior pituitary in pulses, the frequency of which is closely entrained with those of GnRH. In contrast, secretion of FSH is influenced by a number of regulatory molecules, including GnRH, estradiol, inhibin, and activin. The close temporal relationship between changes in levels of inhibin B and FSH in the mid-follicular phase suggests that the release of inhibin B by the preovulatory follicle critically regulates pituitary FSH secretion. Polycystic ovarian syndrome (PCOS) is one of the most common endocrine disorders affecting ovulation, and abnormal ovarian morphology as detected by ultrasonography remains the most sensitive diagnostic marker for this disorder. The etiology of PCOS is unclear, but its effective treatment by both anti-estrogens and by exogenous FSH suggests that a primary disorder of FSH regulation may be central. To investigate the possible role of inhibin B in the pathology of PCOS, serum inhibin B levels were measured in 10 women with PCOS on cycle day 5 of a spontaneous or progestrogen-provoked bleed and compared with levels on cycle day 5 of 10 women with regular ovulatory cycles. The mean serum inhibin B levels in the PCOS patients were significantly higher at 248 (+/- 43.4) pg/mL compared with normal controls, 126 (+/- 18.6) pg/mL (P < 0.01). Ten women with clomiphene resistant PCOS and 5 normal controls consented to undergo serial blood sampling on cycle day 5. Time Series Analysis using a Fourier Transformation to analyze the power spectrum of the data revealed that in normal women there is a distinct periodicity in inhibin B levels with a clear peak detectable every 60-70 min (P < 0.05), whereas in women with ovulatory dysfunction due to PCOS, no such pattern of regular pulsatility was seen. Four women with PCOS whose anovulation was successfully treated with laparoscopic ovarian diathermy (LOD) underwent repeat venous sampling following LOD. Their serum inhibin B levels fell to the upper limit of the normal range (160 +/- 38.5) pg/mL, and pulsatility was initiated. It is possible that inhibin B pulses are being generated directly by the ovary in response to pulses of GnRH in the peripheral circulation, or indirectly in response to FSH pulses arising in the pituitary. The function of inhibin B pulses in the mid-follicular phase of the normal cycle remains to be elucidated, but the absence of the normal pulsatile pattern in women with PCOS, in conjunction with high basal levels of inhibin B arising from the multiple small follicles characteristic of the PCOS ovary, appears to reinforce the development of a large cohort of small, developmentally arrested, and ultimately atretic follicles in these patients. Initiation of normal inhibin B pulsatility by LOD in patients with polycystic ovaries appears to correlate with the post-operative onset of ovular cycles.     

Synchronicity of frequently sampled, 24-h concentrations of circulating leptin, luteinizing hormone, and estradiol in healthy women

Leptin, an adipocyte hormone, is a trophic factor for the reproductive system; however, it is still unknown whether there is a dynamic relation between fluctuations in circulating leptin and hypothalamic-pituitary-ovarian (HPO) axis hormones. To test the hypothesis that fluctuations in plasma leptin concentrations are related to the levels of luteinizing hormone (LH) and estradiol, we sampled plasma from six healthy women every 7 min for 24 h during days 8-11 of the menstrual cycle. Cross-correlation analysis throughout the 24-h cycle revealed a relation between release patterns of leptin and LH, with a lag of 42-84 min but no significant cross-correlation between LH and estradiol. The ultradian fluctuations in leptin levels showed pattern synchrony with those of both LH and estradiol as determined by cross-approximate entropy (cross-ApEn). At night, as leptin levels rose to their peak, the pulsatility profiles of LH changed significantly and became synchronous with those of leptin. LH pulses were fewer, of longer duration, higher amplitude, and larger area than during the day. Moreover, the synchronicity of LH and leptin occurred late at night, at which time estradiol and leptin also exhibited significantly stronger pattern coupling than during the day. We propose that leptin may regulate the minute-to-minute oscillations in the levels of LH and estradiol, and that the nocturnal rise in leptin may determine the change in nocturnal LH profile in the mid-to-late follicular phase that precedes ovulation. This may explain the disruption of hypothalamic-pituitary-ovarian function that is characteristic of states of low leptin release, such as anorexia nervosa and cachexia.     

Guanylyl cyclase inhibition reduces contractility and decreases cGMP and cAMP in isolated rat hearts

Objectives of the current studies were to characterize the pattern of GnRH secretion in the cerebrospinal fluid of the bovine third ventricle, determine its correspondence with the tonic and surge release of LH in ovariectomized cows, and examine the dynamics of GnRH pulse generator activity in response to known modulators of LH release (suckling; neuropeptide Y [NPY]). In ovariectomized cows, both tonic release patterns and estradiol-induced surges of GnRH and LH were highly correlated (0.95; p < 0.01). Collectively, LH pulses at the baseline began coincident with (84%) or within one sampling point after (100%) the onset of a GnRH pulse, and all estradiol-induced LH surges were accompanied by corresponding surges of GnRH. A 500- microg dose of NPY caused immediate cessation of LH pulses and lowered (p < 0.001) plasma concentrations of LH for at least 4 h. This corresponded with declines (p < 0.05) in both GnRH pulse amplitude and frequency, but GnRH pulses were completely inhibited for only 1.5-3 h. In intact, anestrous cows, GnRH pulse frequency did not differ before and 48-54 h after weaning on Day 18 postpartum, but concentrations of GnRH (p < 0.05) and amplitudes of GnRH pulses (4 of 7 cows) increased in association with weaning and heightened secretion of LH. We conclude that the study of GnRH secretory dynamics in third-ventricle CSF provides a reasonable approach for examining the activity and regulation of the hypothalamic pulse generator in adult cattle. However, data generated using this approach must be interpreted in their broadest context. Although strong neurally mediated inhibitors of LH pulsatility (suckling; NPY) had robust effects on one or more GnRH secretory characteristics in CSF, only high doses of NPY briefly abolished GnRH pulses. This implies that the GnRH signal received at the hypophyseal portal vessels under these conditions may differ quantitatively or qualitatively from those in CSF, and theoretically would be undetectable or below a biologically effective threshold when LH pulses are absent.     

The negative feedback actions of progesterone on gonadotropin-releasing hormone secretion are transduced by the classical progesterone receptor

Progesterone (P) powerfully inhibits gonadotropin-releasing hormone (GnRH) secretion in ewes, as in other species, but the neural mechanisms underlying this effect remain poorly understood. Using an estrogen (E)-free ovine model, we investigated the immediate GnRH and luteinizing hormone (LH) response to acute manipulations of circulating P concentrations and whether this response was mediated by the nuclear P receptor. Simultaneous hypophyseal portal and jugular blood samples were collected over 36 hr: 0-12 hr, in the presence of exogenous P (P treatment begun 8 days earlier); 12-24 hr, P implant removed; 24-36 hr, P implant reinserted. P removal caused a significant rapid increase in the GnRH pulse frequency, which was detectable within two pulses (175 min). P insertion suppressed the GnRH pulse frequency even faster: the effect detectable within one pulse (49 min). LH pulsatility was modulated identically. The next two experiments demonstrated that these effects of P are mediated by the nuclear P receptor since intracerebroventricularly infused P suppressed LH release but 3alpha-hydroxy-5alpha-pregnan-20-one, which operates through the type A gamma-aminobutyric acid receptor, was without effect and pretreatment with the P-receptor antagonist RU486 blocked the ability of P to inhibit LH. Our final study showed that P exerts its acute suppression of GnRH through an E-dependent system because the effects of P on LH secretion, lost after long-term E deprivation, are restored after 2 weeks of E treatment. Thus we demonstrate that P acutely inhibits GnRH through an E-dependent nuclear P-receptor system.     

Importance of the gonadotropin-releasing hormone (GnRH) surge for induction of the preovulatory luteinizing hormone surge of the ewe: dose-response relationship and excess of GnRH

The preovulatory LH surge in the ewe is stimulated by a large sustained surge of GnRH. We have previously demonstrated that the duration of this GnRH signal exceeds that necessary to initiate and sustain the LH surge. The objective of the present study was to determine whether a similar excess exists for amplitude of the GnRH surge. Experiments were performed using an animal model in which GnRH secretion was blocked by progesterone, which in itself does not block the pituitary response to GnRH. To assess the amplitude of the GnRH surge needed to induce the LH surge, we introduced artificial GnRH surges of normal contour and duration but varying amplitudes. Twelve ewes were run through 3 successive artificial follicular phases (total of 36). Six of these artificial follicular phases were positive controls, in which progesterone was removed, the estradiol stimulus was provided, and vehicle was infused. In these control cycles, animals generated endogenous LH surges. In the remaining artificial follicular phases, progesterone was not withdrawn, the estradiol stimulus was provided, and either vehicle (negative control) or GnRH solutions of varying concentrations (experimental) were infused. The circulating GnRH concentrations achieved by infusion were monitored. No LH surges were observed in negative controls, whereas LH surges were induced in experimental cycles provided a sufficient dose of GnRH was infused. A highly significant dose-response relationship was observed between the amplitude of the GnRH surge and both the amplitude of the LH surge and the area under the curve describing the LH response, but no such relationship existed between the amplitude of the GnRH surge and the duration of the LH response. In numerous cases, LH surges similar to those in the positive control animals resulted from infusion of amounts of GnRH estimated to be considerably less than those delivered to the pituitary during the endogenously generated GnRH/LH surge. These findings indicate that, in the ewe, increased GnRH secretion drives the preovulatory LH surge in a dose-dependent fashion, and they provide evidence that the amplitude of the GnRH surge may exceed that needed to generate the LH surge.     

Variation of dorsal horn cell dendritic spread with map scale

OBJECTIVE: To examine the hypothesis that, in polycystic ovary syndrome (PCOS), ovarian steroids induce adrenal enzyme dysfunction or adrenal androgen hyperresponsiveness to ACTH. DESIGN: Prospective controlled clinical study. SETTING: Reproductive endocrinology unit of an academic medical center. PATIENTS: Twelve women with PCOS who had adrenal androgen excess were compared with five weight-matched ovulatory women. In half of the women with PCOS, prestudy screening was suggestive of mild 3 beta-hydroxysteroid dehydrogenase (HSD) deficiency. INTERVENTIONS: Basal and adrenal dynamic blood sampling before and after GnRH agonist (GnRH-a) administration for 6 months. MAIN OUTCOME MEASURES: Basal E2 and androgen levels as well as dexamethasone-suppressed, ACTH-stimulated 17 alpha-hydroxyprogesterone, 17 alpha-hydroxypregnenolone, and androgen levels before and after ovarian suppression. RESULTS: Although none of the subjects with PCOS proved to have mild 3 beta-HSD deficiency, the majority of them (58%) met the criteria for 17,20 lyase hyperactivity before and after GnRH-a therapy. As a group, the remaining subjects with PCOS exhibited an elevated DHEAS response to ACTH before GnRH-a treatment, which may have normalized after GnRH-a treatment. CONCLUSION: Adrenal androgen excess in PCOS may be heterogeneous in etiology, whereas 17,20 lyase hyperactivity appears to be an intrinsic adrenal disorder, adrenal androgen hyperresponsiveness to ACTH may be ovarian induced. Reliance on historical controls may lead to overdiagnosis of mild 3 beta-HSD deficiency.     

Effects of gonadotropin-releasing hormone pulse frequency modulation on the reproductive axis of photoinhibited male Siberian hamsters

In Siberian hamsters, photostimulation evokes differential release of the gonadotropins, with FSH rising rapidly and LH levels rising much later. We have tested the hypothesis that differential release of gonadotropins in this species can be mediated by changes in the frequency of pulsatile GnRH stimulation. Photoinhibited Siberian hamsters received GnRH pulses at frequencies of 1 pulse every 45 (fast), 90 (medium), or 180 min (slow). Animals were killed at 0, 3, 5, 10, 20, and 30 days after treatment. There was a clear GnRH pulse frequency effect on LH release, with fast pulses > medium pulses > slow pulses > short-day (SD) controls. In addition, 10 days of fast-frequency GnRH pulses produced LH levels significantly greater than LH levels in animals exposed to 10 days of medium or slow GnRH pulse frequencies. Pulsatile GnRH produced the following serum FSH relationships: medium pulses > fast pulses > SD. The FSH response to slow GnRH frequency fell between the two faster frequencies. The effect of GnRH pulse frequency on paired testes weight was as follows: fast pulses = medium pulses > slow pulses > SD controls. The differing GnRH pulse frequencies produced the following testosterone relationships; fast pulses > medium pulses = slow pulses = SD controls. These results agree with studies showing that slower GnRH pulse frequencies facilitate FSH release, while faster GnRH pulse frequencies favor LH release. Our observations are also consistent with the idea that the singular release of FSH after transfer of hamsters to a long-day photoperiod is mediated by alterations in the frequency of endogenous pulsatile GnRH release.     

On the dynamics between gonadotrophin surge-inhibiting factor and gonadotrophin releasing hormone (GnRH): role of self-priming and desensitization in the luteinizing hormone response to GnRH after follicle stimulating hormone treatment

The effects were studied of follicle stimulating hormone (FSH)-induced production of gonadotrophin surge-inhibiting factor (GnSIF) on three phases of the pituitary responsiveness to gonadotrophin releasing hormone (GnRH): the unprimed, primed and desensitized phases. Rats were injected with FSH on two occasions during the oestrous cycle. Spontaneous luteinizing hormone (LH) surges were measured as well as GnRH-induced LH surges on the day of pro-oestrus during infusions with 100-4000 pmol GnRH/rat/10 h, in phenobarbital blocked rats. The spontaneous LH surges were attenuated or completely inhibited by the FSH treatment. FSH suppresses and prolongs the unprimed LH response and delays GnRH self-priming, especially during infusions with low concentrations of GnRH. This treatment does not affect the total LH response (area under curve) to the highest concentrations of GnRH and after ovariectomy. On the other hand, this response is suppressed during infusions with the lower concentrations of GnRH. Hence, FSH, via GnSIF, delays maximal priming of the LH response to GnRH, whereas the suppression of LH release is a consequence of the GnRH-induced progressed state of desensitization. The inconsistent effects of FSH on the mid-cycle LH surges are explained as a result of the interaction between the relative strengths of GnRH and GnSIF.     

The pattern and tempo of the pubertal reaugmentation of open-loop pulsatile gonadotropin-releasing hormone release assessed indirectly in the male rhesus monkey (Macaca mulatta)

The purpose of this study was to determine the pattern and tempo of the open-loop reaugmentation of pulsatile GnRH release at the time of puberty in the male rhesus monkey. Episodic LH secretion from the in situ pituitary, in which responsiveness to GnRH was first heightened and subsequently sustained by priming with an i.v. intermittent infusion of the synthetic peptide, was used as an index of GnRH discharges. Ten male monkeys were castrated between 12 and 20 months of age, implanted with indwelling venous catheters, and housed in specialized cages that permitted remote access to the venous circulation with minimal restraint and without interfering with the light-dark cycle. Endogenous GnRH release was assessed by examining moment-to-moment changes in circulating LH concentrations measured at 12-min intervals for 7 h while GnRH priming was temporarily interrupted. A discharge of GnRH was inferred whenever a pulse of LH secretion was identified by a pulse detection program. Examination of nocturnal pulsatile GnRH release (1900-0200 h) was initiated as early as 14 months of age. GnRH release was assessed at 40-day intervals before 20 months of age and at 10-day intervals whenever possible thereafter. A simple algorithm was developed to identify the age at which a developmental increase in hypophysiotropic drive to the gonadotroph occurred. This was termed day zero and was considered to represent the age at which a pubertal mode of GnRH release was initiated. After the initiation of pubertal GnRH release was established, alternate nighttime and daytime (1100-1800 h) assessments of GnRH were performed. Before day zero, which was observed between 24 and 29 months of age, a stable, low frequency (<1 pulse/7 h), low amplitude pattern of pulsatile GnRH release was observed. Termination of the prepubertal mode of GnRH pulse generator activity was manifest as a relatively rapid nocturnal shift to a robust high-frequency pattern of activity. In some animals, the nocturnal acceleration to an adult GnRH pulse frequency (6-7 pulses/7 h) was attained within an epoch of only 30 days. Although initiation of the pubertal acceleration in nocturnal GnRH pulse generator activity seemed to be associated with an increase in GnRH pulse amplitude, it was not possible to decipher the subsequent developmental changes in this parameter. In some animals, the pattern of pulsatile GnRH release after the initiation of the pubertal acceleration was punctuated by periods of diminished activity, which seemed to be unrelated to the state of the pituitary-adrenal axis. These findings demonstrate that the neurobiological mechanisms that lead to the termination of the prepubertal mode of diminished GnRH release, and that therefore initiate the insidious process of puberty, have the potential to unfold with a surprisingly rapid time course. The extent to which the intrinsic tempo of the pubertal acceleration of pulsatile GnRH release in the agonadal situation is dampened by testicular feedback in the intact monkey remains to be established.     

Progesterone can block transmission of the estradiol-induced signal for luteinizing hormone surge generation during a specific period of time immediately after activation of the gonadotropin-releasing hormone surge-generating system

The preovulatory GnRH/LH surge in the ewe is stimulated by a rise in the circulating estradiol concentration that occurs in conjunction with preovulatory ovarian follicle development. In the presence of high levels of progesterone, such as during the luteal phase of the estrous/menstrual cycle, the stimulatory effects of elevated estradiol on GnRH/LH secretion are blocked. Recent work in the ewe has shown that a relatively short period of estradiol exposure can stimulate a GnRH/LH surge that begins after estrogenic support has been removed. This result suggests that surge generation is characterized by an estradiol-dependent period (during which the signal is read) and an estradiol-independent period (during which a cascade of neuronal events transmits the stimulatory signal to the GnRH neurosecretory system, which releases a surge of GnRH). In this series of studies, we addressed the hypothesis that progesterone can block transmission of the stimulatory estradiol signal after it has been read. Nine ovariectomized ewes were run through repeated artificial estrous cycles by sequential addition and removal of exogenous steroids. In study one, ewes received three treatments in a randomized cross-over design. Exposure to a follicular phase estradiol concentration for 10 h (positive control treatment) stimulated an LH surge in all ewes, as determined in hourly jugular blood samples. Maintenance of luteal phase progesterone concentrations throughout the artificial follicular phase (2 x CIDR-G devices, negative control) blocked the stimulatory effects of a 10-h estradiol signal, and no ewes that received this treatment expressed an LH surge. In the experimental group, exposure to luteal phase levels of progesterone, during the period after the surge generating system had been activated by estradiol, blocked the LH surge in six of nine ewes. This result demonstrates that progesterone can block the surge, even when applied after the surge-generating system has been activated and, therefore, that it inhibits either the transmission of the estradiol signal and/or the release of the GnRH/LH surge. In study 2, we assessed whether sensitivity to the inhibitory effects of progesterone was confined to a specific stage of the transmission of the estradiol signal. Eight ewes were exposed to four treatments, over successive artificial estrous cycles. Positive and negative controls were similar to those described in Study 1, except the duration of the stimulatory estradiol signal was reduced to 8 h. The two experimental groups consisted of an EARLY P (progesterone) treatment, in which progesterone was given from hours 8-13 after estradiol insertion (immediately after estradiol removal), and a LATE P treatment, in which progesterone was given from hours 13-18 (immediately before LH surge secretion). As expected, LH surges were stimulated and blocked, in response to the positive and negative controls, respectively. Whereas the EARLY P treatment blocked the LH surge in seven of eight ewes, the LATE P treatment was only successful in inhibiting a surge in one of eight animals. This result demonstrates that progesterone can block the estradiol-induced surge-generating signal soon after the onset of signal transmission (immediately after estradiol removal) but not during the later stages of signal transmission (at the time of GnRH/LH surge onset).     

Hypothalamic-pituitary-ovarian response to clomiphene citrate in women with polycystic ovary syndrome

OBJECTIVE: To examine the hypothalamic-pituitary sites of clomiphene citrate (CC) action in women with polycystic ovarian syndrome (PCOS). DESIGN: Prospective controlled trial. PATIENTS, PARTICIPANTS: Seventeen women with PCOS and 9 normal-cycling women. INTERVENTIONS: Subjects with PCOS received CC, 150 mg/d for 5 days. MAIN OUTCOME MEASURES: Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels and LH pulse characteristics and their response to gonadotropin-releasing hormone (GnRH, 10 micrograms) were examined before and after 3 days of CC in PCOS subjects during a 12-hour frequent sampling study (n = 8). Daily urinary estrone glucuronide and pregnanediol glucuronide levels after CC were compared with concentrations in normal-cycling women through one menstrual cycle. In another nine PCOS subjects, pituitary and ovarian hormonal cyclicity was monitored by daily blood sampling. RESULTS: Thirteen of 17 treated cycles were ovulatory with normal luteal phases. In the ovulatory cycles, serum LH, FSH, estradiol (E2), and estrone levels increased after CC. Luteinizing hormone pulse frequency was unchanged, but LH pulse amplitude increased significantly after CC. Both LH and FSH response to exogenous GnRH was significantly attenuated after CC treatment. In anovulatory cycles, serum LH, FSH, and E2 increased initially and then returned to baseline and remained unchanged for the ensuring 40 days. CONCLUSIONS: Clomiphene citrate-induced ovulation in women with PCOS is accompanied by increased secretion of LH and FSH with enhanced estrogen secretion. The increased LH pulse amplitude after CC, together with decreased pituitary sensitivity to GnRH, suggests a hypothalamic effect.     

Nocturnal decreases in nitric oxide and cyclic GMP contents in the chick brain and their prevention by light

The diurnal variations in the contents of nitric oxide (NO) and cyclic GMP were studied in the chick brain. NO and cyclic GMP contents in the chick brain were lower at night than during the day and were inversely correlated with high night-time tissue melatonin levels. Furthermore, when animals were kept in light at night, tissue melatonin levels remained at low diurnal values, whereas NO and cyclic GMP contents remained high. Since we have previously shown that physiological concentrations of melatonin inhibit nitric oxide synthase (NOS) activity in different brain areas, the nocturnal decrease in brain NO and cyclic GMP contents may be, in part, a consequence of the nocturnal inhibitory effect of melatonin on NOS activity.