Synchronous secretion of luteinizing hormone and prolactin in the human luteal phase: neuroendocrine mechanisms

Intrapituitary mechanisms underlying the control of fertility: key players in seasonal breeding

Recent studies have shown that, in conjunction with dynamic changes in the secretion of GnRH from the hypothalamus, paracrine interactions within the pituitary gland play an important role in the regulation of fertility during the annual reproductive cycle. Morphological studies have provided evidence for close associations between gonadotropes and lactotropes and gap junction coupling between these cells in a variety of species. The physiological significance of this cellular interaction was supported by subsequent studies revealing the expression of prolactin receptors in both the pars distalis and pars tuberalis regions of the pituitary. This cellular interaction is critical for adequate gonadotropin output because, in the presence of dopamine, prolactin can negatively regulate the LH response to GnRH. Receptor signaling studies showed that signal convergence at the level of protein kinase C and phospholipase C within the gonadotrope underlies the resulting inhibition of LH secretion. Although this is a conserved mechanism present in all species studied so far, in seasonal breeders such as the sheep and the horse, this mechanism is regulated by photoperiod, as it is only apparent during the long days of spring and summer. At this time of year, the nonbreeding season of the sheep coincides with the breeding season of the horse, indicating that this inhibitory system plays different roles in short- and long-day breeders. Although in the sheep, it contributes to the complete suppression of the reproductive axis, in the horse, it is likely to participate in the fine-tuning of gonadotropin output by preventing gonadotrope desensitization. The photoperiodic regulation of this inhibitory mechanism appears to rely on alterations in the folliculostellate cell population. Indeed, electron microscopic studies have recently shown increased folliculostellate cell area together with upregulation of their adherens junctions during the spring and summer. The association between gonadotropes and lactotropes could also underlie an interaction between the gonadotropic and prolactin axes in the opposite direction. In support of this alternative, a series of studies have demonstrated that GnRH stimulates prolactin secretion in sheep through a mechanism that does not involve the mediatory actions of LH or FSH and that this stimulatory effect of GnRH on the prolactin axis is seasonally regulated. Collectively, these findings highlight the importance of intercellular communications within the pituitary in the control of gonadotropin and prolactin secretion during the annual reproductive cycle in seasonal breeders.

Disruption of the young-adult synchrony between luteinizing hormone release and oscillations in follicle-stimulating hormone, prolactin, and nocturnal penile tumescence (NPT) in healthy older men

The healthy human male hypothalamo-pituitary-gonadal axis exhibits age-dependent loss of coordinate LH-testosterone secretion. A putative independent defect in Leydig-cell steroidogenesis with aging would confound the attribution of such LH-testosterone asynchrony to a hypothalamo-pituitary locus per se. Accordingly, here we appraise by sampling every 2.5 min overnight the joint synchrony of moment-to-moment LH release with simultaneously monitored pituitary FSH secretion, prolactin release, and nocturnal penile tumescence (NPT) oscillations, as a neurophysiological correlate of sleep regulation) in 10 young (ages 21-34) and 8 older (ages 62-72) healthy men. Joint synchrony for paired LH-FSH, LH-prolactin, and LH-NPT observations in young vs. older individuals was quantified by the cross-approximate entropy (cross-ApEn) statistic, with larger cross-ApEn values indicating greater two-variable asynchrony. Concomitantly, we assessed (possible) univariate changes with age for each of LH, FSH, prolactin, and NPT, as quantified by approximate entropy (ApEn). Hormone assays were performed by random-access direct chemiluminescence analyzer. Overnight mean (+/- SEM) serum LH concentrations (IU/L) were equivalent in older (3.1 +/- 0.31 IU/L) and younger (2.9 +/- 0.29) men, as were their serum total testosterone concentrations; viz., 425 +/- 48 (older) and 523 +/- 40 (younger) ng/dL. However, all three sets of paired time-series were significantly more asynchronous in the older cohort. First, cross-ApEn of paired LH-FSH release was significantly higher (or more asynchronous) in older subjects; viz., 1.902 +/- 0.022 in older men vs. 1.607 +/- 0.058 in younger individuals (P = 0.0005). Second, cross-ApEn of paired LH and prolactin release was 1.744 +/- 0.085 in older volunteers vs. 1.346 +/- 0.084 in younger subjects (P = 0.0046). Third, and most notably, cross-ApEn for the joint LH-NPT observation time-series was significantly greater in older subjects at 1.771 +/- 0.056 vs. 1.223 +/- 0.086 (young) (P = 0.0001), thereby denoting loss of coordination between (neural) signals directing intermittent LH secretion and those governing sleep-associated penile tumescence in older men. Among one-variable results, only ApEn of LH release was significantly higher in older individuals at 1.323 +/- 0.058 vs. 0.897 +/- 0.089 in younger subjects (P = 0.0019), signifying greater disorderliness of the LH secretory process in aged men. Individual ApEn values of FSH and prolactin release and NPT were age-invariant. In ensemble, the present clinical experiments indicate that, within the aging male reproductive axis, bihormonal network disruption is more pronounced than individual signal disruption. We suggest that abrogation of joint synchrony among hypothalamically directed pituitary hormones and a neurogenically organized sexual response (nocturnal penile tumescence) can be unified thematically under an hypothesis of disrupted central nervous system hypothalamo-pituitary network coordination in human aging. Such implicit disarray of multinodal communication is of consequence both scientifically and clinically, especially in proposing aging theories and intervention strategies.

Partial uncoupling of luteinizing hormone and prolactin pulse coincidence in hyperandrogenemic women

A partly synchronized pulsatile secretion of luteinizing hormone (LH) and prolactin has previously been suggested as an indication of the coupling of the respective pulse generators under certain conditions. In women with hyperandrogenemic chronic anovulation, episodic LH secretion is disturbed. It was, therefore, the aim of the present study to evaluate possible changes in episodic prolactin secretion pattern and in LH/prolactin co-pulsatility, and to relate the results to the accelerated LH pulse frequencies often seen in patients with hyperandrogenemic chronic anovulation. Blood samples of 32 patients with hyperandrogenemia were taken at 10-min intervals between 10.00 and 20.00. Nine regularly cycling women with normal hormone levels served as controls. In the women with hyperandrogenemia, despite an average 41% rise of LH pulse frequency, prolactin pulse frequency decreased slightly by 14% as compared to controls; no correlation between the two parameters was found (r = 0.162). The number of coincident LH and prolactin pulses increased continuously with accelerating LH frequency. The best fitting function was a hyperbola which was limited by the maximal observed prolactin frequency. As a consequence, the fraction of LH pulses that were co-secreted with prolactin episodes decreased with higher LH pulse frequencies, while the fraction of prolactin pulses concomitant with LH pulses increased. Our data provide evidence that in women with hyperandrogenemic chronic anovulation a pathological LH pulse frequency is no longer coupled with pulsatile prolactin secretion, suggesting an isolated alteration of the central neuronal control mechanism for LH secretion.

The duration of prolactin secretory bursts from the pituitary is independent from both prolactin and gonadal steroid plasma levels in women and in men

The intrinsic secretory characteristics of prolactin (PRL) have been investigated using newly developed algorhythms for instantaneous secretory rate (ISR) computation. PRL secretory rate, its intrinsic pulsatile characteristics and their possible dependance from gonadal steroids were investigated in five groups of subjects: a) 11 women during the follicular and luteal phase of the same menstrual cycle; b) 5 healthy postmenopausal women; c) 6 women affected by functional hyperprolactinemia; d) 5 normal men; e) 4 agonadal subjects before and during testosterone replacement therapy. All subjects underwent a 6 hours pulsatility study, from 08:00 to 14:00, sampling every 10 minutes. PRL plasma concentrations were determined using a RIA system and the presence of PRL secretory pulses was evaluated with program DETECT, both on plasma time series and after ISR computation. A distinct PRL episodic release was observed in all groups (follicular phase: 5.5 +/- 0.5, luteal phase: 6.5 +/- 0.6, postmenopause: 5 +/- 1, hyperprolactinemic women: 4.2 +/- 0.8, men: 4.8 +/- 0.4, agonadal before testosterone: 6 +/- 1, agonadal during testosterone administration: 5.3 +/- 0.3 peaks/6h), but mainly the computation of ISR allowed to demonstrate that the duration of the lactotropes secretory events was constant in all groups studied. PRL secretory bursts duration ranged between 23.1 +/- 1.8 and 25.4 +/- 2.5 minutes independently both on PRL or on sex steroid plasma levels. In conclusion, the present report shows that in different physiological conditions the intrinsic secretory bursts from lactotropes are constant in duration independently from the functional state, sex and the steroid hormone levels.

Beta-endorphin levels in women with elevated prolactin and following bromocriptine therapy

1. Plasma levels of beta-endorphin were not significantly different in women with normal plasma prolactin or women with hyperprolactinemia. 2. A bromocriptine induced decrease in plasma prolactin was not accompanied by a decrease in beta-endorphin. 3. This study suggests that no direct link exists between plasma prolactin levels and endogenous beta-endorphin.

FSH secretory pattern and degree of concordance with LH in amenorrheic, fertile, and postmenopausal women

Pulsatile secretion of gonadotropin was investigated in amenorrheic patients and in fertile and postmenopausal women to assess both follicle-stimulating hormone (FSH) episodic secretion and its temporal coupling with luteinizing hormone (LH). Three groups of amenorrheic patients were studied: hyperandrogenic (n = 20), hypogonadotropic (n = 51), and normogonadotropic (n = 31). Nineteen fertile women (during the follicular and luteal phases of the cycle) and sixteen postmenopausal women were investigated as reference groups. All subjects demonstrated the presence of a distinct pulsatile pattern with LH and FSH pulses/4 h as follows: hyperandrogenic 3.95 +/- 0.26 and 3.85 +/- 0.2, hypogonadotropic 3.76 +/- 0.26 and 3.9 +/- 0.16, normogonadotropic 3.5 +/- 0.2 and 3.9 +/- 0.17 LH and FSH pulses/4 h, respectively (means +/- SE). Normal controls showed 4.1 +/- 0.2 and 3.1 +/- 0.2 pulses/4 h for LH (P < 0.05) and 3.2 +/- 0.1 and 3.6 +/- 0.3 pulses/4 h for FSH, during follicular and luteal phases, respectively. Postmenopausal women showed 3.6 +/- 0.2 and 3.0 +/- 0.3 pulses/4 h for LH and FSH, respectively. Specific concordance (SC) index demonstrated that LH and FSH were significantly and simultaneously secreted in all groups. Conversely, LH and FSH were not temporally related during the luteal phase. In conclusion, we report a distinct FSH episodic secretion and its temporal linkage with LH pulses irrespective of plasma concentrations of gonadal steroids in secondary amenorrhea.

Synchronous secretion of LH and prolactin during the normal menstrual cycle

Integrated hourly concentrations of day-time prolactin and LH showed significant positive correlations (p < 0.05-0.001) on the day of the pre-ovulatory mid cycle LH surge (n = 3) and during the mid luteal phase (n = 6) in a group of regularly cyclic women. No correlations between these two hormones were seen during any other stage of the cycle. Consistent significant correlations were not evident between prolactin and oestradiol, prolactin and progesterone, LH and oestradiol or LH and progesterone during any other stage of the cycle.

Nocturnal prolactin pulses in relation to luteinizing hormone and thyrotropin

The two hypothalamic releasing factors, luteinizing hormone releasing hormone (LHRH) and thyrotropin releasing hormone (TRH), have been shown to stimulate pituitary prolactin (PRL) release as well as their respective pituitary hormones, luteinizing hormone (LH) and thyrotropin (TSH). In this study the influence of LH and TSH regulatory mechanisms on nocturnal PRL secretion was investigated by evaluating whether the coincidence of PRL with LH and TSH pulses occurred more frequently than would be expected if the hormone generators were not coupled. Thirty night studies were conducted in twelve healthy male subjects. Six subjects underwent 3 studies and 6 subjects 2 studies. Blood was collected into aliquots at 10 min intervals throughout the night and plasma concentrations of PRL, TSH, and LH were determined. From the plasma profiles, hormone secretory rates were calculated using a method of deconvolution. Significant plasma and secretory hormone pulses were identified by a peak detection computer program. For statistical analysis the night studies of each subject were concatenated. Concomitance between the plasma pulses of both TSH and LH with PRL was insufficient to reject the null hypothesis of random coincidence. An increase in the number of subjects demonstrating significant coincidence between the hormone pulses was obtained when secretory pulses were analysed. Seven of the 12 and 10 of the 12 subjects showed significant concomitance between PRL and respectively TSH and LH. This proportion was sufficient to confirm copulsatility between PRL and LH. These results suggest that LH regulatory mechanisms are involved in the generation of the nocturnal pulsatile PRL profile, TRH may also play a role in the secretion of PRL at a central level, but was not reflected in the plasma or secretory profiles because of other overriding regulatory factors.

Frequency of prolactin pulsatile release in normal men and in agonadal patients is neither coupled to LH release nor influenced by androgen modulation

OBJECTIVE

We wished to examine and characterize the prolactin pulsatile secretory pattern in both normal and agonadal males in order to assess whether there was any concordance with LH secretion.

DESIGN

Patients were sampled every 5 minutes for 12 hours.

PATIENTS

We studied five normal and four agonadal men, the latter group before and on testosterone enanthate (TE) (200 mg i.m. every 15 days) treatment.

MEASUREMENTS

Prolactin and luteinizing hormone plasma levels were determined using commercial RIA systems. Pulse detection was performed using the DETECT program and the degree of concordance between luteinizing hormone and prolactin was established computing the specific concordance index.

RESULTS

We demonstrated the presence of a frequent PRL secretory pattern in normal men (22.8 +/- 1.8 peaks/12h; mean +/- SEM) and in agonadal patients, both in basal conditions and during testosterone treatment (20.5 +/- 2.8 and 18 +/- 1.6 peaks/12h, respectively). The testosterone treatment in agonadal men significantly reduced luteinizing hormone pulse frequency (baseline: 27.5 +/- 2, testosterone administration: 18 +/- 1.3 peaks/12h, P < 0.01) but did not affect pulsatile prolactin release. Using a 10 and 15 minute sampling protocol, we observed that prolactin pulse frequency significantly decreased (P < 0.01) and was similar to the frequencies estimated in previous reports. When luteinizing hormone and prolactin time series were studied to evaluate the possible presence of a specific concordance (SC) between the secretory events of the two hormones, no significant degree of concomitancy was observed neither using the specific concordance index or the cross-correlation analysis.

CONCLUSIONS

This report demonstrates (a) the presence of frequent pulsatile release of prolactin in both controls and agonadal patients (baseline and on testosterone enanthate), (b) the use of an appropriate sampling interval (5 minutes) to unmask the prolactin pulsatile release, (c) that in men, luteinizing hormone secretory events are not temporally linked to prolactin secretion, and (d) that androgens, even if reducing luteinizing hormone pulse frequency in agonadal patients, do not significantly affect prolactin pulsatile secretion, suggesting that testosterone and its metabolites do not affect lactotroph activity.

Pulsatile secretion of gonadotropins and prolactin during the follicular and luteal phases of the menstrual cycle: analysis of instantaneous secretion rate and secretory concomitance

OBJECTIVE

To characterize the pulsatile secretions of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin (PRL) during the menstrual cycle and to statistically evaluate their secretory concomitance.

DESIGN

Pulsatility study performed during the midfollicular and midluteal phases of a same menstrual cycle, blood samples being collected every 10 minutes for 6 hours.

SETTING

Participants investigated in the Division of Endocrinology, University Hospital.

PARTICIPANTS

Nine healthy women (22 to 38 years) with regular menstrual cycles.

MAIN OUTCOME MEASURES

Plasma LH, FSH, and PRL values were analyzed as raw and deconvoluted data, and the specific (nonrandom) secretory concomitance was evaluated statistically.

RESULTS

The pulsatile secretion of LH was confirmed, and that of FSH and PRL was clearly established during both phases of the cycle by characterization of peak frequency, period, and amplitude. A specific secretory concomitance was assessed between LH and FSH in the follicular but not the luteal phase, and a tight concomitance between LH and PRL was demonstrated during both phases.

CONCLUSIONS

These results are supportive of significant pulsatile secretions of the three hormones during the menstrual cycle, and they are demonstrative of a definite copulsatility of these hormones, suggestive of common regulatory factors in the complex temporal patterns of gonadotropin and PRL secretions along the cycle.

GnRH antagonists suppress prolactin release in non-human primates

GnRH antagonists, such as Antide, are being evaluated for potential contraceptive applications. Although their contraceptive efficacy clearly results from their rapid inhibitory effects on gonadotropin release, there remains the possibility of other incidental effects. Under certain physiological conditions, the release of prolactin (Prl) appears to be temporally related to the secretion of luteinizing hormone (LH) and hence by inference to the secretion of GnRH. Here, we examined the effects of the GnRH antagonist Antide on the release of LH and Prl. Under agonadal conditions, a remarkable concordance was seen between LH and Prl pulses with up to 100% of pulses being coincident. Administration of Antide resulted in a rapid parallel decline in both LH and Prl with LH levels falling by 50% within 2 h and Prl levels falling by 30-40%. At this dose of Antide (1.0 mg/kg, sc), pulsatile release of LH and Prl continued albeit at a much reduced amplitude. The administration of a bolus of exogenous GnRH in the face of GnRHant-induced suppression resulted in prompt release of LH and Prl in all 3 monkeys. Since Antide inhibits the release of LH and Prl in a parallel fashion, and GnRH re-stimulates the release of both hormones in a parallel fashion, we conclude that the synchronous pulsatile release of LH and Prl observed in the agonadal monkey is due to a direct action of GnRH. What this action is for Prl release, and how it relates to the control of dopamine or other neuroendocrine mechanisms normally controlling the release of Prl remains unclear. It also remains to be seen whether this GnRH antagonist-induced suppression of Prl will have physiologic significance.

Elevated peritoneal fluid luteinizing hormone and prolactin concentrations in infertile women with endometriosis

In this study, we compared (Mann-Whitney U-test) the peritoneal fluid FSH, LH and PRL levels, measured by RIA, at the follicular and luteal phases of the menstrual cycle in women with (n = 43; age 25-44 years) and with no evidence of endometriosis (n = 35; age 25-39 years) who were considered as controls. Both follicular and luteal phase FSH concentrations of women with endometriosis were not statistically different (n = 22 vs 18; 0.32-5.8 vs 0.50-8.2 IU/l, P = 0.247; n = 13 vs 14; 0.6-6.5 vs 0.66-6.7 IU/l, P = 0.604) compared to their respective controls. In contrast to FSH, the concentrations of LH at follicular (n = 19 vs 17; 3.1-34.2 vs 2.3-12.2 IU/l, P = 0.01) and luteal (n = 17 vs 15; 2.1-95.4 vs 1.3-17.9 IU/l, P = 0.02) phases of the test group was significantly elevated at both phases of the cycle. With respect to differences in PRL concentrations at follicular phase no significant change (n = 21 vs 16; 1030-5800 vs 1305-4650 mIU/l; P = 0.255) was observed. The greatest difference in luteal PRL concentrations (P = 0.007) was obtained between the women with endometriosis and controls (n = 17 vs 17; 1895-8600 vs 1041-5000 mIU/l). The results suggest that disordered synchronization of neuroendocrine mechanisms controlling LH and PRL may be the underlying abnormality causing infertility in our group of patients with endometriosis.

Suppressive actions of a gonadotropin-releasing hormone antagonist on luteinizing hormone, follicle-stimulating hormone, and prolactin release in estrogen-deficient postmenopausal women

We investigated time- and dose-dependent actions of a gonadotropin-releasing hormone antagonist, the "Nal-Glu" peptide [Ac-D2Nal1, 4CIDPhe2, D3Pal3, Arg5, DGlu6(AA), DAla10], in nine healthy estrogen-withdrawn postmenopausal women. Gonadotropin-releasing hormone antagonist was administered subcutaneously at doses of 10, 30, 100, and 300 micrograms/kg. Suppression of immunoactive luteinizing hormone concentrations was achieved with a 30 micrograms/kg dose of antagonist. Suppression of immunoactive follicle-stimulating hormone levels was less (40%) even at the highest antagonist dose (300 micrograms/kg). Bioactive luteinizing hormone concentrations also significantly decreased (greater than 60%) at the two antagonist doses tested (30 and 300 micrograms/kg). However, the lower antagonist dose showed an "escape" of bioactive luteinizing hormone values after 18 hours. No suppressive effects of the antagonist on prolactin secretion occurred at any dose tested. We conclude that this gonadotropin-releasing hormone antagonist can achieve effective, potent, and long-lasting suppression of pituitary secretion of biologically active luteinizing hormone at higher doses, but secretion of biologically active luteinizing hormone may "escape" at lower doses.

In vivo studies on paracrine actions of pituitary angiotensin II in stimulating prolactin release in rats

The present experiments were performed to test the hypothesis that, in vivo, intrapituitary angiotensin II (ANG II) mediates the effect of luteinizing hormone-releasing hormone (LHRH) on prolactin release. After intravenous administration of LHRH (100 ng/100 microliters saline), plasma levels of both luteinizing hormone (LH) and prolactin were increased in ovariectomized rats pretreated with estradiol and progesterone. Intravenous administration of saralasin or sarthran (ANG II receptor blockers) reduced or abolished, respectively, the LHRH-induced increase in prolactin without affecting the rise in LH. In other ovariectomized steroid-treated rats, saralasin did not affect the increase in LH or prolactin induced by 10 min of restraint stress. Finally, in intact female rats on the day of proestrus, neither saralasin nor sarthran affected the mid-cycle prolactin surge. Taken together, these results show that in vivo exogenous LHRH stimulates prolactin release via a paracrine action of pituitary ANG II. However, under other conditions in which both LH and prolactin (and presumably endogenous LHRH) are elevated, pituitary ANG II does not appear to be involved in the prolactin rise.

Prolactin and luteinizing hormone profiles of cured acromegalic subjects

The 24-h PRL and LH hormone profiles were analysed of 16 cured male acromegalic patients who had undergone selective transsphenoidal surgery 4-9 years previously. Eight of these patients also underwent pituitary irradiation. Blood samples were taken at 20-min intervals; the PRL and LH data were analysed with the cluster program. ARIMA modelling, cross-correlation techniques, Fourier analysis, and cosinor analysis. About 10-11 PRL and LH peaks were demonstrated for both non-irradiated and irradiated patients. The absolute heights of PRL pulses and the mean valley levels were significantly greater for irradiated patients than for non-irradiated patients, but the increment in amplitude did not differ. A significant diurnal rhythm for PRL was found for all non-irradiated patients but for only one irradiated patient. LH pulse area and amplitude were lower in the group of irradiated patients. The incremental responses of LH and PRL to GnRH and TRH, respectively, were lower in irradiated patients than in non-irradiated patients. During the night (0200-0800 h) the number of PRL pulses decreased in non-irradiated patients but not in irradiated patients. Pulse nadirs and amplitudes increased during the evening and night in non-irradiated patients but were constant in irradiated subjects. Bivariate modelling of the data for 14 patients revealed significant cross-correlations between LH and PRL pulses in nine subjects. This study demonstrates that the pulsatile secretion of PRL and LH in treated acromegalics is basically normal. Additional radiation therapy, however, may lead to damage of the hypothalamus, as reflected by the absence of a circadian PRL rhythm. A direct influence on the pituitary by radiation is indicated by the decreased magnitude of LH pulses and the diminished response of LH and PRL after injection of GnRH and TRH, respectively.

Prolactin secretion in idiopathic hypogonadotropic hypogonadism during pulsatile luteinizing hormone-releasing hormone long-term administration

Recent data seem to suggest that LHRH may be involved in the modulation of PRL secretion. We studied the PRL pattern in 9 males (age range 18-38 yr) with idiopathic hypogonadotropic hypogonadism (IHH) before and during long-term pulsatile LHRH therapy (120-160 ng/kg bw every 120 min sc) in order to evaluate variations in the spontaneous PRL secretion or LHRH-induced presence of PRL pulse. LH, FSH and PRL secretion was evaluated every 15 min for 3 h on day 0, day 30 and days 90-150. Before and during LHRH therapy PRL 24-h integrated concentration (IC) and gonadotropin or PRL response to LHRH test (50 micrograms iv/bolus) were evaluated. On day 0 spontaneous PRL pulses were found in 2 IHH patients. On day 30 PRL pulses were found in 4 cases. On days 30-90 PRL pulses were sporadically concomitant with LHRH-induced LH pulses. Mean PRL levels and 24-h IC of PRL were found to be significantly (p less than 0.05) increased during pulsatile LHRH administration. A significant positive (p less than 0.01) correlation was observed between testosterone and PRL levels during LHRH therapy. When compared to a significant LH response to LHRH iv bolus, no modification of PRL secretion was found. The present study did not show any relationship between LHRH administration and PRL secretion. It might be hypothesized that LHRH does not play a determinant role in PRL secretion and does not seem to modulate PRL secretory pattern in IHH males.

Random and Non-Random Coincidence Between Luteinizing Hormone Peaks and Follicle-Stimulating Hormone, Alpha Subunit, Prolactin and Gonadotropin-Releasing Hormone ulsations

Abstract We have examined the co-pulsatility of luteinizing hormone (LH) and prolactin, LH and follicle-stimulating hormone (FSH), and LH and alpha subunit in normal men. We tested whether the degree of physiologically observed co-pulsatility (peak coincidence) significantly exceeded expected random concordance between independently pulsating hormone series. To this end, computer simulations were used to create synthetic endocrine time series pulsating randomly and independently at known frequencies. Resultant predictions of the mean, variance and probability distribution of the number of randomly coincident peaks permitted us to test the null hypothesis that physiologically observed hormone co-pulsatility was due to chance peak associations alone. Physiological observations were made in 33 normal men and in six ovariectomized ewes subjected to combined hypothalamo-pituitary and jugular venous catheterization. The following salient results were obtained: 1) random peak coincidence rates between independently pulsating hormone series were substantial at high pulse frequencies, but such random rates were significantly exceeded in the case of gonadotropin-releasing hormone and LH peaks (P< 0.0001); 2) random coincidence was further increased when coincidence was defined as peak maxima occurring not only simultaneously but also within some defined time window (e.g. +/-10 min, as commonly done in the literature); 3) significant co-pulsatility could be demonstrated for simultaneous LH and FSH pulsations in normal men (P< 0.0001); 4) coincidence rates for 10-min lagged (but not for simultaneous) LH and prolactin pulses were significantly more likely than chance associations; 5) observed coincidence between LH and a subunit pulses significantly exceeded expected (random) peak overlap (P<0.001); and 6) in contrast, hormone peaks in different men were only randomly associated. We conclude that based upon the means, variances and probability distributions calculated here, available reports on peak coincidence between pulsatile neuroendocrine time series must be re-examined in the light of high rates of random coincidence observed between independently pulsating hormone series.

Effects of the antidopaminergic drug veralipride on LH and PRL secretion in postmenopausal women

Patterns of LH and PRL secretion have been evaluated in 15 postmenopausal women before and after the chronic blockage of the D2 dopamine receptors with veralipride (100 mg twice daily, for 30 days). In addition, the possible influence of the antidopaminergic drug on the activity of the endogenous opioid system has been evaluated by the infusion of the opioid antagonist naloxone, performed before and during veralipride administration. Mean plasma LH levels were significantly blunted (p less than 0.05) and mean plasma PRL levels were significantly increased (p less than 0.001) by veralipride administration. The frequency of both LH and PRL secretory pulses was not modified, while the mean pulse amplitude of both hormones was significantly increased (p less than 0.05 for LH; p less than 0.001 for PRL) by veralipride administration. In untreated postmenopausal women naloxone infusion did not modify LH secretion. Following veralipride, the infusion of naloxone significantly increased (p less than 0.05) the mean plasma LH levels, had no influence on the frequency and significantly reduced (p less than 0.01) the amplitude of LH pulses, expressed as the percent increase from the nadir to the peak. Both before and after veralipride administration, naloxone failed to modify the pattern of PRL secretion. In untreated postmenopausal women, the percentage of concomitant PRL and LH pulses was significantly higher (p less than 0.001) during naloxone than during saline infusion, and this effect was amplified by veralipride administration (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Prolactin and its response to the luteinizing hormone-releasing hormone thyrotropin-releasing hormone test in patients with endometriosis before, during, and after treatment with danazol

Basal levels of prolactin (PRL) were studied in 16 normal women and in 60 women with endometriosis, 37 of whom were infertile. In addition, the authors studied the response to an intravenous (IV) injection of luteinizing hormone-releasing hormone (LH-RH) (100 micrograms) plus thyrotropin-releasing hormone (TRH) (300 micrograms) in the 16 normal women and in 18 endometriosis patients, examining the basal PRL and thyrotropin, and at 15, 30, 45, 60, and 120 minutes after the IV bolus. After laparoscopy and/or conservative surgery, the patients were treated with danazol for 6 months and a second laparoscopy was performed. The LH-RH/TRH test was carried out in the third month of danazol treatment in 6 endometriosis patients and before the second laparoscopy in 11 patients. The results show that there was both an increase in the mean basal levels of PRL and in the percentage of cases of moderate hyperprolactinemia in endometriosis patients. There also was a greater rise in PRL with the LH-RH/TRH test in moderate and severe endometriosis. The PRL response was significantly greater in endometriosis than in normal women, and was not related to TSH response. Danazol treatment reduced significantly the PRL response. The PRL response before treatment was significantly higher in patients who after treatment showed persistent endometriosis at the second laparoscopy. This could suggest a lower effectiveness of danazol in patients with endometriosis and a PRL hyper-response to LH-RH/TRH.

Prolactin-inhibiting activity of GnRH associated peptide in cultured human pituitary cells

The 56-amino-acid extension of GnRH in the human GnRH precursor (pHGnRH 14-69 or GAP) has previously been shown to inhibit PRL secretion from cultured rat pituitary cells. We have studied the effect of GAP and shorter sequences on prolactin secretion from human and rat pituitary cells. Bacterially synthesized GAP inhibited PRL secretion from human pituitary cells. At 10(-6) M GAP inhibition of prolactin release was 67.7% which was similar to that observed in rat pituitary cells (65.5%). A series of shorter peptide sequences (pHGnRH 14-26, pHGnRH 14-36, pHGnRH 14-37.NH2, pHGnRH 28-36, pHGnRH 38-49 and pHGnRH 51-66) which are potentially processed from GAP at basic amino acid residues had no effect on prolactin secretion from human or rat pituitary cells at doses up to 10(-5) M.

Gonadotropin-releasing hormone pacemaker sensitivity to negative feedback inhibition by estradiol in women with hypothalamic amenorrhea

To better understand the pathophysiology of hypothalamic amenorrhea (HA), the frequency of luteinizing hormone (LH) pulsatility and the LH response to gonadotropin-releasing hormone (GnRH) was assessed before and after clomiphene citrate (CC) in 18 women with HA and 10 normal women in the early follicular phase (EFP). The HA women showed a greater acceleration of LH pulsatility after CC than EFP women but there was a decrease in their LH response to GnRH. Naloxone caused an increase in LH pulsatility in HA but not EFP women, although this effect was less than that seen with CC. We conclude that, in HA women, the GnRH pacemaker, but not the pituitary, is inhibited by increased sensitivity to the negative feedback effect of estradiol and increased opiate tone.

Pulsatile secretion of prolactin and luteinizing hormone and their synchronous relationship during the human menstrual cycle

Recent investigations have demonstrated the pulsatile nature of prolactin (PRL) secretion and the synchronous relationship between PRL and LH pulses in normal and hypogonadal women. The present study was designed to confirm this synchrony and to investigate the characteristics of PRL pulses at different stages of the menstrual cycle. Blood samples were obtained at 10-minute intervals, beginning at 10.00 hours, for a duration of 4-7 hours, from women during the follicular (n = 11), preovulatory (n = 2) and luteal (n = 10) phases. Detectable pulses in plasma PRL concentrations were present in almost all subjects during each phase of the cycle. During the total 121-hour blood sampling throughout the 3 phases, 62 PRL pulses and 74 LH pulses were detected and about 80% of the PRL pulses were observed to coincide with LH pulses. The mean (+/- SD) pulse frequency of PRL was significantly lower during the luteal phase (0.28 +/- 0.17 pulses/hour) than during the follicular (0.64 +/- 0.25 pulses/hour) and preovulatory (0.72 +/- 0.16 pulses/hour) phases, while the mean pulse amplitude of PRL was significantly greater during the luteal phase (6.8 +/- 2.3 ng/ml) than during the follicular (3.6 +/- 1.2 ng/ml) and preovulatory (4.1 +/- 1.0 ng/ml) phases. These changes in pulse frequency and amplitude were also observed in LH pulses between the follicular and luteal phases, except at the LH surge, when LH pulse amplitude increased markedly, but that of PRL did not alter. Furthermore, a positive linear correlation between the pulse frequency of PRL and LH (r = 0.74, p less than 0.001) was found throughout the 3 phases of the cycle. These results demonstrate that a marked degree of synchrony between PRL and LH pulses is observed during the menstrual cycle and suggest that the frequency and amplitude of PRL pulses vary from the follicular to luteal phases, except at the LH surge, almost in parallel with those of LH pulses.

Positive and negative feed-back effect of progesterone on luteinizing hormone secretion in post-menopausal women

Progesterone is known to exert a biphasic feedback effect on luteinizing hormone (LH) secretion in animals and it has been demonstrated that this effect is dependent upon both duration of exposure to progesterone and the dose administered. In this paper we sought to determine whether a similar biphasic effect exists in humans. The pattern of LH secretion was assessed in six healthy oestrogen treated post-menopausal women before and after they were given progesterone (50 mg/day) for 1 and 7 days. Progesterone treatment for 1 day resulted in a significant elevation in the basal serum LH concentration and in individual LH pulse amplitude with no change in LH pulse frequency. In contrast, progesterone treatment for 7 days increased LH pulse amplitude with no change in basal serum LH concentrations and a significant reduction in LH pulse frequency. We concluded that firstly, progesterone does exert a biphasic feedback effect on LH secretion and that the nature of this effect is determined by the duration of exposure to the progesterone stimulus. Secondly, as LH pulsatility has been shown to be an accurate indicator of GnRH pulsatility, that the reduction in LH pulse frequency after a long exposure to progesterone is due to a hypothalamic effect of progesterone whereas the positive feedback effect may be the result of a pituitary or hypothalamic action.

Episodic pulsatile secretion of FSH, LH, prolactin, oestradiol, oestrone, and LH circadian variations in polycystic ovary syndrome

Pulsatile secretion of LH, FSH, PRL, oestradiol and oestrone was studied in a group of 16 patients with micropolycystic ovary syndrome (PCOS) and compared with that of normal ovulatory women in the fifth to sixth day of the cycle. Hormone concentrations were measured at 10 min intervals for 8 h starting at 0930 h. In seven subjects, the study was prolonged for 24 h, with 20 min interval samples, in an attempt to evaluate the circadian rhythm of LH by cosinor analysis. Significant fluctuations occurred in the concentration of each hormone. Values shown are mean +/- SD. PCOS subjects had high LH mean values (27.9 +/- 5.9 IU/l) (P less than 0.005). LH pulse amplitude was higher than controls (11.6 +/- 3.7 IU/l versus 5.2 +/- 1.8 IU/l; P less than 0.005) while no consistent changes in frequency or interpulse interval (62.0 +/- 10.7 min versus 65.8 +/- 19.2 min; P = NS) were found. A mean of 4.8 +/- 1.2 pulses of FSH occurred in 8 h and the mean pulse amplitude was 2.68 +/- 1.11 with no differences from controls. All patients were normoprolactinaemic. A mean of 5.5 +/- 1.9 pulses occurred in 8 h, the interpulse interval was 76.1 +/- 14.4 min and the amplitude was 2.87 +/- 0.76 ng/ml and there were no significant differences from controls; 75% of PRL pulses showed a temporal relationship with LH pulses. Oestrone mean basal values were higher in PCOS (47.2 +/- 12.5 pg/ml) than controls (32.0 +/- 9.9 pg/ml; P less than 0.02), while no differences were observed as regards oestradiol. Oestradiol pulse amplitude was nearly the same as oestrone (43.6 +/- 18.8 pg/ml and 37.7 +/- 16.1 pg/ml, respectively); 6.0 +/- 2.2 pulses and 6.0 +/- 1.6 pulses occurred in 8 h with an interpulse interval of 81.1 +/- 27.1 min and 71.8 +/- 11.1 min, respectively. Sixty-five per cent of LH pulses were followed by an oestradiol and oestrone peak. The mean time of the appearance was 17 +/- 15 min and 25 +/- 23 min, respectively. In the PCOS group a consistent 24 h rhythm in mean plasma LH levels was found with the highest hormone values at 1720 h (P less than 0.05) unrelated to apparent sleep and different from that of adult women. Pulse frequency showed a significant slowing during the night with the longest interpulse interval at 0327 h (P less than 0.03) while no significant periodicity was observed in LH pulse amplitude.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of prolactin responses to gonadotropin releasing hormone by acute testosterone infusions in normal women

The administration of gonadotropin releasing hormone (GnRH) has been shown to stimulate prolactin (PRL), suggesting its role as an inducer of PRL release. This study addresses whether testosterone may modulate the release of PRL with GnRH during the early follicular phase when this stimulatory effect is not usually observed. Chromatographically pure testosterone was administered intravenously to 13 women in 2 doses (100 micrograms and 1000 micrograms) over a 6-hour period. GnRH (100 micrograms) was administered as a bolus 2 hours before and 4 hours after beginning testosterone. In addition, 3 women received testosterone twice, 3 months apart, with testolactone pretreatment on the second occasion. Serum testosterone rose in all patients and achieved maximum steady-state levels by 120 minutes. Serum estradiol (E2) was increased in subjects receiving the larger dose of testosterone but was unchanged with the lower dose and with the addition of testolactone. PRL did not increase significantly after GnRH before testosterone infusion but showed a significant increase after testosterone as well as after testosterone with testolactone. This effect did not appear to be dose-related.

Inhibition of prolactin secretion by antiserum to the alpha- and beta-subunits of gonadotropin

This study was undertaken to determine whether antiserum to the alpha- and beta-subunits of human gonadotropin could affect prolactin secretion from human pituitary cell monolayers. The addition of antiserum to the alpha-subunit of follicle-stimulating hormone, but not to the alpha-subunit of luteinizing hormone, at a 1:10,000 dilution inhibited basal prolactin secretion. The addition of these antisera failed to inhibit prolactin secretion in the face of 10(-5) mol/L gonadotropin-releasing hormone. Coincubation of antiserum to the beta-subunit of luteinizing hormone or the beta-subunit of follicle-stimulating hormone at a 1:10,000 dilution failed to inhibit basal prolactin secretion; however, coincubation of gonadotropin-releasing hormone with antiserum to the beta-subunit of either luteinizing hormone or follicle-stimulating hormone significantly inhibited the release of prolactin. These observations led us to conclude that basal and gonadotropin-releasing hormone-mediated prolactin secretion can be affected by gonadotropin subunits.

Role of endogenous opioids in reducing the frequency of pulsatile luteinizing hormone secretion induced by progesterone in normal women

It is well-established that the frequency of LH pulses varies during the normal menstrual cycle with a significant reduction in frequency in the luteal phase. Previous studies have indicated that both progesterone and opioids are able to reduce the frequency of LH pulses and in this study we sought to clarify the possible interaction between progesterone, endogenous opioids and GnRH neurons. Sixteen normal women in the mid-follicular phase (days 8-12) were randomly allocated to a control or treatment group and LH pulsatility assessed on one or two occasions by taking blood samples at 15 min intervals over 8 h. For the control women, LH pulsatility was assessed on one occasion during a saline infusion. The treated women received progesterone (50-100 mg/d for 7 d) at the end of which LH pulsatility was assessed before and after a naloxone infusion (2 mg/h for 8 h). Mean +/- SEM LH pulse frequency in the control women was 4.9 +/- 0.5 pulses/8 h which was significantly decreased to 3.0 +/- 0.3 pulses/8 h (P less than 0.01) in the progesterone treated women but not different from 5.5 +/- 0.3 pulses/8 h in those also treated with naloxone. Mean +/- SEM LH pulse amplitude in the control women was 2.3 +/- 0.3 IU/l, which was significantly increased to 4.8 +/- 0.7 IU/l (P less than 0.05) in the progesterone treated group, and to 3.7 +/- 0.4 IU/l (P less than 0.05) in the progesterone-treated women after naloxone. We conclude that progesterone slows the frequency of LH pulsatility by increasing endogenous opioid activity in the hypothalamus which may in turn inhibit the firing rate of the GnRH neurons.

Increased plasma and pituitary prolactin concentrations in adult male rats with selective elevation of FSH levels may be explained by reduced testosterone and increased estradiol production

The roles of testosterone and estradiol in regulating prolactin concentrations were studied in acutely castrated adult male rats receiving subcutaneous Silastic implants of the sex steroids. Testosterone was administered in increasing doses, from subphysiologic to intact levels, both alone and in combination with a small, single dose of estradiol. The study was designed to assess whether a change in the relative rates of sex steroid production could account for an increase in PRL release in the absence of other testicular factors. At very low levels of plasma testosterone, FSH and LH levels were indistinguishable from castrate controls. As plasma testosterone concentration increased, both plasma FSH and LH levels were suppressed progressively to intact levels. When a subphysiologic dose of testosterone was coadministered with a small dose of estradiol, the combined effects produced a midcastrate level of FSH but maintained a normal level of LH similar to the selective increase in FSH concentration observed in men with germinal aplasia. Although PRL levels were indistinguishable in intact and castrate controls, testosterone replacement by capsule increased prolactin in a dose-related manner so that, at the physiologic level of testosterone, prolactin was elevated two-fold (P less than 0.01), similar to the level achieved with estradiol replacement alone. Pituitary prolactin levels also increased with increasing doses of testosterone but values remained within the range measured in intact controls. When estradiol was coadministered with testosterone, the combination produced different effects depending on the testosterone dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies of prolactin secretion in polycystic ovary syndrome

In order to investigate the postulated relationship between hyperprolactinaemia and polycystic ovary syndrome (PCOS) we have studied 62 patients with PCOS. Only two patients had persistent prolactin (PRL) concentrations greater than the normal range on both random sampling and after blood sampling from intravenous cannula over 2 hours. Twenty-eight of the remaining patients had basal PRL secretion studied in more detail. Samples were collected at 15 min intervals during a 6 h period in all 28 patients and hourly samples were collected overnight from four patients. Results failed to demonstrate differences from control subjects in mean basal PRL concentrations, in spontaneous fluctuations or in increments related to stress, food or sleep. Lactotroph response to thyrotrophin releasing hormone, luteinising hormone releasing hormone and insulin stress testing in PCOS were determined. Results confirm a previous observation that normal PRL increments occur after ovulation and a blunted response follows a period of anovulation. This study has failed to find a consistent abnormality of lactotroph function in patients with PCOS other than that associated with anovulation.

Paracrine interactions in the anterior pituitary

The topographical affinity between certain cell types in rat anterior pituitary as well as the presence of biogenic amines, neuropeptides, growth and tissue factors in specific cell types suggest participation of paracrine control mechanisms in the regulation of anterior pituitary hormone secretion. Due to the recent advances in the separation of pituitary cell types and the development of three-dimensional cell cultures, direct experimental evidence for control by intercellular messengers has become available. The stimulation of PRL release from superfused pituitary cell aggregates by LHRH has been shown to be mediated by gonadotrophs. Gonadotrophs appear to secrete a factor with PRL-releasing activity. Gonadotrophs also modulate the stimulation of PRL release by angiotensin II. Interaction of somatotrophs with an unknown small-sized cell type strongly amplifies the GH response to adrenaline, GRF and VIP. The latter phenomenon requires the permissive action of glucocorticoids. Some of these in vitro observations can be correlated with recently reported in vivo actions of LHRH, PRL and angiotensin II and with pathophysiological changes in the pituitary.

The effect of physiological changes in ovarian steroids on the prolactin response to gonadotrophin releasing factor

This study was designed to assess the effect of an altered level of serum oestrogen and progesterone on the prolactin (PRL) response to gonadotrophin releasing hormone (GnRH). Six normal women were studied in the early follicular phase and the mid-luteal phase of one cycle and five menopausal women were studied before and after treatment with progesterone. Blood samples were collected at 15 min intervals for 6 h after a basal collection period of 30 min. Intravenous boluses of GnRH (1 microgram, 10 micrograms and 50 micrograms) were given at 0, 2 and 4 h. Basal samples were assayed for 17 beta-oestradiol (E2), oestrone (E1) and progesterone (P); LH, FSH and PRL were measured in all samples. Serum PRL was significantly elevated in all groups after 10 micrograms of GnRH with maximum increments (+/- SEM) ranging from 3.9 +/- 1.3 micrograms/l in early follicular phase women to 14.7 +/- 4.7 micrograms/l in progesterone-treated menopausal women. The PRL response to GnRH was significantly greater in the luteal phase and in menopausal women compared to early follicular phase women. There was a significant correlation between the maximum PRL response and the maximum LH response to GnRH in all the women studied (r = 0.7; P less than 0.01). A significant correlation was also found between the maximum PRL response and the basal serum oestrogen concentration in the normal cycling women (r = 0.8; P less than 0.01), but not when the menopausal women were included in the analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Definition of bioactive prolactin pulsations during the menstrual cycle

Patterns of circulating prolactin bioactivity during three stages of the menstrual cycle were studied in detail in four normally cycling women. Serial blood samples were withdrawn at 10 or 15 min intervals for up to 8 h. Plasma prolaction concentrations were quantitated by a bioassay which is based on the replication of a rat lymphoma cell line (Nb2 node) and by conventional radioimmunoassay. A total of 50-103 samples from each patient was analysed. Using a threshold-based algorithm, definite pulsations of prolactin biological (B) and immunological (I) activity were detected at most stages of the menstrual cycle. The periodicity of these peaks ranges from 1 to 1 1/2 h. However, pulsations were less evident in one subject who had asymptomatic hyperprolactinaemia although circulating prolactin was fully bioactive (mean B:I ratios being 1.02-1.25). B:I ratios in the three normoprolactinaemic women were generally lower, ranging from 0.39 +/- 0.02 to 0.93 +/- 0.03. Elevations in the B:I ratio of normoprolactinaemic women were associated with bioactive peaks; this was not always the case in the hyperprolactinaemic subject. Thus, the lack of symptoms in this hyperprolactinaemic subject could not be due to bioinactive prolactin, but might perhaps be due to the absence of episodic prolactin secretion which would desensitise target organs.

Prolonged suppression of plasma LH levels in male rats after a single injection of an LH-RH agonist in poly(DL-lactide-co-glycolide) microcapsules

The authors have examined the effects of a subcutaneous injection of the LH-RH agonist D-Trp6-LH-RH formulated in biodegradable poly(DL-lactide-co-glycolide) microcapsules on plasma levels of D-Trp6LH-RH, LH, and PRL in adult, gonadectomized male rats. Immunoreactive D-Trp6-LH-RH was detectable in the plasma of these animals at 1, 2, 3, and 4 weeks after injection. LH concentrations were greatly reduced 1 week after administering the D-Trp6-LH-RH microcapsule, continued to decrease during the following week, and remained suppressed until the end of the study, 6 weeks after the injection. Plasma PRL levels appeared elevated 1 to 2 weeks after the injection and suppressed thereafter, but these effects were significant only in animals rendered hyperprolactinemic by transplantation of an isologous pituitary under the renal capsule. These results demonstrate that an LH-RH agonist formulated in biodegradable microcapsules and administered as a subcutaneous injection can exert marked biologic effects in rats for at least 6 weeks. These findings also suggest that prolonged exposure to an LH-RH agonist may first produce stimulation, followed by an inhibition of PRL release from both in situ and ectopic pituitaries.