Unusual prolactin response to luteinizing hormone-releasing hormone in some anovulatory women

Gonadotropin-releasing hormone receptor gene expression in rat anterior pituitary

Gonadotropin-releasing hormone (GnRH) effects on the lactotroph function have been widely studied, but they probably result from paracrine interactions. No visual data about GnRH receptor in the pituitary are available. In order to identify the GnRH target cells in the pituitary of adult rats, the cellular distribution of rat GnRH receptor mRNA was investigated by electron microscopy, usingin situ hybridization on ultrathin pituitary frozen sections.In situ hybridization was performed using a digoxigenin-labeled oligonucleotide probe revealed by an indirect immunogold reaction. Gonadotropin-releasing hormone receptor mRNA was found in the cytoplasmic matrix, apposed to the endoplasmic reticulum and the nucleus of the gonadotrophs, which were identified by their ultrastructural characteristics, and by the presence of luteinizing hormone (LH) immunoreactivity. It was also found in the lactotrophs, which were revealed by the immunocytological detection of prolactin. No GnRH receptor mRNA was detected in corticotrophs, somatotrophs, thyrotrophs or hepatocytes. This result, without excluding paracrine effects, clearly showed that in addition to the gonadotrophs, the lactototrophs are likely to be direct target cells for the hypothalamic GnRH.

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.

Gonadotropin-releasing hormone antagonists attenuate estrogen/progesterone-induced hyperprolactinemia in monkeys

Previous studies have documented that exogenous gonadotropin-releasing hormone (GnRH) stimulates prolactin (PRL) secretion and augments thyrotropin-releasing hormone-induced PRL release. Further, the concomitant pulsatile release of PRL and luteinizing hormone (LH) suggests that GnRH may be an important regulator of PRL release in certain physiologic states. The authors explored this possibility by evaluating the effect of a GnRH antagonist ([Ac-pClPhe1, pClPhe2, DTrp3, DAla10]-GnRH; GnRH-antagonist) on PRL secretion in monkeys with induced hyperprolactinemia. Monkeys were given estradiol (E2) benzoate 25 mg/kg intramuscularly (IM) on cycle days 1 to 28, and a 3-cm progesterone (P) silastic capsule was placed on cycle day 15 and removed on day 28. On cycle days 15 to 28, monkeys were given IM injections of 1 mg/kg GnRH-antagonist (n = 3), 2 mg/kg GnRH-antagonist (n = 3), or vehicle (n = 3). Daily blood samples were assayed for E2, P, and PRL. The degree of PRL elevation was calculated as percent increase in area under the curve for days 15 to 28 when compared with days 1 through 14 (baseline). Luteinizing hormone levels were calculated similarly. Results indicate a dose-dependent effect of GnRH-antagonist on PRL secretion, with the larger dose producing a significantly lower hyperprolactinemic response, as well as a decline in LH. Thus, GnRH-antagonist attenuates induced hyperprolactinemia in a dose similar to that which suppresses LH release. These findings suggest that GnRH is a physiologic regulator of pituitary PRL secretion. In addition, GnRH analogs may be of benefit in controlled ovarian hyperstimulation by attenuating gonadotropin-induced hyperprolactinemia, thereby reducing potential adverse effects on fertility.

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.

Periovulatory plasma prolactin response to synthetic growth hormone-releasing hormone in normal women

Following the demonstration of a positive prolactin (PRL) response to growth hormone-releasing hormone (GHRH) in acromegalic and anorexic women, we have injected GHRH (50 micrograms intravenously as a bolus) in normal women during various phases of their menstrual cycle in order to establish whether a positive response was present also in normal subjects. Synthetic GHRH 1-44 elicited a significant increase in circulating PRL levels in eight women studied during the periovulatory phase of the menstrual cycle. In contrast, no significant changes in circulating PRL levels after GHRH administration were found in nine women during the midfollicular phase or in five women during the midluteal phase. A temporal correlation between the midcycle gonadotropin peak and the positive response to GHRH has been observed. Synthetic GHRH elicited the expected increase in GH levels during all phases of the cycle studied. Our data demonstrate that GHRH is capable of stimulating a PRL response in normal subjects and raise the possibility that PRL secretion is regulated by several hormones of hypothalamic origin.

Plasma prolactin response to gonadotropin-releasing hormone during benzodiazepine treatment

Previously we observed that prolactin (PRL) is secreted in response to gonadotropin-releasing hormone (GnRH) in normal women during the periovulatory phase of the menstrual cycle. Because sedative drugs affect the neurotransmitters involved in the regulation of PRL secretion, we investigated PRL responsiveness to GnRH in pre- and postmenopausal female subjects during prolonged treatment with benzodiazepines (six-60 months). In both pre-and postmenopausal patients who were not on benzodiazepine treatment, GnRH infusion (0.2 micrograms/min for 3 hr) was ineffective in eliciting a PRL response. In six premenopausal women treated with benzodiazepines, basal PRL concentrations were not influenced by the drug in four subjects (range 4.0-15.7 ng/ml) and were slightly elevated in two subjects (23 and 30 ng/ml). In six treated postmenopausal women, basal PRL concentrations were in the normal range (7.5-11.0 ng/ml). GnRH infusion induced a progressive increase in PRL concentrations which reached a peak at 120 min in the premenopausal subjects (mean % SEM increase: 64 +/- 30.5%) and at 60-90 min in the postmenopausal subjects (mean % increase: 110.6 +/- 34.7%). A saline infusion, performed on a separate day during benzodiazepine treatment as a control, did not influence PRL.

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.

Abnormal serum prolactin responses to luteinizing hormone-releasing hormone (LHRH) in patients with anorexia nervosa and bulimia

Abnormal responses of serum prolactin (PRL) to luteinizing hormone-releasing hormone (LHRH) stimulation have been observed in anovulatory women and in hypogonadal patients. Various endocrinological abnormalities have been demonstrated in patients with anorexia nervosa (AN). The present study was undertaken to further investigate responses of serum PRL, growth hormone (GH), luteinizing hormone (LH) and follicle stimulating hormone (FSH) to LHRH stimulation in 65 patients with AN and in 12 patients with bulimia before therapy and in the AN patients after several months of treatment, and in comparison to 12 normal women of the same age. Serum PRL responses to LHRH were positive (peak PRL levels greater than 25 ng/ml and delta increase in PRL greater than 10 ng/ml) in 16.9% of AN and 16.6% of bulimic patients; they were negative (absent) in all controls. Following restoration of the AN patients to normal body weight, the PRL responses to LHRH became normalized in those patients whose eating disorder behavior also returned to normal. However, in those patients whose eating disorder patterns continued to be abnormal, abnormal PRL responses persisted. The bulimic patients were of normal body weight, and yet had abnormal PRL responses. Thus, the responses of PRL correlated more closely with the behavior of the underlying eating disorder rather than with body weight gain or normal body weight.

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)

Gonadotropin releasing hormone elicits abnormal hormone responses in schizophrenia

We studied the non-specific responses of GH and PRL to gonadotropin releasing hormone (GnRH) in eleven male patients aged 18-30 in whom a diagnosis of acute schizophrenia was made according to Crow's criteria. GnRH administration was followed by a significant increase in plasma GH in five patients; plasma PRL increased in two patients. The two prolactin responders were also GH responders. Non-specific GH response was confirmed on repeated testing in two patients in whom GnRH stimulation was performed twice. During saline control, non-specific hormone responses were not observed. The abnormal hormone responses observed in acute schizophrenia are probably due to the disordered monoamine regulation characteristic of this condition.

Estrogen dependence of the periovulatory plasma prolactin response to gonadotropin-releasing hormone in normal women

It has been previously reported that GnRH is capable of inducing a PRL response in intact and castrated men treated with estradiol benzoate for 8-9 days. To further support the hypothesis of an estrogen-dependence of the PRL response to GnRH, GnRH was administered, either as a bolus or as a continuous infusion, to 45 normal women during various phases of their menstrual cycles. Synthetic GnRH (100 micrograms intravenous bolus) elicited a significant increase (mean 175%) in circulating PRL levels in nine women studied during the periovulatory phase of the menstrual cycle (days 14-17). Similarly, GnRH infusion (0.2 micrograms/min X 3 h) induced a PRL response (mean 148%) in six women studied during the same period. In contrast, saline infusion induced a modest decrease (37%) in plasma PRL levels in five women studied during the periovulatory period. No significant changes in circulating PRL levels were found after GnRH administration as a bolus or a continuous infusion, in 13 women during the late follicular phase (days 10-13) and in 12 women during the midluteal phase (days 21-24). Synthetic GnRH elicited the expected increase in gonadotropin levels during all phases of the cycle studied. The maximal response was found for both LH and FSH during the periovulatory phase of the cycle. In conclusion, the data confirm that GnRH is capable of stimulating a PRL response in humans and again suggest that this response is estrogen-dependent. Finally, a temporal correlation between the midcycle gonadotropin peak and the positive PRL response to exogenous GnRH has been established.

Gonadotrophin releasing hormone provokes prolactin release in hypergonadotrophic hypogonadal women: a response not altered by dexamethasone

The prolactin response to 100 micrograms of intravenous gonadotrophin releasing hormone was studied in seven hypergonadotrophic hypogonadal and four eugonadal women. Prolactin rose from a mean basal level of 7.3 +/- 1.6 ng/ml to a mean peak level of 20.8 +/- 5.2 ng/ml in the hypogonadal women, and did not change significantly from a mean basal level of 7.7 +/- 1.2 ng/ml in the eugonadal women. Dexamethasone suppression did not alter the gonadotrophin or prolactin response to GnRH. Hypergonadotrophic hypogonadal women, like some patients with acromegaly, anorexia nervosa, and anovulatory disorders, show an augmented release of prolactin after GnRH administration.

Exaggerated prolactin response of thyrotropin-releasing hormone in women with anovulatory cycles: possible role of endogenous estrogens and effect of bromocriptine

Twenty-one women 18 to 36 years old, presenting with chronic anovulation, were compared with 10 normally cycling women. The patients were characterized by low progesterone (P) levels (0.93 +/- 0.14 ng/ml versus 15.5 +/- 1.4 in controls), whereas 17 beta-estradiol (E2) was moderately decreased (110.2 +/- 8.3 pg/ml versus 162.8 +/- 14.5 in controls) realizing a relative hyperestrogenism. Basal prolactin (PRL) levels were not elevated (12.1 +/- 0.97 ng/ml versus 9.2 +/- 0.7 in controls), but after thyrotropin-releasing hormone (TRH) stimulation an exaggerated response was observed (114.5 +/- 7 ng/ml versus 55.8 +/- 9 in controls). Patients were treated with bromocriptine (1.25 mg 2 times a day) for 3 months. Fifteen responded with ovulatory cycles, and five became pregnant. Progesterone increased significantly (10.2 +/- 1.3 ng/ml), whereas in patients who did not ovulate P increased only slightly (1.56 +/- 0.18 ng/ml). The particular endocrine profile of these patients (P/E2 imbalance) realizing relative hyperestrogenism may be responsible for the exaggerated PRL response to TRH. Bromocriptine, in reducing this transient, or masked, hyperprolactinemia, allows in many patients the return to ovulatory cycles. This mechanism may be one of the possible pathways leading to chronic functional or organic hyperprolactinemia.

Severe leukopenia and mild thrombocytopenia after chronic bromocriptine (CB-154) administration

A 23-year-old woman was receiving bromocriptine (CB-154, 7.5-10 mg/day, for a hyperprolactinemic galactorrhea-amenorrhea syndrome. She also had insulin-dependent diabetes. After three months the bromocriptine therapy was stopped because she developed severe leukopenia (leukocyte counts about 1,800/cu mm) and mild thrombocytopenia (platelet count about 130,000/cu mm). Five months after stopping the bromocriptine therapy, the leukocyte count returned to normal (4,400/cu mm), as did the platelet count (238,000/cu mm). Prior to bromocriptine therapy, the patient's leukocyte and platelet counts ranged between 5,500 and 6,000/cu mm and 250,000 and 300,000/cu mm, respectively. While taking bromocriptine she was on insulin maintenance therapy and took no other drugs. Regular menses had returned and spontaneous galactorrhea had disappeared during bromocriptine therapy, and serum prolactin levels became normal. After stopping bromocriptine therapy the patient again became basally hyperprolactinemic and amenorrheic, with spontaneous galactorrhea. The article discusses possible mechanisms of this hematologic reaction.

Effects of prolactin and bromocriptine on the luteal phase in infertile women

Infertile women with regular periods but with shortened luteal phases were found to have higher mean levels of serum prolactin and lower serum progesterone levels in the midluteal phase than women with apparently normal ovarian function (P less than 0.001). Serum estrogens and gonadotropins did not differ from the reference group but the ratio FSH/LH was reduced in the midluteal phase (P less than 0.05). LHRH-loading test in the midfollicular phase also resulted in a lower ratio of FSH/LH (P less than 0.05). Thirty-six infertile women with short luteal phases were treated with bromocriptine in a double-blind fashion. The drug moderately reduced the length of the cycle (P less than 0.01). The hyperthermia of the luteal phase was measured planimetrically. Both the total area and the area per day of the luteal phase were significantly increased during the cycles of active treatment (P less than 0.02 and 0.05, respectively). Prolactin was depressed by the drug. After cessation of therapy a very significant rebound elevation of prolactin for at least 2 wk was noted. Bromocriptine therapy further reduced FSH levels at midcycle. Estrogens were elevated during the midluteal phase whereas progesterone was not affected by the treatment. Seven conceptions occurred during the study, six of which during placebo treatment. The conception cycles were characterized by significantly higher levels of progesterone and estrogens during the luteal phase as opposed to the infertile cycles. Four of the pregnancies terminated in spontaneous abortion. The endocrine data of these conception cycles did not differ from those of the successful ones.