Increase In PRL Research Articles

Effect of long‐term cabergoline therapy on the immunological pattern and pituitary function of patients with idiopathic hyperprolactinaemia positive for antipituitary antibodies

The occurrence of antipituitary antibodies (APA) in patients with idiopathic hyperprolactinaemia (IH) and the effects of dopamine agonists on these antibodies and long-term pituitary function outcome have been so far not evaluated. This longitudinal study was aimed at investigating, in patients with IH the occurrence of APA and the effect of cabergoline on the pituitary function and behaviour of APA. Sixty-six patients with IH were studied. APA (by indirect immunofluorescence) and pituitary function were investigated every year for 3 years. Seventeen patients resulted APA positive (Group 1) and 49 APA negative (Group 2). Eight patients of Group 1 (Group 1a) and 24 of Group 2 (Group 2a) were asymptomatic and then not treated; instead, nine patients in Group 1 (Group 1b) and 25 in Group 2 (Group 2b), showing symptoms of hyperprolactinaemia, were treated with cabergoline for 2 years. Among the untreated patients, during the follow-up, those with APA positive (Group 1a) showed an increase of APA titres and PRL levels with partial pituitary impairment in some of them; instead those with APA negative (Group 2a) persisted negative with normal pituitary function despite persistent hyperprolactinaemia. Among the treated patients, those with APA positive (Group 1b) showed normalization of PRL levels, APA disappearance and recovery of pituitary function (when initially impaired) during cabergoline treatment, persisting also at last observation (off-therapy). Instead all patients of Group 2b persisted with APA negative during the follow-up with normalization of PRL levels and stable normal pituitary function during cabergoline therapy but showing a further increase of PRL at the last observation. The presence of APA in some patients with IH suggests a possible occurrence of autoimmune hypophysitis at potential/subclinical stage; an early and prolonged cabergoline therapy could interrupt the progression to an overt clinical stage of the disease. However, the small amount of patients investigated suggests caution against generalization of our assumption and prompts to further controlled studies on a more numerous population to verify these conclusions.

Five years follow-up of invasive prolactinomas with special reference to the control of cavernous sinus invasion

Few data are presently available on the effective control of cavernous sinus (CS) invasion of invasive prolactinomas. The aim of this retrospective study, through a mean period of 5 years follow up, is to observe the tumor shrinkage of CS invasive prolactinomas, as well as PRL normalization with bromocriptine therapy. 68 patients met the criteria of invasive prolactinomas (Grade III or IV in the classification scheme of Knosp and colleagues; serum PRL level greater than 200 ng/ml). 33 patients underwent bromocriptine therapy as the initial treatment, and 14 of these 33 had combined treatment with microsurgery and/or radiotherapy. The other 35 patients received microsurgery as the primary treatment, after which two patients had normal PRL without taking bromocriptine and other 33 patients received bromocriptine treatment after microsurgery. Tumor volume on magnetic resonance images had completely disappeared in 50 patients (74%), while all the other 18 patients had residual tumor in the parasellar areas, invading the CS, and 14 patients had a secondary empty sella due to tumor shrinkage. Of those 14 patients, seven still had elevated PRL levels; five had optic chiasmal herniation by different degrees (P < 0.05). There were 49 patients with normal PRL levels (72%); five patients with PRL levels more than 200 ng/ml. After the treatment, 14 patients with tumor volume disappearance on MR images and PRL normalization therefore withdrew from bromocriptine therapy. During a subsequent one-and-a-half-year follow-up, tumor recurrence and PRL increase were not found in those 14 patients. Twenty-seven patients maintained normal PRL levels with low-dose bromocriptine, of which 20 patients had their tumor disappear while seven patients had CS residual tumor. About three-fourths of prolactinomas with CS invasion can be effectively controlled not only with regard to tumor volume disappearance but also in serum PRL normalization. Residual tumor in the CS areas with PRL normalization and no pressure symptoms can be treated with low-dose of bromocriptine so as to achieve long-term tumor volume control and endocrine control. Great attention should be paid to CS residual tumors accompanying the empty sella, especially in cases with optic chiasmal herniation.

Accuracy of scanning laser polarimetry, scanning laser tomography in a glaucoma screening trial

Abstract Purpose: To compare the usefulness of scanning laser polarimetry (GDx‐VCC), scanning laser tomography (HRT) and their combined evaluation in glaucoma screening. Methods: In a non‐population‐based pre‐publicized trial, self‐recruited Caucasian participants were screened for glaucoma with GDx‐VCC, HRT, and by independent clinical examination. Cases with possible glaucoma as found with any of the screening methods underwent a detailed clinical investigation to verify or exclude glaucoma. Results: Of the 136 attendees 118 participants (218 eyes) successfully underwent the GDx‐VCC and HRT II measurements. Twenty‐three eyes of 13 participants had glaucoma. Seventeen glaucomatous eyes had early damage. Evaluated separately, the GDx‐VCC screening test (borderline=normal) performed best with 7.5 positive likelihood ratio (PLR). PRL for all HRT parameters was &lt;3.7. Combining different threshold criteria, for GDx‐VCC PLR increased to 14.0‐17.7, but no useful increase was seen for HRT (PRL&lt;4.7 for all combinations). Combination of the best HRT and GDx‐VCC criteria resulted in PRL increase compared to the HRT combinations, but PRL decrease compared to the GDx‐VCC combinations (PRL&lt;12.7 for all combinations). Conclusions: In this population with relatively high risk for mild glaucomatous damage, a combination of different GDx‐VCC criteria but not HRT criteria or combinations containing HRT criteria were useful for glaucoma screening.

Etiological diagnosis of hyperprolactinemia

There are numerous etiologies of hyperprolactinemia, a common reason for consultation. Diagnostic measures must be capable of identifying the tumors, the most frequent of which are prolactin adenomas. Hypothalamic–pituitary MRI is the reference morphological examination. In clinical practice, it is usually performed very early, following the discovery of increased plasma concentrations of PRL. This approach is warranted for marked increase in PRL in the absence of drugs with hyperprolactinemic effects (> 10 × upper limit of normal) since a diagnosis of PRL adenoma is extremely likely under such circumstances. When hyperprolactinemia is moderate, which is the most common finding in practice, all etiologies are possible in theory and it is important to follow a rational diagnostic plan (history-taking to identify use of any drugs with hyperprolactinemic effects paying attention to renal and hepatic history, investigation for endocrine diseases occasionally associated with hyperprolactinemia such as hypothyroidism or polycystic ovary syndrome (PCOS), confirmation of hyperprolactinemia by a second assay when the initial level is less than five times the upper normal limit, pregnancy testing for women of childbearing age) in order to rule out all non-tumoral causes of hyperprolactinemia before proceeding with imaging. Absence of any consequences of hyperprolactinemia on gonadic function or the existence of a concomitant disease that could account for the clinical signs, demonstration of wide variations in PRL from one assay to another in a single patient could prompt screening for macroprolactinemia before MRI is ordered. Macroprolactinoma could also occur in the case of normal or doubtful MRI or discrepancy in response to medical or surgical treatment. T1- and T2-weighted coronal sections (with or without T1 after gadolinium injection) are generally sufficient for diagnosis of microprolactinoma. Dynamic tests may be useful if MRI is normal or unclear. Gadolinium injection with sagittal and axial sections is essential for examination of large lesions. In this case, when the increase of PRL is moderate (< 150 mg/ml), a non-lactotropic lesion may be suspected without misdiagnosing a hook effect. Careful analysis of the images allows differentiation between tumoral lesions and pituitary hyperplasia.

Diagnostic étiologique d'une hyperprolactinémie

There are numerous etiologies of hyperprolactinemia, a common reason for consultation. Diagnostic measures must be capable of identifying the tumors, the most frequent of which are prolactin adenomas. Hypothalamic-pituitary MRI is the reference morphological examination. In clinical practice, it is usually performed very early, following the discovery of increased plasma concentrations of PRL. This approach is warranted for marked increase in PRL in the absence of drugs with hyperprolactinemic effects (> 10 x upper limit of normal) since a diagnosis of PRL adenoma is extremely likely under such circumstances. When hyperprolactinemia is moderate, which is the most common finding in practice, all etiologies are possible in theory and it is important to follow a rational diagnostic plan (history-taking to identify use of any drugs with hyperprolactinemic effects paying attention to renal and hepatic history, investigation for endocrine diseases occasionally associated with hyperprolactinemia such as hypothyroidism or polycystic ovary syndrome (PCOS), confirmation of hyperprolactinemia by a second assay when the initial level is less than 5 times the upper normal limit, pregnancy testing for women of childbearing age) in order to rule out all non-tumoral causes of hyperprolactinemia before proceeding with imaging. Absence of any consequences of hyperprolactinemia on gonadic function or the existence of a concomitant disease that could account for the clinical signs, demonstration of wide variations in PRL from one assay to another in a single patient could prompt screening for macroprolactinemia before MRI is ordered. Macroprolactinoma could also occur in the case of normal or doubtful MRI or discrepancy in response to medical or surgical treatment. T1- and T2-weighted coronal sections (with or without T1 after gadolinium injection) are generally sufficient for diagnosis of microprolactinoma. Dynamic tests may be useful if MRI is normal or unclear. Gadolinium injection with sagittal and axial sections is essential for examination of large lesions. In this case, when the increase of PRL is moderate (< 150 mg/ml), a non-lactotropic lesion may be suspected without misdiagnosing a hook effect. Careful analysis of the images allows differentiation between tumoral lesions and pituitary hyperplasia.

Effect of leptin on prolactin and insulin-like growth factor-I secretion by cultured rat endometrial stromal cells

To study the possible effect of leptin on PRL and insulin-like growth factor (IGF)-I secretion from rat endometrial stromal cells. The effect of recombinant murine leptin on the secretion of PRL and IGF-I by cultured rat endometrial cells was investigated. Academic institutions. Laboratory bred virgin female rats aged 3-4 months. Endometrial stromal cell (ESC) cultures in the fourth passage stimulated with 1-1,000 ng/mL of leptin for 24 hours and with 1 ng/mL leptin for 24-72 hours. Measurement of PRL and IGF-I levels in the conditioned media by enzyme immunoassay. Endometrial stromal cells grown in vitro secreted both PRL and IGF-I into the medium and the concentrations significantly increased with passage of time even in the absence of leptin. The increase in PRL was seen mainly at 72 hours and in IGF-I at 24 and 72 hours. Presence of leptin in the culture medium (1-1,000 ng/mL) further enhanced PRL secretion in a dose-dependent manner and this effect was seen with all leptin doses used. Leptin also increased PRL secretion in a time-dependent manner and the increase was seen at 24, 48, and 72 hours. Leptin did not significantly affect IGF-I secretion either in a dose- or a time-dependent manner. Biological effects of leptin on the rat endometrium include dose- and time-dependent stimulatory effects on stromal cell PRL secretion.

Development of a real-time (Q) PCR assay to measure variation in expression of prolactin receptor mRNA in the hypothalamus and pituitary gland during late embryogenesis in turkeys and chickens

Changes in levels of PRLR mRNA in the pituitary gland and hypothalamus of chickens and turkeys from embryonic day (ED) 15 and ED21 to 1 day post-hatch, respectively, were measured by real-time PCR. In both species, PRLR mRNA increased from low levels during the last week of ED to reach maxima at the peri-hatch period. Similarly, circulating levels of PRL also increased during this interval and were highly correlated with levels of the PRLR mRNA in both the pituitary gland and hypothalamus. This suggests that PRL was up-regulating its receptor. In support of this, stimulation of the turkey pituitary gland with VIP on ED24 resulted in a 4- and 3-fold increase in PRL and PRLR, respectively. Since VIP had no direct effect on the levels of PRLR transcript in the hypothalamus, it is likely that VIP is acting indirectly through increased PRL to up-regulate the number of receptors.

Hormonal and metabolic responses to acute ghrelin administration in patients with bulimia nervosa

Ghrelin is generally influenced by energy balance status and is inversely associated with body mass index (BMI), being reduced in simple obesity, notable exception being Prader Willi syndrome, and elevated in several conditions of undernutrition, including anorexia nervosa (AN). Interestingly, ghrelin levels have also been found elevated in patients with bulimia nervosa (BN) in spite of normal BMI. In humans, intravenous (iv) ghrelin administration induces endocrine (increase in GH, PRL, ACTH and cortisol) and metabolic (increase in glucose and decrease in insulin) effects as well as an increase in appetite and food intake. In AN, ghrelin administration surprisingly leads to a decreased GH response and absence of glycemic variations but normal PRL, ACTH and insulin response. This pattern would reflect a decrease in sensitivity to ghrelin or, alternatively, the metabolic status of AN. To further clarify the function of ghrelin in eating disorders, the endocrine and metabolic response to acute iv ghrelin (1.0 microg/kg) was studied in seven young women with purging BN (BW, BMI, mean+/-SEM: 20.3+/-0.5 kg/m2). Circulating total ghrelin levels were also measured. The results in BW were compared to those recorded in a group of nine healthy women (HW; BMI 22.3+/-2.5 kg/m2). The GH response to ghrelin in BW overlapped with that in HW. Ghrelin administration also led to a similar increase in PRL, ACTH, cortisol and glucose levels in the two groups. Insulin levels were not significantly modified by ghrelin administration in either group. The overlapping endocrine and metabolic response to ghrelin in the two groups occurred with regard to circulating total ghrelin levels which were higher in BW than in HW. In conclusion, BN, a condition of ghrelin hypersecretion, is connoted by a normal endocrine and metabolic response to exogenous ghrelin administration.

Pharmacodynamic effects of opiate receptor antagonism: An agonist challenge study

Background Pharmacodynamic effects of opiate antagonists and agonists such as naltrexone (NTX) and fentanyl (FE) have been documented in separate studies and various populations. However, no data are available for a direct comparison in the same group of subjects. Methods NTX 50mg QD and a matched placebo were compared in a randomized double-blind crossover study conducted in a research hospital setting. NTX was administered for 3 days to 16 healthy males. ACTH, cortisol, FSH, LH, PRL and pupillary diameter (PD) were measured on Day 1. On Day 3, blockade of agonist-induced effects was tested by use of an IV bolus of FE. Results On Day 1, NTX induced an increase in LH, ACTH and cortisol (p<0.01 each; 90%CI ratio[1.29–1.91],[1.42–2.40],[1.26–2.06]). No effect was observed on FSH, PRL and PD. On Day 3, NTX was associated with a blockade of the following FE effects: increase in ACTH (p<0.0001,[0.15–0.59]), cortisol (p=0.01,[0.38–0.81]) and PRL (p<0.0001,[0.12–0.22]) and reduction in PD (p<0.0001,[2.47–3.32]). NTX did not influence pain perception during the cold pressor test performed after FE. Conclusion Blockade of FE-induced changes in PRL and PD were the most significant treatment effects observed. In contrast to FE-induced decreases in ACTH/cortisol reported in stressed or surgical patients, an increase was observed in healthy volunteers. This effect was blocked by NTX. Clinical Pharmacology & Therapeutics (2005) 77, P28–P28; doi: 10.1016/j.clpt.2004.11.110

Preserved inhibitory effect of recurrent hypoglycaemia on the male gonadotrophic axis

Hypoglycaemia-induced decreases in male LH and testosterone concentrations are possibly mediated by activation of the hypothalamus-pituitary-adrenal (HPA) axis or by an increase in PRL. As counterregulatory stress hormone release is attenuated during recurrent hypoglycaemia, we questioned whether the gonadotrophic axis and PRL adapt similarly. We performed two consecutive hypoglycaemic clamps on day 1 and one clamp on the following day in 15 healthy men. Blood concentrations of gonadotrophins, PRL, testosterone, ACTH and cortisol were measured during the first and the third clamp, taking place at the same time of day. During hypoglycaemia, serum concentrations of LH and testosterone decreased (P < 0.003 for both), PRL, ACTH and cortisol increased (P < 0.001), and FSH remained unchanged (P = 0.90). The hypoglycaemia-induced decreases in LH and testosterone concentrations were similar during the first and the last clamp (P > 0.28 for both) whereas the increase in PRL, ACTH and cortisol was markedly attenuated during the third clamp (P < 0.001). LH and testosterone responses do not adapt to recurrent hypoglycaemia, whereas the increase in PRL is attenuated, indicating adaptation. Considering the marked decrease in the responses of PRL and the HPA axis after antecedent hypoglycaemia, the data suggest that the hypoglycaemia-induced decreases in LH and testosterone concentrations, not adapting to recurrent hypoglycaemia, are mediated independently, probably by blood glucose itself.

Rhythmic secretion of prolactin in rats: action of oxytocin coordinated by vasoactive intestinal polypeptide of suprachiasmatic nucleus origin.

Prolactin (PRL) is secreted from lactotrophs of the anterior pituitary gland of rats in a unique pattern in response to uterine cervical stimulation (CS) during mating. Surges of PRL secretion occur in response to relief from hypothalamic dopaminergic inhibition and stimulation by hypothalamic releasing neurohormones. In this study, we characterized the role of oxytocin (OT) in this system and the involvement of vasoactive intestinal polypeptide (VIP) from the suprachiasmatic nucleus (SCN) in controlling OT and PRL secretion of CS rats. The effect of OT on PRL secretion was demonstrated in cultured lactotrophs showing simultaneous enhanced secretion rate and increased intracellular Ca(2+). Neurosecretory OT cells of the hypothalamic paraventricular nucleus that express VIP receptors were identified by using immunocytochemical techniques in combination with the retrogradely transported neuronal tracer Fluoro-Gold (iv injected). OT measurements of serial blood samples obtained from ovariectomized (OVX) CS rats displayed a prominent increase at the time of the afternoon PRL peak. The injection of VIP antisense oligonucleotides into the SCN abolished the afternoon increase of OT and PRL in CS-OVX animals. These findings suggest that VIP from the SCN contributes to the regulation of OT and PRL secretion in CS rats. We propose that in CS rats the regulatory mechanism(s) for PRL secretion comprise coordinated action of neuroendocrine dopaminergic and OT cells, both governed by the daily rhythm of VIP-ergic output from the SCN. This hypothesis is illustrated with a mathematical model.

The endocrine response to acute ghrelin administration is blunted in patients with anorexia nervosa, a ghrelin hypersecretory state.

Ghrelin, a gastric-derived natural ligand of the GH secretagogue (GHS)-receptor (GHS-R), strongly stimulates GH secretion but also possesses other neuroendocrine actions, stimulates food intake and modulates the endocrine pancreas and energy homeostasis. Ghrelin secretion is negatively modulated by food intake. Similarly, glucose and also insulin probably exert an inhibitory effect on ghrelin secretion. Fasting ghrelin levels are reduced in obesity, elevated in anorexia nervosa and restored by weight recovery. The chronic elevation of circulating ghrelin levels in anorexia suggested the hypothesis of an alteration of the sensitivity to the orexigenic action of ghrelin in this condition. The aim of this study was to define the endocrine actions of ghrelin in patients with anorexia nervosa. We enrolled nine women with anorexia nervosa of restricter type [AN; age (mean +/- SEM) 24.2 +/- 1.8 years; body mass index (BMI) 14.7 +/- 0.4 kg/m2] and seven normal young women in their early follicular phase as control group (NW; age 30.6 +/- 3.1 years; BMI 20.3 +/- 0.5 kg/m2). In all the subjects we studied the GH, PRL, ACTH, cortisol, insulin and glucose responses to acute ghrelin administration (1.0 microg/kg as i.v. bolus). The GH response to GHRH (1.0 microg/kg as i.v. bolus) and basal ghrelin and IGF-I levels were also evaluated in all the subjects. Basal morning ghrelin and GH levels in AN (643.6 +/- 21.3 ng/l and 10.4 +/- 0.5 microg/l, respectively) were higher (P < 0.05) than in NW (233.5 +/- 14.2 ng/l and 0.7 +/- 0.7 microg/l, respectively). However, IGF-I levels in AN (145.3 +/- 10.9 microg/l) were lower (P < 0.05) than in NW (325.4 +/- 12.6 microg/l). The GH response to GHRH in AN was higher (P < 0.05) than that in NW, but in AN the GH response to ghrelin was lower (P < 0.05) than that in NW. In AN and NW ghrelin also induced similar increases (P < 0.05) in PRL, ACTH and cortisol levels. Ghrelin administration was followed by significant increase in glucose levels in NW (P < 0.05) but not in AN. This study demonstrates that anorexia nervosa, a clinical condition of ghrelin hypersecretion, shows a specific reduction in the GH response to ghrelin, despite the hyper-responsiveness to GHRH administration. The impaired GH response to ghrelin in anorexia nervosa agrees with previous evidence of blunted GH response to synthetic GH secretagogues and could reflect desensitization of the GHS receptor induced by the chronic elevation of ghrelin levels in this pathological state.

Acetylcholine does not play a major role in mediating the endocrine responses to ghrelin, a natural ligand of the GH secretagogue receptor, in humans.

Ghrelin is a 28 amino residue peptide produced predominantly by the stomach with substantially lower amounts deriving from other central and peripheral tissues. Ghrelin is a natural ligand of the GH secretagogue (GHS) receptor (GHS-R) and possesses a potent GH-releasing activity for which the acylation in serine 3 is essential. Ghrelin also possesses other endocrine and non-endocrine activities reflecting central and peripheral GHS-R distribution and stimulates PRL, ACTH and cortisol secretion, has been reported able to induce hyperglycaemia and to decrease insulin levels and has orexigenic activity. Moreover, ghrelin stimulates gastric motility and acid secretion and its action is mediated by acetylcholine which, in turn, is known to play a stimulatory influence on GH, ACTH and insulin secretion. In order to clarify the influence, if any, of acetylcholine on the endocrine activities of ghrelin, we studied the effects of cholinergic enhancement by pyridostigmine (PD, 120 mg p.o. at -60 minutes) and blockade by pirenzepine (PIR, 100 mg p.o. at -60 minutes) on GH, PRL, cortisol, insulin and glucose responses to human acylated ghrelin (1.0 microg/kg i.v. at 0 minutes) in seven normal young volunteers [age (mean +/- SEM): 28.3 +/- 3.1 years; BMI: 21.9 +/- 0.9 kg/m2]. In the same subjects, the effects of PD and PIR on the GH response to GHRH (1.0 microg/kg i.v. at 0 minutes) have also been studied. The administration of ghrelin induced a prompt increase in circulating GH levels (hAUC: 5452.4 +/- 904.9 microg*min/L) which was markedly higher (P < 0.01) than that elicited by GHRH (966.9 +/- 20.50 microg*min/L). Ghrelin also induced a significant increase in PRL (1273.5 +/- 199.7 microg*min/L) and cortisol levels (15505.1 +/- 796.3 microg*min/L) and a decrease in insulin levels (Delta hAUC: -198.1 +/- 39.2 mU*min/L) which was preceded by an increase in plasma glucose levels (8743.8 +/- 593.0 mg*min/dL). The GH response to GHRH was markedly potentiated by PD (4363.3 +/- 917.3 microg*min/L; P < 0.01 vs. GHRH alone). In turn, PD did not modify either the GH response to ghrelin (6564.2 +/- 1753.5 microg*min/L) or its stimulatory effect on PRL and cortisol as well as its effects on insulin and glucose levels. The GH response to GHRH was inhibited by PIR (171.5 +/- 34.7 microg*min/L, P < 0.01 vs. GHRH alone) which, in turn, did not significantly modify the GH response to ghrelin (4044.0 +/- 948.8 microg*min/L). PIR also did not modify the effects of ghrelin on PRL, cortisol, insulin and glucose levels. The endocrine activities of ghrelin are not affected significantly by cholinergic enhancement and muscarinic blockade. Thus, acetylcholine does not play a major role in the endocrine actions of ghrelin. Moreover, as the cholinergic system influences GH secretion via modulation of somatostatin release, the present data agree with the assumption that ghrelin is partially refractory to the influence of somatostatin.

Prolactin regulation of neonatal ovine uterine gland morphogenesis.

Uterine gland development or adenogenesis in the neonatal ovine uterus involves budding, proliferation, and branching morphogenesis of the glandular epithelium (GE) from the luminal epithelium (LE) between birth (postnatal day or PND 0) and PND 56. This critical developmental event is coincident with increases in serum PRL and expression of long and short PRL receptors specifically in the nascent and proliferating GE. In study one, ewes were treated with a placebo pellet as a control (CX) or a bromocryptine mesylate pellet from PNDs 0-56. On PND 56, the endometrium of bromocryptine mesylate ewes contained fewer glands, particularly in the stratum spongiosum that contained numerous coiled and branched glands in CX uteri. In study two, ewes were treated with saline as a CX or recombinant ovine PRL from PNDs 0-56. Treatment with PRL increased gland number and density on PND 14 and PND 56. In study three, expression of signal transducers and activators of transcription (STAT) 1, 3, and 5 proteins was detected in the developing glands from PNDs 7-56. In study four, Western blot analyses indicated that PRL increased levels of phosphorylated STATs 1 and 5, but not STAT 3, and phosphorylated ERK 1 and 2 MAPKs and c-Jun N-terminal kinase/stress-activated protein kinase proteins in explanted PND 28 ovine uteri. Collectively, results indicate that PRL regulates endometrial adenogenesis in the neonatal ovine uterus.

Ovarian dependence for pituitary tumorigenesis in D2 dopamine receptor-deficient mice.

Hypophyseotropic dopamine exerts a tonic inhibitory tone on pituitary lactotrophs by the activation of dopamine D2 receptors (D2R). Ablation of D2R through gene knock-out approaches results in hyperprolactinemia and prolactinomas. This phenotype is more severe and develops more rapidly in female mice. We tested whether the female hypersensitivity is due solely to the loss of D2R inhibitory tone or concomitant stimulation by ovarian factors. C57BL/6J congenic D2R(-/-) mice were ovariectomized at 2 months of age and serum PRL levels were measured serially. Ovariectomy attenuated hyperprolactinemia and after 18 months, D2R(-/-) mice had average pituitary weights of 4 mg, compared with 60 mg in the intact group. 17beta-Estradiol did not restore PRL secretion or pituitary weight. Although the pharmacologic dose of estradiol slightly increased pituitary weight in wild-type and D2R(-/-) mice, it inhibited serum PRL in both intact and ovariectomized females and in castrated males. For comparison, we tested the estradiol response of wild-type 129S6/SvEv mice in the same paradigm and found the expected increase in pituitary weight and serum PRL. Our results demonstrate that the development of hyperprolactinemia and prolactinomas in mice lacking D2R is dependent on ovarian stimulation and likely involves a factor(s) in addition to estrogen. Furthermore, we showed that estradiol-induced proliferation and PRL secretion can be differentially regulated in a strain-specific manner. These findings illustrate the importance of genetic background when analyzing endocrine regulation in mutant mouse models.

Endocrine responses to ghrelin in adult patients with isolated childhood-onset growth hormone deficiency.

Ghrelin, a 28 amino acid acylated peptide, is a natural ligand of the GH secretagogues (GHS) receptor (GHS-R), which is specific for synthetic GHS. Similar to synthetic GHS, ghrelin strongly stimulates GH secretion but also displays significant stimulatory effects on lactotroph and corticotroph secretion. It has been hypothesized that isolated GH deficiency (GHD) could reflect hypothalamic impairment that would theoretically involve defect in ghrelin activity. In the present study, we verified the effects of ghrelin (1 microg/kg i.v.) on GH, PRL, ACTH and cortisol levels in adult patients with isolated severe GHD [five males and one female, age (mean +/- SEM) 24.7 +/- 2.6 years, BMI 25.7 +/- 2.7 kg/m2]. In all patients, the GH response to insulin-induced hypoglycaemia (ITT, 0.1 IU regular insulin i.v.) and GH releasing hormone (GHRH) (1 microg/kg i.v.) + arginine (ARG, 0.5 g/kg i.v.) was also studied. The hormonal responses in GHD were compared with those in age-matched normal subjects (NS, seven males, age 28.6 +/- 2.9 years, BMI 22.1 +/- 0.8 kg/m2). IGF-I levels in GHD were markedly lower than in NS (69.8 +/- 11.3 vs. 167.9 +/- 19.2 microg/l, P < 0.003). Ghrelin administration induced significant increase in GH, PRL, ACTH and cortisol levels in all GHD. In GHD, the GH response to ghrelin was higher (P < 0.05) than that to GHRH + ARG, which, in turn, was higher (P < 0.05) than that to ITT (9.2 +/- 4.1 vs. 5.3 +/- 1.7 vs. 1.4 +/- 0.4 microg/l). These GH (1 microg/l = 2 mU/l) responses in GHD were markedly lower (P < 0.0001) than those in NS (ghrelin vs. GHRH + ARG vs. ITT 92.1 +/- 16.7 vs. 65.3 +/- 8.9 vs. 17.7 +/- 3.5 microg/l). In GHD, the highest individual peak GH response to ghrelin was markedly lower than the lowest peak GH response in NS (28.5 vs. 42.9 microg/l). GHD and NS showed overlapping PRL (1 microg/l = 32 mU/l) (10.0 +/- 1.4 vs. 14.9 +/- 2.2 microg/l), ACTH (22.3 +/- 5.3 vs. 18.7 +/- 4.6 pmol/l) and cortisol responses (598.1 +/- 52.4 vs. 486.9 +/- 38.9 nmol/l). This study shows that ghrelin is one of the most powerful provocative stimuli of GH secretion, even in those patients with isolated severe GHD. In this condition, however, the somatotroph response is markedly reduced while the lactotroph and corticotroph responsiveness to ghrelin is fully preserved, indicating that this endocrine activity is fully independent of mechanisms underlying the GH-releasing effect. These results do not support the hypothesis that ghrelin deficiency is a major cause of isolated GH deficiency but suggest that ghrelin might represent a reliable provocative test to evaluate the maximal GH secretory capacity provided that appropriate cut-off limits are assumed.

Impact of two or three daily subcutaneous injections of hexarelin, a synthetic growth hormone (GH) secretagogue, on 24-h GH, prolactin, adrenocorticotropin and cortisol secretion in humans

To extend the insights on the action of GH secretagogues (GHS) on pituitary function, we studied the impact of intermittent daily s.c. administration of a peptidyl GHS, hexarelin (HEX), on 24-h GH, PRL, ACTH and cortisol release in healthy volunteers. We investigated the impact of two or three times daily s.c. administration of a short-acting peptidyl GHS, the hexapeptide HEX (1.5 microg/kg) on 24-h GH, PRL, ACTH and cortisol secretion (sampling every 20 min) in six normal young men. To monitor possible down-regulation, the effect of 1 microg/kg i.v. HEX at the end of each 24-h sampling period was studied. Multi-parameter deconvolution analysis was used to quantitate pulsatile GH, PRL, ACTH and cortisol secretion and estimate the corresponding hormone half-lives. Complementary to deconvolution analysis, approximate entropy was used as a scale- and model-independent statistic to quantify the serial orderliness or pattern regularity of hormone measurements. Mean and integrated (24-h) serum GH concentrations were increased from baseline values to the same extent by two and three HEX injections. Both HEX schedules equally increased GH secretory burst mass (but not burst frequency), mean daily GH production rate, GH half-life and irregularity of GH release patterns. No change occurred in the secretion of IGF-I, PRL, ACTH and cortisol. Intravenous HEX at the end of each spontaneous 24-h profile induced a significant rise in GH, PRL, ACTH and cortisol. Prior HEX administration blunted the GH response, abolished that of ACTH and cortisol and did not modify the PRL increase. The study showed that two or three daily s.c. injections of HEX augmented 24-h GH secretion equally, amplifying selectively GH secretory pulse mass without altering lactotroph and corticotroph secretion. IGF-I levels were not modified by these 1-day HEX treatment schedules.

Involvement of mitogen-activated protein kinase in cyclic adenosine 3',5'-monophosphate-induced hormone gene expression in rat pituitary GH(3) cells.

We examined whether mitogen-activated protein (MAP) kinase was activated by stimulation of the cAMP pathway and whether MAP kinase activation was involved in synthesis of PRL and GH in GH(3) cells. Treatment of the cells with a cAMP analog, 8-(4-chlorophenylthio)cAMP (CPT-cAMP), activated MAP kinase and increased PRL at both the protein and messenger RNA levels. The protein and messenger RNA of GH were decreased by the treatment. We constructed the luciferase reporter genes after the promoters of PRL and GH and found the activation of both promoters by the CPT-cAMP treatment. We confirmed that overexpression of the catalytic subunit of cAMP-dependent protein kinase had essentially the same effects on MAP kinase activation and synthesis of PRL and GH as the CPT-cAMP treatment. Furthermore, treatment of the cells with pituitary adenylate cyclase-activating polypeptide 27 activated MAP kinase. The activation of PRL promoter by CPT-cAMP and pituitary adenylate cyclase-activating polypeptide 27 was abolished by pretreatment with PD098059 and H89. Although the increase in PRL and GH secretion by CPT-cAMP was inhibited by H89, PD098059 had no effect on secretion. These results suggest that cAMP-induced MAP kinase activation is essential for PRL gene expression, but not for secretion of PRL and GH.

The role of human chorionic gonadotropin on decidualization of endometrial stromal cells in vitro.

Although decidualization of endometrial stromal cells (ESC) is crucial for blastocyst implantation and maintenance of pregnancy, its complex mechanism still remains largely unknown. It has long been believed that hCG can directly induce in vitro decidualization of ESC via cAMP signaling. Recently, however, it has been reported that the LH/CG receptor is not present in human endometrium, and the direct effect of hCG on decidualization has become controversial. To reevaluate the exact effect of hCG on decidualization, human ESC were isolated and cultured with hCG and/or ovarian steroids. ESC treated with 17beta-estradiol plus progesterone (E(2)/P) transformed morphologically and produced significant PRL, whereas ESC treated with hCG alone showed no significant increase in PRL in culture medium and exhibited no morphological changes. Moreover, hCG did not promote E(2)/P-induced PRL production or intracellular cAMP accumulation, and protein kinase A inhibitor failed to block E(2)/P-induced PRL production. These results suggest that hCG does not directly affect in vitro decidualization of human ESC and that the process of E(2)/P-induced in vitro decidualization might consist of several pathways, including the intracellular cAMP signaling cascade.

Pyridostigmine and metoclopramide do not restore the TSH response to TRH inhibited by L-thyroxine treatment in children with goiter.

To define the role of somatostatin and dopamine in TSH suppression induced by L-thyroxine, 16 children (12 F, 4 M) on suppressive doses of L-thyroxine (3-4 microg/kg/day) for endemic goiter were studied. Firstly a conventional TRH test was performed in all subjects, in order to evaluate TSH, PRL and GH (basal study). A week later a second TRH test was carried out; one hour before the test, however, group A (9 patients) was given 60 mg pyridostigmine bromide po (pyridostigmine study) and group B (7 patients) 10 mg metoclopramide po (metoclopramide study). In the basal study, TSH was suppressed in both groups and levels did not increase following TRH administration, while PRL increased significantly and GH levels remained stable. In the pyridostigmine study, TSH levels did not increase following TRH administration, while PRL and GH levels were both significantly raised. In the metoclopramide study, TSH and GH levels were not raised following TRH administration, while a significantly greater increase of PRL was observed. In conclusion, suppressive doses of L-thyroxine inhibit the TSH response to TRH, while they do not seem to affect GH and PRL secretion. Somatostatin and/or dopamine do not seem to play a significant role in the L-thyroxine-induced TSH suppression.