Evaluation of the anterior pituitary function in the acute phase after spontaneous subarachnoid hemorrhage

BACKGROUND

Subarachnoid hemorrhage (SAH) is a potential cause of hypopituitarism. Most of the studies regarding the relationship between SAH and anterior pituitary function were retrospective and hormonal assessment was performed several months after SAH.

AIM

To prospectively evaluate the prevalence of anterior pituitary hormone deficiencies in the acute phase after spontaneous SAH and their possible correlation with clinical and radiological parameters.

METHODS

Pituitary function was tested in 60 patients within 72 h after spontaneous SAH.

RESULTS

56.9% of the patients showed at least one anterior pituitary hormone deficiency: gonadotropin and GH secretion failure represented the most prevalent hormonal deficiencies (33.3 and 22.0%, respectively), whereas ACTH and TSH deficiency was less frequent (7.1 and 1.8%, respectively). With the exception of secondary hypogonadism, the prevalence of other pituitary hormone deficiencies is in agreement with previous studies, which evaluated pituitary function on longterm follow up after SAH. No correlation was found between hypopituitarism and clinical status, as assessed with Hunt-Hess and Glascow Coma Scales. Moreover, no correlation was found between hypopituitarism and bleeding severity evaluated with Fisher's scale.

CONCLUSIONS

We demonstrated a high prevalence of anterior pituitary hormone deficiencies acutely after SAH. Although part of GH and gonadotropin deficiencies might be a consequence of functional alteration due to SAH itself, the finding of low cortisol levels in this stressful condition strongly suggests the presence of true hypocortisolism. Therefore, an evaluation of pituitary function shortly after SAH might be useful to identify a subset of patients who deserve a more accurate follow-up.

Birthdating studies reshape models for pituitary gland cell specification

The intermediate and anterior lobes of the pituitary gland are derived from an invagination of oral ectoderm that forms Rathke's pouch. During gestation proliferating cells are enriched around the pouch lumen, and they appear to delaminate as they exit the cell cycle and differentiate. During late mouse gestation and the postnatal period, anterior lobe progenitors re-enter the cell cycle and expand the populations of specialized, hormone-producing cells. At birth, all cell types are present, and their localization appears stratified based on cell type. We conducted a birth dating study of Rathke's pouch derivatives to determine whether the location of specialized cells at birth is correlated with the timing of cell cycle exit. We find that all of the anterior lobe cell types initiate differentiation concurrently with a peak between e11.5 and e13.5. Differentiation of intermediate lobe melanotropes is delayed relative to anterior lobe cell types. We discovered that specialized cell types are not grouped together based on birth date and are dispersed throughout the anterior lobe. Thus, the apparent stratification of specialized cells at birth is not correlated with cell cycle exit. Thus, the currently popular model of cell specification, dependent upon timing of extrinsic, directional gradients of signaling molecules, needs revision. We propose that signals intrinsic to Rathke's pouch are necessary for cell specification between e11.5 and e13.5 and that cell-cell communication likely plays an important role in regulating this process.

Encoding and decoding photoperiod in the mammalian pars tuberalis

In mammals, the nocturnal melatonin signal is well established as a key hormonal indicator of seasonal changes in day-length, providing the brain with an internal representation of the external photoperiod. The pars tuberalis (PT) of the pituitary gland is the major site of expression of the G-coupled receptor MT1 in the brain and is considered as the main site of integration of the photoperiodic melatonin signal. Recent studies have revealed how the photoperiodic melatonin signal is encoded and conveyed by the PT to the brain and the pituitary, but much remains to be resolved. The development of new animal models and techniques such as cDNA arrays or high throughput sequencing has recently shed the light onto the regulatory networks that might be involved. This review considers the current understanding of the mechanisms driving photoperiodism in the mammalian PT with a particular focus on the seasonal prolactin secretion.

Chemokines and chemokine receptors: new actors in neuroendocrine regulations

Chemokines are small secreted proteins that chemoattract and activate immune and non-immune cells. Their role in the immune system is well-known, and it has recently been suggested that they may also play a role in the central nervous system (CNS). Indeed, they do not only act as immunoinflammatory mediators in the brain but they also act as potential modulators in neurotransmission. Although we are only beginning to be aware of the implication of chemokines in neuroendocrine functions, this review aims at summarizing what is known in that booming field of research. First we describe the expression of chemokines and their receptors in the CNS with a focus on the hypothalamo-pituitary system. Secondly, we present what is known on some chemokines in the regulation of neuroendocrine functions such as cell migration, stress, thermoregulation, drinking and feeding as well as anterior pituitary functions. We suggest that chemokines provide a fine modulatory tuning system of neuroendocrine regulations.

MicroRNA expression in ACTH-producing pituitary tumors: up-regulation of microRNA-122 and -493 in pituitary carcinomas

MicroRNAs (miRNAs) are involved in cell proliferation, differentiation, and apoptosis, and can function as tumor suppressor genes or oncogenes. The expression of miRNAs in pituitary carcinomas has not been previously examined. We used miRNA profiling with 1,145 probes to study miRNA expression in normal anterior pituitary (6 cases), adrenocorticotropin (ACTH)-producing adenomas (8 cases), and ACTH-producing pituitary carcinomas (two cases). Real-time RT-PCR and in situ hybridization were used to confirm and independently validate miRNAs that were significantly up-regulated or down-regulated between the pituitary tissues. There were more miRNAs up- (188) or down-regulated (160) between adenomas and normal pituitaries compared to carcinomas and normal pituitaries (92 up- and 91 down-regulated) or between carcinomas and adenomas (46 up- and 52 down-regulated). Both real-time RT-PCR and in situ hybridization showed significant up-regulation of miRNA-122 between pituitary carcinomas and adenomas. MiRNA-493 was also up-regulated in carcinomas compared to ACTH adenomas. Analysis of genes that miRNA-493 interacts with included LGALS3 and RUNX2 ( http://microrna.sanger.ac.uk ) both of which have been shown to have roles in pituitary tumor cell growth. These results provide information about marker miRNAs that may lead to further insights into the regulation of pituitary tumor growth and development.

Cell life and death in the anterior pituitary gland: role of oestrogens

Apoptotic processes play an important role in the maintenance of cell numbers in the anterior pituitary gland during physiological endocrine events. In this review, we summarise the regulation of apoptosis of anterior pituitary cells, particularly lactotrophs, somatotrophs and gonadotrophs, and analyse the possible mechanisms involved in oestrogen-induced apoptosis in anterior pituitary cells. Oestrogens exert apoptotic actions in several cell types and act as modulators of pituitary cell renewal, sensitising cells to both mitogenic and apoptotic signals. Local synthesis of growth factors and cytokines induced by oestradiol as well as changes in phenotypic features that enhance the responsiveness of anterior pituitary cells to pro-apoptotic factors may account for cyclical apoptotic activity in anterior pituitary cells during the oestrous cycle. Considering that tissue homeostasis results from a balance between cell proliferation and death and that mechanisms involved in apoptosis are tightly regulated, defects in cell death processes could have a considerable physiopathological impact.

Circadian timekeeping and multiple timescale neuroendocrine rhythms

The hormones secreted by the anterior pituitary gland regulate major functions such as reproduction, as well as body growth and metabolism. Their efficiency of action highly depends on their temporal profile of release in the blood stream. This review summarises the recent evidence suggesting that the circadian clock genes that pace our daily rhythms may also contribute to the regulation of pituitary pulsatility, even in the non 24-h range. This inter-relation between molecular circadian oscillators and endocrine rhythmicities is discussed in light of the longstanding literature that has considered the involvement of the central circadian pacemaker located within the suprachiasmatic nuclei. Other arguments that suggest a role for circadian clock genes outside the suprachiasmatic nuclei are also presented, with a special emphasis on endocrine pituitary cells and hypothalamic neuroendocrine neurones that directly pace pituitary secretion rates.

Role of orexins in the hypothalamic-pituitary-ovarian relationships

Appropriate nutritional and vigilance states are needed for reproduction. In previous works, we described the influence of the hormonal milieu of proestrus on the orexinergic system and we found that orexin receptor 1 expression in the hypothalamus, but not other neural areas, and the adenohypophysis was under the influence of oestradiol and the time of the day. Information from the sexual hormonal milieu of proestrous afternoon impacts on various components of the orexinergic system and alertness on this particular night of proestrus would be of importance for successful reproduction. In this review, we summarize the available experimental data supporting the participation of orexins in the hypothalamic-pituitary-ovarian relationships. All together, these results suggest a role of the orexinergic system as an integrative link among vital functions such as reproduction, food intake, alertness and the inner biological clock.

Use of mutant mouse lines to investigate origin of gonadotropin-releasing hormone-1 neurons: lineage independent of the adenohypophysis

Mutant mouse lines have been used to study the development of specific neuronal populations and brain structures as well as behaviors. In this report, single- and double-mutant mice were used to examine the lineage of GnRH-1 cells. GnRH is essential for vertebrate reproduction, with either GnRH-1 or GnRH-3 controlling release of gonadotropins from the anterior pituitary, depending on the species. It is clear that the neuroendocrine GnRH cells migrate from extracentral nervous system locations into the forebrain. However, the embryonic origin of GnRH-1 and GnRH-3 cells is controversial and has been suggested to be nasal placode, adenohypophyseal (anterior pituitary) placode, or neural crest, again dependent on the species examined. We found that mutant mice with either missing or disrupted anterior pituitaries (Gli2(-/-), Gli1(-/-)Gli2(-/-), and Lhx3(-/-)) exhibit a normal GnRH-1 neuronal population and that these cells are still found associated with the developing vomeronasal organ. These results indicate that in mice, GnRH-1 cells develop independent of the adenohypophyseal placode and are associated early with the formation of the nasal placode.

The regulatory role of neurotensin on the hypothalamic-anterior pituitary axons: emphasis on the control of thyroid-related functions

Neurotensin (NT) is a 13 amino acid neurohormone and/or neuromodulator, located in the synaptic vesicles and released from the neuronal terminals in a calcium-dependent manner. This peptide is present among mammalian and nonmammalian species, mainly in the central nervous system and the gastrointestinal tract. Due to its neuroendocrine activity, NT has been related to the pathophysiology of a series of disorders, such as schizophrenia, drug-abuse, Parkinson's disease, cancer, stroke, eating disorders and other neurodegenerative conditions. Moreover, NT participates in the physiology of pain-induction, central blood pressure control and inflammation. NT also plays an important interactive role in all components of the hypothalamic-anterior pituitary circuit, which is mediated by an endocrine, paracrine or/and autocrine manner, towards most of the anatomical regions that define this circuit. A considerable amount of data implicates NT in thyroid-related regulation through this circuit, the exact mechanisms of which should be further investigated for the potential development of more targeted approaches towards the treatment of thyroid-related endocrine diseases. The aim of this study was to provide an up-to-date review of the literature concerning the regulatory role of NT on the hypothalamic-anterior pituitary axons, with an emphasis on the control of thyroid-related functions.

Living-cell imaging of transgenic rat anterior pituitary cells in primary culture reveals novel characteristics of folliculo-stellate cells

Folliculo-stellate (FS) cells in the anterior pituitary gland appear to possess multifunctional properties. Recently, the development of transgenic rats (S100b-green fluorescent protein (GFP) rats) that express GFP specifically in FS cells in the anterior pituitary gland has allowed us to distinguish and observe living FS cells in other kinds of pituitary cells. We used S100b-GFP rats to investigate the topographic affinity of FS cells for other pituitary cells. We observed living FS cells in enzymatically dispersed anterior pituitary cells of S100b-GFP rats under a fluorescent microscope, and noted that FS cells markedly extended and contracted cytoplasmic processes and formed interconnections with neighboring FS cells. In addition, FS cells adhered to small clusters of GFP-negative cells, which were primarily hormone-producing cells, and these clusters further aggregated during the course of cytoplasmic contraction. In the presence of laminin, fibronectin, and varying types of collagen, FS cells showed marked changes in shape and specific proliferative activity; however, GFP-negative cells did not. On reverse transcription-PCR analysis and immunohistochemistry, FS cells were shown to express integrin subunits, which are the cell surface receptors for extracellular matrix (ECM). In the anterior pituitary gland, FS cells and the various types of hormone-producing cells generate a unique topography in the presence of basement membrane components and interstitial collagens. The novel characteristics of FS cells observed in the present study suggest that in the anterior pituitary gland, FS cells play important roles in determining and/or maintaining local cellular arrangement in the presence of ECM components.

[Apoplectic macroadenomas: the outcome of the residual pituitary gland]

BACKGROUND AND PURPOSE

The purpose of this retrospective study was to assess the MRI aspects and the function of the residual pituitary gland (RPG) after surgical decompression of an apoplectic pituitary macroadenoma, and to attempt to answer the question of whether an intra-adenomatous apoplexy necessarily leads to hypophyseal apoplexy.

METHODS

Between 1992 and 2008, 150 pituitary macroadenomas were surgically treated via the trans-sphenoidal approach, 19 of which presented an apoplectic feature (13%). They were subdivided into three groups: pure hemorrhage, hemorrhagic infarction, and ischemic infarction. The imaging was studied after surgery to identify the RPG and establish a correlation with the endocrine status.

RESULTS

After surgery five of 19 patients had normal adenohypophyseal function (27%), eight (42%) had panhypopituitarism, and six (31%) complete or partial corticotropic hypopituitarism. The RPG was identified on MRI in 13 patients (69%), four of them (31%) with normal adenohypophyseal function. The RPG was clearly identified intraoperatively in nine patients (47%), four of whom (44%) had normal adenohypophyseal function. One patient presented preoperative diabetes insipidus, which disappeared immediately after surgery, and two other patients developed postoperative diabetes insipidus: in one patient it quickly declined and in the other one it persisted, requiring replacement. According to the radiological classification of Hardy and Vezina modified by the Mohr (Mohr et Hardy, 1982) grade, the patients were subdivided up as follows: one grade II-0, four grade II-A, 11 grade II-B, two grade C, and one grade IV-B+D.

CONCLUSION

The repercussions of adenomatous apoplexy on the RPG is significant: only 27% of the patients retained normal pituitary function. Furthermore, although the RPG was identified on the MRI in more than two-thirds of the cases, more than half had adenohypophyseal failure: therefore, the visualization of a RPG does not mean that its functions are preserved. The involvement of the neurohypophysis is much rarer: one patient of 19 (5%). The implications of the ischemic or compressive damage on the normal pituitary gland are discussed.

Should anterior pituitary function be tested during follow-up of all patients presenting at the emergency department because of traumatic brain injury?

CONTEXT

A wide range (15-56%) of prevalences of anterior pituitary insufficiency are reported in patients after traumatic brain injury (TBI). However, different study populations, study designs, and diagnostic procedures were used. No data are available on emergency-department-based cohorts of TBI patients.

OBJECTIVE

To assess the prevalence of pituitary dysfunction in an emergency-department-based cohort of TBI patients using strict endocrinological diagnostic criteria.

METHODS

Of all the patients presenting in the emergency department with TBI over a 2-year period, 516 matched the inclusion criteria. One hundred and seven patients (77 with mild TBI and 30 with moderate/severe TBI) agreed to participate. They were screened for anterior pituitary insufficiency by GHRH-arginine testing, evaluation of fasting morning hormone levels (cortisol, TSH, free thyroxine, FSH, LH, and 17beta-estradiol or testosterone), and menstrual history 3-30 months after TBI. Abnormal screening results were defined as low peak GH to GHRH-arginine, or low levels of any of the end-organ hormones with low or normal pituitary hormone levels. Patients with abnormal screening results were extensively evaluated, including additional hormone provocation tests (insulin tolerance test, ACTH stimulation test, and repeated GHRH-arginine test) and assessment of free testosterone levels.

RESULTS

Screening results were abnormal in 15 of 107 patients. In a subsequent extensive endocrine evaluation, anterior pituitary dysfunction was diagnosed in only one patient (partial hypocortisolism).

CONCLUSION

By applying strict diagnostic criteria to an emergency-department-based cohort of TBI patients, it was shown that anterior pituitary dysfunction is rare (<1%). Routine pituitary screening in unselected patients after TBI is unlikely to be cost-effective.

Estrogen receptors and signaling pathways in lactotropes and somatotropes

Estrogens are crucial determinants in the regulation of anterior pituitary function and maintenance of tissue homeostasis. Estrogen actions in this gland are exerted through both classical and non-classical mechanisms of action. This review summarizes the expression of classical α- and β-estrogen receptors and variant isoforms of estrogen receptors in anterior pituitary cell subpopulations. We also analyze estrogen receptor signaling pathways involved in estrogenic actions in the anterior pituitary gland, especially in lactotropes and somatotropes. Complex interactions between multiple signaling pathways are involved in estrogen regulation of hormone secretion, cell proliferation and cell death in this gland. Insight into these pituitary responses to estrogens would help to understand pituitary function and tumorigenesis.

Excitatory and inhibitory effects of prolactin release activated by nerve stimulation in rat anterior pituitary

BACKGROUND

A series of studies showed the presence of substantial amount of nerve fibers and their close relationship with the anterior pituitary gland cells. Our previous studies have suggested that aside from the classical theory of humoral regulation, the rat anterior pituitary has direct neural regulation on adrenocorticotropic hormone release. In rat anterior pituitary, typical synapses are found on every type of the hormone-secreting cells, many on lactotrophs. The present study was aimed at investigating the physiological significance of this synaptic relationship on prolactin release.

METHODS

The anterior pituitary of rat was sliced and stimulated with electrical field in a self-designed perfusion chamber. The perfusate was continuously collected in aliquots and measured by radioimmunoassay for prolactin levels. After statistic analysis, differences of prolactin concentrations within and between groups were outlined.

RESULTS

The results showed that stimulation at frequency of 2 Hz caused a quick enhancement of prolactin release, when stimulated at 10 Hz, prolactin release was found to be inhibited which came slower and lasted longer. The effect of nerve stimulation on prolactin release is diphasic and frequency dependent.

CONCLUSIONS

The present in vitro study offers the first physiological evidence that stimulation of nerve fibers can affect prolactin release in rat anterior pituitary. Low frequency stimulation enhances prolactin release and high frequency mainly inhibits it.

How to make a teleost adenohypophysis: molecular pathways of pituitary development in zebrafish

The anterior pituitary gland, or adenohypophysis (AH), represents the key component of the vertebrate hypothalamo-hypophyseal axis, where it functions at the interphase of the nervous and endocrine system to regulate basic body functions like growth, metabolism and reproduction. For developmental biologists, the adenohypophysis serves as an excellent model system for the studies of organogenesis and differential cell fate specification. Previous research, mainly done in mouse, identified numerous extrinsic signaling cues and intrinsic transcription factors that orchestrate the gland's developmental progression. In the past years, the zebrafish has emerged as a powerful tool to elucidate the genetic networks controlling vertebrate development, behavior and disease. Based on mutants isolated in forward genetic screens and on gene knock-downs using morpholino oligonucleotide (oligo) antisense technology, our current understanding of the molecular machinery driving adenohypophyseal ontogeny could be considerably improved. In addition, comparative analyses have shed further light onto the evolution of this rather recently invented organ. The goal of this review is to summarize current knowledge of the genetic and molecular control of zebrafish pituitary development, with special focus on most recent findings, including some thus far unpublished data from our own laboratory on the transcription factor Six1. In addition, zebrafish data will be discussed in comparison with current understanding of adenohypophysis development in mouse.

Disposal of cell debris from surplus lactotrophs of pituitary gland

In rats submitted to physiological and experimental stimulation of lactotrophic secretion, as in pregnancy and lactation as well as after estrogen treatment, there is a remarkable proliferation of lactotrophs in the pituitary gland. After interruption of the stimuli, this situation is reversed to basal conditions via a massive programmed cell death of the surplus lactotrophs. The regressive changes occurring in lactotrophs are autolytic in nature, until the advanced stages of degeneration when the cell debris generated by this process are engulfed by phagocytes exhibiting the morphological characteristics of stellate cells. These cells can be seen within the anterior pituitary parenchyma adherent to the wall of capillaries and in the lumen of blood vessels. The number of stellate cells with engulfed lactotroph cell remnants is relatively small in comparison to the massive cell death, an observation that suggests a rapid clearance of cell debris and phagocytic cells from the pituitary parenchyma into the blood stream. The migration of stellate cells from the adenohypophysis involves the degradation of the basement membrane and rearrangement of the capillary wall components. The final disposal of cell debris of regressing lactotrophs within the anterior pituitary therefore appears to be effected by coordination of a pituitary and systemic mononuclear phagocytic system.

The long-term effect of low protein diet on the somatostatin hypothalamic neuronal system and the pituitary growth hormone cells in growing ewe

Three-month old Polish Lowland female lambs were fed isocaloric diets containing 14.2% (standard) or 8.1% of proteins for twenty weeks. Changes in body weight were characteristic for normal growth performance in all animals, but daily body gain calculated for the whole experimental period was significantly lower in lambs fed a low protein diet (87.9 +/- 13.5 and 158 +/- 13.8 g/day, respectively). Two series of blood collections (4 hrs with 15 min interval) were performed at age of 21 and 26 weeks in order to analyze the growth hormone (GH) concentration in the peripheral blood. The results obtained by radioimmunoassay showed that at both ages the mean concentration of GH was significantly higher in the group fed a low protein diet (4.84 +/- 2.23 and 3.68 +/- 1.86 vs 1.46 +/- 0.72 and 1.48 +/- 0.44 ng/ml, respectively) and this difference was associated with significant elevation of the pulse amplitude (3.83 +/- 4.23 and 4.54 +/- 3.06 vs 1.48 +/- 1.11 and 1.31 +/- 0.68 ng/ml, respectively). Using immunocytochemistry, the somatostatin in the hypothalamus and the GH in the pituitary cells were analyzed in all animals slaughtered at age of 8 months. Lowering the content of dietary proteins diminished markedly the content of immunoreactive somatostatin in the median eminence (ME) and augmented the concentrations of the immunoproduct in the somatostatin perikarya. In the pituitary gland, a marked increase of the number of GH-producing cells was observed. The results obtained indicate that chronic restriction of dietary proteins, irrespective of sufficient energy supply, augment the secretion of GH via a decrease in the hypothalamic somatostatin output due to the suppression of its axonal transport.

Seasonal variations of gonadotropins in the pars distalis male Viscacha pituitary. Effect of chronic melatonin treatment

The gonadotropes, LH and FSH cells, were immunohistochemically identified in the pituitary pars distalis of the adult male viscacha (Lagostomus maximus maximus) using specific antibodies against hLHbeta and hFSHbeta with the streptavidin-biotin-peroxidase complex. The distribution, size and percentage immunopositive area of these cells were analyzed by image analysis in viscachas captured during the annual reproductive cycle and after the chronic administration of melatonin. The LHbeta and FSHbeta cells showed seasonal changes in the distribution, size and percentage immunopositive area. The LHbeta cells were found widely distributed throughout the pars distalis during the reproductive period, and they were found in the ventro-medial region in the pars distalis during the gonadal regression and gonadal recovery periods. The LHbeta cells reached the largest size and immunopositive area during the reproductive period and the smallest size and immunopositive area during the gonadal regression period. The FSHbeta cells were found in the ventro-medial region during reproductive and gonadal regression periods. The FSHbeta cells were found widely distributed throughout the pars distalis during the gonadal recovery period when they showed the maximum percentage immunopositive area. A decrease in the size of LHbeta and FSHbeta cells was observed after the chronic administration of melatonin. Moreover, it produces a decrease in the immunopositive area occupied by the LHbeta cells but not in the immunopositive area occupied by the FSHbeta cells. Our results show great activity of LHbeta and FSHbeta cells in different moments of the annual reproductive cycle demonstrating that these cells do not secrete in parallel. Moreover, melatonin acts differentially on the activity of the gonadotrope cells.

The trophic effects of oestrogen on male rat anterior pituitary lactotrophs

Rapid but often transient changes in mitotic and apoptotic activity are important components of the pituitary response to changes in the hormonal environment. For example, bilateral adrenalectomy and orchidectomy each result in a wave of increased mitosis lasting approximately 1 week, mediated by the same population of trophically active and, to a large extent, endocrinologically inactive cells. By contrast to these tonic inhibitors of pituitary trophic activity, reports of a progressive increase in lactotroph numbers during pregnancy suggest that oestrogen is a potent and persistent pituitary mitogen. By comparing the amplitude and duration of male rat anterior pituitary mitotic responses to oestrogen treatment, to adrenalectomy, and to a combination of the two, the present study aimed to further clarify the characteristics of the oestrogen-induced trophic response, in particular whether lactotrophs are the predominant cell type involved. Adrenalectomy produced a wave of increased mitotic activity, which resolved within 7 days as expected, whereas oestrogen induced a significant increase in mitotic activity, which was sustained for the 14-day duration of the study. The trophic effects of combining adrenalectomy and oestrogen treatment were not additive in that the statistically insignificant upward trend in mitotic index during the first few days compared to oestrogen treatment alone was entirely abolished by oestrogen pre-treatment. The increase in mitotic activity in lactotrophs induced by oestrogen either with or without adrenalectomy did not result in an increase in the relative size of the prolactin-positive compared to prolactin-negative pituitary parenchymal cell numbers by the end of the study. Despite the marked increase in the lactotroph population that is reported during pregnancy, these data indicate that at least the early (i.e. within 2 weeks) mitotic response to pharmacological doses of oestrogen increases mitotic activity in the lactotroph subpopulation by only 5-8% relative to other cellular subpopulations. Unexpectedly, the mitotic response to oestrogen principally occurs in non-prolactin-containing cells and results in the recruitment, amongst other trophically responsive populations, of the entire subpopulation of prolactin-, adrenocorticotrophic hormone- and luteinising hormone-negative cells that respond mitotically to adrenalectomy. Oestrogen therefore has a previously unrecognised non-cell type-specific trophic effect in the pituitary that obscures the relative expansion of the lactotroph population by inducing concurrent increases in numbers of prolactin-negative cells, the nature of which at least in part remains to be determined.

Thyroid hormones and the adrenergic nervous system

This paper reviews the various possible relationships between thyroid hormones and the adrenergic nervous system. These concern the sympathetic influence on thyroid hormone secretion, thyroid hormone - induced changes of sympathetic activity or adrenoceptor changes - the effects of catecholamines on thyroid hormone metabolism and, finally, the clinical benefits of beta-adrenoceptor blocking drugs on symptoms and signs of hyperthyroidism.

Estrogens exert a rapid apoptotic action in anterior pituitary cells

It is now accepted that estrogens not only stimulate lactotrope proliferation but also sensitize anterior pituitary cells to proapoptotic stimuli. In addition to their classical mechanism of action through binding to intracellular estrogen receptors (ERs), there is increasing evidence that estrogens exert rapid actions mediated by cell membrane-localized ERs (mERs). In the present study, we examined the involvement of membrane-initiated steroid signaling in the proapoptotic action of estradiol in primary cultures of anterior pituitary cells from ovariectomized rats by using estren, a synthetic estrogen with no effect on classical transcription and a cell-impermeable 17beta-estradiol conjugate (E2-BSA). Both compounds induced cell death of anterior pituitary cells after 60 min of incubation as assessed by flow cytometry and the [3-(4,5-dimethylthiazol-2-yl)]-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay. Estren, E2, and E2-BSA induced apoptosis of lactotropes and somatotropes as evaluated by the deoxynucleotidyltransferase-mediated dUTP nick end-labeling assay and immunodetection of prolactin (PRL) and growth hormone (GH). The proapoptotic effect of E2-BSA was abrogated by ICI-182,780, an antagonist of ERs. The expression of membrane-associated ERalpha was observed in PRL- and GH-bearing cells. Our results indicate that estradiol is able to exert a rapid apoptotic action in anterior pituitary cells, especially lactotropes and somatotropes, by a mechanism triggered by mERs. This mechanism could be involved in anterior pituitary cell turnover.

Novel expression of type 1 corticotropin-releasing hormone receptor in multiple endocrine cell types in the murine anterior pituitary

The CRH family of ligands signals via two distinct receptors, CRH-R1 and CRH-R2. Previous studies localized CRH-R1 and CRH-R2 to a subset of anterior pituitary corticotropes and gonadotropes, respectively. However, numerous studies have indicated that stress and CRH activity can alter the secretion of multiple anterior pituitary hormones, suggesting a broader expression of the CRH receptors in pituitary. To examine this hypothesis, the in vivo expression of CRH-R1 and CRH-R2 mRNA was further characterized in adult mouse pituitary. Quantitative RT-PCR analysis demonstrated that CRH-R1 mRNA is greater than 100-fold more abundant than CRH-R2 mRNA in male and female mouse pituitaries. Dual in situ hybridization analysis identified cell-specific CRH-R1 expression in the anterior pituitary. At least half of the CRH-R1-positive cells expressed proopiomelanocortin-mRNA (50% in females; 70% in males). In females, a significant percentage of the cells expressing CRH-R1 also expressed transcript for prolactin (40%), LHbeta (10%), or TSH (3%), all novel sites of CRH-R1 expression. Similarly in males, a percentage of CRH-R1-positive cells expressed prolactin (12%), LHbeta (13%), and TSH (5%). RT-PCR studies with immortalized murine anterior pituitary cell lines showed CRH-R1 and/or CRH-R2 expression in corticotropes (AtT-20 cells), gonadotropes (alphaT3-1 and LbetaT2 cells), and thyrotropes (alphaTSH cells). Whereas CRH-R1 expression in corticotropes is well established, the presence of CRH-R1 mRNA in a subset of lactotropes, gonadotropes, and thyrotropes establishes these cell types as novel sites of murine CRH-R1 expression and highlights the pituitary as an important site of interaction between the hypothalamus-pituitary-adrenal and multiple endocrine axes.

Estradiol increases the Bax/Bcl-2 ratio and induces apoptosis in the anterior pituitary gland

BACKGROUND

Estrogens are recognized as acting as modulators of pituitary cell renewal, sensitizing cells to mitogenic and apoptotic signals, thus participating in anterior pituitary homeostasis during the estrous cycle. The balance of pro- and antiapoptotic proteins of the Bcl-2 family is known to regulate cell survival and apoptosis.

AIMS

In order to understand the mechanisms underlying apoptosis during the estrous cycle, we evaluated the expression of the proapoptotic protein Bax and the antiapoptotic proteins Bcl-2 and Bcl-xL in the anterior pituitary gland in cycling female rats as well as the influence of estradiol on the expression of these proteins in anterior pituitary cells of ovariectomized rats.

METHODS/RESULTS

As determined by Western blot, the expression of Bax was higher in anterior pituitary glands from rats at proestrus than at diestrus I, Bcl-2 protein levels showed no difference and Bcl-xL expression was lower, thus increasing the Bax/Bcl-2 ratio at proestrus. Assessed by annexin V binding and flow cytometry, the percentage of apoptotic anterior pituitary cells was higher in rats at proestrus than at diestrus I. Chronic estrogen treatment in ovariectomized rats enhanced the Bax/Bcl-2 ratio and induced apoptosis. Moreover, incubation of cultured anterior pituitary cells from ovariectomized rats with 17beta-estradiol for 24 h increased the Bax/Bcl-2 ratio, decreased Bcl-xL expression and induced apoptosis.

CONCLUSION

Our results demonstrate that estradiol increases the ratio between proapoptotic and antiapoptotic proteins of the Bcl-2 family. This effect could participate in the sensitizing action of estrogens to proapoptotic stimuli and therefore be involved in the high apoptotic rate observed at proestrus in the anterior pituitary gland.