The pars tuberalis of the hypophysis: a modulator of the pars distalis?

1992 ◽  
Vol 126 (4) ◽  
pp. 285-290 ◽  
Author(s):  
Werner H Wittkowski ◽  
Andreas H Schulze-Bonhage ◽  
Tobias M Böckers
Keyword(s):  
Close Contact ◽  
Melatonin Receptors ◽  
Portal System ◽  
Secretory Cells ◽  
Specific Cell ◽  
Pars Tuberalis ◽  
Pars Distalis ◽  
Functional Connection ◽  
Morphological Alterations ◽  
Functional Changes

The pineal hormone melatonin is known to influence circadian systems. Melatonin is also ascribed to mediate photoperiodic effects on the regulation of the hypothalamo-hypophyseal-gonadal axis. Other endocrine actions, especially a thyrotropic influence, have been postulated. Site and mechanism of action of melatonin, however, are still matters of speculation. In search of a functional cascade of (i) photoperiodic stimuli, (ii) their hormonal messenger melatonin, and (iii) endocrine targets, the pars tuberalis has gained a key position. The recent discovery and characterization of melatonin receptors located in the pars tuberalis of several species support such a functional significance. Earlier results point to a functional connection of the pars tuberalis with the pineal gland: the pars tuberalis is known for a pattern of differentiation distinctly different from other parts of the adenohypophysis. It contains a specific cell population with a morphology typical of peptide secreting cells. Like the hypothalamic nerve endings of the median eminence, they are in close contact with the primary plexus of the portal system. In contrast to secretory cells of the pars distalis, the specific cells of the pars tuberalis do not respond with morphological alterations to functional changes of peripheral endocrine glands. Yet, photoperiodic stimuli obviously influence morphology and functional activity of the pars tuberalis-specific cells. Investigations during recent years have led to the tentative conclusion that the pars tuberalis represents the hypophysial "receptor"for melatonin as the chemical messenger of photoperiodic stimuli. Depending on melatonin secretion pattern and melatonin receptivity, the pars tuberalis seems to modulate at least gonadotropic and thyrotropic activity of the pars distalis via a peptide hormone distributed in the pars distalis by the portal plexus. Such an intrahypophysial regulatory concept may explain the widespread actions of melatonin on endocrine targets.

scholarly journals Some Observations on the Cytology of the Adenohypophysis of the Non-parous Female Rabbit

1959 ◽  
Vol s3-100 (51) ◽  
pp. 463-482
Author(s):  
M. ALLANSON ◽  
C. L. FOSTER ◽  
G. MENZIES
Keyword(s):  
Proteolytic Enzymes ◽  
Portal System ◽  
Pars Intermedia ◽  
Pars Tuberalis ◽  
Pars Distalis ◽  
Electron Microscopic ◽  
Female Rabbit ◽  
Lipid Inclusions ◽  
Cytological Characteristics ◽  
Hypophysial Portal

Evidence is presented which suggests that in this animal the pars tuberalis may have some function in addition to acting as a bed for the hypophysial portal system, since its cells appear rich in RNA. The granules of the cells of the pars intermedia are shown to be PAS-positive, but this reaction, unlike that of the basiphil cells of the pars distalis proper and the zona tuberalis, is readily prevented by pretreatment of sections with proteolytic enzymes. A study of the basiphil cells of the pars distalis proper and of the zona tuberalis, based on cytological characteristics, size, and shape, provides some evidence for the existence of two, and possibly three, kinds of basiphil cell. The lipid inclusions of the adenohypophysial cells and their relationship to the Golgi elements are described, together with some brief preliminary observations upon the electron microscopic characteristics of acidophil and basiphil cells.

The development of melatonin-binding sites in the ovine fetus

1994 ◽  
Vol 142 (3) ◽  
pp. 475-484 ◽  
Author(s):  
R J A Helliwell ◽  
L M Williams
Keyword(s):  
G Protein ◽  
Binding Sites ◽  
Early Stage ◽  
Specific Binding ◽  
Melatonin Receptors ◽  
Pars Tuberalis ◽  
Dependent Manner ◽  
Pars Distalis ◽  
Specific Expression ◽  
Fetal Sheep

Abstract The pineal hormone, melatonin, is important in the timing of seasonal reproduction in the sheep. Melatonin of maternal origin readily crosses the placenta; its function in the fetal sheep is, however, unclear. To gain an insight into the role of melatonin in ovine development we have identified specific melatonin receptors throughout gestation using 2-[125I]iodomelatonin and quantitative in vitro autoradiography. Specific binding was found at the earliest time studied at 30 days of gestation, over the developing thyroid (term=145 days). At 31 days of gestation specific labelling was found over the thyroid and pituitary glands, the spinal nerves, nasal cavity and developing bronchi. This binding was diminished by over 50% in the presence of 10−4 m GTPγS (an analogue of guanosine triphosphate) indicating that the 2-[125I]iodomelatonin binding at this early stage of gestation represents a receptor coupled to a regulatory G-protein. By 40 days of gestation specific binding was found over the nasal epithelium, cochlear epithelium, regions of the brain, especially the hind brain and the vestibulocochlear and glossopharyngeal nerves, and both the pars distalis and pars tuberalis of the pituitary. As gestation proceeded, labelling over the pars distalis appeared to become more scattered in nature while that on the pars tuberalis remained consistent. Saturation studies of both the neuronal and pituitary binding sites at 121 days of gestation and in the newborn lamb revealed a single class of high-affinity binding sites with Kd values in the picomolar range. Also at 121 days of gestation, binding over the fetal pars tuberalis was diminished in a dose-dependent manner by GTPγS, again confirming that specific binding is indicative of a receptor coupled to a regulatory G-protein. These data demonstrate a potential for sensitivity to melatonin from early in gestation, as well as the developmentally specific expression of the melatonin receptor in certain tissues, and suggest a wider role for melatonin in ovine fetal development than previously considered. Journal of Endocrinology (1994) 142, 475–484

scholarly journals Identification, cellular and subcellular distribution of 21 and 72 kDa proteins (tuberalins?) secreted by specific cells of the pars tuberalis

2001 ◽  
Vol 168 (3) ◽  
pp. 363-379 ◽  
Author(s):  
M Guerra ◽  
EM Rodriguez
Keyword(s):  
Subcellular Distribution ◽  
Secretory Granules ◽  
Light And Electron Microscopy ◽  
Melatonin Receptors ◽  
Practical Reasons ◽  
Pars Tuberalis ◽  
Secretory Product ◽  
Pars Distalis ◽  
Beta Chain ◽  
Type 3

The cell types of the pars tuberalis (PT) are the follicular cells, the pars distalis cells and the so-called PT-specific cells. The latter are distinct endocrine cells displaying melatonin receptors. Although the nature of the secretory product(s) of the PT-specific cells has not yet been clarified, the function of these cells has started to be unfolded. For practical reasons, previous authors have designated the, as yet, unidentified PT hormone(s) as tuberalin(s). PT-specific cells synthesise the common alpha subunit of the pars distalis glycoprotein hormones, and it has been suggested that tuberalin would correspond to the beta chain of a specific glycoprotein secreted by these cells. The aims of the present investigation were to identify the compounds secreted by the specific cells of bovine PT, and to establish their cellular and subcellular distribution. For this purpose, proteins secreted into the culture medium of PT explants were separated by electrophoresis and used to raise antibodies. Two of these proteins, with an apparent molecular mass of 21 and 72, generated antibodies (Ab-21 and Ab-72) that differentially immunoreacted with PT-specific cells. These two antibodies were used for immunoblotting of conditioned medium and of PT explants, and for light and electron microscopy immunocytochemistry. In immunoblots, Ab-21 reacted with compounds of 21, 22, 47 and 52 kDa, whereas Ab-72 revealed a compound of 72 kDa only. Ab-72 immunoreactive material corresponded to a protein, here designated as tuberalin I, secreted by a small population of PT-specific cells (type 2 cells), and stored in 140 nm secretory granules. Immunoreactive tuberalin I was missing from bovine pars distalis and from rat PT. The predominant population of PT-specific cells (type 3 cells) secreted and stored, within 280 nm secretory granules, an Ab-21 immunoreactive protein, here designated as tuberalin II. All cells of rat PT immunoreacted with Ab-21. In the cells of bovine and rat PT, immunoreactive tuberalin II was mostly confined to a paranuclear spot; this spot also bound wheat germ agglutinin and reacted with an antibody against the alpha chain of glycoprotein pars distalis hormones. It is suggested that tuberalin II would correspond to the beta chain of a specific glycoprotein secreted by type 3 PT-specific cells. In bovine PT, the cells displaying immunoreactive tuberalins I and II did not react with any of the antibodies against pars distalis hormones.

A carnivore species (Canis familiaris) expresses circadian melatonin rhythm in the peripheral blood and melatonin receptors in the brain

1994 ◽  
Vol 131 (2) ◽  
pp. 191-200 ◽  
Author(s):  
Bojidar Stankov ◽  
Morten Møller ◽  
Valeria Lucini ◽  
Simona Capsoni ◽  
Franco Fraschini
Keyword(s):  
Peripheral Blood ◽  
Binding Sites ◽  
Specific Binding ◽  
Canis Familiaris ◽  
Melatonin Receptors ◽  
Pars Tuberalis ◽  
Pars Distalis ◽  
Melatonin Rhythm ◽  
Carnivore Species ◽  
The Brain

Stankov B, Møller, M, Lucini V, Capsoni S, Fraschini F. A carnivore species (Canis familiaris) expresses circadian melatonin rhythm in the peripheral blood and melatonin receptors in the brain. Eur J Endocrinol 1994;131:191–200. ISSN 0804–4643 Dogs kept under controlled photoperiodic conditions of 12 h light and 12 h dark expressed a clear diurnal melatonin rhythm in the peripheral blood, with a swift peak restricted to the late part of the scotophase. The highest density of high-affinity, G-protein-linked 2-[125I]iodomelatonin binding sites was found in the pars tuberalis of the pituitary gland. Binding sites were found also in the pars distalis, and light microscopy/high-resolution autoradiography showed that binding was located exclusively over the chromophobe and basophilic cells forming the adenopituitary zona tuberalis, well developed in this species, and extending into the gland as a continuation of pars tuberalis. Cords of basophilic cells located in the pars distalis proper also expressed high receptor density. The eosinophils in the adenohypophysis and the neural lobe were devoid of binding. Heavily labeled were the external laminar and the mitral cell layers of the olfactory bulbs, but no binding was detected in the filae nervi olfactorii or tractus olfactorius. The hypothalamic suprachiasmatic nuclei were discernible clearly. Quantitative autoradiography inhibition experiments revealed that the apparent melatonin inhibitory constant (ic50) in all those areas was around 0.1 nmol/l, which is a physiologically appropriate value considering the peripheral blood melatonin levels. Co-incubation with guanosine 5′-O-(3-thiotriphosphate) (GTPΓS) led to a consequential decrease in the binding density. The specific binding observed in other areas (hippocampus, frontal, parietal, occipital cortex and cerebellum) was rather weak, diffuse and could not be attributed to a particular layer; the apparent ic50 for melatonin was about 1 μmol/l, and co-incubation with GTPΓS did not modify the binding density. Collectively, these data show that the dog posesses all the prerequisites for an efficient network adapted to photoperiodic time measurements. A circadian melatonin signal in the peripheral blood and an apparently functional readout receptor system located in key positions within the brain are both present in this species. Bojidar Stankov, Chair of Chemotherapy, Department of Pharmacology, University of Milan, 32 Via Vanvitelli, 20129 Milano, Italy

Correlative transmission and high-resolution scanning electron microscopic studies on pituitary cells

1990 ◽  
Vol 48 (3) ◽  
pp. 20-21
Author(s):  
S. Tai
Keyword(s):  
Cell Types ◽  
Depth Of Field ◽  
Secretory Cells ◽  
Specific Cell ◽  
Pituitary Cells ◽  
Electron Microscopic ◽  
3 Dimensional ◽  
Microscopic Studies ◽  
Structure And Activity ◽  
Intracellular Structure

Extensive cytological and histological research, correlated with physiological experimental analysis, have been done on the anterior pituitaries of many different vertebrates which have provided the knowledge to create the concept that specific cell types synthesize, store and release their specific hormones. These hormones are stored in or associated with granules. Nevertheless, there are still many doubts - that need further studies, specially on the ultrastructure and physiology of these endocrine cells during the process of synthesis, transport and secretion, whereas some new methods may provide the information about the intracellular structure and activity in detail.In the present work, ultrastructural study of the hormone-secretory cells of chicken pituitaries have been done by using TEM as well as HR-SEM, to correlate the informations obtained from 2-dimensional TEM micrography with the 3-dimensional SEM topographic images, which have a continous surface with larger depth of field that - offers the adventage to interpretate some intracellular structures which were not possible to see using TEM.

Constipation in patients with comorbidity

2021 ◽  
Author(s):  
Е.А. Лялюкова ◽  
Е.Н. Логинова
Keyword(s):  
Gastrointestinal Tract ◽  
Neurological Diseases ◽  
The Elderly ◽  
Lifestyle Changes ◽  
Secretory Cells ◽  
Endocrine Disorders ◽  
Silver Age ◽  
Functional Changes ◽  
Slowing Down ◽  
Age Related

Пациенты пожилого и старческого возраста в силу физиологических причин и коморбидной патологии имеют высокий риск развития запора. Причиной запора чаще всего являются алиментарные факторы и возраст-ассоциированные заболевания и повреждения толстой кишки (дивертикулярная болезнь, ишемия толстой кишки, ректоцеле, геморрой и другие); метаболические, эндокринные расстройства и неврологические заболевания. Возрастные анатомические, структурные и функциональные изменения пищеварительной системы вносят свой вклад в развитие запоров у пожилых. У пациентов «серебряного возраста» отмечено увеличение длины желудочно-кишечного тракта, прогрессирование атрофических, склеротических изменений слизистой и подслизистой оболочки, снижение количества секреторных клеток, замещение мышечных волокон соединительной тканью и др. Все это способствует замедлению транзита по желудочно-кишечному тракту и нарушению акта дефекации. Образ жизни пожилых людей также может способствовать развитию запора. Низкое содержание в рационе клетчатки, употребление преимущественно термически обработанной пищи, нарушение ритма питания (прием пищи 1-2 раза в день) являются одной из причин возникновения запоров у пожилых, чему способствуют трудности при жевании вследствие стоматологических проблем. Колоноскопия показана всем пациентам пожилого и старческого возраста с запором, а выявление «симптомов тревоги» необходимо проводить при каждом визите пациента. Вне зависимости от причины вторичного запора, все пациенты должны осуществлять ряд мер немедикаментозного характера, включающих изменение образа жизни, диету с включением достаточного количества клетчатки и потребление жидкости. Физические методы лечения могут включать лечебную гимнастику, массаж толстой кишки для стимуляции моторной активности кишечника в определенное время. При неэффективности немедикаментозных мероприятий рекомендуется использование осмотических слабительных, а также средств, увеличивающих объем каловых масс. Высокая эффективность и безопасность псиллиума позволяет рекомендовать его в лечении хронического запора у пожилых пациентов. Elderly and senile patients, due to physiological reasons and comorbid pathology, have a high risk of constipation. The causes of constipation are more often nutritional factors and age-associated diseases and damage to the colon (diverticular disease, colon ischemia, rectocele, hemorrhoids, and others); metabolic, endocrine disorders and neurological diseases. Age-related anatomical, structural and functional changes in the digestive system contribute to the development of constipation in the elderly. In patients of «silver age», there was an increase in the length of the gastrointestinal tract, the progression of atrophic, sclerotic changes in the mucous and submucosa, a decrease in the number of secretory cells, replacement of muscle fibers with connective tissue, etc. All this contributes to the slowing down of transit through the gastrointestinal tract and the violation of the act of defecation. Elderly lifestyles can also contribute to constipation. The low fiber content in the diet, the use of mainly thermally processed food, the violation of the rhythm of the diet (eating 1-2 times a day) are one of the causes of constipation in the elderly, which is facilitated by difficulty in chewing due to dental problems. Colonoscopy is ordered for all elderly and senile patients with constipation, and the identification of «anxiety symptoms» should be carried out at each patient visit. Regardless of the cause of secondary constipation, all patients should take a number of non-pharmacological measures, including lifestyle changes, a diet with adequate fiber, and fluid intake. Physical therapies may include medical gymnastics, colon massage to stimulate bowel movement at specific times. If non-drug measures are ineffective, it is recommended to use osmotic laxatives, as well as agents that increase the volume of feces. Psyllium supplementation is recommended for treatment of chronic constipation in elderly patients due to its high efficacy and safety.

In vivo changes in the intestinal reflexes and the response to CCK in the inflamed small intestine of the rat

2000 ◽  
Vol 279 (3) ◽  
pp. G543-G551 ◽  
Author(s):  
D. Torrents ◽  
P. Vergara
Keyword(s):  
Small Intestine ◽  
Motor Activity ◽  
Intestinal Inflammation ◽  
Trichinella Spiralis ◽  
Motor Responses ◽  
Morphological Alterations ◽  
Functional Changes ◽  
Residual Response ◽  
Abnormal Motor

Functional motor changes and morphological alterations have been associated with intestinal inflammation. The aim of our study was to evaluate functional alterations of intestinal reflexes and of the responses to CCK in the Trichinella spiralis model of intestinal inflammation. Rats were prepared with strain gauges and electrodes in the small intestine to evaluate spontaneous motor activity, the ascending contraction of the peristaltic reflex, and the motor responses to CCK-8 infusion. Infected animals showed increased motor activity at the duodenum and jejunum but not at the ileum. Ascending contraction was increased in both duodenum and ileum. Ascending excitation after Nω-nitro-l-arginine was still increased as well as the residual response after atropine. Response to CCK-8 during intestinal inflammation was changed in the jejunum, in which it turned from the inhibition shown in healthy animals to excitation. NADPH-diaphorase staining did not show any changes between distribution and density of positive neurons in either healthy or infected animals. In conclusion, intestinal inflammation induces functional changes in the motor activity that could explain the abnormal motor responses observed in inflammatory disorders.

scholarly journals Clock genes in calendar cells as the basis of annual timekeeping in mammals--a unifying hypothesis

2003 ◽  
Vol 179 (1) ◽  
pp. 1-13 ◽  
Author(s):  
GA Lincoln ◽  
H Andersson ◽  
A Loudon
Keyword(s):  
Gene Expression ◽  
Molecular Mechanism ◽  
Clock Genes ◽  
Prolactin Secretion ◽  
Secretory Cells ◽  
Dark Phase ◽  
Pars Tuberalis ◽  
Cry Protein ◽  
Wide Range

Melatonin-based photoperiod time-measurement and circannual rhythm generation are long-term time-keeping systems used to regulate seasonal cycles in physiology and behaviour in a wide range of mammals including man. We summarise recent evidence that temporal, melatonin-controlled expression of clock genes in specific calendar cells may provide a molecular mechanism for long-term timing. The agranular secretory cells of the pars tuberalis (PT) of the pituitary gland provide a model cell-type because they express a high density of melatonin (mt1) receptors and are implicated in photoperiod/circannual regulation of prolactin secretion and the associated seasonal biological responses. Studies of seasonal breeding hamsters and sheep indicate that circadian clock gene expression in the PT is modulated by photoperiod via the melatonin signal. In the Syrian and Siberian hamster PT, the high amplitude Per1 rhythm associated with dawn is suppressed under short photoperiods, an effect that is mimicked by melatonin treatment. More extensive studies in sheep show that many clock genes (e.g. Bmal1, Clock, Per1, Per2, Cry1 and Cry2) are expressed in the PT, and their expression oscillates through the 24-h light/darkness cycle in a temporal sequence distinct from that in the hypothalamic suprachiasmatic nucleus (central circadian pacemaker). Activation of Per1 occurs in the early light phase (dawn), while activation of Cry1 occurs in the dark phase (dusk), thus photoperiod-induced changes in the relative phase of Per and Cry gene expression acting through PER/CRY protein/protein interaction provide a potential mechanism for decoding the melatonin signal and generating a long-term photoperiodic response. The current challenge is to identify other calendar cells in the central nervous system regulating long-term cycles in reproduction, body weight and other seasonal characteristics and to establish whether clock genes provide a conserved molecular mechanism for long-term timekeeping.

scholarly journals Astrocytes and Adenosine A2A Receptors: Active Players in Alzheimer’s Disease

2021 ◽  
Vol 15 ◽  
Author(s):  
Cátia R. Lopes ◽  
Rodrigo A. Cunha ◽  
Paula Agostinho
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Amyloid Β ◽  
The Elderly ◽  
Synaptic Function ◽  
Morphological Alterations ◽  
Functional Changes ◽  
A2a Receptors ◽  
Novel Therapeutic Strategies

Astrocytes, through their numerous processes, establish a bidirectional communication with neurons that is crucial to regulate synaptic plasticity, the purported neurophysiological basis of memory. This evidence contributed to change the classic “neurocentric” view of Alzheimer’s disease (AD), being astrocytes increasingly considered a key player in this neurodegenerative disease. AD, the most common form of dementia in the elderly, is characterized by a deterioration of memory and of other cognitive functions. Although, early cognitive deficits have been associated with synaptic loss and dysfunction caused by amyloid-β peptides (Aβ), accumulating evidences support a role of astrocytes in AD. Astrocyte atrophy and reactivity occurring at early and later stages of AD, respectively, involve morphological alterations that translate into functional changes. However, the main signals responsible for astrocytic alterations in AD and their impact on synaptic function remain to be defined. One possible candidate is adenosine, which can be formed upon extracellular catabolism of ATP released by astrocytes. Adenosine can act as a homeostatic modulator and also as a neuromodulator at the synaptic level, through the activation of adenosine receptors, mainly of A1R and A2AR subtypes. These receptors are also present in astrocytes, being particularly relevant in pathological conditions, to control the morphofunctional responses of astrocytes. Here, we will focus on the role of A2AR, since they are particularly associated with neurodegeneration and also with memory processes. Furthermore, A2AR levels are increased in the AD brain, namely in astrocytes where they can control key astrocytic functions. Thus, unveiling the role of A2AR in astrocytes function might shed light on novel therapeutic strategies for AD.

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