Functional importance of blood flow dynamics and partial oxygen pressure in the anterior pituitary

Neuropeptide oxytocin facilitates its own brain-to-periphery uptake

The hypothalamo-neurohypophyseal system is a neuroendocrine conduit through which the neurohormones oxytocin and arginine vasopressin are released from the brain into the general circulation, influencing functions like salt balance and reproduction. However, the precise mechanism for rapid neurohormone transport to the periphery remains unclear. We show, using live imaging in zebrafish, that both hyperosmotic physiological challenge and optogenetic stimulation of oxytocin neurons elicit a local increase in neurohypophyseal blood flow velocities and a change in capillary diameter. This response is dictated by the geometry of the hypophyseal vascular microcircuit. Genetic ablation of oxytocin neurons and inhibition of oxytocin receptor signaling attenuate the changes in capillary blood flow and diameter. Both the osmotic challenge and oxytocin neuronal activation elicit a local rise in neurohypophyseal capillary permeability in an oxytocin-signaling-dependent manner. We propose that oxytocin-dependent neurovascular coupling facilitates its efficient uptake into the blood circulation, suggesting a self-perpetuating stimulus-secretion-uptake mechanism for peripheral hormone transfer.

Indocyanine green angiography to evaluate immediate hypoparathyroidism after thyroid cancer surgery

INTRODUCTION

Indocyanine green (ICG) fluorescence angiography has been introduced to assess parathyroid perfusion intraoperatively. This study aimed to evaluate whether the number of well-vascularized parathyroid glands identified using ICG fluorescence could predict the maintenance of adequate parathyroid hormone (PTH) levels in the immediate postoperative period.

MATERIALS AND METHODS

A retrospective study was conducted on 150 consecutive patients who underwent total thyroidectomy for papillary thyroid cancer between March 2021 and December 2023. Parathyroid perfusion was assessed using ICG fluorescence angiography, and glands were classified on a scale from 0 (no vascularization) to 2 (good vascularization). PTH levels were measured 1 h postoperatively, and biochemical hypoparathyroidism was defined as PTH < 15 pg/dL. Statistical analyses were performed using Fisher's exact test and Chi-square test, with p < 0.05 considered significant.

RESULTS

Transient biochemical hypoparathyroidism occurred in 34.7% of patients. Among patients with two or more well-vascularized parathyroid glands (score 2), 70.2% did not experience a decrease in parathyroid hormone levels below 15 pg/mL (NPV 70.2%, 95% CI: 62.4-78.1%). However, 29.8% of patients with two or more well-vascularized glands still developed hypoparathyroidism, highlighting the limitations of using this metric alone to predict postoperative outcomes. The overall accuracy for predicting hypoparathyroidism was 70% (95% CI: 62.7-77.3%). No patient developed permanent hypoparathyroidism.

CONCLUSION

ICG fluorescence angiography is a reliable tool for assessing parathyroid gland perfusion during thyroidectomy. However, the identification of two or more well-vascularized parathyroid glands does not completely exclude the risk of transient hypoparathyroidism, indicating that additional factors must be considered in predicting postoperative outcomes.

Intraoperative indocyanine green angiography in preventing hypoparathyroidism after thyroid cancer surgery

BACKGROUND

The aim of this study was to determine whether the use of indocyanine green angiography to identify devascularized parathyroids during thyroidectomy for thyroid cancer would decrease the rates of postoperative hypoparathyroidism.

METHODS

Retrospective study of patients who had undergone total thyroidectomy for treatment of thyroid cancer between March 2021 and March 2023. The indocyanine group included patients with all four parathyroids identified and evaluated by indocyanine green angiography at the end of the procedure. Those with parathyroid glands classified with no vascularization had the glands autotransplanted. A group without indocyanine angiography was used to compare results.

RESULTS

The analysis included 100 patients in each group. Indocyanine angiography identified 14.75% of devascularized parathyroids at surgery. The number of parathyroids with a score of 2 (i.e., good vascularization) was not a safe predictor of normal parathyroid hormone levels after surgery. Indeed, 29.2% of the patients with three parathyroids with a score of 2 developed transient hypoparathyroidism. Permanent hypoparathyroidism occurred in 7% of the patients without indocyanine group and in none of the patients in the indocyanine group (p = 0.014).

CONCLUSION

Intraoperative angiography with indocyanine green could contribute to reduce the occurrence of permanent hypoparathyroidism in patients undergoing surgical treatment for thyroid cancer.

"One-and-a-Half" Interdural Transcavernous Pituitary Transposition/Rotation for Protection of Hypophyseal Portal System in Adult Peripheral Retroinfundibular Craniopharyngioma

BACKGROUND AND OBJECTIVES

Craniopharyngiomas originate from the pituitary stalk (PS) and extend along the pituitary-hypothalamic axis. Peripheral retroinfundibular craniopharyngiomas, particularly, may have worse surgery outcomes than other types. This study aims to investigate the advantage of using "one-and-a-half" interdural transcavernous pituitary transposition/rotation to dissect the tumor from the residual stalk and hypophyseal portal system for this subtype of craniopharyngioma.

METHODS

From August 2018 to February 2023, patients with peripheral retroinfundibular craniopharyngioma underwent surgical treatment. We analyzed clinical information, surgical records, imaging, and examination findings. The surgical procedure, including "one-and-a-half" interdural transcavernous pituitary transposition and rotation, was explained. Postoperative follow-up included endocrinological tests, MRI examinations, and urination surveys.

RESULTS

Among the 52 patients diagnosed with craniopharyngioma who underwent surgical treatment, 9 were classified as peripheral retroinfundibular craniopharyngioma, and they received "one-and-a-half" interdural transcavernous pituitary transposition and stalk rotation. In 6 cases, the residual PS and most of the hypophyseal portal system were preserved. Gross total resection was achieved in 5 patients and near total resection in 1 patient. One patient had a transection of the bilateral inferior hypophyseal arteries and 5 unilaterally. None experienced permanent diabetes insipidus, but varying degrees of anterior pituitary dysfunction postoperatively required hormone replacement therapy, which gradually decreased over time.

CONCLUSION

The natural anatomic corridor, "one-and-a-half" interdural transcavernous pituitary transposition, and stalk rotation provide increased working space compared with intradural or extradural pituitary transposition. Simultaneously rotating the tumor and pituitary enables a specific attack angle for lesion dissection after the anteriorly displaced residual stalk is rotated laterally. This approach preserves the residual PS and hypophyseal portal system, avoiding complications of diabetes insipidus and hypopituitarism. In most cases, only one side of the inferior hypophyseal artery needs to be sacrificed, ensuring normal pituitary function.

The Contribution of Cell Imaging to the Study of Anterior Pituitary Function and Its Regulation

Advances in the knowledge of the neuroendocrine system are closely related to the development of cellular imaging and labeling techniques. This synergy ranges from the staining techniques that allowed the first characterizations of the anterior pituitary gland, its relationship with the hypothalamus, and the birth of neuroendocrinology; through the development of fluorescence microscopy applications, specific labeling strategies, transgenic systems, and intracellular calcium sensors that enabled the study of processes and dynamics at the cellular and tissue level; until the advent of super-resolution microscopy, miniscopes, optogenetics, fiber photometry, and other imaging methods that allowed high spatiotemporal resolution and long-term three-dimensional cellular activity recordings in living systems in a conscious and freely moving condition. In this review, we briefly summarize the main contributions of cellular imaging techniques that have allowed relevant advances in the field of neuroendocrinology and paradigm shifts that have improved our understanding of the function of the hypothalamic-pituitary axes. The development of these methods and equipment is the result of the integration of knowledge achieved by the integration of several disciplines and effort to solve scientific questions and problems of high impact on health and society that this system entails.

Development of the Pituitary Gland

The development of the anterior pituitary gland occurs in distinct sequential developmental steps, leading to the formation of a complex organ containing five different cell types secreting six different hormones. During this process, the temporal and spatial expression of a cascade of signaling molecules and transcription factors plays a crucial role in organ commitment, cell proliferation, patterning, and terminal differentiation. The morphogenesis of the gland and the emergence of distinct cell types from a common primordium are governed by complex regulatory networks involving transcription factors and signaling molecules that may be either intrinsic to the developing pituitary or extrinsic, originating from the ventral diencephalon, the oral ectoderm, and the surrounding mesenchyme. Endocrine cells of the pituitary gland are organized into structural and functional networks that contribute to the coordinated response of endocrine cells to stimuli; these cellular networks are formed during embryonic development and are maintained or may be modified in adulthood, contributing to the plasticity of the gland. Abnormalities in any of the steps of pituitary development may lead to congenital hypopituitarism that includes a spectrum of disorders from isolated to combined hormone deficiencies including syndromic disorders such as septo-optic dysplasia. Over the past decade, the acceleration of next-generation sequencing has allowed for rapid analysis of the patient genome to identify novel mutations and novel candidate genes associated with hypothalmo-pituitary development. Subsequent functional analysis using patient fibroblast cells, and the generation of stem cells derived from patient cells, is fast replacing the need for animal models while providing a more physiologically relevant characterization of novel mutations. Furthermore, CRISPR-Cas9 as the method for gene editing is replacing previous laborious and time-consuming gene editing methods that were commonly used, thus yielding knockout cell lines in a fraction of the time. © 2020 American Physiological Society. Compr Physiol 10:389-413, 2020.

Comparing the Superficial Vasculature of the Central Nervous System in Six Laboratory Animals: A Hypothesis About the Role of the "Circle of Willis"

We provide images of the entire central nervous system vasculature, and compare the anatomical findings in six different laboratory animals. A detailed understanding of the specific anatomy for each is important in the design of experimental modeling and for understanding the specific function of each target organ. Six different types of animals, the Korean wild mouse, C57BL/6J mouse, F344 rat, mongolian gerbil, Syrian hamsters, and guinea pigs, were included. To stain the blood vessels in each of the animals, Alcian blue reagent was used to perfuse each species. The bifurcation and anastomotic patterns of the anterior cerebral arteries differed in each species. The vascular supply to the olfactory nerve was visualized as a single artery supplying both olfactory nerves, and arteries supplying the lateral portion of the olfactory nerves originating from the olfactory bulb area. The posterior communicating arteries of the six animals demonstrated unique morphologies. The shape of the hypophyseal portal system varied by species. Most animals used in this study had a hexagonal Circle of Willis, except for the Korean wild mouse. Using this approach, we successfully mapped the brain vascular system in six different species of animals. This information and the images created can guide other researchers as they design research studies and create experimental models for new surgical procedures and approaches. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc. Anat Rec, 302:2049-2061, 2019. © 2019 American Association for Anatomy.

Imaging endocrinology in animal models of endocrine disease

Endocrine organs secrete a variety of hormones involved in the regulation of a multitude of body functions. Although pancreatic islets were discovered at the turn of the 19th century, other endocrine glands remained commonly described as diffuse endocrine systems. Over the last two decades, development of new imaging techniques and genetically-modified animals with cell-specific fluorescent tags or specific hormone deficiencies have enabled in vivo imaging of endocrine organs and revealed intricate endocrine cell network structures and plasticity. Overall, these new tools have revolutionized our understanding of endocrine function. The overarching aim of this Review is to describe the current mechanistic understanding that has emerged from imaging studies of endocrine cell network structure/function relationships in animal models, with a particular emphasis on the pituitary gland and the endocrine pancreas.

An updated view of hypothalamic-vascular-pituitary unit function and plasticity

The discoveries of novel functional adaptations of the hypothalamus and anterior pituitary gland for physiological regulation have transformed our understanding of their interaction. The activity of a small proportion of hypothalamic neurons can control complex hormonal signalling, which is disconnected from a simple stimulus and the subsequent hormone secretion relationship and is dependent on physiological status. The interrelationship of the terminals of hypothalamic neurons and pituitary cells with the vasculature has an important role in determining the pattern of neurohormone exposure. Cells in the pituitary gland form networks with distinct organizational motifs that are related to the duration and pattern of output, and modifications of these networks occur in different physiological states, can persist after cessation of demand and result in enhanced function. Consequently, the hypothalamus and pituitary can no longer be considered as having a simple stratified relationship: with the vasculature they form a tripartite system, which must function in concert for appropriate hypothalamic regulation of physiological processes, such as reproduction. An improved understanding of the mechanisms underlying these regulatory features has implications for current and future therapies that correct defects in hypothalamic-pituitary axes. In addition, recapitulating proper network organization will be an important challenge for regenerative stem cell treatment.

A journey through the pituitary gland: Development, structure and function, with emphasis on embryo-foetal and later development

The pituitary gland and the hypothalamus are morphologically and functionally associated in the endocrine and neuroendocrine control of other endocrine glands. They therefore play a key role in a number of regulatory feedback processes that co-ordinate the whole endocrine system. Here we review the neuroendocrine system, from the discoveries that led to its identification to some recently clarified embryological, functional, and morphological aspects. In particular we review the pituitary gland and the main notions related to its development, organization, cell differentiation, and vascularization. Given the crucial importance of the factors controlling neuroendocrine system development to understand parvocellular neuron function and the aetiology of the congenital disorders related to hypothalamic-pituitary axis dysfunction, we also provide an overview of the molecular and genetic studies that have advanced our knowledge in the field. Through the action of the hypothalamus, the pituitary gland is involved in the control of a broad range of key aspects of our lives: the review focuses on the hypothalamic-pituitary-gonadal axis, particularly GnRH, whose abnormal secretion is associated with clinical conditions involving delayed or absent puberty and reproductive dysfunction.

Anterior and intermediate pituitary tissues express claudin 4 in follicle stellate cells and claudins 2 and 5 in endothelial cells

Follicle-stellate cells are pituitary non-granular cells that are arranged between secretory cells or organized in follicles with small lumens. Cells from the follicles exhibit the typical phenotype of a transporting epithelium, including apical microvilli with a cilium and tight junctions. Freeze-fracture electron microscopy images show that the tight junctions consist of 5-7 anastomosing strands and that cultured follicle-stellate cells develop a trans-epithelial electrical resistance characteristic of "tight" epithelia. Here, we investigate the molecular composition of the tight junction from follicle stellate cells. We found that the rat anterior pituitary lobe expresses mRNAs for claudins 2, 4 and 5; the proteins of all these claudins are observed in the anterior lobe, whereas the intermediate lobe expresses claudins 2 and 5 and the posterior lobe contains only claudin 5. Follicle-stellate cells, identified by their protein marker S100β, expresses claudin 4 in the apical membrane, in co-localization with dipeptidyl-peptidase and near acetylated β-tubulin. Claudin 4 partially co-localizes with E-cadherin, indicating that a fraction of the protein is located in the basolateral domain. Follicle-stellate-enriched cell cultures develop patches of polygonal cells expressing claudin 4 and E-cadherin, encircled by extensive monolayers of fusiform cells. Claudin 2 stains specifically blood vessels, identified by claudin 5 and VE-cadherin labels. Thus, follicles in the anterior pituitary consist of "tight" epithelia that can carry out intense vectorial transport, together with a high cation movement in blood vessels, possibly related to the ion requirements of excitable secretory cells for hormone secretion.

Principles of endocrinology

The endocrine system plays a major role in human survival. Endocrine glands secrete chemical messengers or hormones that affect every tissue of the body, including the periodontium, during the life of the individual. As the endocrine system influences a broad assortment of biological activities necessary for life, a general understanding of the principal components and functions of this system is essential. A fundamental assessment of hormone structure, mechanism of action and hormone transport, as well as influence on homeostasis is reviewed. A concise evaluation of the functions of the central endocrine glands, the functions of the major peripheral endocrine glands (other than gonadal tissues) and the known relationships of these hormones to the periodontium is examined.

Minireview: intraislet regulation of insulin secretion in humans

The higher organization of β-cells into spheroid structures termed islets of Langerhans is critical for the proper regulation of insulin secretion. Thus, rodent β-cells form a functional syncytium that integrates and propagates information encoded by secretagogues, producing a "gain-of-function" in hormone release through the generation of coordinated cell-cell activity. By contrast, human islets possess divergent topology, and this may have repercussions for the cell-cell communication pathways that mediate the population dynamics underlying the intraislet regulation of insulin secretion. This is pertinent for type 2 diabetes mellitus pathogenesis, and its study in rodent models, because environmental and genetic factors may converge on these processes in a species-specific manner to precipitate the defective insulin secretion associated with glucose intolerance. The aim of the present minireview is therefore to discuss the structural and functional underpinnings that influence insulin secretion from human islets, and the possibility that dyscoordination between individual β-cells may play an important role in some forms of type 2 diabetes mellitus.

Small-animal PET with a σ-ligand, 11C-SA4503, detects spontaneous pituitary tumors in aged rats

Pituitary tumors are often detected only after death or at late stages of the disease when they are macroadenomas with a low surgical cure rate. Spontaneous pituitary tumors occur in rats over 1 y of age. In an ongoing study of changes in σ-1 agonist binding related to aging, several of our rats developed such tumors. The aim of the current study was to assess the kinetics of (11)C-SA4503 ((11)C-labeled 1-[2-(3,4-dimethoxyphenthyl)]-4-(3-phenylpropyl)-piperazine dihydrochloride) in tumor and brain and to evaluate the utility of this tracer in the detection of pituitary tumors.

METHODS

Small-animal PET scans of the brain region of male Wistar Hannover rats (age, 18-32 mo) were acquired using the σ-1 agonist tracer (11)C-SA4503. The time-dependent uptake of (11)C in the entire brain, tumor or normal pituitary, and thyroid was measured. A 2-tissue-compartment model was fitted to the PET data, using metabolite-corrected plasma radioactivity as the input function.

RESULTS

Pituitary tumors showed up as bright hot spots in the scans. The total distribution volume (VT) of the tracer was significantly higher in the tumor than in the normal pituitary. Surprisingly, a higher VT was also seen in the brain and thyroid tissue of animals with pituitary tumors than in healthy rats. The increase in VT in the brain and thyroid was not related to a change in nondisplaceable binding potential (BPND) but rather to an increase in the partition coefficient (K1/k2) of (11)C-SA4503. The increase in VT in the tumor on the other hand was accompanied by a significant increase in BPND. Western blotting analysis indicated that pituitary tumors overexpressed σ-1 receptors.

CONCLUSION

The overexpression of σ-1 receptors in spontaneous pituitary tumors is detected as an increase in uptake and BPND of (11)C-SA4503. Therefore, this tracer may have promise for the detection of pituitary adenomas, using PET.

Anterior pituitary cell networks

Both endocrine and non-endocrine cells of the pituitary gland are organized into structural and functional networks which are formed during embryonic development but which may be modified throughout life. Structural mapping of the various endocrine cell types has highlighted the existence of distinct network motifs and relationships with the vasculature which may relate to temporal differences in their output. Functional characterization of the network activity of growth hormone and prolactin cells has revealed a role for cell organization in gene regulation, the plasticity of pituitary hormone output and remarkably the ability to memorize altered demand. As such, the description of these endocrine cell networks alters the concept of the pituitary from a gland which simply responds to external regulation to that of an oscillator which may memorize information and constantly adapt its coordinated networks' responses to the flow of hypothalamic inputs.

A tridimensional view of pituitary development and function

Recent advances in tridimensional (3D) tissue imaging have considerably enriched our view of the pituitary gland and its development. Whereas traditional histology of the pituitary anterior lobe portrayed this tissue as a patchwork of cells, 3D imaging revealed that cells of each lineage form extensive and structured homotypic networks. In the adult gland these networks contribute to the robustness and coordination of the cell response to secretagogs. In addition, the network organization adapts to changes in endocrine environment, as revealed by the sexually dimorphic growth hormone (GH) cell network. Further work is required to establish better the molecular basis for homotypic and heterotypic interactions in the pituitary as well as the implications of these interactions for pituitary function and dysfunction in humans.

Cellular and molecular specificity of pituitary gland physiology

The anterior pituitary gland has the ability to respond to complex signals derived from central and peripheral systems. Perception of these signals and their integration are mediated by cell interactions and cross-talk of multiple signaling transduction pathways and transcriptional regulatory networks that cooperate for hormone secretion, cell plasticity, and ultimately specific pituitary responses that are essential for an appropriate physiological response. We discuss the physiopathological and molecular mechanisms related to this integrative regulatory system of the anterior pituitary gland and how it contributes to modulate the gland functions and impacts on body homeostasis.

Coordination of calcium signals by pituitary endocrine cells in situ

The pulsatile secretion of hormones from the mammalian pituitary gland drives a wide range of homeostatic responses by dynamically altering the functional set-point of effector tissues. To accomplish this, endocrine cell populations residing within the intact pituitary display large-scale changes in coordinated calcium-spiking activity in response to various hypothalamic and peripheral inputs. Although the pituitary gland is structurally compartmentalized into specific and intermingled endocrine cell networks, providing a clear morphological basis for such coordinated activity, the mechanisms which facilitate the timely propagation of information between cells in situ remain largely unexplored. Therefore, the aim of the current review is to highlight the range of signalling modalities known to be employed by endocrine cells to coordinate intracellular calcium rises, and discuss how these mechanisms are integrated at the population level to orchestrate cell function and tissue output.

Endocrine cells and blood vessels work in tandem to generate hormone pulses

Hormones are dynamically collected by fenestrated capillaries to generate pulses, which are then decoded by target tissues to mount a biological response. To generate hormone pulses, endocrine systems have evolved mechanisms to tightly regulate blood perfusion and oxygenation, coordinate endocrine cell responses to secretory stimuli, and regulate hormone uptake from the perivascular space into the bloodstream. Based on recent findings, we review here the mechanisms that exist in endocrine systems to regulate blood flow, and facilitate coordinated cell activity and output under both normal physiological and pathological conditions in the pituitary gland and pancreas.