Ultrastructure of the pars intermedia of the adult sheep hypophysis

Summary Light microscopy of coronal sections of the sheep pars intermedia revealed a compact, incompletely lobulated V-shaped region about 15–20 cells thick, situated between the pars distalis and the pars nervosa. A prominent hypophysial cleft and follicles containing a colloid-like substance were seen.Using electron microscopy, five cell types could be distinguished: pars intermedia glandular cells, pars distalis-like glandular cells, interstitial cells, follicular cells and cleft lining cells. The polyhedral to pear-shaped pars intermedia glandular cells predominated. They contained dense-cored, membrane-bound granules near the Golgi complex, and larger, irregular vesicles with finely granular contents of varying electron density throughout the remaining cytoplasm; exocytotic release of granules was occasionally observed. Smaller numbers of cells resembling those seen in the pars distalis were scattered throughout the pars intermedia. Interstitial cells usually possessed elongated cytoplasmic processes which extended between the glandular cells, and were characterized by deeply indented nuclei, elaborate junctional complexes and an absence of cytoplasmic granules. Cells lining the follicles resembled the interstitial cells. The major cells bordering the hypophysial cleft were triangular in section and bore irregular microvilli on their free surface. The pars intermedia appeared to be less vascular than the remainder of the hypophysis and only occasional fenestrated capillaries were seen. Nerve profiles were rare.     

Extravascular circulation in the pituitary of Mugil cephalus (Teleostei)

Summary Extravascular circulation in the pituitary of Mugil cephalus was investigated by injecting live fish with horseradish peroxidase and studying the distribution of the enzyme in the gland. The principal components of the extravascular circulatory system are the pericapillary spaces, and, arising from them, the interlobular and circumhypophyseal spaces. Extensions of these spaces penetrate the glandular parenchyma of the pars distalis, where they merge with pericellular spaces. In the neurohypophysis, pericapillary spaces are connected to the periaxonal spaces.Capillaries penetrating from the proximal neurohypophysis into the pars distalis are accompanied by neurosecretory axons. These axons form a mass of tissue which is limited near the capillaries by the pericapillary spaces and near the adenohypophysis by the interlobular spaces. Toward the interior of the adenohypophysis the amount of nervous tissue accompanying the capillaries progressively diminishes, thus reducing the distance between pericapillary and interlobular spaces. Within the pars distalis, the neurosecretory axons accompanying the capillaries are sparse, and the secretory and stellate cells are mostly located directly adjacent to the pericapillary spaces. In the neuro-intermediate lobe, interlobular spaces outline the neuro-adenohypophyseal boundary.The relationship between extravascular spaces and hormone-secreting cells varies in the different regions of the adenohypophysis depending upon the type of neurosecretory innervation in the respective region. In the regions of prolactin and gonadotropin cells, where neurosecretory axons are in direct contact with the secretory cells, the hormone-secreting and stellate cells are adjacent to the pericapillary spaces. In the regions of ACTH and STH cells, secretory and stellate cells are found adjacent to the interlobular spaces, which are interposed between the cells and the neurosecretory axons.Abbreviations AH adenohypophysis - CH circumhypophyseal - DNH distal neurohypophysis - HRP horseradish peroxidase - NH neurohypophysis - NS neurosecretory - PD pars distalis - PI pars intermedia - PPD proximal pars distalis - RNH rostral neurohypophysis - RPD rostral pars distalis This research was supported by a grant from the National Council for Research and Development, Israel, and the GKSS Geesthacht-Tesperhude, Federal Republic of Germany     

Granulated ‘marginal cell layer’ in the rat anterior pituitary gland

A granulated ‘marginal layer cell’ was observed in the lining of Rathke's residual pouch of 5 and 10 day-old rat anterior pituitary glands. Immunohistochemistry was not employed to identify the precise function of these cells. However, the cytological characteristics of nearly all of the cells indicated that they resembled GH-secreting cells, with a few displaying morphological features of corticotrophs. In pituitary glands of 5–20 day-old rats, both ends of Rathke's residual pouch extended into the pars distalis at the site of transitional zone of this lobe and of the pars intermedia. The cells within the ‘invading’ residual pouch contained numerous microvilli. In the middle portion of the residual pouch, cavities lined by ‘marginal layer cells’ had numerous microvilli and were adjoined by junctional complexes. In the adult rat pituitary gland, there were no granulated cells in the ‘marginal cell layer’ and no invasion of the residual pouch into the anterior lobe. From these data the possible source of the follicle and of the folliculo-stellate cells in the anterior pituitary of the rat is proposed.     

The pituitary gland of the coelacanth fish Latimeria chalumnae Smith: General structure and adenohypophysial cell types

The pituitary gland of Latimeria chalumnae is situated rostroventral to the telencephalon. The hollow pituitary stalk is bent forward and is ventrally connected to a saccus-vasculosus-like organ, rostrally to a neurointermediate lobe. The infundibular lumen protrudes far into the neurohypophysial lobules. The elongated principal part (pars cerebralis) of the pars distalis is partly embedded in a dorsal depression of the pars intermedia and caudally invaded by the neurohypophysis. It may be divided into rostral and proximal pars distalis and includes a ramified hypophysial cleft, which continues rostrally as a duct with adjacent islets of pars distalis tissue (parts of a pars buccalis). The adenohypophysis consists of cell cords and follicles. Eight tinctorial cell types can be distinguished: in the rostral islets: large basophils with acidophil globules, in the rostral pars distalis: small basophils, large basophils with amphiphil characters and erythrosin-, orange G-positive acidophils; in the proximal pars distalis: orange G-positive acidophils and small and large basophils, having similar staining properties; in the pars intermedia: one amphiphil cell type.     

Postnatal development of the interstitial cells (palisade cells) of the pars intermedia in the cat pituitary gland. An immunocytochemical and ultrastructural study.

The postnatal development of the interstitial agranulated cells (so-called palisade cells) of the pars intermedia in the cat was investigated immunocytochemically and at the ultrastructural level. Since the first postnatal days, a strong vimentin immunoreactivity and a weaker S-100 protein immunoreactivity were detected in the marginal cells lining the pituitary cleft and in the interstitial bipolar cells located within the pars intermedia. No glial fibrillary acidic protein cells have been found in the pars intermedia of any of the animals studied. This immunocytochemical pattern was maintained throughout the postnatal development. Ultrastructurally these cells showed a vast number of cytoplasmic filaments and well-developed junctional complexes. Secretory granules were never seen. In older animals they lined microcavities and microchannels where they project microvilli and present pinocytotic vesicles on their apical surface. No transitional forms between these cells and granulated secretory cells were found. There is a large number of axons and synaptic endings in contact with the granulated secretory cells. From our findings we guess that palisade cells are not a glial derivative, but they may share a common origin with secretory granulated cells.     

Immunocytochemistry of a “private” luteinizing-hormone-releasing hormone system in the pituitary

Summary Immunocytochemistry of paraffin sections of Bouin-fixed rat pituitaries with antiserum to luteinizinghormone-releasing hormone (LHRH) revealed two types of cells. Type I cells exhibit granular staining throughout their cytoplasm. The immunoreactivity of type II cells is confined to a much smaller area of the cytoplasm. Type I cells are located in the ventral margin of the pars intermedia, the region between the pars intermedia and the pars distalis, and the pars distalis adjacent to this region. Type II cells have a broader distribution in the pars distalis, but tend to concentrate in the region of the pars distalis near the pars intermedia. Type I cells are distinct from gonadotropes. Type II cells appear to comprise a subgroup of gonadotropes. Staining in type I, but not type II, cells in pituitary explants, maintained in serum-free media for seven days, is as intense as that in normal pituitary tissue. The data suggest that the type I cells are producing an intrinsic LHRH-like material and may be responsible, in part, for the regulation of some gonadotropes.Supported by NIH grants HD12932, NS15843 and NS15809 (LAS), National Science Foundation grant BNS 82-05643 (LAS), and a grant from the Phillippe Foundation (JYL)     

Immunocytochemical localization of vimentin in the posterior lobe of the cat, rabbit and rat pituitary glands

The presence and distribution of vimentin, a subunit of intermediate filaments, in the neural lobe and in the pars intermedia of the cat, rabbit and rat pituitary glands were investigated immunocytochemically. In the pars intermedia, our study revealed the presence of vimentin in glial-like cells located between glandular secretory cells of the three species and in the cells of the marginal layer of the cat and rat hypophyseal cleft. In the neural lobe of the cat and rabbit pituitary glands, there was a large amount of cell processes and immunoreactive pituicytes. In contrast, in the rat neural lobe, few pituicytes exhibited immunoreactivity, and these were located principally in the posterior region near the pituitary stalk. The significance of immunoreactive vimentin in these cells is discussed.     

Distribution of 3H-thymidine in the postnatal hypophysis of the C57BL mouse

The distribution of cells labelled with 3H-thymidine was determined autoradiographically in the adenohypophysis and neurohypophysis of the C57BL mouse during postnatal phases ranging from the newborn to 24 days of age, as well as in the adult. In the newborn, labelled cells are scarce in the neurohypophysis but common in the adenohypophysis. The neurohypophysis shows a surge in labelling at 5-9 days, with a sharp decline thereafter. In the adenohypophysis, labelled nuclei are scarce in the pars tuberalis after 19 days, whereas the pars intermedia and pars distalis continue to show labelled cells. In the pars distalis, at all phases, label occurs in the marginal cells along the hypophysial cleft as well as in deeper-lying cells representing follicular cells. In the adult, follicular cells are more commonly labelled relative to other cells of the hypophysis.     

Localization of acetylcholinesterase and choline acetyltransferase in the rat pituitary gland

Summary Experiments were conducted to determine the presence of two cholinergic biomarkers, acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) in the rat pituitary. A histochemical procedure for AChE was used to provide visualization of structures containing this enzyme. Radiochemical methods provided a sensitive assay for measuring ChAT activity. Nerve fibres staining for AChE activity were observed in the neurointermediate lobe, with the greatest concentrations appearing at the junction region with the pituitary stalk. Cells staining for AChE were found in the pars distalis and pars intermedia. ChAT activity correlated well with AChE distribution in pars nervosa and pars intermedia but not in pars distalis. The greatest levels of ChAT activity were in pars intermedia and the region where the stalk joins the pituitary. Significant values were also found for the pars nervosa. The presence of AChE and ChAT in pars intermedia and pars nervosa is evidence for a cholinergic innervation to these regions. In pars distalis, where other investigators have found muscarinic receptors, intense staining for AChE and absence of ChAT activity may indicate non-innervated, acetylcholine-sensitive sites.     

Immunohistochemically detected ontogeny of prolactin and growth hormone cells in the African catfish Clarias gariepinus

The chronological appearance of selected endocrine cells in the pituitary of African catfish Clarias gariepinus (Burchell, 1822) was studied morphologically, histologically and immunohistochemically by using antisera raised against catfish growth hormone (cgGH) and recombinant tilapia prolactin I (tPRL). cgGH- and tPRL-like immunoreactive cells were visible from day 1 post fertilisation (hatching) throughout the juvenile and the adult stage. From 1 to 90 days after hatching, the larval pituitary is oval in shape with a distinctly shaped rostral pars distalis, proximal pars distalis and pars intermedia. From day 120 onwards allometric growth of the rostral and proximal pars distalis extended the prolactin and growth hormone cells anteriorily and posteriorily, respectively. Size and activity of the prolactin and growth hormone cells, measured by the ratio of cell surface to nuclear surface remained constant until day 40 and showed a growth spurt thereafter. Growth hormone content, measured with a catfish-specific radio-immunoassay from hatching until 60 h post hatching, increased exponentially between 30 and 60 h.     

Distribution of immunoreactivities for adenohypophysial hormones in the pituitary gland of the polypteriform fish, Polypterus endlicheri

Polypteriform fish constitutes the most primitive living descendent of the ancient bony fish. In polypteriform fish, only proopiomelanocortin (POMC) has been identified so far in the adenohypophysis, which is surprising in view of their evolutionary importance. In the present study, distribution of immunoreactive adenohypophysial hormones was examined in juvenile individuals of Polypterus endlicheri. Antisera to tetrapod and fish adenohypophysial hormones were used as immunostaining probes. Adrenocorticotropin (ACTH)-like cells were detected by antisera to salmon POMC N-terminal peptide, porcine ACTH and mammalian alpha-melanotropin (MSH), and were distributed in the rostral pars distalis in close proximity to the hypophysial duct. MSH-like cells were found in the pars intermedia, and were stained by anti-salmon N-Ac-beta-endorphin II as well as anti-mammalian alpha-MSH and anti-salmon POMC-N terminal peptide. Prolactin (PRL)-like cells were detected only after application of anti-sturgeon PRL, and were distributed in the rostral pars distalis, where PRL-positive material was found in columnar mucinous cells lining the diverticuli of the hypophysial duct. Growth hormone (GH)-like cells were stained with antisera to sturgeon GH, human GH, salmon GH and blue shark GH, and were distributed in the proximal pars distalis. Somatolactin (SL)-like cells were stained with anti-salmon SL, and were distributed in the pars intermedia. Two types of glycoprotein hormone-positive cells were detected in the proximal pars distalis. Although both types of cells were stained with several antisera to glycoprotein hormones, such as sturgeon LHbeta and salmon LHbeta, it was difficult to know which types of cells produce LH, FSH, or TSH. Thus, the present study revealed seven types of adenohypophysial hormone-like cells in the Polypterus pituitary gland, which may provide the morphological basis for better understanding on evolution of the pituitary gland and the adenohypophysial hormones in vertebrates.     

Histology of the pituitary gland of the grey mullet, Mugil cephalus L.

The present communication deals with a histological study of the pituitary gland of the teleost fish Mugil cephalus , found in the estuarine waters of Cochin area. Six different cell types were identified in the pituitary gland on the basis of their grouping, distribution and staining properties. The prolactin and the TSH cells (thyroid stimulating hormone producing cells or thyrotrops) were identified in the rostral pars distalis and the ACTH cells (adrenocorticotropic hormone producing cells or corticotrops) in the interphase between the neurohypophysis and the rostral pars distalis. The STH cells (somatotropic hormone producing cells or somatotrops) and the gonadotropic cells were distinguished in the proximal pars distalis and the MSH cells (melanin stimulating hormone producing cells or melanotrops) in the pars intermedia.     

Immunohistochemical evidence of progestin target cells in the pituitary gland of ovariectomized rat

Progestin (P) target cells were identified in the pituitary gland of gonadectomized female rats which had been primed with estrogen (E). P staining was localized using the immunohistochemical avidin-biotin-peroxidase (ABP) complex method. Dark brown precipitates were primarily found over the cytoplasm of cells in the pars distalis, but not in the pars intermedia nor in the pars nervosa. The majority of P-sensitive cells in the pars distalis were identical with luteotrophs, a few being lactotrophs. These observations suggest a role of P in the regulation of production and secretion of gonadotrophins in the pituitary glands of female rats.     

Life span changes in the presence of alpha-melanocyte-stimulating-hormone-containing cells in the human pituitary.

Since recent circumstantial evidence has suggested possible functions of alpha-MSH in intrauterine growth and labour, the presence of this hormone in the human pituitary was determined by means of the indirect immunofluorescence procedure during development and adulthood. Cross reaction of the antibodies with other peptides was measured after which they were purified by solid phase absorption. Experiments on the rat pituitary showed that staining of alpha-MSH- and ACTH-containing cells could be obtained well until 48 h after death. In the pars distalis the ability of ACTH-containing cells to take up stain increased during the period of post-mortem storage. In the youngest human fetus studied (15 weeks) only alpha-MSH-containing cells were found in the pars intermedia and no ACTH-containing cells were observed. In the other fetal pituitaries a distinct pars intermedia containing more alpha-MSH cells than ACTH cells was found. In the pars distalis of the fetuses more ACTH- than alpha-MSH-containing cells were observed. From birth to 19 years, progressively fewer alpha-MSH containing cells could be detected in the 'zona intermedia' and pars distalis, while in adults only a few such cells were found in either area. Irrespective of age, sex, cause of death or therapy, alpha-MSH-containing cells were found in all pituitaries throughout life. The number of ACTH containing cells gradually increased in the zona intermedia and pars distalis and reached a high adult level in the latter structure. In the pituitaries of seven anencephalics, no alpha-MSH-containing cells were present. The presence of alpha-MSH in the fetal pars intermedia, the change in the ratio of the alpha-MSH/ACTH cells during the course of development, and the absence of alpha-MSH in anencephaly all support the possibility that human fetal pituitary alpha-MSH is involved in both intrauterine growth and fetal adrenal function and thus also in parturition.     

The Cell Types in the Adenohypophysis of the Marine Teleost Crenilabrus melops

Sagittal sections from pituitaries of winter and spring fish were stained with a number of methods including alcian blue-PAS-orange G, Herlant's tetrachrome, Luxol fast blue-PAS-orange G and lead haematoxylin. By these methods seven different endocrine cell types were readily demonstrated in the adenohypophysis. In the rostral pars distalis (RPD), there were conspicuous vacuoles (intra- and possibly extracellular) in the prolactin cell zone of all animals. The ACTH cells in the RPD were very numerous. In the proximal pars distalis (PPD), the growth hormone cells were arranged in coiling bands that were predominantly dorsal and juxtaposed to neurohypophysis. Two types of basophils were readily distinguished: both were predominantly ventral in the proximal pars distalis, though the type I basophil also formed a constant group in the dorsal region of the pituitary, between the PPD and the RPD. The pars intermedia contained two cell types — a lead haematoxylin-positive cell and a PAS-positive cell. The pituitary morphology is compared with that of other teleosts.     

Pituitary cytology of the freshwater teleost Anabas testudineus (Bloch)

In the pituitary of A. testudineus the rostral pars distalis (RPD), proximal pars distalis (PPD) and pars intermedia (PI) are arranged in a rostro-caudal axis. The rostral neurohypophysis (NH) extends dorsal to the pars distalis, while the caudal part vertically penetrates into the PI and ramifies in its component. The RPD mainly consists of erythrosinophils and PgH-positive cells which are comparable to the lactotropes and corticotropes mentioned in the literature. In the nonbreeding season, acidophils are the predominant cells of the PPD and are largely confined to its dorsal aspect. The two types of cyanophils present in the PPD could not be differentiated with the various techniques used in this study. However, those cyanophils which increase in number and are active during the spawning season may be the gonadotropes, while those which are cytologically inactive may be the thyrotropes. The pars intermedia consists of PAS+ and PhH+ cells. Trichrome and tetrachrome staining techniques revealed the presence of acidophils, cyanophils and amphiphils in the PI.     

Pituitary cytology of the chimaeroid fish Hydrolagus colliei (Lay and Bennett).

The pituitary of Hydrolagus colliei is divided into the adenohypophysis, neurohypophysis and an oral Rachendachhypophyse. The adenohypophysis is further divided into rostral and proximal pars distalis and neurointermediate lobe. The neurohypophysis is restricted to the pars intermedia only. The rostral pars distalis is composed of acidophils, chromophobes, lightly PAS+ cells and amphiphils. The amphiphils were stained with Heidenhain's iron haematoxylin and lead haematoxylin also. The proximal pars distalis is formed of cyanophils where the granules are AF and PAS positive, acidophils, chromophobes and H.Pb+ cells. The pars intermedia has perviascular amphiphils which are H.Pb+, lightly PAS+ cells and chromophobes. Few AF+ cells were also identified. All the component parts of the adenohypophysis have follicular cavities which are probably developed from the hypophysial cavity, which is well seen in the young specimen as a single cavity extending antero-posteriorly throughout the adenohypophysis.     

Immunohistochemical Localization of Growth Hormone and Prolactin in the Pituitary Gland of Acipenser güldenstaedti Brandt (Chondrostei)

Abstract Prolactin (LTH) and growth hormone (GH) containing cells in A. güldenstaedti have been localized by means of anti-ovine prolactin and anti-bovine growth hormone respectively, coupled indirectly to peroxidase, and localized histochemically with hydrogen peroxide as substrate and 3,3′-diaminobenzidine as capturing agent. The distribution of the anti-prolactin positive cells has been demonstrated and correlated histologically with the acidophilic cells both in the rostral and proximal pars distalis. This cell type is elongated and arranged in follicles in the rostral pars distalis; in the proximal pars distalis they are smaller and oval, without any special orientation. Neither of the other cell types which are scattered among these acidophils contain prolactin. The anti-bovine growth hormone positive cells are evenly distributed in the proximal pars distalis above the hypophysial cleft, and some are also found in the pars intermedia. The anti-GH positive cells have been correlated histologically with the amphiphilic cells in the proximal pars distalis. These cells are arranged in cell cords in close contact with the secondary capillary plexus, near its origin from the primary capillary plexus covering the median eminence.     

Ontogenesis of the α-MSH, β-MSH and ACTH cells in the foetal hypophysis of the rat. Correlation with the growth of the adrenals and adrenocortical activity

Pituitary sections from 15 to 21 day-old rat foetuses have been studied with the immunofluorescence technique, using antibodies anti alpha-MSH, anti beta-MSH and anti beta (1-24) ACTH. The first ACTH cells appear on day 17 of pregnancy in the pars distalis of the hypophysis and only on day 18 in the pars intermedia. beta-msh cells have been observed on day 16 in the pars anterior and on day 17 in the pars intermedia, while alpha-MSH cells appear only on day 18 and exclusively in the pars intermedia. The cytodifferentiation of the beta-MSH and ACTH cells occurs in the pars intermedia with about a 24 hours delay in comparison to that of the pars distalis. The first revealed cells are always located in the posterior half of the pituitary gland. The corticostimulating activity of the hypophysis has been tested with the fluorescence intensity of the corticotrophs, the adrenal weight, the adrenal content in corticosterone and the plasma corticosterone level. The fluorescence of the corticotrophs increases on day 18, shows a maximum on day 19 and decreases until term. The adrenal weight rises regularly between day 16 to day 20, thereafer the increase subsides. Adrenal and plasma corticosterone concentrations reach a peak on day 19 of pregnancy. These data suggest that hypophyseal corticostimulating activity is very high between days 18 and 19 and decreases between days 19 and 21.