Ultrastructure of STH cells of the pars distalis of hepatectomized mice

Summary An electron microscopic analysis was performed on the pars distalis of the hypophysis of hepatectomized mice. Intact and sham operated mice served as controls. The STH cells presented striking changes that were most intense and widespread in those animals sacrificed at midnight of the second day after hepatectomy. These changes can be summarized as follows: 1) Hypertrophy of the Golgi complex with increased number of immature granules within the Golgi zone. This change appeared also in otherwise unmodified STH cells. 2) Strong dilatation of the endoplasmic reticulum whose cisternae contained much electron dense material. 3) Granules with partially diminished electron density, some of them in spatial relation with the plasma membrane and others swelling and bursting within the cytoplasm. All transitions between unchanged 350–400 m granules and extremely altered ones, were seen. 4) Release sites, characterized by dense zones in the plasmalemma, close to aggregates of electron lucent microvesicles, and almost empty granule membranes. 5) Increase in the density of the mitochondria which appeared grouped near the Golgi zone. 6) Increase in the number of large lysosomes of the autophagic vacuole type. 7) Irregular nuclear outlines. These data suggest increased synthesis and release of growth hormone in STH cells stimulated by hepatectomy.Work carried out with the financial assistance of a grant of the Comision de Investigation cientifica de la Universidad Nacional de La Plata. Thanks are due to the members of the technical staff of the Institute for their technical assistance.     

Immunocytochemical effects of thyroxine stimulation on the adenohypophysis of dwarf (dw) mutant mice

The effects of dietary thyroxine on the immunoreactivity of cells in the pars distalis of the adenohypophysis in dwarf (dw/dw) mice were determined by ultrastructural immunocytochemistry. In nontreated dwarfs only adrenocorticotropic hormone (ACTH) cells and luteinizing hormone (LH) cells showed positive reactions to their respective antibodies, whereas no cells showed immunoreactivity to antibodies to growth hormone (GH), thyroid-stimulating hormone (TSH), or prolactin (Prl). In dwarfs supplemented postnatally with dietary thyroxine for 9 wks, the treatment failed to produced immunoreactive GH, TSH or Prl cells. However, LH cells became more prominent and fully developed, with denser concentrations of immunoreactive particles overlying the secretory granules than occurred in nontreated dwarfs. In thyroxine-treated dwarfs, ACTH cells were similar in ultrastructural features and immunoreactivity to those in nontreated dwarfs.     

Fine structure of somatotrophs and mammotrophs in the pituitary pars distalis of the little (lit) mutant mouse

The cellular pathology and postnatal differentiation of somatotrophs and mammotrophs in the pars distalis of little (lit/lit) and normal (+/+; lit/+) mice were studied by means of electron microscopy. The results indicate that in little the pituitary at birth contains recognizable somatotrophs and mammotrophs; however, between 14 and 24 days of age a contrast between little and normal becomes conspicuous with respect to the somatotrophs. Little somatotrophs are less heavily populated with granules, have granules of smaller size, and show less developed organelles than do normal somatotrophs at comparable stages. Beyond 24 days the little somatotrophs become more difficult to locate, and those that do occur show a minimal increase in complexity from that present at 14 days. In contrast, the mammotrophs in little are similar in appearance to normal mammotrophs and show increasing complexity as development proceeds, often sending forth cellular processes between neighboring cells, as do normal mammotrophs.     

Ultrastructure of STH cells in the pars distalis of the hypophysis of mice bearing transplanted hepatomas

Summary An electron microscopic analysis was performed on the pars distalis of the hypophysis of mice bearing transplanted hepatomas. Normal mice served as controls. In animals bearing a fast growing as well as in those bearing a slow growing hepatoma, the STH cells presented changes indicating increased release and synthesis of its secretory product. These changes can be summarized as follows: 1) Increased number of granuledepleted STH cells which were very irregular in size and shape. 2) Very irregular and sometimes bizarre nuclei. 3) Plasma membranes irregular and convoluted. 4) Increased quantity of endoplasmic reticulum which appeared sometimes dilated and contained material of varying electron density. 5) Abundant, irregular and frequently ramified mitochondria. 6) Hypertrophic Golgi system with increased number of microvesicles. 7) Increased number of large lysosomes of different type. 8) Increased number of fat droplets.Work carried out with the financial assistance of grants of the Consejo Nacional de Investigaciones Científicas y Técnicas de la Republica Argentina and the Comisión de Investigación Científica de la Universidad Nacional de La Plata. Thanks are due to the members of the technical Staff of the Institute for their technical assistance.     

Ultrastructure of STH cells of the pars distalis of castrated male mice after hepatectomy

Summary An electron microscopic study aimed at differentiation between castration gonadotrophs and posthepatectomy STH cells was performed on the pars distalis of the pituitary of castrated male mice, after partial hepatectomy. The ultrastructural features observed permit the distinction of both cell types. In the present experiments some remarkable ultrastructural changes, other than those described in a previous report, have been found in STH cells of hepatectomized mice with or without previous castration. Most of them contained masses of heterogeneous electron density, suggesting fusion of granules. These masses and some secretion granules were observed close to the plasma membrane, apparently in the process of discharging material into the pericapillary space. Granular extrusion was more frequent than normally. An increased number of lysosomes, probably related to the digestion of overproduced secretion material, was evident. The appearance of concentric lamellar formations might be related to an increase in cell movements. STH cells with severe cytoplasmic damage were also found, indicating an increased rate of cell loss.Work carried out with the financial assistance by a grant from the Comisión de Investigación Científica de la Universidad Nacional de La Plata. Thanks are due to the members of the Technical Staff of the Institute for their technical assistance.     

A comparative in vitro study on LHRH responsiveness of LH cells of the pars tuberalis and pars distalis

Summary The aim of the present study was to test whether the luteinizing-hormone (LH) cells in the pars tuberalis (PT) of the rat and mouse respond to LH-releasing hormone (LHRH) as do those of the pars distalis. A part of the basal hypothalamus containing the pituitary stalk, median eminence and the pars tuberalis (H-PT), was dissected out and incubated in vitro.The LH-secreting capacity of the PT was investigated after removal of the pituitary body (i.e., partes distalis, intermedia and nervosa). First, some rat and mouse H-PT tissues were treated with synthetic LHRH (100ng/ml), while others were incubated without LHRH. After 24 h of incubation, variable amounts of LH release were detected in the medium. This LH discharge, however, was not LHRH-dependent but proportional to the number of PT LH cells that were immunohistochemically detected in each incubated tissue. Since there was marked individual variation in the number of LH cells in the PT, the LH levels in the incubation medium were next compared before and after LHRH treatment using the same H-PT of the rat. An effect of LHRH could not clearly be shown in this experiment.Finally, the cytological response of the PT to LHRH was investigated by incubating both the H-PT and pituitary body connected to the intact pituitary stalk. Immunohistochemical examination of LHRH-treated tissues after 24 h revealed that, in females of both rats and mice, hormone depletion occurred in LH cells of the pars distalis but not in those of the PT. These results indicate that although LH cells in the PT can release LH in vitro, their mode of hormone synthesis and/or discharge differs from that of LH cells in the pars distalis. Since there was a marked individual variation and small LH-secreting capacity by the PT tissue, it seems unlikely, at least in rats and mice, that LH of PT origin plays an important role in the normal physiological state.     

Immunocytochemical studies on the pituitary pars distalis of the Japanese long-fingered bat,Miniopterus schreibersii fuliginosus

Summary Immunocytochemical studies were performed to describe the characteristics of cell types and their distribution in the pars distalis of Japanese long-fingered bat, Miniopterus schreibersii fuliginosus, collected at various stages of the reproductive cycle. Six distinct cell types have been identified in the pars distalis by the unlabeled immunoperoxidase technique and by the ABC method. Growth hormone (GH) and prolactin (PRL) cells were immunostained with antisera against chicken GH and ovine PRL. The GH-immunoreactive cells were round or oval orangeophilic cells distributed throughout the pars distalis with prominent aggregation in the posterolateral region. The PRL cells were pleomorphic carminophilic cells that occurred in small groups within the central and dorsocaudal regions of the pars distalis. They were sparsely distributed in the central region of the pars distalis in the hibernating bats, but increased significantly in the pregnant and lactating bats. The adrenocorticotropic (ACTH) cells were large round or polygonal amphophilic cells in the rostroventral and ventrolateral regions of the pars distalis. The thyrotropic (TSH) cells were small rounded or polygonal and distributed mainly in the ventrolateral region of the pars distalis. Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) cells were identified immunocytochemically with antisera against the specific beta subunits of ovine LH and rat FSH. There were two populations of LH and FSH cells, one aggregated in the zona tuberalis and the other scattered singly throughout the rest of the pars distalis. The aggregated cells were immunoreactive with both antisera directed to LH and FSH, while scattered cells were reactive solely with antiserum to either LH or FSH and exhibited seasonal variations. In females, the proportional volume of the pars distalis occupied by LH cells was significantly reduced during pregnancy and lactation. No evidence of involution was observed in pars distalis cells except for PRL cells in males or females during hibernation.     

Cytological changes in the pars distalis of the female rat hypophysis grafted under the kidney capsule

Summary Intact female rats received transplants of two hypophysial partes distales under the kidney capsule. The plasma levels of prolactin were determined, and the ultrastructure of the grafted gland was studied 15, 45 and 90 days after the operation. Although prolactin levels in the three experimental groups were significantly higher than those in control rats, a decrease in prolactin level was detected in the 45-day samples. Parallel ultrastructural changes suggest that between the 45th and 90th postoperative day a process is initiated leading to hyperplasia and hypertrophy of prolactotrophs.Supported by Grants from PLAMIRH (93.173.2-77) and from the Dirección de Investigaciones, Universidad Austral (S-77-28)     

Fine structure of the chromophobe in the pars distalis of the common snapping turtle,Chelydra serpentina

Summary Chromophobes of the pars distalis in young Chelydra serpentina have sparse cytoplasm with no specific granules; however, many cytoplasmic filaments are present. The chromophobes are connected to the other cell types by desmosomes, while different types of junctional specializations occur between adjacent chromophobes. Cytoplasmic filaments traverse the cytoplasm in a random manner and terminate on both the junctional complexes and the nuclear envelope. It is proposed that, in addition to providing a structural framework, the chromophobes may be involved in integrating cellular responses of the parenchyma to changes in the endocrine milieu.Supported in part by a General Research Support Grant RR05402, NIH to Dr. Tseng and a Human Development Grant HD-03484, NIH to Dr. Yntema.     

Postnatal development of somatotrophs and mammotrophs in the pars distalis of the C57BL mouse

Summary The pars distalis of the pituitary gland of the C57BL mouse was studied by means of electron microscopy during postnatal stages of males ranging in age from newborn through 24 days, with particular emphasis on the somatotrophs and mammotrophs. During this period, growth curves were plotted in order to correlate postnatal growth patterns with the state of differentiation of the somatotrophs in the pars distalis. In the newborn, the somatotrophs show well developed organelles, including rough endoplasmic reticulum and Golgi complexes. These cells are not as densely packed with granules as the adult somatotrophs; however, from days 5 through 24, they show a progressive accumulation of granules. Although mammotrophs are scarce in the newborn, they are readily distinguishable in the pars distalis at 5 days. Male mice in small litters show a progressive increase in body weight between birth and 11–12 days, at which time the rate slackens until 18–19 days when the rate again increases. Growth curves for mice from large litters are similar to those from smaller litters, except that the transitory decrease in rate is more prominent.Supported by NIH grant no. HD12308 from the National Institute of Child Health and Human Development, USPHSThe authors wish to thank Pratima Ganguly for technical assistance     

Ultrastructure of the nongranulated cells and morphology of the extracellular spaces in the pars distalis of adult and pouch-young tammar wallabies (Macropus eugenii)

Summary Differentiated nongranulated (folliculo-stellate) cells were observed in the centre and periphery of the cords of cells in the pars distalis of the adult tammar wallaby (Macropus eugenii). The nongranulated cells formed follicles containing a small lumen; the cell apices were joined by junctional complexes including zonulae adhaerentes and maculae adhaerentes (desmosomes). Follicles of granulated cells were also occasionally found. Follicles were rarely observed in the adult, but were numerous and generally larger in pouch-young wallabies. Moreover, whereas the involvement of granulated cells in the follicles of the adult was infrequent, they were common components of follicular structures in the pouch-young. The marginal cells at the periphery of the pars distalis in contact with the hypophysial cleft had many of the cytological characteristics of the nongranulated cells in the central pars distalis. In both adult and pouch-young wallabies, nongranulated cells at the periphery of the cell cords were juxtaposed such that they formed sinusoid-like spaces or lacunae, presumably as part of the extravascular channel system. The observations are discussed in light of the proposed phagocytotic, metabolite and/or hormone transport and stem cell roles attributed to these cells.This work was supported by a travel grant and grant-in-aid of research from the N.S.E.R.C. (J.F.L.) and from the A.R.G.C. and the N.I.H. (M.B.R.)     

Structure of the nongranulated cells in the hypophyseal rostral pars distalis of cyclostomes and actinopterygians

Summary The structure of the nongranulated cells in the sea lamprey adenohypophysis and similar cells of the rostral pars distalis in a number of actinopterygian fishes was examined with the aim of determining the role(s) of these cells in pituitary function.A number of possible roles are proposed for the nongranulated cells. In salmonids and Amia calva the cells may be involved in the active movement of material into or from the follicle lumina. The structure of the nongranulated cells in in vitro cultured and in in vivo transplanted trout rostral pars distalis also suggests a phagocytotic role for these cells. In teleosts with a non-follicular rostral pars distalis the nongranulated cells appear to play roles in the release of granules from the prolactin cells and in the subsequent dispersal of the hormone (and/or carrier substance) into the peripheral circulation.We wish to thank Dr. B.I. Baker who performed the trout pituitary in vitro cultures and Professor M. Hyder who was closely involved with the collection of the Tilapia specimens. We also wish to thank Mr. R. Lindsay and Mrs. L. Lin for their technical assistance and Drs. F.W.H. Beamish and R. Sonstegard for their help in supplying some of the animals used in this study. —The work was supported in part by a grant-in-aid of research from the National Research Council of Canada to J.F.L. and in part by a negotiated NRC grant. The paper is number 138 in the physiology of migration series.     

The ontogenesis of monoaminergic nerve fibres in the hypophysis of Rana temporaria with special reference to the pars distalis

Summary In Rana temporaria tadpoles, fluorescent fibres appear in the prospective eminentia mediana, the pars intermedia and the pars distalis at Gosner's stage 25. During prometamorphosis the amount of fluorescent material increases around the developing primary capillary plexus in the eminentia mediana. In the pars intermedia the fibres form a dense fluorescent network but in the pars distalis the fibres are few and delicate.At stages 42–43, the onset of climax, the pars distalis fibres disappear. The possible functional significance of the pars distalis fibres is discussed.The background adaptation ability appears at stages 28–29, while the fluorescent pars intermedia innervation is observable at stage 25.     

Effect of cyproterone acetate on cells of the pars distalis of the adenohypophysis in the Beagle Bitch

Summary The effects of oral administration of 100 mg per kg per day cyproterone acetate (CPA) for four weeks on cells of the pars distalis, as revealed by the immunoperoxidase technique and chemical staining, were studied in the ovariectomized beagle bitch. For immunochemical staining antisera to the following hormones were used: canine GH, canine PRL, porcine ACTH, bovine TSH, bovine LH and human FSH¹. The most striking effects of the treatment were an overall increase in the relative proportion of GH cells and a marked morphological indication of high secretory activity in these cells. In contrast, PRL cells were not affected significantly. In all ovariectomized control bitches a marked atrophy of the cells stained for FSH (FSH cells) and hypertrophy of the cells shown to contain LH(LH cells) were observed. FSH cells became enlarged, while LH cells appeared reduced in size by administration of CPA. In some treated bitches ACTH/MSH cells showed atrophy and regressive changes, whereas TSH cells seemed to become enlarged and were more densely arranged. These structural responses indicate that, in addition to its partial antigonadotropic properties, CPA as a synthetic progesterone derivative may stimulate GH secretion and possibly suppress CRH-ACTH activity in the ovariectomized beagle bitch.Abbreviations of Hormones cited in this Paper ACTH Adrenocorticotropin - FSH Follicle Stimulating Hormone - GH Growth Hormone - LH Luteinizing Hormone - MSH Melanocyte Stimulating Hormone - PRL Prolactin - TSH Thyrotropin - CRH Corticotropin Releasing Hormone The authors are grateful to Dr. Christel Schoebel and Mrs. P. Kurth for carrying out the experimental work on animals, to Dr. H. Wiemann for the statistical analysis, to Mrs. B. Schilk, G. Soulioti and Miss U. Tüshaus for their excellent technical assistance, and to Dr. P. Guenzel for his advice and encouragementRecipient of a Research Scholarship from the Arabic Republic of Egypt     

Ultrastructure of the pars distalis of the lizard Anolis carolinensis with special reference to the identification of the gonadotropic cell

Summary Five categories of granulated cells were distinguished by their ultrastructural features, and quantitative analyses were made of the pars distalis cells in normal and castrated lizards. The gonadotropin-producing cell was identified on the basis of its uniform distribution in the gland as well as from cytological changes resulting from castration. The secretory granules of the gonadotropic cell vary in size (100–500 m) and density, and lipid bodies are commonly present. Following castration, the endoplasmic reticulum proliferates, forming many small, rough-surfaced, dilated cisternae which do not coalesce greatly as in other vertebrate species. Degranulation is accompanied by hypertrophy and hyperplasia of the mitochondria and by the appearance in the cytoplasm of conspicuous clusters of microfilaments. The designated gonadotropic cell was the only class of secretory cell showing consistent changes following three weeks of castration.In addition to the uniformly distributed gonadotrope cell, two secretory cells occur mainly in the rostral half of the gland, and two in the caudal half. Tentative identification of the cell types is discussed in the light of available information on the localization of the hormones in the pars distalis of this species.Grateful recognition is given to the Electron Microscope Laboratory of the University of California, Berkeley, for use of their facilities, and to Emily Reid for her assistance with the illustrations.Member of Consejo Nacional de Investigaciones Cientificas y Técnicas.     

Effect of cyproterone acetate,d-norgestrel and progesterone on cells of the pars distalis of the adenohypophysis in the beagle bitch

Summary The effects of short-term (8 weeks) treatment with different doses of cyproterone acetate (CPA), d-norgestrel (d-N) and progesterone on cells of the pars distalis, as revealed by the immunoperoxidase technique, were studied in cycle-synchronized beagle bitches (first anoestrus). Pituitary glands from non-treated primiparous beagle bitches at the 6th and 9th week of pregnancy were also included. For immunochemical staining specific antisera to the following hormones were used: canine GH, canine PRL, porcine ACTH, bovine TSH, bovine LH and human FSH. Morphological features of high secretory activity in GH cells were evident even after the human oral contraceptive doses of CPA and d-N, and after a dose as low as 0.1 mg/kg/day subcutaneously (s.c.) of progesterone. In contrast, PRL cells did not show any significant treatment-related effects except in those animals which received the highest dose of d-N (0.5 mg/kg/day per os). In this group, as well as in all pregnant bitches, hyperplasia and hypertrophy of PRL cells were found. In the animals treated with the highest doses of CPA (4.0 mg/kg/day per os) and progesterone (42.5 mg/kg/day s.c.) as well as in pregnant bitches, ACTH/MSH and TSH cells showed marked atrophy and regressive changes. Similar morphological signs of depressed secretory activity were also observed in the cells shown to contain FSH and/or LH as a result of treatment with the highest dose of progesterone and at the 9th week of pregnancy. These structural responses indicate that quantitative and/or qualitative differences may exist between progesterone, the synthetic progesterone derivative CPA and the nortestosterone type progestagen d-N with regard to their effect on pituitary hormone secretion in the beagle bitch.Abbreviations ACTH Adrenocorticotropin - FSH Follicle Stimulating Hormone - GH Growth Hormone - LH Luteinizing Hormone - MSH Melanocyte Stimulating Hormone - PRL Prolactin - TSH Thyrotropin - CRH Corticotropin Releasing Hormone - TRH Thyrotropin Releasing Hormone The authors are grateful to Dr. Christel Schöbel and Mrs. P. Kurth for carrying out the experimental work on animals, to Mrs. B. Schilk and Miss U. Tüshaus for their excellent technical assistance, and to Dr. P. Günzel for his advice and encouragement     

Immunohistochemical localization of FSH and LH in the pars distalis of vervet (Cercopithecus aethiops) and babbon (Papio hamadryas) pituitaries

Summary Antisera against oLH¹, oLH and hFSH were used to localize gonadotropic cells in the pars distalis of Cercopithecus aethiops and Papio hamadryas. Three separate cell types were observed for FSH and LH: 85% of immunohistochemically identified gonadotropic cells reacted to all the various antisera; 10% reacted with the anti-LH antibody only; and 5% with the anti-hFSH antibody only. Comparisons between adjacent serial sections treated with various antisera, other than anti-gonadotropic hormones, demonstrated that the gonadotropic cells of these monkeys did not respond to these antisera.

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Résumé Des anticorps anti-LH ovine, anti-LH ovine et anti-FSH humaine ont été utilisés pour localiser les cellules gonadotropes dans la pars distalis de l'hypophyse des Singes Cercopithecus aethiops et Papio hamadryas. Trois catégories cellulaires distinctes, réagissant avec des anticorps anti-hormones gonadotropes, ont été observées. 85% des cellules immunoréactives identifiées en tant que cellules gonadotropes réagissent simultanément avec les différents anticorps mentionnés; 10% des cellules gonadotropes réagissent seulement avec l'anticorps anti-oLH et 5% de ces cellules seulement avec l'anticorps anti-hFSH. La comparaison avec des coupes adjacentes traitées par divers anticorps autres que les anticorps anti-gonadotropines prouve que les cellules gonadotropes de ces Singes ne réagissent jamais simultanément avec l'un ou l'autre de ces anticorps.

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Abbreviations used in this Article oLH ovine luteinizing hormone - hFSH human follicle stimulating hormone - ACTH corticotropin - GH growth hormone - LPH lipotropin - TSH thyrotropin     

Effects of Methallibure (ICI 33,828) on the pars distalis of pituitary,testis and thumb pad of the green frog,Rana esculenta L.

Summary The influence of ICI compound 33,828 (1--methylallylthiocarbamoyl-2-methylthiocarbamoylhydrazine = Methallibure) on the pars distalis of pituitary, testes and thumb pads was investigated in the intact adult male green frog, Rana esculenta. Methallibure affected the gonadotropic basophils (particularly the B2 cells) of the pars distalis, which showed varying degrees of degranulation and underwent a notable decrease in their percentage. Within the testis this compound caused the arrest of spermatogenesis. The most uniform effect of Methallibure was observed in the thumb pads, which invariably showed regression of the epidermis and glandular epithelium. No histological changes occurred in the thyroid and adrenal glands and the B1 and A1 cells of the pars distalis remained unchanged cytologically. It is concluded, in concordance with the available data, that Methallibure is a non-steroidal antigonadotropic compound. The important question about its mode of action has been brought into discussion.Work supported by the National Research Council of Italy, and the Population Council (Grant No. M70.082 C) of New York.     

Cytological changes in the pars distalis of pituitary of the green frog,Rana esculenta L., during the reproductive cycle

Summary The cytological changes in the pars distalis of pituitary of male and female green frog, Rana esculenta during the reproductive cycle have been studied by examining the form, cytoplasmic granulation and numerical proportions of the different cell types. Some sex differences were recorded, particularly in relative total number of cells in a median sagittal section of the pars distalis. No extensive cytological changes occur during the hibernation period, but there are striking alterations at the time of spring awakening, during spawning months and during replenishment of the spent gonads i.e. during late summer and autumn months. Important changes are to be observed in the acidophils type one (A1) and basophils type two (B2) and three (B3). Changes in the A1 cells during breeding season have been speculated as being in support of the spawning activity of the animal. The B2 cells exhibit most profound changes which correlate precisely with the morphological changes in gonads, and these cells are considered as the FSH-gonadotrops. The functional significance of the B3 cells is discussed and it is suggested that they might be the source of an ICSH- or LH-like hormone.The work has been supported by grant from the National Research Council of Italy.The award of postdoctoral fellowship by the National Research Council of Italy is gratefully acknowledged.     

An electron microscopic study of stellate cells and cavities in the pars distalis of frog pituitary

Stellate cells in the pars distalis of adult Rana ridibunda were observed electron microscopically under normal and experimental conditions (TRH injection). The stellate cells have lengthy processes extending into the intercellular spaces between the secretory cells and scanty cytoplasm surrounding the nucleus. Occasional desmosomes link stellate cells to adjacent secretory cells. In the pars distalis of animals injected with thyrotropic-releasing hormone (TRH), the stellate cells form large cavities (2-6 mum) filled with heterogeneous material. Their cytoplasm contains well-developed Golgi complexes and some lysosomes; these are the principal morphological alterations as compared to those observed in control animals. It is suggested that stellate cells could play an active role in addition to providing a structural framework for the pars distalis.