Thyrotrophs Research Articles

Localization of thyrotropin-releasing hormone receptor and thyrotroph embryonic factor on mouse chromosome 15.

We report the localization of two genes expressed in anterior pituitary thyrotrope cells, thyrotropin- releasing hormone receptor (Trhr) and thyrotroph em- bryonic factor (Tey'), on mouse Chr 15. Trhr is a G-pro- tein-coupled receptor that activates the inositol phos- pholipid-calcium-protein kinase C transduction pathway upon the binding of the hypothalamic factor, thyrotropin-releasing hormone (TRH; Straub et al. 1990). TRH increases the production and secretion of thyroid stimulating hormone (TSH) by anterior pitu- itary thyrotrope cells. TSH is necessary for growth because of its role in the development of the thyroid gland and the production of thyroid hormone. Tefis a leucine zipper transcription factor that is related to the bZIP family (Drolet et al. 1991). While Tefis expressed broadly in the adult, expression in the embryo is con- fined to the developing thyrotrope cells of the anterior pituitary (Drolet et al. 1991). This expression follows the same temporal and spatial pattern of the beta sub- unit of TSH (Tshb). Moreover, Tefhas been shown to bind three sites in the mouse TSHb promoter and stim- ulate Tshb promoter activity in transiently transfected CV-1 cells (Drolet et al. 1991). Using an interspecific backcross provided by The Jackson Laboratory, (C57BL/6J x M. spretus)F1 x M. spretus, we localized Trhr and Tel on mouse Chr 15. We first linked Trhr and Tefto mouse Chr 15 by hap- lotype analysis with two simple sequence repeat mark- ers that were previously characterized on this cross, D15Mit3 and D15Mit16 (The Jackson Laboratory, un- published results). We then confirmed the localization of Trhr and Tef with D15Mit10. Trhr and Tef were typed with RFLPs that were detected by Southern blot analysis, performed as pre- viously described (Lossie et al. 1993). A 980-bp EcoRV to BstXII fragment, which corresponds to amino acids 371 to 393 plus 900 bp of 3' untranslated

A thyrotrope-specific variant of Pit-1 transactivates the thyrotropin beta promoter.

Thyrotropin (TSH) beta is a subunit of TSH, the expression of which is limited to the thyrotrope cells of the anterior pituitary gland. Tissue-specific expression of the mouse TSH beta gene is conferred by sequences between -270 and -80 of the 5'-flanking region. We have investigated tissue-specific expression of the TSH beta promoter in two thyrotrope-derived cell types: 1) TtT-97 thyrotropic tumors, which express the endogenous TSH beta gene, and 2) an alpha-TSH cell line, which was generated from a thyrotropic tumor that has lost the ability to express the TSH beta gene. The pituitary-specific transcription factor Pit-1 is present in thyrotropes and interacts with three cis-acting elements in the functionally important region of the TSH beta promoter. Pit-1 protein is present in TtT-97 tumor cells but is absent from alpha-TSH cells. Reintroduction of Pit-1 into alpha-TSH cells by transient transfection does not restore TSH beta promoter activity. We have identified an alternately spliced variant of Pit-1, called Pit-1T, the mRNA and protein expression of which is limited to thyrotrope-derived cells. Pit-1T contains a 14-amino acid insert in the transactivation domain due to an alternate 3' splice acceptor site. Transiently transfected Pit-1T increases TSH beta promoter activity in TtT-97 thyrotropic tumor cells, whereas additional Pit-1 has no effect. The alpha-TSH cell line, which lacks all Pit-1 proteins, requires both isoforms in order to stimulate TSH beta promoter activity. These data suggest that Pit-1T is a thyrotrope-specific splice variant of Pit-1 that is required for TSH beta promoter stimulation; furthermore, both Pit-1 and Pit-1T are required for TSH beta promoter activity in thyrotrope cells.

Mutation of the POU-specific domain of Pit-1 and hypopituitarism without pituitary hypoplasia.

A point mutation in the POU-specific portion of the human gene that encodes the tissue-specific POU-domain transcription factor, Pit-1, results in hypopituitarism, with deficiencies of growth hormone, prolactin, and thyroid-stimulating hormone. In two unrelated Dutch families, a mutation in Pit-1 that altered an alanine in the first putative alpha helix of the POU-specific domain to proline was observed. This mutation generated a protein capable of binding to DNA response elements but unable to effectively activate its known target genes, growth hormone and prolactin. The phenotype of the affected individuals suggests that the mutant Pit-1 protein is competent to initiate other programs of gene activation required for normal proliferation of somatotrope, lactotrope, and thyrotrope cell types. Thus, a mutation in the POU-specific domain of Pit-1 has a selective effect on a subset of Pit-1 target genes.

The Pituitary Gland in Hyperthyroidism

The pituitary glands of 33 patients (24 women and 9 men, 18 to 78 years old) who died in thyrotoxicosis (18 with Graves' disease and 15 with toxic multinodular goiter [Plummer's disease]) were examined by histologic and immunocytologic methods. Thirteen patients (39%) died in "thyroid storm." The avidin-biotin-peroxidase complex immunostaining method was used to demonstrate the spectrum of pituitary hormones, including growth hormone, prolactin, adrenocorticotropic hormone, thyrotropin, follicle-stimulating hormone, luteinizing hormone, and alpha-subunit. The most striking finding was a pronounced decrease or loss of immunoreactivity to thyrotropin in all thyrotoxic cases, a consistent change that allowed ready distinction of thyrotoxic from euthyroid pituitary glands. When immunoreactive thyrotrophs were identified, they were sparse and small and demonstrated only faint thyrotropin reactivity. No morphologic differences were noted between the pituitary glands of patients with Graves' disease or Plummer's disease or between sexes. Loss of thyrotropin immunoreactivity was found to be reversible in that thyrotropic cells in the pituitary glands of 16 additional concurrently studied patients, who had thyrotoxicosis but were treated and subsequently had normal thyroid function or hypothyroidism, appeared normal or even hyperplastic. Other types of adenohypophysial cells in both the thyrotoxic and the successfully treated groups exhibited no abnormalities. Pituitary adenomas were incidental findings in 6 of the 33 patients (18%). Their immunotypic spectrum included three prolactin-immunoreactive tumors, two growth hormone-containing adenomas (one of which was plurihormonal), and one tumor with follicle-stimulating hormone and luteinizing hormone; no thyrotropin-containing adenomas were noted. No examples of pituitary hyperplasia were encountered in pituitary glands of thyrotoxic patients, and no hypophysitis or fibrosis was noted.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and Characterization of Mouse Complementary DNAs Encoding α and β Thyroid Hormone Receptors from Thyrotrope Cells: The Mouse Pituitary-Specific β2 Isoform Differs at the Amino Terminus from the Corresponding Species fromRat Pituitary Tumor Cells

Thyroid hormones (T3) and their receptors (TR) play a critical role in the function of the pituitary gland, particularly in thyrotropes, where they regulate expression of the alpha- and beta-subunits of TSH. Since the pituitary gland is composed of several cell types, we undertook a characterization of TR subtypes in a murine thyrotropic tumor (TtT-97), an excellent model in which to study thyroid hormone action in thyrotropes. We screened a thyrotrope cDNA library with rat TR alpha 1 and TR beta 1 cDNA probes and isolated cDNAs encoding the mouse TR alpha 1 and TR beta 1 isoforms as well as a partial clone corresponding to the non-T3 binding carboxy-terminal alpha 2 variant. The polymerase chain reaction was used to amplify additional cDNAs for the specific 5' domains of the mouse TR beta 1 and the pituitary-specific TR beta 2 amino-terminal variant. Using hybridization probes that discriminate between the alpha and beta isoforms and their variants, we demonstrated that thyrotropes contain TR alpha 1 and alpha 2 mRNAs as well as transcripts encoding Rev-erbA, which arise by transcription from the opposite strand of the TR alpha gene. In thyrotropes, the ratio of alpha 2 to TR alpha 1 mRNA levels more closely resembled the distribution in mouse brain than that in heart, where the mRNA levels of TR alpha 1 and alpha 2 are comparable. TR beta 1 and TR beta 2 mRNAs were detected in thyrotropes and were of similar size (approximately 6.4 kilobases). Despite the almost complete conservation between the rat and mouse TR beta 1 sequences at the protein level, the mouse and rat TR beta 2-specific N-terminal domains were less conserved, and the mouse protein was shorter by 39 amino acids at the N-terminus. Of the receptor species, only the mRNA encoding the TR beta 2 isoform, which was restricted to thyrotropes, was decreased by T3 treatment, although the mRNA for the alpha 2 variant was also reduced by T3 in thyrotropes and heart tissue. Levels of TR beta 1 mRNA were not changed in liver, but were increased in thyrotropic tumors and also somewhat in brain, an organ that is not responsive to T3 by classical criteria.

Immunocytochemical study of cell type distribution in the pituitary of Barbus barbus (Teleostei, Cyprinidae)

Antisera to mammalian pituitary and placental hormones have been used to identify and localize the different cell types in the pituitary of the barbel ( Barbus barbus, L.). The immunocytochemical labeling employed the immunoperoxidase technique or the immunogold silver staining procedure. Corticotrophic and prolactin cells, visualized using antisera to human adrenocorticotropic hormone and ovine prolactin (PRL), respectively, occur in the rostral pars distalis (RPD). Antisera against mammalian gonadotropins [ovine folliclestimulating hormone (FSH); bovine luteinizing hormone] or porcine growth hormone selectively cross-react with two different cell populations occupying the major part of the proximal pars distalis (PPD). Thyrotropic cells, stained by an antiserum to whole human thyroidstimulating hormone preabsorbed with porcine FSH, are scattered throughout the PPD and found amongst growth hormone and gonadotrophic cells. The majority of pars intermedia cells are stained with anti-melanophore stimulating hormone whereas the scattered PAS positive cells are revealed by both anti-ovine PRL and anti-bovine placental lactogen (or chorionic somatomammotropin). The latter antiserum also cross-reacts with the PRL cells of the RPD. Our results indicate that the distribution of the different cell types in Barbus barbus is similar to that described in other families of teleosts. This report is also the first demonstration of antigenic similarity between mammalian placental lactogen and fish prolactin.

The effect of sodium perchlorate and ionizing irradiation on the thyroid parenchymal and pituitary thyrotropic cells.

In a 46-week-experiment on 72 female mice the influence of peroral 1.2% sodium perchlorate application, total ionizing irradiation with 8 Gy on 5 consecutive days and their interaction on the pituitary-thyroid axis was studied by histological and stereological methods. It was observed that perchlorate alone caused long-term and strong hypothyroidism with hypertrophic and hyperplastic thyroid epithelial cells as well as pituitary thyrotropic cells. When only irradiation was used, no uniform changes in the structure and function of these cells could be detected. The interaction of perchlorate and irradiation showed similar effects as thyrostatics alone, with some exceptions; paradoxically, minor hyperplasia of thyrotropic as well as of parafollicular cells was observed. A high percentage of the follicular cell carcinoma was found after perchlorate application and after its combination with irradiation. No medullary carcinoma was found.

Protein Factors in Thyrotropic Tumor Nuclear Extracts Bind to a Region of the Mouse Thyrotropin β-Subunit Promoter Essential for Expression in Thyrotropes

The beta-subunit gene of TSH is specifically expressed in thyrotrope cells of the anterior pituitary gland. To define the particular TSH beta-subunit gene sequences responsible for tissue-specific expression, TSH beta promoter fragments were assessed for promoter activity by gene transfer into TSH-expressing thyrotropic tumor cells (TtT-97). Previous studies have shown that the murine TSH beta gene promoter was more efficiently used in TtT-97 cells compared to other pituitary-derived cells or nonpituitary fibroblasts and that a 191-basepair DNA sequence of the 5' flanking region between -271 and -80 was sufficient for maximal promoter activity in thyrotropes. Further deletional analysis within this region has localized the area responsible for expression in thyrotropes to a 37-basepair region between -117 and -80 up-stream of the major transcriptional initiation site. DNase-I protection assays demonstrated that this functionally defined 5' flanking area, in addition to the adjacent sequences immediately up-stream and down-stream, interacts with protein factors present in nuclear extracts from TtT-97 tumor cells. When fused to a heterologous promoter, fragments derived from the region between -271 and -80 exhibited cell-specific activity, although this was not conferred solely by the TSH beta promoter fragment from -117 to -80. Heterologous promoter activity was further stimulated when fragments containing the areas from -271 or -201 to -77 were used, suggesting combinatorial cis interactions between these regions of the TSH beta promoter. DNase-I protection studies suggest that there are multiple protein-binding domains in the mouse TSH beta 5' flanking sequence. Only the more proximal domains, which encompass important promoter elements, appear to be required for efficient expression in thyrotropes, whereas other more up-stream sites of protein interaction may be involved in regulatory aspects of TSH beta gene expression.

Thyrotrope Expression and Thyroid Hormone Inhibition Map to Different Regions of the Mouse Glycoprotein Hormone α-Subunit Gene Promoter*

The alpha-subunit gene of the glycoprotein hormones is normally expressed in pituitary thyrotropes and gonadotropes and in placental cells. Thus, this gene must contain elements that mediate expression and hormonal responses in different cell types. The localization of DNA regions important for expression and regulation of the alpha-subunit gene in thyrotrope cells has not previously been reported. In these studies luciferase expression constructs containing 1700 basepairs of 5' flanking DNA derived from the mouse alpha-subunit gene were introduced by electroporation into freshly dispersed cells from TSH-producing mouse pituitary tumors (TtT 97). This promoter functioned with greater efficiency in thyrotropes than in nonthyrotrope pituitary GH4 cells and L-cell fibroblasts. Primer extension confirmed that transcription from the alpha-subunit constructs initiated at the same site as the endogenous gene. Studies using 5' truncations showed a progressive loss of alpha-subunit promoter activity in thyrotropes between -480 and -120, with regions upstream of -254 contributing substantially to expression in thyrotrope cells. Thyroid hormone inhibited alpha-subunit promoter activity in a dose-dependent fashion, although in vivo treatment of tumors with thyroid hormone before transfection was necessary to achieve maximal inhibition. Thyroid hormone inhibition of alpha-subunit promoter activity also occurred in GH4 cells, but no effect was observed in L-cells. Studies using 5' truncations localized a region responsible for thyroid hormone inhibition between -62 and +43, encompassing the TATA sequence and the transcriptional initiation site. When this region was compared to the thyroid hormone inhibitory regions of the alpha-subunit genes from other species and the mouse TSH beta-subunit gene, a 6-basepair motif, 5' (G/A)GTG(G/A)G 3', emerged as a possible consensus sequence for a thyroid hormone inhibitory element.

Thyrotropin-releasing hormone-immunoreactive system in the brain and pituitary gland of the sea bass ( Dicentrarchus labrax, teleostei)

The immunohistochemical distribution of thyrotropin-releasing hormone-like immunoreactivity (TRH-ir) in the brain and pituitary of the sea bass ( Dicentrarchus labrax) was examined on cryostat sections of tissues perfuse fixed in a formaldehyde-glutaraldehyde mixture. TRH-ir fibres were found in many areas of the brain: dorsal and ventral telencephalon, preoptic and tuberal hypothalamus, thalamus, midbrain tegmentum, optic tectum, and medulla oblongata. In the hypothalamus the densest area of innervation was the nucleus anterioris tuberis and medial nucleus recessus lateralis, where small TRH-ir cell bodies were also found. In the pituitary gland, TRH-ir fibres were numerous in the posterior neurohypophysis, and these appeared to form varicosities between groups of melanocorticotropic cells of the pars intermedia. No clear relationship was seen between TRH-ir fibres and the thyrotropic cells, or any other cell type of the pars distalis. In the brain stem a notable feature was the prominent innervation of groups of motoneurons by beaded TRH-ir fibres. These observations suggest that in teleost fishes the role of TRH may be related to pars intermedia function, rather than the thyrotropin- or prolactin-releasing function established in tetrapods. In addition the tripeptide may act as a central neurotransmitter involved in sensory and autonomic motor integration.

Identification ofCis-Acting Promoter Elements Important for Expression of the Mouse Glycoprotein Hormone α-Subunit Gene in Thyrotropes

The glycoprotein hormone alpha-subunit gene is expressed in a cell-specific manner in the anterior pituitary and placenta. Previous studies have shown that the region between -178 to -111 is indispensable for placental-specific expression of the human alpha-subunit gene. Using gene transfer techniques with chimeric luciferase plasmids, this report identifies regions of the mouse alpha-subunit promoter that are important for transcriptional activation in primary thyrotropic cells. Transient expression of a series of 5' flanking DNA deletions resulted in stepwise reductions of basal promoter activity between -480 to -417 (4-fold), -254 to -177 (5-fold), and -177 to -120 (3.5-fold). DNase-I protection analysis with nuclear extracts from thyrotropic tumor cells revealed specific protein-DNA interactions within each of these functionally defined regions. These were mapped to positions -474 to -452, -447 to -419, -213 to -170, and -158 to -101 within the 5' flanking region. In contrast, in mouse fibroblast L-cells no significant difference in alpha-subunit promoter activity was found by deleting the region from -480 to -177. However, a 3-fold decrease, similar to that found in primary thyrotropes, was found by deleting the region from -177 to -120. Further, a smaller region between -138 and -122 was the only area detected by the DNase-I protection assay using L-cell nuclear extracts. Thus, several cis-acting promoter elements located up-stream of position -177 are important for expression in thyrotropes. These elements also bind nuclear factors present in thyrotropes but not in nonpituitary fibroblasts and, therefore, differ from those mediating expression of the human alpha-subunit gene in the placenta.

Thyrotropin-Secreting Pituitary Adenomas: Clinical and Biochemical Heterogeneity

To evaluate the clinical and biochemical features of patients with TSH (thyroid-stimulating hormone, thyrotropin)-secreting pituitary tumors; to measure the biologic activity in vitro of circulating TSH from selected patients before and after pituitary surgery. Case series. Patients in an endocrinology unit. Nine patients with TSH-secreting pituitary tumors. All patients had hyperthyroidism, elevated free thyroxine and triiodothyronine levels, and detected levels of TSH. The free alpha subunit, a tumor marker for neoplasms of gonadotropic or thyrotropic cell origin, was elevated in all nine patients. Seven of the nine patients had been treated with thionamides, radioactive iodine, or thyroidectomy for presumed primary hyperthyroidism. The delay from the initial treatment of hyperthyroidism to the correct diagnosis of a pituitary neoplasm was 6.2 +/- 4.8 (mean +/- SD) years. Two of the seven patients with macroadenomas died in the perioperative period (one at NIH, one at a referring hospital). Of the remaining five patients with macroadenomas, four have residual tumor and inappropriate TSH secretion, despite surgery and radiation therapy, at follow-up from 3.5 to 6 years. In contrast, the two patients with microadenomas are clinically cured 2.5 and 4 years after transsphenoidal adenomectomy. The biologic to immunologic (B/I) ratio of serum TSH, determined preoperatively in five patients with TSH-secreting tumors, was elevated compared with euthyroid subjects. In three patients the B/I ratio of serum TSH was also measured after pituitary surgery; in two the elevated B/I ratio returned to normal after successful pituitary adenomectomy, while in the third this ratio remained elevated after incomplete adenoma resection. With the routine availability of ultrasensitive TSH assays and their increasing use to confirm thyrotoxicosis from all causes, we expect that TSH-secreting pituitary tumors will be diagnosed earlier, before inappropriate antithyroid therapy, permitting an improved outcome.

Morphometric evaluation of subcellular changes induced by in vivo TRH treatment in the pituitary gland of Rana perezi: Effects on prolactin and thyrotropic cells

The effects of synthetic thyrotropin-releasing hormone on pituitary prolactin and thyrotropic cells were investigated in adult male Rana perezi (formerly Rana ridibunda) frogs. Animals were given daily injections of synthetic thyrotropin-releasing hormone into the dorsal lymph sac. Prolactin and thyrotropic cells were identified by the colloidal-gold method, using anti-human prolactin and anti-human-beta-thyrotropin hormone as primary antisera. The stereological parameters of the rough endoplasmic reticulum, Golgi complex, and secretory granules of prolactin and thyrotropic cells were evaluated by ultrastructural morphometry (point-counting method). Thyrotropin-releasing hormone caused cytological changes in both cell-types which were consistent with increased synthesis and release of both prolactin and thyrotropin. These changes were still significant after 48 h treatment in the case of thyrotropic cells, while in prolactin cells the thyrotropin-releasing hormone increased the number of secretory granules. After 6 days, the cells resembled essentially those used as controls. These results indicate that thyrotropin-releasing hormone stimulates the synthesis and release of prolactin and thyrotropin, and that the response of each cell type to this hypothalamic stimulus follows a different time-course.

Immunocytochemical and ultrastructural characterization of the cell types in the adenohypophysis of Sparus aurata L. (Teleost)

The structure and immunocytochemistry of the adenohypophysis of sexually mature male specimens of Sparus aurata (gilthead sea bream) were studied. The adenohypophysis was composed of rostral pars distalis (RPD), proximal pars distalis (PPD), and pars intermedia (PI). In the RPD the prolactin cells were organized into follicles which occupied a very reduced area as corresponds to that in saltwater fishes; the corticotropic cells were surrounding the pars nervosa branches and the prolactin follicles. The PPD showed somatotropic, gonadotropic, and thyrotropic cells. The somatotropic cells were isolated, clustered, or surrounding the pars nervosa branches. Only one polymorphic cell type of gonadotropic cells was found in the PPD ventral and dorsal areas and around the PI. The PI was composed mainly of melanotropic cells and a PAS-positive cell layer adjacent to the neurohypophysis. The ultrastructure of the presumptive endocrine cells was reported and their distribution was discussed in relation to those of other teleosts.

Influence of starvation on hormonal control of hypophyseal secretion in rats

The reduction of hypophyseal hormone secretion during starvation is not completely understood. A previous study showed that the concomitant reduction of plasma TSH and T3 may be related to an increased sensitivity of the thyrotrope cell to T3. This suggests that regulation of hypophyseal secretion by peripheral hormones may be altered in starved rats. As GH and PRL secretion are under the control of thyroid and steroid hormones, the aim of the present study was to investigate the modification of feed-back control by T3 or E2 on hypophyseal secretion during starvation. For this purpose, pituitary GH, PRL and TSH contents and their plasma responses to TRH injection were measured in euthyroid, thyroidectomized (Tx), T3-supplemented Tx and E2-treated male Wistar rats before and after a 3-day starvation. TRH (0.25 micrograms/100 g) was injected iv through a chronically-implanted catheter. Our results show that GH content and GH plasma response to TRH are dramatically increased in T3-treated Tx starved rats, suggesting that starvation also increases the effectiveness of T3 influence on somatotrope cell secretion. By contrast, effects of T3 on PRL secretion remain unchanged during starvation. Furthermore, starvation in E2-treated rats is associated with a marked rise in the PRL and GH responsiveness to TRH without any significant change of hormonal pituitary content. This suggests that, in starved rats, E2 increases the effects of TRH on lactotrope and somatotrope secretion. No significant effect on TSH secretion could be demonstrated. Thus, starvation seems to act differentially on the feed-back mechanisms controlling the hormonal secretion of the three adenohypophyseal target cells to TRH.

Cytological responses of the pituitary (rostral pars distalis) and immunoreactive corticotropin-releasing factor (CRF) in the goldfish treated with dopamine antagonists

The in vivo effects of three dopamine (DA) antagonists on the cytology of the rostral pars distalis (RPD) were investigated in young goldfish ( Carassius auratus L.). Pimozide, sulpiride, and domperidone were injected for 5 (low dose, Experiment I) and 7 days (higher dose, Experiment II). Cytological and immunocytochemical techniques using antisera to (1–24) ACTH and (1–39) ACTH, human β-thyrotropin (TSHβ), and synthetic (1–41) CRF were applied to pituitary and brain sections. Cytometrical studies showed that the three drugs induced similar quantitative changes in the cells of the RPD. Prolactin (PRL)-secreting cell hypertrophy was significant in Experiment 11, whereas the nuclear enlargement was significant in both experiments. The numbers of cytoplasmic granules were similar in control and treated goldfish. Thyrotropic (TSH) cells and their nuclei were significantly enlarged in both experiments; their content in immunoreactive TSH was not clearly modified. Corticotropic (ACTH) cells showed significant nuclear and cellular hypertrophy, and labeled granules were often concentrated along the cell membrane. The amount of immunoreactive CRF present in the rostral neurohypophysial ramifications was reduced in the majority of treated fish. Solvent-injected controls showed no significant changes in the RPD. These results suggest that DA inhibits PRL cell activity in goldfish. TSH and ACTH cells appear stimulated by DA-receptor blockers, although differential effects on synthesis and release cannot be evaluated in in vivo experiments. A release of corticotropin-releasing factor may be involved in the ACTH cell stimulation. These data are compared with those obtained in other vertebrates.

Immunohistochemical localization of thyrotropic cells during amphibian morphogenesis: A stereological study

TSH-like producing cells have been studied using the peroxidase-antiperoxidase (PAP) immunohistochemical technique and rabbit anti-human thyrotropin (TSH) antiserum in the pars distalis of five species of amphibian anuran tadpoles at different stages of development as well as in 1-year-old postmetamorphic animals. This cell type has been identified and located in the pars distalis ventral zone of Bufo calamita showing no changes in its distribution pattern throughout development, and in Rana perezi where TSH-like cells were located in the central zone of the gland in premetamorphic stages, occupying the ventral zone at the end of metamorphosis. No immunoreaction has been observed in the other species studied ( Hyla meridionalis, Alytes cisternasii, and Pelobates cultripes). Morphometry and stereology were used to evaluate the changes observed in pars distalis volume and TSH immunoreactive cells during development. Pars distalis volume increased during the larval growth period and decreased throughout the metamorphic climax. TSH volume density and cellular area showed different evolutions in the species studied. The correlation between these parameters suggests a greatly proliferative period followed by an increase in cellular size. The changes observed in TSH total volume as well as the physiological data found by other authors lead us to conclude that there are two phases in amphibian development: first a period of TSH storage (pre- and prometamorphosis) and second a period of TSH release at metamorphic climax.

Neuroendocrine significance of vasoactive intestinal polypeptide.

The new data reported here, and available in the literature, are interpreted to indicate that acute release of PRL in stress is probably mediated by secretion of VIP and PHI arising from a subpopulation of paraventricular cells in the tuberoinfundibular system, and that this secretion is under serotonergic control, presumably by way of the raphe nuclear projection to the hypothalamus. The acute PRL response to suckling response is only partially under VIP/PHI control, and may be regulated by an as yet unidentified neural lobe hormone. In addition to the hypothalamic component of PRL regulation, there is a well-defined population of VIP cells within the pituitary, representing the only known example of VIP expression outside of nerve cells. This population of VIP cells is exquisitely responsive to thyroid status, and in common with the thyrotrope cell, is activated by hypothyroidism. Since VIP secretion is enhanced in the hypothyroid pituitary, and VIP release is stimulated by TRH, it is reasonable to postulate that paracrine VIP secretion may play a role in the reasonable to postulate that paracrine VIP secretion may play a role in the hyperprolactinemia prolactinemia that occurs in the hypothyroid human, although this is clearly not the case for the rat in whom hyperprolactinemia was not demonstrable. The role of VIP/PHI in human pituitary disease is unknown. We have been unable to identify any tumors that contain immunoreactive material using tissues prepared by standard methods. It may be that the demonstration of VIP/PHI is more demanding and will require better techniques for staining. The role of tuberoinfundibular VIP hypersecretion remains to be established but the evidence for stress-induced PRL hypersecretion in man encourages us to believe that at least some cases may be due to excessive hypothalamic activity. Additional potential neuroendocrine actions of VIP are in the secretomotor control of the ovary and thyroid, and in the regulation of somatostatin secretion and synthesis. In dispersed cell cultures (but not in whole hypothalamic slices from adult animals), VIP stimulates somatostatin secretion and independently stimulates the formation of somatostatin mRNA, an effect that can be duplicated in mixed cultures by treatment with forskolin, a postreceptor cAMP stimulator. In work carried out by Montminy and colleagues, the cAMP action has shown to be mediated by formation of a soluble protein that appears to activate the somatostatin gene promotor through interaction with a specific gene sequence.

Thyroid and Pituitary Function Following Allogeneic Bone Marrow Transplantation

Thyroid function was evaluated in 13 consecutive patients with chronic myelogenous leukemia to verify in allogeneic bone marrow transplantation if the fractionated irradiation protocol with low dose rate, previously applied to reduce the damage to various organs, also prevents the 43% incidence of primary hypothyroidism that occurs after the administration of single dose with higher dose rate. Following bone marrow transplantation, decreased plasma levels of total thyroxine and triiodothyronine and impaired response of thyrotropic cells to thyrotropin-releasing hormone were observed. These alterations reverted to normal in nine months and none of the patients was hypothyroid at the end of follow-up. The damage to thyrotropic cells appears to be selective because the secretion of prolactin was not impaired and that of gonadotropins even increased, as a consequence of gonadal failure. Longer follow-up is needed to determine if this irradiation protocol, which prevents the complication of permanent primary hypothyroidism and does not cause any destruction of thyroid cells, may increase the risk of irradiation-related thyroid tumors.

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

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 beta or FSH and exhibited seasonal variations.(ABSTRACT TRUNCATED AT 250 WORDS)