Thyrotroph Cells Research Articles

Secretory activity of Poecilia latipinna (teleostei) pituitary in vitro: rostral pars distalis and proximal pars distalis

The ultrastructure of each adenohypophysial secretory cell type was examined in pituitaries of adult female mollies ( Poecilia latipinna) after various periods in vitro, and with varied medium osmotic pressure (OP), Na +, and Ca 2+ concentrations. Prolactin (PRL) cells were markedly activated by 18 hr, and after 7 or 14 days were almost totally degranulated, with massive arrays of Golgi and RER. Reduction in OP, but not Na + or Ca 2+, caused an additional activation of PRL cells after periods of 18 hr or longer. Corticotroph (ACTH) cells became noticeably activated by 4 hr, and were possibly affected by OP, but not Na + or Ca 2+. Growth hormone (GH) cells were activated by 6 hr, and after 18 hr were quite degranulated with extensive arrays of RER. OP had no effect on GH cells before 3 days, when reduced OP appeared to cause an additional activation, with the appearance of large irregular secretory granule (SG)-like inclusions. Na + and Ca 2+ again had no effect. Gonadotrophic (GtH) cells appeared to be little affected by in vitro incubation; however, the very active cells from vitellogenic fish underwent a reduction in dilated RER after prolonged culture. Thyrotrophic (TSH) cells gradually became activated in vitro, but the response again varied with the sexual condition of the fish. Neither GtH nor TSH cells were affected by OP, Na +, or Ca 2+. The findings are discussed in relation to hypothalamic control, via releasing/inhibiting factors, of adenohypophysial cell activity.

Ultrastructural detection of the onset of pituitary thyrotroph sensitivity to lowered thyroid hormone concentrations in the fetal sheep.

The goitrogen methylthiouracil was administered orally to pregnant ewes of known gestational ages to induce hypothyroidism in both mother and fetus. Developing pituitary thyrotrophic cells were studied using electron microscopy to detect the earliest gestational age at which morphological changes occurred in response to lowered plasma thyroid hormone concentrations. At 50 days of gestation, the pituitaries of fetuses exposed to the goitrogen were indistinguishable from untreated control glands. However, at 58 days and subsequent ages, "thyroidectomy' cells were observed in pituitaries of all hypothyroid fetuses. These findings indicate that fetal sheep pituitary thyrotrophs are sensitive to lowered thyroid hormone concentrations by 58 days of gestation, suggesting that thyroid-thyrotroph interaction exists at this early stage of development.

Argyrophil granules in the human pituitary

In order to assess the value of the Grimelius silver method in adenohypophysial cell identification and adenoma diagnosis, 22 nontumorous adenohypophyses and 50 pituitary adenomas were investigated. Grimelius positivity was localized, as documented by mirror sections, predominantly in PAS and led hematoxylin positive cells; but a few negative cells contained argyrophil granules as well. The immunoperoxidase method revealed Grimelius positivity primarily in corticotrophs, thyrotrophs and gonadotrophs, and occasionally in somatotrophs and lactotrophs. Argyrophilia was readily demonstrated in 11 out of 13 corticotroph cell adenomas, in 1 out of 1 thyrotroph cell adenoma, in 5 of 11 null cell adenomas and in 4 out of 5 oncocytomas. No argyrophilia was detected in 5 growth hormone cell adenomas and 5 prolactin cell adenomas. One our of 5 mixed, growth hormone cell-prolactin cell adenomas, and 1 out of 5 acidophil stem cell adenomas showed Grimelius positivity. By electron microscopy, silver grains were localized in the secretory granules. It can be concluded that no specific hormonal products account for argyrophilia.

Immunoperoxidase staining of primate pituitaries with antibodies against the beta subunits of human pituitary glycoprotein hormones.

The immunocytochemical specificity of antibodies against the beta subunits of human pituitary glycoprotein hormones was tested on human and monkey hypophyses. Anti-luteinizing hormone (LH) beta stained only gonadotrophic cells in both species, and anti-thyroid-stimulating hormone (TSH) beta only thyrotrophic cells. In monkeys, anti-follicle-stimulating hormone (FSH) beta demonstrated only gonadotrophs, but in man the antibody stained thyrotrophs equally well. Staining of the two cell types was diminished to a similar degree by dilution of the anti-FSH beta antibody. Human gonadotroph heterogeneity was revealed by absorption of anti-FSH beta with LH beta or TSH beta, which abolished immunostaining of a subset of gonadotrophs. Limitations in the immunocytochemical specificity of antibodies against beta subunits of pituitary glycoprotein hormones may be a consequence of incomplete purity of the generating antigens, structural overlap among the beta subunit of the three hormones, or a combination of these.

Effect of TRH and dopamine on cyclic AMP levels in enriched mammotroph and thyrotroph cells

Populations of normal anterior pituitary cells enriched in thyrotrophs or mammotrophs prepared by velocity sedimentation were used to investigate the effect of modulators of TSH and prolactin secretion on cyclic AMP accumulation. In both thyrotroph-enriched and mammotroph-enriched fractions, IBMX increased cyclic AMP accumulation. In the presence of IBMX, TRH invoked an increase in cyclic AMP suggesting that TRH modulates cyclic AMP accumulation in both of these cell types from normal pituitary glands. In the mammotrophrich fraction, dopamine inhibited the increase in cyclic AMP induced by TRH. In contrast however, in the thyrotroph-enriched fraction dopamine lowered neither cyclic AMP concentration nor TSH secretion. Thus the inhibiting effect of dopamine on cyclic AMP appears to be specific for prolactin-secreting cells.

Separation of rat pituitary thyrotrophic cells.

A method for the enrichment of live thyrotrophic pituitary cells is described. Pituitary glands of young male rats were removed into Earle's solution and dispersed in a 0.1% trypsin solution containing 0.5% bovine serum albumin, pH 7.2. Nylon fibres (25 microgram) were used for the separation of the thyrotrophic cells, by stringing them across a plastic frame which fitted a plastic Petri dish containing the cell suspension. The fibres were washed with light petroleum (b.p. 60--80 degree C) and carbon tetrachloride, hydrolysed with 3 M-HCL for 30 min at room temperature and washed with distilled water and phosphate-buffered saline (pH 7.2). The fibres were treated with thyrotrophin releasing hormone (TRH) alone or in the presence of soluble carbodiimide solution. After incubation for 1 h at room temperature, the fibres were transferred to a new Earle's medium and cells were released from the fibres by plucking them with a needle. The separated thyrotrophic cells were identified by radioimmunoassay and by electron microscopy. Using the above-mentioned methods, enrichment of thyrotrophic cells was obtained. Thus, the amounts of TSH, prolactin, LH and GH released, during 2 h of incubation, by 1.5 x 10(6) unseparated cells were 6.8 +/- 0.65, 4.1 +/- 0.47, 4.8 +/- 0.52 and 5.2 +/- 0.68 microgram respectively, while the same number of purified thyrotrophic cells released 76.1 +/- 0.42, 1.2 +/- 0.3, 0.6 +/- 0.35 and 1.6 +/- 0.22 microgram of the same hormones (means +/- S.E.M.).

Enriched Populations of Rat Pituitary Thyrotrophs in Monolayer Culture*

Rat anterior pituitary cells were dissociated and subjected to 4 h of unit gravity sedimentation. Eighty-five 8-ml fractions were collected, and nine pooled fractions were placed in monolayer culture for 1 week. The attached cells were immunocytochemically stained for TSH using an antiserum previously shown to be specific for the beta subunit of TSH and all culture media saved for subsequent assay of TSH. Thyrotrophs were localized both immunocytochemically and by radioimmunoassay to 1-2 fractions from the top of the sedimentation chamber. Typically, it was found that 60-80% of the cells in these fractions were immunocytochemically identified as thyrotrophs. Electron microscopic observations indicated that such cells displayed the classical morphological features associated with thyrotrophs. The enriched thyrotroph cultures responded to 1.0 mM dibutyryl cyclic AMP with an increased release of TSH indicating that the intracellular secretory machinery was not altered by the procedures employed. In all cases, the basal TSH secretion decreased with time in culture. In addition, the fractions containing the most TSH in the culture media were usually one fraction lighter (lower sedimentation rate) than the fractions which were found immunocytochemically to contain the highest percentage of thyrotrophs. The results suggest the possibility of two functionally distinct thyrotroph cell types as has been suggested for the pituitary somatotrophs.

Accumulation of secretory granules in pituitary clonal cells derived from the epithelium of Rathke's pouch.

2A8 clonal cells derived from the epithelium of Rahtke's pouch of the fetal rat are essentially agranular when grown in vitro, in spite of their active secretion of hormones, i.e., ACTH, prolactin and growth hormone. These cells do not produce detectable amounts of thyrotrophic or gonadotrophic hormones in vitro. When the growth medium (Ham's F10) was supplemented with rat median eminence extract (MEE), L-thyroxin and fresh serum from hypophysectomized rats, some of the 2A8 cells accumulated and stored secretory granules which were characteristic of the cells of the intact pituitary gland. Typical thyrotrophic and gonadotrophic cells also became recognizable and all six anterior pituitary hormones were released into the culture medium. Growth of 2A8 cells in this modified culture medium resulted in an increased production of all hormones with increasing time in culture. These results indicate that the processes that lead to the accumulation of typical mature secretory granules which characterize the individual pituitary cell types are initiated or promoted by some unidentified factor or factors which are present in fresh rat serum. It is also apparent that fresh rat serum can promote the differentiation of gonadotrophs and thyrotrophs in vitro.

IMMUNOCHEMICAL COMPARISONS BETWEEN A LOW MOLECULAR WEIGHT ADENOHYPOPHYSEAL CONSTITUENT AND THE GONADOTROPHINS

A biologically active peptide (called sperm-releasing substance, abbreviated SRS) with a molecular weight of about 5000, prepared from bovine adenohypophyses, has been compared with the known adenohypophyseal glycoprotein hormones using immunological methods. By means of immunofluorescence it can be seen that antisera against SRS have an affinity for the gonadotrophic cells in the anterior pituitary. Using complement fixation assay and immunodiffusion, no similarity between SRS and FSH can be found, while there are great resemblances between the reactions of LH and those of SRS. From the radioimmunoassay studies, it can be seen that the alpha-subunit of LH reacts in the same way as SRS in the different systems. However, using immunofluorescence, the antiserum against SRS has an affinity for the gonadotrophic cells only, like anti-LHbeta, and not for the thyrotrophic cells, as has anti-LHalpha. The reasons for these different results are discussed.

Pituitary control of pigmentation in xanthic, moor, and white Carassius auratus L.

After hypophy sectomy some of the melanophores in moor fantail goldfish (Carassius auratus L.) underwent lysis and the remaining cells showed melanin aggregation. The orange colour in xanthic. moor, and white fantail varieties of goldfish 'pales' after hypophysectomy. Homogenates of whole pituitary, pars distalis, or neurointermediate lobe tissue given as intraperitoneal injections effected a marked increase in the melanophore index in hypophysectomized moor fantails and intensified the orange colour in hypophy sectomized moor and xanthic fantails.Ovine prolactin, ovine thyrotrophs (TSH), ovine somatotrophs (STH), and a combination of ovine luteinizing hormone (LH) and porcine follicle-stimulating hormone (FSH) were effective in increasing the melanophore index in hypophy sectomized moor fantails. Of these four preparations the LH–FSH combination was the most potent. Saline and thyroxine were without effect.Ovine prolactin, ovine STH. and a combination of ovine LH and porcine FSH restored the orange colour of hypophysectomized xanthic and moor fantails. Of these three preparations the LH–FSH was most potent. Saline, ovine TSH. and thyroxine were without effect.Differences were found in the apparent activity of prolactin, thyrotroph, gonadotroph, and putative melanocyte-stimulaling hormone (MSH) cells in the pituitaries of the three varieties of goldfish but these could not be directly correlated with pigmentation differences between the groups.

TRH AND PROLACTIN (HPr) IN PLASMA OF NEWBORNS DURING THE FIRST HOURS OF LIFE

HPr has been measured by radioimmunoassay (RIA) with FRIESEN materials. TRH RIA was performed by Dr Oliver. The mean (ng±SD/ml) HPr in paired maternal and cord plasma (n=13) was respectively 77.5±45.5 and 91.2±21.2. Mean HPr in plasma collected during the first six hours of life in 16 individual newborns was 144.7±63.9. Longitudinal study of 3 newborns indicates a small rise of HPr occurs between 30 min and 6 hrs. Measurement of plasma TRH in paired mothers and newborn gives the following results (pg/ml and range): mother 15.0 (7–29), cord= 41.8 (27–47), 20′ = 39.6 (33–49), 40′ = 44 (39–49), A separate study indicated no differences for plasma TRH in the cord between venous and arterial blood (n=2). In conclusion: 1) There is no sharp rise of HPr during the first hours of life as has been shown for TSH. 2) High plasma TRH in the newborn is probably responsible for the acute stimulation of pituitary thyroid axis. As it has been demonstrated previously that cord TSH is not high it can be postulated that TRH is ineffective in utero to stimulate thyrotroph cells.

Effect of thyroxine on the ultrastructure of the hypophyseal proximal pars distalis in Tilapia zillii.

The effects of exogenous L-thyroxine on the fine structure of the proximal pars distalis cells were examined in Tilapia zillii. In thyroxine-treated animals the thyrotrophic cells appeared marginally smaller and less active whereas the somatotrophs appeared markedly more active, with increased endoplasmic reticulum, larger mitochondria, and more granule release when compared with the same cell types in control animals. The gonadotrophs were similar in appearance in both thyroxine-treated and control groups.The possible interrelated activity of the somatotrophs and the TSH–thyroid axis is discussed.

Thyrotropin-Releasing Hormone Secretory Physiology: Studies by Radioimmunoassay and Affinity Chromatography1

Thyrotropin-releasing hormone (TRH) in rat blood and mathanol extracts of hypothalami has been quantified by a specific TRH radioimmunoassay, in conjunction with TRH affinity chromatography. Blood TRH was found to be elevated dramatically after 1 h by the physiologic stimulus, ambient cold (4 C), which was also attended by a 2-fold rise in serum thyrotropin (TSH). The acute administration of parenteral triodothyronine (T3) over a period of 48 h prior to identical cold exposure completely abolished the rise in serum TSH. Blood TRH however, rose in a fashion qualitatively similar to that seen in euthyroid animals. Similarly, chronic induction (32 days) of experimental euthyroidism, hypothyroidism, and hyperthyroidism, which altered metabolic states were corroborated by measurement of serum thyroxine (T4) and TSH, did not result in any significant changes in either the hypothalamic content or blood concentration of TRH. These data provide direct documentation that the regulatory control of pituitary TSH secretion by T4 and/or T3 is not mediated by inhibiting the hypothalamic secretion of TRH, but presumably by inhibiting the actions of TRH at the level of the pituitary thyrotroph cell.

Thyroid stimulators in health and disease.

Thyroid function in health is largely controlled by thyroid-stimulating hormone (TSH) produced by the thyrotroph cells of the anterior pituitary. Alterations of intrathyroidal iodine content may also be involved in autoregulation by the thyroid, particularly in states of iodine deficiency and excess (Ingbar, 1972). During pregnancy placental thyroid-stimulating agents-human chorionic thyrotrophin (HCT) and human molar thyrotrophin (HMT)-are produced. In the common variety of hyperthyroidism, Graves' disease, thyroid function appears to be regulated by thyroid-stimulating immunoglobulins (TSI) (Smith & Hall, 1974a). Human molar thyrotrophin can be produced by trophoblastic tumours in both sexes and thyroid-stimulating factors have been reported to be released by malignant tumours of the gut and by bronchogenic carcinomas, although this is one of the rarest of the ectopic hormone syndromes.

Further studies on the ultrastructure of the pars distalis of castrated male mice pituitary.

The fine structure of the pars distalis of castrated male mice has been examined. Different stages of degranulation and endoplasmic reticulum dilatation were found in gonadotroph cells. Some somatotroph cells contained an unusual number of lysosomes, which might be involved in the digestion of overproduced secretion material. The luteotroph cells frequently showed a remarkable hypertrophy of the Golgi complex. All the thyrotroph cells presented unusual cytoplasmic vacuoles and some abnormal mitochondria. Agranular cells containing large amounts of lysosomes were also evident. A peculiar parenchymal type of cell showing a prominent rough endoplasmic reticulum appeared isolated or in small groups. These cells are different from hypertrophic thyrotroph or gonadotroph cells, and would perform a very active protein synthesis. The lack of previous information about most of the features described here, might be due to the long period of castration undergone by the animals in the present experiment.

Electrical properties of cells in the adenohypophysis--an in vivo study.

Measurements of transmembrane potential, membrane resistance, and membrane capacitance in cells of the rat adenohypophysis show these parameters to be significantly lower than those for neuronal cells. The examination of a relatively pure population of ‘hypersecreting’ thyrotrophic cells, produced by the chronic adminstration of propylthiouracil, resulted in a significant change in the mean amplitude of the transmembrane potential, but no significant changes in the other membrane electrical parameters.

Mitosis of the rat anterior pituitary cells: an electron microscope study.

Mitosis of the rat anterior pituitary cells was studied with the electron microscope. Most mitotic cells found in the anterior pituitary contained a number of secretory granules, and a somatotrophic cell in metaphase contained a Golgi apparatus with newly formed secretory granules. Hypertrophied thyrotrophic cells after thyroidectomy underwent mitosis. Some prolactin-producing cells in mitosis contained a great number of vacuolated cisterns of rough endoplasmic reticulum, which were the characteristic results of long term administration of estrogen to female rats. Hypertrophy of the anterior pituitary glands after removal of a target organ or the administration of estrogen may be brought about by the proliferation of cells of a specific type corresponding to the experiment. This proliferation carried out by mitotic cell division of fully differentiated adenohypophyseal cells. The theory that highly differentiated cells producing specific hormone cannot synthesize DNA and divide by mitosis was shown to be erroneous.The outer layer of a kinetochore was bent by the pulling force of chromosomal spindle tubules. As the inner layer was not bent in this case, it became clear that the spindle tubules do not penetrate through the kinetochore, and the contraction of chromosomal tubules is believed to exert the force for the initial movement of anaphase chromosomes.

Effect of Thyroid States on Amino Acid Uptake and Incorporation in the Chicken Anterior Pituitary

RECENTLY Tonoue and Yamamoto (1967a, b, 1968) demonstrated that amino acid metabolism in the rat pituitary gland is regulated by the feedback relationship between the thyroid and pituitary. For example, thyroidectomy stimulated amino acid uptake by the pituitary and the stimulation was depressed by injection of thyroxine. Thyroidectomy enhanced amino acid incorporation into pituitary proteins, and thyroxine injection was effective in suppression of this increased incorporation. Furthermore, they showed evidence that these changes in amino acid metabolism are closely associated with those of thyrotroph cells.Mikami (1958) has reached the conclusion the thyrotroph cells are confined largely to the cephalic lobe of the pars distalis of fowl hypophysis, because after thyroidectomy a marked hypertrophy and thyroidectomy cells are observed within this lobe, and thyrotrophic potency of the cephalic lobe is much higher than that of the caudal lobe.In view of this specialty in the fowl pituitary it seemed of…

The Effect of Different Levels of Vitamin A on the Anterior Pituitary of Young Bulls

Summary Eighteen young bulls were maintained on a ration supplemented with different levels of vitamin A. The behaviour of various cell types of the anterior pituitary was studied. Advanced vitamin A deficiency caused a decrease of alpha cells and gonadotroph cells and an increase of chromophobe cells. There was a significant increase of thyrotroph cells in the anterior pituitary glands of bulls receiving clover hay, as compared with those animals receiving vitamin A in a pure form.

Effects of estrogen on pituitary morphology in goitrogen treated rats. An electron microscopic study.

AbstractThe influence on pituitary cytology of propylthiouracil (PTU) and estradiol benzoate (EB) administered singly and in combination was studied by electron microscopy in adult female rats. PTU alone induced striking changes in the morphology of thyrotroph cells, which were all transformed into typical thyroidectomy cells, characterized by enormously dilated ergastoplasmic sacs; the acidophils were degranulated and some of them took the appearance of relatively quiescent prolactin cells rather than degranulated somatotrophs. EB alone caused no definite changes in the morphology of thyrotroph cells; its essential effect was the development of a large number of prolactin cells. When both treatments were combined, thyroidectomy cells were found, existing side by side with untransformed thyrotrophs and exhibiting less dilated ergastoplasmic sacs than after PTU alone; prolactin cells were present in great number and showed a more developed ergastoplasm than after EB alone. Thyroid weight and height of the follicular cells were not changed by EB given singly; they were both increased under the influence of PTU; thyroid weight but not mean height of the follicular cells was slightly less increased when EB was added to PTU. It is tentatively concluded that estrogen may have a dual action on the thyro‐pituitary axis: on one hand, a depressing influence on thyrotroph cells and on the other hand a direct stimulatory effect on the thyroid gland.