Thyroid Hormone Status Regulates Preprotachykinin-A Gene Expression in Male Rat Anterior Pituitary*
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Substance P (SP) and substance K (SK) are mammalian tachykinin peptides derived from a single preprotachykinin- A (PPT-A) gene and are widely but selectively distributed in neural and endocrine tissues. SP is present in the rat anterior pituitary, and its content there varies with the thyroid status of the animal. The present studies were undertaken to determine whether the PPT-A gene is expressed in the anterior pituitary and if so, whether PPT-A messenger RNA (mRNA) abundance is regulated by thyroid hormone status. Male rats were surgically or chemically thyroidectomized or made hyperthyroid by thyroid hormone (T3) injection. Total RNA was isolated from individual anterior pituitaries, and PPT-A mRNA abundance was determined by dot blot procedures. In parallel groups of rats, anterior pituitaries were extracted for measurement of SP and SK by specific RIAs. Surgical or chemical thyroidectomy increased PPT-A mRNA abundance 4 to 6-fold and increased both SP and SK content in the anterior pituitary. Administration of T3 to thyroidectomized rats reversed the increase in both PPT-A mRNA abundance and SP and SK content in the adenohypophysis. T3 administration to euthyroid rats also decreased PPT-A mRNA abundance and SP and SK content in the anterior pituitary. The coordinate presence of PPT-A mRNA with SP and SK in the anterior pituitary strongly suggests that these peptides are synthesized within this gland. (Endocrinobgy121: 1555–1561,1987)Keywords:
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Today much attention is paid to the study of the pituitary ultrastructure of laboratory animals and humans. But there is not enough available literature to study the most important organ of internal secretion of productive animal. The aim of our work is to study the structure of the ultrastructure of cells of the anterior pituitary gland of cattle in the definitive period of postnatal ontogenesis. Histological, morphometric, and electron microscopic techniques were used to study the cellular composition of the anterior pituitary gland of cattle. It was revealed that the anterior lobe of the pituitary gland occupies 64 % of the entire pituitary parenchyma, while the posterior and middle lobes occupy 27% and 9%, respectively. After using general histological methods there are detected the functionally inactive chromophobes (41%) and chromophilic cells, which include acidophils (38%) and basophils (21%) in the anterior lobe of the pituitary gland. The electron microscopic studies in the parenchyma of the anterior pituitary gland let find Somatotropes that differ in the presence of a large number of secretory granules in the cytoplasm. Lactotropes are less common than somatotropes and differ from them in larger secretory granules. Corticotropes, gonadotropes and thyrotropes with a minimum content of secretory granules are the least detected. All identified endocrine cells are at different stages of functional activity.
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In order to determine if the monodeiodination of 131I-labeled thyroxine (T4*) to 3,5,3′-triiodothyronine (T3*) which occurs in the anterior pituitary is dependent upon hypothalamic influences, the metabolic fate of T4* in intraocular pituitary transplants has been examined chromatographically. Concentration of total radioactivity in the transplants was similar to that of the normal in situ pituitary, but the proportion of T3* was much reduced. In normal rat anterior pituitary, the relative amount of T3* was 17 % of the total radioactivity in 2 experiments; transplants, on the other hand, showed no T3* in one experiment and 9% in a second. In thyroidectomized rats the relative proportion of T3* in the anterior pituitary rose to 26 %. These findings are interpreted to indicate that monodeiodination of T4* to T3* is related to the functional activity of the anterior pituitary and that this activity depends upon intact hypothalamic-pituitary connections. (Endocrinology78: 302, 1966)
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Interleukin-6 (IL-6) binding site in the rat anterior pituitary gland was characterized using radioiodinated human recombinant (hr) IL-6. Results showed that the anterior pituitary gland contained 170 binding sites per cell of a single class with a dissociation constant of 2.7 x 10(-9) M. The binding of 125I-hrIL-6 to the rat anterior pituitary gland was competitively inhibited by unlabeled hrIL-6, but not by hrIL-1 alpha, hrIL-1 beta, hrIL-2 or hr-interferon-gamma, indicating these binding sites are specific for IL-6. We also demonstrated mouse IL-6 receptor gene expression in the rat anterior pituitary gland by Northern blot analysis. Furthermore, the IL-6 receptor was detected on human gonadotrophs by the double immunofluorescence method. Our findings demonstrate the presence and expression of IL-6 binding site in the rat anterior pituitary gland and the presence of IL-6 binding site on human gonadotrophs, suggesting the important role of IL-6 binding site in pituitary hormone release in both species.
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Anterior pituitary cells derived from hypothyroid rats were enzymatically dispersed and then fractionated by equilibrium sedimentation through a metrizamide density gradient. Populations relatively enriched in thyrotrophs, somatotrophs, mammotrophs, or gonadotrophs were obtained. The thyrotroph-enriched fraction was put into short term culture and tested for hormone responsiveness. TRH stimulated TSH release with an ED50 of 8 X 10(-10) M, and this TRH effect was inhibited by T3 with an ED50 of 1.6 X 10(-11) M free T3. Metrizamide density gradient centrifugation is a useful technique for obtaining relatively enriched populations of viable anterior pituitary cell types.
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According to recent reports, substance P (SP) is localized in the anterior pituitary gland within subsets of thyrotropes and somatotropes, although earlier electron-microscopic studies described the presence of this tachykinin in mammotropes and gonadotropes. Transgenic mice overexpressing the growth-hormone-releasing hormone (GHRH) gene have markedly enlarged pituitary glands, due to hyperstimulation of the somatotropes. Therefore, we speculated that if somatotropes are able to synthesize tachykinins, these peptides should be greatly increased in the anterior pituitary of transgenic GHRH mice. We found that, in accordance with our working hypothesis, both SP and neurokinin A (NKA) were markedly increased in the anterior pituitary gland of male and female transgenic mice, compared with their respective normal controls. In male transgenic mice, NKA was 13.6- and SP 20.2-fold higher than in the anterior pituitary from normal mice. In female transgenic mice, NKA was 40- and SP 100-fold higher than in the anterior pituitary from normal female mice. In male transgenic mice, NKA and neuropeptide K (NPK) contents in the anterior pituitary showed no significant changes between 26 and 50 days of age but significantly increased between 50 days and 5 months of age. The concentration of NKA in the anterior pituitary did not show significant differences between 26 days and 5 months of age, but NPK concentrations in the anterior pituitary significantly decreased with age. In female transgenic mice, NKA content and concentration in the anterior pituitary increased after 35 days of age, but NPK concentrations significantly decreased after 26 days of age. Triiodothyronine markedly decreased anterior pituitary tachykinins, but ovariectomy and estrogen administration failed to significantly affect tachykinin concentrations in the anterior pituitary of transgenic mice. Tachykinin immunostaining was detected in some somatotropes, but tachykinins were also present in cells that were not GH positive. These findings indicate that hyperstimulated somatotropes contain increased stores of tachykinins and that these cells are a source of tachykinins in the anterior pituitary. Tachykinin stores in the anterior pituitary of transgenic mice were affected by thyroid hormones but seem to be insensitive to estrogens. The GHRH transgenic mice may be an interesting model to study the regulation of tachykinin stores in the anterior pituitary gland.
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According to the consideration that glycoprotein hormones such as TSH, FSH and LH or their transmitters may be revealed by PAS-granules in the β cell of the anterior hypophysis, I monthly observed the changes of the pituitary PAS-positive cells in male matured rats, which had been fed under the condition of room temperature in Osaka (3°C-32°C). And these observations were compared with the changes under the exposure to heat (32°C-34°C) and cold (2°C).In winter, the cells containing PAS-positive granules presented various degrees of degranulation in the PAS-stained sections and two cases of them were observed like “T-cell”. In summer, the sections showed that PAS-positive cells were atrophic. The results of the exposed cases to heat and cold corresponded with that of monthly observed cases. From the present observation it could not be possible to identify “thyrotrophs”, “FSH gonadotrophs” and “LH gonadotrophs” respectively. But, it was noticed that these changes seemed to be more sensitive in the central zone of the anterior lobe than in the so-called “sex-zone”, and in the exposure to cold PAS-positive cells increased in the central zone.
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