Human pituitary tumours express the bHLH transcription factors NeuroD1 and ASH1
Elisabetta FerrettiGiulia Di StefanoFrancesca ZazzeroniRita GalloAmato FratticciR. CarfagniniS. AngiulliAntonio SantoroGiuseppe MinnitiG. TamburranoEdoardo AlesseGiuseppe CantoreAlberto GulinoMarie-Lise Jaffrain-Réa
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Portions of sheep anterior pituitary lobe tissue were extracted under acid conditions and assayed for the two neurophysins (oN-III and oN-I/II) by radioimmunoassay. In all tissues examined, oN-III and oN-I/II immunoreactivi-ties were detected. Using a combination of isoelectric focusing and polyacrylamide gel electrophoresis, the neurophysins of the anterior pituitary gland behaved like oN-III and oN-I/II. oN-III of the anterior pituitary was purified by affinity chromatography and high-performance liquid chromatography. This corticotroph oN possessed an amino acid analysis similar to that of oN III and an N-terminal amino acid sequence, including residues 1–24, identical to that of authentic oN-III. These findings support the work of others who have identified neurohypophysial hormones in the anterior pituitary gland.
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The role that metabolic products play in regulating the hypothalamic‐pituitary‐adrenal (HPA) axis during strenuous exercise is speculative. This investigation examined the extent to which lactic acid, a major metabolite of anaerobic exercise, directly affects hypothalamic‐pituitary function. Specifically, β‐endorphin secretion was measured from AtT‐20 (D‐16) mouse corticotroph tumor cells treated either acutely (15 min − 180 min) or chronically (1 day − 3 day) with physiologic levels of lactate (0.5 × 10 −3 M to 5 × 10 −2 M ) or lactate in combination with the corticotroph releasing factors: corticotroph releasing hormone (CRH), arginine vasopressin (AVP), norepinephrine and/or epinephrine. Findings with AtT‐20 cell cultures were shown to be representative of responses in primary cultures of rat anterior pituitary. Lactic acid did not alter the spontaneous release of β‐endorphin by AtT‐20 cells under either acute or chronic conditions. While CRH, norepinephrine, and epinephrine evoked significant increases in β‐endorphin release, lactate, in combination with these secretagogues did not alter their effects. Similarly, lactic acid failed to alter basal or stimulated release of β‐endorphin by primary cultures of rat anterior pituitary. The addition of lactate (3 × 10 3 M ) to rat hypothalamic explants did, however, produce a modest but significant reduction in spontaneous CRH release, suggesting that lactate may facilitate the return to basal secretion following exercise. The present findings show that physiologic concentrations of lactate have no effect, either alone or in combination with other pituitary secretagogues, on corticotroph secretion. Whereas a physiologic action for lactate within the hypothalamus is possible, the present findings indicate that lactate is an inhibitor of CRH release. Thus, lactate does not appear to play a direct role in the profound activation of the HPA axis that occurs in response to strenuous exercise.
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Angiotensin II (Ang II) participates in the regulation of anterior pituitary hormone secretion by acting either directly on the anterior pituitary or indirectly on the hypothalamus. When applied directly on pituitary cells, Ang II increases both ACTH and PRL secretion and has also been reported to affect GH secretion. Three distinct subtypes of Ang II receptors (AT1A, AT1B, and AT2) have been identified; they are unequally distributed and differently regulated in various tissues. We have previously demonstrated that only AT1A receptors are present in the hypothalamus while anterior pituitary cells express predominantly the AT1B subtype. Using in situ hybridization in combination with immunohistochemistry, the aim of the present study was to identify the phenotype of the endocrine cell expressing AT1B receptor messenger RNA (mRNA) in the anterior pituitary of adult male Sprague-Dawley rats. Expression of AT1B receptor mRNA was present in 33.9 ± 1.0% of anterior pituitary cells. AT1B mRNA is predominantly expressed by lactotropes (78.2 ± 2.1% of AT1B mRNA-expressing cells) and to a lower degree by corticotropes (18.3 ± 2.1%) and is not detectable in somatotropes, mammosomatotropes, gonadotropes, or thyrotropes. These results indicate that in adult male rats, Ang II, which has been shown to be synthesized in gonadotropes, can directly stimulate PRL and ACTH release from lactotropes and corticotropes through activation of AT1B receptors. As only 53.8 ± 2.7% of lactotropes and 23.6 ± 2.8% of corticotropes expressed AT1B mRNA, our findings suggest a functional heterogeneity of both cell types regarding their sensitivity to Ang II.
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Background There is evidence suggesting cross-talk among gland cells of the anterior pituitary. We had reported a rare form of synaptoid contact between corticotrophs in the anterior pituitary of the dog. We then found similar synaptoid contacts with different characteristics in the rat, as described in the present article. Methods Male Sprague-Dawley rats were used. The anterior pituitaries were prepared for ultrastructural study of substance P immunoreactivity of the anterior pituitary. Routine preembedding immunohistochemical staining was conducted, the sections were embedded in Epon 812 (Serva Feinbiochemica, Heidelberg, New York), and ultrathin sections were prepared. Results In the anterior pituitary of the rat, synaptoid contacts were found between corticotrophs and lactotrophs. They appeared very close to typical synapses in the central nervous system, aside from evident weakness of presynaptic density. Conclusions The presence of synaptoid contacts suggests a form of cross-talk between the gland cells in the anterior pituitary of the rat. Anat. Rec. 251:181–184, 1998. © 1998 Wiley-Liss, Inc.
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Abstract The Wistar‐Kyoto (WKY) rat shows signs of persistent activation of the hypothalamic‐pituitary‐adrenal axis, but the cause and site of this activation is not yet known. Chronically activated corticotrophs generally show blunted adrenocorticotropic hormone (ACTH) response to corticotropin releasing factor (CRF); therefore, the anterior pituitary responsiveness to ACTH secretagogues, CRF and vasopressin, was compared in male WKY and Wistar rats. Anterior pituitary CRF binding and CRF receptor mRNA expression was significantly decreased in WKY rats. ACTH response to CRF or vasopressin was markedly impaired, and vasopressin failed to potentiate the CRF‐stimulated ACTH release in cultured WKY anterior pituitary cells. In contrast, CRF and vasopressin alone and in combination stimulated large, concentration‐dependent increases in ACTH release in Wistar anterior pituitary cells. By contrast to the decreased ACTH secretory responses, steady‐state anterior pituitary pro‐opiomelanocortin mRNA levels were approximately 12‐fold greater in WKY rats compared to Wistar rats, and they further increased in response to CRF stimulation. These findings suggest that, although the WKY rat corticotroph is under a chronic state of activation or disinhibition, the in vitro secretory responses to classic ACTH secretagogues are impaired.
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The role that metabolic products play in regulating the hypothalamic-pituitary-adrenal (HPA) axis during strenuous exercise is speculative. This investigation examined the extent to which lactic acid, a major metabolite of anaerobic exercise, directly affects hypothalamic-pituitary function. Specifically, β-endorphin secretion was measured from AtT-20 (D-16) mouse corticotroph tumor cells treated either acutely (15 min - 180 min) or chronically (1 day - 3 day) with physiologic levels of lactate (0.5 × 10-3M to 5 × 10-2M) or lactate in combination with the corticotroph releasing factors: corticotroph releasing hormone (CRH), arginine vasopressin (AVP), norepinephrine and/or epinephrine. Findings with AtT-20 cell cultures were shown to be representative of responses in primary cultures of rat anterior pituitary. Lactic acid did not alter the spontaneous release of β-endorphin by AtT-20 cells under either acute or chronic conditions. While CRH, norepinephrine, and epinephrine evoked significant increases in β-endorphin release, lactate, in combination with these se-cretagogues did not alter their effects. Similarly, lactic acid failed to alter basal or stimulated release of β-endorphin by primary cultures of rat anterior pituitary. The addition of lactate (3 × 103M) to rat hypothalamic explants did, however, produce a modest but significant reduction in spontaneous CRH release, suggesting that lactate may facilitate the return to basal secretion following exercise. The present findings show that physiologic concentrations of lactate have no effect, either alone or in combination with other pituitary secretagogues, on corticotroph secretion. Whereas a physiologic action for lactate within the hypothalamus is possible, the present findings indicate that lactate is an inhibitor of CRH release. Thus, lactate does not appear to play a direct role in the profound activation of the HPA axis that occurs in response to strenuous exercise.
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Anterior pituitary corticotrope function was analyzed in the long sleep (LS) and short sleep (SS) lines of mice selectively bred for differences in sensitivity to ethanol. In vivo challenge with acute ethanol or CRH administration or the stress of novel handling resulted in a more pronounced increase in serum corticosterone levels in LS mice compared with SS mice. Likewise, in vivo administration of ethanol resulted in 3‐fold higher levels of anterior pituitary pro‐ACTH/endorphin mRNA in LS mice compared with SS mice. However, this differential regulation of the HPA axis during in vivo analysis was not observed during in vitro studies of anterior pituitary corticotrope function. Primary cultures of LS and SS anterior pituicytes responded appropriately but equivalently to a variety of secretagogues known to stimulate anterior pituitary ACTH secretion. These secretagogues included CRH (10 n m ), dibutyryl‐cAMP (1 m m ), vasopressin (100 n m ), and phorbol 12‐myristate 13‐acetate (10 n m ). Ethanol had no direct stimulatory effect on pituitary ACTH secretion. Quantitation of anterior pituitary corticotrope peptide biosynthesis was determined by immunoprecipitation and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis of extracts from [ 35 S]methionine‐labeled anterior pituitary explants and from [ 35 S]methionine‐labeled primary cultures of anterior pituitary cells. LS mice pro‐ACTH/endorphin biosynthesis in pituitary explants was 2‐fold greater than pro‐ACTH/endorphin biosynthesis in SS mice pituitary explants. However, in culture, isolated from hypothalamic and adrenal factors, the LS anterior pituitary pro‐ACTH/endorphin biosynthetic rate became eguivalent to the SS anterior pituitary pro‐ACTH/endorphin biosynthetic rate. The results suggest that the differential regulation of LS and SS anterior pituitary corticotropes observed in vivo is not due to genetic differences in LS and SS anterior pituitary corticotrope function.
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