Isolation of rat pituitary granules and the study of their biochemical properties and hormonal activities

A simple and rapid method is described for the isolation of the acidophilic and basophilic granules from the anterior pituitary gland of the rat. The method involves chromatography of pituitary particulates on columns of No. 545 Celite equilibrated and developed with 0.25 M sucrose. Mitochondria are retained quantitatively on the column. The granules and microsomes which are not retained on the Celite are further fractionated on a discontinuous density sucrose gradient and by differential centrifugation. Essentially homogeneous populations of acidophilic and basophilic granules were obtained as indicated by 1) extensive electron microscopic studies, 2) enzymatic determinations, and 3) fatty acid and RNA analyses on the granule pellets. Microfiltration studies indicated that the acidophilic granules were smaller than 450 mmicro, but greater than 300 mmicro in diameter. They were found, unlike the basophilic granules, to be partially stable to extraction with water, but were unstable on incubation in 1 mM EDTA at 37 degrees . Magnesium ions were not detected in the granules. The acidophilic and basophilic granules contained, respectively, 5 and 8 per cent of the protein present in the whole homogenate. Extensive hormone studies showed that growth and lactogenic hormones were associated with the acidophilic granules, while thyroid-stimulating hormone and gonadotropin were associated with the basophilic granules. ACTH was not present in significant amounts in either of the granule fractions, but was localized in a particulate fraction which contained microsomes and small granules. The association of the pituitary hormones with specific granules and cell types is discussed.

Further studies on the theta cell of the mouse anterior pituitary as revealed by electron microscopy, with special reference to the mode of secretion

Theta cells reported previously as a new cell type in the anterior pituitary of the mouse were examined with the electron microscope. This type of cell is distinguished by the presence of pleomorphic secretory granules, a characteristic arrangement of the rough surfaced variety of endoplasmic reticulum, a well developed Golgi complex, and an eccentrically located nucleus. The secretory granules are seen at first as small granules of low density within the Golgi vesicles. While they are within the Golgi vesicles they become larger and denser. Simultaneously they move from the proximal to the distal part of the Golgi region and finally emerge from the Golgi area as mature granules in the cytoplasm. Thus, secretory granules are always enveloped by a limiting membrane which originates from the wall of the Golgi vesicle. At the stage of granule-extrusion, the cell membrane fuses with the limiting membrane of the granules and openings in the cell membrane appear at the place of extrusion. The granules then appear to lie within inpocketings of the cell membrane. They lose their density within these inpocketings or within the cytoplasm and occasionally show fragmentation. After complete loss of density, the granules are extruded as amorphous materials to the territory outside of the cell.

Adrenal and hypophyseal non-Hodgkin's lymphoma presenting with panhypopituitarism

We report a case of non-Hodgkin's lymphoma presenting as anterior pituitary failure and found to have involvement of two endocrine glands, the pituitary and the adrenals.

Supra- and extrasellar pituitary microadenoma as a cause of Cushing's disease

There has been accumulating evidence that pituitary adenomas which cause Cushing's disease are located not only in sella turcica but also in various extrasellar and intracranial regions. We describe a case of Cushing's disease caused by a supra- and extrasellar ACTH-producing microadenoma, which originated in the anterior pituitary and extended upward without connecting to the stalk. The pituitary microadenoma was identified and removed by transsphenoidal microsurgery. After the surgery the patient experienced complete remission. This type of pituitary microadenoma is considered to be rare, but in order to accomplish successful surgical treatment, it is necessary to consider that pituitary adenomas which cause Cushing's disease may be located in such an unusual position.

Heterotrimeric G-protein candidates for Ge in the ACTH secretory pathway

The mouse AtT-20/D16-16 anterior pituitary tumour cell line was used to identify candidate heterotrimeric G-proteins for G-exocytosis (Ge) which mediates calcium ion-stimulated adrenocorticotrophin (ACTH) secretion in this cell line. AtT-20 cells express several heterotrimeric G-protein alpha subunits; Gs alpha, Gt alpha, Gq alpha, G11alpha, G12alpha, G13alpha, G14alpha, G15alpha, Gz alpha, Gi2alpha, Gi3alpha, and Go alpha and so heterotrimeric G-protein selective agents were used to differentiate between these candidates. Agents which stimulate ACTH secretion via Ge were not pertussis toxin (PTX)-sensitive nor was cholera toxin (CTX) able to stimulate ACTH secretion from permeabilised cells in the absence of calcium. G-protein antagonists which inhibit activation of Gs, Gi, and Gq subfamilies did not attenuate Ge-stimulated ACTH secretion from permeabilised AtT-20 cells. In AtT-20 cells the stimulatory G-protein involved in the late stages of the ACTH secretory pathway does not belong to the Gs, Gi (with the exception of Gz) or Gq subfamilies of heterotrimeric G-proteins leaving Gz, G12 or G13 as the strongest candidates for Ge.

Induction of ectopic corticotropic tumor in mouse embryos by exo utero cell transplantation and its effects on the fetal adrenal gland

To establish an in vivo experimental system for developmental endocrinology research, AtT-20 cells, a corticotropic tumor cell line, were transplanted by exo utero manipulation into mouse embryos on embryonic day 14. The induced tumor secreted ACTH in situ, and the circulating ACTH level was elevated. This was the first model for studying the regulation of ACTH in the mouse fetal adrenal in vivo and the first continuous ACTH treatment model in rodent fetuses. The changes in the adrenal gland from the tumor-induced embryos were analyzed by light microscopic morphometry, immunohistochemistry for steroidogenic enzymes, and electron microscopy. In the treated adrenal, the volume of the inner cortical zone was significantly larger than that in controls. In the inner zone, cell density was decreased, and average cell size was increased, whereas bromodeoxyuridine-incorporation was not increased. The enlarged inner zone cells expressed an enhanced level of cytochrome P45011beta, the corticosterone-synthesizing enzyme, and the serum corticosterone level was increased. Electron microscopy showed an active form of the organelles involved in steroidogenesis. These findings indicate that ACTH stimulates both adrenocortical hypertrophy and steroidogenesis in fetal mice. Potential perspectives of the novel paradigm in this research for molecular developmental endocrine study are discussed.

Simian virus 40 T antigen-induced gonadotroph adenomas: a model of human null cell adenomas

The cell of origin of human null cell pituitary adenomas is disputed. Although these tumors, by definition, do not produce any of the anterior pituitary hormones in vivo, they have been shown to express gonadotropin subunit genes, release gonadotropin hormones in vitro, and express the gonadotroph-associated transcription factor steroidogenic factor-1. However, they demonstrate variable responses to releasing hormones in vitro, raising questions about their origin from differentiated gonadotrophs or pluripotent stem cells. In this set of experiments, transgenic mice carrying a temperature-sensitive mutant (TSA58) of simian virus 40 T antigen driven by human FSHbeta regulatory elements were produced. These animals developed slow growing, multifocal pituitary nodules that demonstrated secretion of FSH with serum FSH levels 10-fold higher in male transgenic animals and 5-fold higher in female transgenic animals than those in nontransgenic controls. Anterior pituitary pathology progressed from diffuse gonadotroph hyperplasia to nodular adenomas with persistent, but decreasing, immunoreactivity for FSHbeta and LHbeta. Ultrastructural characteristics of the tumors were identical to those of human null cell adenomas. These results support the hypothesis that human null cell adenomas are derived from gonadotrophs and provide an animal model for further study of this disease.

Subcellular localization of epitope-tagged neurotrophins in neuroendocrine cells

A growing body of evidence suggests that neurotrophins (NTs) play a critical role in synaptic plasticity and other activity dependent processes in the CNS. Release of these growth factors by neurons and neuroendocrine cells was recently shown to occur via the regulated secretory pathway, representing a possible mechanism for preferentially supplying NTs locally to active synapses. However, the identity and characteristics of the intracellular storage compartment for NTs undergoing stimulus-coupled secretion remains controversial. As a step towards addressing these issues we have investigated the subcellular localization of epitope-tagged nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) in neuroendocrine cells. Placement of the myc-epitope tag at the neurotrophin carboxy terminus did not affect essential properties of the NTs such as their ability to induce Trk tyrosine phosphorylation or their sorting into the regulated secretory pathway in PC12 and AtT-20 neuroendocrine cells. Epitope-tagged NTs colocalize with dense core vesicle (DCV)-markers at the light microscopic level in both cell lines investigated. Furthermore, at an EM level immunoreactivity (IR) for myc-tagged NGF was found over dense core granules (DCGs) in PC12 cells. These data provide evidence that NTs can be stored in DCVs in neuronal model cell lines and, potentially, in neurons as well.

New analogs of human growth hormone-releasing hormone (1-29) with high and prolonged antagonistic activity

Based on our previous results, in conjunction with various structural considerations, 19 new analogs of the GHRH antagonist [PhAc-Tyr1,D-Arg2,Phe(pCl)6,Abu15,Nle27,Agm29]++ +hGHRH(1-29) (MZ-5-156) were synthesized by the solid-phase method. These compounds were designed to develop further analogs of this class with increased receptor-binding affinity. All analogs had Abu15 and Nle27 modifications and were acylated with phenylacetic acid at the N-terminus. Most of the analogs had D-Arg2 and Phe(pCl)6 substituents and Agm29 or Arg29-NH2 at the C-terminus. Additional single substitutions consisted of the incorporation of D- or L-Tic1, D-Tic2, Tic6 or Phe(pNO2)6 and Arg29-NH2. The Arg29-NH2 analog of MZ-5-156 (KT-48) was further modified by single substitutions using Pal1; D-Tpi2; D- or L-Phe4; Phe(pX)6 X = F, Cl, I; Tyr7; Aib8; Tyr(Me)10 or Phe(pCl)10. Four peptides had multiple substitutions. All the analogs were evaluated for their ability to inhibit GH release induced by hGHRH(1-29)NH2 in vitro and some were also tested in vivo. Peptides [PhAc-Tyr1,D-Arg2,Phe(pI)6,Abu15,Nle27]hGHRH(1-2 9)NH2 (KT-30), [PhAc-Tyr1,D-Arg2,Phe(pCl)6,Aib8,Abu15,Nle27] hGHRH(1-29)NH2 (KT-50) and [PhAc-Tyr1,D-Arg2,Phe(pCl)6,Tyr(Me)10,Abu15,Nle27]h GHRH(1-29)NH2 (KT-40) with Phe(pI)6, Aib8 or Tyr(Me)10 modifications, respectively, showed high and prolonged inhibitory effect in superfused rat pituitary system. Analog KT-50 also exhibited a strong and long-term inhibitory activity in vivo in rats. Most of the new analogs showed high binding affinities to rat pituitary GHRH receptors.

Molecular cloning and tissue distribution of cDNA encoding a novel chemoattractant-like receptor

With the application of a homology screening strategy, including PCR amplification and southern blot hybridization, a novel cDNA was cloned from rat liver and anterior pituitary libraries. It was found to encode a 371-amino acid protein which has the characteristics of a heptahelix receptor and shows structural identity to members of the chemoattractant receptor family. A primary receptor message of 3.5 kb size was identified by northern blot hybridization. This RNA species showed high expression in heart and lung, while expression was lower in small intestines, colon, kidney, liver, uterus, and in brain. Another larger RNA species of 6.3 kb appeared in heart and lung. In situ hybridization histochemistry performed on tissue from liver and kidney revealed a mainly vascular distribution of the receptor message.

Regulation of human prohormone convertase 2 promoter activity by the transcription factor EGR-1

Prohormone convertases are involved in the tissue-specific endoproteolytic processing of prohormones and neuropeptide precursors within the secretory pathway. In the present study, we have isolated genomic clones comprising the 5'-terminal region of the human prohormone convertase 2 (PC2) gene and established characteristics of the PC2 promoter region. The proximal promoter region is very G+C-rich and does not contain a canonical TATA box or a CAAT box. Transient expression assays with a set of human PC2 gene fragments containing progressive 5' deletions demonstrate that the proximal promoter region is capable of directing high levels of neuroendocrine-specific expression of reporter gene constructs. In addition, we show that the transcription factor EGR-1 interacts with two distinct elements within the proximal human PC2 promoter region. Transfection experiments also demonstrate that EGR-1 is able to enhance PC2 promoter activity.

Distinct molecular events during secretory granule biogenesis revealed by sensitivities to brefeldin A

The biogenesis of peptide hormone secretory granules involves a series of sorting, modification, and trafficking steps that initiate in the trans-Golgi and trans-Golgi network (TGN). To investigate their temporal order and interrelationships, we have developed a pulse-chase protocol that follows the synthesis and packaging of a sulfated hormone, pro-opiomelanocortin (POMC). In AtT-20 cells, sulfate is incorporated into POMC predominantly on N-linked endoglycosidase H-resistant oligosaccharides. Subcellular fractionation and pharmacological studies confirm that this sulfation occurs at the trans-Golgi/TGN. Subsequent to sulfation, POMC undergoes a number of molecular events before final storage in dense-core granules. The first step involves the transfer of POMC from the sulfation compartment to a processing compartment (immature secretory granules, ISGs): Inhibiting export of pulse-labeled POMC by brefeldin A (BFA) or a 20 degrees C block prevents its proteolytic conversion to mature adrenocorticotropic hormone. Proteolytic cleavage products were found in vesicular fractions corresponding to ISGs, suggesting that the processing machinery is not appreciably activated until POMC exits the sulfation compartment. A large portion of the labeled hormone is secreted from ISGs as incompletely processed intermediates. This unregulated secretory process occurs only during a limited time window: Granules that have matured for 2 to 3 h exhibit very little unregulated release, as evidenced by the efficient storage of the 15-kDa N-terminal fragment that is generated by a relatively late cleavage event within the maturing granule. The second step of granule biogenesis thus involves two maturation events: proteolytic activation of POMC in ISGs and a transition of the organelle from a state of high unregulated release to one that favors intracellular storage. By using BFA, we show that the two processes occurring in ISGs may be uncoupled: although the unregulated secretion from ISGs is impaired by BFA, proteolytic processing of POMC within this organelle proceeds unaffected. The finding that BFA impairs constitutive secretion from both the TGN and ISGs also suggests that these secretory processes may be related in mechanism. Finally, our data indicate that the unusually high levels of unregulated secretion often associated with endocrine tumors may result, at least in part, from inefficient storage of secretory products at the level of ISGs.

Sapecin B, a novel fly toxin, blocks macroscopic K+ currents in the GH3 rat pituitary cell line

Sapecin B is structurally homologous to charybdotoxin (CTX), which is found in scorpion venom. This study investigated the effects of sapecin B on the Ca(2+)-activated K+ currents [IK(Ca)] and the rapidly inactivating K+ currents in clonal rat GH3 pituitary cells with whole cell voltage-clamp methods. Sapecin B (20 nM) reversibly blocked the CTX-sensitive Ix(Ca) (the BK current) in a dose-dependent manner, with a half-maximal inhibitory concentration of approximately 0.9 nM, comparable to that of 0.08-0.4 nM for CTX. The Ca2+ currents in GH3 cells, however, were not affected by sapecin B (40 nM), indicating that the blockade of IK(Ca) by sapecin B is not a secondary effect of Ca2+ current inhibition. The effect of sapecin B on IK(Ca) resembled that of CTX, as expected from the structural similarities shared by CTX and sapecin B. We also found that sapecin B largely inhibited the 4-aminopyridine-sensitive, rapidly inactivating K+ currents in a dose-dependent manner, with a half-maximal inhibitory concentration of approximately 40 nM, whereas CTX had little effect on this current in GH3 cells. Sapecin B may thus provide a useful tool, complementary to CTX, for probing the functional role of molecular domains in the BK channels and the structural similarities common to the BK and the rapidly inactivating A-type K+ channels.

A comparison of proliferation indices in human anterior pituitary adenomas using formalin-fixed tissue and in vitro cell culture

The authors compared detection methods for cell proliferation in human anterior pituitary adenomas using histological sections and dispersed cell culture. After tumor cells had been grown for 4 days in dispersed culture, bromodeoxyuridine (BUdR), proliferating cell nuclear antigen (PCNA), and Ki-67 were compared by double immunostaining and contrasted with single staining of PCNA and Ki-67 indices in the corresponding histological sections from 12 human pituitary adenomas. In vitro, the BUdR labeling index was positive in six of 12 tumors (range < 0.1-5.1%), 10 of 12 tumors were PCNA-positive (range < 0.1-100%), and Ki-67 was positive in 10 of 12 adenomas (range < 0.1-8%). In vitro, BUdR and Ki-67 gave similar proliferative indices for 10 of 12 adenomas. In vivo, the PCNA labeling index was positive in 12 of 12 adenomas (range 0.9-95%) and Ki-67 was positive in 11 of 12 adenomas (range < 0.1-2%). Tumors with a labeling index less than 0.1% were considered to be negative for proliferation. High PCNA values were found in vitro and in vivo, whereas Ki-67 labeling indices were similar in vitro and in vivo for nine of 12 adenomas. It is concluded that Ki-67 proliferative indices in vivo reflect those found in vitro, at least after 4 days in dispersed culture, but that PCNA overestimates pituitary adenoma proliferation in histological sections as well as in dispersed culture.