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D W Hsu

Publications and source records attributed to D W Hsu.

36 records · Page 2Linked to original sources
PubMed1992

Glycoprotein hormone alpha-subunit production in somatotroph adenomas with and without Gs alpha mutations.

Activating mutations of the Gs alpha subunit have been identified in a subset of somatotroph adenomas. The mutant form of the Gs alpha subunit causes persistent activation of adenylyl cyclase and consequently results in high intracellular levels of cAMP. Because cAMP is known to stimulate the synthesis of the glycoprotein hormone (GPH) alpha-subunit as well as GH, we examined somatotroph tumors with and without Gs alpha mutations for GPH alpha-subunit production. GPH alpha-subunit production was assessed in vivo by measuring serum hormone levels and in vitro by analyzing hormone secretion by cultured pituitary tumor cells. DNA was extracted from the pituitary tumors of 26 acromegalic patients. The Gs alpha gene was amplified by the polymerase chain reaction and screened for mutations at codons 201 and 227 using oligonucleotide specific hybridization. Nine of the 26 tumors (35%) had point mutations at Arg 201. Seven of these tumors contained a CGT to TGT mutation (Arg to Cys) and 2 contained a CGT to CAT mutation (Arg to His). No mutations were detected at codon 227. There were no significant differences in age, sex distribution, tumor size, or serum levels of GH or insulin-like growth factor-1 between the groups of patients with or was Gs alpha mutations. The mean serum level of the free GPH alpha-subunit was 1.9-fold higher in the group with Gs alpha mutations (0.48 +/- 0.37 micrograms/L) than in patients without mutations (0.25 +/- 0.17) (P less than 0.05). In pituitary tumor cell culture, 75% of somatotroph tumors with Gs alpha mutations secreted free GPH alpha-subunit into the media compared with 45% of tumors without Gs alpha mutations. The amount of GPH alpha-subunit secretion was 12-fold greater in the group of tumors containing the Gs alpha mutation (P less than 0.05). Immunocytochemical detection of the free GPH alpha-subunit was similar in the two groups of patients with 75% positive for the GPH alpha-subunit in tumors with Gs alpha mutations and 67% positive in tumors without mutations (P = 0.69). We conclude that GPH alpha-subunit production occurs in somatotroph tumors with and without Gs alpha mutations. The increased levels of GPH alpha-subunit secretion in vivo and in vitro suggest that the Gs alpha mutation may increase the amount of preexisting GPH alpha-subunit biosynthesis in the tumors, perhaps via activation of the cAMP pathway.

Adenoma↗
PubMed1991

Somatostatin regulation of glycoprotein hormone and free subunit secretion in clinically nonfunctioning and somatotroph adenomas in vitro.

There is increasing evidence that clinically nonfunctioning pituitary tumors produce and secrete glycoprotein hormone and/or free alpha- and beta-subunits. In addition, hypersecretion of free alpha-subunit occurs in up to 37% of patients with somatotroph adenomas. An understanding of glycoprotein hormone regulation is important in developing effective therapeutic strategies for patients with tumors associated with intact glycoprotein hormone and free subunit hypersecretion. We investigated glycoprotein hormone and free subunit secretion by somatostatin in primary dispersed cultures of pituitary tumor cells from 23 patients with pituitary adenomas. Fifteen tumors from patients with clinically nonfunctioning adenomas (group 1) and 8 tumors from patients with somatotroph adenomas and cosecretion of alpha-subunit (group 2) were studied. Cultures were incubated with control or somatostatin-supplemented media for 24 h. Media samples from group 1 tumors were assayed for intact glycoprotein hormones and free alpha- and beta-subunits secretion levels, while media samples from group 2 cultures were assayed for alpha-subunit and GH secretion levels. Significant (P less than 0.05-0.001) inhibition of secretion of 1 or more intact hormones and/or free subunits was found in 10 of the 15 group 1 tumors. SRIF[10(-7) M] suppressed intact gonadotropin secretion in 60% of FSH-producing tumors and 30% of LH-producing tumors. Media concentrations of FSH beta and LH beta were decreased in 31% and 50% of group 1 tumors, respectively, following somatostatin treatment in those tumors which secreted free beta-subunits. alpha-Subunit was secreted by 12 of the 15 tumors, but significant (P less than 0.02-0.01) inhibition by somatostatin was observed in only 2 tumors. In contrast, significant (P less than 0.05-0.001) inhibition of alpha-subunit in the somatotroph adenomas was found in 6 of the 8 tumors. Significant decreases in alpha-subunit were observed only in those tumors where GH was also significantly inhibited by somatostatin. We conclude that 1) somatostatin inhibits intact glycoprotein or free subunit secretion in the majority of clinically nonfunctioning pituitary tumors in vitro and 2) alpha-subunit secretion is suppressed in 17% and 69% of clinically nonfunctioning and somatotroph adenomas, respectively, consistent with a differential regulation of alpha-subunit by somatostatin in these two tumor types.

Adenoma↗
PubMed1991

Coexpression of galanin and adrenocorticotropic hormone in human pituitary and pituitary adenomas.

Galanin is a neuropeptide that regulates the secretion of several pituitary hormones, including prolactin (PRL) and growth hormone (GH). Galaninlike immunoreactivity (Gal-IR) and galanin mRNA in the rat anterior pituitary is cell lineage specific, with predominant expression in lactotrophs and somatotrophs. The authors examined the cellular distribution of human Gal-IR in seven normal postmortem pituitaries and 62 pituitary tumors by immunoperoxidase staining. In contrast to the rat, Gal-IR in human anterior pituitaries was present in corticotrophs scattered throughout the gland, but not in lactotrophs, somatotrophs, thyrotrophs, or gonadotrophs. Distinct Gal-IR also was present in hyperplastic and neoplastic corticotrophs in 19 of 22 patients with Cushing's disease. In noncorticotroph cell tumors, unequivocal Gal-IR was present in 5 of 11 GH-secreting tumors associated with clinical acromegaly, 9 of 18 nonfunctioning pituitary adenomas, and 2 of 14 prolactinomas. Of these galanin-positive tumors, four of the five GH-secreting adenomas, six of the nine nonfunctioning adenomas, and both of the prolactinomas also contained adrenocorticotropic hormone immunoreactivity (ACTH-IR). Immunostaining and in situ hybridization on adjacent sections using an 35S-labeled probe complementary to human galanin mRNA demonstrated predominant galanin expression in normal corticotrophs. Immunoelectron microscopy confirmed the presence of Gal-IR in pituitary cells characteristic of corticotrophs in both normal and neoplastic pituitaries. Thus, as in the rat, galanin gene expression in the human pituitary is cell-type specific. Unlike the rat, however, human galanin gene expression is restricted to the corticotroph lineage. Studies of tumors confirmed the observed coexpression of galanin and adrenocorticotropic hormone. The divergent cell type specificity of galanin production in human and rat pituitaries reflects different patterns of gene activation in these two species. In addition, these results suggest that galanin in the human pituitary may participate locally in the regulation of the hypothalamic-pituitary-adrenal axis.

Adenoma↗
PubMed1990

Estrogen increases galanin immunoreactivity in hyperplastic prolactin-secreting cells in Fisher 344 rats.

Galanin is a widely distributed regulatory peptide which modulates the pituitary secretion of PRL and GH. Estrogen administration strongly stimulates galanin gene expression in the rat anterior pituitary. In adult female Fischer 344 rats, estrogen also induces hyperplasia of lactotropes. We used immunocytochemical analysis to assess the effects of estrogen on galanin-like immunoreactivity (Gal-IR) in the rat pituitary and hypothalamus during sc diethylstilbestrol (DES) implantation and after its removal at 30 days. In the anterior pituitary, DES implantation increased the portion of Gal-IR-containing cells from less than 2% in the control rats to 18.3% after 3 days of DES and 36% after 30 days. These changes paralleled the lactotrope hyperplasia exhibited in response to DES exposure. Ten and 30 days after removal of the DES capsules, the percentage of Gal-IR-containing cells in the anterior pituitary decreased to 6.3% and 1.5%, respectively. Colocalization studies revealed that Gal-IR-containing cells were predominantly lactotropes. Immunoelectron microscopy demonstrated that Gal-IR was concentrated in the Golgi region of these hyperplastic lactotropes and suggests that little of the synthesized galanin is secreted. The distribution of Gal-IR in the hypothalamus, median eminence, and neurohypophysis was unaffected by DES treatment. These data demonstrate that galanin is synthesized by hyperplastic pituitary lactotropes of Fischer 344 rats and that peptide accumulation is dependent on the presence of circulating estrogens. In contrast, neuronal galanin synthesis in the hypothalamus does not appear to be regulated by estrogen.

Animals↗
PubMed1990

The importance of dopamine in the pathogenesis of experimental prolactinomas.

The factors responsible for the production of prolactin-secreting tumors are obscure. One hypothesis, that chronic loss of dopamine control from the hypothalamus may be associated with prolactinoma formation, was tested. Female adult Fischer 344 rats were subjected to ovariectomy and were then given subcutaneous implants of diethylstilbestrol (DES) Silastic capsules to produce lactotrophic hyperplasia. Sequential studies assessed the neuronal activity of the tuberoinfundibular dopaminergic neurons of the arcuate nucleus of the hypothalamus (A12) during and after this estrogen-induced pituitary growth. Immunocytochemical staining for tyrosine hydroxylase was used as a marker for dopamine synthesis, plasma radioimmunoassay provided plasma prolactin levels, and magnetic resonance imaging and histological studies were performed to examine the structural changes occurring in the pituitary gland. Animals were sacrificed from 3 to 67 days after DES implantation. To determine the reversibility of the estrogen-induced changes, rats were also sacrificed at different time intervals after the removal of 30-, 40-, or 60-day DES implants. After 30 days of DES treatment, plasma prolactin levels increased 40-fold and pituitary weight increased more than threefold. Tyrosine hydroxylase immunoreactivity diminished gradually and was almost completely depleted at 30 days. Pituitary histology revealed marked prolactin cell hyperplasia. These changes were completely reversible; removal of the capsule after 30 days resulted in eventual normalization of plasma prolactin levels and pituitary size and in restoration of tyrosine hydroxylase immunoreactivity in the A12 region. Sixty days of DES treatment produced large hemorrhagic tumors with sustained high plasma prolactin levels and an irreversibly distorted A12 area. These observations suggest that in these animals loss of dopamine regulation secondary to estrogen stimulation initially produces prolactin hyperplasia but that prolonged loss leads to adenoma formation.

Animals↗
PubMed1989

Vasoactive intestinal peptide in the human pituitary gland and adenomas. An immunocytochemical study.

Recent evidence indicates that vasoactive intestinal peptide (VIP) may be involved in normal pituitary function. Immunocytochemistry was used to localize VIP in human biopsied pituitary adenomas and postmortem anterior pituitary glands. Paraffin sections were immunostained for VIP with the avidin-biotin-peroxidase technique. Strong VIP-like immunoreactivity (VIP-LI) was observed in 16 of 17 prolactinomas, 12 of 14 growth hormone-secreting tumors associated with acromegaly, four of 12 ACTH-secreting tumors, and 14 of 18 nonfunctioning pituitary adenomas. In most cases, VIP was colocalized with the classical pituitary hormones. Six of the 18 nonfunctioning tumors had no demonstrable hormone immunoreactivity; five of these stained strongly for VIP, whereas one was negative. Of 18 normal anterior pituitaries, 12 showed strong diffuse staining for VIP throughout the gland. One pituitary with VIP-LI came from an individual who had undergone pituitary stalk transection. Double-immunoenzyme labeling and immunoelectron microscopy demonstrated VIP-LI in many lactotrophs, scattered thyrotrophs, corticotrophs, and in an occasional gonadotroph. These results suggest the following: 1) VIP is present in more than one cell type in normal and adenomatous human pituitaries; and 2) VIP may be involved in the function and development of pituitary tumors.

Adenoma↗
PubMed1988

Expression of X hapten immunoreactivity by human and rat adenohypophyseal cells.

The monoclonal antibody Hy2D4 was found to label a previously undescribed subset of rat and human anterior pituitary cells. The antibody binding site appears to be a carbohydrate moiety previously named "X hapten." Double-label immunofluorescence studies in both normal rat and postmortem human pituitaries showed that this antigen is distributed on a subset of adrenocorticotropic hormone (ACTH)-positive cells, but is not detectable in cells immunoreactive for growth hormone, prolactin (PRL), thyroid-stimulating hormone, or luteinizing hormone. Since X hapten labeling revealed a biological subdivision of corticotroph cells, it was expected that some ACTH-positive tumors would be immunoreactive, but that tumors of other hormonal types would be negative. Instead, in 21 surgical specimens examined, tumors of all hormonal types were found to show immunoreactivity. To determine whether experimental proliferative changes in the pituitary could explain the shift in the cell type expressing the antigen, PRL-cell hyperplasia was induced in rats through chronic (8-week) exposure to diethylstilbestrol. The fraction of X-positive cells increased in these hyperplastic glands almost ninefold and, as in human adenomas, many non-corticotroph cells expressed the X marker in this model. However, the non-corticotroph cells expressing X were predominantly growth hormone cells, not the proliferative PRL cells. Thus, expression of the antigen does not necessarily imply that a cell is in a proliferative mode. While it is not known what role an altered expression of this antigen might play, the antibody offers a probe into cellular biology of human and experimental pituitary tumors.

Adenoma↗
PubMed1987

Glycoprotein hormone genes are expressed in clinically nonfunctioning pituitary adenomas.

Approximately 25% of patients with pituitary adenomas have no clinical or biochemical evidence for excess hormone secretion and are classified as having null cell or nonfunctioning adenomas. To characterize the cell type of these tumors, we analyzed pituitary hormone gene expression in clinically nonfunctioning pituitary adenomas using specific oligonucleotide probes for the messenger (m)RNAs encoding growth hormone, prolactin, ACTH, and the glycoprotein hormone subunits, alpha, luteinizing hormone (LH)beta, follicle-stimulating hormone (FSH)beta, and thyroid-stimulating hormone (TSH)beta. Expression of one or more of the anterior pituitary hormone genes was found in 12/14 (86%) of the patients with clinically classified nonfunctioning adenomas. Expression of one or more of the glycoprotein hormone genes (alpha, LH beta, FSH beta, TSH beta) was identified most commonly (79%) with expression of multiple beta-subunit genes in many cases. Expression of alpha-subunit mRNA was found in each of the adenomas from patients expressing one of the beta-subunit mRNAs and in three patients with no detectable beta-subunit mRNA. Although FSH beta and LH beta mRNAs were found with similar frequencies in nonfunctioning adenomas, expression of FSH beta mRNA was generally much more abundant. TSH beta mRNA was detected in only one adenoma. The levels of glycoprotein hormone subunit mRNAs were variable in different adenomas, but the lengths of the mRNAs and transcriptional start sites for the alpha- and beta-subunit genes were the same in the pituitary adenomas and in normal pituitary. Growth hormone and prolactin gene expression were not observed in the nonfunctioning adenomas, but ACTH mRNA was found in a single case. Immunohistochemistry of the adenomas confirmed production of one or more pituitary hormones in 13/14 (93%) nonfunctioning tumors, with a distribution of hormone production similar to that of the hormone mRNAs. These data indicate that pituitary adenomas originating from cells producing glycoprotein hormones are common, but are difficult to recognize clinically because of the absence of characteristic endocrine syndromes and defective hormone biosynthesis and secretion.

Adenoma↗
PubMed1987

Luteinizing hormone-secreting pituitary tumor: biosynthetic characterization and clinical studies.

Although gonadotropin-secreting pituitary adenomas are increasingly recognized, tumors secreting only LH are rare. Since gonadotropin production by pituitary adenomas may reflect imbalanced glycoprotein biosynthesis, we studied tumor LH and subunit biosynthesis and secretion in a patient with a LH- and alpha-subunit-producing pituitary tumor. Northern blot analysis of RNA from the tumor revealed the presence of mRNAs encoding both alpha- and beta-subunits of LH with a marked excess of the mRNA encoding LH beta. Analysis of tumor extracts by gel filtration chromatography confirmed an excess of free LH beta relative to free alpha-subunit. Clinical studies demonstrated that the secretion of LH and alpha-subunit by the tumor increased in response to the acute administration of LHRH (100 micrograms, iv) and decreased during a 4-h dopamine infusion (4 micrograms/kg X min). During a 4-week course of LHRH analog (D-Trp6-Pro9-NEt-LHRH) administration, given as a daily sc dose (8 micrograms/kg X day), serum LH and alpha-subunit concentrations increased 7- and 3-fold, respectively, consistent with a chronic agonist effect. Chronic administration of bromocriptine resulted in reduction of serum LH and alpha-subunit levels to normal.

Adenoma↗
PubMed1987

Hormone production in clinically nonfunctioning pituitary adenomas.

Pituitary tumors in which no excess hormone secretion can be identified clinically have been considered as nonfunctioning or null-cell adenomas. Immunocytochemical data presented here suggest that many of these tumors contain subunits of the glycoprotein hormones. Of 160 patients referred for pituitary surgery, 37 (23%) had no evidence of excess hormone secretion on preoperative endocrine evaluation. Immunocytochemical staining of these tumors was carried out using antibodies specific for prolactin, growth hormone, adrenocorticotropic hormone, the beta subunits of luteinizing hormone (beta-LH), follicle-stimulating hormone (beta-FSH), and thyroid-stimulating hormone (beta-TSH), and the alpha subunit. One or more of these pituitary hormones were detected in 73% of cases. The alpha and beta subunits were detected most frequently, being found in 68% of cases; 27% had staining for one or more beta subunits and 37.9% had staining for both alpha and beta subunits. The incidence was: beta-FSH in 58%, beta-LH in 47%, beta-TSH in 33%, and the alpha subunit in 42%. Staining for multiple glycoprotein hormones was common (52%), and mixed glycoprotein hormones and prolactin cell types were found in 16% of cases. These data suggest that most apparently nonfunctioning pituitary tumors contain immunoreactive hormones and the majority of these are subunits of the glycoprotein hormones. Since the glycoprotein hormone beta subunits must combine with the alpha subunit to produce biologically active hormones, the production of the subunits alone may not have endocrine manifestations.

Adenoma↗
PubMed1986

Effect of dexamethasone on blood-brain barrier in the normal mouse.

Dexamethasone ameliorates cerebral edema, but its effect on normal blood-brain barrier is unknown, as is the site of action. Sixteen normal mice were given dexamethasone, 3 mg/kg intramuscularly or 2 mg/kg intravenously. One to two hours later 10 mg of horseradish peroxidase (HRP) in 0.1 ml of saline was administered intravenously and allowed to circulate for 15 minutes. Brain slices were examined by light and electron microscopy. The number of HRP-permeable arteriolar segments per brain was less in dexamethasone-treated than in control mice (p less than 0.001). In addition, the number of small HRP-filled endothelial vesicles of capillaries and of HRP-permeable and -impermeable arterial segments was less in dexamethasone-treated mice than that for similar vessels in control mice (p less than 0.005, p less than 0.05, and p less than 0.01, respectively). The total number of small vesicles and the number of larger HRP-filled vesicles in arterioles was the same in treated and control mice. Dexamethasone therefore decreased the normal permeability of cerebral blood vessels to HRP. This decrease was accompanied by a decrease in the number of HRP-containing small endothelial vesicles. These data suggest that dexamethasone influences cerebral edema by decreasing the permeability of the cerebral vasculature for macromolecules.

Animals↗
PubMed1986

Expression of chorionic gonadotropin-beta-like messenger ribonucleic acid in an alpha-subunit-secreting pituitary adenoma.

The mRNA and protein products produced by an alpha-subunit-secreting pituitary tumor were studied to further characterize the early steps in glycoprotein hormone biosynthesis. alpha-Subunit mRNA was readily detected by RNA blot hybridization to alpha-subunit cDNA and was qualitatively normal, with a length of about 800 bases. Although only excess free alpha-subunit was secreted by the tumor, abundant beta-subunit mRNA hybridized to a cDNA which recognized both LH beta and CG beta sequences. Surprisingly, the beta-subunit mRNA in the pituitary tumor was characteristic of CG beta mRNA. The beta-subunit mRNA migrated in parallel with placental CG beta mRNA (approximately 1000 bases) and was easily resolved from LH beta mRNA (approximately 700 bases). Using site-specific hybridization and oligonucleotide-primed extension, the beta-subunit mRNA in pituitary tumor was found to have an extended 5'-untranslated tract (366 bases) characteristic of CG beta gene transcripts rather than LH beta gene transcripts, in which the 5'-untranslated tract is only 9 bases. Activation of the CG beta-like promoter rather than the LH beta promoter indicates that the cellular mechanisms regulating tissue-specific expression of the beta-subunit gene were altered by the neoplastic changes in the pituitary tumor. Protein analysis of tumor homogenate demonstrated large amounts of alpha-subunit in the form of intact FSH and small amounts of intact LH and free alpha-subunit. Despite the presence of abundant CG beta-like mRNA in the tumor, intact hCG or hCG beta was not detected. The uncoupling of beta-subunit gene expression and protein biosynthesis in the setting of ongoing alpha-subunit biosynthesis provides a potential mechanism for unbalanced synthesis and secretion of free alpha-subunit.

Adenoma↗
PubMed1980

Effects of insulin-induced hypoglycemia on cerebrovascular permeability to horseradish peroxidase.

The effects of hypoglycemia on cerebrovascular permeability to a protein, horseradish peroxidase (HRP), were studied in mice given 3 or 8 units of crytalline zinc insulin intraperitoneally. HRP (10 mg in 0.1 ml saline) was injected intravenously 15 to 20 minutes prior to sacrifice. Both mildly and severely hypoglycemic groups of mice showed a drastic reduction in the normal transit of HRP across cerebral arterioles. The number of normally-stained vessel segments and of HRP-filled endothelial vesicles decreased in insulin-treated mice. In the brains of severely hypoglycemic mice, however, increased parenchymal HRP accumulation occurred. A ruptured blood vessel was found in the center of one-fourth of the focal exudates examined. Electron microscopic examination revealed thrombin, sometimes extending through the vessel wall, and hemorrhage, yet inter-endothelial tight junctions remained intact. Seizures were associated with severe hypoglycemia in 6 out of 10 mice with serum glucose levels below 40 mg/100 ml following 8 units of insulin, but the number of focal exudates per brain was similar in all 10 mice. We conclude that insulin-induced hypoglycemia is associated with decreased HRP transit across cerebral arterioles, and that severe insulin shock is also accompanied by actual rupture of vessel walls and extravasation of blood and HRP into the parenchyma of the brain.

Animals↗
PubMed1977

Ultrastructural localization of glial fibrillary acidic protein in mouse cerebellum by immunoperoxidase labeling.

Glial fibrillary acidic protein was localized at the electron microscope level in the cerebellum of adult mice by indirect immunoperoxidase histology. In confirmation of previous studies at the light microscope level, the antigen was detectable in astrocytes and their processes, but not in neurons or their processes, or in oligodendroglia. Astrocytic processes were stained in white matter, in the granular layet surrounding synaptic glomerular complexes, and in the molecular layer in the form of radially oriented fibers and of sheaths surrounding Purkinje cell dendrites. Astrocytic endfeet impinging on meninges and perivascular membranes were also antigen positive. In astrocytic perikarya and processes, the immunohistochemical reaction product appears both as a diffuse cytoplasmic label and as elongated strands, which by their distribution and frequency could be considered glial filaments.

Animals↗
PubMed1977

Protein transport across cerebral vessels during metrazole-induced convulsions.

The effects of pentylenetetrazole-induced convulsions on cerebrovascular permeability for horseradish peroxidase were studied in locally anesthetized, artificially respired, paralyzed cats. Horseradish peroxidase circulated for 1, 2.5, 5, 10, 30, and 60 min and accumulated in medium-size, i.e., arterial or venous, blood vessel walls. Cerebral neuropil was permeated earliest in thalamic nuclei including medial and lateral geniculate nuclei. No tight junctions containing horseradish peroxidase were found. With 1.0 and 2.5 min circulation of horseradish peroxidase, arterial adventitia and basement membranes contained more peroxidase than surrounding interstitial space in contrast to veins and capillaries. Convulsions increased the number of endothelial vesicles containing horseradish peroxidase in arteries, veins, and capillaries but total number (stained plus unstained) of endothelial vesicles was increased slightly only in capillaries. We conclude that increased permeability is initially at the arterial level, although veins may also become permeable. The role of the endothelial vesicles in transit or protein in and out of the nervous system is not clear.

Animals↗