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S Melmed

Publications and source records attributed to S Melmed.

At least 199 records · Page 11Linked to original sources
PubMed1986

Insulin-like growth factor I regulates growth hormone secretion and messenger ribonucleic acid levels in human pituitary tumor cells.

GH secretion and mRNA levels were measured in cultured human GH adenoma cells incubated in serum-free medium for up to 48 h. A human recombinant insulin-like growth factor I (IGF-I) analog, Thr-59-IGF-I (6.5 nM), inhibited basal GH secretion by up to 60% in tumor cell cultures. The 30-50% stimulation of GH secretion by GH-releasing hormone (GHRH) was prevented by simultaneous exposure of the cells to IGF-I (6.5 nM). Gel electrophoresis of total RNA derived from GH cell adenoma tissue, followed by transfer and hybridization with 32P-labeled human GH cDNA, revealed a distinct mRNA species of about 1.0 kilobases. Using cytoplasmic dot blot hybridization, IGF-I inhibited the levels of human GH mRNA sequences in these cells and also prevented the GHRH-induced stimulation of GH mRNA. A monoclonal antibody to the type I IGF-I receptor (alpha IR3) prevented the inhibitory effects of IGF-I on basal and GHRH-stimulated GH secretion. This antibody also prevented the IGF-I-induced suppression of GH mRNA sequences. PRL secretion in these cells was not altered by IGF-I. Furthermore, relative levels of beta-actin mRNA were unaltered by IGF-I. Thus, IGF-I suppresses basal and GHRH-stimulated GH secretion and GH mRNA levels in pituitary adenoma cells, indicating that IGF-I acts selectively on the somatotroph to directly regulate GH gene expression.

Adenoma↗
PubMed1986

Expression of the myc cellular proto-oncogene in human thyroid tissue.

The expression of cellular oncogenes was examined in human thyroid tissue. Four thyroid adenomas and three thyroid carcinomas expressed c-myc oncogene mRNA transcripts, which were not expressed in normal thyroid tissues. Agarose gel electrophoresis of poly(A) RNA extracts of adenoma tissues followed by hybridization with v-myc DNA yielded two distinct c-myc mRNA species [2.1 and 4.0 kilobases (kb)]. Thyroid cancer tissue poly(A) RNA revealed a predominant larger c-myc mRNA species (approximately 6 kb) and a smaller 2.1-kb species. After enzymatic dispersion of thyroid adenoma cells, cytoplasmic dot blot hybridization of immobilized thyroid adenoma RNA extracts with the v-myc cDNA probe showed stimulation of c-myc mRNA expression by TSH in a dose- and time-dependent manner. After 72-h pretreatment with serum-free medium, the quiescent adenoma cells yielded a negligible hybridization signal which was stimulated by TSH (10 mU/ml) after 6 h of treatment. Although normal cultured thyroid cells did not contain detectable c-myc mRNA, TSH also stimulated the myc protooncogene expression in a time-dependent manner in normal thyroid cells. These results demonstrate the expression of c-myc mRNA in human thyroid tumors and the in vitro induction of c-myc mRNA in both normal and adenoma thyroid cell cultures by TSH.

Adenocarcinoma, Papillary↗
PubMed1986

Effects of insulin on rat anterior pituitary cells. Inhibition of growth hormone secretion and mRNA levels.

We recently reported that insulin inhibits basal and cortisone- and T3-stimulated GH secretion by GH3 rat pituitary tumor cells. The effects of purified semisynthetic human insulin were therefore tested on long-term GH secretion in normal pituitary cells. Primary monolayer cultures derived from male rat pituitaries were grown in serum-free defined medium. Insulin (7 nM) maximally inhibited basal GH secretion by almost 60% after 72 h, with 50% of maximal GH suppression occurring with 1.75 nM insulin. Insulin receptor antiserum blocked the suppression of GH by 7 nM insulin, but had no effect on the suppression of GH by IGF-I (3.25 nM). GRF (100 pM) stimulated GH two- to threefold during 48 h. Insulin (7 nM) prevented the stimulation of GH induced by up to 1 nM GRF (P less than 0.01) and this suppression was also selectively blocked by insulin receptor antiserum. The inhibition of GRF-stimulated GH required a lag period of 48 h and the dose of insulin required for 50% inhibition of GRF stimulation was 3.5 nM. Insulin did not alter the degradation rate of 125I-GH in these cultures and medium glucose concentrations were not different in control or insulin-treated wells for up to 72 h of incubation. The insulin-induced suppression of GH was also observed when cells were grown in glucose-free medium. Insulin did not nonselectively suppress cell secretion, as PRL secretion was mildly stimulated (P less than 0.01) by insulin in the same cultures. Fibroblast growth factor, epidermal growth factor, and insulin A-chain at similar doses did not alter basal or GRF-stimulated GH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Pituitary tumors secreting growth hormone and prolactin.

The pathophysiology of functional adenomas of the anterior pituitary gland can be understood in the context of the central neural control of anterior pituitary secretion and by the fact that the cell types of the anterior pituitary gland generally express a single polypeptide hormone. Functional pituitary adenomas arise de novo from one or more of these cell types, but a defect in hypothalamic regulation can contribute to tumorigenesis and sometimes result in persistent tumor recurrence despite local surgical cure. The recent advances in molecular biology, radioimmunoassay, neuroradiology, and transsphenoidal microneurosurgery techniques have greatly improved our understanding of the pathophysiology of these tumors, enhanced diagnostic accuracy, and led to newer medical and surgical therapeutic approaches. This conference reviews the molecular and cellular pathophysiology, causes, diagnosis, clinical features, and medical and surgical management of the two common functional pituitary adenomas, prolactinoma and somatotropinoma.

Adenoma↗
PubMed1985

Cardiac morphology in rats with growth hormone-producing tumours.

Cardiac enlargement and dysfunction are common in patients with acromegaly. Whether these changes are a direct consequence of growth hormone excess is obscured by the high frequency of hypertension, diabetes mellitus, or atherosclerosis in acromegalic patients. In this study, the effects of chronic elevations of growth hormone (GH) upon the heart were studied in rats with GH-producing tumours implanted subcutaneously for 4 weeks. Geometric measurements and histology were employed to detect the presence of cardiac changes. Increased mass was observed in the tumour-bearing animals. When compared with controls, in tumour-bearing rats there were significantly greater (P less than 0.05) right (0.17 +/- 0.03 v. 0.13 +/- 0.01 g) and left (0.62 +/- 0.05 v. 0.50 +/- 0.04 g) ventricular weights, external cardiac dimensions, and myocardial fibre diameters (9.4 +/- 0.6 v. 8.3 +/- 0.4 micron). However, these increases were linearly-related to increased body mass in the tumour-bearing group so that the ratios of ventricular weights to body weight were similar in both groups. Furthermore, no pathologic changes such as myocardial fibrosis or asymmetric septal hypertrophy were present in the tumour-bearing rats. Thus, under the conditions of this study, growth hormone excess induced cardiac growth, which appeared to represent a manifestation of generalized body growth rather than a distinct pathologic process.

Animals↗
PubMed1985

Insulin suppresses triiodothyronine-induced growth hormone secretion by GH3 rat pituitary cells.

Physiological doses of insulin were shown by us to suppress basal and hydrocortisone (HCT)-induced GH secretion and GH mRNA levels in GH3 rat pituitary cells. Because T3 stimulates GH gene expression, the effects of semisynthetic human insulin were tested on T3-induced GH secretion. Cells were first incubated for 48 h in medium containing insulin and fetal calf serum (10%) depleted of T3 and T4 by ion exchange resin. Insulin suppression of basal GH secretion was independent of T3, as insulin (0.7 nM) suppressed basal secretion of GH by 40% in T3-depleted cells. Medium glucose concentrations and cell proliferation did not differ in control or insulin-treated wells. The 4-fold increase in GH secretion induced by added T3 (0.5 nM) during 72 h was suppressed up to 40% by insulin (P less than 0.001). This suppression was maximal with 3.5 nM insulin and occurred after a lag period of 48 h. The previously described 20-fold synergistic stimulation of GH by T3 (0.5 nM) together with HCT (1 microM) was also suppressed by insulin (3.5 nM) by 80% during 72 h of incubation. The selectivity of the inhibitory effects of insulin on GH were also shown when the T3-induced suppression of PRL secretion was reversed by insulin treatment. The data show that physiological doses of insulin antagonize T3-induced stimulation of GH secretion and also partially block the synergistic stimulation of GH by T3 and HCT. As T3 and HCT probably stimulate GH gene transcription at different sites, insulin may suppress GH gene expression at a more distal site. Alternatively, the inhibitory effects of insulin on T3-induced GH secretion in these cells may be posttranscriptional.

Animals↗
PubMed1985

Insulin suppresses rat growth hormone messenger ribonucleic acid levels in rat pituitary tumor cells.

Insulin has been shown to suppress growth hormone (GH) secretion by rat pituitary tumor cells (GH3) independently of glucose utilization. The effects of physiologic doses of insulin were therefore tested on cytoplasmic levels of GH messenger ribonucleic acid (mRNA) sequences. Insulin (3.5 nM) treatment of cells for 5 days suppressed the hybridization of cytoplasmic GH mRNA with 32P-cDNA for rGH by 50%. The three- to fourfold induction of cytoplasmic GH mRNA by hydrocortisone (1 microM) was also suppressed by insulin (3.5 nM) by 40%. The results show a direct suppression of cytoplasmic rGH mRNA concentration by physiologic doses of insulin. These findings may be due to either decreased rate of GH gene transcription, increased intracellular breakdown, or decreased nuclear-cytoplasmic transport of GH mRNA caused by insulin.

Animals↗
PubMed1985

Localization of somatostatin receptors in secretion vesicles in anterior pituitary cells and pancreatic islets.

Secretion vesicles in anterior pituitary cells and pancreatic islets appear to translocate somatostatin receptors from the cell interior to the plasma membrane. In this study we attempted to localize somatostatin receptors on either the cytoplasmic or the intraluminal surface of the secretion vesicles. 125I-somatostatin binding was determined in intact secretion vesicles and vesicles disrupted either by sonication or solubilization. The binding of 125I-somatostatin was identical in intact and disrupted vesicles, indicating cytoplasmic orientation of somatostatin receptors. Pronase treatment of intact secretion vesicles removed approximately 90% of specific somatostatin binding. Sonication of pronase treated secretion vesicles did not reveal latent somatostatin binding sites. Gold-conjugated somatostatin binds to isolated secretion vesicles confirming the presence of somatostatin binding sites on the outer surface of these vesicles. We conclude that somatostatin binding sites are located on the cytoplasmic surface of secretion vesicles isolated from anterior pituitary cells and pancreatic islets.

Animals↗
PubMed1984

Insulin suppresses growth hormone secretion by rat pituitary cells.

The effects of insulin on basal and hydrocortisone-induced growth hormone (GH) secretion were studied in rat pituitary tumor cells (GH3). Cells were grown in monolayer culture and exposed to exogenously added insulin for up to 8 d. Basal GH secretion was inhibited by insulin (0.7 nM) after a 48-h lag period by approximately 50% (P less than 0.01, vs. untreated control cells). The suppression of GH secretion was reversible, as removal of added insulin resulted in return of GH secretion to normal levels after 24 h. Maximal suppression of basal GH secretion was achieved by 0.7 nM insulin, and these effects were prevented by simultaneous exposure of the cells to guinea pig anti-insulin serum (1:2,000). No effects of insulin on cell replication were evident, and glucose concentration in the medium did not differ in control or insulin-treated wells. Insulin (7 nM) significantly suppressed the fivefold hydrocortisone-induced GH stimulation during 5 d of incubation with up to 1,000 nM of the steroid (P less than 0.001). These inhibitory effects were similarly observed in glucose- and pyruvate-free medium, and in the presence of 2-deoxyglucose. Insulin also reversed the suppression of prolactin (PRL) secretion induced by hydrocortisone (1 uM), and actually stimulated basal PRL secretion by over 50%. Insulin did not alter the inhibitory effect of hydrocortisone on GH3 cell proliferation. Although higher doses (13 nM) of insulin-like growth factor (IGF-I) also suppressed basal GH secretion, IGF-I did not alter the GH and PRL secretory changes induced by hydrocortisone. The results show that insulin exerts a direct, specific inhibitory effect on basal and hydrocortisone-induced GH secretion by GH3 cells unrelated to glucose utilization by the cells.

Animals↗
PubMed1983

Dopaminergic regulation of prolactin and growth hormone synthesis in rat pituitary tumor cells.

The dopaminergic regulation of prolactin (PRL) and growth hormone (GH) synthesis were studied in monolayer cultures of rat pituitary tumor (GH3) cells. PRL synthesis could not be inhibited by dopamine at concentrations ranging from 10(-9) to 10(-5) M. Bromocriptine inhibited PRL synthesis only at the very high concentration of 10(-5) M, and this effect was not reversible by metoclopramide. GH synthesis was inhibited by 10(-6) and 10(-5) M dopamine but not by bromocriptine, and the dopamine effect was blocked by metoclopramide. These results suggest the existence of a defective dopaminergic regulation of PRL and GH synthesis in GH3 cells.

Animals↗
PubMed1983

Hepatocyte insulin binding and action in rats with somatomammotrophic tumours.

The effects of chronic elevations of growth hormone levels on hepatic insulin binding and action were studied in rats with subcutaneously implanted growth hormone-producing tumours. These animals were significantly heavier (p less than 0.001; 388 +/- 29 versus 239 +/- 4 g), had elevated insulin levels, (6.8 +/- 0.6 versus 3.3 +/- 0.5 ng/ml), lower glucose concentrations (6.0 +/- 0.4 versus 9.3 +/- 0.5 mmol/l) and larger hepatocyte diameters (28.7 +/- 0.6 versus 24.0 +/- 0.4 micron) and surface areas (2661 +/- 119 versus 1835 +/- 65 micron2) than control rats. Insulin binding and action [net (C14)-glucose incorporation into glycogen] were compared in hepatocytes isolated from these two groups. Because of the difference in hepatocyte size, insulin binding was normalized for cell surface area. Binding of the tracer alone (0.9 +/- 0.05 versus 1.3 +/- 0.12%/cm2) and capacity of the high affinity, low capacity receptor (30.9 +/- 5.9 versus 65.2 +/- 5.9 sites/micron2) were significantly decreased (p less than 0.02) in tumour-bearing rats. Dose-response curves of insulin action in hepatocytes chronically exposed to excess growth hormone were shifted to the right. The maximal response was also significantly decreased. However, the relation between the amount of insulin bound and the proportion of the maximum insulin effect obtained were similar in cells from the two groups. Thus, in rat hepatocytes chronically exposed to excess growth hormone, both a receptor and a post-receptor defect occur while the insulin receptor itself functions normally.

Animals↗
PubMed1983

Modulation of ectopic secretion of human chorionic gonadotropin by cultured ovarian adenocarcinoma cells.

Modulation of ectopic human chorionic gonadotropin (hCG) secretion by a human nontrophoblastic ovarian papillary cystadenocarcinoma cell line maintained in monolayer culture was studied. Exposure of cells to methotrexate (MTX, 0.1 microM) significantly enhanced hormone secretion while actual cell replication was decreased. In contrast, exposure of cells to actinomycin D (25 pM) for 24 hr completely abolished hormone secretion and resulted in death of all cells. Exposure of the cells to hypothalamic peptides (thyrotropin-releasing hormone, gonadotropin-releasing hormone, and somatostatin) did not alter hCG production. hCG secretion was stimulated after 24-hr incubation with dibutyryl cAMP (100 microM) and by prostaglandin F1 alpha (10 microM). Two separate mechanisms of modulation of ectopic hCG by these cells are possible: a cAMP-mediated stimulation independent of cell-growth kinetics after exposure to dibutyryl cAMP and prostaglandin F1 alpha, and a selective inhibition of DNA synthesis which results in slowing of cell replication and concomitant increase in hCG production per cell.

Bucladesine↗
PubMed1983

Pathophysiology of acromegaly.

This review discusses the pathophysiology of acromegaly. Acromegaly has been classified in this paper into distinct entities based on etiology, ultrastructural features of the pituitary, and cytogenesis. This classification has been proposed based on clinical signs, immunoperoxidase techniques, transmission electromicroscopy and immunoelectron microscopy. Pituitary causes of acromegaly include densely granulated adenomas, sparsely granulated adenomas, mixed growth hormone and prolactin cell adenomas, acidophil stem cell adenomas, mammosomatotroph cell adenomas, and pleurihormonal adenomas. GH cell hyperplasia and GH cell carcinoma are also discussed. Extrapituitary causes of acromegaly include eutopic GH cell adenoma in the sphenoid sinus or parapharyngeal region and excess GHRF secretion which may be eutopic or ectopic. The pathological, clinical, and biochemical evidence in favor of a pituitary or hypothalamic etiology of acromegaly has been reviewed. Finally, a multistage theory of GH cell tumorigenesis has been proposed as a model in an attempt to unify the genetic, environmental and biochemical factors implicated in the pathogenesis of acromegaly.

Acromegaly↗
PubMed1983

Human chorionic gonadotropin stimulates proliferation of Nb 2 rat lymphoma cells.

The effects of an onco-fetal hormone, hCG, were tested on replication of Nb 2 node rat lymphoma cells, which have previously been shown to be responsive to lactogenic hormone stimulation. Cells were maintained in suspension culture in Ham's F-10 medium containing horse serum (15%) and fetal calf serum (2.5%). Forty-eight hours before experiments, medium was replaced with horse serum (10%) only. In the absence of added hCG, cell doubling time was about 24 h. Purified hCG preparations (CR 119) and the Second International Standard for hCG (WHO) stimulated lymphoma cell replication after 72 h of exposure to the cells. The stimulation was dose dependent, beginning at 100 pg/ml and peaking at 10 ng/ml (140% vs. controls, P less than 0.001). Specific hCG antiserum (SB6) did not alter cell replication, but when added simultaneously with hCG, completely blocked the stimulation induced by hCG (10 ng/ml). No effect on cell proliferation was seen when the beta-subunit of hCG, the common glycoprotein alpha-subunit, human LH, FSH, or placental lactogen was added to the cells. These results indicate that hCG can stimulate proliferation of rat lymphoma cells in vitro. If hCG affects human tumors in a similar fashion, the ectopic production of the hormone by tumors may stimulate growth of the neoplasm.

Animals↗
PubMed1983

Isolation of human-mouse somatic cell hybrids producing human prolactin: dominant expression of hormone secretion and regulation.

Human PRL (hPRL)-secreting adenoma cells obtained at hypophysectomy were fused with a mutant mouse fibroblast line (LMTK-) which is aminopterin sensitive due to a deficiency in the enzyme thymidine kinase. After fusion with polyethylene glycol, cells containing nuclear material from the two parental lines (heterokaryons) were selected in medium containing hypoxanthine, aminopterin, and thymidine, and resultant clones were screened for hPRL secretion. Functional human X mouse somatic cell hybrid clones secreting hPRL were isolated in order to study hPRL gene expression and regulation. Positive hybrid clones were subcultured and have sustained hPRL secretion. The hybrid nature of the cells was confirmed by fibroblastic morphology resembling the mouse parental cell, mixed karyotype of mouse and human chromosomes, and mixed isozyme banding pattern for human and mouse glucose-6-phosphate dehydrogenase and malic enzyme. Specific expression of the hPRL gene was demonstrated by the presence of electron microscopic secretory granules (650-800 nm), positive immunoperoxidase staining using anti-hPRL serum, and sustained secretion of immunoreactive hPRL, which comigrated with [125I] hPRL standard on Sephadex chromatography. Hormonal modulation of hPRL gene expression by TRH was dominantly expressed in the hybrid cell. Human chromosome 6 was identified in hybrid cells secreting hPRL, and the cells expressed human malic enzyme, a marker for this chromosome, thus confirming the chromosome assignment of the hPRL gene. The results show that functional replicating hybrids secreting hPRL can be isolated. The technique provides a useful in vitro model for the study of hPRL gene expression and modulation.

Animals↗
PubMed1982

Establishment of functional human pituitary tumor cell cultures.

Five primary human pituitary tumor cell cultures were initiated from adenoma fragments obtained from patients with prolactin-secreting adenomas and acromegaly. Functional cell cultures were maintained and propagated in monolayer or suspension culture for up to 9 months. Optimal cell viability and growth were achieved using Ham's F10 medium enriched with 20% fetal bovine serum, although cells from a patient with acromegaly also grew in serum-free, defined, hormone-containing medium. Bromocriptine (100 ng/ml) did not alter the growth curve of replicating cells derived from a patient with acromegaly. These cells initially secreted 5.5 micrograms human growth hormone/10(6) cells, and hormone production diminished after 6 wk. Prolactin secretion by cells derived from prolactinomas (0.5 to 1.3 micrograms/10(6) cells/24 h) was stimulated by thyrotropin-releasing hormone (10 ng/ml) in two of the cultures. Both dopamine (10 ng/ml) and nickel chloride (1 mM) suppressed PRL secretion. These studies demonstrate that responsive human pituitary tumor cell cultures can be initiated and maintained.

Adenoma↗