[Differentiated thyroid carcinomas manifesting as toxic adenoma]

BACKGROUND

Hot thyroid nodules are generally benign. We report two exceptional cases of thyroid carcinomas mimicking toxic adenomas.

CASE REPORTS

A 35-year-old man and a 55-year-old woman had thyroid carcinoma behaving as an autonomously hyperfunctioning nodule.

DISCUSSION

Only twenty similar cases have been reported in the literature. While a hot nodule on radio-iodine scan is unlikely to be malignant, the possibility of carcinoma should not be overlooked. Surgery should therefore be the preferred treatment of toxic adenoma.

Nuclear effects of the cAMP pathway activation in somatotrophs

Activation of the cAMP pathway from the cell surface to the nucleus plays a major role in somatotroph differentiation and growth. This pathway is regulated mainly by the antagonistic hypothalamic hormones GHRH and somatostatin. Several pituitary-specific, as well as ubiquitous, expressed genes are regulated by cAMP in GH-secreting cells. Among them are the GH, GHF-1/Pit-1, c-fos and GHRH-receptor genes. Protein kinase A phosphorylation of Ser 133 of the transcription factor cAMP-responsive element binding protein (CREB), seems to play a pivotal role in the activation of the cAMP pathway in normal and tumoral somatotrophs. The oncogenic activating mutations of the G-protein as subunit stimulate transcription and CREB phosphorylation in somatotroph cells. The implications of the nuclear targets of cAMP in the differentiation and growth of somatotrophs are discussed in this review.

[Pituitary adenoma: mechanisms of endocrine oncogenesis]

Molecular studies on pituitary adenomas support a major role of molecular alterations in the pathogenesis of pituitary adenomas. Nevertheless, alterations in the neuro-hormonal control of the pituitary could also be involved in pituitary tumors formation. The finding that most pituitary adenomas are monoclonal has stimulated a search for somatic mutations. For instance, activating mutations of the Gs protein, leading to constitutive stimulation of the cAMP pathway, have been found in a subset of GH-secreting adenomas. But GHRH (growth hormone-releasing hormone) tumoral hypersecretion also stimulates the cAMP pathway and causes acromegaly. Pituitary tumor formation might result from accumulation of several alterations that would determine the tumoral phenotype. The majority of these alterations remains to be found.

Effects of chronic octreotide treatment on GH secretory dynamics and tumor growth in rats bearing an ectopic somatotroph (GC) tumor

The effects of octreotide, a long-acting somatostatin agonist selective of the sstr2/sstr3/sstr5 receptor subtypes, on ectopic GH secretion and tumor growth were investigated in Wistar-Furth female rats implanted with GH secreting (GC) cells which express mostly somatostatin receptors of the sstr1 and sstr2 subtypes. Octreotide dose dependently inhibited thymidine incorporation (-57%) and GH secretion (-41%) from GC cells in culture. In vivo, 6 weeks after GC cell implantation, plasma GH, IGF-1 and insulin levels were highly elevated. Cluster analysis of GH secretory dynamics revealed that GH secretion was less pulsatile in GC-implanted than in control animals. Furthermore, in GC-implanted animals, passive immunization either with SRIH or GHRH antisera, did not affect GH plasma levels. Three weeks after GC cell implantation, when tumors became palpable, octreotide (1 micrograms/h/kg BW) or saline was infused constantly for three weeks by osmotic minipumps. In octreotide treated rats, GH, IGF-1 and insulin levels were not different from sham-implanted animals and tumors weight were reduced by 80%. High affinity somatostatin binding sites were found in equivalent amounts on tumors from octreotide-treated or saline-treated animals. These findings indicate that GH secretion in GC-rats is mainly derived from the tumors and independent of hypothalamic control and that octreotide reduces both GH secretion and tumor growth. We conclude that the GC-implanted rat represents a good animal model to test the antisecretory and antitrophic properties of somatostatin analogs in vivo.

The cyclic adenosine 3',5'-monophosphate-responsive factor CREB is constitutively activated in human somatotroph adenomas

Oncogenic gsp proteins appear to stimulate the transformation of pituitary somatotrophs by inducing the constitutive activation of adenyl cyclase. Previous work implicating the cAMP-responsive transcription factor CREB as a biochemical intermediate in the proliferative response to cAMP led us to examine whether CREB activity was correspondingly elevated in human somatotroph adenomas. In a series of 15 human GH-secreting tumors, we found that each of these contained elevated levels of Ser133-phosphorylated and, hence, activated CREB compared with nonfunctioning pituitary tumors. Four of the GH-secreting adenomas contained an oncogenic gsp gene by polymerase chain reaction analysis, and two additional adenomas expressed wild-type G alpha s protein at 5- to 10-fold higher levels than nonfunctioning pituitary tumors. As both oncogenic gsp and overexpressed G alpha s proteins can induce Ser133 phosphorylation and cAMP-responsive gene expression in transfected GC somatotroph cells, our studies indicate that these proteins may promote somatotroph transformation in part by inducing the transcription of specific CREB-dependent target genes.

Molecular and pharmacological characterization of somatostatin receptor subtypes in adrenal, extraadrenal, and malignant pheochromocytomas

SRIH receptors were quantified by radioautography in 33 pheochromocytomas and 5 normal adrenals. Binding was evenly distributed over the tumors, whereas it was more intense in adrenal medulla than cortex. Binding levels were significantly higher in tumoral than in normal tissue, but did not differ among tumors. At 100 nmol/L, SRIH-14 and octreotide (or BIM23014 in cross-linking experiments to a 57-kilodalton component) comparably displaced SRIH binding, BIM23042 and BIM23052 were less potent, and BIM23056 was inefficient. In increasing doses, the rank order of potency was SRIH-14 > SRIH-28 > octreotide > BIM23052 >> BIM23042 >> > BIM23056. All five species of SRIH receptor (SSTR1-5) messenger ribonucleic acids (mRNAs) were measurable in pheochromocytomas and normal adrenals, SSTR2 and SSTR4 mRNA were the most expressed moieties. The proportion of SSTR5 mRNA species was higher in normal adrenals (21%) than in pheochromocytomas (6%). In the presence of guanylylimidodiphosphate, SRIH binding was reduced by 83%. However, SRIH did not alter basal or forskolin-stimulated adenylyl cyclase activity. Taken together, these pharmacological and molecular data indicate that SRIH binding on pheochromocytomas depends on a mixed population of receptors, mainly of the SSTR2 and SSTR4 subtypes, efficiently coupled to G proteins, but not to adenylyl cyclase inhibition.

Short-term effects of octreotide on blood pressure and plasma catecholamines and neuropeptide Y levels in patients with phaeochromocytoma: a placebo-controlled trial

OBJECTIVE

The observation that phaeochromocytoma possess specific somatostatin binding sites led us to test the hypothesis that octreotide may have antisecretory potential in patients with phaeochromocytoma. We therefore compared the effects of octreotide and placebo on blood pressure and plasma catecholamines and neuropeptide Y.

PATIENTS

Ten consecutive patients referred to a tertiary care centre for the diagnosis and treatment of a phaeochromocytoma.

DESIGN AND MEASUREMENTS

We performed a crossover comparison of either three 100 micrograms subcutaneous injections of octreotide over one day or 3 injections of octreotide vehicle over another. Blood pressure was measured over 24 hours on each test day using an automatic ambulatory recorder. Blood samples were collected before (at 0800 and 0900 h) and after (at 1000, 1100, 1200, 1300 and 1500 h) placebo or octreotide injection. Plasma catecholamines were assayed by high-performance liquid chromatography and neuropeptide Y was determined using a two-site amplified enzyme immunoassay. All patients then underwent surgery and tumoral somatostatin binding site density was determined by quantitative autoradiography.

RESULTS

Compared to placebo, octreotide did not alter mean 24-hour ambulatory blood pressure or plasma neuropeptide Y, or plasma or urinary catecholamine, levels. Although a moderate reduction in plasma noradrenaline was found in the two patients with the highest tumoral somatostatin binding site densities, overall octreotide-induced variations in plasma noradrenaline did not correlate with somatostatin binding site density. Blood glucose increased from 5.4 +/- 0.3 on placebo to 7.8 +/- 0.5 mmol/l on octreotide (P < 0.01).

CONCLUSION

In the present controlled conditions, short-term administration of octreotide had no antisecretory effect in patients with phaeochromocytoma.

Neuroendocrine regulation of growth hormone

This short review is focused on the neuroendocrine regulation of growth hormone (GH) pulsatile secretory pattern and GH gene expression. The neuronal network involved in the central control of GH includes extrahypothalamic neurons such as the noradrenergic and cholinergic systems, which regulate the two antagonistic neurohormonal systems: somatostatin (SRIH) and GH-releasing hormone (GHRH). Intrahypothalamic Proopiomelanocortin- and Galanin-containing interneurons also participate in the regulation of SRIH and GHRH neuronal activity, which also is dependent on sex steroids and GH and/or insulin-like growth factor I (IGF-I) feedback. cAMP (controlled mainly by GHRH and SRIH), thyroid and glucocorticoid hormones. IGF-I and activin are among the factors that regulate GH gene expression at the transcriptional level and may play a role in somatotroph differentiation and proliferation during ontogeny as well as physiological and pathological states such as acromegaly.

Presence of somatostatin receptors negatively coupled to adenylate cyclase in ectopic growth hormone-releasing hormone- and alpha-subunit-secreting tumors from acromegalic patients responsive to octreotide

The functional study of SRIH receptors was performed in ectopic GHRH-secreting tumors from two patients with acromegaly; patient 1 presented with multiple endocrine neoplasia type 1 with GHRH- and insulin-secreting pancreatic tumors, and patient 2 presented with a multihormone-secreting carcinoid tumor (including GHRH and alpha-subunit secretion, as demonstrated by clinical and immunohistochemical studies). In both cases, plasma GH levels were responsive to octreotide. In patient 2, plasma GHRH and alpha-subunit levels were responsive to octreotide. In vitro perifusion studies of a tumor fragment from patient 1 also showed inhibition of GHRH secretion by SRIH. A high density of specific SRIH-binding sites was visualized by autoradiography in GHRH tumors from both patients. SRIH specific binding was much higher in the GHRH tumors (6.6-8.4 fmol/surface unit) than in the insulinoma (1.9 fmol/surface unit). The binding inhibition constant (IC50) was in the nanomolar range (0.9-3 nmol/L) in the GHRH tumors. SRIH-14 inhibited forskolin-stimulated adenylate cyclase in the GHRH tumors from both patients, but not in the insulinoma. The functional SRIH receptors negatively coupled to adenylate cyclase present in ectopic GHRH-secreting tumors mediate the inhibitory effect of octreotide on GHRH secretion and on previously underrecognized ectopic alpha-subunit secretion from carcinoid tumors.

[Endocrine evaluation and evolution of intrasellar craniopharyngioma (CPIS): study of 8 cases]

BACKGROUND

Craniopharyngiomas generally develop either in the suprasellar region or in both suprasellar and intrasellar regions. Purely intrasellar craniopharyngiomas are rare in children; they have special clinical and radiological features and pose specific therapeutic problems.

POPULATION AND METHODS

Eight patients (five girls and three boys), aged 7 to 17 years, were admitted from 1976 to 1992 with a diagnosis of intrasellar craniopharyngioma without extrasellar development. Search for endocrine deficiencies was performed in all these patients as well as radiological investigation (skull X-rays, CT scan and MRI).

RESULTS

Persistent delayed growth was the main complaint in seven out of the eight patients. Headache was seen in three patients. The tumor was fortuitously discovered after cranial traumatism in one. Initial endocrine investigations showed growth hormone deficiency in all patients; deficiency in thyrotropin was seen in five, in adenocorticotropin in six. Three patients had moderately increased levels of blood prolactin and four had delayed puberty with gonadotropin deficiency. Only one patient presented with diabetes insipidus. X-rays showed enlarged sella turcica in seven of the eight patients with calcifications in three and a cystic lesion in five. Two patients were operated on because of a doubtful diagnosis: their condition is stable 1.5 and 12 year later, respectively. The tumor volume remained stable with a follow-up of 1.5-9 years in five other patients; its volume gradualled increased in another patient requiring surgical removal 18 months after diagnosis. Antehypophysar deficiency generally increased in all patients, operated on or not, and five patients out of six have gonadotropin deficiency.

CONCLUSIONS

These intrasellar craniopharyngiomas remain generally stable so that the greatest care must be taken in proposing surgical treatment.

Somatostatin receptors, adenylate cyclase activity, and growth hormone (GH) response to octreotide in GH-secreting adenomas

To determine the cellular mechanism(s) of the variability in GH responsiveness to octreotide in acromegaly, somatostatin (SRIH) receptor status was studied in 37 GH-secreting adenomas. SRIH receptor binding was always present in all GH-secreting adenomas either in membrane preparations (Exp A; n = 17) or by quantitative autoradiography (Exp B; n = 20). In membranes, maximal binding capacities ranged from 83-2331 fmol/mg protein; affinity was in the nanomolar range (Kd, 1.3 +/- 0.2 nmol/L). By quantitative autoradiography, SRIH-14 and octreotide were equally active in displacing [125I]SRIH binding in tumors (Spearman correlation rho = 0.92). IC50 values ranged from 3-22 nmol/L (mean +/- SE, 8.0 +/- 1.3 nmol/L). In Exp A, basal adenylate cyclase (AC) activity was high in 7 tumors (841 +/- 306 pmol/L cAMP x 30 min/mg protein) compared to that in the other 10 (252 +/- 92 pmol/L cAMP x 30 min/mg protein). In these 7 tumors, GH-releasing hormone (0.1 mumol/L) stimulation of AC was lower (53 +/- 11% vs. 297 +/- 48%), whereas SRIH (1 mumol/L) inhibition was higher (52 +/- 5% vs. 34 +/- 5%). Similar results were obtained with Exp B tumors. In both experiments, no correlation was apparent between SRIH-binding capacity and inhibition of AC. In Exp B, a variable decrease in mean plasma GH levels was observed (> or = 80% in 5 patients, between 50-80% in 8 patients, and < or = 50% in 5 patients) after a single sc injection of octreotide (100 micrograms). A modest correlation was found between the GH response to octreotide and SRIH-binding capacity (rho = 0.48) or SRIH inhibition of AC (rho = 0.61). The IC50 values to displace SRIH binding were lower in poorly responsive patients than in highly responsive ones (IC50, 4.6 +/- 1.9 and 13.9 +/- 2.7 nmol/L, respectively). These data indicate that an absence of SRIH receptors cannot account for the weak response to SRIH therapy in 20-30% of acromegalic patients. Alternatively, the weak correlation between either SRIH binding or SRIH inhibition of AC with octreotide inhibition of plasma GH levels might reflect the heterogeneity of SRIH receptor subtypes in GH-secreting adenomas.