Response of thyrotropin-secreting pituitary adenomas to a long-acting somatostatin analogue

Thyrotropin-secreting pituitary adenomas: epidemiology, diagnosis, and management

Inappropriate secretion of TSH was first described in 1960 in a patient with evidence of hyperthyroidism and expanded sella on imaging. It was later found that a type of pituitary adenoma that secretes TSH (thyrotropinoma) was the underlying cause. The objective of the present review article is to summarize data on the epidemiology, pathogenesis, diagnosis, and management of thyrotropinomas. The prevalence of thyrotropinomas is lower than that of other pituitary adenomas. Early diagnosis is now possible thanks to the availability of magnetic resonance imaging and sensitive laboratory assays. As a corollary, many patients now present earlier in the course of their disease and have smaller tumors at the time of diagnosis. Treatment also has evolved over time. Transsphenoidal surgery is still considered definitive therapy. Meanwhile, radiation therapy, including radiosurgery, is effective in achieving tumor control in the majority of patients. In the past, radiation therapy was used as second line treatment in patients with residual or recurrent tumor after surgery. However, the availability of somatostatin analogs, which can lead to normalization of thyroid function as well as shrink these tumors, has led to an increase in the role of medical therapy in patients who are not in remission after pituitary surgery. In addition, dopamine agonists have shown some efficacy in the management of these tumors. Better understanding of the molecular pathogenesis of thyrotropinomas may lead to rationally designed therapies for patients with thyrotropinomas.

Differential expression of somatostatin receptor subtypes in gastric cancer

AIM: To examine the expression of somatostatin receptor subtypes (SSTRs), including SSTR1, SSTR2, SSTR3, SSTR4 and SSTR5, in gastric cancer and to analyze their relationship with clinical and pathological characteristics.

METHODS: The expression of SSTRs in 58 gastric cancer specimens and adjacent normal stomach tissue specimens were examined by immunohistochemical staining. Correlations between SSTR expression and clinical and pathological parameters were analyzed by the chi-square test.

RESULTS: All five SSTR subtypes were expressed in gastric cancer tissues, with SSTR3 having the highest expression. SSTR5 expression increased significantly in gastric cancer compared with that in normal gastric tissue (P < 0.05). SSTR4 expression was significantly lower in gastric cancer with lymph node metastasis than in gastric cancer without lymph node metastasis (P < 0.05). SSTR3 expression in highly and moderately differentiated gastric cancer was significantly higher than that in poorly differentiated gastric cancer (P < 0.05). SSTR2 was lowly expressed in each group; SSTR1 expression was higher than SSTR5 expression in normal stomach tissue, but was lower in gastric cancer tissue.

CONCLUSION: Our results indicated that SSRT5, SSTR3 and SSTR4 may play important roles in the development of gastric cancer.

Pathologic and clinical features of pituitary adenomas showing TSH immunoreactivity

Patients with thyrotropin-secreting pituitary adenomas may present with mass effect, hypopituitarism, and/or hyperthyroidism. The spectrum of pathologic and clinical features of patients whose tumors demonstrate β-thyrotropin immunoreactivity (β-TSH IR) has not been characterized. To characterize the phenotype of patients with pituitary adenomas with positive β-TSH IR, we conducted a retrospective analysis of patient records of all adult patients (n = 1,223) undergoing pituitary surgery in our institution over one decade (1999-2009). The search identified 166 adults with tumors which had β-TSH IR. These patients were individually matched to 166 patients whose tumors revealed no β-TSH IR. Clinical, pathological, imaging and biochemical data were extracted. 332 patients, aged 51.4 ± 15.1 years [150 women (45 %) and 182 men (55 %)], with pituitary adenomas (mean tumor diameter ± SD: 22.7 ± 9.0 mm) were studied. The degree of β-TSH IR was associated with the presence of central hyperthyroidism (p < 0.0001) or goiter (p = 0.0217). Patients whose tumors expressed more extensive β-TSH IR were less likely to develop pituitary apoplexy than those without β-TSH IR (p = 0.0428). In addition, the degree of β-TSH IR correlated with the presence of immunoreactivity for β-FSH (p < 0.0001), β-LH (p < 0.0001), alpha subunit (p < 0.0001), and GH (p = 0.0036).

CONCLUSIONS

Pituitary adenomas expressing β-TSH IR were more likely to demonstrate immunoreactivity for β-FSH, β-LH, GH or alpha subunit. Patients with such tumors were more likely to exhibit hyperthyroidism and goiter, but less likely to develop pituitary apoplexy than patients without β-TSH IR. These findings suggest that β-TSH IR is associated with specific phenotypic features in patients with pituitary adenomas.

TSH-Secreting Pituitary Adenoma: Current Management and Review

The neurosurgical literature contains little information about the current management of patients with thyroid-stimulating hormone (TSH)-secreting pituitary adenomas or about the usefulness of the somatostatin analogue octreotide in such cases. While TSH-secreting pituitary adenomas are rare, our review and illustrative case demonstrate the effectiveness of pretreating patients with octreotide therapy not only to reduce tumor size prior to surgical resection but also to increase the possibility of clinical remission.A 52-year-old male presented with signs and symptoms of hyperthyroidism and elevated TSH, thyroxine, and triiodothyronine. Magnetic resonance imaging revealed a pituitary macroadenoma with extension into the suprasellar cistern. The patient was treated with octreotide for 6 months prior to surgery. Approximately 3 months after initiation of octreotide therapy, the patient exhibited excellent biochemical and clinical response. Tumor shrinkage of nearly 50% was associated with resolution of suprasellar extension and optic nerve compression. Subsequent transsphenoidal surgery for resection of residual adenoma was followed by symptomatic and hormonal remission without the need for reinstitution of octreotide therapy.Pretreatment with octreotide for TSH-secreting pituitary adenomas has a beneficial effect on disease symptoms and reduces tumor mass. We suggest that patients with these rare tumors can be managed with a combination of octreotide therapy and subsequent surgical removal of residual tumor. Although this combination treatment helps to facilitate clinical remission, only short-term follow-up has been reported and thus the optimal management of these patients remains to be determined.

In vivo and in vitro response to octreotide LAR in a TSH-secreting adenoma: characterization of somatostatin receptor expression and role of subtype 5

Thyrotropin-secreting pituitary adenomas (TSHomas) are a rare cause of hyperthyroidism and account for less than 2% of pituitary adenomas. Medical therapy with somatostatin analogues (SSAs) effectively reduces TSH secretion in approximately 80% of patients and induces shrinkage in about 45% of tumors. According with previous data, resistance to SSA treatment might be due to heterogeneity in somatostatin receptors (SSTRs) expression. We report the case of TSHoma in a 41-year-old man treated with octreotide LAR that caused a dramatic decrease of TSH and thyroid hormones and tumor shrinkage already after 3 months of pre-surgical therapy. In search of potential molecular determinants of octreotide effectiveness, we measured, in primary cultures from this tumor, SSTR and dopamine D2 receptor (D2R) expression, and octreotide and/or cabergoline effects on TSH secretion and cell proliferation. SSTR5 and D2R expression was higher than SSTR2. Octreotide significantly inhibited TSH secretion more effectively than cabergoline (P<0.001), whereas the combined treatment was comparable with cabergoline alone. Similarly, octreotide resulted more effective than cabergoline on cell proliferation, while the combination did not show any additive or synergistic effects. In conclusion, the significant antisecretive and antiproliferative effect of octreotide in this patient might be related to the high expression of SSTR5, in the presence of SSTR2. After reviewing the literature, indeed, in line with previous observations, we hypothesize that SSTR5/SSTR2 ratio in TSHomas may represent a useful marker in predicting the outcome of therapy with SSAs. The role of D2R should be further explored considering that the presence of D2R can influence SSTRs functionality.

Thyrotropin-secreting pituitary adenoma in an adolescent boy: challenges in management

Thyrotropinomas tend to be aggressive, invasive tumors that are difficult to resect because of their marked fibrosis and their proximity to vital structures such as the optic chiasm. The latter characteristic also limits the use of radiation therapy. In the few cases reported of children younger than 18 years whose thyrotropinomas were treated surgically, the results were disappointing. We present here the case of a 16-year-old boy with a thyrotropin-secreting pituitary macroadenoma who underwent partial resection via a transsphenoidal approach and was left with significant residual tumor and continued hyperthyroidism. He subsequently received 4 years of long-acting release somatostatin therapy, during which he has remained euthyroid without requiring antithyroid medication. To our knowledge, this is thus far the longest duration of somatostatin therapy in the pediatric age group. This regimen also achieved a decrease in compression of the optic nerve and prevented further tumor growth. We review here the current literature on somatostatin analog treatment including molecular mechanisms and promising new treatment modalities, such as the heterodimerization of dopamine and somatostatin receptors. We conclude that this has been a useful adjuvant treatment for our adolescent patient.

The somatostatin receptor subtype 5 in neuroendocrine tumours

IMPORTANCE OF THE FIELD

In recent years, scientific work has been intensified to unravel new (patho-) physiological insights, particularly regarding the functional role of somatostatin (SRIF) receptor subtype 5 (sst) and the development of novel sst(5)-targeted SRIF analogues, in order to broaden medical therapeutic opportunities in patients suffering from neuroendocrine diseases.

AREAS COVERED IN THIS REVIEW

The scope of this review is primarily focused upon recent insights in sst(5)-receptor physiology, novel sst(5)-targeted treatment options predominantly directed towards pituitary adenomas, and gastroenteropancreatic neuroendocrine tumours.

WHAT THE READER WILL GAIN

An understanding of the potential that novel sst(5)-targeted SRIF analogues might have in the medical treatment of Cushing's disease and acromegaly, as demonstrated by translational research, based on pathophysiological data combined with results from clinical trials.

TAKE HOME MESSAGE

The role of targeting sst(5) in gastroenteropancreatic neuroendocrine tumours remains to be established. The sst(5) subtype might function as sst(2) modulator in terms of receptor internalization and desensitization, and seems less important compared with sst(2)-preferring SRIF analogues in the regulation of human insulin secretion by the pancreas. Finally, absence of sst(5) in corticotroph adenomas could be related to tumour aggressiveness in Cushing's disease.

Somatostatin analogues: treatment of pituitary and neuroendocrine tumors

This chapter summarizes the most recent data on the use of the somatostatin analogues (SSAs), octreotide (OCT) and lanreotide for the treatment of patients with pituitary and neuroendocrine tumors (NETs). These two analogues have a high affinity for somatostatin receptor (SSR) sub-types 2 and 5. The major indications of these compounds are GH- and TSH-secreting pituitary adenomas, secreting NETs and non-functioning NETs in progression. Pasireotide is a new analogue, with a receptor pattern different from previous analogues since it binds with high affinity to SSR types 1, 2, 3 and 5. This analogue will be available to treat patients with ACTH-secreting adenomas in a short time. A recent study has also demonstrated a beneficial effect of OCT long-acting release in patients with non-functioning NETs independently from their progression status. These data open the treatment with SSAs in all NET patients.

Ablative thyroid treatment for thyrotoxicosis due to thyrotropin-producing pituitary tumours

Thyrotropin (TSH)-secreting pituitary adenomas (TSHomas) are rare tumours. It has been suggested that thyroid surgery or radioiodine treatment should not be considered in patients with such tumours as these treatments may facilitate rapid tumour expansion. We studied the effects of thyroid ablative treatment on tumour size and thyroid status in two patients with TSHomas. Patients studied were: (1) a female with a TSHoma who declined to undergo pituitary surgery and underwent a total thyroidectomy instead and (2) a male patient who opted for radioiodine treatment for his recurrent TSHoma. Changes in tumour size on serial magnetic resonance imaging scans, and restoration of euthyroidism were studied. No marked changes in tumour size or features of aggressiveness occurred in these patients over periods of 8 and 12 years. Euthyroidism was restored and maintained in both patients. Ablative thyroid treatment can be a safe and successful option to treat TSHomas.

[Therapeutic possibilities in patients with selective pituitary resistance to thyroid hormones]

Selective pituitary resistance to thyroid hormones (SPRTH) is a non-neoplastic form of inappropriate secretion of thyrotropin (TSH). The etiology of this hormonal resistance is linked to inactivating mutations in the thyroid hormone receptor beta (TR-beta) gene. These mutations affect critical portions of the receptor's triiodothyronine (T3)-binding domain. Clinically, SPRTH is characterized by hyperthyroidism with goiter and absence of pituitary mass in the morphologic study. Laboratory data show an elevation of free T3 and free thyroxine concentrations without suppression of TSH, with normal molar subunit alpha/TSH ratio. At this time, there is no specific therapy for SPRHT. Beta blockers, such as atenolol, and benzodiazepines have been used as a symptomatic therapy. Among the drugs with the capacity for reducing TSH secretion are TR agonists, such as triiodothyroacetic acid, D-thyroxine, triiodothyropropionic acid, and L-T3.

Activation of phosphatidylinositol 3-kinase signaling promotes aberrant pituitary growth in a mouse model of thyroid-stimulating hormone-secreting pituitary tumors

TSH-secreting pituitary tumors (TSHomas) are pituitary tumors that constitutively secrete TSH. Molecular mechanisms underlying this abnormality are largely undefined. We recently created a knock-in mutant mouse harboring a mutation (denoted as PV) in the thyroid hormone receptor-beta gene (TRbeta(PV/PV) mouse). As these mice age, they spontaneously develop TSHomas. Using this mouse model, we investigated the role of the phosphatidylinositol 3-kinase (PI3K)-AKT signaling pathway in the pathogenesis of TSHomas. Concurrent with aberrant growth of pituitaries, AKT and its downstream effectors, mammalian target rapamycin and p70(S6K), were activated to contribute to increased cell proliferation and pituitary growth. In addition, activation of AKT led to decreased apoptosis by inhibiting proapoptotic activity of Bcl-2-associated death promoter, further contributing to the aberrant cell proliferation. These results suggest an activated PI3K-AKT pathway could underscore tumorigenesis, raising the possibility that this pathway could be a potential therapeutic target in TSHomas. Indeed, TRbeta(PV/PV) mice treated with a PI3K-specific inhibitor, LY294002, showed a significant decrease in pituitary growth. The progrowth signaling via AKT-mammalian target rapamycin-p70(S6K) and cyclin D1/cyclin-dependent kinase were inhibited, and proapoptotic activity of Bcl-2-associated death promoter was increased by LY294002 treatment. Thus, activation of the PI3K-AKT pathway mediates, at least in part, the aberrant pituitary growth, and the intervention of this signaling pathway presents a novel therapeutic opportunity for TSHomas.

Future clinical prospects in somatostatin/cortistatin/somatostatin receptor field

Somatostatin receptors (sst), somatostatin (SS) and cortistatin (CST) are widely expressed in the various systems in the human and rodent organisms and are "responsible" for maintaining homeostasis, which is essential for survival. Because of their broad expression pattern sst, SS and CST interactions may play regulatory roles in both physiology and pathophysiology in mammalian organisms. SS analogue treatment strategies as well as the use of SS analogues for diagnostic purposes have been established in diseases of different origins. This review focuses on the currently determined role for SS analogues in today's clinical practice and the potential clinical prospects for SS, CST and sst interactions in the future, with a focus on neuroendocrine and non-neuroendocrine tumours and immune-mediated diseases. Moreover, the role of new SS analogues and new insights in sst physiology will be discussed.

Somatostatin receptor subtypes mRNA in TSH-secreting pituitary adenomas: a case showing a dramatic reduction in tumor size during short octreotide treatment

TSH-secreting adenoma is a rare pituitary adenoma, and the expression levels of the specific subtypes of somatostatin receptors (sstr) mRNAs have remained obscure. To determine the quantitative expression of the sstr1-5 mRNAs in TSH-secreting adenomas that may be related to the efficacy of treatment with a somatostatin analogue, expression of the sstr1-5 mRNAs was examined and compared in TSH-secreting adenomas and other pituitary adenomas. The pituitary adenomas were obtained at transsphenoidal surgery from 4 cases of TSH-secreting adenoma, including 1 patient showing a significant shrinkage of the tumor size after only 10 days of octreotide treatment, 2 patients without tumor size reduction and 1 patient without treatment, and 5 GH-secreting adenomas, 6 prolactinomas, 5 nonfunctioning adenomas, 4 ACTH-secreting adenomas and normal pituitaries at autopsy from 4 normal subjects. In comparison to the normal pituitary, sstr2A>sstr1>sstr5>sstr3 mRNAs were expressed in the TSH-secreting adenomas examined. No expression of sstr2B or sstr4 mRNA was observed. The expression level of sstr2 mRNA was significantly higher than those in normal pituitary, prolactinomas, ACTH-secreting and nonfunctioning pituitary adenomas. The patient with marked shrinkage of the tumor showed the highest expression of both sstr2 and sstr5 mRNAs among all the cases of pituitary adenoma. A TSH-secreting tumor without shrinkage showed a similar expression level of sstr2 mRNA. These findings demonstrated that TSH-secreting adenomas express sstr1, 2A, 3 and 5 mRNAs, predominantly sstr2A, and in addition to the expression of sstr2 mRNA, the expression level of sstr5 mRNA may be a factor affecting the tumor shrinkage by somatostatin analogues against TSH-secreting adenomas.

Preclinical and clinical experiences with the role of somatostatin receptors in the treatment of pituitary adenomas

The patho-physiological role of somatostatin receptor subtypes (sst) in neuro endocrine diseases has gained enhanced scientific interest in the past few years. The development of novel somatotropin-release inhibiting factor analogs, both sst-specific and universal ligands, seem promising as a tool to further increase fundamental insights in sst function. Eventually, this research should result in novel medical therapeutic opportunities in patients suffering from neuro-endocrine diseases. In the present review, the functional role of sst in all types of pituitary adenomas, based on recent preclinical and clinical studies, is being discussed.

Expression of type 5 somatostatin receptor in TSH-secreting pituitary adenomas: a possible marker for predicting long-term response to octreotide therapy

In TSH-secreting pituitary adenomas (TSHoma), octreotide (OCT) therapy reduces tumor size and TSH secretion in some cases but not in others. As OCT acts through various types of somatostatin receptors (SSTRs), the different responses of TSHoma to OCT might be explained by the differences of SSTR expression. We therefore studied the expression of subtype-specific SSTR mRNA transcripts in tumor tissues by RT-PCR. Type 2 (SSTR2) mRNA transcripts were detected in all 8 tumors but those of SSTR3 and SSTR5 were demonstrated only in 5 of them. Serum TSH levels were decreased by OCT administration test in all patients but OCT therapy was effective in two patients out of three. SSTR5 mRNA was detected in two tumors from the responder, but not in one tumor that was resistant to OCT. These observations suggest that the temporal decrease of TSH by OCT may be mediated by SSTR2, and that the long term response to OCT therapy may be related with the expression of SSTR5. Therefore, the expression of SSTR5 in TSHoma may be a useful marker for predicting the outcome of the therapy, but further studies with larger numbers of patients are necessary.

Ablative thyroid treatment for thyrotoxicosis due to thyrotropin-producing pituitary tumours

BACKGROUND

Thyrotropin (TSH)-secreting pituitary adenomas (TSHomas) are rare tumours that can be invasive. It has been suggested that thyroid surgery or radioiodine treatment should not be considered in patients with such tumours as these treatments may facilitate rapid and aggressive tumour expansion.

AIM

To study the effects of thyroid ablative treatment on tumour size and thyroid status in two patients with TSHomas in whom the size of the adenoma was clearly documented before treatment was started.

METHODS

Patients studied were: (1) a female patient with a TSHoma who declined to undergo pituitary surgery and underwent a total thyroidectomy instead and (2) a male patient who opted for radioiodine treatment for his recurrent TSHoma. Changes in tumour size on serial magnetic resonance imaging scans, and restoration of euthyroidism were studied.

RESULTS

No marked changes in tumour size or features of aggressiveness occurred in these patients over periods of 8 and 12 years. Euthyroidism was restored and maintained in both patients.

CONCLUSIONS

Ablative thyroid treatment can be a safe and successful option to treat TSHomas, but long-term and close follow-up of these patients is mandatory to ensure that the size and behaviour of the tumours do not change markedly.

The proliferative status of thyrotropes is dependent on modulation of specific cell cycle regulators by thyroid hormone

In this report we have examined changes in cell growth parameters, cell cycle effectors, and signaling pathways that accompany thyrotrope growth arrest by thyroid hormone (TH) and growth resumption after its withdrawal. Flow cytometry and immunohistochemistry of proliferation markers demonstrated that TH treatment of thyrotrope tumors resulted in a reduction in the fraction of cells in S-phase that is restored upon TH withdrawal. This is accompanied by dephosphorylation and rephosphorylation of retinoblastoma (Rb) protein. The expression levels of cyclin-dependent kinase 2 and cyclin A, as well as cyclin-dependent kinase 1 and cyclin B, were decreased by TH, and after withdrawal not only did these regulators of Rb phosphorylation and mitosis increase in their expression but so too did the D1 and D3 cyclins. We also noted a rapid induction and subsequent disappearance of the type 5 receptor for the growth inhibitor somatostatin with TH treatment and withdrawal, respectively. Because somatostatin can arrest growth by activating MAPK pathways, we examined these pathways in TtT-97 tumors and found that the ERK pathway and several of its upstream and downstream effectors, including cAMP response element binding protein, were activated with TH treatment and deactivated after its withdrawal. This led to the hypothesis that TH, acting through increased type 5 somatostatin receptor, could activate the ERK pathway leading to cAMP response element binding protein-dependent decreased expression of critical cell cycle proteins, specifically cyclin A, resulting in hypophosphorylation of Rb and its subsequent arrest of S-phase progression. These processes are reversed when TH is withdrawn, resulting in an increase in the fraction of S-phase cells.

A rare case and a rapid tumor response to therapy: dramatic reduction in tumor size during octreotide treatment in a patient with TSH-secreting pituitary macroadenoma

Thyrotropin (TSH)-secreting pituitary adenomas are the less frequent form of presentation of pituitary tumors. The presence of somatostatin receptors on TSH-secreting adenomas allows treatment of central hyperthyroidism with somatostatin analogs. We report a 21-yr-old woman with TSH-secreting pituitary macroadenoma, who was diagnosed based on the symptoms of hyperthyroidism, the lack of inhibition of serum TSH despite an increased serum free thyroxine (FT4), a low response of serum TSH to thyrotropin-releasing hormone, and a pituitary tumor as revealed by magnetic resonance imaging. The treatment with the somatostatin analog octreotid resulted in inhibition of serum TSH and FT4 to euthyroid levels with concomitant clinical improvements such as the disappearance of sweating, tachycardia, and finger tremors within 7 d. The tumor size diminished dramatically within 6 wk during treatment of one monthly im injection of 20 mg octreotide-LAR. These effects were continued over 2 yr after the start of octreotide-LAR therapy. Therefore, octreotide-LAR appears to be a useful therapeutic tool to facilitate the medical treatment of TSH-secreting pituitary tumors.

Medical management of thyrotropin-secreting pituitary adenomas

Thyrotropin-secreting pituitary tumors (TSH-omas) are a rare cause of hyperthyroidism and account for less than 1% of all pituitary adenomas. It is however noteworthy that the number of reported cases tripled in the last years as a consequence of the routine use of ultrasensitive immunometric assays for measuring TSH levels. Contrary to previous RIAs, ultrasensitive TSH assays allow a clear distinction between patients with suppressed and those with non-suppressed circulating TSH concentrations, i.e. between patients with primary hyperthyroidism (Graves' disease or toxic nodular goiter) and those with central hyperthyroidism (TSH-oma or pituitary resistance to thyroid hormone action). Failure to recognize the presence of a TSH-oma may result in dramatic consequences, such as improper thyroid ablation that may cause the pituitary tumor volume to further expand. The medical treatment of TSH-omas mainly rests on the administration of somatostatin analogs, such as octreotide and lanreotide. In fact, administration of dopamine agonists failed to persistently block TSH secretion in almost all patients and caused tumor shrinkage only in those with combined hypersecretion of TSH and PRL. On the contrary, somatostatin analogs were effective in reducing TSH and alpha-subunit secretion in more than 90% of cases with consequent normalization of FT4 and FT3 levels and restoration of the euthyroid state in the majority of them. In about one third of patients, a clear shrinkage of tumor mass and vision improvement could be demonstrated. Tachyphylaxis, cholelithiasis and carbohydrate intolerance occurred in a minority of treated patients. Whether somatostatin analog treatment may be an alternative to surgery and/or irradiation in patients with TSH-oma remains to be established. Nonetheless, the long-acting somatostatin preparations represent a useful tool for long-term treatment of such a rare pituitary tumors.

Hypothalamic hormones and cancer

The use of peptide analogs for the therapy of various cancers is reviewed. Inhibition of the pituitary-gonadal axis forms the basis for oncological applications of luteinizing hormone-releasing hormone (LH-RH) agonists and antagonists, but direct effects on tumors may also play a role. Analogs of somatostatin are likewise used for treatment of various tumors. Radiolabeled somatostatin analogs have been successfully applied for the localization of tumors expressing somatostatin receptors. Studies on the role of tumoral LH-RH, growth hormone-releasing hormone (GH-RH), and bombesin/GRP and their receptors in the proliferation of various tumors are summarized, but the complete elucidation of all the mechanisms involved will require much additional work. Human tumors producing hypothalamic hormones are also discussed. Treatment of many cancers remains a major challenge, but new therapeutic modalities are being developed based on antagonists of GH-RH and bombesin, which inhibit growth factors or their receptors. Other approaches consist of the use of cytotoxic analogs of LH-RH, bombesin, and somatostatin, which can be targeted to receptors for these peptides in various cancers and their metastases. These new classes of peptide analogs should lead to a more effective treatment for various cancers.

Thyrotropin-secreting pituitary adenomas. Clinical and biological heterogeneity and current treatment

Thyrotropin (TSH)-secreting pituitary adenomas represent about 1-2% of all pituitary adenomas and cause secondary or central hyperthyroidism. TSH-secreting adenomas are part of the syndrome of 'inappropriate secretion of TSH' (SITSH). The hormonal profile is characterized by nonsuppressed TSH in the presence of high levels of free thyroid hormones (FT3 and FT4). Previous reports have described the surgical cure of TSH adenoma to be more difficult than other functional adenomas because of large and invasive features. However, with the current introduction of ultrasensitive immunometric assays, TSH-secreting adenomas are more often recognized. Early diagnosis of TSH-secreting adenomas leads to a high rate of remission of hyperthyroidism after surgery. However, some of those type of adenomas have clinical heterogeneity, and subsequently cannot be cured by surgery alone. We present our experiences and review reported cases of TSH-secreting adenomas to direct current management.

Pituitary macroadenoma secreting thyrotropin and growth hormone: remission of bihormonal hypersecretion in response to lanreotide therapy

We report a case of mixed TSH- and GH-secreting pituitary adenoma in a 60-year-old female patient. She presented with bitemporal hemianopsia and large invasive pituitary macroadenoma. Blood hormone levels determinations revealed elevated thyroid hormones, TSH, and IGF-1 with a relatively low GH. The patient had a mild acromegalic appearance but did not display signs of thyrotoxicosis or goiter. She underwent two pituitary surgical procedures followed by radiotherapy, but despite treatment was still hormonally active. Pathological examination of the resected tumor immunostained positively for both TSH and GH. The patient was subsequently treated with injections of lanreotide, a depot long-acting somatostatin analog, resulting in suppression of blood TSH, thyroid hormones, alpha-subunits, GH and IGF-1.

Effectiveness of long-acting octreotide in suppressing hormonogenesis and tumor growth in thyrotropin-secreting pituitary adenomas: report of two cases

BACKGROUND

The subcutaneous (s.c.) administration of somatostatin analogs, such as octreotide acetate (SMS) and lanreotide, in patients with thyrotropin (TSH)-secreting pituitary adenomas (TSPA's)--thyrotropinomas with residual tumor after initial surgical therapy is effective in controlling hyperthyroidism, as well as curtailing tumor growth in the majority of patients. Long-acting preparations of the above agents, i.e. SMS-LAR and lanreotide-SR, have been synthesized and can be administered as depot injections intramuscularly (i.m.) at intervals of several weeks. Recent studies have reported on preliminary data regarding the use of such preparations in patients with TSPA's.

MATERIALS AND METHODS

We present two cases of TSPA's with residual tumor following transsphenoidal adenomectomy. Neither of the two patients underwent external beam pituitary irradiation. The presence and extent of tumoral TSH hypersecretion was assessed by standard biochemical and dynamic endocrine testing, while tumor size was evaluated by conventional radiographic techniques.

RESULTS

In both patients, TSH secretion was effectively suppressed by SMS-LAR. Moreover, administration of this compound halted further tumor growth, as well as resulted in improved patient comfort, for 12 and 10 months respectively.

CONCLUSION

Our date corroborate earlier reports on the usefulness of SMS-LAR in the medical management of patients with TSPA's who have residual disease after initial pituitary surgery and/or irradiation.

S, Leite V, Canadas V. Tratamento medicamentoso dos tumores hipofisários. parte II: adenomas secretores de ACTH, TSH e adenomas clinicamente não-funcionantes

Este artigo revisa o potencial papel do tratamento medicamentoso para os adenomas hipofisários secretores de ACTH, TSH e aqueles clinicamente não-funcionantes (ACNF), Metirapona, mitotano e cetoconazol (preferível por causar menos efeitos colaterais) são as drogas mais eficazes no controle do hipercortisolismo, mas nenhuma delas supera a eficácia da cirurgia transesfenoidal (TSA). O tratamento medicamentoso da doença de Cushing está, portanto, melhor indicado para pacientes aguardando o efeito pleno da radioterapia ou, como alternativa para esta última, em casos de hipercortisolismo persistente após TSA, e para pacientes com rejeição ou limitações clínicas para a cirurgia. Outra indicação potencial seria em idosos com microadenomas ou pequenos macroadenomas, ou em casos associados a sela vazia. No que se refere aos adenomas secretores de TSH, os análogos somatostatínicos (SRIFa) proporcionam normalização dos hormônios tiroideanos em até 95% dos casos. Assim, eles podem se mostrar úteis em casos de insucesso da cirurgia ou como terapia primária de casos selecionados. Ocasionalmente, agonistas dopaminérgicos (DA), sobretudo a cabergolina, também podem ser eficazes. Em contraste, DA e SRIFa raramente induzem uma significante redução das dimensões dos ACNFs. Por isso, em pacientes com tais tumores, essas drogas devem ser principalmente consideradas diante de contra-indicações ou limitações clínicas para a cirurgia ou quando a cirurgia e a radioterapia tenham sido mal-sucedidas.

Long-term surgical outcome in 16 patients with thyrotropin pituitary adenoma

OBJECT

Thyrotropin-secreting pituitary adenomas are rare lesions of the endocrinological system. Although introduction of a hypersensitive radioimmunoassay for thyrotropin enables the recognition of inappropriate secretion of this hormone, the aforementioned lesions remain uncommon and unfamiliar to most neurosurgeons. It has been reported previously that surgical cure of thyrotropin-secreting adenomas is more difficult than in other functional adenomas because of the large size and invasive features of the former. However, the long-term outcome after surgery has not been well documented. The authors report on a surgical series of 16 patients with thyrotropin adenoma and the results of long-term follow up.

METHODS

Sixteen patients ages 23 to 62 years (12 women and four men) underwent transsphenoidal removal of thyrotropin adenomas between 1983 and 1999. These patients had the syndrome of inappropriate thyrotropin secretion (SITS) with pituitary mass lesions. Four of the patients had undergone previous subtotal thyroidectomy and/or radioiodine thyroid ablation, and 11 had been treated with antithyroid medication. Radiological investigations demonstrated macroadenomas in 14 patients, and 10 of those had cavernous sinus invasion. Surgical findings showed unusually fibrous and firm tumors in 13 (81.2%) of 16 patients. Preoperative octreotide administration was revealed to be effective for serum thyrotropin reduction as well as tumor shrinkage. Transsphenoidal surgery was performed with no morbidity resulting. Surgical remission was achieved in 10 (62.5%) of 16 patients, and total remission was achieved in 14 patients (87.5%) with a combination of additional radiation or medical therapy. In the other two patients, SITS persisted because of tumor rests in the cavernous sinus. Therefore, radiation and/or antithyroid therapy was administered. In the mean follow-up period of 7.5 years (range 11 months-15.8 years), no recurrence of tumor was observed on magnetic resonance images, whereas recurrence of SITS was found in two patients with no tumor regrowth. In addition, coexistent primary hyperthyroidism was found in two other patients despite remission of SITS after surgery.

CONCLUSIONS

Transsphenoidal surgery can achieve a good long-term outcome in patients with thyrotropin-secreting pituitary adenomas if surgery is performed before these become larger, invasive tumors. In the authors' experience, thyrotropin-secreting adenomas are fibrous and firm, which makes it difficult to achieve surgical remission. In addition, even satisfactory resection of the tumor sometimes results in recurrence of SITS or hyperthyroid symptoms due to coexistent primary hyperthyroidism. It is emphasized that a careful follow-up review is necessary after surgery, especially in patients with a long preoperative history of hyperthyroidism.

Evaluation of the treatment of thyrotropin-secreting pituitary adenomas with a slow release formulation of the somatostatin analog lanreotide

Somatostatin analogs have been shown to be effective for the treatment of TSH-secreting pituitary adenomas. However, their use in this indication is limited by the fact that available analogs require several daily sc injections. The present study was performed to evaluate the effects of a slow release formulation of the somatostatin analog lanreotide (SR-L) on both hormone secretion and tumor size and to assess the tolerance in a series of thyrotropinomas treated for 6 months. Eighteen patients with hyperthyroidism related to a TSH-secreting pituitary adenoma, evidenced by pituitary magnetic resonance imaging, were studied. After a basal assessment, each patient received 30 mg SR-L, im, every 14 days for 1 month. Then, according to the free T3 (fT3) plasma level measured, 9 of 18 patients were injected twice monthly, and 7 of 18 patients received SR-L every 10 days for 5 additional months. One patient was dismissed from the study in month 1 of the study for side-effects and another in month 3 for noncompliance to the protocol. Clinical and biological evaluations (plasma TSH, free alpha-subunit, fT4, fT3, and lanreotide levels) were performed before and in months 1, 3, and 6 of treatment. Pituitary magnetic resonance imaging and gallbladder ultrasonography were performed both at entry and at the end of the study. Clinical signs of hyperthyroidism improved within 1 month in all 16 evaluable patients. Mean (+/- SEM) plasma lanreotide levels reached 1.11 +/- 0.43 and 1.69 +/- 0.65 ng/mL in month 3 using 2 and 3 injections/month, respectively, then remained stable until the end of the study. During therapy, the plasma TSH level decreased from 2.72 +/- 0.32 to 1.89 +/-0.27 mU/L (P < 0.01), with parallel significant changes in free alpha-subunit. During the same period, plasma fT4 and fT3 levels decreased from 37.9 +/- 2.9 to 19.7 +/- 2.3 pmol/L (P < 0.01) and from 14.6 +/- 1.1 to 8.3 +/- 0.8 pmol/L (P < 0.01), respectively. No statistically significant change in mean adenoma size was observed after 6 months of treatment. Side-effects, including pain at the injection point, abdominal cramps, and diarrhea, were mild and transient and did not lead to interruption of the treatment. No gallstones occurred during the study. SR-L appears to be able to suppress clinical signs of hyperthyroidism in our series of patients with TSH-secreting pituitary adenomas. The analog also reduces plasma TSH and thyroid hormone levels, which were normalized in 13 of 16 cases. The effect was maintained throughout the treatment using 2 or 3 SR-L injections monthly without any problem of tolerance. We conclude that SR-L is a safe and effective treatment of thyrotropinomas and avoids the drawbacks of the modes of administration of other somatostatin analogs, given three times daily.

Pituitary disorders. Drug treatment options

Pituitary diseases are relatively common entities in the general population. They include pituitary adenomas and hypopituitarism. Pituitary tumours can cause symptoms of mass effect and hormonal hypersecretion that can be reversed with surgical resection or debulking of the adenoma, radiotherapy, or medical treatment. Transsphenoidal adenomectomy is the treatment of choice for acromegaly, Cushing's disease, gonadotropin-secreting tumours; and thyrotropin (TSH)-secreting adenomas. Pituitary irradiation and medical therapy are secondary options. Conversely, medical treatment is the primary choice for prolactinomas. Dopamine agonists are very effective in the treatment of prolactin (PRL)-secreting tumours, with rates of control as high as 80 to 90% for microprolactinomas (< 10 mm) and 60 to 75% for macroprolactinomas (> or = 10 mm). Somatostatin analogues have also shown efficacy in patients with acromegaly who have not responded to surgery or in patients with TSH-secreting adenomas who have not improved with surgery and radiotherapy. In patients with Cushing's disease, who are not cured surgically or who relapse after pituitary adenomectomy and irradiation, steroidogenic inhibitors can be an efficient method of controlling the hypercortisolism. Pituitary insufficiency is the partial or complete loss of the anterior hypophyseal function, which is due to hypothalamic or pituitary disease. Although the classic sequence of loss of pituitary secretion is growth hormone (GH), gonadotropins, TSH, and corticotropin (ACTH), the order to begin the replacement therapy of the deficient hormone(s) is cortisol, thyroxine, androgens/estrogens and, if necessary, GH. There are multiple preparations that can be used to achieve clinical and biochemical improvement. In general, the hormone replacement therapy is lifelong.

Successful Therapy for a Mixed Thyrotropin- and Prolactin-Secreting Pituitary Macroadenoma With Cabergoline

OBJECTIVE

To describe the first case of a mixed thyrotropin (TSH)- and prolactin-secreting pituitary macroadenoma that responded to therapy with cabergoline.

METHODS

We present a case report with clinical, laboratory, and radiologic details.

RESULTS

An 84-year-old woman with central hyperthyroidism due to a mixed TSH- and prolactin-secreting pituitary macroadenoma was successfully treated with orally administered cabergoline, 0.25 mg twice per week. Serial assays of thyroid and pituitary hormones were done, and magnetic resonance imaging of the pituitary was performed before and 16 weeks after initiation of cabergoline therapy. The patient had complete resolution of the increased pituitary hormone indices within 6 weeks after implementation of therapy, and these results were sustained for more than 16 weeks. A magnetic resonance imaging scan showed no change in tumor size at 16 weeks of therapy.

CONCLUSION

When medical treatment of TSH-secreting tumors is considered, choices of efficacious drugs are limited. To our knowledge, this report describes the first case of a long-acting dopamine agonist used successfully to control hypersecretion of a mixed TSH- and prolactin-secreting macroadenoma. Oral administration of cabergoline twice a week was effective, convenient, and well tolerated. Further evaluation of cabergoline, when indicated as medical therapy for TSH-secreting tumors, is warranted.

Medical therapy for gonadotroph and thyrotroph tumors

Gonadotroph adenomas, a common type of pituitary tumor, are not associated with syndromes of hormonal hypersecretion and thus present as pituitary macroadenomas with mass effects, or as incidentally discovered pituitary masses. When indicated, primary therapy is neurosurgery, but there may be a limited role for medical therapy in patients with residual disease. Thyrotroph adenomas are rare neoplasms that present with hyperthyroidism and local mass effects. Medical therapy may be effective in controlling tumor growth and in achieving euthyroidism, when surgery or radiation, or both, do not control the tumor.

Central hyperthyroidism

Central hyperthyroidism is a rare condition in which thyrotoxicosis results from primary overproduction of TSH by the pituitary gland with subsequent thyroid enlargement and hyperfunction. The two known causes of central hyperthyroidism are TSH-producing pituitary tumors (TSHomas) and the syndrome of PRTH. Both of these entities are characterized by clinical thyrotoxicosis, diffuse goiters, elevated circulating levels of free T4 and T3, and a nonsuppressed serum TSH. It is critical to distinguish central hyperthyroidism from the much more common types of primary hyperthyroidism, all of which have undetectable TSH values. TSHomas and PRTH can usually be differentiated from one another by measuring the serum alpha-subunit and the TSH response to intravenous TRH or exogenous thyroid hormone, and by pituitary imaging studies. TSHomas are usually benign adenomas arising from the monoclonal expansion of neoplastic thyrotropes. Causative oncogenes have not yet been convincingly identified. PRTH is a nonneoplastic disorder caused by inherited mutations in the gene for the thyroid hormone receptor beta; it is a poorly understood variant of GRTH. For unclear reasons, in PRTH, the pituitary gland is resistant to the feedback inhibitory effects of circulating thyroid hormones while peripheral tissues respond normally, causing patients to experience the toxic peripheral effects of thyroid hormone excess. TSHomas are best treated by transphenoidal surgical removal. Radiotherapy is indicated for inoperable or incompletely resected tumors. Octreotide administration is a useful adjunct for preoperatively reducing tumor size and for the medical management of surgical treatment failures. PRTH is ideally treated by chronically suppressing TSH secretion with medications such as D-thyroxine, TRIAC, octreotide, or bromocriptine. If such therapy is ineffective or unavailable, thyroid ablation with radioiodine or surgery may be employed with subsequent close monitoring of both thyroid hormone status and pituitary gland size.

An abnormality of thyroid hormone receptor expression may explain abnormal thyrotropin production in thyrotropin-secreting pituitary tumors

Thyrotropin (TSH)-secreting pituitary adenomas cause hyperthyroxinemia in the presence of "inappropriately" elevated concentrations of TSH. TSH production under these circumstances escapes the normal negative feedback effect of thyroid hormone. We propose that this defective negative feedback is mediated by an abnormality of thyroid hormone receptor (TR) expression. Two TSH-secreting pituitary adenomas were analyzed by immunocytochemistry for TR isoform protein expression and by semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) for TR isoform mRNA expression. The results obtained from these tumors were compared with the findings from six normal human pituitaries. Neither tumor examined expressed detectable levels of nuclear TRalpha or TRbeta proteins, in contrast to the normal pituitaries studied, which expressed all TR isoforms. Application of RT-PCR, however, revealed mRNAs encoding each TR isoform in all tumorous and normal tissues examined. Semiquantitative RT-PCR revealed similar levels of expression of TRalpha and TRbeta isoform mRNAs in tumors and normal tissue, in contrast to the observed difference in TR proteins. Absent TRalpha and TRbeta protein expression, in association with normal mRNA levels, implies a post-transcriptional defect in TR mRNA processing in TSH-secreting adenomas. Reduced TR expression in these tumors may explain defective negative feedback of thyroid hormone on TSH production, and may also contribute to uncontrolled tumor growth.

A prospective multicenter trial of octreotide in 24 patients with visual defects caused by nonfunctioning and gonadotropin-secreting pituitary adenomas. French Multicenter Octreotide Study Group

OBJECTIVE

The somatostatin analog octreotide has been demonstrated to improve optic tract compression caused by pituitary macroadenomas within hours of its administration and/or reduce tumor size in some patients. We report the results of a prospective multicenter study of the effects of octreotide on visual function and tumor size in patients with nonfunctioning pituitary adenomas or gonadotropin-secreting adenomas.

METHODS

Twenty-four patients with visual defects caused by histologically confirmed macroadenomas were administered octreotide via continuous subcutaneous infusion, as follows: 100 micrograms the 1st day and, if necessary, 200 micrograms the 2nd and then 100 or 200 micrograms three times daily if visual function improved. Vision was assessed after 4 days, 1 month, and 2 months, including tumor size evaluation. Visual improvement was defined by a net gain of at least 2/10 in acuity and/or of more than 20% of the surface of one isopter (a reduction in tumor volume of > or = 20% of the initial measurement); opposite changes were defined as deterioration.

RESULTS

Visual improvement was noted in 13 of 24 patients, 10 of 23 patients and 9 of 22 patients, and was not noted in 11 of 24 patients, 14 of 23 patients, and 13 of 22 patients after 4 days, 1 month, and 2 months, respectively. After 2 months, three adenomas had shrunk, three had not changed in size, and one had increased; visual function improved in the seven patients with these adenomas. Octreotide was discontinued in 13 patients for lack of efficacy.

CONCLUSION

The incidence of visual improvement and tumor shrinkage noted in this study was higher than previously reported. Our data suggest that early onset of visual improvement might help in deciding which patients profit from octreotide. However, concomitant gain in visual acuity with deterioration in visual fields or visual improvement with an increase (moderate) in tumor size can occur.

Pituitary tumours in the elderly

Pituitary tumours in the elderly are a neglected topic in the literature of endocrinology and gerontology. Data from autopsy studies in the elderly show that the commonest tumours are microadenomas, which are either immunocytochemically negative or stain for prolactin. Prolactin-secreting pituitary tumours, however, appear rarely in clinical series of patients in this age group and non-functioning adenomas are the commonest tumour seen, although pituitary metastasis and craniopharyngiomas also occur. Diagnosis can be difficult, but the commonest presentation is visual field loss. Hypopituitarism may be diagnosed late and incidental radiological diagnosis is not uncommon. There are few data which specifically answer the question, but there is a suggestion that the syndromes associated with hormonal hypersecretion may be milder in this age group. Conventional treatment with drugs, surgery and radiotherapy should be decided on an individual basis as these therapies appear to be well tolerated and beneficial in selected patients.

Indium-111 pentetreotide single-photon emission tomography in patients with TSH-secreting pituitary adenomas: correlation with the effect of a single administration of octreotide on serum TSH levels

Few data are available on the visualization of somatostatin receptors in vivo in patients with thyrotropin (TSH)-secreting adenoma. We studied five patients with TSH-secreting adenomas using single-photon emission tomography (SPET) after administration of indium-111 pentetreotide. The intensity of 111In-pentetreotide uptake by the tumours was correlated with the degree of TSH suppression after a single administration of 100 microg octreotide s. c. Five patients (three women and two men) aged 27-46 years were investigated. Except for one patient with acromegaly, all had pure TSH-secreting tumours. One patient was previously untreated, while two had received octreotide, one antithyroid drugs, and one radioiodine. In all patients SPET demonstrated increased uptake of 111In-pentetreotide by the pituitary adenoma. The target to non-target ratio (T/nT) of 111In-pentetreotide uptake was higher than 10 in three patients. Administration of 100 microg octreotide s. c. caused a significant reduction in TSH levels from 4.8+/-1.4 mU/l to a nadir of 3.1+/-1.1 mU/l after 6 h (P<<0.001 by ANOVA). Suppression of TSH secretion ranged from 30% to 60% of the baseline value. The T/nT ratio showed a trend toward a direct relationship with the degree of TSH inhibition after acute octreotide administration (r=0.67; P=NS). Our study showed that 111In-pentetreotide scan visualized somatostatin receptors in all five of the patients with TSH-secreting pituitary adenomas, confirming the frequent presence of somatostatin receptors in these rare tumours, even though the correlation with the TSH inhibition after a single administration of octreotide did not reach significance.

A case of thyrotropin-secreting pituitary microadenoma with normal thyrotropin alpha-subunit level

We present a 32-year-old male with a thyrotropin (TSH)-secreting pituitary microadenoma with normal alpha-subunit (SU) and/or alpha-SU/TSH molar ratio. An interesting feature of this patient is that the size of the pituitary tumor remained unchanged during a 6-year follow-up without treatment. The tumor was clearly visualized with somatostatin receptor imaging, indicating that it was somatostatin receptor-positive. Subcutaneous injection of 100 microg octreotide acetate three times daily resulted in significant reduction of TSH and free thyroid hormones 6 weeks after initiation of treatment. However, tumor size was not changed 3 months after initiation of octreotide therapy and thyroid hormones, but not TSH level, eventually increased in spite of increasing the octreotide dosage up to 600 microg/day. This led to discontinuation of treatment. The patient responded only temporarily to octreotide in spite of somatostatin receptors. This case further demonstrates that a normal alpha-SU and/or alpha-SU/TSH molar ratio cannot exclude the possibility of a TSH-secreting pituitary adenoma.

A Plurihormonal TSH-Secreting Pituitary Microadenoma: Report of a Case with an Atypical Clinical Presentation and Transient Response to Bromocriptine Therapy

Inappropriate secretion of thyrotropin (TSH) is a rare cause of hyperthyroidism, and it is caused by either a TSH-producing pituitary adenoma (usually a macroadenoma) or to selective pituitary resistance to thyroid hormone. The case of a 31-yr-old male who presented with clinical features of thyrotoxicosis, including episodes of thyrotoxic paralysis, and a thyroid profile characterized by free hyperthyroxinemia and hypertriiodothyronemia with a nonsuppressed, inadequately normal TSH is reported. Dynamic testing showed both, lack of TSH stimulation by thyroid-releasing hormone (TRH), and lack of suppression by T3, consistent with autonomous TSH secretion. Pituitary MRI revealed a microadenoma. Seventy five percent of the patients serum TSH immunoreactivity eluted as u-subunit in Sephadex G-100 chromatography. A diagnosis of TSH-secreting microadenoma was established, and the patient was treated successfully with bromocriptine, which resulted in both clinical and biochemical resolution of his hyperthyroidism. Two months later, he became hyperthyroid again during bromocriptine therapy. Octreotide was started with adequate control of his symptoms and normalization of his free T4 level. He eventually underwent transsphenoidal surgery with successful resection of a chromophobic microadenoma which immunostained for TSH, growth hormone (GH), luteinizing hormone (LN), and follicle-stimulating hormone (FSH). One month postoperatively he is clinically and biochemically euthyroid on no medications.

Thyrotropin-secreting pituitary adenomas

Normal or elevated thyrotropin (TSH) levels in hyperthyroid patients are characteristic of rare TSH-secreting pituitary adenoma (TSH-oma), which is easily detectable by computed tomographic (CT) scan or magnetic resonance imaging (MRI). Other diagnostic aids are an absent/impaired TSH response to thyrotropin-releasing hormone (TRH), discrepant TSH and alpha-subunit responses to TRH, high sex hormone-binding globulin (SHBG) levels, high alpha-subunit levels, and a high alpha-subunit/TSH molar ratio. Familial studies help rule out thyroid hormone resistance (RTH). Surgical removal of TSH-oma leads to clinical and biochemical remission in most patients. In surgical failures, radiotherapy and octreotide treatment have a high success rate. Undetectable TSH 1 week postsurgery suggests a definitive cure, backed up by tests for cosecreted hormones from the adenoma and dynamic tests of TSH suppression.

Mechanisms of action of somatostatin on human TSH-secreting adenoma cells

The mechanisms of somatostatin (SRIH) action on thyroid-stimulating hormone (TSH) secretion were examined using human TSH-secreting adenoma cells. SRIH (10(-7) M) inhibited TSH secretion through a pertussis toxin-sensitive G protein. SRIH also inhibited forskolin- and 8-bromo-adenosine 3',5'-cyclic monophosphate (8-BrcAMP)-induced TSH secretion. The mechanisms of this inhibition were investigated by measuring intracellular Ca2+ concentration ([Ca2+]i) and by electrophysiological experiments. Application of 10(-7) M SRIH reduced the [Ca2+]i, whereas forskolin and 8-BrcAMP increased the [Ca2+]i. Simultaneous application of SRIH abolished the forskolin-and the 8-BrcAMP-induced [Ca2+]i increase, indicating that the SRIH-induced decrease in [Ca2+]i was independent of the reduction in intracellular cAMP. Under current clamp using the whole cell clamp, 10(-7) M SRIH hyperpolarized the membrane and arrested Ca(2+)-dependent action potentials, which accounted for the SRIH-induced decrease in [Ca2+]i. Voltage clamp experiments revealed that this membrane hyperpolarization resulted from the activation of an inward-rectifying K+ current through a pertussis toxin-sensitive G protein. Intracellular injection of cAMP (100 microM) through the patch pipette did not abolish the SRIH-induced K+ current, indicating that the activation of SRIH-induced K+ channels was independent of intracellular cAMP. From these data, we concluded that SRIH-induced membrane hyperpolarization was responsible for the [Ca2+]i decrease, which in turn inhibited TSH secretion. Application of thyrotropin-releasing hormone (TRH; 10(-7) M) caused an increase in the [Ca2+]i, composed of an initial transient increase followed by a sustained increase. SRIH inhibited the sustained increase in [Ca2+]i. SRIH also inhibited the TRH-induced decrease in the membrane conductance.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical features and differential diagnosis of pituitary tumours with emphasis on acromegaly

Pituitary adenomas are frequently encountered, benign intracranial tumours. Clinically classified according to their capacity to produce and secrete hormones, pituitary tumours are diagnosed from the clinical manifestations and biochemical findings of specific pituitary hormone overproduction or of impaired pituitary function due to pressure on normal pituitary cells, the pituitary stalk or the hypothalamus. Additionally, the tumour may result in neurological manifestations due to its effect as an intracranial space-occupying lesion. Pituitary adenomas may present acutely with pituitary apoplexy after intrapituitary haemorrhage or infarction. The subsequent hypofunction of the pituitary with concomitant neurological sequelae of an expanding intracranial mass are often associated with excruciating headache, diplopia and visual field defects. Gradually developing neurological deficits or secondary endocrine failure over several years may precede the recognition of non-secretory tumours (30-40% of pituitary adenomas) as well as some of the hormone-producing adenomas, especially when they expand beyond the confines of the sella turcica. Asymptomatic masses occur in the pituitary in 5-27% of unselected autopsy series. About 10-20% of pituitaries imaged as part of a brain study contain lesions 'consistent with a pituitary adenoma', with about half being pituitary adenomas ('incidentalomas'). Many advocate screening such cases for a wide spectrum of pituitary function abnormalities. Clinical judgement should be utilized to determine the extent of the work-up and the frequency of follow-up. Acromegaly, a clinical syndrome caused by excess growth hormone secretion, accounts for one-sixth of resected pituitary tumours. This disorder leads to chronic progressive disability and a shortened life span, with approximately 50% of untreated acromegalic patients experiencing premature death. The prevalence of acromegaly has been estimated to range from 50 to 70 per million, with the age of diagnosis usually between the third and fifth decades. Conditions associated with acromegaly include glucose intolerance, diabetes mellitus, lipid abnormalities, cholelithiasis, goitre, and hyperthyroidism, respiratory complications, hypertension, cardiovascular disease, and calcium metabolism abnormalities. An association between acromegaly and cancer, especially of the colon, is now recognized. Epidemiological series have indicated that cancer of the colon, breast and other types of malignancy are a cause of death with increased frequency in acromegalics compared with expected rates. Hypopituitary symptoms secondary to the mass effect of macroadenomas in acromegalic patients are common. Among premenopausal women, menstrual irregularities and galactorrhoea have been reported in 40-70%, while more than half of the men complain of impotence and decreased libido.(ABSTRACT TRUNCATED AT 400 WORDS)

Glycoprotein-secreting pituitary adenomas

In the past, pituitary tumours that produce one or more of the glycoproteins (TSH, LH, FSH and alpha subunit) were thought to be rare. However, using modern immunocytochemical and molecular biology techniques, these tumours are being recognized with increasing frequency. Many of these tumours produce glycoprotein alpha and beta subunits in addition to intact glycoproteins. Hormone production is often low compared with tumour size, and serum hormone levels may not be elevated in these patients. Tumours that produce the gonadotrophins (LH or FSH) or alpha subunit account for the majority of clinically non-functioning pituitary adenomas. They do not cause a specific clinical syndrome, and usually present with symptoms of a large mass lesion and/or hypopituitarism. Optimal treatment of these tumours is often difficult. The initial approach is usually transsphenoidal surgery, followed by radiation therapy if there are symptoms due to residual tumour. Medical therapy of gonadotrophin and alpha subunit tumours may include the use of dopamine agonists or somatostatin analogues, although neither has been shown to consistently decrease tumour size. Preliminary trials with experimental GnRH antagonists suggest that these agents may be useful as adjuvant therapy of gonadotrophin tumours. Tumours that produce TSH are rare. Patients present with hyperthyroidism, which is often misdiagnosed as Graves' disease, as well as with symptoms of a pituitary mass lesion. Almost all TSH tumours secrete excess amounts of free alpha subunit. Optimal treatment of these tumours includes transsphenoidal surgery, followed by radiation therapy for residual tumour. The somatostatin analogue octreotide is effective in reducing excess TSH secretion from these tumours, and causes a reduction in tumour volume in a significant minority of patients.

Influence of octreotide on the gastric emptying of solids and liquids in normal healthy subjects

BACKGROUND

The effects of octreotide on small intestinal and gall-bladder motility are well established. However, the influence of octreotide on the gastric emptying rate of both solids and liquids in normal healthy volunteers has never been studied.

METHODS

In nine healthy subjects, the gastric emptying rate of liquids and solids was studied in basal condition and 30 min after subcutaneous administration of 50 micrograms of octreotide, using the combined 14C-octanoic acid/13C-glycine breath test. To determine if the results were entirely due to alterations in gastric emptying, 14/13CO2 excretion rates of intraduodenally administered 14C-octanoic acid and 13C-glycine were measured in basal condition and after subcutaneous injection of octreotide.

RESULTS

After subcutaneous injection of octreotide, the gastric emptying rate of solids was decreased in all but one subject, while the gastric emptying rate of fluids was decreased in all subjects. Nevertheless, 14/13CO2 excretion rates in the breath after intraduodenally administered 14C-octanoic acid and 13C-glycine, were similar in basal condition and after subcutaneous injection of octreotide.

CONCLUSIONS

Subcutaneous injection of a single physiological dose of octreotide induces a marked delay in the gastric emptying of solids and liquids in young healthy volunteers. The combined 14C-octanoic acid/13C-glycine breath test is very well suited to demonstrate this effect, since the absorption and metabolism of octanoic acid and glycine remains unaltered after administration of octreotide.

Effects of a slow-release formulation of the new somatostatin analogue lanreotide in TSH-secreting pituitary adenomas

OBJECTIVE

Somatostatin analogues have been proposed for the treatment of thyrotrophinomas. However, this treatment requires several s.c. injections a day to be effective. The present study had the following aims: (i) appraisal of the efficacy of a single dose of two somatostatin analogues (lanreotide and octreotide) to acutely inhibit TSH secretion of TSH-secreting pituitary adenomas; (ii) assessment of the efficacy of a single injection of a slow release formulation of lanreotide (SR-L) in reducing TSH and thyroid hormone secretions in the same cases; and (iii) evaluation of the effects of SR-L used for 3-6 months on hormone secretion and tumour size.

PATIENTS

Four patients with hyperthyroidism linked to a TSH-secreting pituitary adenoma found on pituitary magnetic resonance imaging (MRI) and subsequently proved by immunohistochemistry were studied.

METHODS

In the first step of the study the patients received in a random order, vehicle, 150 micrograms octreotide and 500 micrograms lanreotide as a single s.c. injection. Measurements of plasma TSH, free T4 (fT4), free T3 (fT3) and free alpha subunit (fAS) levels were carried out before injection and then every other hour for 8 hours. In the second part of the study, after a basal blood sample (0800 h), each patient received 30 mg lanreotide as an i.m. injection of SR-L. Blood was sampled 2 hours later and then three times a week for 3 weeks in order to measure plasma TSH, fT4, fT3 and lanreotide levels using radioimmunoassays. The patients then received one SR-L injection twice or in one case three times a month for 3-6 months. Plasma TSH, fT4 and fT3 levels were measured monthly and a pituitary MRI was performed at the end of the treatment with SR-L.

RESULTS

500 micrograms lanreotide acutely reduced plasma TSH and fAS levels to the same extent as 150 micrograms octreotide. Two hours after a single i.m. injection of SR-L plasma lanreotide levels reached 7.8 +/- 0.6 micrograms/l and then progressively decreased, being 1.8 +/- 0.2 microgram/l on day 2 and 1.1 +/- 0.3 microgram/l on day 14 after the injection. Plasma TSH level decreased from basal value (mean +/- SEM 4.4 +/- 1.2 mlU/l) within 2 hours (2.5 +/- 0.8 mlU/l) and further declined to 0.8 +/- 0.2 ml/Ul on day 2 following the injection. Depending on the patient, plasma TSH levels were reduced for a period of 6-15 days. Plasma fT4, fT3 levels were normalized on day 2 and remained in the normal range for a period of time of 9-20 days. During long-term treatment, abdominal cramps and diarrhoea appeared, leading to interruption of the treatment in one patient. The treatment was well tolerated in the other three patients. Plasma TSH and thyroid hormone levels progressively decreased during the treatment. No change in adenoma volume was observed after 3-6 months of therapy.

CONCLUSIONS

This study shows that (i) lanreotide is able to inhibit acutely TSH secretion in thyrotrophinomas and that a single s.c. injection of 500 micrograms lanreotide is as effective as 150 micrograms octreotide; (ii) SR-L appears to be able to reduce plasma TSH and to normalize fT4 and fT3 levels for 9-20 days in patients with thyrotrophinomas; (iii) this effect is maintained throughout the treatment using two or three SR-L injections monthly for months. These results suggest that SR-L could be used as a treatment of thyrotrophinomas and avoids the drawbacks of the modes of administration of other somatostatin analogues used in such cases.

Hyperthyroidism secondary to a pituitary adenoma secreting TSH, FSH, alpha-subunit and GH

A 51-year-old man had been treated for hyperthyroidism with antithyroid drugs for 8 years. He was then found to have a large pituitary adenoma with biochemical evidence of overproduction of TSH, FSH and alpha-subunit. Subsequent immunocytochemical and tissue culture studies confirmed secretion of these hormones. In addition, the tumour stained for GH and was capable of GH production in vitro. This combination of hormones produced by a pituitary adenoma has not been previously reported.

Acute and long-term effects of octreotide in patients with ACTH-dependent Cushing's syndrome

PURPOSE

Octreotide is of proven efficacy in the management of patients with acromegaly, thyrotropin-secreting pituitary adenomas, and certain gastrointestinal tumors, but its effect in Cushing's syndrome is less clear.

PATIENTS AND METHODS

We studied 10 patients who presented with adrenocorticotropic hormone (ACTH)-dependent Cushing's syndrome, 3 of whom were previously adrenalectomized. Serum cortisol or ACTH levels were measured before and during the administration of octreotide 50 to 500 micrograms every 8 hours for 24 to 72 hours.

RESULTS

Treatment was effective in four patients: serum cortisol levels decreased to within or below the normal range in Patients 1, 2, and 3, and ACTH levels were substantially lowered in Patient 4, who had previously been adrenalectomized for a metastatic islet cell tumor. These responses were sustained during long-term treatment for 2 to 72 weeks. All four patients showed no evidence of a pituitary tumor on computed tomographic or magnetic resonance imaging and had proven (Patients 3 and 4) or presumed ectopic disease. Of the six patients who did not respond, four had pituitary tumors and two had presumed ectopic ACTH production.

CONCLUSION

We conclude that a short trial of octreotide is warranted in patients with ACTH-dependent Cushing's syndrome who have no demonstrable pituitary tumor. A response to treatment should alert the physician to the possibility of an ectopic ACTH source and will identify patients whose disease may be controllable using octreotide.