In vivo imaging of pituitary tumours using a radiolabelled dopamine D2 receptor radioligand

Pituitary adenoma & nuclear medicine: Recent outcomes and ongoing developments

In order to explore pituitary adenoma (PA), magnetic resonance imaging (MRI) remains the cornerstone. However, there are some limitations and MRI can be non-conclusive. The development of additional imaging modalities like nuclear medicine explorations may help to confirm PA diagnosis, guide management and follow up. Nuclear medicine uses radiopharmaceuticals for imaging with single photon emission computed tomography (SPECT), or positron emission tomography (PET), coupled to CT scan. Radiopharmaceuticals products target specific cellular elements which allow to explore several biological pathways. Nuclear medicine may also be used for therapeutic purposes and recent developments of approach based on Peptide Receptor Radionuclide Therapy (PRRT) for treatment of aggressive PA and pituitary carcinoma will be reviewed. Several radiotracers have been studied in the context of PA, and the aim of this paper is to discuss their respective performances and clinical interest.

Pituitary tumors in childhood: update of diagnosis, treatment and molecular genetics

Pituitary tumors are rare in childhood and adolescence, with a reported prevalence of up to one per 1 million children. Only 2-6% of surgically treated pituitary tumors occur in children. Although pituitary tumors in children are almost never malignant and hormonal secretion is rare, these tumors may result in significant morbidity. Tumors within the pituitary fossa are mainly of two types: craniopharyngiomas and adenomas. Craniopharyngiomas cause symptoms by compressing normal pituitary, causing hormonal deficiencies and producing mass effects on surrounding tissues and the brain; adenomas produce a variety of hormonal conditions such as hyperprolactinemia, Cushing disease and acromegaly or gigantism. Little is known about the genetic causes of sporadic lesions, which comprise the majority of pituitary tumors, but in children, more frequently than in adults, pituitary tumors may be a manifestation of genetic conditions such as multiple endocrine neoplasia type 1, Carney complex, familial isolated pituitary adenoma and McCune-Albright syndrome. The study of pituitary tumorigenesis in the context of these genetic syndromes has advanced our knowledge of the molecular basis of pituitary tumors and may lead to new therapeutic developments.

Cushing's disease in dogs: cabergoline treatment

The treatment of pituitary-dependent hyperadrenocorticism (PDH) in dogs has for a long time been focused on inhibiting the adrenal gland using drugs such as o-p'-DDD, Ketoconazole and Trilostane, without attacking the primary cause: the corticotrophinoma. Corticotroph cells can express the D2 dopaminergic receptor; therefore cabergoline (Cbg) could be effective as a treatment. Follow-up over 4 years was carried out in 40 dogs with PDH that were treated with Cbg (0.07 mg/kg/week. Out of the 40 dogs, 17 responded to Cbg (42.5%). A year after the treatment, there was a significant decrease in ACTH (p<0.0001), alpha-MSH (p<0.01), urinary cortisol/creatinine ratio (p<0.001), and of the tumor size (p<0.0001) evaluated by nuclear magnetic resonance. Dogs responding to Cbg lived significantly longer (p<0.001) than those in the control group. To conclude, Cbg is useful in 42.5% of dogs with PDH, justifying its use as a treatment.

Current concepts and controversies in the management of non-functioning giant pituitary macroadenomas

Despite their histologically benign nature, giant and 'invasive' pituitary tumors are one of the most complex neurosurgical challenges. In the present article, we discuss the current approaches to the management of giant pituitary tumors. Giant non-functioning pituitary tumors are usually confined inferiorly by the sellar dura, superiorly by the elevated diaphragma sellae, and laterally by an intact medial wall of the cavernous sinus. If the anatomical extensions of the tumor are understood and a radical tumor resection is achieved, the visual and long-term outcome can be extremely rewarding. The goals of surgery are to make a pathologic diagnosis and since the majority of these tumors are endocrinologically silent, the second goal should be to decompress the neural tissue. With the increasing experience and better understanding of anatomy of these tumors, trans-sphenoidal approaches have now replaced craniotomy for the excision of these tumors.

Diagnostic imaging of dopamine receptors in pituitary adenomas

Dopamine D2 receptor scintigraphy of pituitary adenomas is feasible by single-photon emission computed tomography using (123)I-S-(-)-N-[(1-ethyl-2-pyrrolidinyl)methyl]-2-hydroxy-3-iodo-6-methoxybenzamide ((123)I-IBZM) and (123)I-epidepride. (123)I-epidepride is generally superior to (123)I-IBZM for the visualization of D2 receptors on pituitary macroadenomas. However, (123)I-IBZM and (123)I-epidepride scintigraphy are generally not useful to predict the response to dopaminergic treatment in pituitary tumour patients. These techniques might allow discrimination of non-functioning pituitary macroadenomas from other non-tumour pathologies in the sellar region. Dopamine D2 receptors on pituitary tumours can also be studied using positron emission tomography with (11)C-N-raclopride and (11)C-N-methylspiperone.

The value of Tc-99m tetrofosmin in the imaging of pituitary adenomas

AIM

Magnetic resonance imaging (MRI) and computerized tomography (CT) are used in the diagnosis and follow-up of pituitary adenoma cases. Sometimes, these methods cannot display the post-operative residual tissue. It has been shown that some radionuclides were taken up by the pituitary adenomas. The aim of this study was to evaluate the uptake of the technetium-99m (Tc-99m) tetrofosmin (TF) in the pituitary adenoma and normal pituitary tissue and assess the ability of Tc-99m TF to predict tumor malignancy in pituitary gland.

METHODS

The patients with pituitary adenoma (7 invasive and 8 non-invasive) were compared with control group (no. 13). Single-photon emission computed tomography (SPECT) imaging of pituitary gland was performed in both groups. Tc-99m uptake indices were evaluated statistically with the use of Mann-Whitney U test.

RESULTS

The average tetrofosmin uptake index of pituitary adenoma is 2.44+/-1.54 for the patients and 1.69+/-0.71 for the control group. Any significant difference was not observed between the groups (p 0.3). The average index was calculated as 3.04+/-2.15 for invasive adenomas and 1.92+/-0.33 for the non-invasive group, and there was no significant difference between the two groups regarding uptake of the agent (p 0.53). Furthermore, it was determined that the invasive and non-invasive adenomas displayed an uptake of Tc-99m TF similar to normal pituitary tissue.

CONCLUSIONS

Since the pituitary adenoma and normal pituitary tissue gave similar results regarding Tc-99m TF uptake, it was concluded that this agent would not be useful in the diagnosis of pituitary adenoma.

Positron emission tomography in acromegaly and other pituitary adenoma patients

BACKGROUND

Positron emission tomography (PET) is a well-recognized technique used in research, especially for intracranial studies, as well as for clinical practice, and has contributed to the fast development in neuroscience during the last decades.

PROCEDURES

We have used PET in pituitary tumors for in vivo characterization with respect to metabolism, 11C-L-methionine and 18F-fluorodeoxyglucose, receptor properties, 11C-N-methylspiperone and 11C-raclopride, and monoamine oxidase B enzyme content, 11C-L-deprenyl; further, for diagnosing and outlining the tumors in differential diagnostic perspectives and in the follow-up of treatment.

OBSERVATIONS

11C-raclopride, a specific dopamine antagonist, demonstrated high amounts of dopamine D2 binding in prolactinomas and some growth hormone-secreting adenomas. There was a significant correlation between high amounts of D2 receptors and the positive treatment effect of dopamine agonist therapy. When 11C-L-methionine and 18F-fluorodeoxyglucose were used for metabolic mapping, the highest metabolic activity was found in the prolactinomas, which correlated well with the serum prolactin levels. The growth hormone adenomas also showed high metabolic rates. At treatment follow-up, a considerable decrease in 11C-L-methionine uptake was observed in all tumors that responded positively to the treatment and thus foretold that the medical treatment, both concerning dopamine agonist and somatostatin analogue, was effective. In this respect, PET was valuable to monitor treatment. PET was also shown valuable in differential diagnosing between pituitary adenomas, meningiomas and skull base neuromas.

CONCLUSION

We have found PET to be highly valuable in the research and clinical handling of patients with a pituitary adenoma for in vivo tumor characterization.

In vivo and in vitro detection of dopamine d2 receptors in uveal melanomas

Scintigraphy with radiolabeled benzamides was used in melanoma patients. Studies with a newer benzamide called 123I-epidepride, a high-affinity D2 receptor (D2R) antagonist, showed high sensitivity in D2R-positive pituitary adenomas. We evaluated the presence of D2R in patients with uveal melanomas in vivo with 123I-epidepride, and in vitro in melanomas, using immunohistochemistry (IHC) and 125I-epidepride autoradiography. We studied the in vivo tumor-to-background (TB) ratios in six patients with posterior uveal melanoma (one previously enucleated). IHC was performed in 3 of 6 tumors after enucleation and in another 20 uveal melanomas, 7 metastatic lymph nodes from skin melanoma, and 2 normal specimens. 125I-epidepride autoradiography was performed in 10 uveal melanomas (3 of which were studied in vivo), 7 metastases, and 2 normal samples. Radioligand uptake was present in the affected eye of 5 patients with uveal melanoma (TB = 3.1-6.1) and absent in the operated one (TB = 1). Eight uveal tumors were positive at IHC (35%), 14 weakly positive (61%), and 1 negative (4%). Two metastases were positive (29%), 2 weakly positive (29%), and 3 negative (42%). Two uveal tumors were positive at autoradiography (20%), 7 had nonspecific binding (70%), and 1 was negative (10%). One metastasis was positive (14%), while 6 were negative (86%). 123I-epidepride scintigraphy in uveal melanomas seems promising for sensitivity and image quality. D2R was demonstrated in a significant proportion of the melanomas, although 123I-epidepride uptake might also be nonspecific and unrelated to D2R binding. Although further studies on larger series are needed, 123I-epidepride could represent a future tool to study the expression of D2R in other classes of neuroendocrine tumors.

Nelson’s Syndrome: Complete Remission with Cabergoline but Not with Bromocriptine or Cyproheptadine Treatment

A woman affected by Cushing's disease underwent bilateral adrenalectomy followed by radiotherapy of the hypothalamic-pituitary area when she was 18 years old. Thereafter, she used hydrocortisone acetate replacement therapy (35.5 mg divided into two daily doses). At the age of 26 years, the patient exhibited the clinical signs of the Nelson's syndrome, i.e. skin and gingival hyperpigmentation accompanied by amenorrhea, and elevated ACTH plasma levels (2,850 pg/ml, normal range 15-80 pg/ml). The magnetic resonance imaging (MRI) analysis of the sellar region evidenced a pituitary macroadenoma, measuring 14 x 13 mm. The patient was initially treated with cyproheptadine hydrochloride (12 mg/day) for 18 months. There was a partial improvement of the symptoms, with a reduction of the ACTH plasma levels to 112 pg/ml, but without any modification of the tumor mass. Due to sleepiness and weight gain, the cyproheptadine treatment was interrupted and substituted by a cabergoline (0.5 mg twice a week) therapy. Soon after cabergoline was applied an improvement of the clinical symptoms and signs was observed such as a regression of the tumor mass and the normalization of the ACTH plasma titers (38 pg/ml). Later, cabergoline was substituted by bromocriptine (7.5 mg/day) and the plasma levels of ACTH increased again (247 pg/ml), and headache and cutaneous hyperpigmentation were recorded. When cabergoline was reintroduced there was a clinical improvement and normalization of ACTH plasma levels (64 pg/ml). The MRI analysis of the sella region demonstrated a complete remission of the pituitary adenoma. The results obtained show for the first time that a long-term treatment with cabergoline also brings about a complete remission of Nelson's syndrome in the presence of a pituitary macroadenoma.

Cabergoline addition to depot somatostatin analogues in resistant acromegalic patients: efficacy and lack of predictive value of prolactin status

BACKGROUND

Somatostatin analogues (SA) are currently the mainstay in the medical treatment of acromegaly. However, even high doses of depot SA for prolonged periods do not achieve GH-IGF-I normalization in some patients. Even though some data were reported about the addition of cabergoline, a long-acting dopamine agonist (DA), to SA in resistant patients, definite data are still lacking.

DESIGN

Prospective open trial.

PATIENTS

In 19 acromegalic patients with active disease (34-82 years old, seven males, 12 females) resistant to chronic (9-12 months) depot SA (octreotide-LAR, 30 mg/28 days in 13 patients, lanreotide, 60 mg/28 days intramuscularly in six patients) cabergoline was added (combined treatment). In these patients, SA treatment had partially relieved GH and IGF-I hypersecretion but no patient had achieved 'safe' GH and normal IGF-I-values. Eight patients had PRL levels greater than 15 micro g/l (range 16-60 micro g/l; 1 micro g = 21.2 mIU). Immunohistochemistry (IHC) was positive for PRL in four out of eight operated patients.

RESULTS

The addition of cabergoline, using the minimal effective and the maximal tolerated dose (range 1-3.5 mg/week), decreased GH from 6.6 +/- 0.9 to 4.6 +/- 0.6 micro g/l (P = 0.018), and IGF-I from 552 +/- 44 to 428 +/- 54 micro g/l (P = 0.019) after 6 months (median, range 3-18 Months). Combined treatment decreased GH to < 2.5 micro g/l in four patients (21%) and normalized IGF-I for age in eight patients (42%). It obtained a decline of both GH and IGF-I (-49 +/- 7%, and -47 +/- 5%, respectively) in nine patients (47%), and a partial improvement in six (32%) patients (GH decreased by 43 +/- 8% in four, and IGF-I by 35-38% in two patients). No change was observed in two patients, and worsening in two other patients. Results were not dependent on PRL status (serum levels or IHC). Combined treatment was well tolerated.

CONCLUSIONS

The addition of cabergoline to depot SA-resistant acromegalic patients is effective, not dependent on PRL values and normalizes IGF-I levels in 42% of patients. The association of long-acting DA and SA deserves a more relevant role in the therapeutical algorithm of acromegaly.

Dopamine receptor expression and function in clinically nonfunctioning pituitary tumors: comparison with the effectiveness of cabergoline treatment

The aim of this study was to correlate dopamine receptors and D(2) isoform expression with the cabergoline effect on alpha-subunit secretion in vitro and tumor mass in vivo in clinically nonfunctioning pituitary tumors. Eighteen patients were subjected to neurosurgery, and a tumor sample was used for dopamine receptor and D(2) isoform expression evaluation by RT-PCR and the in vitro functional studies. After neurosurgery, nine of 18 patients with persistent tumor were treated with cabergoline and tumor mass was evaluated before and after 1 yr treatment. D(2) receptor was expressed in 67% of cases. D(2long) was found in 50%, D(2short) in 17%, and both D(2) isoforms in 33% of cases. D(4) receptor was also expressed in 17% of cases. The in vitro inhibition of alpha-subunit concentration was found in 56% of cases and was associated with D(2) expression (chi(2) = 5.6; P < 0.05). After 1 yr of cabergoline treatment, tumor shrinkage was evident in 56% of patients and was associated with D(2) expression (chi(2) = 5.6; P < 0.05). The expression of D(2short) rather than D(2long) isoform is associated with the most favorable response of the tumor to cabergoline treatment. In conclusion, this study demonstrates D(2) receptor expression and function in nearly 70% of cases, suggesting a role of this drug in the treatment schedule of clinically nonfunctioning pituitary tumors.

Pituitary tumor endocrinopathies and their endocrine evaluation

Pituitary tumors, depending on their respective cell type, manifest various endocrinopathies. Prolactinomas may present as hypogonadism and galactorrhea and can be diagnosed by measuring morning prolactin levels. Gonadotropinomas rarely cause gonadal hyperstimulation, and dynamic thyrotropin-releasing hormone stimulation testing is often required to elicit a diagnostic gonadotropin and/or subunit secretory response. Acromegaly is a multisystemic debilitating disease for which early diagnosis and treatment are crucial. Diagnostic criteria include a lack of plasma growth hormone suppression during the oral glucose tolerance test and elevation of age- and sex-matched insulin growth factor-1 levels. Patients harboring corticotropin-secreting adenomas characheristically present with signs and symptoms of hypercortisolism. Inferior petrosal sinus sampling for corticotropin may be required for microadenoma localization. Thyrotropinomas produce inappropriate thyrotropin (TSH) secretion and hyperthyroidism. The new third-generation TSH assay has improved the rate of detection of these lesions at an earlier stage.

In vivo and in vitro effects of octreotide, quinagolide and cabergoline in four hyperprolactinaemic acromegalics: correlation with somatostatin and dopamine D2 receptor scintigraphy

OBJECTIVE

GH and PRL cosecretion frequently occurs in acromegaly and the sensitivity of both hormones to somatostatin analogs (SA) and dopamine agonists (DA) alone or in combination, is still debated. This study was designed to evaluate the in vivo and in vitro sensitivity to SA and/or DA and correlate the response in terms of hormone suppression to the results of in vivo somatostatin and dopamine receptor scintigraphy and to the immunohistochemical findings.

DESIGN AND PATIENTS

Scintigraphy using 111In-DTPA-D-Phe(1)-OCT (111In-OCT) and 123I-methoxybenzamide (123I-IBZM) was performed in four patients with acromegaly and high circulating GH, PRL and IGF-I levels. The results were correlated with the response to long-term treatment with octreotide (OCT), quinagolide (QN) and/or cabergoline (CAB), to the in vitro hormone suppression by OCT and DA in primary cultures from the pituitary tumors and to the immunohistochemical findings.

RESULTS

The first patient showed high tumour uptake of 111In-OCT and 123I-IBZM, the second high uptake of only 111In-OCT, while the third one showed faint tumour uptake of only 123I-IBZM, and the fourth a faint uptake of 111In-OCT. In the first and in the fourth patients OCT or CAB administered alone failed to normalize hormone levels while the combined treatment induced circulating GH, IGF-I and PRL normalization. In the second patient OCT administered alone normalized hormone levels while QN reduced PRL levels only. In the third patient both OCT and QN, alone or in combination, failed to normalize hormone levels. However, in this patient GH and PRL suppression was significantly greater after QN than OCT treatment. After medical therapy, all the patients were operated on. Immunohistochemistry showed diffuse GH and focal PRL staining in the first patient, while diffuse GH and PRL staining in the remaining three. In vitro, OCT significantly suppressed GH secretion in the four primary pituitary tumor cultures, while PRL secretion was significantly suppressed only in the second and the fourth cases. Dopamine agonists (DA) significantly suppressed PRL release in all the cultures, while GH secretion was significantly suppressed in three out of four.

CONCLUSIONS

These four acromegalics, presenting similar clinical findings and comparable peripheral hormone levels, showed different responsiveness to SA and DA. Moreover, during the in vitro study on primary tumor cell cultures, OCT and DA displayed an inhibiting activity on GH and PRL secretion positively correlated with the response observed in vivo. This evidence together with the in vivo receptor imaging study suggest the existence of somatostatin and/or dopamine D2 receptor heterogeneity in this class of pituitary tumors. The new potent DA might be primarily considered in the medical treatment of hyperprolactinemic acromegalics, while SA alone or in combination with DA in case of ineffective hormone suppression.

In vivo secretory potential and the effect of combination therapy with octreotide and cabergoline in patients with clinically non-functioning pituitary adenomas

The secretory capacity, in vivo, of clinically non-functioning pituitary adenomas may possibly predict tumour volume reduction during intensive medical therapy. Ten patients (mean (range) 53 years (26-73)) with clinically non-functioning macroadenomas, > or = 10 mm were studied. The secretory capacity of the adenomas was examined using basal, NaCl and TRH-stimulated LH, FSH and alpha-subunit levels. The effect on tumour volume of 6 months' therapy with the combination of a somatostatin analogue, octreotide 200 microg x 3/day and a dopamine-D2-agonist, cabergoline 0.5 mg x 1/day was studied. The basal LH, FSH and alpha-subunit levels were determined before and during 6 months' therapy with octreotide and cabergoline, and MR scans were used to evaluate tumour volume before and during this period of therapy. Octopus-perimetry was used to examine the visual fields. A reduction in tumour volume (mean +/- SEM (range); 30% +/- 4% (18-46%)) during 6 months of combination therapy with octreotide and cabergoline was recorded only in patients with in vivo secretory potential. Tumour volume was not reduced in four patients: in three of these patients it remained unchanged while in one patient it was observed to have increased (by 14%). Of the six patients with pretherapy secretory capacity, one displayed a very high basal level of alpha-subunit (74 microg/l) despite unmeasurable levels of LH and TSH, and an FSH-level of 1 IU/l. The other five patients presented paradoxical LH, FSH and/or alpha-subunit responses to TRH. A reduction in basal levels of LH, FSH and/or alpha-subunit was observed in all six patients, and the maximum reduction of at least one of the hormonal levels was 66% +/- 7% (50-98%). The basal levels of LH, FSH and alpha-subunit in the 10 patients were (mean +/- SEM (range)), 3.0 IU/l +/- 1.0 (0.0-7.4), 12.7 IU/l +/- 5.0 (0.0-39.0) and 9.0 IU/l +/- 7.0 (0.2-74.0). During six months of therapy with octreotide and cabergoline, the basal levels of LH, FSH and alpha-subunit were reduced by > or = 50% in seven patients - including the six patients with in vivo secretion prior to therapy. No new visual field defects were detected during therapy and no deterioration of existing visual field defects was recorded. The medical therapy was well tolerated. The in vivo basal and TRH-stimulated secretory capacity of LH, FSH and alpha-subunit predicted tumour reduction following intensive medical therapy in all of our patients with non-functioning pituitary adenomas.

Hormone levels and tumour size response to quinagolide and cabergoline in patients with prolactin-secreting and clinically non-functioning pituitary adenomas: predictive value of pituitary scintigraphy with 123I-methoxybenzamide

BACKGROUND

Dopamine agonists are indicated as primary therapy for PRL-secreting pituitary adenomas, while controversial results have been reported in nonfunctioning adenomas (NFA).

OBJECTIVE

To evaluate whether the in vivo visualization of dopamine D2 receptor expression detected by pituitary scintigraphy using 123I-methoxybenzamide (123I-IBZM) was correlated with the response to chronic treatment with quinagolide or cabergoline.

PATIENTS

10 patients affected with NFA (5 men and 5 women, age ranging between 25 and 50 years), and 10 with PRL-secreting naive macroadenomas (3 men and 7 women, age ranging between 22 and 59 years), serving as control.

STUDY DESIGN

All patients underwent an acute test with quinagolide: at 3-day intervals and in random order all patients received the drug (0.075 mg at 0800 h), or placebo. Blood samples were taken 15 and 5 minutes before and every 30 minutes for 6 h after drug or placebo administration. The test was considered positive when PRL and/or alpha-subunit levels decreased >/=50% as compared to baseline levels. After 6 months of treatment, 10 patients were randomised to continue the treatment with quinagolide and the remaining 10 received cabergoline for the remaining 6 months. The doses of quinagolide and cabergoline ranged from 0.075 to 0.6 mg/day and from 0.5 to 3 mg/week, respectively. At study entry, a magnetic resonance imaging (MR) study of the pituitary region and 123I-IBZM pituitary scintigraphy were performed. MR was repeated after 12 months of treatment to evaluate tumour shrinkage: reduction of tumour volume = 80% in prolactinomas and = 50% in NFA was considered significant. Basal PRL levels were 9495.0 +/- 1131.6 mU/l in prolactinomas and 602.4 +/- 50.5 mU/l in NFA.

RESULTS

The scintigraphy was negative in 6 out of 10 patients with NFA. Moderate uptake was observed in 3 patients with prolactinoma and 2 patients with NFA whereas intense uptake was observed in the remaining 7 patients with prolactinoma and 2 patients with NFA. Among the 8 patients with NFA and high circulating alpha-subunit levels, the acute test was negative in 5 while it was positive in the remaining 3 patients. The acute test was positive in all 10 patients with prolactinoma. After 12 months of treatment with quinagolide and cabergoline, circulating PRL levels were decreased in all 10 patients with prolactinoma (571.8 +/- 255.9 mU/l), being normalized in 7 patients. Suppression of PRL levels was found in all 10 patients with NFA (89.5 +/- 2.3 mU/l). A significant reduction of alpha-subunit levels was obtained in 9 out of 10 patients with NFA: in 4 out of 8 patients alpha-subunit levels were normalized. Significant adenoma shrinkage was recorded in 4 patients with prolactinoma among the 7 with intense pituitary uptake of 123I-IBZM. Significant adenoma shrinkage was recorded only in the 2 out of 10 patients with NFA with intense pituitary uptake of 123I-IBZM. A significant positive correlation was found between the degree of uptake (considered as score) and the response to quinagolide or cabergoline treatment (considered as percent hormone suppression) either in patients affected with PRL-secreting adenoma (r = 0.856, P < 0.005) or in those affected with NFA (r = 0.787, P < 0.05).

CONCLUSIONS

An intense 123I-IBZM uptake in patients with non-functioning adenomas was predictive of a good response to a chronic treatment with quinagolide and cabergoline. This result suggests that a pituitary 123I-IBZM scintigraphy could be considered in selected patients with non-functioning adenomas before starting medical treatment with dopamine agonists.

Cabergoline

Cabergoline (CAB) (1-[(6-allelylergolin-8 beta-yl)carbonyl]-1-[3-(dimethylamino)propyl]-3-ethyl-urea) is an ergoline derivative with potent, selective and long-lasting inhibitory activity on prolactin (PRL) secretion acting on dopamine receptors present in pituitary lactotrophes. Receptor binding studies have demonstrated that CAB has high in vitro selectivity and affinity for the subtype D2 of the dopamine receptor. In cultures of rat anterior pituitary cells, the concentrations of CAB and bromocriptine required to inhibit PRL secretory activity by 50% (IC50) were 0.1 and 3.4 nmol/l, respectively. As compared to bromocriptine, CAB was more potent in inhibiting the binding of [3H]N-n-propylnorapomorphine and it occupied the receptor for longer. These effects were observed in all areas of the rat brain. In vivo, CAB at doses of 0.125-1 mg twice weekly caused a dose-dependent suppression of PRL secretion in women with hyperprolactinaemia. CAB was shown to be significantly more effective than bromocriptine in inducing a complete biochemical response and clinical efficacy and was better tolerated than bromocriptine in the majority of patients. Notable tumour shrinkage until tumour disappearance was observed during CAB treatment in most patients with macroprolactinoma. CAB was also shown to be effective in patients resistant or poorly responsive to bromocriptine. In view of the limited data on CAB-associated pregnancies and the long half-life of the drug, it is currently recommended that women seeking to became pregnant, once ovulatory cycles have been established, should discontinue CAB therapy 1 month before they intend to conceive. However, no data on negative effects on pregnancy or offspring have been reported. The great efficacy of CAB together with its excellent tolerability makes this drug the current treatment of choice for the majority of patients with hyperprolactinaemic disorders. Very recently, the efficacy of CAB treatment has been reported in patients with acromegaly and clinically non-functioning adenomas with controversial results. CAB was also reported to have some efficacy in patients with Nelson's syndrome and Cushing's disease although these data are available only for limited case reports.