Dopamine agonists for the treatment of pituitary tumours: From ergot extracts to next generation therapies

Thyroid-Stimulating Hormone-Secreting Pituitary Adenoma: Two Cases With Challenging Diagnosis and Management

Background: Thyroid-stimulating hormone (TSH)-secreting pituitary adenomas (TSHomas) are very rare pituitary tumors causing central hyperthyroidism. Most are macroadenomas (≥ 10 mm) with local and systemic comorbidities at diagnosis. The atypical changes in thyroid function tests (TFTs) may be subtle and are often initially missed, while over-secretion of other pituitary hormones is often present. Somatostatin analogs (SSAs) are the recommended first-line medical therapy for these lesions. We report two cases of TSHomas successfully managed with a dopamine agonist (DA) therapy, alone or following transsphenoidal surgery (TSS). Case Presentation: A 47-year-old man presented with significant weight loss, fatigue, and muscle weakness. He was found to have hyperprolactinemia, secondary adrenal insufficiency (AI), and central hypogonadism, which led to the discovery of a 3 cm invasive pituitary adenoma. Additional tests showed an increased IGF1, TSH, and free T4. A Pit-1 multihormonal tumor was documented on pathology after partial resection by TSS. Persistent hyperprolactinemia and central hyperthyroidism responded to DA therapy, as the patient refused therapy. A 66-year-old man with a history of anxiety, hypertension, coronary artery disease, atrial fibrillation, and thyroid nodules, was consulted for severe dizziness and was found to have a 2.4 cm pituitary adenoma on a head CT scan. Lab records showed a progressive supranormal free T4 and TSH increase over the preceding five years. He refused surgery and had an excellent clinical and biochemical response to DA treatment. Conclusion: Prompt detection of central hyperthyroidism by monitoring and correctly interpreting TFT over time is essential for early diagnosis and optimal management of TSHomas. TSH-secreting adenomas may respond to DA therapy.

Bromocriptine improves glucose tolerance in obese mice via central dopamine D2 receptor-independent mechanism

Bromocriptine, generally regarded as a dopamine D2 receptor agonist, has been used to treat patients with type 2 diabetes in the USA; however, its mechanisms of action including the receptors that mediate its anti-diabetic effects remain unclear. Therefore, we herein conducted pharmacological and genetic knockout experiments to investigate how bromocriptine improves glucose metabolism under type 2 diabetic conditions. Bromocriptine transiently increased blood glucose levels in both wild-type and dopamine D2 receptor-deficient mice. This glucose-elevating effect was blocked by the α2-adrenergic receptor antagonist yohimbine. On the other hand, when bromocriptine was administered daily for two weeks, glucose tolerance improved in wild-type mice fed a high-fat diet. Similar anti-diabetic effects of bromocriptine were observed in dopamine D2 receptor-deficient, dopamine D1 receptor-deficient, and orexin-deficient mice under the diet-induced obese condition as well as in genetically obese db/db mice. Bromocriptine-induced improvements in glucose tolerance were not affected by a pretreatment with the autonomic ganglion blocker hexamethonium, which suggested the involvement of the peripheral effects of bromocriptine. Given the biphasic properties of bromocriptine, we examined the drug effect on hepatic endoplasmic reticulum (ER) stress that dually regulates glucose metabolism. In the livers of diet-induced obese mice, the levels of ER stress markers, including C/EBP homologous protein (CHOP), were reduced by the daily administration of bromocriptine. In human hepatoma HepG2 cells, increases in CHOP expression by thapsigargin, a potent inducer of ER stress, were prevented by a pretreatment with low concentrations of bromocriptine, whereas high concentrations induced CHOP expression. These results suggest that low concentrations of bromocriptine caused beneficial ER stress preconditioning, which protected against subsequent severe ER stress in the liver. Therefore, bromocriptine may prevent obesity-induced glucose intolerance via peripheral mechanisms including promotion of hepatic ER homeostasis, but not central dopamine D2 receptor-mediated mechanisms.

Treatment of hyperprolactinemia in women: A Position Statement from the Brazilian Federation of Gynecology and Obstetrics Associations (Febrasgo) and the Brazilian Society of Endocrinology and Metabolism (SBEM)

Dopamine agonists are the first line of treatment for patients with symptomatic hyperprolactinemia due to prolactinomas and in those with idiopathic hyperprolactinemia. Treatment with these agents is effective in 80%-90% of the cases. Infertility treatment of patients with hyperprolactinemia is also carried out with dopamine agonists, aiming for the normalization of prolactin levels. The risk of symptomatic growth of prolactinomas during pregnancy is dependent on the tumor's size, duration of previous treatments, and prolactin levels. Notably, the corresponding risk is relatively low in cases of microprolactinomas (<5%). Remission of hyperprolactinemia occurs in about 30% of the patients after drug treatment and may also occur after pregnancy and menopause. The use of some drugs, such as antidepressants and antipsychotics, is a frequent cause of hyperprolactinemia, and managing this occurrence involves unique considerations. This position statement by the Brazilian Federation of Gynecology and Obstetrics Associations (Febrasgo) and Brazilian Society of Endocrinology and Metabolism (SBEM) addresses the recommendations for measurement of serum prolactin levels and the investigations of symptomatic and asymptomatic hyperprolactinemia and drug-induced hyperprolactinemia in women.

Ropinirole for the Treatment of Hyperprolactinemia: A Dose-Escalation Study of Efficacy and Tolerability

CONTEXT

Treatment of hyperprolactinemia with ergoline dopamine agonists (DAs) can be complicated by intolerance and resistance.

OBJECTIVE

This study examines the efficacy and tolerability of the nonergot DA ropinirole for the long-term treatment of hyperprolactinemia.

METHODS

Twelve hyperprolactinemic women were treated with ropinirole in a 6-month, open-label, dose-escalation trial; 7 of the 12 continued treatment in an extension study for up to 17 months. Ropinirole doses were uptitrated to achieve normal prolactin (PRL) levels, restore menses, and eliminate galactorrhea.

RESULTS

Two of the 12 participants were DA naive; 6 of 12 were ergot DA intolerant; and 1 of 12 had known ergot DA resistance. Baseline PRL levels were 126.2 ± 41.4 ng/mL (SEM). Ropinirole was uptitrated from 0.125 to 0.25 mg/h to a median total daily dose (TDD) of 2 mg/d (1-4 mg/d [interquartile range]). PRL normalization was achieved in 50% of the participants (5 with microadenomas and 1 with idiopathic hyperprolactinemia) at a median effective TDD of 1 mg/d. Of the patients achieving PRL normalization, 83% were ergot DA intolerant. A persistent partial biochemical response (PRL reduction >50% from baseline) was achieved in 17% of the participants. During treatment, menses resumed in 67% of amenorrheic patients; galactorrhea resolved in 67%. Mild adverse effects were reported in 92% of participants; however, ropinirole was not discontinued because of intolerance even among the 50% of individuals with a prior history of ergot DA intolerance and resultant medication discontinuation.

CONCLUSION

These data demonstrate the efficacy and tolerability of ropinirole for the treatment of hyperprolactinemia in patients with microprolactinomas and idiopathic hyperprolactinemia and suggest ropinirole may represent a novel therapeutic alternative for treating hyperprolactinemic disorders in patients with ergot DA intolerance.

An aggressive cabergoline-resistant, temozolomide-responsive macroprolactinoma due to a germline SDHB pathogenic variant in the absence of paraganglioma or pheochromocytoma

Context

Germline succinate dehydrogenase subunit B (SDHB) pathogenic variants are characteristic of familial paraganglioma (PGL) syndrome type 4. This syndrome frequently presents with abdominal PGL and has high tendency for locally aggressive behavior and distant metastasis. The vast majority of pituitary adenomas (PAs) are sporadic. However, PAs can be part of a number of familial tumor syndromes such as multiple endocrine neoplasia type 1 (MEN 1) or more rarely in association with pheochromocytoma and PGL (referred to as 3P syndrome). Only a limited number of PAs in association with SDHB-related PGL has been reported and the vast majority occurred subsequently or simultaneously with pheochromocytoma/PGL (collectively abbreviated as PPGL). In this report, we describe a young patient who had a giant pituitary macroprolactinoma resistant to large doses of cabergoline (CBG) and external beam radiotherapy (XRT). The patient did not have personal history of PPGL but was found to carry a germline SDHB pathogenic variant.

Case report

A 38-year-old woman presented with headache, visual disturbances and galactorrhea and was found to have a 34-mm macroprolactinoma. She was treated with CBG 3-4 mg per week but PA continued to grow and caused significant cranial pressure symptoms. She underwent two transsphenoidal surgeries with rapid tumor recurrence after each one. She received XRT but PA continued to grow. She was finally treated with temozolomide with excellent response. Whole exome and subsequent Sanger sequencing confirmed that she has a pathogenic monoallelic SDHB mutation (NM_003000:c.C343T, p.R115*). PA tissue showed loss of heterozygosity for the same mutation and absent SDHB immunostaining confirming the pathogenic role of this SDHB mutation.

Conclusion

Germline SDHB mutations can rarely cause PA in the absence of PPGL. They should be considered as a possible cause of aggressiveness and resistance to dopamine agonists in similar cases.