Dopamine Agonists: From the 1970s to Today

Cabergoline targets multiple pathways to inhibit PRL secretion and increases stromal fibrosis

OBJECTIVE

Unravel the potential mechanism(s) of the on- and off-target actions of dopamine agonist therapy in both human prolactinoma tumors and neighboring stromal and immune cells.

DESIGN AND METHODS

Five surgically resected prolactinomas (PRLomas) from 3 cabergoline (CBG)-treated patients and 2 treatment-naive patients were analyzed by using single-cell RNA sequencing (scRNA-seq) to compare the cellular composition and transcriptional landscape.

RESULTS

Six major cell populations, namely tumor (88.2%), immune (5.6%), stromal (4.9%), progenitor cells (0.6%), proliferating cells (0.4%), and erythrocytes (0.2%), were observed. Tumor cells from CBG-treated patients expressed lower levels of genes that regulated hormone secretion, such as SCG2, VGF, TIMP1, NNAT, and CALD1, consistent with the inhibitory effects of CBG on hormone processing and secretion. Interestingly, we also observed an increased number of CD8+ T cells in the CBG-treated tissues. These cytotoxic CD8+ T cells expressed killing granule components such as perforin and the granzymes GZMB, GNLY, and KLRD1 as well as the inflammatory cytokine CCL5. Immune cell activation of these CD8+ T cells was further analyzed in a compartment-specific manner, and increased CD25 (IL2R) expression was noted in the CD8+ T cells from the CBG-treated samples. Additionally, and confirming prior reports, we noted a higher stromal cell population in the CBG-treated samples.

CONCLUSIONS

Our scRNA-seq studies revealed key differences in the transcriptomic features of CBG-treated and CBG-untreated PRLomas in both tumor and microenvironment cellular constituents, and for the first time, describe the previously unknown activation of CD8+ T cells following CBG treatment, which may play a role in the tumoricidal actions of CBG.

Sleep and local field potential effect of the D2 receptor agonist bromocriptine during the estrus cycle and postpartum period in female rats

BACKGROUND

Pituitary lactotrophs are under tonic dopaminergic inhibitory control and bromocriptine treatment blocks prolactin secretion.

METHODS

Sleep and local field potential were addressed for 72 h after bromocriptine treatments applied during the different stages of the estrus cycle and for 24 h in the early- and middle postpartum period characterized by spontaneously different dynamics of prolactin release in female rats.

RESULTS

Sleep changes showed strong dependency on the estrus cycle phase of the drug application. Strongest increase of wakefulness and reduction of slow wave sleep- and rapid eye movements sleep appeared during diestrus-proestrus and middle postpartum treatments. Stronger sleep-wake effects appeared in the dark phase in case of the estrus cycle treatments, but in the light phase in postpartum treatments. Slow wave sleep and REM sleep loss in case of estrus cycle treatments was not compensated at all and sleep loss seen in the first day post-injection was gained further later. In opposition, slow wave sleep loss in the light phase after bromocriptine injections showed compensation in the postpartum period treatments. Bromocriptine treatments resulted in a depression of local field potential delta power during slow wave sleep while an enhancement in beta and gamma power during wakefulness regardless of the treatment timing.

CONCLUSIONS

These results can be explained by the interplay of dopamine D2 receptor agonism, lack of prolactin release and the spontaneous homeostatic sleep drive being altered in the different stages of the estrus cycle and the postpartum period.

Comparing pyridoxine with dopaminergic agonists (cabergoline and bromocriptine): Unveiling the strategy for lactation inhibition - A systematic review of clinical trials

This systematic review aims to evaluate the efficacy and safety of Pyridoxine compared to Dopaminergic agonists (cabergoline and bromocriptine) in post-partum lactation inhibition. Cochrane Central, PubMed/MEDLINE, Cochrane Central, ScienceDirect, ClinicalTrials.gov, Web of Science, CINAHL and Google Scholar, covering the period from inception to November 2023. Additionally, the bibliographies of included articles and previous meta-analyses were screened for any relevant articles. The systematic review was conducted according to the Cochrane Handbook for Systematic Reviews of Interventions. The outcomes of interest encompassed inhibition of lactation, breast pain/tenderness, breast engorgement, milk secretion, fever, mastitis, prolactin level and adverse events related to pyridoxine, cabergoline and bromocriptine. Methodological quality assessment was conducted using the Cochrane risk of bias assessment tool for rigorous evaluation. Three clinical trials assessed the effectiveness of pyridoxine and dopaminergic agents (cabergoline and bromocriptine) for lactation inhibition. It was assessed by using different assessment methods such as a scale for milk secretion, serum prolactin levels, and questionnaires for assessing breast engorgement, breast pain, and milk leakage. On the global assessment of the therapeutic efficacy of dopaminergic agents, it was found that there was significant inhibition of lactation as compared to pyridoxine (p < 0.001). In conclusion, this systematic review contributes significant insights into lactation inhibition interventions. Dopaminergic agonists, specifically cabergoline and bromocriptine, stand out as more effective and tolerable choices compared to Pyridoxine. These findings provide a foundation for informed clinical decisions and underscore the need for careful consideration of lactation inhibition strategies in diverse clinical contexts.

Acute retinal pigment epitheliitis during treatment of hyperprolactinaemia

BACKGROUND

Acute retinal pigment epitheliitis (ARPE) is a rare, idiopathic and self-limiting disease. The article aims to present ARPE in a patient using D2 dopamine receptor agonists for the treatment of hyperprolactinemia.

CASE PRESENTATION

A 28-year-old female during hyperprolactinaemia treatment suffered from a dyschromatopsia and a central visual field defect in the left eye. She noticed a deterioration of vision and discontinued the cabergoline administration. The woman had not been diagnosed with other chronic conditions and exhibited no symptoms of infection. Upon admission, the patient was subjected to a test for COVID-19, which was negative. The ophthalmological examination revealed a decrease in visual acuity to distance in the left eye, which amounted to 18/20 on the Snellen chart. A central scotoma was noted on the Amsler chart and a loss of pigment epithelium was visible on the fundus of the left eye. Fluorescein angiography showed a discrete window defect in the left one, with no signs of leakage. Optical coherence tomography (OCT) scans of the maculae revealed a characteristic change in the photoreceptor layer and retinal pigment epithelium (RPE) in the fovea in the left eye. The electrophysiological tests revealed decreased function of cells in macular region. A magnetic resonance imaging (MRI) of the head and orbits demonstrated an asymmetric pituitary gland without chiasm compression and discrete signal enhancement from the left optic nerve. The patient underwent observation during hospitalisation. She reported improved colour vision and a decreased scotoma in the centre of her visual field. In regular outpatient follow-ups, successive improvements in visual acuity, as well as a decreased RPE damage and outer photoreceptor layer loss during an OCT test were observed.

CONCLUSIONS

A case of ARPE is reported in a patient taking medications for hyperprolactinemia. The role of dopamine receptor antagonists in the photoreceptor function and causation of ARPE needs further evaluation.

The role of surgical management for prolactin-secreting tumors in the era of dopaminergic agonists: An international multicenter report

OBJECTIVE

First-line prolactin-secreting tumor (PST) management typically involves treatment with dopamine agonists and the role of surgery remains to be further explored. We examined the international experience of 12 neurosurgical centers to assess the patient characteristics, safety profile, and effectiveness of surgery for PST management.

METHODS

Patients surgically treated for PST from January 2017 through December 2020 were evaluated for surgical characteristics, outcomes, and safety.

RESULTS

Among 272 patients identified (65.1% female), the mean age was 38.0 ± 14.3 years. Overall, 54.4% of PST were macroadenomas. Minor complications were seen in 39.3% of patients and major complications were in 4.4%. The most common major complications were epistaxis and worsened vision. Most minor complications involved electrolyte/sodium dysregulation. At 3-6 months, local control on imaging was achieved in 94.8% of cases and residual/recurrent tumor was seen in 19.3%. Reoperations were required for 2.9% of cases. On multivariate analysis, previous surgery was significantly predictive of intraoperative complications (6.14 OR, p < 0.01) and major complications (14.12 OR, p < 0.01). Previous pharmacotherapy (0.27 OR, p = 0.02) and cavernous sinus invasion (0.19 OR, p = 0.03) were significantly protective against early endocrinological cure. Knosp classification was highly predictive of residual tumor or PST recurrence on 6-month follow-up imaging (4.60 OR, p < 0.01). There was noted institutional variation in clinical factors and outcomes.

CONCLUSION

Our results evaluate a modern, multicenter, global series of PST. These data can serve as a benchmark to compare with DA therapy and other surgical series. Further study and longer term outcomes could provide insight into how patients benefit from surgical treatment.

Impaired Prolactin-Lowering Effects of Metformin in Women with Polycystic Ovary Syndrome

The effect of metformin on prolactin concentration seems to be sex-dependent. The aim of this study was to determine whether the androgen status modulates the impact of metformin on plasma prolactin levels in women. This study included two matched groups of prediabetic women with hyperprolactinemia: 25 with PCOS and 25 control subjects with androgen levels within the reference range and with normal ovarian morphology. Glucose homeostasis markers, prolactin, the remaining anterior pituitary hormones, sex hormones, SHBG and IGF-1 were determined before and after six months of metformin treatment. At baseline, both groups differed in LH, LH/FSH ratio, testosterone, FAI, DHEA-S, androstenedione and estradiol. Although metformin improved insulin sensitivity and increased SHBG in both study groups, these effects were more pronounced in control subjects than in women with PCOS. In control subjects, the drug decreased total and monomeric prolactin and increased LH. In women with PCOS, metformin reduced LH, LH/FSH ratio, testosterone and FAI. In the control group, the impact on total and monomeric prolactin positively correlated with their baseline levels and with the degree of improvement in insulin sensitivity, as well as negatively correlated with testosterone and FAI. In women with PCOS, treatment-induced changes in testosterone and FAI positively correlated with the changes in LH and LH/FSH ratio. The obtained results suggest that the prolactin-lowering properties of metformin are less pronounced in women with coexisting PCOS than in women with elevated prolactin levels, probably owing to the increased production of endogenous testosterone.

Approach to the Patient With Prolactinoma

Prolactinomas are the most common pituitary tumor histotype, with microprolactinomas being prevalent in women and macroprolactinomas in men. Hyperprolactinemia is among the most common causes of hypogonadotropic hypogonadism in both sexes, prompting medical advice for hypogonadism (infertility, oligo-amenorrhea, impotence, osteoporosis/osteopenia) in both sexes, and for signs and symptoms of mass effects (hypopituitarism, visual loss, optic chiasm compression, cranial nerve deficits, headaches) predominantly in men. Diagnostic workup involves a single prolactin measurement and pituitary imaging, but some laboratory artifacts (ie, the "hook effect" and macroprolactin) can complicate or delay the diagnosis. The treatment of choice for prolactinomas is represented by dopamine agonists, mainly cabergoline, which are able to induce disease control, restore fertility in both sexes, and definitively cure one-third of patients, thus permitting treatment discontinuation. Pregnancy and menopause may promote spontaneous prolactin decline and anticipate cabergoline discontinuation in women. Surgery and/or radiotherapy are indicated in case of resistance to cabergoline not overcome by the increase in drug dose up to the maximally tolerated or the patient's personal choice of surgery. The evidence of resistance to cabergoline in invasive and proliferative tumors may indicate biological aggressiveness, thus requiring alternative therapeutic approaches mainly based on temozolomide use as monotherapy or combined with radiotherapy. In uncontrolled patients, new medical approaches (alternative hormonal treatments, cytotoxic drugs, peptide receptor radionuclide therapy, mTOR/Akt inhibitors, tyrosine kinase inhibitors, or immunotherapy) may be offered but the experience collected to date is still very scant. This article reviews different facets of prolactinomas and discusses approaches to the condition in more common clinical situations.

Antiangiogenic Effect of Dopamine and Dopaminergic Agonists as an Adjuvant Therapeutic Option in the Treatment of Cancer, Endometriosis, and Osteoarthritis

Dopamine (DA) and dopamine agonists (DA-Ag) have shown antiangiogenic potential through the vascular endothelial growth factor (VEGF) pathway. They inhibit VEGF and VEGF receptor 2 (VEGFR 2) functions through the dopamine receptor D2 (D2R), preventing important angiogenesis-related processes such as proliferation, migration, and vascular permeability. However, few studies have demonstrated the antiangiogenic mechanism and efficacy of DA and DA-Ag in diseases such as cancer, endometriosis, and osteoarthritis (OA). Therefore, the objective of this review was to describe the mechanisms of the antiangiogenic action of the DA-D2R/VEGF-VEGFR 2 system and to compile related findings from experimental studies and clinical trials on cancer, endometriosis, and OA. Advanced searches were performed in PubMed, Web of Science, SciFinder, ProQuest, EBSCO, Scopus, Science Direct, Google Scholar, PubChem, NCBI Bookshelf, DrugBank, livertox, and Clinical Trials. Articles explaining the antiangiogenic effect of DA and DA-Ag in research articles, meta-analyses, books, reviews, databases, and clinical trials were considered. DA and DA-Ag have an antiangiogenic effect that could reinforce the treatment of diseases that do not yet have a fully curative treatment, such as cancer, endometriosis, and OA. In addition, DA and DA-Ag could present advantages over other angiogenic inhibitors, such as monoclonal antibodies.

Vitamin D Status Determines Cardiometabolic Effects of Cabergoline in Women with Elevated Prolactin Levels: A Pilot Study

Both hyperprolactinemia and vitamin D deficiency appear to be associated with increased cardiometabolic risk. This study aimed to determine whether vitamin D status influences the cardiometabolic effects of cabergoline. The study included three matched groups of women with mild to moderate hyperprolactinemia: vitamin D-naive subjects with vitamin D insufficiency (group A), women with vitamin D deficiency/insufficiency successfully treated with vitamin D (group B), and vitamin D-naive individuals with normal vitamin D status (group C). Plasma prolactin, 25-hydroxyvitamin D, estradiol, glucose homeostasis markers, lipids, high-sensitivity C-reactive protein (hsCRP), fibrinogen, homocysteine, and uric acid, as well as the urinary albumin-to-creatinine ratio (UACR), were measured at study entry and after four months of cabergoline treatment. Although cabergoline reduced prolactin levels and increased estradiol levels in all study groups, the effect on prolactin was more pronounced in groups B and C compared to group A. In groups B and C, the drug enhanced glucose homeostasis, increased HDL-cholesterol, and decreased triglycerides, hsCRP, fibrinogen, homocysteine, uric acid, and UACR. In group A, only insulin resistance, hsCRP, and homocysteine were reduced by cabergoline. The effects on insulin sensitivity, HDL-cholesterol, triglycerides, hsCRP, fibrinogen, homocysteine, uric acid, and UACR were proportional to the decrease in prolactin and baseline levels of 25-hydroxyvitamin D. The obtained results suggest that vitamin D status determines cabergoline's cardiometabolic effects.

Cardiometabolic Effects of Cabergoline and Combined Oral Contraceptive Pills in Young Women with Hyperprolactinemia: A Pilot Study

Although dopaminergic agents are the drugs of choice in treatment of prolactin excess, women who cannot be treated with these agents are recommended to receive estrogen preparations. The aim of this study was to compare cardiometabolic effects of both treatment options. The study population included three groups of young women. Subjects with mild-to-moderate hyperprolactinemia received either low-dose cabergoline or oral combined contraceptives (ethinyl estradiol plus desogestrel), while normoprolactinemic women were drug-naive. Plasma prolactin, glucose homeostasis markers, lipids, circulating levels of uric acid, high-sensitivity C-reactive protein (hsCRP), fibrinogen and homocysteine, and the urinary albumin-to-creatinine ratio (UACR) were assessed at entry and six months later. Hyperprolactinemic women differed from normoprolactinemic ones in glucose homeostasis markers, high-density lipoprotein (HDL)-cholesterol, triglycerides, uric acid, hsCRP, fibrinogen, homocysteine and UACR. Cabergoline decreased total and monomeric prolactin levels, which was accompanied by normalization of glucose, insulin sensitivity, glycated hemoglobin, HDL-cholesterol, triglycerides, uric acid, hsCRP, fibrinogen, homocysteine and UACR. Despite a neutral effect on prolactin levels, combined contraceptives worsened insulin sensitivity and increased triglycerides, hsCRP, fibrinogen and UACR. At follow-up, cabergoline-treated women were characterized by a better cardiometabolic profile than women receiving ethinyl estradiol plus desogestrel. Our findings suggest that only cabergoline reduces cardiometabolic risk in young women with hyperprolactinemia.

How to manage intolerance to dopamine agonist in patients with prolactinoma

PURPOSE

Dopamine agonists (DA) are the gold-standard for prolactinoma and hyperprolactinemia treatment. Intolerance to DA leading to drug drop out occurs in 3 to 12% of cases. We provide here a review of published data about DA intolerance and present a case report concerning the use of intravaginal cabergoline.

METHODS

We review the literature on the definition, the pathogenesis, frequency and management of DA intolerance. In addition, the review provides strategies to enhance tolerability and avoid precocious clinical treatment withdrawal.

RESULTS

Cabergoline is often cited as the most tolerable DA and its side effects tend to ameliorate within days to weeks. Restarting the same drug at a lower dose or switching to another DA can be used in cases of intolerance. The vaginal route can be tried specifically if there are gastrointestinal side effects in the oral administration. Symptomatic treatment could be attempted, although mainly based on a strategy used in other diseases.

CONCLUSIONS

Due to limited data, no guidelines have been developed for the management of intolerance in DA treatment. The most frequent management is to perform transsphenoidal surgery. Nevertheless, this manuscript provides data derived from published literature and expert opinion, suggesting new approaches to this clinical issue.

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

Dopamine agonists are a key tool in the therapeutic arsenal of endocrinologists worldwide. They exert their effects by binding to dopamine-2 (D2) receptors expressed by pituitary tumour cells to modulate hormonal secretion and tumour size. They are the established first-line treatment for prolactinomas which express high levels of D2 receptors. Growing data support their use as an adjuvant treatment option for other pituitary tumours including growth hormone, adrenocorticotrophic hormones, thyroid hormone secreting adenomas and nonfunctional pituitary tumours, all of which have been shown to express D2 receptors as well, albeit to varying extents. For those pituitary tumours inadequately treated by dopamine agonist alone, combined agonism of D2 and somatostatin receptors represent a new frontier in clinical development. Here we review the development and role of dopamine agonist for the treatment of prolactinomas, the literature supporting their adjuvant use for the treatment of all other pituitary tumours, and recent progress in the development of the next generation of chimeric compounds that target D2 and other receptor subtypes highly expressed on pituitary tumour cells.

Microglia depletion prevents lactation by inhibition of prolactin secretion

Microglial cells were eliminated from the brain with sustained 3-4 weeks long inhibition of colony stimulating factor 1 receptor by Pexidartinib 3397 (PLX3397). The prepartum treated mice mothers did not feed their pups after parturition. The pups of mothers treated orally only in the postpartum period starting immediately after parturition showed reduced body weight by 15.5 ± 0.22 postnatal days as the treatment progressed without the mothers showing altered caring behaviors. The apparent weight gain of foster pups during a suckling bout was reduced in mother mice fed by PLX3397-containing diet and also in rat dams following sustained intracerebroventricular infusion of PLX3397 in a separate experiment suggesting that lactation was affected by the reduced number of microglia. Prolactin secretion and signaling were markedly reduced in PLX3397-treated mothers. The results suggest that microglial cells are required for prolactin secretion and lactation whereas maternal motivation may not be directly affected by microglia.

The Role of Aromatase Inhibitors in Male Prolactinoma

BACKGROUND

dopamine agonists are the recommended treatment for male prolactinomas, but some patients may develop dopamine-agonist-resistant hyperprolactinemia, leading to persistent hypogonadism that requires treatment with testosterone. However, testosterone replacement therapy may be associated with a decrease in the efficacy of dopamine agonists due to the aromatization of testosterone to estradiol, which can stimulate the proliferation and hyperplasia of lactotroph cells in the pituitary, inducing resistance to dopamine agonists.

OBJECTIVE

this paper systematically reviewed the role of aromatase inhibitors for men with prolactinoma and dopamine-agonist-resistant or persistent hypogonadism following treatment.

METHOD

we performed a systematic review of all studies (according to PRISMA guidelines), assessing the role of aromatase inhibitors, including anastrozole and letrozole, for male prolactinoma. An English-language search for relevant studies was conducted on PubMed from its inception to 1 December 2022. The reference lists of the relevant studies were also reviewed.

RESULTS

our systematic review identified six articles (nine patients), including five case reports and a single case series, on the use of aromatase inhibitors for male prolactinomas. Reducing estrogen levels with an aromatase inhibitor improved sensitivity to dopamine agonists, as the addition of anastrozole or letrozole improves the control of prolactin levels and may lead to the shrinkage of tumors.

CONCLUSION

aromatase inhibitors are of potential value to patients with dopamine-agonist-resistant prolactinoma, or when hypogonadism persists while using high-dose dopamine agonists.

Effects of Anterior Pituitary Adenomas' Hormones on Glucose Metabolism and Its Clinical Implications

Pituitary adenomas have recently become more common and their incidence is increasing yearly. Functional pituitary tumors commonly secrete prolactin, growth hormones, and adrenocorticotropic hormones, which cause diseases such as prolactinoma, acromegaly, and Cushing's disease, but rarely secrete luteinizing, follicle-stimulating, thyroid-stimulating, and melanocyte-stimulating hormones. In addition to the typical clinical manifestations of functional pituitary tumors caused by excessive hormone levels, some pituitary tumors are also accompanied by abnormal glucose metabolism. The effects of these seven hormones on glucose metabolism are important for the treatment of diabetes secondary to pituitary tumors. This review focuses on the effects of hormones on glucose metabolism, providing important clues for the diagnosis and treatment of related diseases.

The dopaminergic control of Cushing's syndrome

Cushing's Syndrome (CS), or chronic endogenous hypercortisolism, is a rare and serious disease due to corticotroph pituitary (Cushing's disease, CD) and extra-pituitary (ectopic CS) tumours overproducing ACTH, or cortisol-secreting adrenal tumours or lesions (adrenal CS). The first-line treatment for CS is represented by the surgical removal of the responsible tumour, but surgery might be unfeasible or ineffective and medical treatment can be required in a relevant percentage of patients with CS, especially CD and ectopic CS. Corticotroph pituitary and extra-pituitary tumours, as well as adrenal tumours and lesions responsible for CS express dopamine receptors (DRs), which have been found to mediate inhibition of hormone secretion and/or cell proliferation in experimental setting, suggesting that dopaminergic system, particularly DRs, might represent a target for the treatment of CS. Dopamine agonists (DAs), particularly cabergoline (CAB), are currently used as off-label treatment for CD, the most common form of CS, demonstrating efficacy in controlling hormone secretion and tumour growth in a relevant number of cases, with the improvement of clinical picture, and displaying good safety profile. Therefore, CAB may be considered a reasonable alternative treatment for persistent or recurrent CD after pituitary surgery failure, but occasionally also before pituitary surgery, as adjuvant treatment, or even instead of pituitary surgery as first-line treatment in case of surgery contraindications or refusal. A certain beneficial effect of CAB has been also reported in ectopic CS. However, the role of DAs in the clinical management of the different types of CS requires further evaluations.

Understanding the Role of Dopamine in Cancer: Past, Present, and Future

Dopamine (DA, 3-hydroxytyramine) is member of the catecholamine family and is classically characterized according to its role in the central nervous system as a neurotransmitter. In recent decades, many novel and intriguing discoveries have been made about the peripheral expression of DA receptors (DRs) and the role of DA signaling in both normal and pathological processes. Drawing from decades of evidence suggesting a link between DA and cancer, the DA pathway (DAP) has recently emerged as a potential target in antitumor therapies. Due to the onerous, expensive, and frequently unsuccessful nature of drug development, the repurposing of dopaminergic drugs for cancer therapy has the potential to greatly benefit patients and drug developers alike. However, the lack of clear mechanistic data supporting the direct involvement of DRs and their downstream signaling components in cancer represents an ongoing challenge that has limited the translation of these drugs to the clinic. Despite this, the breadth of evidence linking DA to cancer and non-tumor cells in the tumor microenvironment (TME) justifies further inquiry into the potential applications of this treatment modality in cancer. Herein, we review the literature characterizing the interplay between the DA signaling axis and cancer, highlighting key findings, and then propose rational lines of investigation to follow.

Metabolic effects of prolactin

Over the last years, the metabolic role of PRL has emerged. PRL excess is known to promote weight gain, obesity, metabolic syndrome, and impairment in gluco-insulinemic and lipid profiles, likely due to the suppression of physiologic dopaminergic tone. Prolactin receptors and dopamine receptors type 2 have been demonstrated to be expressed on both human pancreatic β- cell and adipocytes, supporting a key role of prolactin and dopamine in peripheral metabolic regulation. Medical treatment with the dopamine agonists bromocriptine and cabergoline has been demonstrated to decrease the prevalence of metabolic syndrome and obesity, and significantly improve gluco-insulinemic and lipid profiles. In hyperprolactinemic men with concomitant hypogonadism, correction of hyperprolactinaemia and testosterone replacement has been proven to restore metabolic impairment. In turn, low prolactin levels have also been demonstrated to exert a detrimental effect on weight gain, glucose and lipid metabolism, thus leading to an increased prevalence of metabolic syndrome. Therefore, PRL values ranging from 25 to 100 mg/L, in absence of other recognizable pathological causes, have been proposed to represent a physiological response to the request for an increase in metabolic activity, and nowadays classify the so-called HomeoFIT- PRL as a promoter of metabolic homeostasis. The current review focuses mainly on the effects of hyperprolactinemia and its control by medical treatment with DAs on the modulation of food intake, body weight, gluco-insulinemic and lipid profile. Furthermore, it provides the latest knowledge about the metabolic impact of hypoprolactinemia.

Decoding signaling pathways involved in prolactin-induced neuroprotection: A review

It has been well recognized that prolactin (PRL), a pleiotropic hormone, has many functions in the brain, such as maternal behavior, neurogenesis, and neuronal plasticity, among others. Recently, it has been reported to have a significant role in neuroprotection against excitotoxicity. Glutamate excitotoxicity is a common alteration in many neurological and neurodegenerative diseases, leading to neuronal death. In this sense, several efforts have been made to decrease the progression of these pathologies. Despite various reports of PRL's neuroprotective effect against excitotoxicity, the signaling pathways that underlie this mechanism remain unclear. This review aims to describe the most recent and relevant studies on the molecular signaling pathways, particularly, PI3K/AKT, NF-κB, and JAK2/STAT5, which are currently under investigation and might be implicated in the molecular mechanisms that explain the PRL effects against excitotoxicity and neuroprotection. Remarkable neuroprotective effects of PRL might be useful in the treatment of some neurological diseases.

Resistance to Dopamine Agonists in Pituitary Tumors: Molecular Mechanisms

Pituitary neuroendocrine tumors (PitNET) are commonly benign tumors accounting for 10-25% of intracranial tumors. Prolactin-secreting adenomas represent the most predominant type of all PitNET and for this subtype of tumors, the medical therapy relies on the use of dopamine agonists (DAs). DAs yield an excellent therapeutic response in reducing tumor size and hormonal secretion targeting the dopamine receptor type 2 (D2DR) whose higher expression in prolactin-secreting adenomas compared to other PitNET is now well established. Moreover, although DAs therapy does not represent the first-line therapy for other PitNET, off-label use of DAs is considered in PitNET expressing D2DR. Nevertheless, DAs primary or secondary resistance, occurring in a subset of patients, may involve several molecular mechanisms, presently not fully elucidated. Dopamine receptors (DRs) expression is a prerequisite for a proper DA function in PitNET and several molecular events may negatively modify DR membrane expression, through the DRs down-regulation and intracellular trafficking, and DR signal transduction pathway. The current mini-review will summarise the presently known molecular events that underpin the unsuccessful therapy with DAs.

Artesunate exerts anti-prolactinoma activity by inhibiting mitochondrial metabolism and inducing apoptosis

BACKGROUND

Prolactinoma is the most common hormone-secreting pituitary adenoma. Dopamine receptor agonists (DAs) are effective in reducing prolactin levels and tumor mass, but some prolactinoma patients are resistant to DAs. Treating patients with DA-resistant prolactinoma is challenging. In this study, we examined the anti-prolactinoma effect of artesunate (ART), a potential new treatment option for prolactinoma, and its mechanism of action.

METHODS

Cell Counting Kit-8 (CCK8) and flow cytometry were used to detect the effect of ART on the proliferation, cycle, and apoptosis of rat pituitary adenoma cell line MMQ. The subcellular localization of ART was observed using confocal fluorescence microscopy. The JC-1 mitochondrial membrane potential (MMP) detection and Seahorse assays were used to detect the effect of ART on mitochondrial function. Real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot analysis were used to detect the effect of ART on the expression of prolactin (PRL) and apoptosis-related proteins. A mouse xenograft model of prolactinoma was used to detect the inhibitory effect of ART on MMQ in vivo.

RESULTS

ART specifically inhibited MMQ proliferation and PRL synthesis, induced G0/G1 phase arrest and apoptosis in vitro. ART accumulated in the mitochondria of MMQ cells, inhibiting mitochondrial respiratory function and mediating apoptosis through the mitochondrial pathway. ART also inhibited proliferation and activated the apoptosis of MMQ cells in vivo.

CONCLUSIONS

ART has a strong inhibitory effect on prolactinoma both in vitro and in vivo, and its effects rely on high MMP to inhibit mitochondrial metabolism and induce apoptosis. Our results provide evidence for ART as a candidate drug for the treatment of prolactinoma.

Secretion and Function of Pituitary Prolactin in Evolutionary Perspective

The hypothalamo-pituitary system developed in early vertebrates. Prolactin is an ancient vertebrate hormone released from the pituitary that exerts particularly diverse functions. The purpose of the review is to take a comparative approach in the description of prolactin, its secretion from pituitary lactotrophs, and hormonal functions. Since the reproductive and osmoregulatory roles of prolactin are best established in a variety of species, these functions are the primary subjects of discussion. Different types of prolactin and prolactin receptors developed during vertebrate evolution, which will be described in this review. The signal transduction of prolactin receptors is well conserved among vertebrates enabling us to describe the whole subphylum. Then, the review focuses on the regulation of prolactin release in mammals as we have the most knowledge on this class of vertebrates. Prolactin secretion in response to different reproductive stimuli, such as estrogen-induced release, mating, pregnancy and suckling is detailed. Reproduction in birds is different from that in mammals in several aspects. Prolactin is released during incubation in avian species whose regulation and functional significance are discussed. Little information is available on prolactin in reptiles and amphibians; therefore, they are mentioned only in specific cases to explain certain evolutionary aspects. In turn, the osmoregulatory function of prolactin is well established in fish. The different types of pituitary prolactin in fish play particularly important roles in the adaptation of eutherian species to fresh water environments. To achieve this function, prolactin is released from lactotrophs in hyposmolarity, as they are directly osmosensitive in fish. In turn, the released prolactin acts on branchial epithelia, especially ionocytes of the gill to retain salt and excrete water. This review will highlight the points where comparative data give new ideas or suggest new approaches for investigation in other taxa.