Role of thyrotropin-releasing hormone in prolactin-producing cell models

Relationship between maternal biological features, environmental factors, and newborn neuromotor development associated with visual fixation abilities

Newborn visual fixation abilities predict future cognitive, perceptive, and motor skills. However, little is known about the factors associated with the newborn visual fixation, which is an indicator of neurocognitive abilities. We analyzed maternal biological and environmental characteristics associated with fine motor skills (visual tracking) in 1 month old infants. Fifty-one infants were tested on visual tracking tasks (Infant Visuomotor Behavior Assessment Scale/ Guide for the Assessment of Visual Ability in Infants) and classified according to visual conducts scores. Differences between groups were compared considering motor development (Alberta Infant Motor Scale) maternal mental health (Edinburgh Postnatal Depression Scale and Hamilton Anxiety Scale); home environment (Affordances in the Home Environment for Development Scale); maternal care (Coding Interactive Behavior); breastmilk composition (total fatty acids, proteins, and cortisol); and maternal metabolic profile (serum hormones and interleukins). Mothers of infants with lower visual fixation scores had higher levels of protein in breastmilk at 3 months. Mothers of infants with better visual conduct scores had higher serum levels of T4 (at 1 month) and prolactin (at 3 months). There were no associations between visual ability and motor development, home environment, or maternal care. Early newborn neuromotor development, especially visual and fine motor skills, is associated with maternal biological characteristics (metabolic factors and breastmilk composition), highlighting the importance of early detection of maternal metabolic changes for the healthy neurodevelopment of newborns.

A Century of Prolactin: Emerging Perspectives as a Metabolic Regulator

Prolactin, a hormone that has been studied for almost a century, has evolved from a reproductive regulator to a key player in metabolic health. Initially identified for its lactogenic role, the impact of prolactin on glucose and lipid metabolism became evident in the 1970s, leading to a paradigm shift in our understanding. Deviations in prolactin levels, including hyperprolactinaemia and hypoprolactinaemia, have been associated with adverse effects on glucose and lipid metabolism. Mechanistically, prolactin regulates metabolic homoeostasis by maintaining islet abundance, regulating the hypothalamic energy regulatory centre, balancing adipose tissue expansion, and regulating hepatic metabolism. Given the widespread use of pharmaceutical agents that affect prolactin levels, it is important to examine prolactin-related metabolic effects. Recently, a profound exploration of the intricate metabolic role of prolactin has been conducted, encompassing its rhythm-dependent regulatory influence on metabolism and its correlation with cognitive impairment associated with metabolic diseases. In this review, we highlight the role of prolactin as a metabolic regulator, summarise its metabolic effects, and discuss topics related to the association between prolactin and metabolic comorbidities.

Neuregulin 1 mitigated prolactin deficiency through enhancing TRPM8 signaling under the influence of melatonin in senescent pituitary lactotrophs

The age-related alterations in pituitary function, including changes in prolactin (PRL) production contributes to the systemic susceptibility to age-related diseases. Our previous research has shown the involvement of Nrg1 in regulating the expression and secretion of PRL. However, the precise role of Nrg1 in mitigating the senescence of pituitary lactotrophs and the underlying mechanisms are yet to be comprehended. Here, data from the GEPIA database was used to evaluate the association between transient receptor potential cation channel subfamily M member 8 (TRPM8) and PRL in normal human pituitary tissues, followed by immunofluorescence verification using a human pituitary tissue microarray. TRPM8 levels showed a significant positive association with PRL expression in normal human pituitary tissues, and both TRPM8 and PRL levels declined during aging, suggesting that TRPM8 may regulate pituitary aging by affecting PRL production. It was also found that treatment with exogenous neuregulin 1 (Nrg1) markedly delayed the senescence of GH3 cells (rat lactotroph cell line) generated by D-galactose (D-gal). In addition, melatonin reduced the levels of senescence-related markers in senescent pituitary cells by promoting Nrg1 / ErbB4 signaling, stimulating PRL expression and secretion. Further investigation showed that Nrg1 attenuated senescence in pituitary cells by increasing TRPM8 expression. Downregulation of TRPM8 activation eliminated Nrg1-mediated amelioration of pituitary cell senescence. These findings demonstrate the critical function of Nrg1 / ErbB signaling in delaying pituitary lactotroph cell senescence and enhancing PRL production via promoting TRPM8 expression under the modulation of melatonin.

Current evaluation of amenorrhea: a committee opinion

The purpose of this American Society for Reproductive Medicine Practice Committee Opinion is to provide clinicians with principles and strategies for the diagnostic evaluation of patients presenting with primary or secondary amenorrhea. This revised document replaces the Practice Committee Document titled "Current evaluation of amenorrhea," last published in 2008 (Fertil Steril 2008;90:S219-25).

Bromocriptine sensitivity in bromocriptine-induced drug-resistant prolactinomas is restored by inhibiting FGF19/FGFR4/PRL

PURPOSE

At present, various treatment strategies are available for pituitary adenomas, including medications, surgery and radiation. The guidelines indicate that pharmacological treatments, such as bromocriptine (BRC) and cabergoline (CAB), are important treatments for prolactinomas, but drug resistance is an urgent problem that needs to be addressed. Therefore, exploring the mechanism of drug resistance in prolactinomas is beneficial for clinical treatment.

METHODS

In our research, BRC-induced drug-resistant cells were established. Previous RNA sequencing data and an online database were used for preliminary screening of resistance-related genes. Cell survival was determined by Cell Counting Kit-8 (CCK-8) assay, colony formation assays and flow cytometry. Quantitative real-time polymerase chain reaction (qRT‒PCR), western blotting, immunohistochemistry, immunofluorescence and Co-immunoprecipitation (Co-IP) were used to assess the molecular changes and regulation. The therapeutic efficacy of BRC and FGFR4 inhibitor fisogatinib (FISO) combination was evaluated in drug-resistant cells and xenograft tumors in nude mice.

RESULTS

Consistent with the preliminary results of RNA sequencing and database screening, fibroblast growth factor 19 (FGF19) expression was elevated in drug-resistant cells and tumor samples. With FGF19 silencing, drug-resistant cells exhibited increased sensitivity to BRC and decreased intracellular phosphorylated fibroblast growth factor receptor 4 (FGFR4) levels. After confirming that FGF19 binds to FGFR4 in prolactinoma cells, we found that FGF19/FGFR4 regulated prolactin (PRL) synthesis through the ERK1/2 and JNK signaling pathways. Regarding the effect of targeting FGF19/FGFR4 on BRC efficacy, FISO and BRC synergistically inhibited the growth of tumor cells, promoted apoptosis and reduced PRL levels.

CONCLUSION

Overall, our study revealed FGF19/FGFR4 as a new mechanism involved in the drug resistance of prolactinomas, and combination therapy targeting the pathway could be helpful for the treatment of BRC-induced drug-resistant prolactinomas.

Parallel expression patterns of NR4A nuclear receptor family genes in the pituitary gland of proestrus rats

The NR4A nuclear receptor family (NR4As), encompassing NR4A1, NR4A2, and NR4A3, exerts pivotal roles in cellular processes through intricate expression patterns and interactions. Despite the influence of some NR4As on anterior pituitary functions regulated by the hypothalamus, their physiological expression patterns remain unclear. In our prior work, we demonstrated the specific upregulation of NR4A3 in the rat anterior pituitary gland during the proestrus afternoon, coinciding with a gonadotropin surge. In this study, we investigated changes in pituitary Nr4a gene expression throughout the estrous cycle in rats and a gonadotropin surge-induced model. Nr4a1 and Nr4a2 gene expression significantly increased during proestrus, aligning with previous observations for Nr4a3. Furthermore, prolactin gene expression increased sequentially with rising Nr4a gene expression, while thyroid-stimulating hormone beta gene expression remained stable. Immunohistochemistry revealed a widespread and differential distribution of NR4A proteins in the anterior pituitary, with NR4A1 and NR4A3 being particularly abundant in thyrotrophs, and NR4A2 in gonadotrophs. In estrogen-treated ovariectomized rats, elevated luteinizing hormone secretion corresponded to markedly upregulated expression of Nr4a1, Nr4a2, and Nr4a3. In gonadotroph and somatomammotroph cell lines, gonadotropin- and thyrotropin-releasing hormones transiently and dose-dependently increased the expression of Nr4a genes. These findings suggest that hypothalamic hormone secretion during proestrus may induce the parallel expression of pituitary Nr4a genes, potentially influencing the pituitary gene expression program related to endocrine functions before and after ovulation.

Minerals and the Menstrual Cycle: Impacts on Ovulation and Endometrial Health

The role of minerals in female fertility, particularly in relation to the menstrual cycle, presents a complex area of study that underscores the interplay between nutrition and reproductive health. This narrative review aims to elucidate the impacts of minerals on key aspects of the reproductive system: hormonal regulation, ovarian function and ovulation, endometrial health, and oxidative stress. Despite the attention given to specific micronutrients in relation to reproductive disorders, there is a noticeable absence of a comprehensive review focusing on the impact of minerals throughout the menstrual cycle on female fertility. This narrative review aims to address this gap by examining the influence of minerals on reproductive health. Each mineral's contribution is explored in detail to provide a clearer picture of its importance in supporting female fertility. This comprehensive analysis not only enhances our knowledge of reproductive health but also offers clinicians valuable insights into potential therapeutic strategies and the recommended intake of minerals to promote female reproductive well-being, considering the menstrual cycle. This review stands as the first to offer such a detailed examination of minerals in the context of the menstrual cycle, aiming to elevate the understanding of their critical role in female fertility and reproductive health.

Regulation of phosphosignaling pathways involved in transcription of cell cycle target genes by TRH receptor activation in GH1 cells

Thyrotropin-releasing hormone (TRH) is known to activate several cellular signaling pathway, but the activation of the TRH receptor (TRH-R) has not been reported to regulate gene transcription. The aim of this study was to identify phosphosignaling pathways and phosphoprotein complexes associated with gene transcription in GH1 pituitary cells treated with TRH or its analog, taltirelin (TAL), using label-free bottom-up mass spectrometry-based proteomics. Our detailed analysis provided insight into the mechanism through which TRH-R activation may regulate the transcription of genes related to the cell cycle and proliferation. It involves control of the signaling pathways for β-catenin/Tcf, Notch/RBPJ, p53/p21/Rbl2/E2F, Myc, and YY1/Rb1/E2F through phosphorylation and dephosphorylation of their key components. In many instances, the phosphorylation patterns of differentially phosphorylated phosphoproteins in TRH- or TAL-treated cells were identical or displayed a similar trend in phosphorylation. However, some phosphoproteins, especially components of the Wnt/β-catenin/Tcf and YY1/Rb1/E2F pathways, exhibited different phosphorylation patterns in TRH- and TAL-treated cells. This supports the notion that TRH and TAL may act, at least in part, as biased agonists. Additionally, the deficiency of β-arrestin2 resulted in a reduced number of alterations in phosphorylation, highlighting the critical role of β-arrestin2 in the signal transduction from TRH-R in the plasma membrane to transcription factors in the nucleus.

TRH Regulates the Synthesis and Secretion of Prolactin in Rats with Adenohypophysis through the Differential Expression of miR-126a-5p

Prolactin (PRL) is an important hormone that is secreted by the pituitary gland and plays an important role in the growth, development and reproduction of organisms. Thyrotropin-releasing hormone (TRH) is a common prolactin-releasing factor that regulates the synthesis and secretion of prolactin. In recent studies, microRNAs (miRNAs) have been found to play a key role in the regulation of pituitary hormones. However, there is a lack of systematic studies on the regulatory role that TRH plays on the pituitary transcriptome, and the role of miRNAs in the regulation of PRL synthesis and secretion by TRH lacks experimental evidence. In this study, we first investigated the changes in PRL synthesis and secretion in the rat pituitary gland after TRH administration. The results of transcriptomic analysis after TRH treatment showed that 102 genes, including those that encode Nppc, Fgf1, PRL, Cd63, Npw, and Il23a, were upregulated, and 488 genes, including those that encode Lats1, Cacna2d1, Top2a, and Tfap2a, were downregulated. These genes are all involved in the regulation of prolactin expression. The gene expression of miR-126a-5p, which regulates the level of PRL in the pituitary gland, was screened by analysis prediction software and by a dual luciferase reporter system. The data presented in this study demonstrate that TRH can regulate prolactin synthesis and secretion through miR-126a-5p, thereby improving our understanding of the molecular mechanism of TRH-mediated PRL secretion and providing a theoretical basis for the role of miRNAs in regulating the secretion of pituitary hormones.

Biochemical and physiological insights into TRH receptor-mediated signaling

Thyrotropin-releasing hormone (TRH) is an important endocrine agent that regulates the function of cells in the anterior pituitary and the central and peripheral nervous systems. By controlling the synthesis and release of thyroid hormones, TRH affects many physiological functions, including energy homeostasis. This hormone exerts its effects through G protein-coupled TRH receptors, which signal primarily through G_q/11 but may also utilize other G protein classes under certain conditions. Because of the potential therapeutic benefit, considerable attention has been devoted to the synthesis of new TRH analogs that may have some advantageous properties compared with TRH. In this context, it may be interesting to consider the phenomenon of biased agonism and signaling at the TRH receptor. This possibility is supported by some recent findings. Although knowledge about the mechanisms of TRH receptor-mediated signaling has increased steadily over the past decades, there are still many unanswered questions, particularly about the molecular details of post-receptor signaling. In this review, we summarize what has been learned to date about TRH receptor-mediated signaling, including some previously undiscussed information, and point to future directions in TRH research that may offer new insights into the molecular mechanisms of TRH receptor-triggered actions and possible ways to modulate TRH receptor-mediated signaling.

A single nucleotide polymorphism of the thyrotropin releasing hormone degrading ectoenzyme (TRHDE) gene is associated with post-partum anestrus in Murrah buffalo

Thyrotropin releasing hormone degrading enzyme (TRHDE) gene is implicated in Thyrotropin releasing hormone (TRH) mediated prolactin secretion. It has been shown that the prolactin secretion alters the Gonadotropin-releasinghormone(GnRH) mediated estrous cycle. Therefore, TRHDE may also regulate postpartum anestrus. Earlier studies reported the role of non-synonymous single nucleotide polymorphism (SNPs) in various pathophysiological conditions by altering the structure and function of the proteins. Hence, in the present study, we identified SNPs in the putative promoter, first exon, middle exon and 3'-UTR containing the last exon of TRHDE gene and determined their association with postpartum anestrus (PPA) in Murrah buffaloes. We found one non synonymous SNP (G > C at 118095875 bp on chromosome 4) in the first exon of TRHDE and performed its association analysis in a population sample of 50 extreme PPA (residual PPAI: 123.06 ± 12.98 days) and 50 normal (residual PPAI: -80.46 ± 3.19 days) buffaloes. The residual PPAI value was the observed PPAI adjusted for the effect of 38 non-genetic factors. The analysis showed a significant (P < 0.004167) association of this SNP with PPA in buffaloes. Molecular dynamics simulations (MDS) also supported that the C allele altering Glutamine to Histidine at the amino acid 148 of TRHDE could enhance the stability and rigidity of TRHDE protein, which may lower its activity, increase TRH and prolactin, and reduce GnRH in PPA buffaloes. The MDS analysis further strengthens the association of the SNP (G > C) in the TRHDE gene with PPA condition in Murrah buffaloes. However, further investigation is needed to prove the MDS observations.

Recent findings on hyperprolactinemia and its pathological implications: a literature review

The prolactin hormone (PRL) is often secreted by lactotrophic cells of the anterior pituitary and has been shown to play a role in various biological processes, including breast feeding and reproduction. The predominant form of this hormone is the 23 kDa form and acts through its receptor (PRLR) on the cell membrane. This receptor is a member of the superfamily of hematopoietic/cytokine receptors. PRL also has a 16 kDa subunit with anti-angiogenic, proapoptotic, and anti-inflammatory effects which is produced by the proteolytic breakdown of this hormone under oxidative stress. Although the common side effects of hyperprolactinemia are exerted on the reproductive system, new studies have shown that hyperprolactinemia has a wide variety of effects, including playing a role in the development of autoimmune diseases and increasing the risk of cardiovascular disease, peripartum cardiomyopathy, and diabetes among others. The range of PRL functions is increasing with the discovery of multiple sites of PRL secretion as well as PRLR expression in various tissues. This review summarizes current knowledge of the biology of PRL and its receptor, as well as the role of PRL in human pathophysiology.

β-Arrestin2 Is Critically Involved in the Differential Regulation of Phosphosignaling Pathways by Thyrotropin-Releasing Hormone and Taltirelin

In recent years, thyrotropin-releasing hormone (TRH) and its analogs, including taltirelin (TAL), have demonstrated a range of effects on the central nervous system that represent potential therapeutic agents for the treatment of various neurological disorders, including neurodegenerative diseases. However, the molecular mechanisms of their actions remain poorly understood. In this study, we investigated phosphosignaling dynamics in pituitary GH1 cells affected by TRH and TAL and the putative role of β-arrestin2 in mediating these effects. Our results revealed widespread alterations in many phosphosignaling pathways involving signal transduction via small GTPases, MAP kinases, Ser/Thr- and Tyr-protein kinases, Wnt/β-catenin, and members of the Hippo pathway. The differential TRH- or TAL-induced phosphorylation of numerous proteins suggests that these ligands exhibit some degree of biased agonism at the TRH receptor. The different phosphorylation patterns induced by TRH or TAL in β-arrestin2-deficient cells suggest that the β-arrestin2 scaffold is a key factor determining phosphorylation events after TRH receptor activation. Our results suggest that compounds that modulate kinase and phosphatase activity can be considered as additional adjuvants to enhance the potential therapeutic value of TRH or TAL.

A New Perspective on Thyroid Hormones: Crosstalk with Reproductive Hormones in Females

Accumulating evidence has shown that thyroid hormones (THs) are vital for female reproductive system homeostasis. THs regulate the reproductive functions through thyroid hormone receptors (THRs)-mediated genomic- and integrin-receptor-associated nongenomic mechanisms, depending on TH ligand status and DNA level, as well as transcription and extra-nuclear signaling transduction activities. These processes involve the binding of THs to intracellular THRs and steroid hormone receptors or membrane receptors and the recruitment of hormone-response elements. In addition, THs and other reproductive hormones can activate common signaling pathways due to their structural similarity and shared DNA consensus sequences among thyroid, peptide, and protein hormones and their receptors, thus constituting a complex and reciprocal interaction network. Moreover, THs not only indirectly affect the synthesis, secretion, and action of reproductive hormones, but are also regulated by these hormones at the same time. This crosstalk may be one of the pivotal factors regulating female reproductive behavior and hormone-related diseases, including tumors. Elucidating the interaction mechanism among the aforementioned hormones will contribute to apprehending the etiology of female reproductive diseases, shedding new light on the treatment of gynecological disorders.

Nesfatin-1 and Nesfatin-1-like peptide suppress basal and TRH-Induced expression of prolactin and prolactin regulatory element-binding protein mRNAs in rat GH3 somatolactotrophs

Prolactin (PRL), mainly synthesized and secreted by the lactotrophs and somatolactotrophs of the anterior pituitary, is a pleiotropic hormone that regulates lactation. In the last decade, nesfatin-1 (NESF) and NESF-like peptide (NLP), encoded in nucleobindin 1 and 2 (NUCB1 and NUCB2), respectively, were characterized as metabolic factors with a potential role in the control of pituitary hormones. We hypothesized that NUCBs and their encoded peptides (NESF and NLP) suppress PRL transcription in the pituitary. The main objective of this research was to determine whether exogenous NESF and NLP, and/or endogenous NUCB1 and NUCB2 regulate the expression of prl and preb mRNAs. Using immortalized rat somatolactotrophs (GH3 cells), dose-response studies were performed to test whether NESF and NLP affect prl and preb. Moreover, the ability of these peptides to modulate the effects of the PRL stimulator thyrotropin releasing hormone (TRH) was studied. Besides, the effects of siRNA-mediated knockdown of endogenous NUCBs on prl and preb mRNAs were determined. NESF and NLP reduced the transcription of prl and preb in GH3 cells. Both NESF and NLP also prevented the stimulatory effects of TRH prl and preb expression. The knockdown of endogenous NUCB1 attenuates both basal prl and TRH-induced expression of prl and preb, while the silencing of NUCBs did not affect the actions of exogenous NESF or NLP. Overall, this work reveals that NUCBs and encoded-peptides are novel regulators of PRL. Future research should test whether the effects observed here in GH3 cells are preserved both in vivo and at the post-transcriptional level.

Natriuretic Peptide Expression and Function in GH3 Somatolactotropes and Feline Somatotrope Pituitary Tumours

Patients harbouring mutations in genes encoding C-type natriuretic peptide (CNP; NPPC) or its receptor guanylyl cyclase B (GC-B, NPR2) suffer from severe growth phenotypes; loss-of-function mutations cause achondroplasia, whereas gain-of-function mutations cause skeletal overgrowth. Although most of the effects of CNP/GC-B on growth are mediated directly on bone, evidence suggests the natriuretic peptides may also affect anterior pituitary control of growth. Our previous studies described the expression of NPPC and NPR2 in a range of human pituitary tumours, normal human pituitary, and normal fetal human pituitary. However, the natriuretic peptide system in somatotropes has not been extensively explored. Here, we examine the expression and function of the CNP/GC-B system in rat GH3 somatolactotrope cell line and pituitary tumours from a cohort of feline hypersomatotropism (HST; acromegaly) patients. Using multiplex RT-qPCR, all three natriuretic peptides and their receptors were detected in GH3 cells. The expression of Nppc was significantly enhanced following treatment with either 100 nM TRH or 10 µM forskolin, yet only Npr1 expression was sensitive to forskolin stimulation; the effects of forskolin and TRH on Nppc expression were PKA- and MAPK-dependent, respectively. CNP stimulation of GH3 somatolactotropes significantly inhibited Esr1, Insr and Lepr expression, but dramatically enhanced cFos expression at the same time point. Oestrogen treatment significantly enhanced expression of Nppa, Nppc, Npr1, and Npr2 in GH3 somatolactotropes, but inhibited CNP-stimulated cGMP accumulation. Finally, transcripts for all three natriuretic peptides and receptors were expressed in feline pituitary tumours from patients with HST. NPPC expression was negatively correlated with pituitary tumour volume and SSTR5 expression, but positively correlated with D2R and GHR expression. Collectively, these data provide mechanisms that control expression and function of CNP in somatolactotrope cells, and identify putative transcriptional targets for CNP action in somatotropes.

Reduced dopaminergic tone during lactation is permissive to the hypothalamic stimulus for suckling-induced prolactin release

Dopamine from tuberoinfundibular dopaminergic (TIDA) neurones tonically inhibits prolactin (PRL) secretion. Lactational hyperprolactinaemia is associated with a reduced activity of TIDA neurones. However, it remains controversial whether the suckling-induced PRL surge is driven by an additional decrease in dopamine release or by stimulation from a PRL-releasing factor. In the present study, we further investigated the role of dopamine in the PRL response to suckling. Non-lactating (N-Lac), lactating 4 hour apart from pups (Lac), Lac with pups return and suckling (Lac+S), and post-lactating (P-Lac) rats were evaluated. PRL levels were elevated in Lac rats and increased linearly within 30 minutes of suckling in Lac+S rats. During the rise in PRL levels, dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the median eminence (ME) and neurointermediate lobe of the pituitary did not differ between Lac+S and Lac rats. However, dopamine and DOPAC were equally decreased in Lac and Lac+S compared to N-Lac and P-Lac rats. Suckling, in turn, reduced phosphorylation of tyrosine hydroxylase in the ME of Lac+S. Domperidone and bromocriptine were used to block and activate pituitary dopamine D2 receptors, respectively. Domperidone increased PRL secretion in both N-Lac and Lac rats, and suckling elicited a robust surge of PRL over the high basal levels in domperidone-treated Lac+S rats. Conversely, bromocriptine blocked the PRL response to suckling. The findings obtained in the present study provide evidence that dopamine synthesis and release are tonically reduced during lactation, whereas dopamine is still functional with respect to inhibiting PRL secretion. However, there appears to be no further reduction in dopamine release associated with the suckling-induced rise in PRL. Instead, the lower dopaminergic tone during lactation appears to be required to sensitise the pituitary to a suckling-induced PRL-releasing factor.

The role of neurokinin A and its receptor in the regulation of prolactin secretion by the anterior pituitary of cyclic pigs

In pigs, plasma prolactin concentration markedly changes during the oestrous cycle and the regulation of its secretion is very complex. The contribution of neurokinins in this process has not been sufficiently delineated. The aim of the study was to examine the effects of neurokinin A (NKA) on prolactin synthesis and secretion in cyclic gilts. The expression of NKA precursor (Ppta) and receptor (Tacr2) genes as well as NKA and TACR proteins content in the porcine pituitaries (days 2-3, 9-10, 12-13, 15-16 and 19-20 of the cycle) was determined. Furthermore, the in vitro influence of NKA on the expression of prolactin (Prl), dopamine receptor (D2r), TRH receptor (Trhr) genes and prolactin secretion by the porcine pituitary cells (days 9-10, 15-16 and 19-20 of the cycle) was assessed. The expression of Ppta and Tacr2 as well as NKA and TACR proteins in the pituitary tissue has been changing throughout the oestrous cycle. NKA affected in vitro the expression of studied genes and prolactin secretion depending on the stage of the cycle, dose of NKA and/or duration of the cell incubation. Altogether, the study indicates that NKA is engaged in the modulation of prolactin secretion in the pig during the oestrous cycle.

A Retrospective Observational Study of the Neuroendocrine Stress Response in Patients Undergoing Endoscopic Transsphenoidal Surgery for Removal of Pituitary Adenomas: Total Intravenous Versus Balanced Anesthesia

BACKGROUND

Anesthetic technique affects the neuroendocrine stress response to surgery. In this retrospective study, we compared the neuroendocrine stress response in patients undergoing endoscopic transsphenoidal pituitary adenoma surgery (ETSPAS) with total intravenous anesthesia (TIVA) with propofol-remifentanil or balanced anesthesia (BAL) with sevoflurane-remifentanil.

MATERIALS AND METHODS

Eighty-nine patients undergoing ETSPAS were anesthetized with either propofol-remifentanil (TIVA group, n=62) or sevoflurane-remifentanil (BAL group, n=27). Data were retrospectively collected regarding preoperative and immediate postoperative serum levels of adrenocorticotropic hormone (ACTH) and cortisol (primary outcome measures), as well as other pituitary hormones and their target organ hormones (secondary outcome measures).

RESULTS

There were no significant differences in preoperative pituitary hormone levels between the 2 groups. The immediate postoperative ACTH (89.5 [62.1 to 162.6] vs. 256.0 [92.0 to 570.7] pg/mL; P<0.001) level was lower in the TIVA group than in the BAL group, whereas immediate postoperative cortisol levels were similar between the 2 groups. The immediate postoperative thyroid-stimulating hormone (1.85 [1.21 to 2.98] vs. 1.21 [0.44 to 1.71] μIU/mL; P=0.003), triiodothyronine (91.0 [82.0 to 103.0] vs. 69.1 [64.6 to 76.2] ng/dL; P<0.001), luteinizing hormone (2.2 [1.2 to 4.0] vs. 1.0 [0.5 to 2.3] mIU/mL; P=0.005), and prolactin (22.6±15.8 vs. 12.8±10.2 ng/mL; P=0.005) levels were higher in the TIVA group compared with the BAL group. In both groups, none of the patients who had sufficient preoperative ACTH without hydrocortisone supplementation (n=15) showed hypocortisolism in the immediate postoperative measurement.

CONCLUSIONS

Compared with BAL, TIVA resulted in reduced release of ACTH and increased release of thyroid-stimulating hormone, triiodothyronine, luteinizing hormone, and prolactin in patients undergoing ETSPAS.

Forms of selenium in vitamin-mineral mixes differentially affect the expression of genes responsible for prolactin, ACTH, and α-MSH synthesis and mitochondrial dysfunction in pituitaries of steers grazing endophyte-infected tall fescue

The goal of this study was to test the hypothesis that sodium selenite (inorganic Se, ISe), SEL-PLEX (organic forms of Se, OSe), vs. a 1:1 blend (MIX) of ISe and OSe in a basal vitamin-mineral (VM) mix would differentially alter pituitary transcriptome profiles in growing beef steers grazing an endophyte-infected tall fescue (E+) pasture. Predominately Angus steers (BW = 183 ± 34 kg) were randomly selected from fall-calving cows grazing E+ pasture and consuming VM mixes that contained 35 ppm Se as ISe, OSe, or MIX forms. Steers were weaned, depleted of Se for 98 d, and subjected to summer-long common grazing of a 10.1 ha E+ pasture containing 0.51 ppm ergot alkaloids. Steers were assigned (n = 8 per treatment) to the same Se-form treatments on which they were raised. Selenium treatments were administered by daily top-dressing 85 g of VM mix onto 0.23 kg soyhulls, using in-pasture Calan gates. As previously reported, serum prolactin was greater for MIX (52%) and OSe (59%) steers vs. ISe. Pituitaries were collected at slaughter and changes in global and selected mRNA expression patterns determined by microarray and real-time reverse transcription PCR analyses, respectively. The effects of Se treatment on relative gene expression were subjected to one-way ANOVA. The form of Se affected the expression of 542 annotated genes (P < 0.005). Integrated pathway analysis found a canonical pathway network between prolactin and pro-opiomelanocortin (POMC)/ACTH/α-melanocyte-stimulating hormone (α-MSH) synthesis-related proteins and that mitochondrial dysfunction was a top-affected canonical pathway. Targeted reverse transcription-PCR analysis found that the relative abundance of mRNA encoding prolactin and POMC/ACTH/α-MSH synthesis-related proteins was affected (P < 0.05) by the form of Se, as were (P ≤ 0.05) mitochondrial dysfunction-related proteins (CYB5A, FURIN, GPX4, and PSENEN). OSe steers appeared to have a greater prolactin synthesis capacity (more PRL mRNA) vs. ISe steers through decreased dopamine type two receptor signaling (more DRD2 mRNA), whereas MIX steers had a greater prolactin synthesis capacity (more PRL mRNA) and release potential by increasing thyrotropin-releasing hormone concentrations (less TRH receptor mRNA) than ISe steers. OSe steers also had a greater ACTH and α-MSH synthesis potential (more POMC, PCSK2, CPE, and PAM mRNA) than ISe steers. We conclude that form of Se in VM mixes altered expression of genes responsible for prolactin and POMC/ACTH/α-MSH synthesis, and mitochondrial function, in pituitaries of growing beef steers subjected to summer-long grazing an E+ pasture.

Multiple signaling pathways convey central and peripheral signals to regulate pituitary function: Lessons from human and non-human primate models

The anterior pituitary gland is a key organ involved in the control of multiple physiological functions including growth, reproduction, metabolism and stress. These functions are controlled by five distinct hormone-producing pituitary cell types that produce growth hormone (somatotropes), prolactin (lactotropes), adrenocorticotropin (corticotropes), thyrotropin (thyrotropes) and follicle stimulating hormone/luteinizing hormone (gonadotropes). Classically, the synthesis and release of pituitary hormones was thought to be primarily regulated by central (neuroendocrine) signals. However, it is now becoming apparent that factors produced by pituitary hormone targets (endocrine and non-endocrine organs) can feedback directly to the pituitary to adjust pituitary hormone synthesis and release. Therefore, pituitary cells serve as sensors to integrate central and peripheral signals in order to fine-tune whole-body homeostasis, although it is clear that pituitary cell regulation is species-, age- and sex-dependent. The purpose of this review is to provide a comprehensive, general overview of our current knowledge of both central and peripheral regulators of pituitary cell function and associated intracellular mechanisms, focusing on human and non-human primates.

From Consternation to Revelation: Discovery of a Role for IGSF1 in Pituitary Control of Thyroid Function

Immunoglobulin superfamily, member 1 (IGSF1) is a transmembrane glycoprotein highly expressed in the mammalian pituitary gland. Shortly after its discovery in 1998, the protein was proposed to function as a coreceptor for inhibins (and was even temporarily renamed inhibin binding protein). However, subsequent investigations, both in vitro and in vivo, failed to support a role for IGSF1 in inhibin action. Research on IGSF1 nearly ground to a halt until 2011, when next-generation sequencing identified mutations in the X-linked IGSF1 gene in boys and men with congenital central hypothyroidism. IGSF1 was localized to thyrotrope cells, implicating the protein in pituitary control of the thyroid. Investigations in two Igsf1 knockout mouse models converged to show that IGSF1 deficiency leads to reduced expression of the receptor for thyrotropin-releasing hormone (TRH) and impaired TRH stimulation of thyrotropin secretion, providing a candidate mechanism for the central hypothyroidism observed in patients. Nevertheless, the normal functions of IGSF1 in thyrotropes and other cells remain unresolved. Moreover, IGSF1 mutations are also commonly associated with other clinical phenotypes, including prolactin and growth hormone dysregulation, and macroorchidism. How the loss of IGSF1 produces these characteristics is unknown. Although early studies of IGSF1 ran into roadblocks and blind alleys, armed with the results of detailed clinical investigations, powerful mouse models, and new reagents, the field is now poised to discover IGSF1’s function in endocrine tissues, including the pituitary and testes.

The relationship between serum levels of prolactin and growth hormone in the early postnatal period

BackgroundIn the neonatal period, the pituitary hormones including prolactin (PRL) and human growth hormone (hGH) are secreted in high amounts due to immature feedback mechanisms. As both hormones are secreted in part by the same somatomammotrophic cells, we investigated their relationship in newborns with respect to sex, gestational week, method of delivery, and anthropometric data.MethodsThe serum levels of PRL and hGH were measured in blood drawn from 225 newborns. The newborn data were extracted from medical records.ResultsA positive correlation was found between log-transformations of PRL and hGH (r=0.17; P=0.01; n=225), with a stronger correlation in newborns whose blood samples were taken more than 2 days after birth (r=0.42; P<0.001; n=130). Log-transformations of the PRL/hGH ratio demonstrated a positive correlation with the gestational week (r=0.39; P<0.001; n=200). Multiple regression analysis showed that 15% of the variance in the logarithm of this ratio is attributed to the gestational week.ConclusionIn newborns, serum PRL and hGH levels show a positive correlation that can be explained by common regulatory factors or a drift phenomenon. A higher gestational week is associated with a higher PRL/hGH ratio. Further studies are needed to look for possible confounders and to determine the PRL-hGH relationship in different conditions.

Relationship between chronobiological thyrotropin and prolactin responses to protirelin (TRH) and suicidal behavior in depressed patients

BACKGROUND

So far, investigations of the relationships between suicidality and the activity of the thyrotropic and lactotropic axes are scarce and have yielded conflicting results.

METHODS

We studied the thyrotropin (TSH) and prolactin (PRL) responses to 0800h and 2300h protirelin (TRH) stimulation tests, carried out on the same day, in 122 euthyroid DSM-5 major depressed inpatients with suicidal behavior disorder (SBD) (either current [n=71], or in early remission [n=51]); and 50 healthy hospitalized controls.

RESULTS

Baseline TSH and PRL measurements did not differ across the 3 groups. In SBDs in early remission, the TSH and PRL responses to TRH tests (expressed as the maximum increment above baseline value after TRH [Δ]) were indistinguishable from controls. Current SBDs showed (1) lower 2300h-ΔTSH and lower ΔΔTSH values (differences between 2300h-ΔTSH and 0800h-ΔTSH) than controls and SBDs in early remission; and (2) lower baseline free thyroxine (FT_4B) levels than controls. In the current SBD group, ΔΔPRL values (differences between 2300h-ΔPRL and 0800h-ΔPRL) were correlated negatively with lethality. Moreover, in current SBDs (1) violent suicide attempters (n=15) showed lower FT_4B levels, lower TSH-TRH responses (both at 0800h and 2300h), and lower ΔΔTSH and ΔΔPRL values than controls, while (2) non-violent suicide attempters (n=56) showed lower ΔΔTSH values than controls and higher TSH-TRH responses (both at 0800h and 2300h) than violent suicide attempters.

CONCLUSIONS

Our results suggest that central TRH secretion is not altered in depressed patients with SBD in early remission. The findings that current SBDs exhibit both decreased FT_4B levels and decreased evening TSH responses (and consequently, decreased ΔΔTSH values) support the hypothesis that hypothalamic TRH drive is reduced-leading to an impaired TSH resynthesis in the pituitary during the day after the morning TRH challenge. In violent suicide attempters, the marked abnormalities of TRH test responses might indicate a greatest reduction in hypothalamic TRH drive. These results further strengthen the possibility that a deficit in central TRH function may play a key role in the pathogenesis of suicidal behavior.

Advances in TRH signaling

The activity of the hypothalamus-pituitary-thyroid axis (HPT) is coordinated by hypophysiotropic thyrotropin releasing hormone (TRH) neurons present in the paraventricular nucleus of the hypothalamus. Hypophysiotropic TRH neurons act as energy sensors. TRH controls the synthesis and release of thyrotropin, which activates the synthesis and secretion of thyroid hormones; in target tissues, transporters and deiodinases control their local availability. Thyroid hormones regulate many functions, including energy homeostasis. This review discusses recent evidence that covers several aspects of TRH role in HPT axis regulation. Knowledge about the mechanisms of TRH signaling has steadily increased. New transcription factors engaged in TRH gene expression have been identified, and advances made on how they interact with signaling pathways and define the dynamics of TRH neurons response to acute and/or long-term influences. Albeit yet incomplete, the relationship of TRH neurons activity with positive energy balance has emerged. The importance of tanycytes as a central relay for the feedback control of the axis, as well as for HPT responses to alterations in energy balance, and other stimuli has been reinforced. Finally, some studies have started to shed light on the interference of prenatal and postnatal stress and nutrition on HPT axis programing, which have confirmed the axis susceptibility to early insults.

Developmental and Functional Effects of Steroid Hormones on the Neuroendocrine Axis and Spinal Cord

This review highlights the principal effects of steroid hormones at central and peripheral levels in the neuroendocrine axis. The data discussed highlight the principal role of oestrogens and testosterone in hormonal programming in relation to sexual orientation, reproductive and metabolic programming, and the neuroendocrine mechanism involved in the development of polycystic ovary syndrome phenotype. Moreover, consistent with the wide range of processes in which steroid hormones take part, we discuss the protective effects of progesterone on neurodegenerative disease and the signalling mechanism involved in the genesis of oestrogen-induced pituitary prolactinomas.

Association Between Prolactin and Incidence of Cardiovascular Risk Factors in the Framingham Heart Study

BACKGROUND

Prolactin is an anterior pituitary hormone that may modulate the adverse effects of obesity. Prolactin has been associated with cardiovascular disease mortality, but less is known about whether prolactin predicts incidence of cardiovascular disease risk factors.

METHODS AND RESULTS

Our sample (n=3232, mean age 40.4 years, 52.1% women) was drawn from Framingham Heart Study participants who attended 2 examinations an average of 6.1 years apart. After excluding those with elevated prolactin (>30 mg/dL for women, >20 mg/dL for men), multivariable-adjusted regressions modeled the associations between baseline prolactin and changes in cardiovascular disease risk factors. Models were adjusted for age, sex, baseline value of the risk factor, smoking status, hormone replacement therapy, and menopausal status and additionally for body mass index. Mean prolactin levels were 11.9 mg/dL (SD 5.2) in women and 8.0 mg/dL (SD 2.9) in men. No associations were observed for change in weight, body composition, total cholesterol, triglycerides, or fasting glucose. In women, for example, for each 5-mg/dL increment in prolactin, odds of incident hypercholesterolemia were 1.06, which was not significant (95% CI 0.91-1.23, P=0.46). Some exceptions were of note. In women, for each 5-mg/dL increment in prolactin, we observed increased odds of low high-density lipoprotein cholesterol at follow-up (odds ratio 1.50, 95% CI 1.18-1.91, P=0.001) that persisted after adjustment for body mass index (P=0.001). In men, a 5-mg/dL increment in prolactin was associated with increased odds of incident hypertension (odds ratio 1.61, 95% CI 1.18-2.20 P=0.002) and incident diabetes (odds ratio 1.70, 95% CI 1.04-2.78, P=0.03).

CONCLUSIONS

Prolactin is not associated with a comprehensive panel of incident cardiovascular disease risk factors. Measurement of circulating prolactin levels in the community likely does not provide substantial insight into cardiometabolic risk.