Prolactin: structure, function, and regulation of secretion

Antipsychotic-induced hyperprolactinemia: Toxicologic mechanism and the increased breast cancer risk

Antipsychotic drugs are effective at improving both the positive and negative symptoms of schizophrenia as well as the manic phase of bipolar disorder. Whether an antipsychotic is termed typical or atypical is related to the xenobiotic's propensity to cause extrapyramidal side effects. However, with a few exceptions, drugs of both classes of antipsychotics are known to cause hyperprolactinemia. As many breast cancers are responsive to prolactin concentrations, the persistent increase in prolactin of the antipsychotics has implications for public health and carcinogenesis. The objective of this study was to review the extant literature on hyperprolactinemia due to antipsychotics, and to determine the risk imposed by those drugs on human breast cancer. A summary risk of breast cancer with use of any antipsychotic was found to be 1.19 (95 % confidence interval 1.10-1.30). When limiting usage of antipsychotics to 5 or more years, the summary risk increased to 1.26 (95 % confidence interval 1.12-1.43). And when limited to those studies who evaluated only those medications with the greatest increase in prolactin, the risk increased to 1.59 (95 % confidence interval 1.37-1.85). Given this increased risk of breast cancer, stronger warnings about this increased risk are warranted, and regular monitoring of prolactin levels and breast cancer screening should be part of the management plan for these patients.

Maternal dopamine agonist treatment before pregnancy reverses infertility and hyperprolactinemia in hCG-overexpressing mice through lactation: Evidence of generational effects

Dopamine agonists, such as cabergoline (Cab), have demonstrated efficacy in restoring reproductive function in cases of hyperprolactinemia and hormonal dysregulation. This study investigates the long-term consequences of maternal Cab treatment on the reproductive phenotype of the progeny in a female transgenic (TG) mouse model with hyperprolactinemia and infertility due to human chorionic gonadotropin (hCG) β-subunit overexpression. The TG females that received Cab between weeks 3-4 of life exhibited a reversion of hyperprolactinemia and infertility, whereas WT females retained their fertility. When TG-cab- or WT-Cab-treated females were crossed with WT or TG males, respectively, their female TG offspring showed a reversal of precocious puberty, regularization of estrous cycles, fertility, and prevention of hyperprolactinemia and prolactinomas. Despite the persistent high LH/hCG bioactivity, the normalization of prolactin levels led to a reduction in ovarian luteinization markers and progesterone levels. The TG female pups born to either WT-cab- or TG-cab-treated females exhibited a normalized phenotype, thus suggesting that the effects were indeed due to maternal Cab administration, and not to the transgene. Cross-fostering experiments showed that the long-lasting programming effect of maternal Cab on offspring occurred during lactation because the TG female pups from non-treated WT female/TG male pregnancies, but nursed by Cab-treated females, were free from the altered TG phenotype. These results suggest that Cab treatment before pregnancy may have a multigenerational effect on the hypothalamic-pituitary-gonadal axis of the offspring, mediated during lactation. This highlights potential implications for generational health and clinical practices regarding the use of dopamine agonists during lactation.

The contribution of prolactin in the occurrence of premature cardiovascular disease predominantly through modulating the inflammatory cascade

Cardiovascular disease, mainly coronary atherothrombosis, is an essential contributor to all-cause mortality, accounting for approximately 30% of all global deaths. Imbalances in hormone profiles may play a role in the evolution of atherothrombosis. In the last decade, our clinical research focused on the hormone prolactin (PRL) and its contribution to premature cardiovascular disease. In this narrative review, we aimed to give current insights into how PRL could modulate the inflammatory cascade within the microenvironment of the atherosclerotic plaque, which could lead to increased cardiovascular morbidity and mortality.

Do biological alterations precede the onset of psychosis? A systematic review and meta-analysis of immune, cardiometabolic, prolactin and HPA axis alterations in clinical high-risk for psychosis

First episode psychosis (FEP) individuals show biological abnormalities preceding antipsychotic treatment. However, it remains unclear whether such alterations are also present before the onset of psychosis. We aim to provide estimates of standardized mean differences for immune, cardiometabolic, prolactin, and HPA axis parameters in individuals at clinical high-risk for psychosis (CHR-P) compared to healthy controls (HC) and FEP individuals, and between CHR-P transitioning to psychosis (CHR-T) compared non-transitioning (CHR-NT). A multistep literature search was performed from database inception until September 25, 2023. PRISMA/MOOSE-compliant and pre-registered (PROSPERO: CRD42024507670) systematic review identified studies reporting on immune, cardiovascular or endocrine parameters in CHR-P samples compared with HC or FEP samples or comparing CHR-T vs CHR-NT. Inter-group differences in magnitude of effect were estimated using Hedges g and estimates were pooled using random-effects meta-analysis. Heterogeneity was high for most outcomes. 37 studies were included, total sample 2509 CHR-P, 710 FEP, and 1444 HC individuals. A statistically significant elevation of pro-inflammatory proteins was found among CHR-P compared with HC (k = 12; N = 1710; g = 0.16; p < 0.01) and FEP (k = 7; g = 0.15; p = 0.04) subjects. Interleukin-6 (IL-6) was increased in CHR-P compared to HC (k = 9; N = 1243; g = 0.54; p < 0.01), and interleukin-4 (IL-4) was increased in CHR-T compared with CHR-NT (k = 2; N = 318; g = 0.36; p < 0.01). CHR-P exhibited stronger cortisol awakening response than FEP subjects (k = 3; N = 173; g = 0.51; p = 0.01). CHR-P and FEP individuals did not show statistically significant differences in terms of prolactin levels. An inflammatory state (particularly marked by elevated IL-6 and IL-4 levels) and HPA axis alterations are present in CHR-P individuals.

Mammalian lactation as a framework for teaching development, physiology, and cell biology for social change

Mammalian lactation is a dynamic process that develops throughout the lifespan of an organism. Here we present a framework for a third semester core course in biology that centers course content on lactation allowing examination of the developmental process as a dynamic whole-body experience involving changes occurring at the molecular, cellular, and organ levels of organization. Inequitable economic, socio- and geopolitical systems structure social determinants of health, affecting rates of breastfeeding in human populations. By integrating content exploring the ways social and biological systems impact breastfeeding rates in human populations, students develop abilities to understand the relationship between science and society throughout the course, a critical core competency for engaging in social change. Importantly, they interrogate social systems while simultaneously learning about many canonical biological processes including how natural selection and constraint have shaped the anatomy, physiology, cell biology, and biochemistry of lactation, how proteins, lipids, and carbohydrates are synthesized, processed, and exported through the endomembrane system in eukaryotes, and how neuronal and hormonal feedback mechanisms regulate milk synthesis and secretion. The course is structured using a flipped-classroom design emphasizing revision and student-self assessment that supports development of biological knowledge, social responsibility, and metacognitive skills. Because mammalian lactation includes fascinating, nuanced, and complex components that cross interdisciplinary boundaries, it provides a wealth of opportunities for faculty to teach developmental biology for social change.

Somatic Activating ESR1 Mutation in an Aggressive Prolactinoma

CONTEXT AND OBJECTIVE

The genetic profile of prolactinomas remains poorly understood. Our objective is to identify somatic genetic alterations associated with prolactinomas and to report the identification of an activating ESR1 mutation (ESR1Y537S) in an aggressive prolactinoma.

SETTING

Brigham and Women's Hospital.

DESIGN

Massively parallel-sequencing panel (OncoPanel) was performed in a cohort of patients with prolactinomas to identify mutations and copy number variation.

RESULTS

Twenty subjects (mean age, 38.6 years; 12 women and 8 men) were included in this study. A somatic ESR1Y537S mutation was identified in an aggressive prolactinoma in a postmenopausal woman. No SF3B1 or other somatic mutations were identified. The median number of copy number variation events identified in our samples was 46; the prolactinoma with ESR1Y537S had the highest number with 233 events. In breast cancer, ESR1Y537S has been shown to activate estrogen receptor alpha independent of ligand binding. In patients with resistant breast cancer and ESR1Y537S, elacestrant, a second-line estrogen receptor degrader, improves progression-free survival. Therefore, given the lack of response to multimodality therapies, elacestrant was initiated in this patient after the third cycle of radiotherapy. Elacestrant, along with radiotherapy, controlled tumor growth and significantly reduced prolactin levels.

CONCLUSION

Molecular profiling allowed the identification of ESR1Y537S, in an aggressive prolactinoma. ESR1Y537S was not detected early in the course of the disease and is likely conferring tumor aggressiveness. This finding emphasizes the significance of estrogen receptor signaling in prolactinomas. It also allowed the use of targeted therapy with successful control of disease progression.

Simultaneous Detection of Prolactin and Growth Hormone Using a Dual-label Time-resolved Fluorescence Immunoassay

Prolactin (PRL) and growth hormone (GH) are two important hormones secreted by the pituitary gland, and their abnormal levels are often related to disease status. This study aimed to establish a new dual-label time-resolved fluorescence immunoassay (TRFIA) to quantitatively measure PRL and GH levels in serum. A sandwich TRFIA was optimized and established: anti-PRL/GH antibodies immobilized on 96-well plates captured PRL/GH and then banded together with anti-PRL/GH paired antibodies labeled with europium(III) (Eu3+)/samarium(III) (Sm3+) chelates. Finally, a time-resolved analyzer measured the Eu3+/Sm3+ fluorescence values. Clinical serum samples were used to evaluate the detection performance of this method. The sensitivities of this dual-label TRFIA were 0.35 ng/mL and 0.45 ng/mL, respectively, and the detection range was between 0.1 and 1000 ng/mL. All the cross-reactivities were lower than 1.07%. The intra-assay and interassay coefficients of variation were 2.18-7.85% and 2.25-7.30%, respectively. Compared with the registered TRFIA kits, a high Pearson coefficient (r = 0.9626 and 0.9675) was observed. This dual-label TRFIA has high sensitivity, accuracy and specificity with good clinical detection performance, representing a suitable alternative to existing methods for determining PRL and GH levels, and is expected to be used in the clinic in the future.

Prolactin levels and chronic kidney disease and the subsequent risk of cardiovascular events: A long term population based cohort study

Both the clearance and secretion of prolactin are disrupted in chronic kidney disease (CKD). Evidence indicates that prolactin may play a role in cardiovascular (CV) disturbances. Considering the increased cardiovascular risk associated with CKD, this study investigates the relationship between prolactin levels, CKD, and the risk of CV events in both women and men, with an average follow-up period of 20 years. The study included 2,005 participants from the Tehran Lipid and Glucose Study (TLGS) who met the inclusion criteria. They were reassessed approximately every three years for a median follow-up of 19.0 years (Interquartile range (IQR):16.4-20.2), during which occurrences of CKD and CV events were recorded. A pooled logistic regression model examined the influence of Prolactin on CV events and its interaction with CKD. During follow-up, we identified 156 incident cases of CV events among men and 73 among women. Median (95%CI) PRL levels were 7.4 (5.5-10.5) ng/mL for men and 15.2 (10.3-23) ng/mL for women. The results of analyses showed that a history of CKD was associated with significantly higher odds of CV events for both men 4.2 (95% CI: 2.6-6.8) and women 5.5 (95% CI: 2.6-11.5). Results remained unchanged after adjustment for confounders including age, waist circumference, smoking, education, history of diabetes and hypertension, and family history of CV events. Interaction analyses revealed no statistically significant interaction between CKD and PRL on the odds of CV events in unadjusted and adjusted models. This consistent pattern was observed regardless of gender. Results of population-based data with over a median follow-up period of 20 years showed that CKD independently increases the risk of CV events in both men and women. However, our findings suggest that this elevated risk may not be substantially influenced by prolactin levels. Further investigation may be warranted to confirm these findings.

Association of Genes TRH, PRL and PRLR with Milk Performance, Reproductive Traits and Heat Stress Response in Dairy Cattle

In our previous study, we found that changes in plasma prolactin (PRL) concentration were significantly associated with heat stress in dairy cows, and that PRL plays an important role in milk performance. Microarray sequencing revealed that thyrotropin releasing hormone (TRH) and prolactin receptor (PRLR), two genes important for PRL expression or function, may affect milk performance, reproduction, and heat stress response in dairy cattle. In this study, we further validated the genetic effects of the three genes in Chinese Holsteins. The potential variants within the three genes were first detected in 70 Chinese Holstein bulls and then screened in 1152 Chinese Holstein cows using the KASP (Kompetitive allele-specific PCR) method. In total, 42 variants were identified. Further, 13 SNPs were retained for KASP genotyping, including 8 in TRH, 3 in PRL, and 2 in PRLR. Using SNP-based association analyses, the multiple significant (p < 0.05) associations of these 13 SNPs with milk performance, reproduction, and heat stress response traits were found in the Holstein population. Furthermore, linkage disequilibrium analysis found a haplotype block in each of the TRH and PRL genes. Haplotype-based association analyses showed that haplotype blocks were also significantly (p < 0.05) associated with milk performance, reproduction, and heat stress response traits. Collectively, our results identified the genetic associations of TRH, PRL, and PRLR with milk performance, reproduction, and heat stress response traits in dairy cows, and found the important roles of SNP g.55888602A/C and g.55885455A/G in TRH in all traits, providing important molecular markers for genetic selection of high-yielding dairy cows.

Photoperiod Management in Farm Animal Husbandry: A Review

This review aims to examine the effects of the photoperiod on farm animals and to provide insights into how lighting management can optimize production performance, reproduction, and welfare. The production performance of farm animals is influenced by a variety of factors, such as diet, breed, and environment. Among these, lighting is a crucial component of the feeding environment. With the advancement of intensive farming, lighting measures are increasingly receiving attention. The photoperiod regulates the biological rhythms of animals and affects the secretion of hormones within the animal's body, particularly melatonin. Melatonin regulates the secretion and release of several other hormones through various pathways, such as growth hormone, prolactin, and gonadotropins. Therefore, the environmental light cycle participates in a variety of physiological activities within animals. An appropriate photoperiod can enhance the production performance, reproduction performance, and welfare conditions of farm animals. Choosing the appropriate lighting duration based on different animals, physiological stages, and production purposes can enhance the economic benefits of farms. In this review, we summarized the recent findings on the impact of photoperiods in different farm animal feeding environments on animal husbandry, although research on the suitable photoperiod for some animals might be outdated and is also discussed in this article. For lactating dairy cows, calves, poultry, pigs (excluding boars), and rabbits, continuous light exposure exceeding 12 h per day can be implemented to enhance growth and production performance. In contrast, for boars and goats, daily light exposure should be limited to less than 10 h to optimize reproductive and productive efficiency. Overall, this review aimed to provide theoretical support for research on the optimal photoperiod for farm animals.

Genome-Wide Identification and Characterization of gh/prl/sl Family in Cynoglossus semilaevis

The Chinese tongue sole (Cynoglossus semilaevis) is a marine flatfish of significant economic value, characterized by pronounced female-biased sexual size dimorphism (SSD). Sexual differences of cell number and gene expression within the PIT-1 lineage of the pituitary gland may be crucial for interpreting the female-biased SSD of C. semilaevis. Among hormones secreted by PIT-1 cell lineage, growth hormone (gh), prolactin (prl), prolactin 2 (prl2), and somatolactin (sl) comprise a gene family within the extensive superfamily of class-1 helical cytokines. To better understand the function of the gh/prl/sl in teleost SSD, we firstly identified five genes of the gh/prl/sl family (gh, sl, prl, prl2a, and prl2b) and their receptors (ghra, ghrb, prlra, prlrb, and prlr-like) from C. semilaevis at the genome-wide level. Phylogenetic analyses revealed that the gh/prl/sl family and their receptors were each clustered into five distinct groups. More microsatellites were revealed in the intron 2 of gh gene of female rather than the male and pseudo-male individuals, which is positively correlated with its sexual expression pattern. Interaction network prediction indicated that gh, prl, and sl may collectively contribute to individual growth and development. A FRET experiment showed that ghra can act as a receptor for sl. Additionally, the transcripts of the gh/prl/sl family and their receptors exhibited varying abundances in the pituitary, brain, gonad, and liver of both female and male C. semilaevis, with most ligands showing the highest abundance in the female pituitary. Furthermore, gh and sl were found to be maternally expressed. The knock-down of gh, prl, and sl in the pituitary cells could lead to the expression change of igf1, c-fos, and sos2. This study provided a foundation for further functional characterization of the gh/prl/sl gene family, contributing to a deeper understanding of the growth and reproductive mechanisms in C. semilaevis.

Prolactin in sleep and EEG regulation: New mechanisms and sleep-related brain targets complement classical data

The role of prolactin in sleep regulation has been the subject of extensive research over the past 50 years, resulting in the identification of multiple, disparate functions for the hormone. Prolactin demonstrated a characteristic circadian release pattern with elevation during dark and diminution during light. High prolactin levels were linked to non-rapid eye movement sleep and electroencephalogram delta activity in humans. Conversely, hyperprolactinemia showed strong correlation with REM sleep in rodent studies. Prolactin may be implicated in the alterations in female sleep patterns observed during the reproductive cycle, it may play a role in the REM sleep enhancement following stress and in sleep-related immunological processes. In conclusion, prolactin appears to have a sleep-promoting role, particularly during the dark phase. However, it does not appear to play a central and coherent role in sleep regulation, as observed in some neuropeptides such as orexin. Conversely, its principal function may be to facilitate situational, yet adaptive, changes in sleep patterns in response to challenging physiological phases, such as those associated with stress, immunological challenges, or the reproductive cycle. Neuronal substrates for prolactin-mediated sleep effects remain unknown; however, recent rodent sleep studies may provide insights into the potential sites of these effects.

Stress regulatory hormones and cancer: the contribution of epinephrine and cancer therapeutic value of beta blockers

The word "cancer" evokes myriad emotions, ranging from fear and despair to hope and determination. Cancer is aptly defined as a complex and multifaceted group of diseases that has unapologetically led to the loss of countless lives and affected innumerable families across the globe. The battle with cancer is not only a physical battle, but also an emotional, as well as a psychological skirmish for patients and for their loved ones. Cancer has been a part of our history, stories, and lives for centuries and has challenged the ingenuity of health and medical science, and the resilience of the human spirit. From the early days of surgery and radiation therapy to cutting-edge developments in chemotherapeutic agents, immunotherapy, and targeted treatments, the medical field continues to make significant headway in the fight against cancer. However, even after all these advancements, cancer is still among the leading cause of death globally. This urges us to understand the central hallmarks of neoplastic cells to identify novel molecular targets for the development of promising therapeutic approaches. Growing research suggests that stress mediators, including epinephrine, play a critical role in the development and progression of cancer by inducing neoplastic features through activating adrenergic receptors, particularly β-adrenoreceptors. Further, our experimental data has also shown that epinephrine mediates the growth of T-cell lymphoma by inducing proliferation, glycolysis, and apoptosis evasion via altering the expression levels of key regulators of these vital cellular processes. The beauty of receptor-based therapy lies in its precision and higher therapeutic value. Interestingly, the enhanced expression of β-adrenergic receptors (ADRBs), namely ADRB2 (β2-adrenoreceptor) and ADRB3 (β3-adrenoreceptor) has been noted in many cancers, such as breast, colon, gastric, pancreatic, and prostate and has been reported to play a pivotal role in facilitating cancer growth mainly by promoting proliferation, evasion of apoptosis, angiogenesis, invasion and metastasis, and chemoresistance. The present review article is an attempt to summarize the available findings which indicate a distinct relationship between stress hormones and cancer, with a special emphasis on epinephrine, considered as a key stress regulatory molecule. This article also discusses the possibility of using beta-blockers for cancer therapy.

Kisspeptin as a test of hypothalamic dysfunction in pubertal and reproductive disorders

The hypothalamic-pituitary-gonadal axis is regulated by the gonadotropin-releasing hormone pulse generator in the hypothalamus. This is comprised of neurons that secrete kisspeptin in a pulsatile manner to stimulate the release of GnRH, and, in turn, downstream gonadotropins from the pituitary gland, and subsequently sex steroids and gametogenesis from the gonads. Many reproductive disorders in both males and females are characterized by hypothalamic dysfunction, including functional disorders (such as age-related hypogonadism, obesity-related secondary hypogonadism, hyperprolactinemia, functional hypothalamic amenorrhea and polycystic ovary syndrome), structural pathologies (such as craniopharyngiomas or radiation or surgery-related hypothalamic dysfunction), and pubertal disorders (constitutional delay of growth and puberty and congenital hypogonadotropic hypogonadism). However, in many of these conditions, the relative contribution of hypothalamic dysfunction to the observed hypogonadism is unclear; as to date, there is no direct method of evaluating hypothalamic reproductive function in humans. Indeed, it is not possible to directly measure gonadotropin-releasing hormone levels in the hypothalamo-pituitary portal vessels, such that secondary (i.e., pituitary dysfunction) and tertiary (i.e., hypothalamic dysfunction) hypogonadism are often conflated as one entity. In this review, we examine the evidence for the use of kisspeptin as a method of directly evaluating hypothalamic reproductive dysfunction, and deliberate its potential future role in the evaluation of pubertal and reproductive disorders.

How Hormonal Balance Changes Lives in Women with Psoriasis

Psoriasis is a chronic, immune-mediated skin disease significantly impacting women, with disease severity often modulated by hormonal fluctuations. This review examines the influence of hormonal changes on the course of psoriasis in women, focusing on key life stages-including the menstrual cycle, pregnancy, postpartum, and menopause-and their impact on disease progression and symptomatology. Estrogen, the principal female sex hormone, plays a critical role in immune modulation. Variations in estrogen levels, which occur naturally throughout a woman's life, are associated with fluctuations in psoriasis severity. Low estrogen levels, as seen during menstruation or menopause, are linked to symptom exacerbation, while elevated levels during pregnancy may reduce symptoms in some women. However, responses are variable, with others experiencing no change or worsening during pregnancy. Postpartum, the rapid decline in estrogen often triggers severe flare-ups, while menopause, marked by a sustained estrogen reduction, frequently correlates with increased disease severity and flare frequency. The review also addresses the profound impact of psoriasis on women's quality of life, including physical discomfort, psychological distress, and social stigma. Additionally, fertility concerns are discussed, as severe psoriasis and associated treatments may increase the risk of adverse pregnancy outcomes. Consideration is given to hormonal therapies, lifestyle modifications, and their effects on psoriasis, underscoring the need for personalized treatment approaches that account for hormonal influences. Understanding these hormonal dynamics is essential for developing targeted, effective management strategies that enhance quality of life for women affected by psoriasis.

Milk Composition Is Predictive of Low Milk Supply Using Machine Learning Approaches

Background/Objectives: The causes of low milk supply are multifactorial, including factors such as gene mutations, endocrine disorders, and infrequent milk removal. These factors affect the functional capacity of the mammary gland and, potentially, the concentrations of milk components. This study aimed to investigate the differences in milk composition between mothers with low and normal milk supply and develop predictive machine learning models for identifying low milk supply. Methods: Twenty-four-hour milk production measurements were conducted using the test-weigh method. An array of milk components was measured in 58 women with low milk supply (<600 mL/24 h) and 106 with normal milk supply (≥600 mL/24 h). Machine learning algorithms were employed to develop prediction models integrating milk composition and maternal and infant characteristics. Results: Among the six machine learning algorithms tested, deep learning and gradient boosting machines methods had the best performance metrics. The best-performing model, incorporating 14 milk components and maternal and infant characteristics, achieved an accuracy of 87.9%, an area under the precision-recall curve (AUPRC) of 0.893, and an area under the receiver operating characteristic curve (AUC) of 0.917. Additionally, a simplified model, optimised for clinical applicability, maintained a reasonable accuracy of 78.8%, an AUPRC of 0.776, and an AUC of 0.794. Conclusions: These findings demonstrate the potential of machine learning models to predict low milk supply with high accuracy. Integrating milk composition and maternal and infant characteristics offers a practical approach to identify women at risk of low milk supply, facilitating timely interventions to support breastfeeding and ensure adequate infant nutrition.

Screening with Metoclopramide Test to Reduce Unnecessary Pituitary Magnetic Resonance Studies in Moderate Hyperprolactinemia

BACKGROUND

In prolactinoma diagnosis, current guidelines recommend prolactin (PRL) assessment, considering values exceeding 200 ng/mL highly suggestive of prolactinoma. However, subtler hyperprolactinemia is more common, and to rule out potential prolactinomas, pituitary resonance magnetic imaging (MRI) studies are necessary. These present limitations in terms of availability, costs, and delays in diagnosis. We aimed to evaluate the screening utility of the metoclopramide (MCP) test in identifying patients with moderate hyperprolactinemia for whom MRI studies might be unnecessary.

METHODS

We retrospectively selected patients with moderate hyperprolactinemia, with an MCP test and a pituitary MRI within the same assistance, and with no interfering pharmacological treatment. Increases in PRL (ΔPRLMax) and thyrotropin (ΔTSHMax) after MCP infusion were compared according to MRI findings: patients with microadenoma (<10 mm; n = 23), with macroadenoma (≥10 mm; n = 5), or without adenoma (n = 39).

RESULTS

ΔPRLMax exceeds baseline PRL capability to identify patients with an adenoma (area under the curve = 0.872 vs 0.776). ΔPRLMax below 220% identifies 100% of these patients with 71% of specificity. This screening would have avoided 42% of MRI, resulting in a cost savings of 34%. Analysis of ΔTSHMax only slightly increased specificity when considered as a secondary criterion. Test duration can be shortened to 30 min without compromising its screening capability.

CONCLUSIONS

A short MCP test is a useful and cost-effective screening tool to avoid unnecessary MRI. Its simplicity allows its performance in almost any clinical facility to easily rule out prolactinoma in an important percentage of patients, something of upmost importance especially in regions where MRI facilities or their access are limited.

Comparative Study of Lactogenic Effect and Milk Nutritional Density of Oral Galactagogue in Female Rabbit

BACKGROUND

Hypogalactia and agalactia in lactating mothers are the major causes of child malnutrition, mortality, morbidity, and overall ill health. The development of such treatments requires a well-designed preclinical study with suitable laboratory animals, which needs to be improved. Thus, a suitably designed study with a laboratory animal to analyse galactagogue activity, along with an assessment of the quality and quantity of milk, is required.

OBJECTIVES

This study aimed to evaluate the potential of rabbit as an animal model for studying lactogenic activity.

METHODS

The structural homology of prolactin, gene prolactin receptor, and prolactin hormone in humans, rabbit, and rat was studied using BLAST and PyMol to assess similarity in the lactogenic system. Daily and cumulative milk production and pre-treatment (control) and post-treatment (three drugs) in rabbits were recorded and evaluated by analysing protein, fat, lactose, solid non-- fat, and ash values. All parameters were recorded on the 0th day and at the end of weeks 1, 2, and 3. Mammary gland histopathology was performed to evaluate the effects on mammary glands.

RESULTS

Homology studies revealed that the sequences of the human and rabbit prolactin genes, receptors, and hormones had a high similarity index. Treatment with Domperidone, Metoclopramide, and Shatavari significantly enhanced milk production by enhancing prolactin secretion; only Shatavari increased milk nutrition. Enlargement of the tubuloalveolar ducts of the mammary glands was observed.

CONCLUSION

Our findings suggest that rabbits are robust, reproducible, ethically superior, and preclinically relevant animals for assessing lactogenic activity.

Circulating prolactin levels and the effect of dopaminergic agonists in systemic lupus erythematosus: a systematic review and meta-analysis

This systematic review of clinical studies investigated whether circulating PRL levels differed between subjects with systemic lupus erythematosus (SLE) and healthy controls, the correlation between circulating PRL and SLE activity, and the effect of dopaminergic agonists as adjuvant therapy for SLE. We searched PubMed, Scopus, Web of Science, Cochrane, Embase, and Google Scholar for case-control and cross-sectional studies investigating circulating PRL levels in subjects with SLE and/or its correlation with disease activity, and clinical trials examining the effect of dopaminergic agonists on SLE activity assessed by the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score. Forty-five studies addressing circulating PRL levels in SLE met our inclusion criteria. SLE was associated with an increased odds of hyperprolactinemia (OR 11.69, 95%CI 5.64-24.22) and circulating PRL levels were significantly higher in subjects with SLE than in controls (standardized mean difference of 1.62, 95%CI 1.14-2.09). Circulating PRL was positively correlated with SLE activity assessed by the SLEDAI (correlation coefficient 0.38, 95% CI 0.26-0.48). Two randomized clinical trials with bromocriptine and three prospective open-label trials with quinagolide reported that treatment with dopaminergic agonists was associated with reduced frequency of disease flares and decreased SLEDAI score. Circulating PRL levels were higher in subjects with SLE than in healthy controls and were significantly associated with disease activity. In addition, treatment with the dopaminergic agonists bromocriptine and quinagolide reduced SLE disease activity in small studies and may be a beneficial adjuvant therapy for the disease if larger trials confirm these findings. This review was registered in PROSPERO (CRD42021237156).

Nociceptors are functionally male or female: from mouse to monkey to man

The prevalence of many pain conditions often differs between sexes. In addition to such quantitative distinctions, sexual dimorphism may also be qualitative reflecting differences in mechanisms that promote pain in men and women. A major factor that influences the likelihood of pain perception is the threshold for activation of nociceptors. Peripheral nociceptor sensitization has been demonstrated to be clinically relevant in many pain conditions. Whether peripheral nociceptor sensitization can occur in a sexually dimorphic fashion, however, has not been extensively studied. To address this fundamental knowledge gap, we used patch clamp electrophysiology to evaluate the excitability of dorsal root ganglion neurons from male or female rodents, non-human primates, and humans following exposure to putative sensitizing agents. Previous studies from our laboratory, and others, have shown that prolactin promotes female-selective pain responses in rodents. Consistent with these observations, dorsal root ganglion neurons from female, but not male, mice were selectively sensitized by exposure to prolactin. The sensitizing action of prolactin was also confirmed in dorsal root ganglion neurons from a female macaque monkey. Critically, neurons recovered from female, but not male, human donors were also selectively sensitized by prolactin. In the course of studies of sleep and pain, we unexpectedly observed that an orexin antagonist could normalize pain responses in male animals. We found that orexin B produced sensitization of male, but not female, mouse, macaque, and human dorsal root ganglion neurons. Consistent with functional responses, increased prolactin receptor and orexin receptor 2 expression was observed in female and male mouse dorsal root ganglia, respectively. Immunohistochemical interrogation of cultured human sensory neurons and whole dorsal root ganglia also suggested increased prolactin receptor expression in females and orexin receptor 2 expression in males. These data reveal a functional double dissociation of nociceptor sensitization by sex, which is conserved across species and is likely directly relevant to human pain conditions. To our knowledge, this is the first demonstration of functional sexual dimorphism in human sensory neurons. Patient sex is currently not a common consideration for the choice of pain therapy. Precision medicine, based on patient sex could improve therapeutic outcomes by selectively targeting mechanisms promoting pain in women or men. Additional implications of these findings are that the design of clinical trials for pain therapies should consider the proportions of male or female patients enrolled. Lastly, re-examination of selected past failed clinical trials with subgroup analysis by sex may be warranted.

Overview of Hyperprolactinemia: General Approach and Reproductive Health Implications

Prolactin (PRL) is a polypeptide hormone produced by the lactotrope cells of the anterior pituitary gland. Among its myriads of biological functions, PRL is the main regulator of mammary gland growth and development, as well as of the production and secretion of milk. Hyperprolactinemia represents a frequent consultation cause in medical practice. Nevertheless, elevations in serum PRL are not always pathological. Drug induced hyperprolactinemia is the most common cause, mainly by antipsychotics, followed by other causes such as pituitary neuroendocrine tumors, physiologic conditions, and systemic diseases such as chronic kidney disease and hypothyroidism. When evaluating a patient with hyperprolactinemia it is of utmost importance to consider the diverse etiologies of this condition in order to avoid unnecessary diagnostic workup and treatment. Regarding reproductive health, hyperprolactinemia is a well-documented cause of infertility, as approximately 15-20% of women undergoing infertility evaluation have hyperprolactinemia, which causes secondary amenorrhea, and other menstrual irregularities. Similarly, in men it is a cause of hypogonadism.

Drug induced hypoprolactinemia

Prolactin levels can be influenced by multiple medications primarily through the interaction with dopamine receptors which regulate its secretion. Unlike hyperprolactinemia which has a well-defined clinical phenotype, the effects of hypoprolactinemia beyond inability to lactate are incompletely understood. Recent studies have raised concerns regarding detrimental changes in glucose metabolism, sexual function and psychological profile in patients with low prolactin levels. In contrast with anatomic and genetic etiologies, drug-induced hypoprolactinemia is usually reversible after dose reduction of the offending medication. The most common clinical scenario of drug-induced hypoprolactinemia in the endocrine clinic pertains to patients treated with cabergoline or bromocriptine for prolactin-secreting or other types of pituitary adenomas. Also, data has accumulated regarding hypoprolactinemia in patients receiving aripiprazole for schizophrenia and other psychiatric disorders. These patients warrant careful evaluation for comorbidities. This review aims to increase awareness about the potentially detrimental effects of drug-induced hypoprolactinemia, which should be considered in clinical practice decisions.

Diagnosis of hypoprolactinemia

Prolactin is a polypeptide hormone composed of 199 amino acids, synthesized by lactotroph cells. Its primary effects are on the mammary gland and gonadal axes, but it also influences different organs and systems, particularly metabolic functions. Current literature has mainly focused on the diagnosis, monitoring, and treatment of hyperprolactinemia. Due to the lack of a well-established effective treatment for hypoprolactinemia, it is not clinically emphasized. Therefore, data on its diagnosis is limited. Hypoprolactinemia has been associated with metabolic dysfunctions such as type 2 diabetes mellitus, fatty liver, dyslipidemia, fertility problems, sexual dysfunction, and increased cardiovascular disease. While often seen as a part of combined hormone deficiencies due to pituitary damage, isolated prolactin deficiency is rare. Hypoprolactinemia can serve as a marker for extensive pituitary gland damage and dysfunction.Low or undetectable serum prolactin levels and the absence of a sufficient prolactin peak in the thyrotropin-releasing hormone (TRH) stimulation test are considered diagnostic for hypoprolactinemia. Gender appears to influence both basal prolactin levels and TRH stimulation test responses. Basal prolactin levels of, at least, 5 ng/mL for males and 7 ng/mL for females can be used as cut-off levels for normal prolactin reserve. Minimum peak prolactin responses of 18 ng/mL for males and 41 ng/mL for females to TRH stimulation can exclude hypoprolactinemia. However, larger population studies across different age groups and sexes are needed to better define normal basal prolactin levels and prolactin responses to the TRH stimulation test.

Reference intervals for serum prolactin concentrations: analytical and clinical considerations

Prolactin is a 23 kDa protein synthesised and released by lactotrophs located in the anterior pituitary gland. The main function of prolactin is the development of the mammary glands and the production and maintenance of milk secretion during pregnancy and lactation. Prolactin is present in 3 forms in the circulation monomeric, dimeric and macroprolactin which is one of the causes of variability between assay manufacturers. Although most assays have been standardised using the WHO's 3rd international standard there is still considerable variability between commercially available assays and as such laboratories need to establish their own reference intervals. Clinicians use reference intervals to distinguish between healthy and diseased individuals. Direct methods to establish reference intervals are expensive and time consuming and are impractical for most routine clinical laboratories. Indirect methods using the laboratories own data are more commonly used but also have drawbacks. Determination of reference intervals for prolactin is particularly difficult due to various physiological causes for variation in prolactin levels including age, sex and menopause. The presence of macroprolactin, its detection and methods for reporting its presence adds to reference interval determination complexity and harmonisation of these methods may improve clinical care.

Could low prolactin levels after radiotherapy predict the onset of hypopituitarism?

Both local and external cranial radiotherapy (RT) can induce neurotoxicity and vascular damage of the hypothalamic-pituitary area, which can promote neuroendocrine alterations. While anterior pituitary insufficiency after RT has been extensively characterized, data on the effect of RT on prolactin (PRL) secretion are limited and heterogeneous, with different patterns of PRL behavior described in the literature. A progressive decline in PRL levels, reflecting a time-dependent, slowly evolving radiation-induced damage to the pituitary lactotroph cells has been reported. To date, the association between hypopituitarism and hypoprolactinemia in patients undergoing RT has not yet been fully investigated. The few available data suggest that lower PRL levels can predict an extent damage of the pituitary tissue and a higher degree of hypothalamic dysfunction. However, most studies on the effect of RT on pituitary function do not properly assess PRL secretion, as PRL deficiency is usually detected as part of hypopituitarism and not systematically investigated as an isolated disorder, which may lead to an underestimation of hypoprolactinemia after RT. In addition, the often-inadequate follow-up over a long period of time may contribute to the non-recognition of PRL deficiency after RT. Considering that hypoprolactinemia is associated with various metabolic complications, there is a need to define appropriate diagnostic and management criteria. Therefore, hypoprolactinemia should enter in the clinical investigation of patients at risk for hypopituitarism, mainly in those patients who underwent RT.

Prolactin deficiency in the context of other pituitary hormone abnormalities : Special issue: hypoprolactinemia: a neglected endocrine disorder

Prolactin deficiency is rare. It generally occurs when pituitary disorders, such as large pituitary tumors, pituitary apoplexy, and other conditions associated with sellar mass effect lead to global failure of pituitary function and hypopituitarism. In these situiations, prolactin is commonly the last pituitary hormone affected, after growth hormone and gonadotropins are lost and thyroid-stimulating hormone and adrenocorticotopic hormone secretion is impaired. Prolactin deficiency accompanies several congenital syndromes due to mutations in PROP1 and Pit1/ POU1F and in X-linked IGSF1 deficiency syndrome, and several aqcuired conditions including Sheehan syndrome, IgG4-related hypophysitis, and immune checkpoint-inhibitor-induced hypophysitis. In women, prolactin deficiency prevents lactation following childbirth among other symptoms associated with hypopituitarism. Human prolactin is not available commercially as replacement therapy. However, recombinant human prolactin administered daily to women with hypoprolactinemia and alactogenesis was found to lead to the production of significant milk volume sufficient for lactation.

What do we know about abnormally low prolactin levels in polycystic ovary syndrome? A narrative review

Hyper and hypoprolactinemia seem to be related to the occurrence of metabolic alterations in PCOS patients. In contrast, between significantly elevated and significantly low, prolactin levels seem to be protective against metabolic consequences. In the present review, we found 4 studies investigating hypoprolactinemia in patients with PCOS. We also identified 6 additional studies that reported low levels of PRL in PCOS patients. Although its prevalence is not considered high (13.2-13.9%), its contribution is certainly significant to the metabolic alterations observed in PCOS (insulin resistance, obesity, diabetes mellitus, and fatty liver disease). Dopamine inhibits the secretion of prolactin and GnRH. If dopamine levels are low or the dopamine receptor is less expressed or mutated, the levels of prolactin and GnRH increase, and consequently, LH also increases. On the other hand, hyperprolactinemia, in prolactinomas-typical levels, acting through kisspeptin inhibition causes GnRH suppression and hypogonadotropic hypogonadism. In situations of hypoprolactinemia due to excessive dopamine agonist treatment, dosage reduction is important to minimize the decrease in prolactin levels. Nevertheless, there is a lack of prospective studies confirming these hypotheses, as well as randomized clinical trials with appropriate drugs targeting both hyperprolactin and hypoprolactin in patients with PCOS.

Distribution and calcium signaling function of somatostatin receptor subtypes in rat pituitary

The somatostatin (SST) receptor family controls pituitary hormone secretion, but the distribution and specific roles of these receptors on the excitability and voltage-gated calcium signaling of hormone producing pituitary cells have not been fully characterized. Here we show that the rat pituitary gland expressed Sstr1, Sstr2, Sstr3, and Sstr5 receptor genes in a cell type-specific manner: Sstr1 and Sstr2 in thyrotrophs, Sstr3 in gonadotrophs and lactotrophs, Sstr2, Sstr3, and Sstr5 in somatotrophs, and none in corticotrophs and melanotrophs. Most gonadotrophs and thyrotrophs spontaneously fired high-amplitude single action potentials, which were silenced by SST without affecting intracellular calcium concentrations. In contrast, lactotrophs and somatotrophs spontaneously fired low-amplitude plateau-bursting action potentials in conjunction with calcium transients, both of which were silenced by SST. Moreover, SST inhibited GPCR-induced voltage-gated calcium signaling and hormone secretion in all cell types expressing SST receptors, but the inhibition was more pronounced in somatotrophs. The pattern of inhibition of electrical activity and calcium signaling was consistent with both direct and indirect inhibition of voltage-gated calcium channels, the latter being driven by cell type-specific hyperpolarization. These results indicate that the action of SST in somatotrophs is enhanced by the expression of several types of SST receptors and their slow desensitization, that SST may play a role in the electrical resynchronization of gonadotrophs, thyrotrophs, and lactotrophs, and that the lack of SST receptors in corticotrophs and melanotrophs keeps them excitable and ready to responses to stress.

The relationship between low prolactin and type 2 diabetes

Prolactin (PRL) is secreted throughout life in men and women. At elevated levels, its physiological role in pregnancy and lactation, and pathological effects, are well known. However clinical implications of low circulating PRL are not well established. We conducted a meta-analysis to examine the relationship between low PRL levels and type 2 diabetes. Five papers included cross-sectional studies comprising 8,720 men (mean age range 51.4-60 years) and 3,429 women (49.5-61.6 years), and four papers included cohort studies comprising 2,948 men (52.1-60.0 years) and 3,203 women (49.2-60.1 years). Individuals with pregnancy, lactation and hyperprolactinemia, drugs known to alter circulating PRL levels, or pituitary diseases had been excluded. Although most studies used quartiles to categorize PRL groups for analysis, PRL cut-off values (all measured by chemiluminescence immunoassay) were variably defined between studies: the lowest PRL quartiles ranged from 3.6 ng/ml to 7.2 ng/ml in men and between 4.5 ng/ml to 8 ng/ml in women; and the highest PRL quartiles ranged from 6.9 ng/ml to 13 ng/ml in men and 9.6 ng/ml to 15.8 ng/ml in women. Type 2 diabetes was defined variably using self-reported physician's diagnosis, fasting blood glucose, oral glucose tolerance test or glycated hemoglobin (HbA1C). In cross-sectional studies, compared to individuals in the highest PRL groups (reference), those in the lowest PRL groups had greater risk of type 2 diabetes both in men: odds ratio (OR) and 95% confidence interval = 1.86 (1.56-2.22) and in women: OR = 2.15 (1.63-2.85). In cohort studies, women showed a significant association between low PRL and type 2 diabetes: OR = 1.52 (1.02-2.28) but not men: OR = 1.44 (0.46-4.57). Relatively low heterogeneity was observed (I2 = 25-38.4%) for cross-sectional studies, but higher for cohort studies (I2 = 52.8-79.7%). In conclusion, low PRL is associated with type 2 diabetes, but discrepancy between men and women in the relationship within cohort studies requires further research.

The relationship between psychological stress and ovulatory disorders and its molecular mechanisms: a narrative review

This narrative review explores the relationship between psychological stress and ovulatory disorders, focusing on the molecular mechanisms involved. Ovulation is regulated by the hypothalamus-pituitary-ovarian (HPO) axis, and disruptions in this axis can lead to ovulatory dysfunction. Chronic psychological stress affects the HPO axis, resulting in abnormalities in hypothalamus hormone secretion, pituitary hormone release, and ovarian function. These disruptions cause ovulation disorders and menstrual irregularities. The mechanisms by which psychological stress affects ovulation involve alterations in neuropeptides and hormones, activation of the hypothalamic-pituitary-adrenal (HPA) axis, impairment of follicular development, generation of oxidative stress, and the decline in ovarian reserve function. Understanding these mechanisms is crucial for developing interventions to restore reproductive health. Psychological interventions, such as cognitive-behavioral therapy, have shown promise in improving ovulation and pregnancy rates in women with ovulatory disorders. Further research is needed to explore the specific mechanisms of these interventions and optimize treatment strategies. Addressing psychological factors is essential in managing reproductive health and ovulatory disorders.

The molecular basis of hypoprolactinaemia

Hypoprolactinaemia is an endocrinopathy which is typically encountered as part of a combined pituitary hormone deficiency picture. The vast majority of genetic causes identified to date have been in the context of congenital hypopituitarism with multiple co-existent endocrinopathies. This is primarily with its closest hormonal relation, namely growth hormone. Acquired hypoprolactinaemia is generally rare in paediatric patients, and usually occurs together with other hormonal deficiencies. Congenital hypopituitarism occurs with an incidence of 1:4,000-10,000 cases and mutations in the following transcription factors account for the majority of documented genetic causes: PROP-1, POU1F1, LHX3/4 as well as documented case reports for a smaller subset of transcription factors and other molecules implicated in lactotroph development and prolactin secretion. Isolated prolactin deficiency has been described in a number of sporadic case reports in the literature, but no cases of mutations in the gene have been described to date. A range of genetic polymorphisms affecting multiple components of the prolactin signalling pathway have been identified in the literature, ranging from RNA spliceosome mutations (RNPC3) to loss of function mutations in IGSF-1. As paediatricians gain a greater understanding of the long-term ramifications of hypoprolactinaemia in terms of metabolic syndrome, type 2 diabetes mellitus and impaired fertility, the expectation is that clinicians will measure prolactin more frequently over time. Ultimately, we will encounter further reports of hypoprolactinaemia-related clinical presentations with further genetic mutations, in turn leading to a greater insight into the molecular basis of hypoprolactinaemia in terms of signalling pathways and downstream mediators. In the interim, the greatest untapped reserve of genetic causes remains within the phenotypic spectrum of congenital hypopituitarism.

Evidence-based definition of hypoprolactinemia in European men aged 40-86 years: the European male ageing study

Empirical evidence for a low normal or reference interval for serum prolactin (PRL) is lacking for men, while the implications of very low PRL levels for human health have never been studied. A clinical state of "PRL deficiency" has not been defined except in relation to lactation. Using data from the European Male Ageing Study (EMAS), we analyzed the distribution of PRL in 3,369 community-dwelling European men, aged 40-80 years at phase-1 and free from acute illnesses. In total, 2,948 and 2,644 PRL samples were collected during phase-1 and phase-2 (3 to 5.7 years later). All samples were analysed in the same centre with the same assay. After excluding individuals with known pituitary diseases, PRL ≥ 35 ng/ml, and PRL-altering drugs including antipsychotic agents, selective serotonin reuptake inhibitors, or dopamine agonists, 5,086 data points (2,845 in phase-1 and 2,241 in phase-2) were available for analysis. The results showed that PRL declined minimally with age (slope = -0.02) and did not correlate with BMI. The positively skewed PRL distribution was log-transformed to a symmetrical distribution (skewness reduced from 13.3 to 0.015). Using two-sigma empirical rule (2[]SD about the mean), a threshold at 2.5% of the lower end of the distribution was shown to correspond to a PRL value of 2.98ng/ml. With reference to individuals with PRL levels of 5-34.9 ng/ml (event rate = 6.3%), the adjusted risk of developing type 2 diabetes increased progressively in those with PRL levels of 3-4.9 ng/ml: event rate = 9.3%, OR (95% CI) 1.59 (0.93-2.71), and more so with PRL levels of 0.3-2.9 ng/ml: event rate = 22.7%, OR 5.45 (1.78-16.62). There was also an increasing trend in prediabetes and diabetes based on fasting blood glucose levels was observed with lower categories of PRL. However, PRL levels were not associated with cancer, cardiovascular diseases, depressive symptoms or mortality. Our findings suggest that a PRL level below 3 ng/ml (64 mlU/l) significantly identifies European men with a clinically-important outcome (of type 2 diabetes), offering a lower reference-value for research and clinical practice.

Hypoprolactinemia. Does it matter? Redefining the hypopituitarism and return from a mumpsimus : "Absence of proof is not the proof of absence"

Prolactin (PRL) is secreted by the lactotroph cells in the anterior pituitary gland which is under inhibitory control of dopamine. The mature human PRL has more than 300 physiological actions including lactation, reproduction, homeostasis, neuroprotection, behavior, water and electrolyte balance, immunoregulation and embryonic and fetal development. PRL is involved in the growth and development of mammary gland, preparation of the breast for lactation in the postpartum period, synthesis of milk, and maintenance of milk secretion. Abnormalities in the synthesis and secretion of PRL may result in hyperprolactinemia or hypoprolactinemia. Although hyperprolactinemia has been extensively investigated in the literature, because of the subtle or unclearly defined symptoms, hypoprolactinemia is a less-known and neglected disorder. Failure of lactation is a well-known clinical manifestation of hypoprolactinemia. Recent studies reveal that hypoprolactinemia may have some effects beyond lactation such as increased risk for metabolic abnormalities including insulin resistance, abnormal lipid profile, obesity and sexual dysfunction. Very low level of PRL is suggested to be avoided in patients receiving dopamin agonist treatment to prevent unwanted effects of hypoprolactinemia. Another important point is that hypoprolactinemia is not included in the classification of hypopituitarism. Anterior pituitary failure is traditionally classified as isolated, partial and complete (panhypopituitarism) hypopituitarism regardless of prolactin level. Therefore, there are two kinds of panhypopituitarism: panhypopituitarism with normal or high PRL level and panhypopituitarism with low PRL level. In this review, we present two personal cases, discuss the diagnosis of hypoprolactinemia, hypoprolactinemia associated clinical picture and suggest to redefine the classification of hypopituitarism.

Neuropsychological complications of hypoprolactinemia

Prolactin (PRL) is primarily produced by the pituitary lactotrophic cells and while initially named for its role in lactation, PRL has several other biological roles including immunomodulation, osmotic balance, angiogenesis, calcium metabolism, and appetite regulation. Most of the PRL-related literature has traditionally focused on hyperprolactinemia, whereas hypoprolactinemia has received little attention. There is evidence to suggest that PRL receptors are widely distributed within the central nervous system including the limbic system. Furthermore, PRL has been shown to play key role in the stress regulation pathway. Recent data also suggest that hypoprolactinemia may be associated with increased sexual dysfunction, anxiety, and depression. In this paper we discuss the current understanding regarding the neuropsychological impact of hypoprolactinemia and highlight the need for adequately defining hypoprolactinemia as an entity and consideration for future replacement therapies.

Prolactin: structure, receptors, and functions

Prolactin (PRL) is a 23-kDa protein synthesized and secreted by lactotroph cells of the anterior pituitary gland but also by other peripheral tissues. PRL binds directly to a unique transmembrane receptor (PRLR), and the JAK2/signal transducer and activator of transcription 5 (Stat5) pathway is considered the major downstream pathway for PRLR signaling. To a lesser extent, PRL may be cleaved into the shorter 16-kDa PRL, also called vasoinhibin, whose signaling is not fully known. According to rodent models of PRL signaling inactivation and the identification of human genetic alterations in PRL signaling, a growing number of biological processes are partly mediated by PRL or its downstream effectors. In this review, we focused on PRL structure and signaling and its canonical function in reproduction. In addition to regulating reproductive functions, PRL also plays a role in behavior, notably in initiating nurturing and maternal behavior. We also included recent insights into PRL function in several fields, including migraines, metabolic homeostasis, inflammatory and autoimmune disease, and cancer. Despite the complexity of understanding the many functions of PRL, new research in this field offers interesting perspectives on physiological and pathophysiological processes.

Effects of Prolactin Inhibition on Lipid Metabolism in Goats

Prolactin (PRL) has recently been found to play a role in lipid metabolism in addition to its traditional roles in lactation and reproduction. However, the effects of PRL on lipid metabolism in liver and adipose tissues are unclear. Therefore, we aimed to study the role of PRL on lipid metabolism in goats. Twenty healthy eleven-month-old Yanshan cashmere goats with similar body weights (BWs) were selected and randomly divided into a control (CON) group and a bromocriptine (BCR, a PRL inhibitor, 0.06 mg/kg, BW) group. The experiment lasted for 30 days. Blood was collected on the day before BCR treatment (day 0) and on the 15th and 30th days after BCR treatment (days 15 and 30). On day 30 of treatment, all goats were slaughtered to collect their liver, subcutaneous adipose, and perirenal adipose tissues. A portion of all collected tissues was stored in 4% paraformaldehyde for histological observation, and another portion was immediately stored in liquid nitrogen for RNA extraction. The PRL inhibition had inconclusive effects found on BW and average daily feed intake (ADFI) in goats (p > 0.05). PRL inhibition decreased the hormone-sensitive lipase (HSL) levels on day 30 (p < 0.05), but the effects were inconclusive on days 0 and 15. PRL inhibition had inconclusive effects found on total cholesterol (TCH), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), fatty acid synthase (FAS), 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), and acetyl-CoA carboxylase (ACC) on days 0, 15, and 30 (p > 0.05). Furthermore, hematoxylin-eosin (HE) staining of the liver, subcutaneous adipose, and perirenal adipose sections showed that PRL inhibition had inconclusive effects on the pathological changes in their histomorphology (p > 0.05), but measuring adipocytes showed that the area of perirenal adipocytes decreased in the BCR group (p < 0.05). The qPCR results showed that PRL inhibition increased the expression of PRL, long-form PRL receptor (LPRLR), and short-form PRL receptor (SPRLR) genes, as well as the expression of genes related to lipid metabolism, including sterol regulatory element binding transcription factor 1 (SREBF1); sterol regulatory element binding transcription factor 2 (SREBF2); acetyl-CoA carboxylase alpha (ACACA); fatty acid synthase (FASN); 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR); 7-dehydrocholesterol reductase (DHCR7); peroxisome proliferator-activated receptor gamma (PPARG); and lipase E, hormone-sensitive type (LIPE) in the liver (p < 0.05). In the subcutaneous adipose tissue, PRL inhibition increased SPRLR gene expression (p < 0.05) and decreased the expression of genes related to lipid metabolism, including SREBF1, SREBF2, ACACA, PPARG, and LIPE (p < 0.05). In the perirenal adipose tissue, the inhibition of PRL decreased the expression of the PRL, SREBF2, and HMGCR genes (p < 0.05). In conclusion, the inhibition of PRL decreases the serum HSL levels in cashmere goats; the effects of PRL on lipid metabolism are different in different tissues; and PRL affects lipid metabolic activity by regulating different PRLRs in liver and subcutaneous adipose tissues, as well as by decreasing the expression of the PRL, SREBF2, and HMGCR genes in perirenal adipose tissue.

Effects of gestational age on blood cortisol and prolactin levels during pregnancy in malaria endemic area

BACKGROUND

The hormonal shift occurring in pregnant women is crucial for the outcome of pregnancy. We conducted a study in pregnant women living in a malaria endemic area to determine the potential effect of gestational age on the modulation of the endocrine system by cortisol and prolactin production during pregnancy.

METHODS

Primigravidae and multigravidae with a gestational age between 16-20 weeks were included in the study and followed up to delivery and 6-7 weeks thereafter. Venous blood was collected at scheduled visit: Visit 1 (V1; 16-20 weeks of amenorrhea), Visit 2 (V2; 28 ±1 weeks of pregnancy), Visit 3 (V3; 32 ±1 weeks of pregnancy), Visit4 (V4; delivery) and Visit5 (V5; 6-7 weeks after delivery). In addition, a cord blood sample was also collected during labour at delivery. Nulliparous and primiparous/multiparous non-pregnant women were enrolled in the control group. Cortisol and prolactin plasma concentrations were measured using ichroma II and i-chamber apparatus. Light microscopy was used to detect Plasmodium falciparum infections. A linear mixed-effects regression (LMER) model was used to assess the association between the variation of cortisol titres and prolactin levels during the pregnancy and the post-partum.

RESULTS

Results showed that cortisol and prolactin levels in the peripheral blood were globally up-regulated during pregnancy. Concentrations of cortisol during follow-up was significantly higher in primigravidae than in multigravidae during the whole pregnancy (p<0.024). Moreover, the level of prolactin which was higher before delivery in primigravidae reversed at delivery and postpartum visit, but the difference was not statistically significant during the follow-up (V1 to V5) (p = 0.60). The cortisol level in peripheral blood at delivery was higher than that in the cord blood, and conversely for prolactin. Cortisol and prolactin levels decreased after delivery, though the level of prolactin was still higher than that at enrolment. An increase of one unit of prolactin was associated with the decrease of the average concentration of cortisol by 0.04 ng/ml (p = 0.009). However, when cortisol increases with one unit, the average concentration of prolactin decreases by 1.16 ng/ml (p = 0.013).

CONCLUSION

These results showed that the up-regulation effects of cortisol and prolactin are related to gestational age. A The downward regulation effect that both hormones have on each other during the pregnancy when each increase to 1 unit (1.0 ng/ml) was also reported.

Prolactin's paradox: Friend, foe, or both in immune regulation?

Over 100 diseases have been recognized as autoimmune in nature, collectively affecting ∼20 % of the population in industrialized countries. These conditions are more prevalent among women of childbearing age, reflecting the potential association between alterations in the immune-neuroendocrine network, on the one hand, and autoimmune conditions, on the other. Prolactin (PRL), a polypeptide hormone that is primarily (but not only) secreted by the lactotrophic cells of the pituitary gland, is a critical element of the immune-neuroendocrine network. Although this hormone has several nonimmune functions, its role in regulating immune responses and affecting autoimmune inflammation is particularly enigmatic and controversial. Indeed, PRL interacts with various immune cells to bolster the body defenses, but also potentially to exacerbate autoimmune conditions. Understanding how and when PRL acts as a 'friend or foe' is crucial for unraveling its role as a potential therapeutic target in the management of autoimmune diseases (AIDs). This review therefore provides a critical overview of PRL's role in the immune system, and of the influence of this pleiotropic hormone in the development of autoimmunity.

Revisiting the specific and potentially independent role of the gonad in hormone regulation and reproductive behavior

Gonadal sex steroid hormones are well-studied modulators of reproductive physiology and behavior. Recent behavioral endocrinology research has focused on how the brain dynamically responds to - and may even produce - sex steroids, but the gonadal tissues that primarily release these hormones receive much less attention as a potential mediator of behavioral variation. This Commentary revisits mechanisms by which the reproductive hypothalamic-pituitary-gonadal (HPG) axis can be modulated specifically at the gonadal level. These mechanisms include those that may allow the gonad to be regulated independently of the HPG axis, such as receptors for non-HPG hormones, neural inputs and local production of conventional 'neuropeptides'. Here, I highlight studies that examine variation in these gonadal mechanisms in diverse taxa, with an emphasis on recent transcriptomic work. I then outline how future work can establish functional roles of gonadal mechanisms in reproductive behavior and evaluate gonad responsiveness to environmental cues. When integrated with neural mechanisms, further investigation of gonadal hormone regulation can yield new insight into the control and evolution of steroid-mediated traits, including behavior.

Prolactin mitigates chronic stress-induced maladaptive behaviors and physiology in ovariectomized female rats

Stress is a major risk factor for several neuropsychiatric disorders in women, including postpartum depression. During the postpartum period, diminished ovarian hormone secretion increases susceptibility to developing depressive symptoms. Pleiotropic peptide hormones, like prolactin, are markedly released during lactation and suppress hypothalamic-pituitary-adrenal axis responses in women and acute stress-induced behavioral responses in female rodents. However, the effects of prolactin on chronic stress-induced maladaptive behaviors remain unclear. Here, we used chronic variable stress to induce maladaptive physiology in ovariectomized female rats and concurrently administered prolactin to assess its effects on several depression-relevant behavioral, endocrine, and neural characteristics. We found that chronic stress increased sucrose anhedonia and passive coping in saline-treated, but not prolactin-treated rats. Prolactin treatment did not alter stress-induced thigmotaxis, corticosterone (CORT) concentrations, hippocampal cell activation or survival. However, prolactin treatment reduced basal CORT concentrations and increased dopaminergic cells in the ventral tegmental area. Further, prolactin-treated rats had reduced microglial activation in the ventral hippocampus following chronic stress exposure. Together, these data suggest prolactin mitigates chronic stress-induced maladaptive behaviors and physiology in hypogonadal females. Moreover, these findings imply neuroendocrine-immune mechanisms by which peptide hormones confer stress resilience during periods of low ovarian hormone secretion.

Macroprolactin in mothers and their babies: what is its origin?

OBJECTIVES

Macroprolactinemia is one of the major causes of hyperprolactinemia. The aim of this study was to clarify the origin of macroprolactin (macro-PRL).

METHODS

We examined macro-PRL in the sera of 826 pregnant women and in those of their babies' umbilical cords at delivery. Macro-PRL was evaluated by precipitation with polyethylene glycol (PEG), gel filtration chromatography (GFC), and absorption with protein G (PG).

RESULTS

We detected macro-PRL in 16 out of the 826 pregnant women (1.94 %) and in 14 of their babies, which may indicate the possibility of hereditary origin of macro-PRL. However, the macro-PRL ratios of the babies correlated positively with those of their mothers (r=0.72 for GFC, p<0.001 and r=0.77 for PG, p<0.001), suggesting that the immunoglobulin (Ig)G-type anti-PRL autoantibodies might be actively transferred to babies via the placenta and form macro-PRL by binding to their babies' PRL or PRL-IgG complexes may possibly pass through the placenta. There were two cases in which only mothers had macro-PRL, indicating that the mothers had autoantibodies that did not pass through the placenta, such as IgA, PRL bound to the other proteins or PRL aggregates. No cases were found in which only the babies had macro-PRL and their mothers did not, suggesting that macro-PRL might not arise by non-hereditary congenital causes.

CONCLUSIONS

Macro-PRL in women of reproductive age might be mostly IgG-type anti-PRL autoantibody-bound PRL. The likely origin of macro-PRL in babies is the transplacental transfer of IgG-type anti-PRL autoantibodies or PRL-IgG complexes from the mothers to their babies.

Vitex agnus castus Extract Ze 440: Diterpene and Triterpene's Interactions with Dopamine D2 Receptor

Pre-clinical studies suggest that extracts prepared from the fruits of Vitex agnus castus (VAC) interact with dopamine D2 receptors, leading to reduced prolactin secretion. In previous experiments, dopaminergic activity was mostly evaluated using radioligand binding assays or via the inhibition of prolactin release from rat pituitary cells. Diterpenes featuring a clerodadienol scaffold were identified as major active compounds, but no conclusive data regarding their potency and intrinsic activity are available. Utilising advances in chromatography, we re-examined this topic using HPLC-based tracking of bioactivity via microfractionation of the VAC extract Ze 440. Using a cAMP-based assay, we measured dopaminergic activity in CHO-K1 cells that overexpress the human D2 receptor. Six diterpenes were isolated from two active HPLC microfractions. Viteagnusin I emerged as the most potent diterpene (EC50: 6.6 µM), followed by rotundifuran (EC50: 12.8 µM), whereas vitexilactone was inactive (EC50: >50 µM). Interestingly, triterpenes were also identified as active, with 3-epi-maslinic acid being the most active compound (EC50: 5.1 µM). To better understand these interactions at the molecular level, selected diterpenes and triterpenes were analysed through molecular docking against D2 receptor structures. Our data show that the dopaminergic activity of VAC diterpenes seems to depend on the configuration and on ring substitution in the side chain. This study also highlights for the first time the dopaminergic contribution of triterpenes such as 3-epi-maslinic acid.

Increased Cardiometabolic Risk in Men with Hypoprolactinemia: A Pilot Study

Low prolactin levels in men predispose them to mood disturbances, sexual dysfunction, and diabetes. The purpose of the current study was to assess cardiometabolic risk in males with hypoprolactinemia. This prospective study included three age-matched groups of young and middle-aged men: individuals with cabergoline-induced hypoprolactinemia (n = 15), cabergoline-treated subjects with prolactin levels within the reference range (n = 20), and untreated men with normal prolactin levels (n = 31). In men with hypoprolactinemia, the cabergoline dose was reduced in order to normalize prolactin concentration. Anthropometric parameters, blood pressure, QRISK3 score; plasma concentrations of prolactin, glucose, insulin, lipids, uric acid, high-sensitivity C-reactive protein (hsCRP), fibrinogen, homocysteine, and testosterone; whole-blood levels of glycated hemoglobin (HbA1C); urinary albumin-to-creatinine ratio (UACR); and carotid intima-media thickness were assessed at baseline and six months later. Men with hypoprolactinemia were characterized by higher body mass index, fat content, waist circumference, systolic blood pressure, fasting and 2 h post-load glucose, HbA1C, HOMA1-IR, uric acid, hsCRP, fibrinogen, homocysteine, and UACR; by lower HDL cholesterol and testosterone; by greater intima-media thickness; and by a higher QRISK3 score than their peers with normal prolactin levels. There were no statistically significant differences in the measured parameters between both groups of men with normal prolactin levels. Normalization of prolactin concentration was accompanied by normalization of biochemical variables, systolic blood pressure, and QRISK3 score. Although cabergoline dose reduction did not cause statistically significant changes in the remaining anthropometric parameters and intima-media thickness, six months later, they did not differ from those observed in the remaining study groups. Our findings suggest that iatrogenic hypoprolactinemia is associated with increased cardiometabolic risk, which is reversible and resolves after the normalization of prolactin levels.

Canonical transient receptor potential channels and hypothalamic control of homeostatic functions

Recent molecular biological and electrophysiological studies have identified multiple transient receptor potential (TRP) channels in hypothalamic neurons as critical modulators of homeostatic functions. In particular, the canonical transient receptor potential channels (TRPCs) are expressed in hypothalamic neurons that are vital for the control of fertility and energy homeostasis. Classical neurotransmitters such as serotonin and glutamate and peptide neurotransmitters such as kisspeptin, neurokinin B and pituitary adenylyl cyclase-activating polypeptide signal through their cognate G protein-coupled receptors to activate TPRC 4, 5 channels, which are essentially ligand-gated calcium channels. In addition to neurotransmitters, circulating hormones like insulin and leptin signal through insulin receptor (InsR) and leptin receptor (LRb), respectively, to activate TRPC 5 channels in hypothalamic arcuate nucleus pro-opiomelanocortin (POMC) and kisspeptin (arcuate Kiss1 [Kiss1ARH]) neurons to have profound physiological (excitatory) effects. Besides its overt depolarizing effects, TRPC channels conduct calcium ions into the cytoplasm, which has a plethora of downstream effects. Moreover, not only the expression of Trpc5 mRNA but also the coupling of receptors to TRPC 5 channel opening are regulated in different physiological states. In particular, the mRNA expression of Trpc5 is highly regulated in kisspeptin neurons by circulating estrogens, which ultimately dictates the firing pattern of kisspeptin neurons. In obesity states, InsRs are "uncoupled" from opening TRPC 5 channels in POMC neurons, rendering them less excitable. Therefore, in this review, we will focus on the critical role of TRPC 5 channels in regulating the excitability of Kiss1ARH and POMC neurons in different physiological and pathological states.

Role of Medical and Surgical Treatment in Management of the Patients With Prolactinoma: A Single-Center Experience

BACKGROUND

Current guidelines recommend dopamine agonists (DA) as the primary therapeutic approach for prolactinomas; however, emerging evidence suggests that surgical intervention can also yield favorable outcomes.

OBJECTIVE

To comprehensively evaluate prolactinoma patients undergoing surgical and medical treatments at our pituitary center.

METHODS

Retrospective review of mMedical records from prolactinoma patients treated between 2015 and 2022 was performedwere retrospectively reviewed. The study focused on treatment outcomes and remission rates while investigating factors influencing the success of both treatment modalities in achieving remission.

RESULTS

A total of 301 prolactinoma patients were included, of whom 199 were women. Among them, 235 were managed medically, while 66 underwent surgical intervention. The overall remission rates of patients treated with medical and surgery were similar at the final examination (Respectively respectively 82.9% and 81.8%, p=0.114). Factors associated with remission in both treatment modalities included female sex, low initial prolactin levels, small adenoma size, and absence of cavernous invasion. Compared to DA treatment, Ssurgical treatment demonstrated a higher rate of drug-free remission compared to DA treatment for microadenomas, and macroadenomas without cavernous invasion. In cases with cavernous invasion, standalone surgical treatment yielded a low rate of drug-free remission (7.7%); however, when combined with DA therapy post-surgery, remission rates increased to 66.7%.

CONCLUSION

Medical treatment with DAs remains the preferred option for macroadenomas with cavernous sinus invasion, and giant adenomas, with surgery reserved for selected cases to address complications. Conversely, surgery emerges as the most effective modality for achieving remission in patients with microadenomas, and macroadenomas confined to the sella. The recommendation of DAs as first-line therapy for all patients has been withdrawn in the current guidelines, and individual treatment approaches based on tumor characteristics are emphasized. Our results support this approach.

Diagnostic Utility of the Prolactin Decrease Rate in the Diagnosis of Mild Hyperprolactinemia

Background Previous studies have yielded conflicting findings on the routine use of serial prolactin (PRL) measurement in patients with inconsistent signs or symptoms of mild hyperprolactinemia (HP). Therefore, we aimed to evaluate the effectiveness of serial PRL measurement and a previously undefined parameter which is the PRL decrease rate (PDR) method in the diagnosis of mild HP and prolactinoma. Materials and methods The data obtained from medical charts of patients in the sample population included serial PRL values at 0 minute (min), 30 min, and 60 min as well as macroprolactinemia (mPRL) levels. PDR was defined as the ratio of the difference between the PRL levels at 0 min and 60 min to the PRL level at 0 min. Results  We obtained referral PRL (rPRL) levels from the files of 221 of 268 patients referred for HP. Of those referred, 153 (69.2%) had mild HP. Of the 165 patients in the serial PRL measurement group, HP was detected in 76 (46.1%), and stress-induced PRL elevation was found in 24 (14.5%). Of the 101 patients in the single PRL measurement group, HP was detected in 72 (69.9%; p<0.001). Moreover, a PDR score of 38.1% had 99% specificity and 26% sensitivity in HP exclusion, and a PDR score of 20.6% had 100% specificity and 30% sensitivity in prolactinoma exclusion. Conclusion In cases where clinical findings are insufficient, the serial PRL measurement method combined with the PDR for the diagnosis of prolactinoma and HP appears to be more reliable than the single measurement method.

The influence of the prolactin/vasoinhibin axis on post-stroke lesion volume, astrogliosis, and survival

Ischemic stroke is a significant global health issue, ranking fifth among all causes of death and a leading cause of serious long-term disability. Ischemic stroke leads to severe outcomes, including permanent brain damage and neuronal dysfunction. Therefore, decreasing and preventing neuronal injuries caused by stroke has been the focus of therapeutic research. In recent years, many studies have shown that fluctuations in hormonal levels influence the prognosis of ischemic stroke. Thus, it is relevant to understand the role of hormones in the pathophysiological mechanisms of ischemic stroke for preventing and treating this health issue. Here, we investigate the contribution of the prolactin/vasoinhibin axis, an endocrine system regulating blood vessel growth, immune processes, and neuronal survival, to the pathophysiology of ischemic stroke. Male mice with brain overexpression of prolactin or vasoinhibin by adeno-associated virus (AAV) intracerebroventricular injection or lacking the prolactin receptor (Prlr-/-) were exposed to transient middle cerebral artery occlusion (tMCAO) for 45 min followed by 48 h of reperfusion. Overexpression of vasoinhibin or the absence of the prolactin receptor led to an increased lesion volume and decreased survival rates in mice following tMCAO, whereas overexpression of prolactin had no effect. In addition, astrocytic distribution in the penumbra was altered, glial fibrillary acidic protein and S100b mRNA expressions were reduced, and interleukin-6 mRNA expression increased in the ischemic hemisphere of mice overexpressing vasoinhibin. Of note, prolactin receptor-null mice (Prlr-/-) showed a marked increase in serum vasoinhibin levels. Furthermore, vasoinhibin decreased astrocyte numbers in mixed hippocampal neuron-glia cultures. These observations suggest that increased vasoinhibin levels may hinder astrocytes' protective reactivity. Overall, this study suggests the involvement of the prolactin/vasoinhibin axis in the pathophysiology of ischemic stroke-induced brain injury and provides insights into the impact of its dysregulation on astrocyte reactivity and lesion size. Understanding these mechanisms could help develop therapeutic interventions in ischemic stroke and other related neurological disorders.

Prolactin and Hyperprolactinaemia in Endometriosis-Related Infertility: Are There Clinically Significant Connections?

Endometriosis and hyperprolactinaemia are conditions that might lead to infertility as a consequence. The aim of this article was to present the current knowledge about possible relationships between prolactin/hyperprolactinaemia and endometriosis-related infertility. Experimental studies on local prolactin acting as cytokine and relationship of prolactin and endometriotic tissue, as well as clinical studies on hyperprolactinaemia and endometriosis-related infertility suggest the possible role of prolactin in endometriosis-related infertility, but final proof is still missing and the exact pathogenesis of infertility in such cases is still under investigation. Novel strategies in the treatment of endometriosis-related infertility, based on its connection with prolactin such as the use of prolactin receptor antibodies and prolactin receptor antagonists, are under investigation, but adequate clinical studies have yet to be undertaken.