Chronic hyperprolactinemia evoked by disruption of lactotrope dopamine D2 receptors impacts on liver and adipocyte genes related to glucose and insulin balance

Serum prolactin levels were positively related to metabolic indexes and disorders in male obese patients

PURPOSE

The role of prolactin (PRL) in glucolipid metabolism was inconsistent, and there were few studies on the metabolic role of PRL in obese patients. The study aims to explore association between PRL level and metabolic disorders in male obese patients.

METHODS

A retrospective study was conducted. Eighty-nine male patients with obesity were included, and their clinical data were recorded.

RESULTS

A total of 89 male obese patients were included in this study. Their average age was 24.5 ± 9.0 years and BMI was 42.8 ± 9.1 kg/m2. The average waist circumference and body fat percentage was 129.6 ± 19.6 cm and 42.9 ± 8.0%, respectively. The median prolactin levels were 10.0 ng/ml (range: 3.93-30.1 ng/ml). 79.0% (49/62) of these patients presented with NAFLD and 77.3% (68/88) of them was dyslipidemia. Further, serum prolactin level was positively correlated with BMI (r = 0.225, P = 0.034), body fat percentage (r = 0.326, P = 0.017), ALT (r = 0.273, P = 0.011) and AST (r = 0.245, P = 0.029). Compared with low PRL group (<10 ng/ml), the incidence of morbid obesity and NAFLD was higher in high PRL group (morbid obesity: 71.1% vs 45.5%, P = 0.018 and NAFLD: 91.2% vs 64.3%, P = 0.013). In addition, the risk of NAFLD and morbid obesity in high PRL group (>10 ng/ml) was higher than low PRL group (OR:5.187, 95%CI 1.194-22.544, P = 0.028 and OR: 4.375, 95% CI 1.595-11.994, P = 0.004). The increased risk of NAFLD and morbid obesity in the high PRL group still existed after adjusting for age and Testosterone.

CONCLUSION

Serum prolactin levels were positively associated with deterioration of metabolic indexes in male obese patients, as well as NAFLD and morbid obesity.

Development of novel tools for dissection of central versus peripheral dopamine D2-like receptor signaling in dysglycemia

Dopamine (DA) D2-like receptors in both the central nervous system (CNS) and the periphery are key modulators of metabolism. Moreover, disruption of D2-like receptor signaling is implicated in dysglycemia. Yet, the respective metabolic contributions of CNS versus peripheral D2-like receptors including D2 (D2R) and D3 (D3R) receptors remain poorly understood. To address this, we developed new pharmacological tools, D2-like receptor agonists with diminished and delayed blood-brain barrier capability, to selectively manipulate D2R/D3R signaling in the periphery. We designated bromocriptine methiodide (BrMeI), a quaternary methiodide analogue of D2/3R agonist and diabetes drug bromocriptine, as our lead compound based on preservation of D2R/D3R binding and functional efficacy. We then used BrMeI and unmodified bromocriptine to dissect relative contributions of CNS versus peripheral D2R/D3R signaling in treating dysglycemia. Systemic administration of bromocriptine, with unrestricted access to CNS and peripheral targets, significantly improved both insulin sensitivity and glucose tolerance in obese, dysglycemic mice in vivo. In contrast, metabolic improvements were attenuated when access to bromocriptine was restricted either to the CNS through intracerebroventricular administration or delayed access to the CNS via BrMeI. Our findings demonstrate that the coordinated actions of both CNS and peripheral D2-like receptors are required for correcting dysglycemia. Ultimately, the development of a first-generation of drugs designed to selectively target the periphery provides a blueprint for dissecting mechanisms of central versus peripheral DA signaling and paves the way for novel strategies to treat dysglycemia.

Dopamine receptor agonists mechanism of actions on glucose lowering and their connections with prolactin actions

Robust experiment evidence suggests that prolactin can enhance beta-cell proliferation and increase insulin secretion and sensitivity. Apart from acting as an endocrine hormone, it also function as an adipokine and act on adipocytes to modulate adipogenesis, lipid metabolism and inflammation. Several cross-sectional epidemiologic studies consistently showed that circulating prolactin levels positive correlated with increased insulin sensitivity, lower glucose and lipid levels, and lower prevalence of T2D and metabolic syndrome. Bromocriptine, a dopamine receptor agonist used to treat prolactinoma, is approved by Food and Drug Administration for treatment in type 2 diabetes mellitus since 2009. Prolactin lowering suppress insulin secretion and decrease insulin sensitivity, therefore dopamine receptor agonists which act at the pituitary to lower serum prolactin levels are expected to impair glucose tolerance. Making it more complicating, studies exploring the glucose-lowering mechanism of bromocriptine and cabergoline have resulted in contradictory results; while some demonstrated actions independently on prolactin status, others showed glucose lowering partly explained by prolactin level. Previous studies showed that a moderate increase in central intraventricular prolactin levels stimulates hypothalamic dopamine with a decreased serum prolactin level and improved glucose metabolism. Additionally, sharp wave-ripples from the hippocampus modulates peripheral glucose level within 10 minutes, providing evidence for a mechanistic link between hypothalamus and blood glucose control. Central insulin in the mesolimbic system have been shown to suppress dopamine levels thus comprising a feedback control loop. Central dopamine and prolactin levels plays a key role in the glucose homeostasis control, and their dysregulation could lead to the pathognomonic central insulin resistance depicted in the “ominous octet”. This review aims to provide an in-depth discussion on the glucose-lowering mechanism of dopamine receptor agonists and on the diverse prolactin and dopamine actions on metabolism targets.

Neuroendocrine control of brown adipocyte function by prolactin and growth hormone

Growth hormone (GH) is fundamental for growth and glucose homeostasis, and prolactin for optimal pregnancy and lactation outcome, but additionally, both hormones have multiple functions that include a strong impact on energetic metabolism. In this respect, prolactin and GH receptors have been found in brown, and white adipocytes, as well as in hypothalamic centers regulating thermogenesis. This review describes the neuroendocrine control of the function and plasticity of brown and beige adipocytes, with a special focus on prolactin and GH actions. Most evidence points to a negative association between high prolactin levels and the thermogenic capacity of BAT, except in early development. During lactation and pregnancy, prolactin may be a contributing factor that limits unneeded thermogenesis, downregulating BAT UCP1. Furthermore, animal models of high serum prolactin have low BAT UCP1 levels and whitening of the tissue, while lack of Prlr induces beiging in WAT depots. These actions may involve hypothalamic nuclei, particularly the DMN, POA and ARN, brain centers that participate in thermogenesis. Studies on GH regulation of BAT function present some controversies. Most mouse models with GH excess or deficiency point to an inhibitory role of GH on BAT function. Even so, a stimulatory role of GH on WAT beiging has also been described, in accordance with whole-genome microarrays that demonstrate divergent response signatures of BAT and WAT genes to the loss of GH signaling. Understanding the physiology of BAT and WAT beiging may contribute to the ongoing efforts to curtail obesity.

A cautionary tale: Alien prolactins may induce lesser, no, or opposite effects to homologous hormone!

Cost and availability have often dictated the use of heterologous/alien prolactins in experiments, particularly in vivo. The assumption has been that what is initiated in the target cell is representative of the homologous hormone since many heterologous mammalian prolactins bind to and activate rodent receptors. Here, we examined gene expression in mouse liver in response to a 7-day treatment with recombinant mouse prolactin (mRecPRL), recombinant ovine prolactin (oRecPRL) and pituitary extract ovine prolactin (oPitPRL). Having established mouse ribosomal protein S9 as the most stable reference gene in the liver in the absence and presence of prolactin treatment, we examined expression of the two most highly expressed prolactin receptors (PRLRs) and three members of the Cyp3a group of cytochrome P450 isoenzymes by qRTPCR. For short form (SF) 3 PRLR, mRecPRL doubled expression while for oRecPRL and oPitPRL expression was only 1.3-fold control. For the long form (LF) PRLR, changes were similar to those seen for SF 3 PRLR, such that the SF3:LF PRLR ratio remained the same. Expression of the Cyp3as was also dependent on the prolactin origin and, although mRecPRL always stimulated, the other PRLs caused varying results. Compared to control, Cyp3a16 was stimulated 12-fold by mRecPRL, 3-fold by oRecPRL, and 6-fold by oPitPRL. For Cyp3a41, mRecPRL was 3.7-fold control, oRecPRL was without effect, and oPitPRL was 2-fold control. Importantly, for Cyp3a44, mRecPRL stimulated 2-fold, whereas both oRecPRL and oPitPRL had an opposite, inhibitory effect, with expression at 0.5-fold control. We conclude that homologous hormone had the largest stimulatory effect on expression of all measured genes and that by contrast heterologous hormone showed reduced activity, no activity, or opposite activity, depending on the gene being analyzed. Thus, experimentation using alien heterologous PRL may lead to inaccurate conclusions.

Non-alcoholic fatty liver disease across endocrinopathies: Interaction with sex hormones

Nonalcoholic fatty liver disease (NAFLD) has emerged as the most frequent chronic liver disease globally. NAFLD is strongly associated with metabolic syndrome and it has been recently suggested that to rename NAFLD as metabolic dysfunction-associated fatty liver disease (MAFLD). NAFLD has been studied in different endocrine axes and accumulating body of clinical and experimental studies have suggested that NAFLD is associated with polycystic ovarian syndrome (PCOS), hypopituitarism, growth hormone deficiency (GHD), hypogonadism and other endocrine disorders. In fact, endocrine dysfunction may be considered as the major contributor for the development, progression, and severity of NAFLD. In the present comprehensive review, we discussed the epidemiological and clinical evidence on the epidemiology, pathophysiology, and management of NAFLD in endocrine disorders, with an emphasis on the effects of sex-specific hormones/conditions as well as molecular basis of NAFLD development in these endocrine diseases.

Prolactin and Maternal Metabolism in Women With a Recent GDM Pregnancy and Links to Future T2D: The SWIFT Study

CONTEXT

Prolactin is a multifaceted hormone known to regulate lactation. In women with gestational diabetes mellitus (GDM) history, intensive lactation has been associated with lower relative risk of future type 2 diabetes (T2D). However, the role of prolactin in T2D development and maternal metabolism in women with a recent GDM pregnancy has not been ascertained.

OBJECTIVE

We examined the relationships among prolactin, future T2D risk, and key clinical and metabolic parameters.

METHODS

We utilized a prospective GDM research cohort (the SWIFT study) and followed T2D onset by performing 2-hour 75-g research oral glucose tolerance test (OGTT) at study baseline (6-9 weeks postpartum) and again annually for 2 years, and also by retrieving clinical diagnoses of T2D from 2 years through 10 years of follow up from electronic medical records. Targeted metabolomics and lipidomics were applied on fasting plasma samples collected at study baseline from 2-hour 75-g research OGTTs in a nested case-control study (100 future incident T2D cases vs 100 no T2D controls).

RESULTS

Decreasing prolactin quartiles were associated with increased future T2D risk (adjusted odds ratio 2.48; 95% CI, 0.81-7.58; P = 0.05). In women who maintained normoglycemia during the 10-year follow-up period, higher prolactin at baseline was associated with higher insulin sensitivity (P = 0.038) and HDL-cholesterol (P = 0.01), but lower BMI (P = 0.001) and leptin (P = 0.002). Remarkably, among women who developed future T2D, prolactin was not correlated with a favorable metabolic status (all P > 0.05). Metabolomics and lipidomics showed that lower circulating prolactin strongly correlated with a T2D-high risk lipid profile, with elevated circulating neutral lipids and lower concentrations of specific phospholipids/sphingolipids.

CONCLUSION

In women with recent GDM pregnancy, low circulating prolactin is associated with specific clinical and metabolic parameters and lipid metabolites linked to a high risk of developing T2D.

Nonalcoholic Fatty Liver Disease and Endocrine Axes—A Scoping Review

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease. NAFLD often occurs associated with endocrinopathies. Evidence suggests that endocrine dysfunction may play an important role in NAFLD development, progression, and severity. Our work aimed to explore and summarize the crosstalk between the liver and different endocrine organs, their hormones, and dysfunctions. For instance, our results show that hyperprolactinemia, hypercortisolemia, and polycystic ovary syndrome seem to worsen NAFLD’s pathway. Hypothyroidism and low growth hormone levels also may contribute to NAFLD’s progression, and a bidirectional association between hypercortisolism and hypogonadism and the NAFLD pathway looks likely, given the current evidence. Therefore, we concluded that it appears likely that there is a link between several endocrine disorders and NAFLD other than the typically known type 2 diabetes mellitus and metabolic syndrome (MS). Nevertheless, there is controversial and insufficient evidence in this area of knowledge.

Severe Hyperprolactinemia Promotes Brown Adipose Tissue Whitening and Aggravates High Fat Diet Induced Metabolic Imbalance

BACKGROUND

The association of high serum prolactin and increased body weight is positive but controversial, therefore we hypothesized that additional factors such as diets and the impact of prolactin on brown adipose tissue may condition its metabolic effects.

METHODS

We used LacDrd2KO females with lifelong severe hyperprolactinemia due dopamine-D2 receptor deletion from lactotropes, and slow onset of metabolic disturbances, and compared them to their respective controls (Drd2 ^loxP/loxP ). Food intake, and binge eating was evaluated. We then challenged mice with a High Fat (HFD) or a Control Diet (CD) for 8 weeks, beginning at 3 months of age, when no differences in body weight are found between genotypes. At the end of the protocol brown and white adipose tissues were weighed, and thermogenic and lipogenic markers studied, using real time PCR (Ucp1, Cidea, Pgc1a, Lpl, adiponectin, Prlr) or immunohistochemistry (UCP1). Histochemical analysis of brown adipose tissue, and glucose tolerance tests were performed.

RESULTS

Hyperprolactinemic mice had increased food intake and binge eating behavior. Metabolic effects induced by a HFD were exacerbated in lacDrd2KO mice. Hyperprolactinemia aggravated HFD-induced body weight gain and glucose intolerance. In brown adipose tissue pronounced cellular whitening as well as decreased expression of the thermogenic markers Ucp1 and Pgc1a were observed in response to high prolactin levels, regardless of the diet, and furthermore, hyperprolactinemia potentiated the decrease in Cidea mRNA expression induced by HFD. In subcutaneous white adipose tissue hyperprolactinemia synergistically increased tissue weight, while decreasing Prlr, Adiponectin and Lpl mRNA levels regardless of the diet.

CONCLUSIONS

Pathological hyperprolactinemia has a strong impact in brown adipose tissue, lowering thermogenic markers and evoking tissue whitening. Furthermore, it modifies lipogenic markers in subcutaneous white adipose, and aggravates HFD-induced glucose intolerance and Cidea decrease. Therefore, severe high prolactin levels may target BAT function, and furthermore represent an adjuvant player in the development of obesity induced by high fat diets.

The interplay between prolactin and cardiovascular disease

Hyperprolactinemia can be caused by several conditions and its effects on the hypothalamic-pituitary-gonadal axis are understood in more detail. Nevertheless, in recent decades, other metabolic effects have been studied and data pointed to a potential increased cardiovascular disease (CVD) risk. A recent study showed a decrease in total and LDL- cholesterol only in men with prolactinoma treated with dopamine agonists (DA) supporting the previous results of a population study with increased CVD risk in men harboring prolactinoma. However, other population studies did not find a correlation between prolactin (PRL) levels and CVD risk or mortality. There is also data pointing to an increase in high-density lipoprotein levels, and decreases in triglycerides, carotid-intima-media thickness, C-reactive protein, and homocysteine levels in patients with prolactinoma on DA treatment. PRL was also implicated in endothelial dysfunction in pre and postmenopausal women. Withdrawal of DA resulted in negative changes in vascular parameters and an increase in plasma fibrinogen. It has been shown that PRL levels were positively correlated with blood pressure and inversely correlated with dilatation of the brachial artery and insulin sensitivity, increased homocysteine levels, and elevated D-dimer levels. Regarding possible mechanisms for the association between hyperprolactinemia and CVD risk, they include a possible direct effect of PRL, hypogonadism, and even effects of DA treatment, independently of changes in PRL levels. In conclusion, hyperprolactinemia seems to be associated with impaired endothelial function and DA treatment could improve CVD risk. More studies evaluating CVD risk in hyperprolactinemic patients are important to define a potential indication of treatment beyond hypogonadism.

Galectin-1 impacts on glucose homeostasis by modulating pancreatic insulin release

Type-2 diabetes mellitus (T2DM) is an expanding global health problem, involving defective insulin secretion by pancreatic β-cells and peripheral insulin resistance, leading to impaired glucose regulation. Galectin-1, an endogenous lectin with affinity for N-acetyllactosamine (LacNAc)-containing glycans, has emerged as a regulator of inflammatory and metabolic disorders. However, the role of galectin-1 in glucose homeostasis and pancreatic β-cell function, independently of hypercaloric diets, has not been explored. Here, we identified a phenotype compatible with T2DM, involving alterations in glucose metabolism and pancreatic insulin release, in female but not male mice lacking galectin-1 (Lgals1-/-). Compared with age-matched controls, Lgals1-/female mice exhibited higher body weight and increased food intake ad libitum as well as after fasting and acute re-feeding. Although fasted serum insulin levels and insulin sensitivity were similar in both genotypes, Lgals1-/- female mice presented altered glucose tolerance and higher basal glucose levels depending on the fasting period. Insulin response to glucose overload was impaired, while pancreatic insulin content was enhanced in the absence of galectin-1. Accordingly, recombinant galectin-1 enhanced glucose-stimulated insulin release in vitro. Our study identifies a role for galectin-1 in regulating glucose metabolism through modulation of pancreatic insulin secretion, highlighting novel opportunities to control T2DM.

Global Deletion of the Prolactin Receptor Aggravates Streptozotocin-Induced Diabetes in Mice

Prolactin (PRL) levels are reduced in the circulation of rats with diabetes or obesity, and lower circulating levels of PRL correlate with increased prevalence of diabetes and a higher risk of metabolic alterations in the clinic. Furthermore, PRL stimulates β-cell proliferation, survival, and insulin production and pregnant mice lacking PRL receptors in β-cells develop gestational diabetes. To investigate the protective effect of endogenous PRL against diabetes outside pregnancy, we compared the number of cases and severity of streptozotocin (STZ)-induced hyperglycemia between C57BL/6 mice null for the PRL receptor gene (Prlr^-/- ) and wild-type mice (Prlr^+/+ ). STZ-treated diabetic Prlr^-/- mice showed a higher number of cases and later recovery from hyperglycemia, exacerbated glucose levels, and glucose intolerance compared to the Prlr^+/+ mice counterparts. Consistent with the worsening of hyperglycemia, pancreatic islet density, β-cell number, proliferation, and survival, as well as circulating insulin levels were reduced, whereas α-cell number and pancreatic inflammation were increased in the absence of PRL signaling. Deletion of the PRL receptor did not alter the metabolic parameters in vehicle-treated animals. We conclude that PRL protects whole body glucose homeostasis by reducing β-cell loss and pancreatic inflammation in STZ-induced diabetes. Medications elevating PRL circulating levels may prove to be beneficial in diabetes.

Metabolic functions of prolactin: Physiological and pathological aspects

Prolactin is named after its vital role of promoting milk production during lactation, although it has been implicated in multiple functions within the body, including metabolism and energy homeostasis. Prolactin has been hypothesised to play a key role in driving many of the adaptations of the maternal body to allow the mother to meet the physiological demands of both pregnancy and lactation, including the high energetic demands of the growing foetus followed by milk production to support the offspring after birth. Prolactin receptors are found in many tissues involved in metabolism and food intake, such as the pancreas, liver, hypothalamus, small intestine and adipose tissue. We review the literature examining the effects of prolactin in these various tissues and how they relate to changes in function in physiological states of high prolactin, such as pregnancy and lactation, and in pathological states of hyperprolactinaemia in the adult. In many cases, whether prolactin promotes healthy metabolism or leads to dysregulation of metabolic functions is highly dependent on the situation. Overall, although prolactin may not play a major role in regulating metabolism and body weight outside of pregnancy and lactation, it definitely has the ability to contribute to metabolic function.

Time for a New Perspective on Prolactin in Metabolism

The pituitary hormone prolactin (PRL) regulates a variety of functions beyond reproduction. The association between physiological (pregnancy) and pathological (prolactinoma) hyperprolactinemia and metabolic alterations led to the concept of this hormone being diabetogenic. However, large cohort clinical studies have recently shown that low circulating PRL levels are associated with metabolic disease and represent a risk factor for type 2 diabetes (T2D), whereas high PRL levels are beneficial. Moreover, PRL acts on the pancreas, liver, adipose tissue, and hypothalamus to maintain and promote metabolic homeostasis. By integrating basic and clinical evidence, we hypothesize that upregulation of PRL levels is a mechanism to maintain metabolic homeostasis and, thus, propose that the range of PRL levels considered physiological should be expanded to higher values.

miR-142-3p Regulates Milk Synthesis and Structure of Murine Mammary Glands via PRLR-Mediated Multiple Signaling Pathways

Murine mammary gland is an ideal model for studying the development and milk synthesis in dairy animals. MicroRNAs play an important role in milk synthesis and mammary gland development; however, the molecular mechanism of miR-142-3p continues to be poorly understood. Here, we knocked down miR-142-3p expression in vitro and vivo, increased the prolactin receptor expression and activated many downstream cellular proteins, such as mammalian target of rapamycin, sterol regulatory element-binding transcription factor 1, cyclin D1, and signal transducer and activator of transcription 5. Additionally, miR-142-3p knockdown in mouse mammary gland epithelial cells increased proliferation but not viability, induced cell cycle progression, decreased apoptosis, and increased the expression of triglycerides and β-casein. Moreover, miR-142-3p knockdown in murine mammary gland tissue in vivo affected the structure and function of the mammary gland, which showed an increased number of lobules and ducts and was more capable of producing milk. However, overexpression of miR-142-3p had the opposite effects. In summary, these data reveal that miR-142-3p regulates milk synthesis and the structure of murine mammary glands via PRLR-mediated multiple signaling pathways.

Dopamine D4 receptor protected against hyperglycemia-induced endothelial dysfunction via PI3K /eNOS pathway

Hyperglycemia-induced endothelial dysfunction is generally believed to be the basis of diabetic vascular complications. Dopamine receptors is known to play an important protective role in diabetes. However, the protective effect of dopamine receptors against hyperglycemia-induced endothelial damage in diabetic rats is still unknown. In the present study, we established a cell model of hyperglycemia-induced endothelial dysfunction by treating human umbilical vein endothelial cells (HUVEC) with high glucose. MTT and lactate dehydrogenase assays results showed that high glucose treatment significantly reduced the cell viability and down-regulated dopamine D₄ receptor. Pre-treatment with PD168077, a specific D₄ receptor agonist, greatly improved endothelial cell viability and decreased apoptosis. Furthermore, pharmacological inhibition of phosphoinositide 3-kinase (PI3K) and endothelial nitric oxide synthase (eNOS) eliminated the protective effect of D₄ receptor against endothelial injury. More importantly, the expression level of D₄ receptor was also dramatically down-regulated in the arterial endothelium of rats with streptozotocin-(STZ)-induced diabetes, and the STZ-induced impairment of acetylcholine-induced vasodilation was reversed by activation of D₄ receptor. In conclusion, our results indicated that dopamine D₄ receptor protected against hyperglycemia-induced endothelial dysfunction via the PI3K/eNOS pathway, which may provide a novel strategy in the treatment of diabetes.

Prolactin - a pleiotropic factor in health and disease

The principal role of prolactin in mammals is the regulation of lactation. Prolactin is a hormone that is mainly synthesized and secreted by lactotroph cells in the anterior pituitary gland. Prolactin signalling occurs via a unique transmembrane prolactin receptor (PRL-R). The structure of the PRL-R has now been elucidated and is similar to that of many biologically fundamental receptors of the class 1 haematopoietic cytokine receptor family such as the growth hormone receptor. The PRL-R is expressed in a wide array of tissues, and a growing number of biological processes continue to be attributed to prolactin. In this Review, we focus on the newly discovered roles of prolactin in human health and disease, particularly its involvement in metabolic homeostasis including body weight control, adipose tissue, skin and hair follicles, pancreas, bone, the adrenal response to stress, the control of lactotroph cell homeostasis and maternal behaviour. New data concerning the pathological states of hypoprolactinaemia and hyperprolactinaemia will also be presented and discussed.

The antipsychotics sulpiride induces fatty liver in rats via phosphorylation of insulin receptor substrate-1 at Serine 307-mediated adipose tissue insulin resistance

Cumulative evidence has suggested that many antipsychotics cause metabolic abnormalities. Adipose tissue insulin resistance (Adipo-IR) contributes to the development and progress of metabolic abnormalities including fatty liver by inducing excessive free fatty acid release from adipose tissue. Sulpiride is an old antipsychotic still frequently used in many developing countries. However, its adverse metabolic effects remain poorly understood. Here, chronic administration of sulpiride (80 mg/kg, subcutaneously, once daily for 6 weeks) elevated fasting insulin concentration and the index of the homeostasis model assessment of insulin resistance in rats. More importantly, sulpiride increased hepatic triglyceride accumulation and Oil Red O-stained area, indicating the induction of fatty liver by sulpiride. Sulpiride also increased plasma non-esterified fatty acid concentrations at the baseline and during an oral glucose tolerance test, the Adipo-IR index, and adipocyte size. Adipose gene expression profile revealed that sulpiride decreased mRNA and protein expression of insulin receptor substrate (IRS)-1, but not IRS-2. Furthermore, sulpiride increased phosphorylation of both Ser³⁰⁷ in IRS-1 and Ser⁴⁷³ in Akt at baseline. Co-treatment with bromocriptine (a dopamine D₂ receptor agonist) attenuated sulpiride-induced hyperprolactinemia, but it was without effect on insulin resistance and fatty liver. Therefore, the present results suggest that sulpiride induces fatty liver in rats via phosphorylation of IRS-1 at Ser³⁰⁷-mediated adipose tissue insulin resistance, in which dopamine D₂ receptor is possibly not involved. Our findings may provide new insights into the mechanisms underlying the steatotic effect of the old antipsychotic.