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Background: Long-term follow-up of studies to investigate preventive effects of aspirin on arterial thrombosis indicate that aspirin reduces the incidence and mortality of some cancers in Western populations., Objectives: To explore the effects of aspirin on cancer incidence and mortality in the elderly Japanese., Patients/methods: Patients aged 60 to 85 years, presenting with hypertension, dyslipidemia, or diabetes mellitus (n = 14 601, 7297 in the aspirin group and 7304 in the no-aspirin group) participated the Japanese Primary Prevention Project (JPPP), a multicenter, open-label, randomized, parallel-group trial. A subanalysis of JPPP was performed to analyze the incidence of newly diagnosed cancer and death related to cancer., Results: The cumulative incidence of newly diagnosed cancer was 5.60% (4.65-6.64%) in the aspirin group and 4.14% (3.67-4.66%) in the no-aspirin group. The hazard ratio for newly diagnosed cancer was 1.24 (1.06-1.46), and the cancer incidence was significantly higher in the aspirin group. The cumulative cancer mortality was 1.96% (1.65-2.31%) in the aspirin group and 1.87% (1.56-2.22%) in the no-aspirin group, with no statistically significant difference. The Fine and Gray model suggested that the difference in the incidence of newly diagnosed cancer between the two groups decreased year by year., Conclusions: Low-dose aspirin use did not reduce the cancer incidence or cancer mortality during a 5-year-average study period in the elderly Japanese. The cancer incidence in the aspirin group might decrease, however, to less than that in the no-aspirin group after the study period. Aspirin use might have led to earlier cancer diagnosis in our study.

Accumulation of phosphatidylcholine hydroperoxide (PCOOH), a primary oxidation product of phosphatidylcholine, in blood plasma has been observed in various pathological conditions, including atherosclerosis. In this study, we investigated the use of liquid chromatography-tandem mass spectrometry (LC-MS/MS) to develop a method for accurate quantification of PCOOH (1-palmitoyl-2-hydroperoxyoctadecadienoyl-sn-glycero-3-phosphocholine, 16:0/HpODE PC), focusing on isomers such as 16:0/13-HpODE PC and 16:0/9-HpODE PC. Sodiated PCOOH ([M+Na](+), m/z 812) provided not only a known product ion (m/z 147) but also characteristic product ions (m/z 541 for 16:0/13-HpODE PC and m/z 388 for 16:0/9-HpODE PC). Thus, three multiple reaction monitorings (MRMs) could be performed. MRM (812/147) enabled determination of 16:0/HpODE PC, and MRM (812/541) and MRM (812/388) allowed specific measurement of 16:0/13-HpODE PC and 16:0/9-HpODE PC, respectively. By using this method, we could determine plasma PCOOH concentrations in healthy subjects and patients with angiographically significant stenosis. In healthy subject and patient plasma, the concentration of 16:0/HpODE PC was close to the sum of the concentrations of 16:0/13-HpODE PC and 16:0/9-HpODE PC. This finding shows that radical and/or enzymatic oxidation, rather than singlet oxygen oxidation, is recognized to cause peroxidation of PC. The newly developed LC-MS/MS method appears to be a powerful tool for developing a better understanding of in vivo lipid peroxidation and its involvement in human diseases., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Objective: Impaired glucose tolerance (IGT) is an independent risk factor for atherosclerotic cardiovascular disease. However, due to the lack of appropriate animal models, the underlying mechanisms for IGT-induced atherosclerosis remain to be elucidated in vivo. We recently used selective breeding to establish 2 mouse lines with distinctively different susceptibilities to diet-induced glucose intolerance, designated selectively bred diet-induced glucose intolerance-resistant (SDG-R) and SDG-prone (SDG-P), respectively. Here, we assessed atherosclerotic lesion formation in these mice., Methods: Female SDG-R and SDG-P mice were fed an atherogenic diet (AD; 1.25% cholesterol, 0.5% sodium cholate, and 36% energy as fat) for 20 weeks (8-28 weeks of age). Oral glucose tolerance tests were performed during the AD-feeding period. Atherosclerotic lesion formation was quantitatively analyzed in serial aortic sinus sections by oil red O staining. Plasma lipids were measured after the AD-feeding period., Results: Glucose tolerance was impaired in SDG-P mice as compared to SDG-R mice over the 20-week AD-feeding period. No significant differences were observed in any plasma lipid measurement between the 2 mouse lines. Aortic sinus atherosclerotic lesion formation in SDG-P mice was approximately 4-fold greater than that in SDG-R mice., Conclusion: In 2 mouse lines with different susceptibilities to diet-induced glucose intolerance, IGT accelerated atherosclerotic lesion formation. These mice may therefore serve as useful in vivo models for investigating the causal role of IGT in the pathogenesis of atherosclerosis., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Aims: To clarify the usefulness of protein-sparing modified formula diet in obese type 2 diabetic patients, the effects of partial use of formula diet on weight reduction and changes in related metabolic variables, and the improving rates of risk factors per 1% body weight reduction, were compared with those of conventional subcaloric diet., Subjects and Methods: Obese patients [BMI >25 kg/m²] with diabetic mellitus were randomly assigned to a low-caloric diet with partial use of formula diet group (FD, n = 119) and a conventional low-caloric diet group (CD, n = 110). Subjects in FD took one pack of formula diet (MicroDiet®, 240 kcal/pack) in place of one of three daily low-caloric meals for 24 weeks. Total daily calorie prescribed was same., Result: Weight reduction was greater in FD than in CD (week 24: -3.5 vs -1.4 kg; all p < 0.001). Systolic blood pressure decreased significantly only in FD. HbA1c reduction was greater in FD than in CD. HDL-cholesterol increased significantly more in FD than in CD (week 24: +2.8 vs. +0.6 mg/dl, p < 0.001). Among several improving rates (%) of risk factors/1% body weight reduction, those of HbA1c at weeks 16 and 24, triglyceride at week 8 and HDL-cholesterol at week 24, were significantly higher in FD than CD. Doses of sulfonylurea and thiazolidinedione were significantly decreased in FD than in CD., Conclusion: Partial use of formula diet was much more effective in reducing body weight, and also in improving coronary risk factors than conventional diet in part due to reduced body weight through decreased energy diet intake and due to dietary composition of the formula diet., (© 2013 Asian Oceanian Association for the Study of Obesity . Published by Elsevier Ltd. All rights reserved.)

Increasing evidence indicates that phospholipid oxidation plays important roles in atherosclerosis. Here, we investigated the involvement of Rho-family GTPases inphosphatidylcholine hydroperoxide (PCOOH)-induced THP-1 cell adhesion to ICAM-1. Isoprenoid depletion by fluvastatin and geranylgeranyltransferase inhibition by GGTI-286 suppressed PCOOH-induced cell adhesion to ICAM-1 and F-actin-rich membrane protrusion formation. Pull-down assays demonstrated the activation of Rac1 and Rac2 in PCOOH-treated cells. Pan-Rho-family GTPase inhibitor Clostridium difficile toxin B, Rac-specific inhibitor NSC23776, and RNA interference of the Rac isoforms suppressed the cell adhesion. These findings indicate the involvement of Rac GTPase activation in PCOOH-induced cell adhesion to ICAM-1 via actin reorganization., (Copyright © 2011 Elsevier Inc. All rights reserved.)

An amino group of phosphatidylethanolamine (PE) is considered as a target for nonenzymatic glycation, and the potential involvement of lipid glycation in the pathogenesis of diabetic complications has generated interest. However, unlike an early glycation product of PE (Amadori-PE), the occurrence and roles of advanced glycation end products of PE (AGE-PE) in vivo have been unclear. Here, we developed an LC-MS/MS method for the analysis of AGE-PE [carboxymethyl-PE (CM-PE) and carboxyethyl-PE (CE-PE)]. Collision-induced dissociation of CM-PE and CE-PE produced characteristic ions, permitting neutral loss scanning (NLS) and multiple reaction monitoring (MRM) of AGE-PE. By NLS analysis, a series of AGE-PE molecular species was detected in human erythrocytes and blood plasma. In LC-MS/MS analysis, MRM enabled the separation and determination of the predominant AGE-PE species. Between healthy subjects and diabetic patients, no significant differences were observed in AGE-PE concentrations in erythrocytes and plasma, whereas Amadori-PE concentrations were higher in diabetic patients. These results provide direct evidence for the presence of AGE-PE in human blood, and indicated that, compared with Amadori-PE, AGE-PE is less likely to be accumulated in diabetic blood. The presently developed LC-MS/MS method appears to be a powerful tool for understanding in vivo lipid glycation and its pathophysiological consequence.

Background: JELIS was a large-scale clinical trial that investigated the effects of eicosapentaenoic acid (EPA) on coronary artery disease (CAD). In this paper, the data of patients registered in JELIS were analysed to compare the incidence of CAD between patients with impaired glucose metabolism (IGM) and normoglycemic (NG) patients. The effect of EPA on the incidence of CAD in patients with IGM was also assessed., Methods: The 18,645 hypercholesterolemic patients registered in JELIS were divided into two groups. One group consisted of patients with IGM (n=4565), which included the patients who had diabetes mellitus and patients who had a fasting plasma glucose of 110mg/dL or higher, either at the time of registration or after 6 months. The other group consisted of NG patients (n=14,080). CAD incidence of the two groups over the average 4.6-year follow-up period was compared, and the effect of EPA was assessed., Results: Compared to NG patients, IGM patients had a significantly higher CAD hazard ratio (1.71 in the non-EPA group and 1.63 in the EPA group). The treatment with EPA resulted in a 22% decrease in the CAD incidence (P=0.048) in IGM patients and an 18% decrease (P=0.062) in NG patients., Conclusions: It was found that the CAD risk in IGM patients is higher than in NG patients, and that highly purified EPA is very effective in decreasing the incidence of CAD among Japanese IGM patients, even though the intake of fish is high.

The accumulation of phosphatidylcholine hydroperoxide (PCOOH), a primary oxidation product of phosphatidylcholine (PC), in blood plasma and tissues has been observed in various pathological conditions, including atherosclerosis. However, the biological roles of PCOOH in these conditions remain unknown. To estimate the atherogenicity of PCOOH, we evaluated the effect of PCOOH on THP-1 monocytic cell adherence to immobilized vascular endothelial cell adhesion molecules. THP-1 cell adhesion to intracellular adhesion molecule-1 (ICAM-1) was dose-dependently increased by addition of PCOOH. Phosphatidylcholine hydroxide (a hydroxyl analog of PCOOH) also induced THP-1 cell adhesion to ICAM-1, whereas nonoxidized PC, sn-2 truncated PCs, and other hydroperoxide compounds did not affect the adhesion. In the PCOOH-treated cells, obvious protruding F-actin-rich membrane structures were formed, and lymphocyte function-associated antigen-1 (LFA-1) was localized to the protruding structures. Cytochalasin D, an actin polymerization inhibitor, suppressed the PCOOH-induced cell adhesion to ICAM-1 and the membrane protrusions. These results indicate that PCOOH evokes LFA-1-mediated cell adhesion to ICAM-1 via actin cytoskeletal organization, and the mechanism may participate in monocyte adherence to the arterial wall in the initiation of atherosclerosis.

Increasing evidence of lipid peroxidation in food deterioration and pathophysiology of diseases have revealed the need for a pure lipid hydroperoxide (LOOH) reference as an authentic standard for quantification and as a compound for biological studies in this field. Generally, LOOH is prepared from photo- or enzymatically oxidized lipids; however, separating LOOH from other oxidation products and preparing pure LOOH is difficult. Early studies showed the usability of reaction between hydroperoxide and vinyl ether for preparation of pure LOOH. Because the reactivity of vinyl ether with LOOHs other than fatty acid hydroperoxides has never been reported, here, we employed the reaction for preparation of a wide variety of pure LOOHs. Phospholipid, cholesteryl ester, triacylglycerol, or fatty acid was photo- or enzymatically oxidized; the resultant crude sample containing hydroperoxide was allowed to react with a vinyl ether [2-methoxypropene (MxP)]. Liquid chromatography (LC) and mass spectrometry confirmed that MxP selectively reacts with LOOH, yielding a stable MxP adduct (perketal). The lipophilic perketal was eluted at a position away from that of intact LOOH and identified and isolated by LC. Upon treatment with acid, perketal released the original LOOH, which was finally purified by LC. Using our optimized purification procedures, for instance, we produced 75 mg of pure phosphatidylcholine hydroperoxide (>99%) from 100 mg of phosphatidylcholine. Our developed method expands the concept of the perketal method, which provides pure LOOH references. The LOOHs prepared by the perketal method would be used as "gold standards" in LOOH methodology.

Background: Japan EPA Lipid Intervention Study (JELIS) was a large-scale clinical trial examining the effects of eicosapentaenoic acid (EPA) on coronary artery disease (CAD) in hypercholesterolemic patients. Herein, we focused on risk factors other than low-density lipoprotein cholesterol (LDL-C) to investigate the effects of EPA on CAD among JELIS primary prevention cases., Methods: Hypercholesterolemic patients on statin therapy but without evidence of CAD (n=14,981) were randomly assigned to an EPA group (n=7503) or a control group (n=7478). The relationships between incident CAD, the number of CAD risk factors (hypercholesterolemia; obesity; high triglyceride (TG) or low high-density lipoprotein cholesterol (HDL-C); diabetes; and hypertension) and EPA treatment were investigated., Results: For the control and EPA groups combined, a higher number of risk factors was directly associated with an increased incidence of CAD. Incidence was lower for the EPA group than for the control group regardless of the numbers of risk factors. Compared to patients with normal serum TG and HDL-C levels, those with abnormal levels (TG >or=150 mg/dL; HDL-C <40 mg/dL) had significantly higher CAD hazard ratio (HR: 1.71; 95% CI: 1.11-2.64; P=0.014). In this higher risk group, EPA treatment suppressed the risk of CAD by 53% (HR: 0.47; 95% CI: 0.23-0.98; P=0.043)., Conclusions: Multiple risk factors besides cholesterol are associated with markedly increased incidence of CAD. High TG with low HDL-C represents a particularly potent risk factor. EPA was effective in reducing the incidence of CAD events for patients with this dyslipidemic pattern, suggesting that EPA may be especially beneficial in patients who with abnormal TG and HDL-C levels.

We previously discovered that squalene monohydroperoxide (SQ-OOH) was produced on human forehead skin and suggested that skin squalene (SQ) may be the principal target lipid for oxidative stress (e.g., sunlight exposure). Because of its six double bonds, SQ peroxidation can yield various positional hydroperoxide isomers. However, the structural characterization of skin SQ-OOH isomers has never been reported. Here, we prepared pure SQ-OOH isomers and developed an analytical method for SQ-OOH isomers using a quadrupole/linear ion-trap mass spectrometer (QTRAP) MS/MS system. Collision-induced dissociation produced specific fragment ions for each SQ-OOH isomer, which permitted discrimination between SQ-OOH isomers by multiple reaction monitoring (MRM). When lipid extract from human forehead skin was subjected to LC-MS/MS with MRM, individual SQ-OOH isomers could be separated and detected with a sensitivity of 0.05 ng/injection. The total concentration of SQ-OOH isomers in forehead skin was approximately 956 microg/g skin lipids, but it increased up to 2,760 microg/g skin lipids after 3 h of sunlight exposure. The LC-MS/MS method was useful for investigating the peroxidation mechanisms of SQ as well as SQ-OOH-mediated skin disorders.

Antiangiogenic therapy using drugs and food components is a recognized strategy for the prevention of various angiogenesis-mediated disorders such as tumor growth, diabetic retinopathy, and rheumatoid arthritis. Our preliminary cell culture studies, using both bovine aortic endothelial cells and human umbilical vein endothelial cells (HUVEC) on screening for food-derived antiangiogenic compounds, showed tocotrienol (T3), an unsaturated version of vitamin E, to be a potential angiogenic inhibitor. We therefore investigaged the in vivo antiangiogenic properties of T3 using 2 well-characterized angiogenic models [mouse dorsal air sac (DAS) assay and the chick embryo chorioallantoic membrane (CAM) assay]. In the DAS assay, the increased neovascularization (angiogenesis index, 4.8 +/- 0.6) in tumor cell-implanted mice was suppressed (angiogenesis index, 2.7 +/- 0.6) by dietary supplementation of 10 mg T3-rich oil/d (equivalent to 4.4 mg T3/d). In the CAM assay, T3 (500-1000 microg/egg) inhibited new blood vessel formation on the growing CAM and increased the frequency of avascular zone (36-50%). To evaluate the antiangiogenic mechanism, we conducted cell-culture studies and found that T3 significantly reduced fibroblast growth factor -induced proliferation, migration, and tube formation in HUVEC (P < 0.05), with delta-T3 having the highest activity. Western blot analysis revealed that delta-T3 suppressed the phosphorylation of phosophoinositide-dependent protein kinase (PDK) and Akt, and increased the phosphorylation of apoptosis signal-regulating kinase and p38 in fibroblast growth factor-treated HUVEC, indicating that the antiangiogenic effects of T3 are associated with changes in growth factor-dependent phosphatidylinositol-3 kinase /PDK/Akt signaling as well as induction of apoptosis in endothelial cells. Our findings suggest that T3 has potential as a therapeutic dietary supplement for preventing angiogenic disorders, and therefore future clinical study will be required to evaluate the efficacy and safety of T3.

Hypercholesterolemic patients with type 2 diabetes mellitus are at increased risk of coronary heart disease (CHD); however, direct evidence is very limited in Japanese patients. The J-LIT is the first nationwide study conducted to assess the relationship between serum lipid levels and development of coronary events in Japanese hypercholesterolemic patients. We analyzed the coronary events in the J-LIT study subjects by having type 2 diabetes or not. Of the total 41,801 subjects without prior CHD who received open-label simvastatin, 5mg/day, 6554 (male 40.2%, age 57.8+/-7.8) subjects had type 2 diabetes, while 35,247 (male 30.0%, age 57.8+/-7.9) did not. In this analysis, relative coronary event risks based on a 0.26 mmol/l (10mg/dl) increase in low density lipoprotein-cholesterol (LDL-C), were similar between hypercholesterolemic subjects with and without type 2 diabetes (17.3% versus 19.4%). Although all subjects were treated with simvastatin, the subjects with type 2 diabetes have significantly more coronary events compared to the subjects without type 2 diabetes (1.80/1000 and 0.76/1000 patient-years, respectively). Given the results above, to reduce the risk of coronary events in Japanese patients with both hypercholesterolemia and type 2 diabetes, careful and strict cholesterol management is needed in addition to the control of blood glucose.

Background: Epidemiological and clinical evidence suggests that an increased intake of long-chain n-3 fatty acids protects against mortality from coronary artery disease. We aimed to test the hypothesis that long-term use of eicosapentaenoic acid (EPA) is effective for prevention of major coronary events in hypercholesterolaemic patients in Japan who consume a large amount of fish., Methods: 18 645 patients with a total cholesterol of 6.5 mmol/L or greater were recruited from local physicians throughout Japan between 1996 and 1999. Patients were randomly assigned to receive either 1800 mg of EPA daily with statin (EPA group; n=9326) or statin only (controls; n=9319) with a 5-year follow-up. The primary endpoint was any major coronary event, including sudden cardiac death, fatal and non-fatal myocardial infarction, and other non-fatal events including unstable angina pectoris, angioplasty, stenting, or coronary artery bypass grafting. Analysis was by intention-to-treat. The study was registered at ClinicalTrials.gov, number NCT00231738., Findings: At mean follow-up of 4.6 years, we detected the primary endpoint in 262 (2.8%) patients in the EPA group and 324 (3.5%) in controls-a 19% relative reduction in major coronary events (p=0.011). Post-treatment LDL cholesterol concentrations decreased 25%, from 4.7 mmol/L in both groups. Serum LDL cholesterol was not a significant factor in a reduction of risk for major coronary events. Unstable angina and non-fatal coronary events were also significantly reduced in the EPA group. Sudden cardiac death and coronary death did not differ between groups. In patients with a history of coronary artery disease who were given EPA treatment, major coronary events were reduced by 19% (secondary prevention subgroup: 158 [8.7%] in the EPA group vs 197 [10.7%] in the control group; p=0.048). In patients with no history of coronary artery disease, EPA treatment reduced major coronary events by 18%, but this finding was not significant (104 [1.4%] in the EPA group vs 127 [1.7%] in the control group; p=0.132)., Interpretation: EPA is a promising treatment for prevention of major coronary events, and especially non-fatal coronary events, in Japanese hypercholesterolaemic patients.

Peroxidized phospholipid-mediated cytotoxity is involved in the pathophysiology of a number of diseases [i.e., the abnormal increase of phosphatidylcholine hydroperoxide (PCOOH) found in the plasma of type 2 diabetic patients]. The PCOOH accumulation may relate to Amadori-glycated phosphatidylethanolamine (deoxy-D-fructosyl PE, or Amadori-PE), because Amadori-PE causes oxidative stress. However, lipid glycation inhibitor has not been discovered yet because of the lack of a lipid glycation model useful for inhibitor screening. We optimized and developed a lipid glycation model considering various reaction conditions (glucose concentration, temperature, buffer type, and pH) between PE and glucose. Using the developed model, various protein glycation inhibitors (aminoguanidine, pyridoxamine, and carnosine), antioxidants (ascorbic acid, alpha-tocopherol, quercetin, and rutin), and other food compounds (L-lysine, L-cysteine, pyridoxine, pyridoxal, and pyridoxal 5'-phosphate) were evaluated for their antiglycative properties. Pyridoxal 5'-phosphate and pyridoxal (vitamin B(6) derivatives) were the most effective antiglycative compounds. These pyridoxals could easily be condensed with PE before the glucose/PE reaction occurred. Because PE-pyridoxal 5'-phosphate adduct was detectable in human red blood cells and the increased plasma Amadori-PE concentration in streptozotocin-induced diabetic rats was decreased by dietary supplementation of pyridoxal 5'-phosphate, it is likely that pyridoxal 5'-phosphate acts as a lipid glycation inhibitor in vivo, which possibly contributes to diabetes prevention.

Functional deficiency of lipoprotein lipase (LPL) was found in a patient with severe hypertriglyceridemia. The patient was 39-year-old man with a plasma triglyceride level of 2032 mg/dl, and suffered from recurrent pancreatitis. His post heparin plasma LPL mass was almost normal, but the LPL activity was remarkably decreased. Gene analysis showed that homozygote missense mutation (204 Asp (GAC)-Glu (GAG)) exists in exon 5 of LPL gene. The patient LPL purified from post heparin plasma scarcely hydrolyzed VLDL-triglyceride and also triolein emulsified with Triton X-100 or phosphatidylcholine. When phosphatidylethenolamine, phosphatidylserine and cardiolipin were used as an emulsifier for triolein, triolein-hydrolyzing activity of the patient's LPL was observed and was much higher than that of wild-type LPL. Mutant LPL gene (Asp204-Glu) was made by site-direct mutagenesis and was transfected to COS-1 cell. The expressed LPL (Asp204-Glu) also showed the same properties. These results suggested that the LPL (Asp204-Glu) is a functional deficiency, and the activity could be recovered by using acidic phospholipids as an emulsifier.

Peroxidized phospholipid-mediated cytotoxicity is involved in the pathophysiology of diseases [i.e., an abnormal increase of phosphatidylcholine hydroperoxide (PCOOH) in plasma of type 2 diabetic patients]. The PCOOH accumulation may relate to Amadori-glycated phosphatidylethanolamine (Amadori-PE; deoxy-D-fructosyl phosphatidylethanolamine), because Amadori-PE causes oxidative stress. However, the occurrence of lipid glycation products, including Amadori-PE, in vivo is still unclear. Consequently, we developed an analysis method of Amadori-PE using a quadrupole/linear ion-trap mass spectrometer, the Applied Biosystems QTRAP. In positive ion mode, collision-induced dissociation of Amadori-PE produced a well-characterized diglyceride ion ([M+H-303]+) permitting neutral loss scanning and multiple reaction monitoring (MRM). When lipid extract from diabetic plasma was infused directly into the QTRAP, Amadori-PE molecular species could be screened out by neutral loss scanning. Interfacing liquid chromatography with QTRAP mass spectrometry enabled the separation and determination of predominant plasma Amadori-PE species with sensitivity of approximately 0.1 pmol/injection in MRM. The plasma Amadori-PE level was 0.08 mol% of total PE in healthy subjects and 0.15-0.29 mol% in diabetic patients. Furthermore, plasma Amadori-PE levels were positively correlated with PCOOH (a maker for oxidative stress). These results show the involvement between lipid glycation and lipid peroxidation in diabetes pathogenesis.

Growth hormone (GH) synthesis and release from pituitary somatotropes is controlled by the opposing actions of the hypothalamic neuropeptides, GH-releasing hormone (GHRH) in the arcuate nucleus (ARC), and somatostatin in the periventricular nucleus (PeV) and ARC. There is a striking sex difference in the pattern of GH secretion in rats. We have previously demonstrated in male rats that 70% of GHRH neurons in the ARC contain the estrogen receptor alpha (ER alpha) gene, whereas less than 5% of somatostatin neurons in the ARC and PeV expressed the ER alpha or ER beta gene. In addition, it has been reported that the PeV somatostatin neurons of neither sex possess ER immunoreactivity. However, there is no available data about colocalization of ERs and GHRH and/or somatostatin in the ARC of female rats. In this study, we used in situ hybridization in the adult female rat brain to determine whether GHRH neurons and/or somatostatin neurons in the ARC coexpress the ER alpha or ER beta gene. In the ARC, ER alpha mRNA was seen in the ventrolateral region where GHRH mRNA signals were also observed, and in the dorsomedial region where somatostatin mRNA signals were also observed. From studies using adjacent sections through these areas, the distribution of these cells appeared to overlap in part with that of cells containing ER alpha mRNA. On the other hand, few positive cells for ER beta mRNA were observed in the ARC. The double-label in situ hybridization studies showed that in the ARC, 73.4% of GHRH neurons contain ER alpha mRNA, whereas less than 5% of somatostatin neurons express the ER alpha gene. These results indicated that the majority of the GHRH neurons in ARC have ER alpha, but not ER beta, and few somatostatin neurons in ARC have ER alpha or ER beta in either adult female or male rats, suggesting that colocalization with ERs in GHRH and/or somatostatin neurons is not an important determinant of the gender specific pattern of GH secretion.