Masamichi Yoshika

The central mechanism underlying hypertension: a review of the roles of sodium ions, epithelial sodium channels, the renin–angiotensin–aldosterone system, oxidative stress and endogenous digitalis in the brain

The central nervous system has a key role in regulating the circulatory system by modulating the sympathetic and parasympathetic nervous systems, pituitary hormone release, and the baroreceptor reflex. Digoxin- and ouabain-like immunoreactive materials were found >20 years ago in the hypothalamic nuclei. These factors appeared to localize to the paraventricular and supraoptic nuclei and the nerve fibers at the circumventricular organs and supposed to affect electrolyte balance and blood pressure. The turnover rate of these materials increases with increasing sodium intake. As intracerebroventricular injection of ouabain increases blood pressure via sympathetic activation, an endogenous digitalis-like factor (EDLF) was thought to regulate cardiovascular system-related functions in the brain, particularly after sodium loading. Experiments conducted mainly in rats revealed that the mechanism of action of ouabain in the brain involves sodium ions, epithelial sodium channels (ENaCs) and the renin–angiotensin–aldosterone system (RAAS), all of which are affected by sodium loading. Rats fed a high-sodium diet develop elevated sodium levels in their cerebrospinal fluid, which activates ENaCs. Activated ENaCs and/or increased intracellular sodium in neurons activate the RAAS; this releases EDLF in the brain, activating the sympathetic nervous system. The RAAS promotes oxidative stress in the brain, further activating the RAAS and augmenting sympathetic outflow. Angiotensin II and aldosterone of peripheral origin act in the brain to activate this cascade, increasing sympathetic outflow and leading to hypertension. Thus, the brain Na+–ENaC–RAAS–EDLF axis activates sympathetic outflow and has a crucial role in essential and secondary hypertension. This report provides an overview of the central mechanism underlying hypertension and discusses the use of antihypertensive agents.

Ca2+ entry mode of Na+/Ca2+ exchanger as a new therapeutic target for heart failure with preserved ejection fraction

AIMS Left ventricular (LV) fibrosis and stiffening play crucial roles in the development of heart failure with preserved ejection fraction (HFPEF). Plasma level of digitalis-like factors (DLFs) is increased in patients with hypertension, a principal underlying cardiovascular disease of HFPEF. Digitalis-like factors inhibit ion-pumping function of Na(+)/K(+)-ATPase and activate the Ca(2+) entry mode of Na(+)/Ca(2+) exchanger (NCX). Digitalis-like factors are known to promote collagen production in fibroblasts. The aim of this study was to explore whether the pharmacological inhibition of the NCX entry mode is effective in the prevention of LV fibrosis and in the development of HFPEF. METHODS AND RESULTS (i) Dahl salt-sensitive rats fed 8% NaCl diet from age 6 weeks served as hypertensive HFPEF model. In this model, 24 h urine excretion of DLFs was greater than that in the age-matched control at compensatory hypertrophic and heart failure stages. (ii) Continuous administration of ouabain for 14 weeks developed LV fibrosis without affecting blood pressure in Sprague-Dawley rats. (iii) Ouabain elevated intracellular Ca(2+) concentration through the entry of extracellular Ca(2+), increased the phosphorylation level of p42/44 mitogen-activated protein kinases, and enhanced (3)H-proline incorporation in cardiac fibroblast; and SEA0400, the inhibitor of the NCX entry mode, suppressed these effects. (iv) In the HFPEF model, administration of SEA0400 at subdepressor dose improved the survival rate in association with the attenuation of LV fibrosis and stiffening. CONCLUSION Digitalis-like factors and the subsequently activated NCX entry mode may play an important role in the development of hypertensive HFPEF, and the blockade of the NCX entry mode may be a new therapeutic strategy for this phenotype of heart failure.

An ouabain-like factor is secreted from immortalized hypothalamic cells in an aldosterone-dependent manner

Ouabain-like factor (OLF) modulates blood pressure via sodium pump inhibition in the central nervous system and in the peripheral circulation. Ouabain-like factor (OLF) is thought to be produced in the adrenal gland and hypothalamus, and it may relate locally to the renin-angiotensin-aldosterone system. However, the evidence for the latter was obtained from in vivo experiments using animals. In the present study, we investigated ouabain production in the immortalized hypothalamic cell line N1. First, cell culture supernatant was collected from the immortalized hypothalamic cell line N1 at 0.5, 4, 8, and 24 h. A newly developed enzyme-linked immunosorbent assay (ELISA) that used anti-ouabain antibody showed that immunoreactivity in the supernatant was increased significantly at 24 vs. 0.5 h (0.01±0.004 vs. 0.16±0.033 pmol/mg protein, p<0.01). A combination of HPLC and ELISA was used to characterize N1 cell-derived OLI, showing that the highest peak of OLI had the same retention time as authentic ouabain. Thereafter, N1 cells were cultured with (1-10 μM) aldosterone, and supernatant was collected after 24 h of culture. In addition, N1 cells were cultured with 5 μM eplerenone, a mineralocorticoid receptor blocker, plus aldosterone. OLI was significantly increased in the supernatant of the cells cultured with 10 μM aldosterone (0.40±0.078 pmol/mg protein), and this increase was abolished by the addition of the aldosterone antagonist eplerenone (0.12±0.030 pmol/mg protein). These data suggest that the immortalized hypothalamic N1 cells secrete OLF and that aldosterone stimulates its secretion via mineralocorticoid receptors.

Novel digitalis-like factor, marinobufotoxin, isolated from cultured Y-1 cells, and its hypertensive effect in rats.

Marinobufagenin and telecinobufagin have been identified as digitalis-like factors in mammals. In toads, marinobufagenin-related compounds, such as marinobufotoxin (MBT), have been isolated in some tissues but not in mammals, and its biological action has not been elucidated. Herein, we aimed to explore the possible production and/or secretion of MBT and the biological action in rats. First, the MBT in culture supernatant of the adrenocortical-originated cell line Y-1 was analyzed by high-performance liquid chromatography and sensitive ELISA for marinobufagenin-like immunoreactivity. Moreover, the structural information was obtained by mass spectrometry. To determine the biological action, MBT (9.6 and 0.96 &mgr;g/kg per day) was intraperitoneally infused via an osmotic minipump for 1 week. Blood pressure and renal excretion of marinobufagenin-like immunoreactivity were measured. Marinobufagenin-like immunoreactivity was found in Y-1 cell culture media, and the concentration increased until 24 hours. The structural analysis suggested that marinobufagenin-like immunoreactivities were marinobufagenin and MBT, and tandem mass spectrum analysis revealed them with the specific daughter ions. The highest sensitive ELISA-positive peak of marinobufagenin-like immunoreactivity in the media was MBT. Continuous administration of MBT in rats for 1 week significantly increased systolic blood pressure and renal excretion of marinobufagenin-like immunoreactivity compared with control rats (135±3.0 versus 126±2.0 mm Hg and 1.41±0.286 versus 0.34±0.064 ng/day, respectively). These data suggest that MBT, arginine-suberoyl ester of marinobufagenin, can be a novel digitalis-like factor with hypertensive action and is secreted from the adrenocortical cells.

Validation of two automatic devices: Omron HEM-7252G-HP and Omron HEM-7251G for self-measurement of blood pressure according to the European Society of Hypertension International Protocol revision 2010.

ObjectiveThe aim of this study was to validate the performance of Omron HEM-7252G-HP and Omron HEM-7251G for monitoring upper arm blood pressure (BP) in accordance with the European Society of Hypertension International Protocol revision 2010 (ESH-IP revision 2010). MethodsThree trained medical doctors validated the performance of these devices by comparing data obtained from these devices with those obtained using a standard mercury sphygmomanometer. We included 33 participants (19 men and 14 women for the experiment using HEM-7252G-HP; 16 men and 17 women for the experiment using HEM-7251G). The mean age of the participants was 50±12 and 53±10 years in the respective studies. ResultsThe percentages of test device–observer mercury sphygmomanometer BP differences within 5, 10, and 15 mmHg were 76, 92, and 97% for systolic BP (SBP) and 83, 97, and 99% for diastolic BP (DBP), respectively, in the Omron HEM-7252G-HP and 77, 92, and 99% for SBP and 85, 94, and 98% for DBP, respectively, in the Omron HEM-7251G in the part 1 analysis; both SBP and DBP passed the part 1 and part 2 criteria.The mean differences between the device and mercury readings for SBP and DBP were as follows: HEM-7252G-HP, −1.5±5.1 and −1.2±3.9 mmHg, respectively; HEM-7351G, −0.6±4.7 and −0.2±4.4 mmHg, respectively. ConclusionThe Omron HEM-7252G-HP and HEM-7251G passed all the requirements of the ESH-IP 2010 revision.

Validation of Omron RS8, RS6, and RS3 home blood pressure monitoring devices, in accordance with the European Society of Hypertension International Protocol revision 2010.

Background Allowing patients to measure their blood pressure at home is recognized as being of clinical value. However, it is not known how often these measurements are taken correctly. Blood pressure monitors for home use fall into two types based on the position of the cuff, ie, at the upper arm or the wrist. The latter is particularly convenient, as measurements can be taken fully clothed. This study aimed to evaluate the performance of the wrist-type blood pressure monitors Omron RS8 (HEM-6310F-E), Omron RS6 (HEM-6221-E), and Omron RS3 (HEM-6130-E). Methods A team of three trained doctors validated the performance of these devices by comparing the measurements obtained from these devices with those taken using a standard mercury sphygmomanometer. All the devices met the validation requirements of the European Society of Hypertension International Protocol revision 2010. Results The difference in blood pressure readings between the tested device and the standard mercury sphygmomanometer was within 3 mmHg, which is acceptable according to the European Society of Hypertension guidelines. Conclusion All the home devices tested were found to be suitable for measuring blood pressure at home because their performance fulfilled the requirement of the guidelines.

Validation of home blood pressure-monitoring devices, Omron HEM-1020 and Omron i-Q132 (HEM-1010-E), according to the European Society of Hypertension International Protocol.

ObjectiveAllowing patients to measure their blood pressure (BP) at home is recognized as being of clinical value. However, it is not known whether BP measurement is usually taken correctly outside of a clinical setting. Automated proper wrapping of the cuff and correction of wrong posture will help in taking BP measurement properly. This study aimed to evaluate the performance of the Omron HEM-1020 and the Omron i-Q132 devices, which are equipped with those functions. MethodsA team of three trained doctors validated the performance of these devices by comparing data obtained from both devices with those from a standard mercury sphygmomanometer. Both devices passed the validation requirements of the European Society of Hypertension International Protocol. The magnitude of the difference in BP readings between the tested device and the standard mercury sphygmomanometer was within the range of ±3 mmHg, which is allowed by the European Society of Hypertension guidelines. ConclusionBoth the Omron HEM-1020 and the Omron i-Q132 devices were found to be useful for measuring BP at home because their performance fulfilled the requirement of the guidelines.

Isolation of marinobufotoxin from the supernatant of cultured PC12 cells.

1. Digitalis‐like factors (DLFs) are believed to be involved in sodium metabolism via inhibition of Na+/K+‐ATPase and may cause hypertension. Yet, the source and regulation of secretion of DLFs remain unknown. Recently, marinobufagenin (MBG) was isolated in mammals and implicated in renal sodium and water metabolism. More recently, we isolated marinobufotoxin (MBT), a suberoyl arginine ester of MBG, in Y‐1 cells. We have developed an ELISA to measure MBG‐like immunoreactivity (MBG‐IR) and have characterized MBG‐IR using chromatography. We have also identified a ouabain‐like factor in cultured PC12 cells from a phaeochromocytoma cell line. In the present study, we examined whether MBT was produced in the adrenal medulla.

Soluble FcgammaRIIIa(Mphi) levels in plasma correlate with carotid maximum intima-media thickness (IMT) in subjects undergoing an annual medical checkup.

Macrophages play a major role in the development of vascular lesions in atherogenesis. The cells express FcγRIIIa (CD16) identical to that in NK cells, but with a cell type-specific glycosylation, and these soluble forms (sFcγRIIIa) are present in plasma. We measured sFcγRIIIaMϕ derived from macrophages in plasma from subjects undergoing an annual medical checkup. The levels of sFcγRIIIaMϕ increased with age, and correlated positively with body mass index, blood pressure, LDL cholesterol to HDL cholesterol ratio, triglycerides, hemoglobin A1c, and creatinine, but negatively with HDL-cholesterol levels. The sFcγRIIIaMϕ levels were related to the number of risk factors for atherosclerosis: such as aging, current smoking, diabetes, hypertension, hyper-LDL-cholesterolemia, hypo-HDL-cholesterolemia, and family history of atherosclerotic diseases. In addition, the sFcγRIIIaMϕ levels were correlated with carotid maximum intima-media thickness (IMT). These findings indicate the macrophages are activated during the incipient stage of atherosclerosis, and suggest sFcγRIIIaMϕ may be used as a predictive marker for atherosclerosis.

Validation of three automatic devices for the self-measurement of blood pressure according to the European Society of Hypertension International Protocol revision 2010: the Omron HEM-7130, HEM-7320F, and HEM-7500F.

ObjectiveThe aim of the present study was to validate the Omron HEM-7130, HEM-7320F, and HEM-7500F for monitoring upper arm blood pressure (BP) according to the European Society of Hypertension International Protocol revision 2010 (ESH-IP revision 2010). MethodsThree trained medical doctors validated the performance of these devices by comparing the data obtained from the devices with those of a standard mercury sphygmomanometer. We included 33 participants (20 men and 13 women for the HEM-7130 experiment; 18 men and 15 women for the HEM-7320F experiment; and 21 men and 12 women for the HEM-7500F experiment). The mean age of the participants was 49±15, 50±11, and 50±11 years in the respective studies. ResultsThe mean differences between the device and the mercury readings for systolic and diastolic BP were as follows: HEM-7130, −1.8±5.3 and −0.1±4.0 mmHg, respectively; HEM-7320F, −0.9±4.7 and −1.9±4.4 mmHg, respectively; and HEM-7500F, −1.0±4.6 and −1.1±4.0 mmHg, respectively. These findings indicated that the device was reading lower than the mercury. However, the number of absolute differences between the devices and observers fulfilled the requirement of the ESH-IP revision 2010. ConclusionThe Omron HEM-7130, HEM-7320F, and HEM-7500F passed all the requirements of the ESH-IP 2010 revision. Therefore, we recommend these devices for the home measurement of BP in adults.