Michio Hashimoto

Chronic Administration Of Docosahexaenoic Acid Improves The Performance Of Radial Arm Maze Task In Aged Rats

1. In the present study, we investigated the effect of docosahexaenoic acid (DHA) on spatial memory related learning ability in aged (100 weeks) male Wistar rats.

Influence of docosahexaenoic acid on cerebral lipid peroxide level in aged rats with and without hypercholesterolemia

Female Wistar rats, 100 weeks old, were divided into four groups: one group was fed a high-cholesterol diet, one received a non-cholesterol diet, and the others were fed either a non- or a high-cholesterol diet plus docosahexaenoic acid. The level of lipid peroxide (LPO) in brain tissue was measured with a LPO assay kit. Fatty acid concentrations were analyzed by gas chromatography. Brain LPO in the aged and hypercholesterolemic rats fed docosahexaenoic acid decreased in the cerebrum but not in the brain stem or cerebellum. In the cerebrum, LPO showed a decrease, with an increase in the ratio of docosahexaenoic acid to arachidonic acid. The cerebrum, unlike the other areas of the brain, was more sensitive to docosahexaenoic acid as the concentrations of LPO decreased.

Aging decreases the production of PGI2 in rat aortic endothelial cells.

It has been suggested that progressive pathophysiologic modifications of endothelium are associated with aging. Aging has been shown to influence some specific functions at the cellular level. In the present study, the effects of aging on levels of prostacyclin (PGI2) production were examined in cultured rat aortic endothelial cells from young (six-week-old) and old (100-week-old) Wistar rats. The level of PGI2 production from rat aortic endothelial cells decreased significantly with increasing age, suggesting decreased function of the endothelial cells. The production of PGI2 stimulated by thrombin was decreased in old rat aortic endothelial cells compared to young rat aortic endothelial cells, whereas there was no difference in the rate of intracellular calcium mobilization caused by thrombin. These data indicate that aging nonuniformly affects both basal and agonist-induced levels of PGI2 production in rat aortic endothelial cells, and that this diminution in PGI2 production may be related to the age-related potentiation of various thrombotic events.

Antihypertensive Effect of All-cis-5,8,11,14,17-Icosapentaenoate of Aged Rats Is Associated with an Increase in the Release of ATP from the Caudal Artery

Fish oils have been shown to lower blood pressure in hypertensive subjects. All-cis-5,8,11,14,17-icosapentaenoate (EPA), one of the ω–3 polyunsaturated fatty acids, is known to be one of the major active components in fish oil that has beneficial effects on the cardiovascular system. However, little is known about the antihypertensive effect of EPA alone on blood pressure. In the present study, we have determined the spontaneous and noradrenaline-evoked release of ATP, ADP, AMP, and adenosine from caudal arteries of aged (100 weeks old) Wistar rats which were fed a standard diet or a high cholesterol diet, treated with EPA. Dietary EPA administration increased plasma and caudal arterial EPA concentrations and repressed increases in blood pressure with advancing age in both aged rats with and without hypercholesterolemia. In addition, noradrenaline (1 µmol/l) evoked a significantly greater release of purines from the caudal arteries of EPA-administered aged rats compared to both sets of control rats. Regression analysis revealed a significant relationship between the total amount of purines released from the artery and blood pressure. These results suggest that administration of EPA to aged rats increases the release of ATP from the vascular endothelial cells, leading to repression of the blood pressure rise seen with advancing age.

A nitric oxide-sensitive electrode: requirement of lower oxygen concentration for detecting nitric oxide from the tissue.

In order to directly detect nitric oxide (NO) liberated from isolated tissue, a practical and convenient method using a nitric oxide-sensitive electrode is described. To avoid the nonselective signal caused by ionic substances, the electrode was covered with three layers but remains permeable for gaseous substances. In a solution bubbled with 20% oxygen (pO2, approximately 150 mm Hg), administration of S-nitroso-N-acetyl-d, l-penicillamine (SNAP) at concentrations greater than 10(-7) mol/L elicited an electrode response. Based on a comparison with the chemical determination of NO released from SNAP, the electrode may be able to detect nitric oxide around nmol/L. At least 30 nmol NO per liter in anoxic conditions was reported to be detected by this electrode (Matsui, 1995). In a specially designed small chamber, the electrode was attached on the surface of endothelial side of the isolated aorta of the guinea pig. When carbachol was added to the chamber, the electrode responded when the solution was bubbled with 20% but not with 40% or 95% of oxygen, suggesting a much faster decomposition of nitric oxide in the presence of higher concentrations of oxygen. The electrode response to carbachol was abolished in the presence of NG-monomethyl-L-arginine or nitro arginine. These results suggest that the electrode method described in this manuscript is suitable for detecting nitric oxide liberated from isolated tissues when comparatively low oxygen levels are present in the physiological salt solution.

Prolonged Cold Storage Abolishes Endothelium-Dependent Relaxing Responses to A23187 and Substance P in Porcine Coronary Arteries

In the presence of potassium (K+), A23187 and substance P elicited endothelium-dependent relaxations of porcine coronary arteries. Isoproterenol or hypoxia elicited endothelium-independent relaxations. Rubbing the artery potentiated the contractile response to a low K+ concentration (15.4 mM). After intact arteries had been stored at 5 degrees C for 3 days, K(+)-induced maximal tension was not affected, but contractile responses to 15 mM K+ were potentiated with a decrease in ED50, suggesting that cold storage produces a supersensitivity to K+. Endothelium-dependent relaxations were abolished after 3 days of cold storage, while endothelium-independent relaxations were not inhibited. Cold storage of arteries with l-arginine (1 mM) for 3 days did not alter the relaxation responses to substance P and A23187, indicating that l-arginine does not prevent the loss of endothelium-dependent relaxation. Cold storage for 5 days inhibited the maximal tension to K+ and abolished the supersensitivity. Scanning electron micrographs showed that endothelial cells can be damaged by prolonged cold storage. The changes in tension response of the artery were correlated with the time course of endothelial cell loss resulting from cold storage.

AGE-RELATED CHANGES IN AORTIC SENSITIVITY TO NORADRENALINE AND ACETYLCHOLINE IN RATS

1. The purpose of the present study was to determine the relationship between plasma and tissue lipid levels and the effects of age on vascular responses to noradrenaline (NA) and acetylcholine (ACh).

The effects of transmural pressure on prostacyclin release from porcine endocardial endothelial cells – comparison with vascular endothelial cells

Abstractu2002We assessed the effects of pressure on the release of prostacyclin (PGI2) from cultured endocardial endothelial cells (EECs) and vascular endothelial cells (VECs). EECs were harvested from the right ventricle (RV) and left ventricle (LV) of porcine hearts, and VECs from pulmonary artery (PA), aorta (Ao) and coronary artery (CA). Confluent EECs and VECs were incubated for 30 min under various pressures (0, 50, 100, 150 mmHg) and PGI2 release from each cell was measured. Pressure-induced PGI2 release from LV-EECs was larger than that from RV-EECs. Pressure also increased PGI2 release from both PA- and Ao-VECs, but not from CA-VECs. These findings suggest that endocardium can produce PGI2 in response to pressure and PGI2 released into the coronary blood from the ventricle may play an important role in the prevention of myocardial ischemia.

INHIBITION OF PLATELET AGGREGATION BY ENDOCARDIAL ENDOTHELIAL CELLS

We assessed the anti-platelet properties of endocardial endothelial cells (EECs) by measuring platelet aggregation after brief interaction with EECs isolated from the right ventricles of porcine hearts. Platelet aggregation in response to thrombin was significantly inhibited by brief incubation of platelet suspensions over EEC monolayers. Pretreatment of EECs with indomethacin restored platelet reaction but that with L-NAME and hemoglobin (Hb) did not. The PGI2 content of platelet suspensions after interaction with cultured EECs was significantly correlated with the inhibition of platelet aggregation. These results suggest that EECs inhibit platelet aggregation by releasing PGI2.

Antithrombotic Effects of Endocardial Endothelial Cells-Comparison with Coronary Artery Endothelial Cells

The purpose of this study was to assess the anti-platelet properties of endocardial endothelial cells (EECs) by measuring platelet aggregation after a brief incubation with cultured EECs. EECs were isolated from the right ventricles of porcine hearts and coronary artery endothelial cells (C-ECs) were also isolated from the same animals. After brief incubations (2-min) of platelet suspensions with cultured EEC and CEC monolayers, platelet aggregation in response to thrombin and 6-keto-PGF1 alpha (a stable metabolite of PGI2) content of platelet suspensions were measured. Platelet aggregation was significantly inhibited by a brief incubation of platelet suspensions with EEC and C-ECs monolayers. Pretreatment of EECs and C-ECs with indomethacin (5 x 10(-5) M) restored platelet activity, but pretreatment with N omega-nitro-L-arginine methyl ester (L-NAME, 5 x 10(-5) M) or hemoglobin (1 x 10(-6) M) did not. Platelet/EEC interactions multiplicatively increased the 6-keto-PGF1 alpha content of platelet suspensions and the 6-keto-PGF1 alpha content of platelet suspensions after incubations with EECs correlated significantly with the inhibition of platelet aggregation. Both the anti-aggregation properties and 6-keto-PGF1 alpha production were significantly greater in EECs than in C-ECs. A brief incubation (2-min) with PDGF (10 ng/ml) or TGF-beta (1 and 10 ng/ml) stimulated 6-keto-PGF1 alpha production in EECs but not in C-ECs, although these growth factors stimulated 6-keto-PGF1 alpha production in C-ECs after a longer incubation time (30 or 60 min). In this study, after a brief incubation (2-min) with platelet suspensions, EECs inhibited platelet aggregation mainly through the release of PGI2 but not EDRF. As this anti-aggregation property was significantly greater in EECs than in C-ECs, it is suggested that endocardial endothelial PGI2 may inhibit both intracardiac and intracoronary artery thrombus formation, contributing to the prevention of myocardial ischemia.