Antihypertensive Potential and Mechanism of Action of Astaxanthin: II. Vascular Reactivity and Hemorheology in Spontaneously Hypertensive Rats

Abstract

Diseases such as hypertension, atherosclerosis, hyperlipidemia, and diabetes are associated with vascular, functional and structural changes including endothelial dysfunction, altered contractility and vascular remodeling. The role of vascular endothelium in modulating vascular tone and maintaining cardiovascular homeostasis in blood vessels, through the production of an array of both relaxant (e.g., nitric oxide [NO], prostacyclin) and constrictor factors (such as thromboxane, endothelin), has been widely reported. 1-4)The development of hypertension is accompanied by changes in the rheological properties of blood, particularly by an increased red blood cell (RBC) aggregation, leading to further pathological complications. Plasma viscosity contributes to the cardiovascular risks and may be of special importance in cases of reduced blood flow, as commonly occurs in patients with advanced atherosclerosis, 5) and it is also related to the extension of coronary heart disease.6,7) Effects of rheological properties of blood on thrombogenesis and atherosclerosis has been cited in several reports. [8][9][10] We previously investigated blood pressure (BP) lowering-effects of the dietary astaxanthin (ASX-O) in spontaneously hypertensive rats (SHR).11) The current study was designed to investigate the antihypertensive mechanisms of action of ASX-O by investigating its effects on vascular reactivity in the SHR. Contractile and relaxant responses of the vascular system were studied on aortic rings from ASX-Otreated SHR. Moreover, the effects of ASX-O on blood fluidity and rheology were evaluated by microchannel transit time analysis. MATERIALS AND METHODS General ProceduresMale SHR (7 weeks old) were used in this study. The animals were obtained from colonies of specific pathogen-free rats maintained by Japan Shizuoka Laboratory Company (Japan SLC, Shizuoka, Japan). Housing conditions were thermostatically maintained at 24Ϯ1°C with constant humidity (60%) and lighting (12 h light/dark cycle, light on: 07:30-19:30). The animals were housed for at least 1 week before the experiments and fed a normal diet (Lab MR, NOSAN, Yokohama, Japan) and water given ad libitum. Body weights were measured daily during the experimental period. ASX-O, composed of 5.5% astaxanthin (ASX) in edible oil base, was obtained from Fuji Chemical (Fuji Chemical Industry Co., Ltd., Toyama, Japan) and dissolved and diluted in olive oil (Wako Pure Chemicals, Osaka, Japan). Administered doses were calculated as ASX in the dietary ASX-O. The animals were divided into two groups (8 rats/group) and were treated daily for 7-9 weeks. One group was administered ASX (5 mg/kg/d, p.o.) and the other one was similarly treated with olive oil (1 ml/kg/d).All experimental procedures were performed in accordance with the standards established by the 'Guide for the Care and Use of Laboratory Animals at Toyama Medical and Pharmaceutical University'. Measurement of BP and Heart Rate (HR) in Conscious RatsArterial BP and HR were determined by a tail cuff system. The rats we...

Potential health‐promoting effects of astaxanthin: A high‐value carotenoid mostly from microalgae

“…Subsequently, Hussein et al [74] showed that astaxanthin might modulate the blood fluidity in hypertension, and the antihypertensive effects of astaxanthin might be exerted through mechanisms including normalization of the sensitivity of the adrenoceptor sympathetic pathway, particularly a-adrenoceptors, and by restoration of the vascular tone through attenuation of the angiotensin II-and reactive oxygen species-induced vasoconstriction. In the succedent experiment, Hussein et al [8] further found that astaxanthin significantly reduced the plasma level of NO À 2 and NO À 3 , an indicator of the endogenous formation of NO, and definitive structural alterations in the coronary artery and aorta of spontaneously hypertensive rats were ameliorated by astaxanthin, suggesting that astaxanthin could modulate the oxidative condition and might improve vascular elastin and arterial wall thickness in hypertension.…”

Astaxanthin: structural and functional aspects

“…Astaxanthin from H. pluvialis has also been shown to reduce blood pressure 7,48,49 . Hussein et al 48 suggest that 5mg/kg/day of dietary astaxanthin given to hypertensive rats for 7 weeks modulates blood fluidity in hypertension and that its antihypertensive effect may be due to mechanisms that include the normalization of adrenoceptor sensitivity and the restoration of vascular tonus by attenuating the vasoconstriction induced by reactive oxygen species and angiotensin II.…”

“…Hussein et al 48 suggest that 5mg/kg/day of dietary astaxanthin given to hypertensive rats for 7 weeks modulates blood fluidity in hypertension and that its antihypertensive effect may be due to mechanisms that include the normalization of adrenoceptor sensitivity and the restoration of vascular tonus by attenuating the vasoconstriction induced by reactive oxygen species and angiotensin II. The administration of a higher dose (50 mg/kg/day) for a period of 22 weeks in obese rats reduced not only blood pressure but also other symptoms of the metabolic syndrome.…”

Antihypertensive Potential and Mechanism of Action of Astaxanthin: III. Antioxidant and Histopathological Effects in Spontaneously Hypertensive Rats

“…15,16) We previously investigated the blood pressure (BP) lowering effect of a dietary astaxanthin (ASX-O) in spontaneously hypertensive rats (SHR) 17) and its suggested action mechanisms. 18) In the present study, the effects of ASX-O on the oxidative status and the vascular physiology in SHR were examined. We measured the levels of nitrite/nitrate (NO 2 Ϫ /NO 3 Ϫ ) anions and lipid peroxidation in ASX-O-treated SHR.…”