Identification of an antihypertensive peptide from peptic digest of wakame (Undaria pinnatifida)

A peptide fraction having activity against angiotensin I-converting enzyme (ACE) was separated from the peptic digest of protein prepared from wakame (Undaria pinnatifida) by ion-exchange chromatographies and gel-filtration. Fractions with high ACE inhibitory activity were combined and further chromatographed on a reverse-phase column to yield four tetrapeptides with ACE inhibitory properties. These tetrapeptides were identified by sequence analysis and fast atom bombardment mass spectrometry as Ala-Ile-Tyr-Lys (IC(50): 213 microM), Tyr-Lys-Tyr-Tyr (64.2 microM), Lys-Phe-Tyr-Gly (90.5 microM), and Tyr-Asn-Lys-Leu (21 microM). Each tetrapeptide was synthesized and its antihypertensive activity was determined after oral administration in spontaneously hypertensive rats. The blood pressure significantly decreased after tetrapeptide ingestion. The present study demonstrated that dietary wakame may have beneficial effects on hypertension.     

Cultivation and utilization of Undaria pinnatifida (wakame) as food

A brief review is presented concerning wakame, Undaria pinnatifida, one of the most popular seaweeds used for food in Japan. Although it has been cultivated since about 1940, full-scale cultivation occurred after 1955. As methods for providing ‘seed stock’ and of processing the harvested sporophytes progressed, the yield increased rapidly. The main areas of cultivation are in Japan (e.g. Sanriku, Naruto), Korea and China, while ‘wild’ U. pinnatifida has been introduced into France, New Zealand and Australia. The total world yield of wakame exceeds 500 000 t fresh weight. Cultivated and harvested Undaria is boiled and salted (thus becoming green) and refrigerated; in the factory, it is removed its foreign matter and salt and dried. After checking for quality, the product is packaged in forms convenient for cooking and eating.     

降血压乳酸菌发酵乳对原发性高血压大鼠的降压效果

目的对具有血管紧张素转化酶(ACE)抑制活性的乳酸菌DM9057发酵乳的抗胃肠道酶解能力及原发性高血压大鼠(SHR)体内降压效果进行研究。方法以10 ml/kg和2.5 ml/kg发酵乳一次性和连续灌胃原发性高血压大鼠。结果 DM9057发酵乳具有较好的抗胃肠道酶能力,并且2个剂量均具有较好的降血压效果,其中以10 ml/kg剂量效果最为显著,一次性和连续灌胃后,最大降压值为(17.97±3.82)、(25.46±5.06)mmHg。结论乳酸菌DM9057发酵乳具有较强的抗胃肠道能力,同时在原发性高血压大鼠体内能够发挥一定的降血压作用。     

Antihypertensive effects of onion on NO synthase inhibitor-induced hypertensive rats and spontaneously hypertensive rats

This study was designed to show the effects of onion on blood pressure in N(G)-nitro-L-arginine methyl ester (L-NAME) induced-hypertensive rats and stroke prone spontaneously hypertensive rats (SHRSP) using dried onion at 5% in their diets. For the experiment with L-NAME induced-hypertensive rats, male 6-weeks-old Sprague-Dawley rats were given tap water containing L-NAME to deliver 50 mg/kg BW/day. In this experiment, we found distinct antihypertensive effects of onion on the L-NAME induced-hypertensive rats and the SHRSP. Dietary onion decreased the thiobarbituric acid reactive substances (TBARS) in plasma in these hypertensive rats. Also, onion increased the nitrate/nitrite (products of nitric oxide (NO)) excreted in urine and the NO synthase (NOS) activity in the kidneys in SHRSP. These results suggested that the increased NO caused by the greater NOS activity, and additionally by the increased saving of NO by the antioxidative activity of onion, was one of the cause of the antihypertensive effect of onion in SHRSP. In the L-NAME induced hypertensive rats, onion did not significantly block the inhibition of NOS activity by L-NAME, and decreased nitrate/nitrite excretion in urine was not restored. The mechanism of the antihypertensive effect of onion probably involves increased saving of NO by antioxidative activity of onion in L-NAME induced-hypertensive rats.     

Genetic control of blood pressure in spontaneously hypertensive rats (SHR)

Genetic control of blood pressure in the SHR strain was studied by three separate experiments which consist of cross analysis between the SHR and Donryu, two-way selecton for high and low blood pressure levels, and successive backcrosses to the parental strains. The results obtained were as follows. 1. The data from genetic crosses between the SHR and Donryu showed the phenotype segregation ratio of 1:1 at the backcross and 1:2:1 at the F2 generation. 2. Two-way selection for high and low blood pressure levels was performed from the F2 generation onward. The separation between the two lines occurred immediately after the first selection. Thereafter, the difference increased gradually with generation. The blood pressure level at the seventh generation of selection became approximately equal to those of the parental strains. 3. Two types of the successive backcross were performed from the F1 hybrids by mating the males showing the highest blood pressure level to Donryu females and the females showing the lowest blood pressure level to SHR males on the other. Bimodality was observed in the distribution of blood pressure levels at each generation. Their phenotypic segregation ratios were accordant with 1:1 on the whole. At the intercross generation during successive backcrosses, a trimodal distribution was observed. 4. These results confirmed that the hypertensive trait of the SHR is regulated by a single major gene and other several genes with minor effect. A gene symbol ht was proposed for this major gene. Concurrently, a congenic strain having the ht gene on the genetic background of the Donryu was developed by the successive backcross system.     

Antihypertensive effects of acetic acid and vinegar on spontaneously hypertensive rats

To clarify the possibility of a preventive effect of dietary vinegar on blood pressure, long-term administration of vinegar or the acetic acid to SHR was examined. As a result, it was observed that acetic acid itself, the main component of vinegar, significantly reduced both blood pressure (p<0.05) and renin activity (p<0.01) compared to controls given no acetic acid or vinegar, as well as vinegar. There were no significant differences in angiotensin I-converting enzyme activity in various organs. As for the mechanism of this function, it was suggested that this reduction in blood pressure may be caused by the significant reduction in renin activity and the subsequent decrease in angiotensin II. From this study, it was also suggested that the antihypertensive effect of vinegar is mainly due to the acetic acid in it.     

Antiserum to prolactin lowers blood pressure (BP) in spontaneously hypertensive rats

The role of PRL in the development of hypertension in the SHR was examined by administering PRL antiserum to neonatal SHR. On days 2-7 post partum, male SHR were injected with 50 microliters/day of either antiserum to PRL (which chronically lowers plasma PRL), normal rabbit serum (NRS), or 0.9% NaCl. Heart rate, BP, and body weight were measured biweekly on weeks 6-14 of age. Anti-PRL lowered BP vs. NaCl on weeks 6, 8, 12, and 14 (range 7-17 mm Hg lower). NRS animals showed BP differences from the NaCl group only on weeks 6 and 14, with no consistent effect. Heart rates fell during the study in the NaCl and anti-PRL groups but not in the NRS group. Anti-PRL and NRS groups had higher heart rates than did the NaCl group. Body weights did not differ between groups except on week 14, when the NRS group weighed less than the NaCl group. These results suggest that while PRL is involved in BP regulation in the SHR, it is not involved in the pathogenesis of the genetic hypertension seen in the strain. In addition, the results suggest that the serum treatment may have caused heart damage which led to an elevation in the heart rates of the serum-treated groups.     

The effects of 19-nor-aldosterone on blood pressure of adrenalectomized spontaneously hypertensive rats

The relative hypertensinogenic potencies of recently synthesized 19-nor-aldosterone and its precursor 19-OH-aldosterone were assessed in comparison to that of aldosterone (Aldo) in young (6-week-old) adrenalectomized (ADX) spontaneously hypertensive rats (SHR). Infusion of 19-nor-aldosterone for 2 weeks by Alza mini-osmotic pumps caused significant, dose-dependent increases in the systolic blood pressure (BP) of young ADX SHR; dosages of 0.1 and 0.5 microgram/day raised the BP from 127 +/- 2 mmHg to 164 +/- 9 and 180 +/- 11 mmHg, respectively. During this period, control ADX SHR receiving vehicle only remained normotensive. Similar increases in BP were seen only with infusion of slightly higher dosages of Aldo (0.5 and 1.0 micrograms/day). In contrast, 19-OH-aldosterone infused at higher dosages (10 or 25 micrograms/day) caused little change in BP of ADX SHR. Full suppression of plasma renin activity (PRA) was observed with 0.1 and 0.5 microgram/day 19-nor-aldosterone, whereas Aldo caused similar decreases in PRA only at dosages of 0.5 microgram/day and higher. Interestingly, although infusions of 19-OH-aldosterone did not cause a significant change in BP, these dosages (10 and 25 micrograms/day) significantly suppressed PRA. These studies which show that 19-nor-aldosterone is equipotent to Aldo, and perhaps slightly more active in ADX SHR, indicate that 19-nor-aldosterone is a potentially important hypertensinogenic steroid.     

Nutritional value of the marine algae wakame (Undaria pinnatifida) and nori (Porphyra purpurea) as food supplements

The nutritional properties of seaweeds are incompletely known, and studies on nutrient bioavailability are scarce, although such information is required to evaluate seaweed as a foodstuff. In the present study, samples of wakame (Undaria pinnatifida) and nori (Porphyra purpurea) were analysed to determine their chemical composition. To evaluate the algae as dietary supplements, the effects on rats of the inclusion of these seaweeds in a standard rodent diet were investigated. The control rats were fed a diet containing 100 % standard rodent diet. The wakame diet was obtained by mixing 10 % dried wakame with 90 % standard rodent diet, and the nori diet was obtained by mixing 10 % dried nori with 80 % standard rodent diet and 10 % starch. Food intake and the body weight were measured. Nitrogen ingested and excreted were determined to calculate true digestibility, biological value, net protein utilization and nitrogen balance. Biochemical determinations were made on serum blood samples. The protein content was high (16.8 % for wakame and 33.2 % for nori), the fat content was low (1 % for wakame and 2.8 % for nori) and the carbohydrates comprised 37 % for both seaweeds. The fibre and ash contents in wakame were 16.9 and 28.3 %, respectively, and in nori, they were 7.5 and 21.3 %, respectively. Both seaweeds contain high concentrations of calcium, sodium, potassium, iron and magnesium, and the most abundant vitamin was vitamin A. Few changes were observed in the nutritional parameters, but LDL cholesterol levels were significantly lower in rats fed with seaweed-supplemented diets than in the control rats. Wakame and nori are excellent sources of nutrients and are well accepted by experimental animals.     

Effect of diphenylhydantoin on blood pressure of spontaneously hypertensive rats

Diphenylhydantoin (DPH) has been shown to elicit direct peripheral vasodilatory effects in anaesthetised animals. Since spontaneously hypertensive (SH) rats exhibit many features similar to human essential hypertension, the effect of DPH on blood pressure of these rats was studied. DPH given orally for 5 days elicited dose-dependent fall in systolic blood pressure in conscious SH rats. In addition, repeated administrations of DPH increased the noradrenaline concentration in the hypothalamus. These results suggest that the central noradrenergic mechanisms might be involved in the hypotensive action of DPH in SH rats, probably at the supramedullary level.     

Natriuretic and hypotensive effects of brain natriuretic peptide (BNP) in spontaneously hypertensive rats

Effects of four doses (0.1, 0.2, 1.0 and 2.0 nmol/kg) of brain natriuretic peptide (BNP) on natriuresis and blood pressure were investigated in anesthetized spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). An intravenous injection of 1.0 and 2.0 nmol/kg of BNP caused a significant increase of natriuresis and reduction of blood pressure in SHR and WKY. These effects were essentially identical to the effects of atrial natriuretic peptide (ANP). Remarkable bioactivity elicited by BNP rasises the possibility that BNP has a role in the regulation of blood pressure and water-electrolyte balance. On the other hand, when the effects of BNP on both strains of rats were compared with those of alpha-human ANP reported previously, the hypotensive effect of BNP was less than those of alpha-human ANP only in SHR. It is suggested that BNP might have different bioactivity than that of ANP in SHR.     

Involvement of atrial natriuretic peptide in blood pressure reduction induced by estradiol in spontaneously hypertensive rats

The aim of the present study was to determine the involvement of atrial natriuretic peptide (ANP) in blood pressure (BP) alterations induced by estradiol treatment. Spontaneously hypertensive rats (SHR) and Wistar rats (WR) were ovariectomized and, after 3 weeks, were injected daily for 4 days with estradiol benzoate (E2; 5 microg/100 g/day) or a vehicle. One day after the last injection, the animals were decapitated, blood was collected, and both right and left atrial appendages were quickly removed for determination of ANP by radioimmunoassay (RIA), or used for ANP mRNA determination. Estradiol treatment induced a significant reduction of blood pressure in SHR, but not in WR. This reduction was correlated with the increase of plasma ANP levels that were significantly increased in E2-treated, compared with vehicle-treated, SHR. E2-treated SHR showed significant increases in ANP concentration in the right and left atria compared to the vehicle-treated animals. These observations were confirmed by ANP mRNA. In summary, the present study shows that short-term estradiol treatment reduces the blood pressure of ovariectomized SHR, but not of WR. This reduction was highly correlated with increased plasma estradiol and ANP levels. These results suggest that ANP is involved in mediating the effect of estradiol on blood pressure reduction.     

The effects of maternal mild protein restriction on stroke incidence and blood pressure in stroke-prone spontaneously hypertensive rats (SHRSP)

The effect of maternal protein restriction during pregnancy on the offspring's blood pressure was assessed in stroke-prone spontaneously hypertensive rats (SHRSP) which are genetically predisposed to hypertension and stroke. After the confirmation of pregnancy, the control group was given a 20% casein diet, and the low-protein group was fed a 9% casein diet. After the confirmation of delivery, commercial feed was given to both of the groups. No differences were seen between the control and low-protein offspring in regard to body weight, blood pressure elevation, or life span. One percent saline solution was put in the control and low-protein groups after the age of 11 weeks. Blood pressure increased markedly in the low-protein group, on the blood pressure level in the low-protein group on week 2 after salt loading (242+/-6 mmHg) was significantly higher than that in the control group (223+/-9 mmHg; p<0.05). The survival duration was significantly shorter in the low-protein group (113+/-4 days) than in the control group (135+/-22 days; p<0.05). These results suggest that maternal protein malnutrition in SHRSP exerted a high salt sensitivity and a malignant influence on stroke incidence on offspring.     

Use of nonlinear methods to assess effects of clonidine on blood pressure in spontaneously hypertensive rats

In spontaneously hypertensive rats (SHR),chronic infusion of clonidine failed to decrease blood pressure andblood pressure variability. We used nonlinear methods to get a deeperinsight on the effects of clonidine on blood pressure dynamics. For 24 h and 4 wk, clonidine (0.1 mg · kg¹ · day¹sc) was infused by minipumps in the conscious SHRs, and, for comparison, a vehicle was infused in SHRs and in Wistar-Kyoto rats.Blood pressure was recorded for 30 min before and after treatments. Weused the Lyapunov exponent, approximated by the inverse of thel_max indexderived from the recurrence plot method, to characterize nonlineardynamics. Before treatment,l_max index ofblood pressure was lower (P < 0.01)in the SHRs than in the Wistar-Kyoto rats. Clonidine significantlyincreased l_max(P < 0.01) to the level observed innormotensive rats, at 24 h and up to 4 wk after infusion. We concludethat clonidine has a significant chronic effect on blood pressuredynamics, as evidenced by nonlinear methods. Our study also suggeststhat the mechanisms governing blood pressure variations are nonlinear.

     

Long-term effects of betamethasone on blood pressure and hypothalamo-pituitary-adrenocortical function in spontaneously hypertensive and normotensive rats

An enhanced hypothalamo-pituitary-adrenocortical (HPA) activity has been described during onset of elevated blood pressure in spontaneously hypertensive rats (SHR). An instability of the HPA axis could thus contribute to the development of hypertension in these animals. Glucocorticoid effects on blood pressure and HPA function were studied therefore in SHR and normotensive Wistar-Kyoto (WKY) and Wistar rats. Beginning at 4 weeks of age, the rats were treated with 0.1 and 0.5 microgram betamethasone per milliliter drinking water for 7 weeks. SHR and WKY responded with a significant elevation in average blood pressure. In SHR, mean blood pressure rose from 181.4 +/- 3.9 (mean +/- SEM) to 203.1 +/- 2.8 mm Hg in response to the lower dose of betamethasone and to 209.2 +/- 4.0 mm Hg in response to 0.5 microgram betamethasone per milliliter drinking water. In WKY, blood pressure increased from 134.4 +/- 3.3 to 148.2 +/- 3.0 and 157.9 +/- 4.5 mm Hg in response to the lower and higher dose of betamethasone, respectively. No significant effect was seen in Wistar rats, where the mean blood pressure values changed insignificantly from 133.8 +/- 2.1 to 136.3 +/- 3.2 and 135.6 +/- 2.4 mm Hg. Stress-induced secretion of corticosterone was significantly suppressed in a dose-dependent manner in all three strains. Stress-induced secretion of adrenocorticotropin was markedly reduced by 0.5 microgram betamethasone per milliliter in SHR and by both doses in WKY. No significant effect, however, was seen in Wistar rats. A predisposition to the hypertensiogenic actions of glucocorticoids was found therefore in SHR and WKY, but not in Wistar rats.     

Calcitonin gene-related peptide (CGRP) in normotensive and spontaneously hypertensive rats

With the techniques of specific radioimmunoassay and gel filtration it was found that CGRP was distributed in various tissues of normotensive (WKY) and spontaneously hypertensive rats (SHR) with the highest concentration in the lumbar spinal cord (1197 +/- 94.8 pg/mg tissue) and the lowest in the auricle (15.0 +/- 2.1 pg/mg tissue). In comparison with WKY, CGRP concentration in the plasma was decreased and in the abdominal aorta and hypothalamus was increased in SHR. Gel filtration revealed only one major CGRP molecular form in the tissues. In addition, CGRP reduced the mean arterial pressure (MAP) in SHR in a dose-dependent manner. These data suggest that CGRP may play an important role in the pathogenesis of hypertension and its possible therapy.     

Alpha-tocopherol supplementation favorable effects on blood pressure, blood viscosity and cardiac remodeling of spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) were separated into two groups (n = 6 per group) and, since 5 months old, received alpha-tocopherol (alpha-tocopherol acetate120 IU) or vehicle by daily gavage for 2 weeks. Blood viscosity, blood pressure (BP) and myocardial remodeling were analyzed. The SHRs treated with alpha-tocopherol showed a significant reduction of BP and a major reduction of blood viscosity in comparison with the control SHRs. The cardiac hypertrophy indices showed some differences when the two SHR groups were compared, the LV mass index was not different between the groups; however, the cardiomyocyte size was more than 20% smaller in SHRs treated with alpha-tocopherol than in control SHRs (P < .05). The intramyocardial vessels distribution was more than 45% greater in alpha-tocopherol-treated SHRs than in control rats, significantly improving the vessels-to-myocytes ratio in treated SHRs than in control SHRs (P < .05). In conclusion, present findings strongly suggest a beneficial effect of alpha-tocopherol supplementation to genetically hypertensive rats. This was observed by a reduction of both blood viscosity and BP, and a consequent cardiomyocyte hypertrophy in treated SHRs; an improvement of vessels-to-myocytes ratio in these rats was also observed.     

A transgenic rice seed accumulating an anti-hypertensive peptide reduces the blood pressure of spontaneously hypertensive rats

RPLKPW is a potent anti-hypertensive peptide designed according to the structure of ovokinin(2-7) (RADHPF). In this study, we generated transgenic rice plants that accumulate the RPLKPW peptide as a fusion protein with the rice storage protein glutelin. The engineered peptide is expressed under the control of endosperm-specific glutelin promoters and specifically accumulates in seeds. Oral administration of either the RPLKPW-glutelin fraction or transgenic rice seeds to spontaneously hypertensive rats (SHRs) significantly reduced systolic blood pressures. These results suggest the possible application of transgenic rice seed as a nutraceutical delivery system and specifically for administration of active peptides in hypertension.     

On the role of NMDA receptors in blood pressure regulation in spontaneously hypertensive rats (SHR)

Summary In the present study the binding of [³H]MK-801 to glutamatergic receptors of the NMDA type was compared in spontaneously hypertensive (SHR) and normotensive (WKY) rats in various brain structures (including nucleus tractus solitarii) by quantitative receptor autoradiography. Additionally, blood pressure changes after treatment with the NMDA antagonist MK-801 were studied in both strains. There were no differences between SHR and WKY rats either in the level of [³H]MK-801 binding or in the hypertensive reaction to MK-801.