Arterial responses to bradykinin after ramipril therapy in experimental hypertension

Beneficial effects of docosahexaenoic acid on active avoidance performance in 1K-1C hypertensive rats

The present study evaluated the role of chronic docosahexaenoic acid (DHA) supplementation on active avoidance learning task performance in experimental hypertension. Male Wistar rats were randomly divided into five experimental groups as follows: control, sham, DHA treated, 1K-1C hypertensive, and 1K-1C hypertensive+DHA treated. Hypertension was induced in 1K-1C rats via placing a silver clip (0.20-mm ID) around the left renal artery following a right uninephrectomy. DHA (36 mg/kg/day) was given to the treatment groups for 60 days by gastric gavage. Arterial blood pressure was measured by using the tail-cuff method. Active avoidance responses were determined by an automated shuttle-box. In brain (cerebrum) and hippocampus tissues, thiobarbituric acid reactive substances (TBARS) and nitrite levels were measured by fluorometric methods. DHA supplementation decreased blood pressure in hypertensive rats. Data from active avoidance training indicated that performance of active avoidance learning tasks were significantly impaired in 1K-1C hypertensive rats, but was completely restored by DHA supplementation. Increased cerebrum TBARS levels in 1K-1C rats were abolished by DHA administration. Cerebrum nitrite levels were lower in the DHA, 1K-1C and 1K-1C+DHA treated groups compared to controls. Hippocampus nitrite levels were lower in DHA treated and 1K-1C hypertensive rats compared to controls and higher in 1K-1C+DHA treated rats compared to the 1K-1C group. Our data indicates that DHA supplementation improves the performance of active avoidance learning tasks which is impaired in experimental hypertension. These affirmative changes might be due to a DHA-induced decrease in lipid peroxidation which may in turn limit the consumption of nitric oxide (NO) which promotes active avoidance learning.

The role of docosahexaenoic acid on visual evoked potentials in one kidney-one clip hypertension

PURPOSE

To investigate the effects of polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) on visual evoked potentials (VEPs) in a one kidney-one clip (1K-1C) hypertension model in rats.

METHODS

Five experimental groups were formed: a control group, a sham group, a group supplemented with DHA, a 1K-1C group, and a 1K-1C + DHA group. The DHA groups were treated for 60 days. In the 1K-1C groups, the right kidney was removed and a silver clip with a 0.2-mm gap was placed on the left renal artery.

RESULTS

The DHA-supplemented rats had lower blood pressure than their respective controls (p < 0.01). The increased brain and retina thiobarbituric acid reactive substances (TBARS) levels in hypertensive rats were abolished by DHA administration. The brain nitrite levels were lower in the DHA, 1K-1C and 1K-1C + DHA groups compared with the control group (p < 0.01), and the retina nitrite level was higher in the 1K-1C + DHA group compared with the DHA and 1K-1C groups (p < 0.01). There was an improvement of P(2), N(2) and P(3) components following DHA supplementation in 1K-1C hypertensive rats compared with the 1K-1C group.

CONCLUSION

The present study suggests that DHA supplementation has the potential to prevent VEP changes caused by an experimental model of hypertension. This state might be related to the lipid peroxidation lowering effect of DHA.

The effect of different hypertension models on active avoidance learning

This study tested the effects of different hypertension models on active avoidance learning in rats. Three-month-old male Wistar rats were divided randomly into six groups as follows: control (C), sham operated (sham), two kidney-one clip (2K-1C), one kidney-one clip (1K-1C), deoxycorticosterone-salt (DOCA), and N-omega-nitro-L-arginine-methyl ester (L-NAME) groups. Mean arterial blood pressures were significantly higher in four hypertensive groups compared with control and sham groups. The active avoidance training results indicated that hypertension state is associated with learning impairment. Thiobarbituric acid-reactive substances (TBARS) were determined as an indicator of lipid peroxidation in brain and hippocampus. Additionally, brain and hippocampus nitrite levels were studied.

Cholecalciferol treatment restores the relaxant responses of spontaneously hypertensive rat arteries to bradykinin

The vasodilation and hyperpolarization induced by bradykinin (BK) in the mesenteric vascular bed and mesenteric arteries from spontaneously hypertensive rats (SHR) and from normotensive Wistar rats (NWR), as well as Wistar Kyoto rats (WKY), was investigated before and after prolonged oral treatment with cholecalciferol (125 mg kg(-1) body weight per day) for 3 weeks. The cholecalciferol treatment caused a decrease in the SHR blood pressure, as well as a normalization in the resting potential of the smooth muscle cell membrane of mesenteric arteries and restored their hyperpolarizing response to BK. The concentration-response curves for the vasodilator effect of BK on the mesenteric vascular bed were significantly decreased in SHR and in WKY when compared with NWR. Cholecalciferol treatment improved the maximum responses of the SHR preparation, bringing them to levels similar to those of the NWR preparations, which themselves were unaffected by the treatment. In the presence of apamin, a Ca(2+)-dependent K(+) channel inhibitor, the maximum responses to BK in preparations from NWR or cholecalciferol-treated SHR decreased to values similar to those observed in untreated SHR. Our results indicate that the low responsivity of the SHR resistance vessels to the relaxant effect of BK is due to impaired Ca(2+)-dependent K(+) channels and that reversion of this impairment contributes to the blood pressure reduction caused by the cholecalciferol treatment. However, the mechanism of the low responsivity in WKY remains to be investigated.

Altered frequency of a promoter polymorphism of the kinin B2 receptor gene in hypertensive African-Americans

Components of the kallikrein kinin system have been associated with the pathophysiology of hypertension in animal and human studies. In this study, we examined the distribution of four different polymorphisms of the kinin B1 and B2 receptor genes in a population of 120 normotensive and 77 hypertensive African-Americans. Allelic frequencies for three of the four polymorphisms were significantly different from those previously reported in Caucasian populations. Among the polymorphisms analyzed, a potentially functionally significant polymorphism in the core promoter of the kinin B2 receptor (C-58-->T transition) displayed an increased prevalence of the C-58 allele in the hypertensive patients as compared with the controls (0.75 v. 0.62, P = .009). Thus, this B2 receptor promoter polymorphism may represent a susceptibility marker for essential hypertension in African-Americans.