The Vascular Effects of Isolated Isoflavones — A Focus on the Determinants of Blood Pressure Regulation
Isoflavones are known as naturally-occurring phytoestrogens found in soybeans. They are known to improve cardiovascular health in populations with a higher dietary intake of isoflavone. Previous clinical studies have assessed the impact of supplementation or a dietary intake with mixtures of isoflavones, with few studies discussed the effects of isolated compounds. Henrique Silva published a review study under the title “The Vascular Effects of Isolated Isoflavones—A Focus on the Determinants of Blood Pressure Regulation” in Biology open access journal. The summary of this review is given below:
Objective:
To review the effect of isolated isoflavones on the determinants of blood pressure regulation.
Method:
This article reviews published studies on the cardiovascular effects of isoflavones, including their vasorelaxant effects. The article includes a thorough mechanistic description of isoflavone-mediated vasorelaxation, cellular pathways, and several aspects of pharmacodynamics and pharmacokinetics.
Findings:
The review suggests that isoflavones are able to decrease blood pressure by modulating several cardiovascular activities. In addition to vasorelaxant activity, isoflavones are also able to regulate catecholamine synthesis at the adrenal medulla, baroreceptor sensitivity, and also affect the renin-angiotensin-aldosterone (RAA) endocrine axis.
In a study with stroke-prone male spontaneously hypertensive rats (SHRs), the chronic administration of genistein i.e. 0.6 mg/g diet for 7 weeks decreased the increase of blood pressure caused by dietary sodium chloride. Additionally, intravenous administration of genistein to the brachial artery of healthy human subjects leads to an increase in forearm blood flow. In post-menopausal women, genistein is found to improves flow-mediated dilation of the brachial artery.
Administration of daidzein subcutaneously (0.5 mg/kg) for 6 weeks reduces the mean blood pressure in L-NAME-induced hypertensive rats as compared to untreated animals. Additionally, daidzein (20 mg/kg) is found to decrease blood pressure in multidose rather than in single-dose administrations.
In normotensive human subjects, the chronic administration of formononetin (80 mg/day for 5 weeks) does not change blood pressure or enhance flow-mediated dilation. On the other hand, formononetin administered (50 mg/kg/day) to SHRs for 8 weeks decreased blood pressure and shows endothelium-dependent vasodilation.
In Sprague-Dawley rats, the topical administration of equol to surgically exposed basilar arteries caused weak vasodilation and antioxidant effect. In middle-aged subjects with significant cardiovascular risk, reduction in blood pressure and arterial stiffness was observed with the oral supplementation with trans-tetrahydro daidzein (1 g/day for 5 weeks).
Effect on the Renin-Angiotensin-Aldosterone Axis.
Daidzein is found to restrict ACE activity in vitro and to cause significant hypotensive effects in vivo. There was no effect observed on the RAA axis in vivo with formononetin administration. The chronic administration of equol (10 and 20 mg/kg for 5 weeks) found to inhibit activity on the RAA axis.
Effect on Baroreceptor Sensitivity.
Genistein is the only isoflavone to be able to modulate baroreceptor sensitivity. In male anesthetized Sprague-Dawley rats, 50–200 µmol/L concentration of genistein inhibited the carotid baroreceptor.
Effect on Catecholamine Synthesis.
Genistein and daidzein are found to affect catecholamine synthesis.
Possible Connection between Effects on Immunity and Blood Pressure
Isoflavones affect immune function by modulating the numbers of circulating immune cells (eosinophils and lymphocytes) along with affecting the levels of lymphocytes in the thymus and spleen. They can also modulate the maturation and reactivity of immune cells, such as T lymphocyte, natural killer, macrophage, and dendritic cells, as well as modulate cytokine production.
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