Genistein inhibits carotid sinus baroreceptor activity in anesthetized male rats

The Vascular Effects of Isolated Isoflavones-A Focus on the Determinants of Blood Pressure Regulation

Isoflavones are phytoestrogen compounds with important biological activities, including improvement of cardiovascular health. This activity is most evident in populations with a high isoflavone dietary intake, essentially from soybean-based products. The major isoflavones known to display the most important cardiovascular effects are genistein, daidzein, glycitein, formononetin, and biochanin A, although the closely related metabolite equol is also relevant. Most clinical studies have been focused on the impact of dietary intake or supplementation with mixtures of compounds, with only a few addressing the effect of isolated compounds. This paper reviews the main actions of isolated isoflavones on the vasculature, with particular focus given to their effect on the determinants of blood pressure regulation. Isoflavones exert vasorelaxation due to a multitude of pathways in different vascular beds. They can act in the endothelium to potentiate the release of NO and endothelium-derived hyperpolarization factors. In the vascular smooth muscle, isoflavones modulate calcium and potassium channels, leading to hyperpolarization and relaxation. Some of these effects are influenced by the binding of isoflavones to estrogen receptors and to the inhibition of specific kinase enzymes. The vasorelaxation effects of isoflavones are mostly obtained with plasma concentrations in the micromolar range, which are only attained through supplementation. This paper highlights isolated isoflavones as potentially suitable alternatives to soy-based foodstuffs and supplements and which could enlarge the current therapeutic arsenal. Nonetheless, more studies are needed to better establish their safety profile and elect the most useful applications.

Coumestrol inhibits carotid sinus baroreceptor activity by cAMP/PKA dependent nitric oxide release in anesthetized male rats

Phytoestrogens could offer multiple beneficial effects on the cardiovascular system. Here, we have examined the effects of coumestrol (CMT) on carotid baroreceptors activity (CBA) and the possible mechanisms in male rats. The functional parameters of carotid baroreceptors were measured by recording sinus nerve afferent discharge in anesthetized male rats with perfused isolated carotid sinus. The levels of protein expression were determined by using ELISA and Western blotting. CMT (1 to 100μmolL(-1)) inhibited CBA, which shifted the functional curve of the carotid baroreceptor to the right and downward, with a marked decrease in the peak slope and the peak integral value of carotid sinus nerve discharge in a concentration dependent manner. These effects were not blocked by a specific estrogen receptor antagonist ICI 182,780, but were completely abolished by nitric oxide (NO) synthase inhibitor l-NAME (N(G)-nitro-l-arginine methyl ester). Furthermore, a NO donor, SIN-1(3-morpholion-sydnon-imine), could potentiate these inhibitory effects of CMT. CMT stimulated the phosphorylation of Ser(1176)-eNOS (endothelial nitric oxide synthase) in a dose-dependent manner in carotid bifurcation tissue over a perfusion period of 15min. The rapid activation of eNOS by CMT was blocked by a highly selective PKA (protein kinase A) inhibitor H89. In addition, inhibition of PI3K (phosphatidylinositol-3-kinase) and ERK (extracellular signal-regulated kinase) pathways had no effect on eNOS activation by CMT. CMT inhibited CBA via eNOS activation and NO synthesis. These effects were mediated by the cAMP/PKA pathway and were unrelated to the estrogenic effect.

High sugar intake blunts arterial baroreflex via estrogen receptors in perinatal taurine supplemented rats

In adult rats, perinatal taurine depletion followed by high sugar intake alters neural and renal control of arterial pressure via the renin-angiotensin system. This study tests the hypothesis that perinatal taurine supplementation predisposes adult female rats to the adverse arterial pressure effect of high sugar intake via the renin-angiotensin system, rather than via estrogen. Female Sprague-Dawley rats were fed normal rat chow with 3% taurine (taurine supplementation, TS) or water alone (control, C) from conception to weaning. Their female offspring were fed normal rat chow with either 5% glucose in tap water (TSG, CG) or tap water alone (TSW, CW). At 7-8 weeks of age, the female offspring's renin-angiotensin system or estrogen receptors were inhibited by captopril or tamoxifen, respectively. Body weight, heart weight, kidney weight, mean arterial pressures (MAP), and heart rates were not significantly different among groups without captopril or tamoxifen. Captopril (but not tamoxifen) decreased MAP but not heart rates in all groups. In TSG compared to TSW, CW, and CG groups, baroreflex sensitivity of heart rate (BSHR) and renal nerve activity (BSRA) were significantly decreased. Neither captopril nor tamoxifen altered BSHR in TSG, but tamoxifen (but not captopril) restored TSG BSRA to CW or CG control levels. Perinatal taurine supplementation did not disturb sympathetic and parasympathetic nerve activity in the adult rats on high or basal sugar intake. Compared to its effect in CW and CG groups, tamoxifen increased sympathetic but decreased parasympathetic activity less in TSG and TSW groups. Inhibition of the renin-angiotensin system did not affect autonomic nerve activity in any group. These data suggest that in adult female rats that are perinatally supplemented with taurine, high sugar intake after weaning blunts arterial baroreflex via an estrogen (but not renin-angiotensin) mechanism.