Isabel Rodríguez-Gómez

Vascular deconjugation of quercetin glucuronide: The flavonoid paradox revealed?

SCOPE The dietary flavonoid quercetin exerts protective cardiovascular effects. Because quercetin is rapidly metabolized into less active or inactive glucuronidated metabolites and the plasma concentrations of free quercetin are very low, a huge amount of scientific data generated along decades with the unconjugated compounds in vitro has been questioned. We aimed to determine whether glucuronidated quercetin can deconjugate in situ and whether deconjugation leads to a biological effect. METHODS AND RESULTS Quercetin and quercetin-3-O-glucuronide (Q3GA) were perfused through the isolated rat mesenteric vascular bed. Quercetin was rapidly metabolized in the mesentery. In contrast, the decay of Q3GA was slower and was accompanied by a progressive increase of quercetin in the perfusate and in the tissue over 6 h, which was prevented by the β-glucuronidase inhibitor saccharolactone. Incubation of mesenteric arterial rings mounted in a wire myograph with Q3GA for ≥1 h resulted in a significant inhibition of the contractile response which was also prevented by saccharolactone. Moreover, the intravenous administration of Q3GA resulted in a slow onset and sustained blood pressure lowering effect, demonstrating for the first time that Q3GA has effects in vivo. CONCLUSION We propose that Q3GA behaves as a quercetin carrier in plasma, which deconjugates in situ releasing the aglycone which is the final effector.

Antihypertensive Effects of Peroxisome Proliferator-Activated Receptor-β Activation in Spontaneously Hypertensive Rats

Activation of nuclear hormone receptor peroxisome proliferator-activated receptor &bgr;/&dgr; (PPAR&bgr;) has been shown to improve insulin resistance and plasma high-density lipoprotein levels, but nothing is known about its effects in genetic hypertension. We studied whether the PPAR&bgr; agonist GW0742 might exert antihypertensive effects in spontaneously hypertensive rats (SHRs). The rats were divided into 4 groups, Wistar Kyoto rat-control, Wistar Kyoto rat-treated (GW0742, 5 mg · kg−1 · day−1 by oral gavage), SHR-control, and SHR-treated, and followed for 5 weeks. GW0742 induced a progressive reduction in systolic arterial blood pressure and heart rate in SHRs and reduced the mesenteric arterial remodeling, the increased aortic vasoconstriction to angiotensin II, and the endothelial dysfunction characteristic of SHRs. These effects were accompanied by a significant increase in endothelial NO synthase activity attributed to upregulated endothelial NO synthase and downregulated caveolin 1 protein expression. Moreover, GW0742 inhibited vascular superoxide production, downregulated p22phox and p47phox proteins, decreased both basal and angiotensin II–stimulated NADPH oxidase activity, inhibited extracellular-regulated kinase 1/2 activation, and reduced the expression of the proinflammatory and proatherogenic genes, interleukin 1&bgr;, interleukin 6, or intercellular adhesion molecule 1. None of these effects were observed in Wistar Kyoto rats. PPAR&bgr; activation, both in vitro and in vivo, increased the expression of the regulators of G protein–coupled signaling proteins RGS4 and RGS5, which negatively modulated the vascular actions of angiotensin II. PPAR&bgr; activation exerted antihypertensive effects, restored the vascular structure and function, and reduced the oxidative, proinflammatory, and proatherogenic status of SHRs. We propose PPAR&bgr; as a new therapeutic target in hypertension.

Increased Pressor Sensitivity to Chronic Nitric Oxide Deficiency in Hyperthyroid Rats

Abstract—We studied the effects of a possible interaction between partial nitric oxide deficiency and thyroid hormone excess on the long-term control of blood pressure (BP) and morphological and renal variables and examined the role of the renin-angiotensin system in the increased BP of this interaction. Eight groups (n=8 each) of male Wistar rats were used: a control group; 3 groups that were treated with thyroxine (50 &mgr;g/d), Nw-nitro-l-arginine methyl ester (l-NAME; subpressor dose, 1.5 mg · kg−1 · d−1), or thyroxine plus l-NAME; and another 4 similarly treated groups that received losartan (20 mg · kg−1 · d−1) in their drinking fluid. All treatments were maintained for 3 weeks. The time course of tail systolic BP was recorded once a week. At the end of the experimental period, we measured mean arterial pressure in conscious rats and assessed the morphological, metabolic, plasma, and renal variables. Thyroxine produced a mild BP increase from the second week of treatment and an increase in plasma angiotensin II and plasma nitrates/nitrites by the end of the study. Simultaneous administration of thyroxine and a subpressor dose of l-NAME produced a marked BP increase that reached significance from the first week of treatment. Losartan produced normotension in thyroxine-treated rats and attenuated the BP elevation in thyroxine+l-NAME–treated rats. Hyperthyroid rats showed relative renal and ventricular hypertrophy, absence of absolute left ventricular hypertrophy, and proteinuria. These alterations were not changed by losartan. We conclude that an impaired nitric oxide system might have a counterregulatory homeostatic role against the prohypertensive effects of thyroid hormone and that the renin-angiotensin system plays an important role in thyroxine+l-NAME hypertension.

Lack of beneficial metabolic effects of quercetin in adult spontaneously hypertensive rats

Insulin sensitivity is partly dependent on insulin-mediated nitric oxide (NO) release and antioxidants may decrease insulin resistance by amelioring NO bioavailability. The effects of chronic therapy with the antioxidant quercetin on blood pressure, vascular function and glucose tolerance in male spontaneously hypertensive rats (SHR), a model of genetically hypertension and insulin resistance, were analyzed. Rats were divided into four groups, WKY vehicle, WKY quercetin, SHR vehicle and SHR quercetin. Animals were daily administered by gavage for four weeks: vehicle, quercetin in vehicle (10mg/kg body weight). Blood pressure was followed by tail-cuff plethysmography. Chronic quercetin treatment reduced systolic blood pressure, and significantly reduced left ventricular (-10%) and renal (-6%) hypertrophy. However, oral glucose tolerance test, homeostatic model assessment of insulin resistance, total cholesterol and triglycerides were unaffected by quercetin in both strains of rats. It also improved the blunted aortic endothelium-dependent relaxation to acetylcholine, without affecting both endothelium-dependent relaxation to insulin and endothelium-independent relaxation to sodium nitroprusside in SHR. In WKY rats, quercetin in vitro and in vivo, impaired the relaxation to insulin. Quercetin reduced both plasma malondialdehyde levels and aortic superoxide production in SHR. Furthermore, quercetin inhibited insulin-stimulated protein kinase B (Akt)- and endothelial NO synthase (eNOS) phosphorylation. In conclusion, quercetin reduced blood pressure, left ventricular and renal hypertrophy and improved NO-dependent acetylcholine relaxation. However, and despite its antioxidant effects, quercetin was unable to improve insulin sensitivity possibly through its specific interference with the insulin signalling pathway.

The renin–angiotensin system in thyroid disorders and its role in cardiovascular and renal manifestations

Thyroid disorders are among the most common endocrine diseases and affect virtually all physiological systems, with an especially marked impact on cardiovascular and renal systems. This review summarizes the effects of thyroid hormones on the renin-angiotensin system (RAS) and the participation of the RAS in the cardiovascular and renal manifestations of thyroid disorders. Thyroid hormones are important regulators of cardiac and renal mass, vascular function, renal sodium handling, and consequently blood pressure (BP). The RAS acts globally to control cardiovascular and renal functions, while RAS components act systemically and locally in individual organs. Various authors have implicated the systemic and local RAS in the mediation of functional and structural changes in cardiovascular and renal tissues due to abnormal thyroid hormone levels. This review analyzes the influence of thyroid hormones on RAS components and discusses the role of the RAS in BP, cardiac mass, vascular function, and renal abnormalities in thyroid disorders.

Role of sex, gonadectomy and sex hormones in the development of nitric oxide inhibition‐induced hypertension

In this study we have evaluated the influence of sex, gonadectomy and sex hormones on the development of l‐NAME‐induced hypertension in the rat, focusing our investigation on blood pressure (BP), plasma renin activity (PRA), cardiac hypertrophy and proteinuria. Three experiments were performed to investigate: (i) the influence of sex on the development of l‐NAME‐induced hypertension; (ii) the effects of gonadectomy on the dimorphism of l‐NAME‐induced hypertension; and (iii) the effects of testosterone in ovariectomized female and of 17β‐oestradiol in orchidectomized male rats. Male l‐NAME‐treated rats had higher BP values than females. Orchidectomy of l‐NAME‐treated rats reduced BP to the levels of females and ovariectomy did not affect hypertension in females. Oestrogenized and orchidectomized males had a BP level similar to intact female l‐NAME‐treated rats. However, androgenization and ovariectomy did not change BP in female l‐NAME‐treated rats. PRA was greater in intact male l‐NAME hypertensive rats than in female rats, and gonadectomy protected against the increase in PRA such that PRA was similar among all the groups. Intact female hypertensive rats showed significantly greater ventricular hypertrophy compared with male hypertensive rats. Male l‐NAME hypertensive rats had increased proteinuria that was not present in female rats. Moreover, testosterone increased proteinuria in males and females regardless of the BP level. Male l‐NAME‐treated rats developed higher BP, PRA and proteinuria than female rats, but were more resistant to the development of cardiac hypertrophy. The higher PRA of male l‐NAME‐treated rats might be involved in the sex‐dependent dimorphism of this model of hypertension.

Influence of Thyroid State on Cardiac and Renal Capillary Density and Glomerular Morphology in Rats

The purpose was to analyse the cardiac and renal capillary density and glomerular morphology resulting from a chronic excess or deficiency of thyroid hormones (THs) in rats. We performed histopathological, morphometrical and immunohistochemical analyses in hypothyroid and hyperthyroid rats to evaluate the density of mesenteric, renal and cardiac vessels at 4 weeks after induction of thyroid disorders. The main angiogenic factors in plasma, heart and kidney were measured as possible mediators of vascular changes. Mesenteric vessel branching was augmented and decreased in hyper- and hypothyroid rats respectively. The numerical density of CD31-positive capillaries was higher in left and right ventricles and in cortical and medullary kidney from both hyper- and hypothyroid rats vs controls. Numbers of podocytes and glomeruli per square millimetre were similar among groups. Glomerular area and percentage mesangium were greater in the hyperthyroid vs control or hypothyroid groups. No morphological renal lesions were observed in any group. Vascularisation of the mesenteric bed is related to TH levels, but an increased capillarity was observed in heart and kidney in both thyroid disorders. This increase may be produced by higher tissue levels of angiogenic factors in hypothyroid rats, whereas haemodynamic factors would predominate in hyperthyroid rats. Our results also indicate that the renal dysfunctions of thyroid disorders are not related to cortical or medullary microvascular rarefaction and that the proteinuria of hyperthyroidism is not secondary to a podocyte deficit. Finally, TH or its analogues may be useful to increase capillarity in renal diseases associated with microvascular rarefaction.

Chronic Blockade of Neuronal Nitric Oxide Synthase Does Not Affect Long‐Term Control of Blood Pressure in Normal, Saline‐Drinking or Deoxycorticosterone‐Treated Rats

It has been reported that long‐term selective inhibition of neuronal nitric oxide synthase (nNOS) produces elevated blood pressure (BP) in normal rats. The present study was designed to analyse the possible influences of the sodium‐retaining hormone deoxycorticosterone acetate (DOCA) and of an increased sodium intake on BP effects induced by the chronic blockade of nNOS with 7‐nitroindazole (7NI). Two experiments were performed using 7NI at a dose of either 10 mg kg−1 day−1 (experiment 1) or 30 mg kg−1 day−1 (experiment 2). The following groups were used in both experiments: control rats, and rats that received either 1% saline drinking water (Salt), deoxycorticosterone acetate (DOCA), 7NI, 7NI plus 1% saline (7NI + Salt) or 7NI plus DOCA (7NI + DOCA). The tail systolic BP (SBP) was measured in all rats once a week. At the end of the experimental period, the mean arterial pressure (MAP) and metabolic, morphological and renal variables were measured. There were no significant differences in the tail SBP, final MAP or glomerular filtration rate between the experimental groups and the control group. In both experiments, the plasma renin activity (PRA) was significantly inhibited in the Salt groups and suppressed in the DOCA groups. The PRA significantly increased in the 7NI groups, whereas the 7NI + Salt and 7NI + DOCA groups showed a significant inhibition in PRA, especially compared to the 7NI groups in the two experiments. We conclude that chronic nNOS blockade is unable to increase BP in normal, saline‐drinking or DOCA‐treated rats. Furthermore, the nNOS blockade does not interfere with the counterbalance between renin and an increased sodium intake or retention.

Long-Term Consequences of Uninephrectomy in Male and Female Rats

We investigated the effects of uninephrectomy (UNX) in 6-week-old male and female rats on blood pressure (BP), renal sodium handling, salt sensitivity, oxidative stress, and renal injury over 18 months postsurgery, studying control sham-operated and UNX-operated rats at 6, 12, and 18 months postsurgery, evaluating their renal sodium handling, BP, urinary isoprostanes, N-acetyl-&bgr;-D-glucosaminidase, and proteinuria before and after a 2-week high-salt intake period. At 18 months, plasma variables were measured and kidney samples were taken for the analysis of renal morphology and tissue variables. BP was increased at 6 months in male UNX rats versus controls and at 12 and 18 months in both male and female UNX rats and was increased in male versus female UNX groups at 18 months. UNX did not affect water and sodium excretion under basal conditions and after the different test in male and female rats at different ages. However, the renal function curve was shifted to the right in both male and female UNX rats. High-salt intake increased BP in both UNX groups at 6, 12, and 18 months and in the female control group at 18 months, and it increased proteinuria, N-acetyl-&bgr;-D-glucosaminidase, and isoprostanes in both UNX groups throughout the study. Renal lesions at 18 months were more severe in male versus female UNX rats. In summary, long-term UNX increased the BP, creatinine, proteinuria, pathological signs of renal injury, and salt sensitivity. Earlier BP elevation was observed and morphological lesions were more severe in male than in female UNX rats.

Salt sensitivity in experimental thyroid disorders in rats

This study assessed salt sensitivity, analyzing the effects of an increased saline intake on hemodynamic, morphological, and oxidative stress and renal variables in experimental thyroid disorders. Six groups of male Wistar rats were used: control, hypothyroid, hyperthyroid, and the same groups treated with salt (8% via food intake). Body weight, blood pressure (BP), and heart rate (HR) were recorded weekly for 6 wk. Finally, BP and HR were recorded directly, and morphological, metabolic, plasma, and renal variables were measured. High-salt intake increased BP in thyroxine-treated rats but not in control or hypothyroid rats. High-salt intake increased cardiac mass in all groups, with a greater increase in hyperthyroid rats. Urinary isoprostanes and H(2)O(2) were higher in hyperthyroid rats and were augmented by high-salt intake in all groups, especially in hyperthyroid rats. High-salt intake reduced plasma thyroid hormone levels in hyperthyroid rats. Proteinuria was increased in hyperthyroid rats and aggravated by high-salt intake. Urinary levels of aminopeptidases (glutamyl-, alanyl-, aspartyl-, and cystinylaminopeptidase) were increased in hyperthyroid rats. All aminopeptidases were increased by salt intake in hyperthyroid rats but not in hypothyroid rats. In summary, hyperthyroid rats have enhanced salt sensitivity, and high-salt intake produces increased BP, cardiac hypertrophy, oxidative stress, and signs of renal injury. In contrast, hypothyroid rats are resistant to salt-induced BP elevation and renal injury signs. Urinary aminopeptidases are suitable biomarkers of renal injury.