Salt-sensitive blood pressure and exaggerated vascular reactivity in the hypertension of diabetes mellitus

Associations of retinal microvascular alterations with diabetes mellitus: an OCTA-based cross-sectional study

BACKGROUND

Diabetes, a health crisis afflicting millions worldwide, is increasing rapidly in prevalence. The microvascular complications triggered by diabetes have emerged as the principal cause of renal disease and blindness. The retinal microvascular network may be sensitive to early systemic vascular structural and functional changes. Therefore, this research endeavored to discern the systemic determinants influencing the retinal microvascular network in patients with and without diabetes.

METHODS

The Kailuan Eye Study is a cross-sectional study based on the community-based cohort Kailuan Study. Participants underwent optical coherence tomography angiography (OCTA) (Zeiss Cirrus 5000; Carl Zeiss Meditec) and comprehensive systemic examination. Metrics such as perfusion density (PD), vascular density (VD), foveal avascular zone (FAZ) parameters of the superficial capillary plexus (SCP) in the macula were assessed.

RESULTS

This study included 860 eligible participants (average age = 62.75 ± 6.52 years; 21.9% female), of which 449 were diabetics. People with diabetes had diminished PD and VD in the entire macular and parafoveal regions compared to people without diabetes. Reduced PD in the whole macular region was correlated with higher fasting plasma glucose (FPG, mmol/L) concentration (Beta = -0.19, 95% CI = -0.42 to -0.36, P < 0.001), longer axial length (AL, mm) (Beta = -0.13, 95%CI = -0.48 to -0.25, P = 0.002), and elevated heart rate (Beta = -0.10, 95%CI = -0.14 to -0.19, P = 0.014), after adjusting for younger age (Beta = -0.18, 95%CI = -0.24 to -0.35, P < 0.001), consistent with VD of the whole macular region. A higher FPG level was significantly correlated with lower SCP density of both PD and VD in the macular and parafoveal region (P < 0.05 for all), as well as increased systolic blood pressure and low-density lipoprotein cholesterol concentration (P < 0.01 for all).

CONCLUSIONS

In this large-sample cross-sectional study, OCTA evaluation revealed that high prevalence of diabetes and elevated FPG levels were correlated with reduced retinal VD and PD. Hypertension and hyperlipidemia are important risk factors for the development of atherosclerotic cardiovascular disease but have no significant effect on retinal microvascular abnormalities.

The effect of a low versus high sodium diet on blood pressure in diabetic patients: A systematic review and meta-analysis of clinical trials

There have been numerous clinical trials that have investigated the effect of sodium intake on blood pressure in diabetic patients. The purpose of this systematic review and meta-analysis was to evaluate the clinical trial studies performed on the effect of low sodium diet (LSD) versus high sodium diet (HSD) on blood pressure in diabetic patients. PubMed, Scopus, and Web of Science were systematically searched from database inception to July 10, 2021. Both type 1 and 2 diabetes was considered. Overall, there were 15 studies included in this meta-analysis. The weighted (WMD) mean difference with 95% confidence interval (CI) was calculated using a random-effects model. Risk of bias in the studies was assessed based on the Cochrane collaboration tool and the quality of all the studies was considered as good. Overall, LSD significantly reduced SBP (systolic blood pressure) (WMD: -3.79 mmHg, 95% CI: -6.02, -1.56) and DBP (diastolic blood pressure) (WMD: -1.62 mmHg, 95% CI: -2.84, -0.40), in comparison with HSD, in diabetics. However, LSD had no significant effect on MAP (mean arterial pressure) in comparison with HSD (WMD: -1.81, 95%CI: -5.49, 1.87). Although subgroup analysis could not attenuate heterogeneity in SBP, subgroup analysis in DBP based on duration (≤1 week: WMD: -2.35, 95%CI: -3.69, -1.00, I 2  = 48.9%, p = 0.081, >1 week: WMD: -1.04, 95% CI: -2.83, 0.76, I 2  = 74.7%, p = 0.003) and study design (cross-over: WMD: -1.94, 95% CI: -2.71, -1.17, I 2  = 32.1%, p = 0.183, parallel: WMD: -2.17, 95% CI: -6.48, 2.13, I 2  = 82.4%, p = 0.001) successfully detected sources of heterogeneity. LSD significantly reduced SBP and DBP, however, had no effect on MAP, in comparison with HSD.

Impact of salt intake on urinary albumin excretion in patients with type 2 diabetic nephropathy: a retrospective cohort study based on a generalized additive model

Diabetic kidney disease is an important and common cause of end-stage renal disease. Measurement of urinary albumin excretion (UAE) requires the diagnosis of the stage of diabetic nephropathy and the prognosis of renal function. We aimed to analyze the impact of lifestyle modification on UAE in patients with stage 2 and 3 type 2 diabetic nephropathy who received comprehensive medical care, using a generalized additive model (GAM), an explanatory machine learning model. In this retrospective observational study, we used changes in HbA1c, systolic blood pressure (SBP), and diastolic blood pressure (DBP) levels; body mass index (BMI); and daily salt intake as factors contributing to changes in UAE. In total, 269 patients with type 2 diabetic nephropathy were enrolled (stage 2, 217 patients; stage 3, 52 patients). The rankings that contributed to changes in UAE over 6 months by permutation importance were the changes in daily salt intake, HbA1c, SBP, DBP, and BMI. GAM, which predicts the change in UAE, showed that with increase in the changes in salt intake, SBP, and HbA1c, the delta UAE tended to increase. Salt intake was the most contributory factor for the changes in UAE, and daily salt intake was the best lifestyle factor to explain the changes in UAE. Strict control of salt intake may have beneficial effects on improving UAE in patients with stage 2 and 3 diabetic nephropathy.

Failure to vasodilate in response to salt loading blunts renal blood flow and causes salt-sensitive hypertension

AIMS

Salt-sensitive (SS) hypertension is accompanied by impaired vasodilation in the systemic and renal circulation. However, the causal relationship between vascular dysfunction and salt-induced hypertension remains controversial. We sought to determine whether primary vascular dysfunction, characterized by a failure to vasodilate during salt loading, plays a causal role in the pathogenesis of SS hypertension.

METHODS AND RESULTS

Mice selectively expressing a peroxisome proliferator-activated receptor γ dominant-negative mutation in vascular smooth muscle (S-P467L) exhibited progressive SS hypertension during a 4 week high salt diet (HSD). This was associated with severely impaired vasodilation in systemic and renal vessels. Salt-induced impairment of vasodilation occurred as early as 3 days after HSD, which preceded the onset of SS hypertension. Notably, the overt salt-induced hypertension in S-P467L mice was not driven by higher cardiac output, implying elevations in peripheral vascular resistance. In keeping with this, HSD-fed S-P467L mice exhibited decreased smooth muscle responsiveness to nitric oxide (NO) in systemic vessels. HSD-fed S-P467L mice also exhibited elevated albuminuria and a blunted increase in urinary NO metabolites which was associated with blunted renal blood flow and increased sodium retention mediated by a lack of HSD-induced suppression of NKCC2. Blocking NKCC2 function prevented the salt-induced increase in blood pressure in S-P467L mice.

CONCLUSION

We conclude that failure to vasodilate in response to salt loading causes SS hypertension by restricting renal perfusion and reducing renal NO through a mechanism involving NKCC2 in a mouse model of vascular peroxisome proliferator-activated receptor γ impairment.

Salt Intake and Risk of Disaster Hypertension Among Evacuees in a Shelter After the Great East Japan Earthquake

This study investigated the association between salt intake and risk of disaster hypertension. We analyzed the data of surveys evaluating the health condition of evacuees in shelters after the Great East Japan Earthquake on April 30 and May 5, 2011. Among 272 subjects who completed the basic health condition questionnaire and underwent a medical examination, 158 (58%) had disaster hypertension (systolic blood pressure ≥140 mm Hg or diastolic blood pressure ≥90 mm Hg). Average estimated sodium intake assessed by spot urine was significantly associated with disaster hypertension (odds ratio per 1 g/d, 1.16; 95% CI, 1.05-1.30). When we defined the high risk factors for salt-sensitive hypertension as older age (≥65 years), obesity (body mass index, ≥25 kg/m²), chronic kidney disease, and diabetes mellitus, estimated sodium intake was found to be a risk factor for disaster hypertension in the total group (odds ratio per 1 g/d, 1.27; 95% CI, 1.12-1.43) and even in the group without prevalent hypertension before disaster (n=146; odds ratio per 1 g/d, 1.46; 95% CI, 1.19-1.79). There was an interaction between estimated sodium intake and disaster hypertension according to the presence or absence of high risk of salt-sensitive hypertension in the group without prevalent hypertension (P=0.03). Disaster hypertension conferred a risk of microalbuminuria (odds ratio, 3.00; 95% CI, 1.71-5.26; P<0.001). We conclude that increased estimated sodium intake was associated with disaster hypertension in evacuees after disaster. This association was noted in the population with high risk of salt-sensitive hypertension and without prevalent hypertension before natural disaster. Additionally, disaster hypertension was associated with subclinical organ damage.

The Twin White Herrings: Salt and Sugar

India has the dubious distinction of being a hotspot for both diabetes and hypertension. Increased salt and sugar consumption is believed to fuel these two epidemics. This review is an in-depth analysis of current medical literature on salt and sugar being the two white troublemakers of modern society. The PubMed, Medline, and Embase search for articles published in January 2018, using the terms "salt" [MeSH Terms] OR "sodium chloride" [All Fields] OR "sugar" [All Fields]. India is world's highest consumer of sugar with one of the highest salt consumption per day. Increased salt intake is associated with increased risk of hypertension, left ventricular hypertrophy and fibrosis, cardiovascular events, renal stones, proteinuria, and renal failure. Increased sugar intake is directly linked to increased risk of obesity, fatty liver disease, and metabolic syndrome. Also, increased sugar intake may be indirectly related to the increased risk of type 2 diabetes. Both salt and sugar intake is directly linked to increased systemic and hypothalamic inflammation, endothelial dysfunction, microangiopathy, cardiovascular remodelling, cancers, and death. High fructose corn is especially damaging. There is no safe limit of sugar consumption, as the human body can produce its own glucose. Being nature's gift to mankind, there is no harm in moderate consumption of salt and sugar, however, modest reduction in the consumption of both can substantially reduce the burden of non-communicable diseases. Public health interventions to facilitate this behavioural change must be instituted and encouraged.

Effects of high-sodium intake on systemic blood pressure and vascular responses in spontaneously diabetic WBN/Kob-Leprfa/fa rats

The prevalence of type 2 diabetes mellitus (T2DM) and hypertension has markedly increased worldwide. The purpose of the present study was to examine the effects of a high‐salt intake on the systolic blood pressure (SBP) and vascular responses in WBN/Kob‐Lepr^fa/fa (WBKDF) rats, a new spontaneous animal model of T2DM. Male WBKDF rats and age‐matched Wistar rats at 6 weeks of age were each divided into two groups and fed either a normal‐sodium (NS, 0.26%) diet or high‐sodium (HS, 8%) diet for 14 weeks: (i) Wistar rats on NS diet (Wistar‐NS); (ii) Wistar rats on HS diet (Wistar‐HS); (iii) WBKDF rats on NS diet (WBKDF‐NS); (iv) WBKDF rats on HS diets (WBKDF‐HS). Neither WBKDF‐NS nor Wistar‐NS rats showed significant changes in SBP throughout the experiment, but both WBKDF‐HS and Wistar‐HS exhibited significant elevation of SBP, which was more prominent (P<.01) in WBKDF‐HS than in Wistar‐HS. Phenylephrine‐induced contractions of isolated thoracic aortic rings were significantly (P<.01) enhanced in WBKDF‐HS and Wistar‐HS compared with the respective strain of rats on the NS diet. In contrast, acetylcholine‐ and nitroprusside‐induced relaxation were significantly (P<.01) diminished in both WBKDF‐HS and Wistar‐HS, and these HS diet‐induced changes were more profound (P<.01) in WBKDF rats than in Wistar rats. Significantly (P<.05) higher plasma concentrations of 8‐iso‐prostaglandin F_2α and sodium ions were observed in WBKDF‐HS than in Wistar‐HS. The current study demonstrated that WBKDF‐HS rats developed salt‐sensitive hypertension associated with vascular dysfunction. The WBKDF rat may be a useful model for investigating the etiology of hypertension with T2DM.

A Quantitative Systems Physiology Model of Renal Function and Blood Pressure Regulation: Application in Salt-Sensitive Hypertension

Salt‐sensitivity (SS) refers to changes in blood pressure in response to changes in sodium intake. SS individuals are at greater risk for developing kidney disease, and also respond differently to antihypertensive therapies compared to salt‐resistant (SR) individuals. In this study we used a systems pharmacology model of renal function (presented in a companion article) to evaluate the ability of proposed mechanisms to produce salt‐sensitivity. The model reproduced previously published data on renal functional changes in response to salt‐intake, and also predicted that glomerular pressure, a variable that is not easily evaluated clinically but is a key factor in renal injury, increases with salt intake in SS hypertension. We then used the model to generate mechanistic insight into the differential blood pressure and glomerular pressure responses to angiotensin converting enzyme (ACE) inhibitors, thiazide diuretics, and calcium channel blockers observed in SS and SR hypertension.

Primary proximal tubule hyperreabsorption and impaired tubular transport counterregulation determine glomerular hyperfiltration in diabetes: a modeling analysis

Glomerular hypertension and hyperfiltration in early diabetes are associated with development and progression of diabetic kidney disease. The tubular hypothesis of diabetic hyperfiltration proposes that it is initiated by a primary increase in sodium (Na) reabsorption in the proximal tubule (PT) and the resulting tubuloglomerular feedback (TGF) response and lowering of Bowman space pressure (P_Bow). Here we utilized a mathematical model of the human kidney to investigate over acute and chronic timescales the mechanisms responsible for the magnitude of the hyperfiltration response. The model implicates that the primary hyperreabsorption of Na in the PT produces a Na imbalance that is only partially restored by the hyperfiltration induced by TGF and changes in P_Bow Thus secondary adaptations are needed to restore Na balance. This may include neurohumoral transport regulation and/or pressure-natriuresis (i.e., the decrease in Na reabsorption in response to increased renal perfusion pressure). We explored the role of each tubular segment in contributing to this compensation and the consequences of impairment in tubular compensation. The simulations indicate that impaired secondary downregulation of transport potentiated the rise in glomerular hypertension and hyperfiltration needed to restore Na balance at a given level of primary PT hyperreabsorption. Therefore, we propose for the first time that both the extent of primary PT hyperreabsorption and the degree of impairment of the distal tubular responsiveness to regulatory signals determine the level of glomerular hypertension and hyperfiltration in the diabetic kidney, thereby extending the tubule-centric concept of diabetic hyperfiltration and potential therapeutic approaches beyond the proximal tubule.

Sodium and Its Role in Cardiovascular Disease - The Debate Continues

Guidelines have recommended significant reductions in dietary sodium intake to improve cardiovascular health. However, these dietary sodium intake recommendations have been questioned as emerging evidence has shown that there is a higher risk of cardiovascular disease with a low sodium diet, including in individuals with type 2 diabetes. This may be related to the other pleotropic effects of dietary sodium intake. Therefore, despite recent review of dietary sodium intake guidelines by multiple organizations, including the dietary guidelines for Americans, American Diabetes Association, and American Heart Association, concerns about the impact of the degree of sodium restriction on cardiovascular health continue to be raised. This literature review examines the effects of dietary sodium intake on factors contributing to cardiovascular health, including left ventricular hypertrophy, heart rate, albuminuria, rennin-angiotensin-aldosterone system activation, serum lipids, insulin sensitivity, sympathetic nervous system activation, endothelial function, and immune function. In the last part of this review, the association between dietary sodium intake and cardiovascular outcomes, especially in individuals with diabetes, is explored. Given the increased risk of cardiovascular disease in individuals with diabetes and the increasing incidence of diabetes worldwide, this review is important in summarizing the recent evidence regarding the effects of dietary sodium intake on cardiovascular health, especially in this population.

Effect of low salt diet on insulin resistance in salt-sensitive versus salt-resistant hypertension

Accumulating evidence shows an increase in insulin resistance on salt restriction. We compared the effect of low salt diet on insulin resistance in salt-sensitive versus salt-resistant hypertensive subjects. We also evaluated the relationship between salt sensitivity of blood pressure and salt sensitivity of insulin resistance in a multivariate regression model. Studies were conducted after 1 week of high salt (200 mmol per day sodium) and 1 week of low salt (10 mmol per day sodium) diet. Salt sensitivity was defined as the fall in systolic blood pressure>15 mm Hg on low salt diet. The study includes 389 subjects (44% women; 16% blacks; body mass index, 28.5±4.2 kg/m2). As expected, blood pressure was lower on low salt (129±16/78±9 mm Hg) as compared with high salt diet (145±18/86±10 mm Hg). Fasting plasma glucose, insulin, and homeostasis model assessment were higher on low salt diet (95.4±19.4 mg/dL; 10.8±7.3 mIU/L; 2.6±1.9) as compared with high salt diet (90.6±10.8 mg/dL; 9.4±5.8 mIU/L; 2.1±1.4; P<0.0001 for all). There was no difference in homeostasis model assessment between salt-sensitive (n=193) versus salt-resistant (n=196) subjects on either diet. Increase in homeostasis model assessment on low salt diet was 0.5±1.4 in salt-sensitive and 0.4±1.5 in salt-resistant subjects (P=NS). On multivariate regression analysis, change in systolic blood pressure was not associated with change in homeostasis model assessment after including age, body mass index, sex, change in serum and urine aldosterone, and cortisol into the model. We conclude that the increase in insulin resistance on low salt diet is not affected by salt sensitivity of blood pressure.

Insulin, CCAAT/enhancer-binding proteins and lactate regulate the human 11β-hydroxysteroid dehydrogenase type 2 gene expression in colon cancer cell lines

11β-Hydroxysteroid dehydrogenases (11beta-HSD) modulate mineralocorticoid receptor transactivation by glucocorticoids and regulate access to the glucocorticoid receptor. The isozyme 11beta-HSD2 is selectively expressed in mineralocorticoid target tissues and its activity is reduced in various disease states with abnormal sodium retention and hypertension, including the apparent mineralocorticoid excess. As 50% of patients with essential hypertension are insulin resistant and hyperinsulinemic, we hypothesized that insulin downregulates the 11beta-HSD2 activity. In the present study we show that insulin reduced the 11beta-HSD2 activity in cancer colon cell lines (HCT116, SW620 and HT-29) at the transcriptional level, in a time and dose dependent manner. The downregulation was reversible and required new protein synthesis. Pathway analysis using mRNA profiling revealed that insulin treatment modified the expression of the transcription factor family C/EBPs (CCAAT/enhancer-binding proteins) but also of glycolysis related enzymes. Western blot and real time PCR confirmed an upregulation of C/EBP beta isoforms (LAP and LIP) with a more pronounced increase in the inhibitory isoform LIP. EMSA and reporter gene assays demonstrated the role of C/EBP beta isoforms in HSD11B2 gene expression regulation. In addition, secretion of lactate, a byproduct of glycolysis, was shown to mediate insulin-dependent HSD11B2 downregulation. In summary, we demonstrate that insulin downregulates HSD11B2 through increased LIP expression and augmented lactate secretion. Such mechanisms are of interest and potential significance for sodium reabsorption in the colon.

Physiological changes induced by salt intake in female Spontaneously Diabetic Torii-Lepr(fa) (SDT fatty) rat, a novel obese type 2 diabetic model

Salt plays an important role in the control of blood pressure in obesity and diabetes mellitus. In this study, we investigated physiological changes such as blood pressure and renal function in salt-loaded female Spontaneously Diabetic Torii-Lepr(fa) (SDT fatty) rats. SDT fatty rats were given 1% NaCl in drinking water for 14 weeks, from 4 to 18 weeks of age. Significant salt-sensitive hypertension was observed in the salt-loaded SDT fatty rats. Moreover, the salt-loaded rats showed a decrease of creatinine clearance and deterioration on pathological renal findings, including glomerulosclerosis and tubular and interstitial lesions. Female SDT fatty rat is a useful model for investigating the mechanisms of high salt sensitivity in obesity and diabetes mellitus.

NGAL and NT-proBNP levels in diabetic patients with macroproteinuria

BACKGROUND

In patients with heart failure plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) levels are correlated to urine neutrophil gelatinase-associated lipocalin (NGAL) levels. We prospectively evaluated the relationship among glomerular filtration rate (eGFR), urine albumin-to-creatinine ratio (ACR), urine and serum NGAL and NT-proBNP levels in 20 type II diabetic patients with macroalbuminuria at 4-month intervals.

RESULTS

Compared with 20 age, gender-matched healthy controls, diabetic patients had higher urine and serum NGAL, serum NT-proBNP and lower eGFR. The eGFR of the patients at the baseline, the 4th and the 8th month were 29.6 ± 12.0, 27.8 ± 13.7 and 22.9 ± 10.4 mL/min/1.73 m(2), respectively. No significant change in urine NGAL levels was detected (p > 0.05), whereas there were significant increases in NT-proBNP, serum NGAL and urine ACR and significant decrease in eGFR as the study progressed (p < 0.05). Both the baseline and the 4th month urine ACR were positively correlated to NT-proBNP levels measured at the same periods (r: 0.451; p: 0.046; r: 0.489; p: 0.029 respectively). In all measurements, urine ACR was negatively correlated to serum albumin levels measured at the same periods (r: -0.792; p: 0.000; r: -0.716; p: 0.000; r: -0.531; p: 0.016 respectively). None of eGFR measurements was correlated with NT-proBNP (p > 0.05). Neither serum NGAL nor urinary NGAL levels are associated with NT-proBNP (p > 0.05).

CONCLUSION

Our findings show an association between NT-proBNP and proteinuria in type II diabetic patients with macroalbuminuria but not with serum and urine NGAL.

Association of dietary sodium intake with atherogenesis in experimental diabetes and with cardiovascular disease in patients with Type 1 diabetes

It is recommended that individuals with diabetes restrict their dietary sodium intake. However, although salt intake is correlated with BP (blood pressure), it also partly determines the activation state of the RAAS (renin–angiotensin–aldosterone system), a key mediator of diabetes-associated atherosclerosis. apoE KO (apolipoprotein E knockout) mice were allocated for the induction of diabetes with streptozotocin or citrate buffer (controls) and further randomized to isocaloric diets containing 0.05%, 0.3% or 3.1% sodium with or without the ACEi [ACE (angiotensin-converting enzyme) inhibitor] perindopril. After 6 weeks of study, plaque accumulation was quantified and markers of atherogenesis were assessed using RT–PCR (reverse transcription–PCR) and ELISA. The association of sodium intake and adverse cardiovascular and mortality outcomes were explored in 2648 adults with Type 1 diabetes without prior CVD (cardiovascular disease) from the FinnDiane study. A 0.05% sodium diet was associated with increased plaque accumulation in diabetic apoE KO mice, associated with activation of the RAAS. By contrast, a diet containing 3.1% sodium suppressed atherogenesis associated with suppression of the RAAS, with an efficacy comparable with ACE inhibition. In adults with Type 1 diabetes, low sodium intake was also associated with an increased risk of all-cause mortality and new-onset cardiovascular events. However, high sodium intake was also associated with adverse outcomes, leading to a J-shaped relationship overall. Although BP lowering is an important goal for the management of diabetes, off-target actions to activate the RAAS may contribute to an observed lack of protection from cardiovascular complications in patients with Type 1 diabetes with low sodium intake.

High sodium intake is associated with masked hypertension in Japanese patients with type 2 diabetes and treated hypertension

BACKGROUND

Knowledge regarding the association between dietary sodium intake and the incidence of masked hypertension is limited.

METHODS

A total of 193 Japanese type 2 diabetic outpatients who had been treated with antihypertensive agents and with office blood pressures <140/90 mm Hg were recruited. Masked hypertension was defined as having office blood pressure <140/90 mm Hg and 24-h mean ambulatory blood pressure ≥130/80 mm Hg. The dietary sodium intake was estimated by measuring the 24-h urinary sodium excretion.

RESULTS

Masked hypertension was found in 128 (66.3%) patients. An age- and sex-adjusted univariate logistic regression analysis showed that urinary albumin excretion, renin-angiotensin system inhibitor use, office systolic blood pressure, and amount of dietary sodium intake were significantly associated with masked hypertension. A multivariate logistic regression analysis also identified an older age, renin-angiotensin system inhibitor use, an office elevated systolic blood pressure, and high dietary sodium intake to be independently associated with masked hypertension. When compared with those who consumed a low salt diet (sodium <120 mEq/day), the odds ratio for the risk of exhibiting masked hypertension in patients who consumed a medium salt diet (sodium 120 to <200 mEq/day) or a high salt diet (sodium ≥200 mEq/day) were 5.3 (P < 0.001) and 12.6 (P < 0.001), respectively.

CONCLUSIONS

Masked hypertension is a common feature in type 2 diabetic patients being treated for hypertension. The observed association with sodium intake raised the hypothesis that excessive sodium intake may play a part in the genesis of masked hypertension in these patients.

Nonmodulation as the mechanism for salt sensitivity of blood pressure in individuals with hypertension and type 2 diabetes mellitus

CONTEXT

It is assumed that in individuals with type 2 diabetes mellitus (T2DM), blood pressure sensitivity to salt intake and the frequency of a low renin state are both increased compared with the nondiabetic population. However, studies supporting these assumptions may have been confounded by participant inclusion criteria, and study results may reflect target organ damage.

OBJECTIVE

The objective of this study was to examine in a cohort of T2DM 1) the frequency of salt sensitivity of blood pressure and 2) whether alterations of the renin-angiotensin-aldosterone system (RAAS) contribute to salt sensitivity in this population.

DESIGN, PATIENTS, AND METHODS

Within participants of the HyperPATH cohort, four groups were analyzed: 1) T2DM with hypertension (HTN), n=51; 2) T2DM without HTN, n=30; 3) HTN only, n=451; and 4) normotensive, n=209. Phenotype studies were conducted after participants completed two dietary phases: liberal sodium (200 mmol/d) and low sodium (10 mmol/d) for 7 d each. Participants were admitted overnight to a clinical research center after each diet, and supine measurements of the RAAS before and after a 60-min angiotensin II infusion (3 ng/kg·min) were obtained.

RESULTS

Multivariate regression analysis demonstrated that T2DM status (all individuals with T2DM vs. individuals without T2DM) was not associated with the change in mean arterial pressure between the low and liberal sodium diets after accounting for age, gender, body mass index, race, and baseline blood pressure (T2DM status, P=0.5). Furthermore, two intermediate phenotypes of altered RAAS, low renin, and nonmodulation (NMOD), were associated with salt-sensitive blood pressure but occurred at different frequencies in the T2DM-HTN and HTN groups (low renin, 12% T2DM-HTN vs. 29% HTN; NMOD, 41% T2DM-HTN vs. 27% HTN; P=0.01).

CONCLUSION

The frequency of NMOD in participants with T2DM was significantly higher compared with HTN, suggesting that the salt sensitivity often seen in T2DM is driven by NMOD.

Diabetes and hypertension: the bad companions

High blood pressure is reported in over two-thirds of patients with type 2 diabetes, and its development coincides with the development of hyperglycaemia. Many pathophysiological mechanisms underlie this association. Of these mechanisms, insulin resistance in the nitric-oxide pathway; the stimulatory effect of hyperinsulinaemia on sympathetic drive, smooth muscle growth, and sodium-fluid retention; and the excitatory effect of hyperglycaemia on the renin-angiotensin-aldosterone system seem to be plausible. In patients with diabetes, hypertension confers an enhanced risk of cardiovascular disease. A blood pressure of lower than 140/85 mm Hg is a reasonable therapeutic goal in patients with type 2 diabetes according to clinical trial evidence. People with controlled diabetes have a similar cardiovascular risk to patients without diabetes but with hypertension. A renin-angiotensin system blocker combined with a thiazide-type diuretic might be the best initial antihypertensive regimen for most people with diabetes. In general, the positive effects of antihypertensive drugs on cardiovascular outcomes outweigh the negative effects of antihypertensive drugs on glucose metabolism.

Hypertension in diabetic nephropathy: epidemiology, mechanisms, and management

Hypertension is highly prevalent in patients with diabetic nephropathy. Diabetic nephropathy is the leading cause of CKD and end-stage kidney disease in the United States. The etiology of hypertension in diabetic nephropathy involves mechanisms with multiple inter-related mediators that result in renal sodium reabsorption and peripheral vasoconstriction. The management of hypertension in these patients is focused on treatments that target these mediators. Clinical trials have established that drugs that inhibit the renin-angiotensin-aldosterone system should be used as first-line agents on the basis of their ability to slow down progression of kidney disease and lower albuminuria. There is further interest into how the combination of drugs that inhibit this pathway at multiple steps will contribute further to the management of hypertension and diabetic nephropathy. This article presents an updated review of the mechanisms involved in hypertension in patients with diabetic nephropathy. It also reviews the past clinical trials using single agents as therapeutics and the more recent trials involving novel drugs or drug combinations used to treat these patients. Retrospective analyses of multiple studies are included to better examine the significance of the currently proposed blood pressure targets for patients with diabetic nephropathy.

Altered dietary salt intake for preventing and treating diabetic kidney disease

BACKGROUND

There is strong evidence that our current consumption of salt is a major factor for increased blood pressure (BP) and a modest reduction in salt intake lowers BP whether BP levels are normal or raised. Tight control of BP in diabetics lowers the risk of strokes, heart attacks and heart failure and slows the progression of diabetic kidney disease (DKD). Currently there is no consensus in restricting salt intake in diabetic patients.

OBJECTIVES

To evaluate the effect of altered salt intake on BP and markers of cardiovascular disease and DKD.

SEARCH STRATEGY

In January 2010, we searched the Cochrane Renal Group's Specialised Register, CENTRAL (in The Cochrane Library), MEDLINE (from 1966) and EMBASE (from 1980) to identify appropriate articles.

SELECTION CRITERIA

We included all randomised controlled trials of salt reduction in individuals with type 1 and type 2 diabetes.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed studies and resolved differences by discussion with a third independent author. We calculated mean effect sizes using both the fixed-effect and random-effects models.

MAIN RESULTS

Thirteen studies (254 individuals) met our inclusion criteria. These included 75 individuals with type 1 diabetes and 158 individuals with type 2 diabetes. The median reduction in urinary sodium was 203 mmol/24 h (11.9 g/day) in type 1 diabetes and 125 mmol/24 h (7.3 g/day) in type 2 diabetes. The median duration of salt restriction was one week in both type 1 and type 2 diabetes. BP was reduced in both type 1 and type 2 diabetes. In type 1 diabetes (56 individuals), salt restriction reduced BP by -7.11/-3.13 mm Hg (systolic/diastolic); 95% CI: systolic BP (SBP) -9.13 to -5.10; diastolic BP (DBP) -4.28 to -1.98). In type 2 diabetes (56 individuals), salt restriction reduced BP by -6.90/-2.87 mm Hg (95% CI: SBP -9.84 to -3.95; DBP -4.39 to -1.35). There was a greater reduction in BP in normotensive patients, possibly due to a larger decrease in salt intake in this group.

AUTHORS' CONCLUSIONS

Although the studies are not extensive, this meta-analysis shows a large fall in BP with salt restriction, similar to that of single drug therapy. All diabetics should consider reducing salt intake at least to less than 5-6 g/day in keeping with current recommendations for the general population and may consider lowering salt intake to lower levels, although further studies are needed.

Salt supplementation blunts the blood pressure response to telmisartan with or without hydrochlorothiazide in hypertensive patients with type 2 diabetes

AIMS/HYPOTHESIS

We assessed the effects of sodium chloride (NaCl) supplementation on the blood pressure response to treatment with telmisartan with or without hydrochlorothiazide in hypertensive patients with type 2 diabetes and habitually high (HDS, sodium excretion >200 mmol/24 h on two out of three consecutive occasions) or low (LDS, sodium excretion <100 mmol/24 h on two out of three consecutive occasions) salt intake.

METHODS

Patients received 4 weeks of telmisartan followed by 4 weeks of telmisartan plus hydrochlorothiazide. In a double-blind randomised fashion, patients received sodium chloride (NaCl, 100 mmol/24 h) or placebo capsules in addition to their habitual salt intake during the last 2 weeks of telmisartan and telmisartan plus hydrochlorothiazide therapy. The protocol was repeated with NaCl and placebo capsules administered in reverse order to allow each participant to act as his or her own control. At 0, 4, 8, 14, 18 and 22 weeks, 24 h ambulatory blood pressure (ABP) and 24 h urine collections were performed.

RESULTS

No statistically significant differences were seen in the ABP response in the LDS vs HDS groups to any of the interventions (p = 0.58). NaCl supplementation reduced the effect of telmisartan with or without hydrochlorothiazide on systolic BP by approximately 50% (-5.8 mmHg during NaCl supplementation vs -11.3 mmHg during placebo, mean difference 5.6 mmHg [95% CI 1.7-9.4 mmHg], p = 0.005), irrespective of habitual salt intake. By contrast, addition of hydrochlorothiazide increased the antihypertensive effect of telmisartan on systolic BP by approximately 35% (p = 0.048) in both groups of patients.

CONCLUSIONS/INTERPRETATION

NaCl supplementation blunts the effectiveness of telmisartan with or without hydrochlorothiazide in hypertensive patients with type 2 diabetes, independently of habitual low or high salt intake.

Correlation between increased urinary sodium excretion and decreased left ventricular diastolic function in patients with type 2 diabetes mellitus

BACKGROUND

Increased salt intake may induce hypertension, lead to cardiac hypertrophy, and exacerbate heart failure. When elderly patients develop heart failure, diastolic dysfunction is often observed, although the ejection fraction has decreased. Diabetes mellitus (DM) is an established risk factor for heart failure. However, little is known about the relationship between cardiac function and urinary sodium excretion (U-Na) in patients with DM.

METHODS

We measured 24-hour U-Na; cardiac function was evaluated directly during coronary catheterization in type 2 DM (n = 46) or non-DM (n = 55) patients with preserved cardiac systolic function (ejection fraction > or = 60%). Cardiac diastolic and systolic function was evaluated as - dp/dt and + dp/dt, respectively.

RESULTS

The average of U-Na was 166.6 +/- 61.2 mEq/24 hour (mean +/- SD). In all patients, stepwise multivariate regression analysis revealed that - dp/dt had a negative correlation with serum B-type natriuretic peptide (BNP; beta = - 0.23, P = .021) and U-Na (beta = - 0.24, P = .013). On the other hand, + dp/dt negatively correlated with BNP (beta = - 0.30, P < .001), but did not relate to U-Na. In the DM-patients, stepwise multivariate regression analysis showed that - dp/dt still had a negative correlation with U-Na (beta = - 0.33, P = .025).

CONCLUSION

The results indicated that increased urinary sodium excretion is associated with an impairment of cardiac diastolic function, especially in patients with DM, suggesting that a reduction of salt intake may improve cardiac diastolic function.

Effect of treatment with losartan on salt sensitivity and SGLT2 expression in hypertensive diabetic rats

Sodium-glucose cotransporters (SGLTs) in the kidney, may be involved in hypertension, diabetes and salt sensitivity. We evaluate the effect of losartan on blood pressure (BP) and SGLT2 expression in diabetic rats with high or normal salt diet. Losartan prevented an increase in BP and SGLT2 expression in diabetic rats.

Genes, diet and type 2 diabetes mellitus: a review

Diabetes mellitus is widely recognized as one of the leading causes of death and disability. While insulin insensitivity is an early phenomenon partly related to obesity, pancreatic beta-cell function declines gradually over time even before the onset of clinical hyperglycemia. Several mechanisms have been proposed to be responsible for insulin resistance, including increased non-esterified fatty acids, inflammatory cytokines, adipokines, and mitochondrial dysfunction, as well as glucotoxicity, lipotoxicity, and amyloid formation for beta-cell dysfunction. Moreover, the disease has a strong genetic component, although only a handful of genes have been identified so far. Diabetic management includes diet, exercise and combinations of antihyperglycemic drug treatment with lipid-lowering, antihypertensive, and antiplatelet therapy. Since many persons with type 2 diabetes are insulin resistant and overweight, nutrition therapy often begins with lifestyle strategies to reduce energy intake and increase energy expenditure through physical activity. These strategies should be implemented as soon as diabetes or impaired glucose homoeostasis (pre-diabetes) is diagnosed.

Blood pressure lowering for the prevention and treatment of diabetic kidney disease

The current pandemic of diabetes mellitus will inevitably be followed by an epidemic of chronic kidney disease. It is anticipated that 25-40% of patients with type 1 diabetes and 5-40% of patients with type 2 diabetes will ultimately develop diabetic kidney disease. The control of blood pressure represents a key component for the prevention and management of diabetic nephropathy. There is a strong epidemiological connection between hypertension in diabetes and adverse outcomes in diabetes. Hypertension is closely linked to insulin resistance as part of the 'metabolic syndrome'. Diabetic nephropathy may lead to hypertension through direct actions on renal sodium handling, vascular compliance and vasomotor function. Recent clinical trials also support the utility of blood pressure reduction in the prevention of diabetic kidney disease. In patients with normoalbuminuria, transition to microalbuminuria can be prevented by blood pressure reduction. This action appears to be significant regardless of whether patients have elevated blood pressure or not. The efficacy of ACE inhibition appears to be greater than that achieved by other agents with a similar degree of blood pressure reduction; although large observational studies suggest the risk of microalbuminuria may be reduced by blood pressure reduction, regardless of modality. In patients with established microalbuminuria, ACE inhibitors and angiotensin receptor antagonists (angiotensin receptor blockers [ARBs]) consistently reduce the risk of progression from microalbuminuria to macroalbuminuria, over and above their antihypertensive actions. The clinical utility of combining these strategies remains to be established. In patients with overt nephropathy, blood pressure reduction is associated with reduced urinary albumin excretion and, subsequently, a reduced risk of renal impairment or end stage renal disease. In addition to actions on systemic blood pressure, it is now clear that ACE inhibitors and ARBs also reduce proteinuria in patients with diabetes. This anti-proteinuric activity is distinct from other antihypertensive agents and diuretics. Although there is a clear physiological rationale for blockade of the renin angiotensin system, which is strongly supported by clinical studies, to achieve the optimal lowering of blood pressure, particularly in the setting of established diabetic renal disease, a number of different antihypertensive agents will always be needed. In the end, the choice of agents should be individualised to achieve the maximal tolerated reduction in blood pressure and albuminuria. Ultimately, no matter how it is achieved, so long as it is achieved, renal risk can be reduced by agents that lower blood pressure and albuminuria.

Que nous apprennent les grands essais cliniques de prévention cardiovasculaire et rénale chez le malade diabétique de type 2 hypertendu ?

Type 2 diabetes mellitus and hypertension are frequently associated. Cardiovascular morbidity is a major burden in these patients. Furthermore a renal disease appears in 40% of them that may lead to chronic terminal renal failure. Whatever the stage of the renal disease, it increases the cardiovascular risk. A majority of type 2 diabetic patients will eventually died of cardiovascular complications before having reached chronic terminal renal failure. Many large clinical trials including type 2 diabetic patients with hypertension have been performed in the last 20 years with cardiovascular morbidity and mortality as primary outcomes. These trials mainly evaluated the role of glycemic control, of hypertension as well as the decrease of LDL-cholesterol. Based on these trials, the prescription type of hypertensive type 2 diabetic patient should include, besides hygienic and dietary advices, antidiabetic treatment, thiazide and/or betablocker and platelet inhibitor. Statin should be prescribed for secondary prevention if serum LDL-cholesterol is above 1,3 g/l and for primary prevention depending on serum LDL-cholesterol and on the number of cardiovascular risk factors. The objectives are an HbA1c below 6,5%, a LDL-cholesterol below 1g/l and a blood pressure below 150/80 mmHg. The appearance of diabetic nephropathy alters the treatment and the therapeutic objectives. Many large trials aimed at preventing microalbuminuria (primary prevention), macroproteinuria (secondary prevention), and chronic renal failure (tertiary prevention) have been conducted. For primary prevention, angiotensin-converting-enzyme inhibitors should be prescribed in case of hypertension because they delay the appearance of microalbuminuria. For secondary prevention, angiotensin-converting-enzyme inhibitors and angiotensin-receptor blockers decrease albuminuria excretion rate and delay the appearance of macroproteinuria whatever the blood pressure. Tertiary prevention is based on angiotensin-receptor blockers since they slow down the decrease of renal function. The objectives are a blood pressure below 130/80 mmHg and the regression or the reduction of albuminuria excretion rate. Intensified and target-driven interventions aimed at multiple risk factors implicated in cardiovascular and renal lesions, as successfully performed in the STENO-2 study, reduce the risk of cardiovascular and renal morbidity and mortality. In this article, large clinical trials having the prevention of cardiovascular and renal risks as primary outcomes were analyzed.

Glomerular function reserve and sodium sensitivity

In clinical nephrology, the glomerular filtration rate (GFR) has been recognized as the golden standard to assess renal function. However, a normal GFR does not necessarily mean normal filtration capability of the kidneys, because impaired filtration capability can be compensated for by elevating glomerular hydraulic pressure. Therefore, an early phase of glomerular dysfunction cannot be detected by the baseline GFR alone. On the other hand, glomerular capillary hypertension is widely recognized as one of the strong risk factors for the progression of nephropathies. Now, it is very important to imagine glomerular hemodynamics in each patient with nephropathy for detecting early dysfunction, as well as for evaluating risk factors. Here, I would like to summarize the current status of how an early phase of renal dysfunction can be detected in clinical practice. I truly anticipate that new methods to assess glomerular hemodynamics in humans will be developed in the near future.

Salt-sensitive blood pressure—an intermediate phenotype predisposing to diabetic nephropathy?

BACKGROUND

Family studies point to important genetic determinants of diabetic nephropathy (DN). Blood pressure (BP) is higher in offspring of patients with type 2 diabetes and DN, but the pathomechanisms involved have not been elucidated.

METHODS

We examined the salt sensitivity of BP after 5 days equilibration on a low (20 mmol/day) vs high salt diet (220 mmol/day) in three matched groups of 15 subjects each: (i) control individuals; (ii) offspring of type 2 diabetic parents without DN (DN-); and (iii) offspring of type 2 diabetic parents with DN (DN+). Ambulatory BP and hormones involved in sodium homeostasis [plasma renin activity (PRA), aldosterone and atrial natriuretic peptide (ANP)] as well as the tetrahydrocortisol + 5-allotetrahydrocortisol/tetrahydrocortisone (THF + 5alphaTHF)/THE) ratio in the urine as an index of 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) activity were analysed.

RESULTS

In offspring of DN+ patients on a high salt diet, systolic and diastolic BP was 137/82+/-10/8 mmHg vs 125/77+/-12/8 mmHg in offspring of DN- patients (P<0.01 for systolic BP). The salt-induced difference in mean BP between high and low salt diet was 5.2+/-3.3 mmHg in offspring of DN+ patients vs 0.7+/-4.7 mmHg in offspring of DN- patients (P<0.002). The proportion of 'salt-sensitive' individuals was 67% in offspring of DN+ patients vs 20% in offspring of DN- patients (P<0.05). In all groups, a high salt diet caused a comparable decrease of PRA and p-aldosterone accompanied by an increase in ANP. The urinary (THF + 5alphaTHF)/THE ratio was 1.23+/-0.36 in salt-sensitive individuals and 0.99+/-0.33 (P<0.03) in salt-resistant subjects, consistent with increased activity of 11betaHSD2.

CONCLUSIONS

BP is more salt sensitive in offspring of type 2 diabetic patients with diabetic nephropathy. The salt sensitivity of BP may be an intermediate phenotype in individuals with a high risk of future diabetic nephropathy.

The renin-angiotensin-aldosterone system: cardiorenal effects and implications for renal and cardiovascular disease states

The renin-angiotensin-aldosterone system (RAAS) plays an integral role in maintaining vascular tone, optimal salt and water homeostasis, and cardiac function in humans. However, it has been recognized in recent years that pathologic consequences may also result from overactivity of the RAAS. Clinical disease states such as renal artery stenosis, hypertension, diabetic and nondiabetic nephropathies, left ventricular hypertrophy, coronary atherosclerosis, myocardial infarction, and congestive heart failure (CHF) are examples. Part of the adverse cardiorenal effects of the RAAS may be related to the prominent role that this system plays in the activation of the sympathetic nervous system, the dysregulation of endothelial function and progression of atherosclerosis, as well as inhibition of the fibrinolytic system. Also, direct profibrotic actions of angiotensin II and aldosterone in the kidney and heart promote end organ injury. Current basic science and clinical research supports the use of inhibitors of the RAAS, including angiotensin converting enzyme inhibitors, angiotensin receptor blockers, and aldosterone antagonists in treating hypertension, improving diabetic nephropathy and other forms of chronic kidney disease, preventing or ameliorating CHF, and optimizing prognosis after myocardial infarction.

Evolution of diabetes medical nutrition therapy

Research supports the importance of medical nutrition therapy in achieving diabetes treatment goals. For persons requiring insulin therapy, the first priority is to integrate an insulin regimen into the patient's lifestyle. For type 2 diabetes, the priority is to focus on lifestyle strategies (that is, nutrition and exercise) that will improve metabolic outcomes at diagnosis and as the disease progresses. Patients with diabetes need nutrition recommendations that are supported by scientific evidence and that can be easily understood and translated into everyday life. To achieve positive outcomes, a coordinated team effort that provides continued education and support is essential.

Salt intake, hypertension and diabetes mellitus

Diabetes mellitus affects approximately 135 million people in the world. Diabetes and hypertension are both relatively common diseases in westernised countries. Both entities increase with age. Essential hypertension accounts for the majority of hypertension in people with type 2 diabetes, who constitute more than 90% of those with a dual diagnosis of diabetes and hypertension. The benefit conferred per mm Hg blood pressure reduction appears to be greater in persons with type 2 diabetes than in those with hypertension and non-coexistent diabetes mellitus. Similar to a subset of patients with essential hypertension, type 2 diabetic patients manifest dietary NaCl-induced exacerbation of hypertension. Recent guidelines have emphasised that the target blood pressure levels for patients with diabetes should be lower than in other hypertensive groups. An increased total body sodium and enhanced vascular reactivity are found in people with diabetes and most type 2 diabetic patients are salt sensitive. Type 2 diabetes with hypertension is associated with reduced renal plasma flow when dietary salt intake is high. Experimental, observational and interventional evidence support the benefits of sodium restriction in hypertensives. However, the full effects of sodium restriction are usually not obvious for at least 5 weeks. Other favourable effects of moderate reduction in sodium intake are a regress left ventricular hypertrophy, decrease in diuretic-induced potassium wastage, reduction in proteinuria, protection against stroke and from osteoporosis and renal stones, and enhancement of the antihypertensive effect of the antihypertensive agents.

Impaired saline-stimulated diuresis and natriuresis in the conscious hypertensive glucose-intolerant rat

BACKGROUND

A major complication of type 2 diabetes is renal dysfunction, a condition that worsens with coexistence of systemic hypertension. However, less is known regarding the renal impact of the prediabetic condition characterized by glucose intolerance. Therefore, we tested the hypothesis that chronic glucose intolerance leads to abnormal renal function, a condition also exacerbated by concurrent systemic hypertension.

METHODS

A rat model of concomitant NaCl-sensitive hypertension and glucose intolerance was used to study renal function. Glucose intolerance was produced by administering streptozotocin to neonatal Wistar-Kyoto rats, and systemic hypertension was induced by combining dietary NaCl excess with unilateral nephrectomy. Hemodynamic and renal excretory responses were determined in conscious animals before and after administration of a 30-min isotonic saline challenge (5% of body weight, intravenously).

RESULTS

Nine-month-old glucose-intolerant rats fed a normal NaCl diet did not manifest impairment in saline-stimulated diuresis and natriuresis. By contrast, 3-month-old glucose-intolerant rats fed a high NaCl diet displayed an exaggerated diuretic and natriuretic response to a saline challenge. Although saline-stimulated diuresis and natriuresis were enhanced in the hypertensive rats, they were reduced in the hypertensive glucose-intolerant animals. The reduction in renal excretory function of the latter group was caused by alterations in both glomerular function and tubular reabsorption of fluid and sodium.

CONCLUSIONS

The coexistence of systemic hypertension and glucose intolerance result in impaired renal excretory function. This defect could be important, as hypertension can develop before the onset of overt type 2 diabetes.

The renin-angiotensin and adrenergic nervous system in cardiac hypertrophy in fructose-fed rats

BACKGROUND

Hyperinsulinemia and insulin resistance are associated with left ventricular hypertrophy (LVH) and cardiovascular complications in hypertensive subjects. The aim of this study was to explore the mechanisms for LVH including activation of the renin-angiotensin system system (RAS) and the sympathetic nervous system and their activation by insulin using a rat model of hyperinsulinemia and insulin resistance.

METHODS

Male Sprague-Dawley rats were fed a high-fructose or control diet. The fructose-fed rats (FFR) were divided into four subgroups that were administrated either vehicle or the following antihypertensive drugs (n = 6-8) for 4 weeks: 1) olmesartan, an angiotensin II type 1 (AT1) receptor antagonist; 2) bunazosin, an alpha1-receptor blocker; and 3) hydralazine, a direct vasodilator.

RESULTS

Fructose feeding induced significant increases in mean systolic blood pressure (BP) levels at 4 weeks (control, 117 v fructose, 131 mm Hg), left ventricular weight, and the sum of the insulin level in response to a glucose tolerance test (2 g/kg). Fructose feeding also increased urinary excretion of epinephrine and norepinephrine, the density of cardiac alpha1-adrenergic receptors, and the content of angiotensin II in the left ventricle. All antihypertensive drugs decreased systolic BP, but only the AT1 receptor antagonist attenuated the development of LVH in FFR. The AT1 receptor antagonist did not affect glucose-mediated insulin responses, but did suppress urinary catecholamine excretion and cardiac alpha1-adrenergic receptor density.

CONCLUSIONS

Left ventricular hypertrophy in FFR may be less dependent on systemic elevations of BP and more dependent on the RAS and the sympathetic nervous system. Use of an AT1 receptor antagonist might be the most beneficial way to prevent progression of LVH through direct effects on tissue RAS and the sympathetic nervous system in FFR. As these changes occur in a rat model with hyperinsulinemia, insulin may have a role in promoting LVH by activating the local RAS and sympathetic nervous system activity.

Sodium sensitivity related to albuminuria appearing before hypertension in type 2 diabetic patients

OBJECTIVE

To find whether sodium sensitivity of blood pressure appears before hypertension and whether the sensitivity is related to diabetic nephropathy, we examined type 2 diabetic patients with normal levels of serum creatinine.

RESEARCH DESIGN AND METHODS

A total of 32 patients were divided into three age-matched groups: 11 patients had normoalbuminuria, 12 had microalbuminuria, and 9 had macroalbuminuria. Patients stayed on a diet with ordinary sodium levels for 1 week and a sodium-restricted diet for 1 week, in random order. Urinary excretion of sodium and albumin and systemic blood pressure were measured daily. A pressure-natriuresis curve was drawn by linkage of the two datum points obtained in the steady state during the different diets. We calculated the sodium sensitivity index as the reciprocal of the slope of this curve.

RESULTS

The median sodium sensitivity index and the mean blood pressure were higher in micro- and macroalbuminuric patients than in normoalbuminuric patients. Eighteen patients were without hypertension (<140/90 mmHg); of these, 10 had blood pressure readings <130/85 mmHg with ordinary sodium levels. Urinary albumin was correlated with the index but not with blood pressure. For these 10 patients, the index in those with albuminuria was higher than in those with normoalbuminuria. In such patients with albuminuria, sodium restriction decreased albuminuria and blood pressure.

CONCLUSIONS

In type 2 diabetic patients with albuminuria but normal levels of serum creatinine, sodium sensitivity of blood pressure appears before hypertension and is related to albuminuria; sodium restriction is one treatment for diabetic nephropath, even without hypertension.

Should an angiotensin-converting enzyme inhibitor be standard therapy for patients with atherosclerotic disease?

Angiotensin-converting enzyme (ACE) inhibitors appear to possess unique cardioprotective benefits, even when used in patients without high blood pressure or left ventricular dysfunction (the traditional indications for ACE inhibitor therapy). The ACE inhibitors improve endothelial function and regress both left ventricular hypertrophy and arterial mass better than other antihypertensive agents that lower blood pressure equally as well. These agents promote collateral vessel development and improve prognosis in patients who have had a coronary revascularization procedure (i.e., percutaneous transluminal coronary angioplasty and coronary artery bypass graft surgery). Insulin resistance, present not only in type 2 diabetes but also commonly in patients with hypertension or coronary artery disease, or both, sensitizes the vasculature to the trophic effects of angiotensin II and aldosterone. This may partly explain the improvement in prognosis noted when patients who have atherosclerosis or diabetes are treated with an ACE inhibitor. Therapy with ACE inhibitors has also been shown, in two large, randomized trials, to reduce the incidence of new-onset type 2 diabetes through largely unknown mechanisms. The ACE inhibitors are safe, well tolerated and affordable medications. The data suggest that most people with atherosclerosis should be considered candidates for ACE inhibitor therapy, unless they are intolerant to the medication, or have systolic blood pressures consistently <100 mm Hg. Patients who show evidence of insulin resistance (with or without overt type 2 diabetes) should also be considered as candidates for prophylactic ACE inhibitor therapy. Although angiotensin receptor blockers should not be considered equivalent to ACE inhibitors for this indication, they may be a reasonable alternative for patients intolerant of ACE inhibitors.

NaCl-induced hypertensive rat model of non-insulin-dependent diabetes: role of sympathetic modulation

Systemic hypertension is common in individuals with non-insulin-dependent diabetes (NIDD) and, in this population, markedly increases the risk for cardiovascular complications. The aims of this study were to develop a rat model of combined NaCl-induced hypertension and NIDD, and to determine the contribution of the sympathetic nervous system to the development of the manifest hypertension. Two-day old male Wistar-Kyoto rats were injected with either streptozotocin (90 mg/kg, ip; NIDD) or vehicle (citrate buffer; control). At 4 weeks of age, the animals underwent either a right nephrectomy or a sham operation. Animals in each group were further subdivided, with one group maintained on normal (0.72 %) NaCl diet whereas the other was placed on a high (8%)-NaCl diet. At 6 months of age, diabetes was confirmed by glucose tolerance testing. Hemodynamic parameters were measured in the freely moving animal (ia) before and after the administration of prazosin (peripheral alpha1-adrenergic antagonist, iv) or clonidine (central alpha2-adrenergic agonist). The NIDD rat displayed a higher (P < .05) blood glucose concentration than the nondiabetic control rat during the glucose tolerance test. Elevated dietary NaCl significantly increased mean arterial pressure (MAP) in the uninephrectomized, but not the sham-operated groups. Acute administration of prazosin resulted in a significantly greater reduction in MAP of both hypertensive groups than of their normotensive counterparts. Moreover, clonidine caused a significant reduction in MAP of the hypertensive control rat but not in the normotensive controls. By contrast, both the hypertensive NIDD and the normotensive NIDD rats showed a similar reduction in MAP in response to clonidine administration. The data suggest that the combination of uninephrectomy and dietary NaCl excess confers hypertension on the NIDD rat. Moreover, enhancement of the sympathetic pathway plays an important role in the regulation of arterial pressure in the hypertensive NIDD rat.

Diuretics shift circadian rhythm of blood pressure from nondipper to dipper in essential hypertension

BACKGROUND

Recently, we found that sodium restriction shifted the circadian rhythm of blood pressure from nondipper to dipper in patients with the sodium-sensitive essential hypertension. This study examined whether diuretics can transform the circadian rhythm of blood pressure from nondipper to dipper.

METHODS AND RESULTS

We studied 21 patients with essential hypertension during both a baseline period and a period of treatment with hydrochlorothiazide (25 mg daily). The periods lasted 4 weeks each. Twenty-four hour ambulatory blood pressures were measured on the same day of the week at the end of the each period. In nondippers (n=11), but not in dippers (n=10), a significant interaction existed between diuretic therapy and nocturnal fall in systolic and diastolic blood pressure, which indicated that the degree of nocturnal blood pressure fall was affected by diuretic therapy. Nocturnal fall, which was diminished in nondippers, was restored by diuretic therapy with hydrochlorothiazide, indicating that the circadian rhythm of blood pressure shifted from nondipper to dipper patterns.

CONCLUSIONS

The present study demonstrated that diuretics can restore nocturnal blood pressure decline in a manner similar to sodium restriction, which suggests that the kidneys and sodium metabolism may play important roles in the genesis of the circadian rhythm of blood pressure. Diuretic-based treatment may have an additional therapeutic advantage of reducing the risk for cardiovascular complications by transforming the circadian rhythm of blood pressure.

Nifedipine effectively lowers salt-induced high blood pressure in diabetic rats

This study examined the antihypertensive efficacy of nifedipine (a calcium channel blocker) in salt-loaded alloxan-diabetic rats. Significant increases in basal mean arterial blood pressures were observed after six weeks of high salt (8% NaCl) feeding in both diabetic (p < 0.05) and nondiabetic (p < 0.05) rats. The values were 129.95+/-3.14 mmHg for control (C); 149.22+/-8.83 mmHg for nondiabetic salt-fed (N-SF) and 150.60+/-8.01 mmHg for diabetic salt-fed (D-SF) groups. The non-salt-fed diabetic group (D) had a pressure of 136.75+/-6.66 mmHg. The maximum mean arterial blood pressures in response to noradrenaline (10(-9)-10(-5) M) infusion were significantly (p < 0.05) higher in the N-SF and D-SF groups than in the control. Nifedipine (100 microg/Kg) reduced significantly the pressures (both before and following noradrenaline infusion) in the salt-fed groups (p < 0.001). The inhibitory effect of nifedipine was more marked (p < 0.01) in the diabetic salt-fed than in the nondiabetic salt-fed. It is therefore suggested that nifedipine is effective in lowering salt-induced high blood pressure in diabetic rats.

Salt sensitivity correlates positively with insulin sensitivity in healthy volunteers

BACKGROUND

The aim of the study was to assess the relationship between insulin sensitivity and salt sensitivity in healthy subjects who display a wide range of insulin sensitivity. As a secondary objective, we assessed the relationship between salt sensitivity and the other characteristics of the insulin resistance syndrome.

STUDY DESIGN

Forty-seven normotensive volunteers (age 34 +/- 15 years) with a normal glucose tolerance test were selected. We measured insulin sensitivity using the hyperinsulinaemic euglycaemic clamp (50 mU kg-1 h-1), blood pressure, waist-to-hip ratio, fasting insulin levels, serum lipids and uric acid levels. In a subset of 21, representing a wide range of insulin sensitivity, salt sensitivity was determined as the difference in mean arterial blood pressure (MAP) at the end of a high-salt diet (10 g of NaCl per day for 1 week) vs. a low-salt diet (2 g of NaCl per day for 1 week).

RESULTS

Insulin sensitivity (M/I value, range 0.49-4.41 mg kg-1 min-1 per pmol L-1 x 100) was negatively correlated with MAP (r = -0.54, P < 0. 001) and waist-to-hip ratio (r = - 0.59, P < 0.001) but positively correlated with salt sensitivity (r = 0.47, P = 0.03). Salt sensitivity also correlated with high-density lipoprotein (HDL)-cholesterol (r = 0.46, P = 0.038) but not with waist-to-hip ratio, fasting insulin levels, low-density lipoprotein cholesterol, serum triglycerides or serum uric acid.

CONCLUSIONS

In healthy normotensive subjects who display a wide range of insulin sensitivity, as measured with the euglycaemic clamp technique, salt sensitivity correlates positively with insulin sensitivity and HDL-cholesterol, but not with the other characteristics of the insulin resistance syndrome.

Changes in the circadian rhythm of blood pressure in primary aldosteronism in response to dietary sodium restriction and adrenalectomy

OBJECTIVE

Recently, we found that sodium restriction restored the circadian rhythm of blood pressure from non-dippers to dippers in patients with a sodium-sensitive type of essential hypertension. In the present study, we investigated the effects of sodium restriction on the circadian blood pressure rhythm in patients with primary aldosteronism, a typical sodium-sensitive form of secondary hypertension.

DESIGN AND METHODS

We performed 24 h blood pressure monitoring in eight patients with primary aldosteronism due to unilateral adenoma (Conn's syndrome) during normal-sodium (7-12 g/day of NaCl) and low-sodium (1-3 g/day) diets, and after adrenalectomy.

RESULTS

Sodium restriction lowered the 24 h mean arterial pressure from 116+/-14 to 109+/-12 mmHg (P< 0.01). During a normal-sodium diet, there was no change in systolic, diastolic and mean arterial pressures during the night-time compared with the daytime. In contrast, during a low-sodium diet, all night-time pressure values were significantly lower than those in the daytime. After adrenalectomy, the night-time pressures in patients on a normal-sodium diet were lower than those of the daytime. The nocturnal mean arterial pressure fall was increased by sodium restriction and adrenalectomy.

CONCLUSIONS

These results indicate that the circadian rhythm of blood pressure was disturbed in patients with primary aldosteronism who maintained a relatively high sodium intake. Both adrenalectomy and sodium restriction restored a nocturnal dip in blood pressure in primary aldosteronism. Therefore, sodium restriction affects the circadian blood pressure rhythm in sodium-sensitive types of hypertension, not only in primary hypertension, but also in secondary hypertension.

Insulin-mediated growth in aortic smooth muscle and the vascular renin-angiotensin system

Insulin has been shown to directly affect blood vessel tone and to promote vascular hypertrophy, but the mechanism of these actions remains uncertain. Because angiotensin I (Ang I)-converting enzyme inhibitors have been shown to improve insulin action and to impede the progression of vascular hypertrophy in hypertensive animal models, it is possible that the vascular properties of insulin may be mediated through the tissue renin-angiotensin system (RAS). To evaluate this relationship, we first investigated the effect of insulin on components of the RAS using cultured rat vascular smooth muscle cells (VSMCs). Insulin treatment (1000 microU/mL) markedly increased angiotensinogen mRNA expression and angiotensinogen production. We next investigated the role of the RAS in insulin-mediated cell proliferation, using [3H]thymidine uptake. Studies were done both with insulin alone and in the presence of captopril (1x10(-7) to 10(-5) mol/L) and losartan (1x10(-9) to 10(-7) mol/L). [3H]Thymidine uptake was increased significantly by 1000 microU/mL insulin, and this stimulation was reduced by 1x10(-6) mol/L captopril (-38.8%, P<0.05) and by 1x10(-8) mol/L losartan (-37. 5%, P<0.05). Further studies showed that the degree of insulin-mediated [3H]thymidine uptake in VSMCs could be duplicated by 4x10(-10) mol/L Ang II. Losartan reduced the effects of both Ang II and insulin on [3H]thymidine uptake by about 40% to 45% of baseline (P<0.05). Captopril reduced insulin-mediated [3H]thymidine uptake but did not affect Ang II-mediated [3H]thymidine uptake. In summary, insulin induced significant stimulation of angiotensinogen expression and production and stimulated growth similar to that seen with Ang II in cultured rat VSMCs. Inhibition of Ang II production or its binding to the Ang II type 1 (AT1) receptor inhibited insulin-mediated growth in a fashion similar to that seen with inhibition of Ang II-mediated growth. Thus, insulin can modulate the vascular RAS, and the effect of insulin on vascular growth may be via direct effects on angiotensinogen expression and translation operative through both the AT1 receptor and the conversion of Ang I to Ang II.

Effects of glibenclamide on blood pressure and cardiovascular responsiveness in non-insulin dependent diabetes mellitus

OBJECTIVE

To compare the effects of chronic glibenclamide therapy and placebo on blood pressure and cardiovascular responsiveness in patients with non-insulin-dependent diabetes.

DESIGN AND METHODS

Fourteen patients with non-insulin-dependent diabetes mellitus, seven of whom were receiving angiotensin converting enzyme inhibitor therapy, received glibenclamide or placebo for 1 month in a double-blind, randomized crossover study. At the end of each treatment period patients attended for studies of forearm vascular responsiveness to intra-brachial arterial infusions of angiotensin II, acetylcholine, sodium nitroprusside and noradrenaline, responses of blood pressure to intravenous infusions of noradrenaline and angiotensin II and 24 h ambulatory blood pressure monitoring.

RESULTS

Administration of glibenclamide produced significantly better glycaemic control than placebo (fasting blood glucose level 8.5 +/- 2.4 versus 13.5 +/- 4.5 mmol/l, P < 0.001) and plasma insulin levels were significantly higher during glibenclamide treatment than they were with placebo (12.9 +/- 4.4 versus 9.2 +/- 4.1 mU/l, P < 0.05). Body weights at the ends of the glibenclamide treatment and placebo phases were similar (92.1 +/- 14.3 versus 91.1 +/- 14.3 kg, P = 0.085). Night-time systolic blood pressures were significantly higher during glibenclamide treatment than they were with placebo (128 +/- 17 versus 118 +/- 10 mmHg, P < 0.05) due to there being a smaller day-night difference in systolic blood pressure during glibenclamide treatment that appeared to occur mainly in patients receiving angiotensin converting enzyme inhibitors. Responses of diastolic blood pressure to intravenous infusion of angiotensin II and forearm vascular responses to intra-brachial arterial infusion of angiotensin II were significantly greater during glibenclamide treatment than they were with placebo (P < 0.05). However, the enhancement of forearm vascular responses during glibenclamide treatment appeared to be restricted to patients receiving angiotensin converting enzyme inhibitors. Responses of blood pressure to intravenous infusion of noradrenaline and forearm vascular responses to infusions of noradrenaline, acetylcholine and nitroprusside did not differ between glibenclamide treatment and placebo; neither did basal forearm vascular resistance.

CONCLUSIONS

Glibenclamide therapy is associated with greater responses of blood pressure and forearm vascular responses to infusion of angiotensin and higher nocturnal blood pressures. This effect appears to be influenced by concomitant angiotensin converting enzyme inhibition.

Implications of the linear pressure-natriuresis relationship and importance of sodium sensitivity in hypertension

Although the concept of the pressure-natriuresis curve is very clear, considerable confusion concerning its importance and utility in understanding the pathophysiology of hypertension persists. We recently showed that the pressure-natriuresis curve could be considered linear. In this brief review, we would like to stress the advantages of treating it as a line. Its linear approximation simplifies understanding of the sodium sensitivity of the blood pressure and mechanisms of hypertension. The blood pressure can be expressed as the sum of two components: the non-sodium-sensitive component determined by the x intercept of the pressure-natriuresis curve and the sodium sensitive one determined by the product of the reciprocal of the slope and the amount of sodium intake. Theoretically, it can be affected in two different ways to cause hypertension; either a parallel shift along the blood pressure axis toward a higher blood pressure level due to the increase in the x intercept or a decrease in the slope. The parallel shift induces non-sodium-sensitive hypertension, whereas the decrease in slope induces sodium-sensitive hypertension. Thus, the linear approximation makes the definition of the sodium sensitivity of the blood pressure very clear and, furthermore, suggests that mechanisms of hypertension can be clarified if the determinants of the x intercept and the slope of the pressure-natriuresis curve are known. A clear definition of sodium sensitivity allows us to study its importance as a marker of a greater risk of renal and cardiovascular complications.

Factors influencing LVM in hypertensive type-1 diabetic patients

Diabetes mellitus is associated with a high prevalence of hypertension and left ventricular hypertrophy (LVH), and a causative relationship with abnormal sodium metabolism in diabetic patients has been suggested. Factors influencing left ventricular mass (LVM) were assessed in 30 hypertensive type-1 diabetic patients, mean age 46 +/- 9 (range 24-67) years, with a mean duration of diabetes and hypertension of 19 +/- 10 and 6 +/- 5 years, respectively. In the total study population, casual blood pressure was 163/94 +/- 24/10 mmHg and 24 h blood pressure was 155/87 +/- 17/8 mmHg. Twenty-four-hour urine samples were obtained to measure daily albumin excretion (0.77 +/- 1.06 g) and dietary sodium intake was assessed as 24 h sodium excretion (173 +/- 77 mmol). Creatinine clearance averaged 1.41 +/- 0.53 ml/s. LVM determined by echocardiography was 221 +/- 74 g (range 104-408 g) and 33% of the patients had LVH. Multiple regression analysis identified dietary sodium intake and plasma atrial natriuretic peptide as independent predictors of LVM (R2 = 0.52, p < 0.001). No significant association was found between LVM and blood pressure or albuminuria. The results propose dietary sodium intake as an important factor in the development of LVH in hypertensive type-1 diabetic patients.

Metabolic manifestations of low-dose diuretics

Hypertension has been defined and treated as a disease of abnormal systolic and diastolic blood pressure. Recent data have, however, demonstrated that effective blood-pressure control has not resulted in the expected decrease in coronary artery disease. These findings are probably a result of hypertension being a complex inherited syndrome of cardiovascular risk factors, all of which are genetically linked and all of which contribute to the development of cardiovascular disease in these patients. Included in the hypertension syndrome are abnormalities of lipid profile, insulin resistance, changes in renal function, left ventricular hypertrophy and reduced arterial compliance. In many patients, high blood pressure is a late manifestation of this disease process. Since all cardiovascular risk factors contribute to heart disease in these patients, they should all be considered in the management of this disease process. Diuretics and beta blockers, when used at high doses, negatively impact lipid metabolism and insulin sensitivity, while angiotensin converting enzyme (ACE) inhibitors and calcium antagonists tend to have a neutral effect on these metabolic risk factors. These findings have resulted in decreased use of diuretics and beta blockers in favor of newer agents such as ACE inhibitors and calcium antagonists. However, recent data have demonstrated that when used at low doses (6.25 or 12.5 mg of hydrochlorothiazide), diuretics lack significant metabolic side effects while bringing about significant reductions in blood pressure. Thus, at these doses, hydrochlorothiazide is a useful drug in the treatment of hypertension, both as monotherapy and in combination therapy.