Moderate sucrose ingestion and blood pressure in the rat

Sex-dependent Differences in Liver and Gut Metabolomic Profiles With Acarbose and Calorie Restriction in C57BL/6 Mice

Acarbose, an alpha-glucosidase inhibitor used in treating type 2 diabetes, impairs complex carbohydrate digestion and absorption and extends life span in mice (without a requisite reduction in food intake). To assess sex-differential effects coincident with calorie restriction versus a nonrestricted longevity enhancing intervention, we evaluated the metabolite profiles (by liquid chromatography-mass spectroscopy) from livers and cecal contents of C57BL/6J mice (n = 4/sex/group), which were maintained for 10 months under one of the three diet treatments: ad libitum control diet (CON), ad libitum control diet containing 0.1% acarbose (ACA), or 40% calorie restriction using the control diet (CR). Principal component analysis revealed sex-differential profiles with ACA in livers. Of the identified metabolites (n = 621) in liver, CR significantly altered ~44% (males:187↑/131↓, females:74↑/148↓) compared with CON, in contrast with ACA (M:165↑/61↓, F:52↑/60↓). Dissimilarity in ACA-F liver metabolites was observed for ~50% of common metabolites from ACA-M and CR-M/F. CR resulted in fewer significant cecal metabolite differences (n = 615 metabolites; M:86↑/66↓, F:51↑/48↓ vs CON), relative to ACA treatment (M:32↑/189↓, F:36↑/137↓). Metabolomic profiling identifies sex-differential and tissue-specific effects with amino acid metabolism sub-pathways including those involving tryptophan, branch-chain and sulfur amino acids, and the urea cycle, as well as bile acid, porphyrin, and cofactor metabolism pathways.

Blood Pressure Regulation: Reviewing Evidence for Interplay Between Common Dietary Sugars and Table Salt

A popular concept is that the significant global progression in prevalence and intensification of elevated blood pressure (BP) levels is due in part to dietary indiscretions. Excess intake of several food sources causing overweight/obesity plays an important role in BP perturbations. However, certain nutrients are involved in ways other than via body fat accumulation, particularly table salt (sodium chloride) and popular refined carbohydrates like dietary sugars (sucrose, fructose, high fructose corn syrup). In nondiabetics and diabetics, several functions of salt and sugar influence BP and metabolism. For example, salt intake is linked to volume expansion, insulin resistance, and hypertension, while sugar intake is associated with enhanced salt sensitivity via urinary sodium retention, insulin resistance, and hypertension. The key postulate evaluated here is that when two popular nutrients-salt and dietary sugars-are consumed together in adequate amounts, their respective individual BP effects are significantly amplified. In previous laboratory studies, a sugar challenge did not increase BP in the face of marked sodium depletion, and combining sugar and salt challenges caused a synergistic BP elevation. Among examples of amplification on the clinical side, the greatest increases in BP following sugar challenges were seen in diabetic subjects having the highest sodium excretion. Interplay between table salt and common dietary sugars in BP regulation is a reasonable postulate and should be carefully considered when developing optimal prevention and treatment regimens to ameliorate the worldwide crisis arising from harmful elevated BP levels.

Sugar-sweetened beverage, sugar intake of individuals, and their blood pressure: international study of macro/micronutrients and blood pressure

The obesity epidemic has focused attention on relationships of sugars and sugar-sweetened beverages (SSBs) to cardiovascular risk factors. Here we report cross-sectional associations of SSBs, diet beverages, and sugars with blood pressure (BP) for United Kingdom and US participants of the International Study of Macro/Micronutrients and Blood Pressure. Data collected include four 24-hour dietary recalls, two 24-hour urine collections, 8 BP readings, and questionnaire data for 2696 people ages 40 to 59 years of age from 10 US/United Kingdom population samples. Associations of SSBs, diet beverages, and sugars (fructose, glucose, and sucrose) with BP were assessed by multiple linear regression. SSB intake related directly to BP, with P values of 0.005 to <0.001 (systolic BP) and 0.14 to <0.001 (diastolic BP). SSB intake higher by 1 serving per day (355 mL/24 hours) was associated with systolic/diastolic BP differences of +1.6/+0.8 mm Hg (both P<0.001) and +1.1/+0.4 mm Hg (P<0.001/<0.05) with adjustment for weight and height. Diet beverage intake was inversely associated with BP (P 0.41 to 0.003). Fructose- and glucose-BP associations were direct, with significant sugar-sodium interactions: for individuals with above-median 24-hour urinary sodium excretion, fructose intake higher by 2 SD (5.6% kcal) was associated with systolic/diastolic BP differences of +3.4/+2.2 mm Hg (both P<0.001) and +2.5/+1.7 mm Hg (both P=0.002) with adjustment for weight and height. Observed independent, direct associations of SSB intake and BP are consistent with recent trial data. These findings, plus adverse nutrient intakes among SSB consumers, and greater sugar-BP differences for persons with higher sodium excretion lend support to recommendations that intake of SSBs, sugars, and salt be substantially reduced.

Effect of dietary chromium on resistance artery function and nitric oxide signaling in the sucrose-fed spontaneously hypertensive rat

BACKGROUND

Consumption of high-glycemic index foods contributes to the development of hypertension in some patients. Likewise, in spontaneously hypertensive rats (SHR), high sucrose promotes a secondary rise in systolic blood pressure (SBP). Chromium (III) (Cr(3+)) prevents sucrose-induced hypertension, but leaves the basal hypertension that characterizes SHR intact.

METHODS

Since hypertension entails increased peripheral resistance, we compared effects of Cr(3+) on resistance arteries from SHR fed low-glycemic (starch) versus high-glycemic (sucrose) index diets. Subgroups of SHR also received Cr(3+). Structure, stiffness, and vasodilation of mesenteric resistance arteries were studied using pressurized myography.

RESULTS

Sucrose increased SBP in SHR and, exclusively in sucrose-fed SHR, Cr(3+) reduced SBP and augmented acetylcholine or nitroprusside-dependent vasodilation. Neither sucrose nor Cr(3+) affected artery structure or stiffness. Since Cr(3+) enhanced vasodilation, we assessed endothelial NO synthase (eNOS), guanylate cyclase, cGMP-dependent protein kinase (PKG-1alpha and 1beta), and PKG activity by immunoblotting. Sucrose reduced eNOS, PKG-1beta, and PKG activity. Cr(3+) prevented the effects of sucrose on NO signaling.

CONCLUSION

In hypertension exacerbated by high-glycemic index diet, Cr(3+) reduces SBP. The BP-lowering effect of Cr(3+), selectively on sucrose-induced but not basal hypertension in SHR, involves at least in part, improving vasodilatory function vis-à-vis restoration of NO signaling in resistance arteries.

Sugar-induced blood pressure elevations over the lifespan of three substrains of Wistar rats

OBJECTIVE

Since the majority of studies concerned with sugar-induced blood pressure elevation have principally been short-term, the present investigation followed the effects of heavy sucrose ingestion on systolic blood pressure (SBP) and related parameters over the lifespan of three substrains of Wistar rats.

METHODS

Two hundred twenty-five rats (75 spontaneously hypertensive rats (SHR), 75 Wistar Kyoto rats (WKY), 75 Munich Wistar rats (WAM) were given one of five diets. The baseline diet in terms of calories derived 32% from sucrose, 33% from protein, and 35% from fat. The remaining four diets derived their calories as follows: a high sugar-low protein diet--52% of calories from sucrose, 15% from protein, and 33% from fat; a high sugar-low fat diet--53% of calories from sucrose, 37% from protein, and 10% from fat; a low sugar-high protein diet--11% calories from sucrose, 56% from protein, and 33% from fat, and a low sugar-high fat--13% of calories from sucrose, 32% from protein, and 55% from fat.

RESULTS

All substrains showed the highest systolic blood pressure when ingesting the two diets highest in sucrose. The highest sugar-induced SBP elevation, which remained over the lifespan of all substrains, was found in SHR. WKY had an intermediate elevation. WAM showed the lowest responses, although the average elevation of 6-8 mm Hg was statistically significant. The following parameters could not be correlated with long-term elevation of SBP; body weight, catecholamine excretion, renal function, and plasma renin activity. Only insulin concentrations correlated: insulin concentrations were consistently higher in the two groups of WKY and WAM consuming the high sucrose diets.

CONCLUSIONS

High dietary sucrose can chronically increase SBP in three substrains of Wistar rats. Increased concentrations of circulating insulin were found in WKY and WAM suggesting that the glucose/insulin system was involved, at least in these two substrains, in the maintenance of high SBP levels during chronic, heavy sugar ingestion.

Effects of low sodium diet and unilateral nephrectomy on the development of carbohydrate-induced hypertension

Since there appear to be important interactions between mechanisms of salt-sensitive and carbohydrate-sensitive hypertension, the goal of this study was to evaluate the effects of greatly reducing dietary salt intake and removal of one kidney (to increase salt sensitivity) on the hemodynamic and metabolic responses to carbohydrate-enriched diets in three different rat strains. All three strains of laboratory rat developed significant increases in fasting plasma insulin (1-2 fold, p < 0.03) and triglyceride (2-3 fold, p < 0.01) concentrations in response to fructose (or sucrose) enriched diets, irrespective of salt content. Blood pressure increased significantly in response to carbohydrate feeding in both Sprague-Dawley (S-D) and Dahl salt-sensitive rats, but not in Fischer 344 rats, and decreasing salt intake had no effect on the development of carbohydrate-induced hypertension: e.g., delta BP in S-D rats was +20 mmHg after the fructose-0.5% NaCl diet as compared with +19 mmHg after fructose-0.02% NaCl, and delta BP in Dahl salt-sensitive rats was +22 mmHg after fructose-0.02% NaCl. Finally, nephrectomy neither accentuated the degree of hypertension in fructose-fed S-D rats, nor increased blood pressure in fructose-fed Fischer 344 rats. These results emphasize the strain specific characteristics of carbohydrate-induced hypertension in rats, and indicate that the hemodynamic responses of different rat strains to dietary carbohydrate are not modified by either decreasing salt intake or removing one kidney.

Early lead challenge and subsequent hypertension in Sprague-Dawley rats

OBJECTIVE

The consequences of chronic, low grade lead (Pb) burden from earlier exposure on development of hypertension (HT) and cardiovascular disease is, at best, controversial, even though many epidemiological studies suggest the possibility. Accordingly, we examined ability of a short-term Pb challenge to cause later developing HT in rats.

METHODS

We gave 12 newly weaned Sprague-Dawley rats (SD) a 1% Pb acetate solution to drink for 6 weeks, while 12 control rats drank water. The rats were further subdivided into groups consuming high and low amounts of sugar. All rats were followed for 4 months after cessation of the Pb challenge.

RESULTS

Early Pb challenge caused no significant changes in body weight (BW) from controls; however, systolic blood pressures (SBP) of rats initially receiving Pb continued to rise significantly above their respective dietary controls for months after cessation of challenge. While a high sugar diet alone was associated with elevated SBP, high sugar consumers also challenged with Pb had the highest SBP. Protein excretion did not increase, suggesting, along with other evidence, a lack of significant renal damage.

CONCLUSIONS

Previous exposure to Pb can cause subsequent chronic elevations in SBP.

Systemic effects of ingesting varying amounts of a commercial carbohydrate beverage postexercise

OBJECTIVE

Although the role of postexercise carbohydrate intake in the replenishment of muscle glycogen is well established, large amounts of carbohydrate may affect other systems which are recovering from exercise as well.

METHODS

We varied the timing and amount of a commercial glucose polymer/fructose (CHO) beverage ingested postexercise in 2 groups of 8 normotensive men following 1 hour of cycling exercise. In Study A the subjects ingested 1 L of a 200 g CHO solution or 1 L of water (W) immediately postexercise. The participants in Study B consumed 1 L of a 1.5 g/kg CHO solution, or W, immediately and 2 hours postexercise.

RESULTS

Recovery systolic blood pressure was elevated after 200 g CHO as compared to water, but not after 1.5 g/kg CHO. Diastolic blood pressure was decreased, while heart rate, insulin and glucose increased following both doses of CHO. Despite the potassium (K) content of the beverages, serum K decreased in Study A and B, while a trend was noted following CHO for decreased urinary K excretion at 2 hours and for increased sodium excretion at 4 hours in Study B. Post CHO aldosterone declined more rapidly than after W, and urine volumes were decreased compared to W in both studies 2 hours after CHO.

CONCLUSIONS

We speculate that hyperinsulinemia contributed to the rapid decline in K and aldosterone by creating a flux of K to the intracellular space. It appears that CHO ingestion postexercise results in systemic effects that are related to the amount and timing of CHO consumed.

Effects of high sugar diets on renal fluid, electrolyte and mineral handling in rats: relationship to blood pressure

OBJECTIVE

We examined whether sugar-induced systolic blood pressure (SBP) elevations in rats may develop, in part, through a mechanism common to salt-induced hypertension, i.e., renal retention of water and salt.

DESIGN

Spontaneously hypertensive rats (SHR) ate four diets: two high (> 50% of calories) and two low (< 12% of calories) in sugar (sucrose). SBP, various urinary parameters, and the renal angiotensin and prostaglandin systems were assessed.

RESULTS

SHR consuming diets high in sugar showed significantly decreased urinary volume and excretion of electrolytes, which coincided with increasing SBP. When low sugar diets replaced high sugar diets, SBP and urinary parameters rapidly returned to baseline. SHR received captopril while consuming high sugar diets, and both SBP and urinary parameters assumed baseline values, comparable to ones seen in SHR consuming low sugar diets. A direct angiotensin II receptor antagonist (DuPont 753) did not influence SBP. However, we found decreased PGE2 excretion in SHR consuming excess sugar.

CONCLUSIONS

Salt and water retention occur early during sugar-induced hypertension due to reduced renal excretion, consistent with some part in the pathogenesis. The effects of high sugar diets on SBP were not due to angiotensin II inhibition, however, decreased availability of vasodilatory prostaglandins may play a role in the renal events and sugar-induced hypertension in SHR.

Sucrose does not raise blood pressure in rats maintained on a low salt intake

Diets high in sucrose or fructose have been shown by others to induce a modest elevation of blood pressure in rats. The present experiments were conducted to determine whether the sucrose-induced increase of blood pressure is dependent on the intake of sodium chloride. Four groups of Sprague-Dawley rats were studied: 1) a group maintained on a low salt diet and distilled water (0.45% sodium chloride, no added sucrose), 2) a low salt-high sucrose group (0.45% sodium chloride diet and 7% sucrose in distilled water), 3) a high salt group (4% sodium chloride diet and distilled water), and 4) a high salt-high sucrose group on a diet adjusted daily to maintain the same high intakes of sodium chloride and sucrose as those of groups 2 and 3. Systolic blood pressures were measured by tail-cuff plethysmography during weeks 1-3 of treatment, and direct mean arterial blood pressures were recorded in conscious animals during week 4. Animals on the high salt diet gained weight more slowly than those on the low salt intake. On the low sodium chloride intake, blood pressures were not affected by high dietary sucrose (group 1 versus 2). In contrast, on the high sodium chloride intake, blood pressures were 10-14 mm Hg higher in sucrose-drinking animals than in water-drinking animals (group 3 versus 4). The increments in blood pressures of the high sodium chloride-high sucrose group were not accompanied by greater increments in body weight compared with the animals on the high sodium chloride intake alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertension and sympathetic hyperactivity induced in rats by high-fat or glucose diets

Male Sprague-Dawley rats fed either a high-fat diet or a glucose-enriched diet developed higher blood pressure (BP) than rats fed a control diet. After 8 wk of diet treatment systolic BP was 11% higher (P less than 0.01) in fat-fed rats and 7% higher (P less than 0.05) in glucose-fed rats when compared with rats fed the control diet. Rats fed the high-fat diet developed hypertension only when they were allowed to overeat and become obese and hyperinsulinemic. But when their feeding was restricted to prevent obesity and hyperinsulinemia, they remained normotensive. In contrast, elevated BP developed in rats consuming the glucose diet in the absence of obesity or hyperinsulinemia. After 7 wk of diet treatment, urinary norepinephrine excretion was 1.9 +/- 0.1, 1.9 +/- 0.1, and 1.5 +/- 0.1 micrograms/day in rats fed the high-fat, glucose, and control diets, respectively (P less than 0.05 vs. control). Higher norepinephrine excretion in hypertensive rats suggests that increased sympathetic nervous system (SNS) activity might participate in mediating the effects of dietary fat or glucose on BP. In addition, insulin may contribute to raising BP in rats fed the high-fat diet, either directly or indirectly through its stimulatory effect on the SNS. We conclude that chronic feeding of diets high in fat or glucose increases BP and enhances SNS activity in rats.

Insulin resistance and hypertension

The author has reviewed the development of the concept that insulin resistance is related not only to the hypertensive state but potentially to the initiation and maintenance of high blood pressure. Potential sequelae of insulin resistance and hyperinsulinemia, as they apply to atherogenesis, are also discussed. The impact of present antihypertensive pharmacologic therapy on insulin resistance is addressed, as are future directions in pharmacologic and nonpharmacologic management of hypertension. In addition, the author speculates on possible mechanisms leading to insulin resistance in hypertension.

The Zucker fatty rat as a genetic model of obesity and hypertension

The association of hypertension with obesity has long been recognized; however, because of the lack of suitable animal models of obesity and hypertension, the pathogenesis of the high blood pressure associated with obesity remains poorly understood. We hypothesized that the Zucker fatty rat, a widely studied model of obesity and insulin resistance, might also be characterized by hypertension. Mean arterial pressure directly measured in the unanesthetized, unrestrained obese (fatty) Zucker rat was significantly greater than in two strains of nonobese control rats, the lean Zucker rat and the Lewis rat. The greater blood pressure in the obese rats was not dependent on hyperphagia or increased body weight per se since moderate caloric restriction, achieved by pair-feeding with lean rats, decreased weight gain but did not attenuate hypertension. Pair-fed obese rats retained less sodium than lean control rats, suggesting that greater blood pressure in the obese rats is not a consequence of increased renal retention of sodium. A unique feature of the Zucker strain is that the increased blood pressure appears to be specifically associated with the obese genotype. The findings suggest that the obese Zucker rat might provide a useful experimental model of obesity and hypertension.

Sucrose versus saccharin as an added sweetener in non-insulin-dependent diabetes: short- and medium-term metabolic effects

Seventeen non-insulin-dependent diabetic patients were randomly allocated to their usual diet supplemented daily with either 28 g sucrose or 30 g starch (isoenergetic with sucrose) and saccharin (equivalent sweetness). After 6 weeks, the supplements were reversed. No significant treatment effects were observed on fasting concentrations of blood glucose, plasma insulin or serum triglycerides, or on urinary excretion of glucose, sodium or potassium. Following a standard breakfast with either sucrose or saccharin and starch, no differences between meal responses were observed. This study demonstrates no medium-term metabolic contraindications to including a moderate amount of sucrose in the diets of patients with non-insulin-dependent diabetes mellitus.

Attenuation of fructose-induced hypertension in rats by exercise training

This study was initiated to see if the insulin resistance, hyperinsulinemia, and hypertension that follow feeding normotensive Sprague-Dawley rats a fructose-rich diet could be prevented by letting rats run spontaneously in exercise wheel cages. Blood pressure in sedentary rats increased from (mean +/- SEM) 125 +/- 2 to 148 +/- 3 mm Hg in response to 2 weeks of a high fructose diet, and this increment was significantly (p less than 0.001) attenuated in exercising rats (from 121 +/- 1 to 131 +/- 2 mm Hg). In addition, mean (+/- SEM) plasma insulin concentration was lower in fructose-fed rats allowed to run spontaneously (44 +/- 2 vs 62 +/- 5 microU/ml; p less than 0.01). Finally, resistance to insulin-stimulated glucose uptake was assessed by determining the steady state plasma glucose response to a continuous glucose and exogenous insulin infusion during a period in which endogenous insulin secretion was suppressed. The results of these studies indicated that the mean (+/- SEM) steady state plasma glucose concentration was significantly lower in the exercise-trained rats (127 +/- 5 vs 168 +/- 6 mg/dl; p less than 0.001), despite the fact that the steady state plasma insulin levels were also lower in rats allowed to run spontaneously (75 +/- 4 vs 90 +/- 5 microU/ml; p less than 0.05). Thus, the ability of exercise-trained rats to stimulate glucose disposal was enhanced as compared with that of sedentary rats fed the same fructose-rich diet. These data demonstrate that the insulin resistance, hyperinsulinemia, and hypertension produced in normotensive rats by feeding them a high fructose diet can be attenuated if rats are allowed to run spontaneously.(ABSTRACT TRUNCATED AT 250 WORDS)

Fructose-induced insulin resistance and hypertension in rats

To determine if hypertension could be produced in normal rats by feeding them a fructose-enriched diet, Sprague-Dawley rats were fed either normal chow or a diet containing 66% fructose as a percentage of total calories for approximately 2 weeks. At the end of this period systolic blood pressure had increased from 124 +/- 2 to 145 +/- 2 (SEM) mm Hg in the fructose-fed rats, whereas no change occurred in the control group. In addition, hyperinsulinemia and hypertriglyceridemia were associated with hypertension in fructose-fed rats. The addition of clonidine to the drinking water inhibited fructose-induced hypertension, but not the increase in plasma insulin or triglyceride concentration seen in fructose-fed rats. Thus, the metabolic changes associated with fructose-induced hypertension are unlikely to be secondary to an increase in sympathetic activity. Whether or not this is also true of the hypertension remains to be clarified.

Effect of dietary carbohydrates and copper status on blood pressure of rats

Copper deficiency was induced in rats by feeding diets containing either 62% starch, fructose or glucose deficient in copper for 6 weeks. All copper deficient rats, regardless of the dietary carbohydrate, exhibited decreased ceruloplasmin activity and decreased serum copper concentrations. Rats fed the fructose diet exhibited a more severe copper deficiency as compared to rats fed either starch or glucose. The increased severity of the deficiency was characterized by reduced body weight, serum copper concentration and hematocrit. In all rats fed the copper adequate diets, blood pressure was unaffected by the type of dietary carbohydrate. Significantly reduced systolic blood pressure was evident only in rats fed the fructose diet deficient in copper. When comparing the three carbohydrate diets, the physiological and biochemical lesions induced by copper deprivation could be magnified by feeding fructose.

Chronic sucrose ingestion induces mild hypertension and tachycardia in rats

As a means for increasing sympathetic activity, male weanling rats were given 8% sucrose solution to drink instead of water. After 5 weeks, systolic pressures measured with a tail-cuff method became appreciably elevated, and the elevation was verified when phasic pressures were later recorded directly from femoral catheters. Successful induction of sympathetic overactivity was considered a likely explanation because sucrose-ingesting rats, compared with untreated controls, had faster heart rates and larger hypotensive responses to alpha-adrenergic blockade with phentolamine. Upon graded electrical stimulation of the ventromedial hypothalamus under urethane anesthesia, resulting pressor and sympathetic nerve responses were also larger in sucrose-treated rats. By contrast, pressor responses to injections of norepinephrine or tyramine were unaffected, thereby indicating that cardiovascular sensitivity had not been enhanced by sucrose ingestion. During intravenous glucose tolerance tests, increases in plasma insulin were consistently lower in sucrose-treated than control rats even though corresponding increases in plasma glucose were just transiently higher. These results support the interpretation that chronic sucrose ingestion inhibits pancreatic insulin secretion and elevates blood pressure by stimulating the ventromedial hypothalamus to increase sympathetic activity.