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

Aerobic exercise training prevents impairment in renal parameters and in body composition of rats fed a high sucrose diet

OBJECTIVE

This study aimed to evaluate the effect of swimming training (T) on the renal system and body composition parameters in young animals treated with a high sucrose diet (SUD) during 12 weeks.

RESULTS

The SUD impaired the physical performance, increased the body adiposity index (BAI), Lee index (LI) and retroperitoneal adipose tissue (RAT) weight, plasma creatinine and number renal cells nuclei, decreased urinary volume and urinary creatinine excretion besides creatinine clearance. The T reversed the increased the BAI, LI, RAT weight, plasma and urinary creatinine, creatinine clearance and number renal cells nuclei in addition to promoting decrease in urinary protein excretion. This study found that eight weeks of swimming physical training protected renal function and restored normal glomerular filtration rate (GFR) values. Swimming training also contributed to prevention of the onset of a renal inflammatory process and caused a decrease in the risk of development of obesity promoted by SUD decreasing the body composition parameters (BAI, LI, and RAT weight).

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.

High sugar intake via the renin-angiotensin system blunts the baroreceptor reflex in adult rats that were perinatally depleted of taurine

Perinatal taurine depletion leads to several physiological impairments in adult life, in part, due to taurine’s effects on the renin-angiotensin system, a crucial regulator of growth and differentiation during early life. The present study tests the hypothesis that perinatal taurine depletion predisposes adult female rats to impaired baroreceptor control of arterial pressure by altering the renin-angiotensin system. Female Sprague Dawley (SD) rats were fed normal rat chow and from conception to weaning drank 3% beta-alanine in water (taurine depletion, TD) or water alone (Control, C). Female offspring ate a normal rat chow and drank water with (G) or without (W) 5% glucose throughout the experiment. To test the possible role of the renin-angiotensin system, 50% of the rats received captopril (an angiotensin converting enzyme inhibitor, 400 mg/L) from 7 days before parameter measurements until the end of experiment. At 7-8 weeks of age, arterial pressure, heart rate, baroreflex control of heart rate and renal nerve activity were studied in either conscious, freely moving or anesthetized rats. Perinatal taurine depletion did not alter resting mean arterial pressure or heart rate in the adult female offspring that received either high or normal sugar intake. Captopril treatment slightly decreased mean arterial pressure but not heart rate in all groups. Compared to controls, only the TDG rats displayed blunted baroreflex responses. Captopril treatment normalized baroreflex sensitivity in TDG. The present data indicate that in perinatal taurine depleted female rats, the renin-angiotensin system underlines the ability of high sugar intake to blunt baroreceptor responses.

Maitake mushroom extracts ameliorate progressive hypertension and other chronic metabolic perturbations in aging female rats

OBJECTIVE

We assessed the ability of two commercially-available fractions labeled SX and D derived from the edible maitake mushroom to overcome many age-associated metabolic perturbations such as progressive, age-related elevation of blood pressure, over activity of the renin-angiotensin system (RAS), decreased insulin sensitivity, and inflammation in an in vivo laboratory model.

DESIGN AND METHOD

We divided forty mature, female Sprague-Dawley rats (SD) into five groups of eight. SD ingested regular rat chow containing added sucrose (20% w/w). The groups received baseline diet alone (control) or baseline diet containing captopril, niacin-bound chromium, maitake fraction SX, or maitake fraction D. In addition to blood pressure readings, the following procedures were implemented: losartan and insulin challenges, evaluation of serum ACE activity, glucose tolerance testing, blood chemistries, LNAME challenge, and measurement of various circulating cytokines.

RESULTS

We found that implementation of all test conditions stopped the gradual elevation of systolic blood pressure (SBP) in the SD over the four months of study, even reversing some of the previous elevation that occurred over time. In general, the treatment groups showed decreased activity of the RAS estimated by less lowering of SBP after losartan challenge and decreased serum ACE activity and were more sensitive to exogenous insulin challenge. TNFa levels decreased in all four test groups suggesting a lessening of the inflammatory state.

CONCLUSIONS

We believe our data suggest that maitake mushroom fractions lessen age-related hypertension, at least in part, via effects on the RAS; enhance insulin sensitivity; and reduce some aspects of inflammation--actions that should lead to a longer, healthier life span.

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.

Comparative effects of chromium, vanadium and gymnema sylvestre on sugar-induced blood pressure elevations in SHR

OBJECTIVE

Effects on systolic blood pressure (SBP) of ingesting three agents reported to influence insulin metabolism, i.e., chromium polynicotinate, bis(maltolato)oxovanadium (BMOV), and the herb, Gymnema sylvestre, were assessed simultaneously in spontaneously hypertensive rats (SHR).

METHODS

In the first study, SHR were fed either a starch, sugar, or sugar diet containing chromium polynicotinate, bis(maltolato)oxovanadium (BMOV), or G. sylvestre. Tail SBP was estimated indirectly and various blood chemistries were measured. TBARS formation was determined in hepatic and renal tissue. In a second study, tail SBP was measured in SHR ingesting diets containing different concentrations of BMOV.

RESULTS

Compared to starch, SHR consuming sucrose showed a significant elevation of SBP within days that was maintained for the duration of study. Addition of chromium polynicotinate to the sucrose diet at the beginning of study prevented the sucrose-induced elevation of SBP for 2 weeks, but SBP rose significantly after that. BMOV at high concentrations overcame the sucrose-induced rise in SBP and even decreased SBP below values seen in SHR eating the starch diet, but marked weight loss was noted. A second study examined different concentrations of BMOV. At 0.01% w/w concentration of BMOV, SBP was still significantly decreased, even though SHR did not lose body weight (BW) early on. SHR consuming G. sylvestre showed no change or even elevated SBP. Hepatic thiobarbituric acid reacting substances (TBARS) formation, an estimate of lipid peroxidation, was decreased by chromium polynicotinate and BMOV, and renal TBARS by chromium polynicotinate. Circulating cholesterol concentrations were decreased in the SHR consuming G. sylvestre.

CONCLUSIONS

Chromium decreases the portion of SBP elevated by high sucrose intake as shown previously, but high levels of sucrose ingestion can eventually overcome this. BMOV overcame sucrose-induced elevation of SBP as well as some of the "genetic hypertension." Different from chromium, this decrease was not overcome by high levels of dietary sucrose. The significant lowering of cholesterol with G. sylvestre ingestion indicates some effect on metabolism, but G. sylvestre did not lower and even raised SBP.

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.

Hyperglycemia-induced latent scurvy and atherosclerosis: the scorbutic-metaplasia hypothesis

Latent scurvy is characterized by a reversible atherosclerosis that closely resembles the clinical form of this disease. Acute scurvy is characterized by microvascular complications such as widespread capillary hemorrhaging. Vitamin C (ascorbate) is required for the synthesis of collagen, the protein most critical in the maintenance of vascular integrity. We suggest that in latent scurvy, large blood vessels use modified LDL--in particular lipoprotein(a)--in addition to collagen to maintain macrovascular integrity. By this mechanism, collagen is spared for the maintenance of capillaries, the sites of gas and nutrient exchange. The foam-cell phenotype of atherosclerosis is identified as a mesenchymal genetic program, regulated by the availability of ascorbate. When vitamin C is limited, foam cells develop and induce oxidative modification of LDL, thereby stabilizing large blood vessels via the deposition of LDL. The structural similarity between vitamin C and glucose suggests that hyperglycemia will inhibit cellular uptake of ascorbate, inducing local vitamin C deficiency.