Sugar-induced hypertension in Sprague-Dawley rats

Sodium glucose cotransporter 2 inhibitor suppresses renal injury in rats with renal congestion

Renal congestion is an issue of cardiorenal syndrome in patients with heart failure. Recent clinical and basic studies suggest a renoprotective potential of sodium-glucose cotransporter (SGLT) 2 inhibitors. However, the effect on renal congestion and its mechanism is not fully understood. Thus, we aimed to clarify the effect of SGLT inhibition in a renal congestion model. Renal congestion was induced in the left kidney of male Sprague-Dawley rats by ligation of the inferior vena cava between the renal veins. The SGLT2 inhibitor tofogliflozin or vehicle was orally administered daily from the day before IVC ligation until two days after surgery. On the third postoperative day, both the right control kidney and the left congested kidney were harvested and analyzed. Kidney weight and water content was increased, and renal injury and fibrosis were observed in the left congested kidney. Kidney weight gain and hydration were improved with tofogliflozin treatment. Additionally, this treatment effectively reduced renal injury and fibrosis, particularly in the renal cortex. SGLT2 expression was observed in the congested kidney, but suppressed in the damaged tubular cells. Molecules associated with inflammation were increased in the congested kidney and reversed by tofogliflozin treatment. Mitochondrial dysfunction provoked by renal congestion was also improved by tofogliflozin treatment. Tofogliflozin protects against renal damage induced by renal congestion. SGLT2 inhibitors could be a candidate strategy for renal impairment associated with heart failure.

Diabetes websites lack information on dietary causes, risk factors, and preventions for type 2 diabetes

Introduction

Type 2 diabetes (T2D) is a growing public health burden throughout the world. Many people looking for information on how to prevent T2D will search on diabetes websites. Multiple dietary factors have a significant association with T2D risk, such as high intake of added sugars, refined carbohydrates, saturated fat, and red meat or processed meat; and decreased intake of dietary fiber, and fruits/vegetables. Despite this dietary information being available in the scientific literature, it is unclear whether this information is available in gray literature (websites).

Objective

In this study, we evaluate the use of specific terms from diabetes websites that are significantly associated with causes/risk factors and preventions for T2D from three term categories: (A) dietary factors, (B) nondietary nongenetic (lifestyle-associated) factors, and (C) genetic (non-modifiable) factors. We also evaluate the effect of website type (business, government, nonprofit) on term usage among websites.

Methods

We used web scraping and coding tools to quantify the use of specific terms from 73 diabetes websites. To determine the effect of term category and website type on the usage of specific terms among 73 websites, a repeated measures general linear model was performed.

Results

We found that dietary risk factors that are significantly associated with T2D (e.g., sugar, processed carbohydrates, dietary fat, fruits/vegetables, fiber, processed meat/red meat) were mentioned in significantly fewer websites than either nondietary nongenetic factors (e.g., obesity, physical activity, dyslipidemia, blood pressure) or genetic factors (age, family history, ethnicity). Among websites that provided "eat healthy" guidance, one third provided zero dietary factors associated with type 2 diabetes, and only 30% provided more than two specific dietary factors associates with type 2 diabetes. We also observed that mean percent usage of all terms associated with T2D causes/risk factors and preventions was significantly lower among government websites compared to business websites and nonprofit websites.

Conclusion

Diabetes websites need to increase their usage of dietary factors when discussing causes/risk factors and preventions for T2D; as dietary factors are modifiable and strongly associated with all nondietary nongenetic risk factors, in addition to T2D risk.

Soft drink and non-caloric soft drink intake and their association with blood pressure: the Health Workers Cohort Study

Background

A few prospective studies have investigated the potential association of soft drink and non-caloric soft drink intake with high blood pressure using methods that adequately consider changes in intake over time and hypertensive status at baseline.

Objective

To prospectively examine the association of soft drink and non-caloric soft drink intake with systolic and diastolic blood pressure in a sample of Mexican adults, overall and by hypertension status.

Methods

We used data from the Health Workers Cohort Study spanning from 2004 to 2018 (n = 1,324 adults). Soft drink and non-caloric soft drink intake were assessed with a semiquantitative food frequency questionnaire. We fit multivariable-adjusted fixed-effects models to test the association of soft drink and non-caloric soft drink intake with systolic and diastolic blood pressure. The models were adjusted for potential confounders and considering the potential modifying effect of hypertension status at baseline.

Results

A one-serving increase in soft drink intake was associated with a 2.08 mm Hg (95% CI: 0.21, 3.94) increase in systolic blood pressure and 2.09 mm Hg (95% CI: 0.81, 3.36) increase in diastolic blood pressure over ten years. A stronger association between soft drink intake and diastolic pressure was observed among participants with versus without hypertension at baseline. We found no association between non-caloric soft drink intake and blood pressure.

Conclusions

Our findings support the hypothesis that soft drink intake increases blood pressure. While further studies should be conducted to confirm our findings, food policies and recommendations to limit soft drink intake are likely to help reduce blood pressure at the population level. We probably did not find an association between non-caloric soft drink intake and blood pressure because of the low consumption of this type of beverage in the cohort. More studies will be needed to understand the potential effect of non-caloric beverages on blood pressure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12937-022-00792-y.

Antihypertensive and Vasorelaxant Effects of Citrus aurantifolia Linn. Fruit: Proposed Mechanisms

Background

Citrus aurantifolia Linn. fruit, a natural dietary item, has long been used traditionally to treat hypertension in Pakistan. The current research work aims to explore the effect on blood pressure and its mechanisms.

Methods

The aqueous methanol extract of plant fruit was used to evaluate hypotensive/antihypertensive, vasorelaxation, and safety profiles. Moreover, the in vitro inhibitory effect of AMECA on phosphodiesterase was also evaluated.

Results

In hypotensive studies, extracts of Citrus aurantifolia fruit exhibited a concentration-dependent reduction in SBP, DBP, MAP, and heart rate. A similar effect has been observed on anesthetized rats, but the effects exerted by the extract were not altered significantly in the presence of L-NAME, atropine, captopril, and propranolol. Moreover, in coronary arteries, the extract significantly potentiated relaxations induced by cGMP- and cAMP-dependent relaxing agonists. When exposed to PDEs, the extract concentration dependently subdued cGMP-hydrolyzing activity of different PDEs with IC50 values of 40-130 μg/mL.

Conclusion

It is conceivable that extracts obtained from Citrus aurantifolia fruit produced hypotensive and antihypertensive effects in rats. The extract elicited endothelium-independent vasorelaxation, possibly by acting directly on smooth muscles of the coronary artery and by increasing cGMP and cAMP via nonselective inhibition of vascular PDEs.

Maternal High-Fructose Intake Induces Multigenerational Activation of the Renin-Angiotensin-Aldosterone System

Although maternal high-fructose intake induces cardiometabolic syndrome in adult offspring, whether it induces hypertension in successive multiple generations has not yet been studied. We hypothesized that maternal high-fructose intake induces multigenerational activation of the renin-angiotensin-aldosterone system. Pregnant mice were offered 20% fructose in drinking water, of which subsequent first to fourth generation offspring were raised without being offered fructose. Blood pressure was measured via the tail-cuff method, mRNA expression was determined using the quantitative polymerase chain reaction, and fibrosis was evaluated using trichrome staining. Maternal high-fructose intake statistically significantly increased blood pressure in the first and second, but not the third and fourth, generation offspring as compared to the control group, with maximal increases in serum renin, angiotensin II, and aldosterone in the third generation offspring. It increased the mRNA expression of renin-angiotensin-aldosterone system genes as well as the expression of renin in the kidneys in the first to third generation offspring, with the exception of the vasodilatory Mas1 gene, the mRNA expression of which was the lowest in the second generation offspring. Moreover, it maximally increased fibrosis and the mRNA expression of inflammatory cytokines in the second generation offspring and increased the mRNA expression of oxidative factors in the first to third generation offspring, but maximally decreased the mRNA expression of antioxidant-encoding Sod1 in the second generation offspring. Maternal high-fructose intake induces multigenerational activation of renin-angiotensin-aldosterone system, and the results of this study implicate that it epigenetically induces cardiometabolic syndrome in multiple generations of offspring.

Intra-Abdominal Fat Adipocyte Hypertrophy through a Progressive Alteration of Lipolysis and Lipogenesis in Metabolic Syndrome Rats

This study evaluates the progressive participation of enzymes involved in lipolysis and lipogenesis, leading to adipocyte hypertrophy in a metabolic syndrome (MS) rat model caused by chronic consumption of 30% sucrose in drinking water. A total of 70 male Wistar rats were divided into two groups: C and MS. Each of these groups were then subdivided into five groups which were sacrificed as paired groups every month from the beginning of the treatment until 5 months. The intra-abdominal fat was dissected, and the adipocytes were extracted. Lipoprotein lipase (LPL), hormone-sensitive lipase (HSL), protein kinases A (PKA), and perilipin A expressions were determined. The LPL and HSL activities were evaluated by spectrophotometry. Histological staining was performed in adipose tissue. Significant increases were observed in blood pressure, HOMA-IR, leptin, triglycerides, insulin, intra-abdominal fat, and number of fat cells per field (p = 0.001) and in advanced glycosylation products, adipocyte area, LPL, HSL activities and/or expression (p ≤ 0.01) in the MS groups progressively from the third month onward. Lipogenesis and lipolysis were increased by LPL activity and HSL activity and/or expression. This was associated with hyperinsulinemia and release of non-esterified fatty acids causing a positive feedback loop that contributes to the development of adipocyte hypertrophy.

Hyperglycaemia induced by chronic i.p. and oral glucose loading leads to hypertension through increased Na+ retention in proximal tubule

NEW FINDINGS

What is the central question of the study? Chronic glucose feeding accompanied by glucose injection (i.p.) causes sustained hyperglycaemia and hypertension in rats. The exact reason for the hypertension is not known. We explore some molecular pathways of the renal proximal tubule that might promote Na⁺ retention. What is the main finding and its importance? Development of hypertension was mediated by upregulation of the renal renin-angiotensin system and oxidative stress, acting via the Na⁺ -K⁺ -ATPase α₁ -subunit in the proximal tubule, which appears to pump intracellular Na⁺ into the extracellular space, increasing Na⁺ reabsorption and blood pressure. Targeting the Na⁺ -K⁺ -ATPase α₁ -subunit might provide a therapeutic strategy for treatment of hypertension. Feeding animals glucose-, fructose-, sucrose- and fat-enriched diets can lead to diet-induced hyperglycaemia, the severity of which largely depends on the types and concentrations of the nutrients used and duration of the dietary intervention. As a dietary intervention strategy, we adopted glucose-enriched diet and drinking water, with i.p. glucose injection at a dose previously determined to be effective to establish a sustained hyperglycaemia over a period of 2 weeks. We used four groups of Sprague-Dawley rats: control; glucose treated; glucose plus tempol treated; and glucose plus captopril treated. Blood glucose concentrations started to increase gradually from day 3, peaked (321 mg dl^-1 ) at day 12 and remained at similar levels until the end of the study on day 14 in the glucose treated-group compared with the control group. In contrast, the tempol- and captopril-treated groups showed significantly high glucose concentrations only in the second week. The plasma insulin concentration was significantly increased in glucose-treated animals but not in tempol- and captopril-treated groups when compared with the control rats. We also observed elevated blood pressure in the glucose-treated group compared with the control group, which can be attributed to the increase in angiotensin II concentrations from 46.67 to 99 pg ml^-1 (control versus glucose), increased oxidative stress in the cortical proximal tubule (PT), decreased urine flow, and increased expression and activity of the PT-specific α₁ -subunit of Na⁺ -K⁺ -ATPase in the renal cortex, which is responsible for increased sodium reabsorption from epithelial cells of PT into the peritubular capillaries, leading to increased blood volume and eventual blood pressure. All these events were reversed in captopril- and tempol-treated animals.

Evaluation of antihypertensive potential of Ficus carica fruit

CONTEXT

Ficus carica L. (Moraceae) fruit is said to possess cardiovascular activity and has been used empirically in traditional phytotherapies for the treatment of hypertension and various other cardiovascular diseases.

OBJECTIVE

This study investigated the antihypertensive and cardioinhibitory activity of the aqueous-methanol extract of F. carica fruit in rats.

MATERIALS AND METHODS

Extract in 250, 500 and 1000 mg/kg doses (p.o.) were administered to normotensive Sprague Dawley rats and blood pressure was measured using non-invasive technique. Hypertension was induced in rats by oral administration of 10% glucose for 3 weeks. Hypotensive effect of extract (1000 mg/kg p.o) was studied in normotensive and glucose-treated hypertensive rats. Langendorff's isolated heart technique was used to assess the effect of crude extract on force of contraction and heart rate. In addition, antioxidant potential, TPC, TFC were also assessed by DPPH free radical scavenging activity, Folin-Ciocalteu reagent and AlCl3 assay, respectively. Furthermore, phenolic compounds were analyzed using HPLC-DAD technique.

RESULTS AND DISCUSSION

The 1000 mg/kg dose decreased blood pressure significantly in normotensive and glucose-treated hypertensive rats. The isolated heart study showed that the extract produced negative inotropic and chronotropic effects but it failed to block the stimulatory effect of both adrenaline and CaCl2. HPLC studies on the F. carica extract indicated the presence of quercetin, gallic acid, caffeic acid, vanillic acid, syringic acid, coumaric acid and chromotropic acid.

CONCLUSIONS

This study demonstrated that aqueous methanol extract of F. carica fruit exerted hypotensive and antihypertensive effects in glucose-induced hypertensive rats.

Effect of the Aged Garlic Extract on Cardiovascular Function in Metabolic Syndrome Rats

The antioxidant properties of aged garlic extract (AGE) on cardiovascular functioning (CF) in metabolic syndrome (MS) remains poorly studied. Here we study the AGE effects on CF in a rat model of MS. Control rats plus saline solution (C + SS), MS rats (30% sucrose in drinking water from weaning) plus saline solution (MS + SS), control rats receiving AGE (C + AGE 125 mg/Kg/12 h) and MS rats with AGE (MS + AGE) were studied. MS + SS had increased triglycerides, systolic blood pressure, insulin, leptin, HOMA index, and advanced glycation end products. AGE returned their levels to control values (p < 0.01). Cholesterol was decreased by AGE (p = 0.05). Glutathion and GPx activity were reduced in MS + SS rats and increased with AGE (p = 0.05). Lipid peroxidation was increased in MS + SS and AGE reduced it (p = 0.001). Vascular functioning was deteriorated by MS (increased vasocontraction and reduced vasodilation) and AGE improved it (p = 0.001). Coronary vascular resistance was increased in MS rats and AGE decreased it (p = 0.001). Cardiac performance was not modified by MS but AGE increased it. NO measured in the perfusate liquid from the heart and serum citrulline, nitrites/nitrates were decreased in MS and AGE increased them (p < 0.01). In conclusion, AGE reduces MS-induced cardiovascular risk, through its anti-oxidant properties.

A Grape Seed Procyanidin Extract Ameliorates Fructose-Induced Hypertriglyceridemia in Rats via Enhanced Fecal Bile Acid and Cholesterol Excretion and Inhibition of Hepatic Lipogenesis

The objective of this study was to determine whether a grape seed procyanidin extract (GSPE) exerts a triglyceride-lowering effect in a hyperlipidemic state using the fructose-fed rat model and to elucidate the underlying molecular mechanisms. Rats were fed either a starch control diet or a diet containing 65% fructose for 8 weeks to induce hypertriglyceridemia. During the 9th week of the study, rats were maintained on their respective diet and administered vehicle or GSPE via oral gavage for 7 days. Fructose increased serum triglyceride levels by 171% after 9 weeks, compared to control, while GSPE administration attenuated this effect, resulting in a 41% decrease. GSPE inhibited hepatic lipogenesis via down-regulation of sterol regulatory element binding protein 1c and stearoyl-CoA desaturase 1 in the fructose-fed animals. GSPE increased fecal bile acid and total lipid excretion, decreased serum bile acid levels and increased the expression of genes involved in cholesterol synthesis. However, bile acid biosynthetic gene expression was not increased in the presence of GSPE and fructose. Serum cholesterol levels remained constant, while hepatic cholesterol levels decreased. GSPE did not modulate expression of genes responsible for esterification or biliary export of the newly synthesized cholesterol, but did increase fecal cholesterol excretion, suggesting that in the presence of GSPE and fructose, the liver may secrete more free cholesterol into the plasma which may then be shunted to the proximal small intestine for direct basolateral to apical secretion and subsequent fecal excretion. Our results demonstrate that GSPE effectively lowers serum triglyceride levels in fructose-fed rats after one week administration. This study provides novel insight into the mechanistic actions of GSPE in treating hypertriglyceridemia and demonstrates that it targets hepatic de novo lipogenesis, bile acid homeostasis and non-biliary cholesterol excretion as important mechanisms for reducing hypertriglyceridemia and hepatic lipid accumulation in the presence of fructose.

17β Estradiol Modulates Perfusion Pressure and Expression of 5-LOX and CYP450 4A in the Isolated Kidney of Metabolic Syndrome Female Rats

Prevalence of metabolic syndrome and progression of nephropathy depend on sex. We examined a protective effect of estradiol against nephropathy in metabolic syndrome through the modulation of the arachidonic acid metabolism by activating the 5-lipoxygenase and cytochrome p450 4A pathways. 28 female Wistar rats were divided into four groups of seven animals each: control, intact metabolic syndrome, ovariectomized metabolic syndrome, and metabolic syndrome ovariectomized plus estradiol. Blood pressure, body weight, body fat, triglycerides, insulin, HOMA-index, albuminuria, and TNF-α were increased in ovariectomized metabolic syndrome rats (p < 0.001). The perfusion pressure in isolated kidneys of ovariectomized metabolic syndrome rats in presence of 4 μg of arachidonic acid was increased. The inhibitors of the arachidonic acid metabolism Baicalein, Miconazole, and Indomethacin in these rats decreased the perfusion pressure by 57.62%, 99.83%, and 108.5%, respectively and they decreased creatinine clearance and the arachidonic acid percentage. Phospholipase A2 expression in the kidney of ovariectomized metabolic syndrome rats was not modified. 5-lipoxygenase was increased in metabolic syndrome ovariectomized rats while cytochrome p450 4A was decreased. In conclusion, the loss of estradiol increases renal damage while the treatment with estradiol benefits renal function by modulating arachidonic acid metabolism through the 5-lipoxygenase and cytochrome p450 4A pathways.

Modulation of the activities of catalase, cu-zn, mn superoxide dismutase, and glutathione peroxidase in adipocyte from ovariectomised female rats with metabolic syndrome

The aim of this study was to evaluate the association between estrogen removal, antioxidant enzymes, and oxidative stress generated by obesity in a MS female rat model. Thirty two female Wistar rats were divided into 4 groups: Control (C), MS, MS ovariectomized (Ovx), and MS Ovx plus estradiol (E2). MS was induced by administering 30% sucrose to drinking water for 24 weeks. After sacrifice, intra-abdominal fat was dissected; adipocytes were isolated and lipid peroxidation, non-enzymatic antioxidant capacity, and the activities of Cu-Zn and Mn superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) were determined. There were no significant differences in the activities of Cu-Zn, Mn SOD, CAT, and GPx between the C and MS groups, but in the MS Ovx group there was a statistically significant decrease in the activities of these enzymes when compared to MS and MS Ovx+E2. The increased lipid peroxidation and nonenzymatic antioxidant capacity found in MS Ovx was significantly decreased when compared to MS and MS Ovx+E2. In conclusion, the removal of E2 by ovariectomy decreases the activity of the antioxidant enzymes in the intra-abdominal tissue of MS female rats; this is reflected by increased lipid peroxidation and decreased nonenzymatic antioxidant capacity.

Effect of glycine on the cyclooxygenase pathway of the kidney arachidonic acid metabolism in a rat model of metabolic syndrome

The kidneys are organs that can be severely impaired by metabolic syndrome (MS). This is characterized by the association of various pathologies such as hypertension, dyslipidemia, and type-2 diabetes. Glycine, a nonessential amino acid, is known to possess various protective effects in the kidney, such as a decrease in the deterioration of renal function and a reduction of the damage caused by hypoxia. In a rat model of MS, the effect of glycine on the cyclooxygenase (COX) pathway of arachidonic acid (AA) metabolism was studied in isolated perfused kidney. MS was induced in Wistar rats by feeding them a 30% sucrose solution for 16 weeks. The addition of 1% glycine to their drinking water containing 30% sucrose, for 8 weeks, reduced high blood pressure, triglyceride levels, insulin concentration, homeostatis model assessment (HOMA) index, albuminuria, AA concentration in kidney homogenate, renal perfusion pressure, prostaglandin levels, PLA2 expression, and COX isoform expression, compared with MS rats that did not receive the glycine supplement. Glycine receptor expression decreased significantly with MS, but glycine treatment increased it. The results suggest that in the MS model, 1% glycine treatment protects the kidney from damage provoked by the high sucrose consumption, by acting as an anti-inflammatory on the COX pathway of AA metabolism in kidney.

The aqueous extract of Terminalia superba (Combretaceae) prevents glucose-induced hypertension in rats

AIM OF THE STUDY

The stem bark of Terminalia superba (Combretaceae) (TS) is used in traditional Cameroonian medicine as antihypertensive remedy. The aim of this study was to investigate the hypotensive and the antihypertensive effects of the aqueous extract of the stem bark of Terminalia superba.

MATERIALS AND METHODS

Hypertension was obtained in rats by oral administration of 10% D-glucose for 3 weeks. The acute effects of Terminalia superba were studied on blood pressure (BP) and heart rate (HR) after intravenous administration in normotensive rats (NTR) and glucose hypertensive rats (GHR). The antihypertensive effects were studied after oral administration of the extract (50 and 100 mg/kg/day) or nifedipine (10 mg/kg/day) for 3 weeks. At the end of the experiment, BP and HR were measured and reduced glutathione (GSH), malondialdehyde (MDA) and superoxide dismutase (SOD) activity levels were measured in heart, aorta, liver and kidney.

RESULTS

Intravenous administration of the aqueous extract of Terminalia superba induced a significant hypotensive response without any change in HR. The hypotensive effect of the extract was unaffected by atropine or propranolol but decreased by reserpine (5 mg/kg) and yohimbine (0.1 mg/kg). In addition, the oral administration of the extract significantly prevented the rise in BP in glucose-hypertensive rats. Finally, the treatment with plant extract significantly blunted the decrease in GSH and the increase in MDA levels associated with hypertension, and significantly prevents the increase in aortic SOD activity.

CONCLUSIONS

The present study demonstrates that the aqueous extract of the stem bark of Terminalia superba exhibits hypotensive and anti-hypertensive properties that are, at least in part, related to a withdrawal of sympathetic tone and to an improvement of the antioxidant status, respectively. Overall data validate the use of Terminalia superba as antihypertensive therapy in traditional medicine.

Effects of insulin resistance and testosterone on the participation of cyclooxygenase isoforms in vascular reactivity

Testosterone plays an important role in mediating hypertension and altered vascular reactivity associated with insulin resistance. In addition to other pathways, testosterone-dependent changes in aortic cyclooxygenase (COX-2) mRNA levels affect blood pressure following insulin resistance. However their effects on vascular tone are unclear. We studied the changes in contraction response to phenylephrine (PE) in the aorta and superior mesenteric artery (SMA) from intact and gonadectomized fructose-fed rats. Constriction response to PE was studied in tissues incubated with the COX-1 and COX-2-selective antagonists, SC-560 and NS-398, respectively, and indomethacin, in addition to assessing its role in endothelium-dependent relaxation. Finally changes in COX-2 protein expression and plasma thromboxane A2 (TXA2), a downstream vasoconstrictor metabolite of COX-2, were measured. In fructose-fed rats, castration prevented the increase in blood pressure but not insulin resistance. The involvement of COX-2 in mediating the alpha-adrenergic vasoconstriction was higher in intact rat aorta compared to COX-1, which was prevented by castration. However, in the SMA, COX-2 participation was dependent on testosterone alone. Fructose-induced attenuation of endothelial relaxation was restored by indomethacin, which suggests a pro-vasoconstrictor role for COX. Both diet and testosterone did not alter vascular COX-2 expression thus suggesting the involvement of downstream testosterone-dependent pathways. This is supported by increased plasma TXA2 in the castrated rats compared to intact rats. Isoform-specific actions of COX are tissue-selective in states of insulin resistance and involve potential testosterone-dependent downstream targets. Further studies are needed to investigate the role of androgens and insulin resistance in vascular arachidonic acid metabolism.

Insulin effect on glucose transport in thymocytes and splenocytes from rats with metabolic syndrome

Metabolic syndrome (MS) may comprise several clinical conditions such as obesity, diabetes and inflammatory disorders, which are characterized by metabolic imbalances. The study of glucose transport and regulation by insulin in lymphocytes is important, since the way they increase inflammation and susceptibility to infections are common in MS. We studied glucose internalization in isolated thymocytes and splenocytes, its regulation by insulin, and the role of three glucose transporters (Gluts) in control and in MS rats. Control glucose internalization and insulin responses were lower in splenocytes than in thymocytes. Control and insulin-induced glucose internalization in thymocytes declined with age, while transport by splenocyte continued to respond to insulin. Control thymocyte glucose internalization was blocked by antibodies against Glut 1 and 4, while the insulin response also was blocked by an anti-Glut 3 antibody. On four month old control and insulin-induced response, splenocyte transport was only blocked by Glut 1 and 4 antibodies. At six months splenocyte glucose internalization depended on Glut 1 and was less sensitive to the effects of an anti-Glut 4 antibody. In MS splenocytes the capacity of anti-Glut 1 antibodies to inhibit control and insulin-dependent glucose transport was less significant, and we found that in MS rats, glucose internalization was dependent on Glut 3 and Glut 4. In summary, the altered metabolic state present in MS rats shows signs of modulation of glucose internalization by the Glut1, Glut 3 and Glut 4 transporters, compared with its own age control.

Gum Guar fiber associated with fructose reduces serum triacylglycerol but did not improve the glucose tolerance in rats

INTRODUCTION

The increased intake of dietary fructose can be associated with alterations on energy homeostasis and lipid/carbohydrate metabolism, such as insulin resistance and dislipidemia. On the other hand, the ingestion of soluble fiber gum guar could improve benefic mechanism on glucose tolerance and lipids profile.

OBJECTIVE

The aim of the present study were to investigate the effects of the supplemental feeding partially hydrolyzed gum guar on glucose and lipid homeostasis, in rats fed with fructose solution.

METHODS

The study was performed on thirty day-old male Wistar rats randomly assigned into four groups: control(C) or treated with fructose (F-20%), fiber (FB-5%), or fructose plus fiber (F-20% + FB-5% = FF) solution for 30 days on glucose tolerance (OGTT), triacylglycerol concentration in the liver by chloroform/methanol method, glucose, triacylglycerol and total cholesterol serum concentration by assayed by enzymatic colorimetric method, insulin receptor (IR) concentration in the liver by Western Blotting.

RESULTS

The total body weight gain was not different between groups; in regards of total caloric intake, in the F group was significantly higher and in the FB group was lower than other groups. The triacylglycerol concentration in the liver of FF group was significantly higher than F group, the triacylglycerol concentration in the serum was higher the F group compared with other groups. The OGTT reveal impaired on glucose tolerance in the F, FB, FF compared with C. The IR concentration in the liver was lower in the F, FB, FF compared with C, no significant difference was observed between groups for IR concentration in the gastrocnemius muscle. No significant difference was observed between groups for carcass fat content and serum total cholesterol.

CONCLUSION

Fructose induced important alterations on glucose tolerance and lipid metabolism, despite of fiber showed reversion of part this alterations. The association fructose plus fiber to seem decrease insulin receptor concentration in the liver, with consequent impair on glucose tolerance.

Reducing consumption of sugar-sweetened beverages is associated with reduced blood pressure: a prospective study among United States adults

BACKGROUND

Increased consumption of sugar-sweetened beverages (SSBs) has been associated with an elevated risk of obesity, metabolic syndrome, and type II diabetes mellitus. However, the effects of SSB consumption on blood pressure (BP) are uncertain. The objective of this study was to determine the relationship between changes in SSB consumption and changes in BP among adults.

METHODS AND RESULTS

This was a prospective analysis of 810 adults who participated in the PREMIER Study (an 18-month behavioral intervention trial). BP and dietary intake (by two 24-hour recalls) were measured at baseline and at 6 and 18 months. Mixed-effects models were applied to estimate the changes in BP in responding to changes in SSB consumption. At baseline, mean SSB intake was 0.9+/-1.0 servings per day (10.5+/-11.9 fl oz/d), and mean systolic BP/diastolic BP was 134.9+/-9.6/84.8+/-4.2 mm Hg. After potential confounders were controlled for, a reduction in SSB of 1 serving per day was associated with a 1.8-mm Hg (95% confidence interval, 1.2 to 2.4) reduction in systolic BP and 1.1-mm Hg (95% confidence interval, 0.7 to 1.4) reduction in diastolic BP over 18 months. After additional adjustment for weight change over the same period, a reduction in SSB intake was still significantly associated with reductions in systolic and diastolic BPs (P<0.05). Reduced intake of sugars was also significantly associated with reduced BP. No association was found for diet beverage consumption or caffeine intake and BP. These findings suggest that sugars may be the nutrients that contribute to the observed association between SSB and BP.

CONCLUSIONS

Reduced consumption of SSB and sugars was significantly associated with reduced BP. Reducing SSB and sugar consumption may be an important dietary strategy to lower BP.

CLINICAL TRIAL REGISTRATION

URL: http://clinicaltrials.gov. Unique identifier: NCT00000616.

Effect of gonadectomy on the metabolism of arachidonic acid in isolated kidney of a rat model of metabolic syndrome

Influence of sex on arachidonic acid metabolism, a pathway involved in the link between metabolic syndrome (MS) and renal damage, was studied in isolated perfused kidney. Metabolic syndrome was induced by feeding 30% sucrose solution for 24 weeks to intact and gonadectomized female (Ovx) and male (Cas) rats. Systolic blood pressure, albuminuria, as well as prostaglandin E(2) and thromboxane B(2) from urine and perfusate increased in MS male and MS ovariectomized females; castration reduced them in MS males. Perfusion of arachidonic acid in kidneys from MS males increased perfusion pressure compared with controls. No difference appeared in perfusion pressure between control and MS females. Castration diminished perfusion pressure in MS; the opposite was observed in Ovx MS. Perfusion with arachidonic acid plus indomethacin decreased perfusion pressure in MS male kidneys and in Cas MS. In Ovx MS, arachidonic acid plus indomethacin decreased perfusion pressure, but not in female control, MS, and Ovx control. Increase in perfusion pressure with arachidonic acid in both male MS and Ovx MS was related to cyclooxygenase (COX)-1 and COX-2 overexpression in kidney. Castration reduced the expression of COX-1 and COX-2 in MS to control levels. The results suggest that the alteration in arachidonic acid metabolism associated with changes in the expression of COX-1 and COX-2 induced by sucrose intake, and influenced by sex hormones, may contribute to renal damage.

Effect of Sex Hormones on Non-Esterified Fatty Acids, Intra-Abdominal Fat Accumulation, and Hypertension Induced by Sucrose Diet in Male Rats

Sucrose-fed rats (1) had higher intra-abdominal fat mass and plasma non-esterified fatty acids and lower testosterone levels, (2) were hypertensive, and (3) had lower plasma NO metabolites than controls. The lack of testosterone by castration of sucrose-fed rats decreased high blood pressure and circulating non-esterified fatty acids and increased NO metabolites. The administration of testosterone to castrated sucrose-fed rats restored hypertension, fat accumulation, and high-circulating non-esterified fatty acids, and lowered NO metabolite levels whereas estradiol treatment did not significantly affect these variables in castrated animals. This study proposes that the low levels of testosterone found in sucrose-fed rats are sufficient to maintain central obesity and increased circulating non-esterified fatty acids, which contribute to the development of hypertension in sucrose-fed rats by modulating the biosynthesis of NO.

Isolated Heart Function after Ischemia and Reperfusion in Sucrose-Fed Rats: Influence of Gender and Treatment

Sucrose-fed rats (HTG) develop hypertension, hypertriglyceridemia, and other features of the metabolic syndrome. This condition, nowadays a world epidemic, is more prevalent in males and increases the risk of cardiovascular diseases. Weanling male and female rats were given either tap water in control (C) or 30% sucrose solution in HTG groups and commercial rat chow for 3, 5, or 8 months. We studied possible variations in cardiac function, due to gender and length of treatment, in isolated heart after ischemia-reperfusion, since an impaired performance may be more easily detected under stress. Together, sucrose treatment and age affected all cardiac variables. Gender had significant effect on coronary vascular resistance and postischemic levels of the enzyme CK-MB; the percentages of retained cardiac enzymes after ischemia were higher in C and HTG females. C and HTG males had a higher incidence of arrhythmias than females, but only HTG males suffered lethal ventricular fibrillation.

Castration modifies aortic vasoreactivity and serum fatty acids in a sucrose-fed rat model of metabolic syndrome

Levels of testosterone and estradiol influence the incidence of cardiovascular diseases: generally, estrogens in females are protective before menopause; coronaropathies, hypertension, and dyslipidemias in normal men are more frequent at comparable ages. We investigated the modulation by castration of in vitro vasoreactivity, serum lipid content, and systolic blood pressure (SBP) in rats with sucrose-induced metabolic syndrome. The main characteristics of the rat model are: hypertriglyceridemia, moderately high blood pressure, intra-abdominal accumulation of adipose tissue, hyperinsulinemia, nephropathy, increased oxidative stress, and altered vasoreactivity. Male weanling rats received 30% sucrose solution for 16 weeks (metabolic syndrome; MS), controls (C) had plain water; both had commercial rodent chow. They were subdivided into five groups with two subgroups each: Group 1, intact C and MS rats, Groups 2-5, C and MS rats castrated for periods of 16, 12, 8, and 4 weeks. At the end of the study period, systolic blood pressure was measured, and blood and aortas were obtained for fatty acid determination and vasoreactivity assays, respectively. After 16 weeks' sucrose treatment MS aortas showed hypercontractility and decreased vasodilation. Palmitic and palmitoleic acids were increased in MS versus C. Arachidonic acid levels in MS were lower than in intact or castrated C. Long-term castration of 16 weeks normalized the levels of palmitic and oleic acids. With the shorter periods of castration, contractility increased and relaxation decreased in C and MS, but it was more significant in C. Regarding fatty acid composition, long-term castration increased polyunsaturated (arachidonic and eicosapentaenoic) fatty acids. The shorter periods did not modify the fatty acid profile in either C or MS. Metabolic syndrome altered SBP, aortic reactivity, and levels of fatty acids; castration of long duration normalized them in some cases.

Antihypertensive effect of total flavones extracted from seed residues of Hippophae rhamnoides L. in sucrose-fed rats

The study was designed to investigate the antihypertensive effect of total flavones extracted from seed residues of Hippophae rhamnoides L. (TFH-SR) and its underlying mechanism in chronic sucrose-fed rats by evaluating its ability to regulate insulin and angiotensin || levels. Feeding of high-sucrose diet (HS: 77% of kcal from carbohydrate, 16% from protein and 6% from lipid, respectively) for 6 weeks resulted in significant rise in systolic blood pressure (SBP) by 25.60%, plasma insulin by 114.24%, triglycerides by 85.14% and activated angiotensin || contents in heart and kidney. However, TFH-SR treatment significantly suppressed the elevated hypertension, hyperinsulinemia and dyslipidemia. Furthermore, TFH-SR (especially at the dose of 150mg/kg/day) increased the circulatory blood angiotensin || level as effective as angiotensin || receptor blocker. These results indicated that TFH-SR exerted its antihypertensive effects at least in part by improving insulin sensitivity and blocking angiotensin || signal pathway. Findings of the present study suggested that TFH-SR might prove to be of potential use in the management of hyperinsulinemia in non-diabetic state with cardiovascular diseases.

Hypotensive and vasorelaxant effects of the procyanidin fraction from Guazuma ulmifolia bark in normotensive and hypertensive rats

THE AIM OF THE STUDY

was to investigate the in vivo and in vitro cardiovascular activity of a procyanidin fraction (PCF) obtained from acetone extract of Guazuma ulmifolia bark which has traditionally been used as an antihypertensive agent.

RESULTS

10 mg/kg PCF doses orally administered to sugar-fed hypertensive rats decreased both the systolic arterial pressure and the heart rate, whereas the same doses intravenously administered induced arterial hypotension which was attenuated by NG-nitro-L-arginine methylester (L-NAME 31 mg/kg) pretreatment. In these experiments we employed carbachol as a positive control test. The PCF reduced the contraction induced by norepinephrine (1x10(-7) M) in isolated aortic rings of normotensive (IC50=35.3+/-12.4 ng/mL) and sugar-fed hypertensive (IC50=101.3+/-57.2 ng/mL) rats. This relaxant activity was inhibited by either vascular endothelium removal or L-NAME (30 microM) pretreatment, while indomethacin (10 microM) or atropine (10 microM) had no effect. Preliminary analysis of the PCF by HPLC-DAD-MS and FAB+ mass spectrometry allowed the detection of the main components such as the complex of procyanidin oligomers consisting mainly of tetramers and trimers.

CONCLUSIONS

Guazuma ulmifolia bark possesses long-lasting antihypertensive and vasorelaxing properties linked to the endothelium related factors, where nitric oxide is involved.

Effects of sex hormone levels on aortic vascular reactivity and variables associated with the metabolic syndrome in sucrose-fed female rats

We studied the effect of varying levels of sex hormones, induced by ovariectomy and administration of testosterone or estradiol, on aortic reactivity in female rats with metabolic syndrome (MS) induced by a sucrose diet. Vasoreactivity of aortic rings, blood pressure, intra-abdominal fat, serum triglycerides, nitrates and nitrites, and TBARS were evaluated. Intact MS and ovariectomized MS had higher BP than intact control (C) and ovariectomized C, respectively; estradiol administration decreased BP in ovariectomized MS but not in ovariectomized C. Triglycerides and fat were both higher in MS. Triglycerides were not modified by surgery or hormone treatment, but ovariectomy increased fat. When ovariectomy was combined with hormones, however, fat was reduced to the level of intact rats. Ovariectomy decreased, but hormones increased, serum nitrates and nitrites. Vasoconstriction was larger in intact MS and ovariectomized MS + testosterone aortas than in intact C and ovariectomized C + testosterone, respectively. Vasodilation was reduced in intact MS and ovariectomized MS + testosterone compared with intact C, ovariectomized C + testosterone, ovariectomized MS, and ovariectomized MS + estradiol. The results suggest endothelial dysfunction in intact MS and ovariectomized MS + testosterone, but protection by ovariectomy + estradiol in MS due to hormones. Indomethacin reduced all contractions, but the effect was greater in estradiol-treated rats. l-NAME increased contractility, more in the ovariectomized C and MS groups and less in the estradiol-treated groups.

Hemodynamic changes in postprandial state

Several experimental data suggest that single sugar intake may induce heart rate acceleration and blood pressure elevation as a result of sympathetic activation secondary to insulin response and from alterations in endothelial function due to activation of oxidative stress. These hemodynamic effects might be more marked in patients with arterial hypertension or metabolic disorders, in particular in hypertensive patients with diabetes. A high-fat load may also induce activation of oxidative stress and endothelial dysfunction. However, the long-term effect of repeated intake of single sugar and fat on blood pressure, oxidative stress, and endothelial function should be tested in controlled trials. On the contrary, a balanced mixed meal (50% carbohydrates) does not induce any significant blood pressure changes. Nevertheless, acarbose treatment is able to reduce hypertension incidence in patients with impaired glucose tolerance and to improve endothelial function. In elderly subjects, in particular with type 2 diabetes or with severe dysautonomia, sigle sugar intake may account for nonhypoglycemic postprandial dizziness.

Modulation of aortic vascular reactivity by sex hormones in a male rat model of metabolic syndrome

Modulation by sex hormones of aortic reactivity in rats with the metabolic syndrome (MS) was investigated. The following groups of weanling male Wistar rats were used: control rats (C) received regular tap water while MS rats received 30% sucrose in their drinking water; both had rodent chow for 24 weeks. These two groups were further subdivided into the following four groups: intact (Int), castrated (Cas), castrated plus testosterone (T) and castrated plus estradiol (E). Vascular response of thoracic aortic rings to norepinephrine (NE), acetylcholine (ACh), indomethacin (Indo) and nitro-l-arginine-methyl ester (L-NAME) was investigated. Blood pressure (BP) and serum nitrates and nitrites were measured. BP and serum nitrates and nitrites were modified by castration and treatments with either T or E. Vasoconstriction in Int MS and Cas MS+T aortas was larger than in C and Cas C+T, respectively. Vasodilation in Int MS and Cas MS+T was reduced in comparison with C and Cas C+T, Cas MS and Cas MS+E. Indomethacin decreased vasoconstriction in all groups (P<0.002) but Int C and Cas C+T remained significantly smaller than Int MS and Cas MS+T. l-NAME in NE-contracted vessels induced a significant increase in vasoconstriction, except in Cas C+E rats; the responses of Int MS and Cas MS+T were significantly larger than in Int C and Cas C+T. The results suggest endothelial dysfunction in Int MS and Cas MS+T and a protective effect resulting from castration and castration plus E in MS animals, indicating a sex hormone influence.

Fructose-induced hypertension in Wistar–Kyoto rats: interaction with moderately high dietary saltThis paper is one of a selection of papers published in this Special Issue, entitled The Cellular and Molecular Basis of Cardiovascular Dysfunction, Dhalla 70th Birthday Tribute

We investigated the effects of 4% fructose plus moderately high salt (MHS) (4% NaCl) treatment on tissue aldehyde conjugates, platelet cytosolic free calcium ([Ca2+]i), renal morphology, and systolic blood pressure (SBP) in Wistar–Kyoto rats, and whether these effects were reversible (R) after withdrawal of treatment. At age 7 weeks, rats were divided into 4 groups: NS group, given normal salt (NS) diet (0.7% NaCl) for 18 weeks; NS+F(R) group, NS diet and fructose in water for 14 weeks, then 4 weeks fructose withdrawal; MHS+F group, NS diet and fructose for 6 weeks, then MHS diet and fructose for 12 weeks; and MHS+F(R) group, NS diet and fructose for 6 weeks, then MHS diet and fructose for 8 weeks, then MHS and fructose withdrawal for 4 weeks. SBP in the NS+F(R) group increased during fructose treatment, but normalized within 1 week of withdrawal. Tissue aldehyde conjugates and platelet [Ca2+]i were normal at completion. Adverse renal vascular changes did not reverse to normal and were similar to those of the salt plus fructose-treated groups. This may have implications for future development of hypertension. MHS did not cause any additional increase in SBP or associated tissue alterations when added to fructose treatment. However, the SBP and tissue changes persisted even after discontinuation of treatment. The fructose and salt combination may result in long-lasting vascular alterations leading to hypertension.

Gonadectomy prevents endothelial dysfunction in fructose-fed male rats, a factor contributing to the development of hypertension

Insulin resistance has been shown to be associated with increased blood pressure (BP). The sex hormones estrogen and testosterone have opposing effects in the development of increased BP. Since testosterone has been implicated in increased BP following insulin resistance, we have tried to dissect out the effects of insulin resistance on endothelium-dependent vasorelaxation in the presence and absence of testosterone. Both gonadectomized and sham-operated male Wistar rats fed with a high-fructose diet developed insulin resistance, but BP increased only in the sham-operated rats. Reintroduction of testosterone in vivo restored the increase in BP, thereby abolishing the protective effects of gonadectomy. Fructose feeding did not affect plasma testosterone levels. Insulin resistance induced endothelial dysfunction in the mesenteric arteries of sham-operated rats, which was prevented by gonadectomy, thus suggesting a key role for testosterone in the pathogenesis of secondary vascular complications. Subsequent to blocking the actions of endothelium-dependent hyperpolarizing factor (EDHF), relaxation to acetylcholine (ACh) was lower in sham-operated fructose-fed rats compared with other groups, suggesting the involvement of nitric oxide (NO) in vasorelaxation. Inhibition of NO synthesis nearly abolished the ACh-evoked relaxation in both fructose-fed groups, thus suggesting a testosterone-independent impairment of EDHF-mediated relaxation. The improvement in endothelial function following gonadectomy could be ascribed to a NO component, although plasma nitrite and nitrate levels were unchanged. In summary, testosterone is essential in vivo for the development of endothelial dysfunction and hypertension secondary to insulin resistance, suggesting a facilitatory role for testosterone in increasing BP in fructose-fed male rats.

Effects of high-sucrose feeding on insulin resistance and hemodynamic responses to insulin in spontaneously hypertensive rats

This study was designed to investigate the effects of a sucrose diet on vascular and metabolic actions of insulin in spontaneously hypertensive rats (SHR). Male SHR were randomized to receive a sucrose or regular chow diet for 4 wk. Age-matched, chow-fed Wistar-Kyoto (WKY) rats were used as normotensive control. In a first series of experiments, the three groups of rats had pulsed Doppler flow probes and intravascular catheters implanted to determine blood pressure, heart rate, and blood flows. Insulin sensitivity was assessed during a euglycemic hyperinsulinemic clamp performed in conscious rats. In a second series of experiments, new groups of rats were used to examine glucose transport activity in isolated muscles and to determine endothelial nitric oxide synthase (eNOS) protein expression in muscles and endothelin content in vascular tissues. Sucrose feeding was shown to markedly enhance the pressor response to insulin and its hindquarter vasoconstrictor effect when compared with chow-fed SHR. A reduction in eNOS protein content in muscle, but no change in vascular endothelin-1 protein, was noted in sucrose-fed SHR when compared with WKY rats, but these changes were not different from those noted in chow-fed SHR. Similar reductions in insulin-stimulated glucose transport were observed in soleus muscles from both groups of SHR when compared with WKY rats. In extensor digitorum longus muscles, a significant reduction in insulin-stimulated glucose transport was only seen in sucrose-fed rats when compared with the other two groups. Environmental factors, that is, high intake of simple sugars, could possibly potentiate the genetic predisposition in SHR to endothelial dysfunction and insulin resistance.

Ethanolic extract of Spirulina maxima alters the vasomotor reactivity of aortic rings from obese rats

BACKGROUND

Aortic rings with endothelium excised from fructose-fed obese rats develop more tension in response to phenylephrine and relax less in response to carbachol than corresponding rings from lean rats. This altered vascular reactivity is prevented when Spirulina maxima is added to the fructose-rich diet. In the present study the effects of a raw ethanolic extract of Spirulina maxima on the vasomotor responses of aorta rings from sucrose-fed obese hypertensive rats were analyzed.

METHODS

The experiments were performed on aorta rings from sucrose-fed obese male rats. For each experiment, a pair of rings from the same aorta (one with intact endothelium, the other without a functional endothelium) was used. In this study we analyzed, in vitro, the effects of the ethanolic extract of Spirulina maxima on the reactivity of the aortic rings to phenylephrine and to carbachol.

RESULTS

On rings with endothelium, the extract produced the following effects: a) a concentration-dependent (0.06-1.0 mg/mL) decrease of the contractile response to phenylephrine; b) a rightward shift and a decrease in maximal developed tension, of the concentration-response curve to phenylephrine; c) a concentration-dependent relaxation of phenylephrine-precontracted rings. These effects persisted in the presence of indomethacin but were prevented by L-NAME. The extract had no effect on the concentration-response curve of phenylephrine-precontracted rings to carbachol. On endothelium-denuded rings the extract caused a significant rightward shift of the concentration response curve to phenylephrine without any effect on maximal tension development.

CONCLUSIONS

These results suggest that, in rings from obese rats, the extract, in addition to increasing the synthesis/release of NO, also inhibits the synthesis/release of a cyclooxygenase-dependent vasoconstrictor metabolite of arachidonic acid, which is increased in obesity.

Hypertension, single sugars and fatty acids

Macronutrients may induce various hemodynamic effects. In the fructose-fed rat blood pressure increase is associated with insulin resistance and enhanced sympathetic activity. In humans, oral glucose intake induces a slight and transient increase of blood pressure secondary to sympathetic activation. This increase may be higher in hypertensive subjects and followed by a significant fall in blood pressure in elderly subjects. Saturated fatty acid-enriched diet induces in male rats a significant increase in blood pressure related to sympathetic activation. Some observational and interventional studies suggest that n-3 polyunsaturated fatty-acids may reduce blood pressure in humans. Thus, both carbohydrates and fatty acid balance may contribute to blood pressure changes. The clinical relevance of these data should be evaluated in long-term trials, in particular in overweight and hypertensive subjects.

Isolated heart function during ischemia and reperfusion in sucrose-fed rats. Effect of insulin infusion

In myocardial damage due to ischemia-reperfusion, the administration of insulin together with glucose and potassium may be protective, although in some patients and animal models, it is ineffective. In a rat model (HTG) with characteristics of the metabolic syndrome, induced by sucrose feeding, ischemia-reperfusion of the isolated heart evidences a less favorable outcome than in control animals, particularly males. We investigated the effect of insulin infusion during the reperfusion period in isolated hearts from control and HTG male and female rats. Weanling Wistar rats were given commercial rat chow and tap water (C rats) or 30% sucrose solution (HTG rats) for 8 months. They developed moderate hypertension and hyperinsulinemia, central adiposity, nephropathy, and hypertriglyceridemia. Cardiac function was recorded in a Langendorff preparation subjected to 25 min ischemia and 15 min reperfusion. The handicapped functionality of HTG hearts is more apparent under conditions of stress. Insulin administration improved particularly mechanical work and +dp/dt max variables. The effect of sex was observed on the type of arrhythmias developed during reperfusion: Only the males showed lethal ventricular fibrillation, which disappeared after insulin administration. Females had lower levels of cardiac enzymes creatine kinase (CKMB) and lactic dehydrogenase (LDH), but their performance was not hindered, probably on account of protective factors such as estrogens. Summing up, the pathological features of the HTG model did not prevent insulin from exerting some of its beneficial effects in HTG hearts. Sex differences in the outcome were more apparent in the type of arrhythmias after reperfusion; they were lethal in HTG males only, but insulin prevented their onset.

Antioxidant enzymes in hypertensive and hypertriglyceridemic rats: effect of gender

In a model of hypertensive and hypertriglyceridemic rats (HTG), in which oxidative stress is increased, the influence of gender upon activities of catalase (CAT), glutathione peroxidase (GPX), and superoxide dismutase (SOD) was investigated. Statistically significant differences between antioxidant enzyme activities and treatment with relation to gender were analyzed. Weanling Wistar rats were given normal rat chow and either tap water for control group or 30% sucrose solution for HTG group, for 5-6 months. At the end of the experimental period, blood pressure was significantly higher in both male and female HTG groups, but males showed higher values than females. Serum, heart, kidney, and liver were obtained to determine antioxidant enzyme activities. Activities of CAT and GPX tended to be higher in male animals. A larger number of significant changes in enzyme activities associated with gender appears in HTG than in controls, which indicates the harmful effect of the treatment.

Changes in lipid metabolism and antioxidant defense status in spontaneously hypertensive rats and Wistar rats fed a diet enriched with fructose and saturated fatty acids

OBJECTIVE

Larger doses of fructose and saturated fat have been associated with oxidative stress and development of hypertension. The effects of modest amounts of fructose and saturated fatty acids on oxidative stress are unknown.

METHODS

To increase knowledge on this question, 10-wk-old spontaneously hypertensive rats and Wistar rats were fed for 8 wk with a control diet or an experimental diet enriched with fructose (18%) and saturated fatty acids (11%; FS diet). The total antioxidant status of organs and red blood cells was assayed by monitoring the rate of free radical-induced red blood cell hemolysis. Sensitivity of very low-density lipoprotein and low-density lipoprotein (VLDL-LDL) to copper-induced lipid peroxidation was determined as the production of thiobarbituric acid-reactive substances. Antioxidant enzymes and vitamins were also measured to establish the oxidative stress effect.

RESULTS

The FS diet did not affect blood pressure in either strain, but it increased plasma insulin concentrations only in Wistar rats without affecting those of glucose of either strain. The FS diet significantly enhanced plasma and VLDL-LDL triacylglycerol concentrations without affecting concentrations of VLDL-LDL thiobarbituric acid-reactive substances. The decreased content of arachidonic acid and total polyunsaturated fatty acids in VLDL-LDL by the FS diet may have prevented lipid peroxidation in this fraction. Moreover, FS consumption by both strains was accompanied by a significant increase in total antioxidant capacity of adipose tissue, muscle, heart, and liver. This may have resulted from increased tissue ascorbic acid levels and glutathione peroxidase and glutathione reductase activities in tissues.

CONCLUSIONS

These findings clearly indicate that the FS diet did not alter blood pressure of spontaneously hypertensive rats and Wistar rats. The FS diet resulted in hypertriglyceridemia but increased the total antioxidant status, which may prevent lipid peroxidation in these rats.

Activities of antioxidant enzymes in two stages of pathology development in sucrose-fed rats

The activities of catalase in liver, heart and kidney as well as glutathione peroxidase and superoxide dismutase in liver, heart, kidney, and serum from hypertriglyceridemic and hypertensive female and male rats were measured at 3 and 8 months of daily administration of sucrose in their drinking water. This treatment induces high levels of serum triglycerides, central obesity, moderate hypertension, hyperinsulinemia, and an increase in lipoper oxida tion, among other alterations. The experimental periods were chosen on the basis of previous observations: at 3 months the level of serum triglycerides increases significantly above the normal value and remains without major changes thereafter, but the blood pressure only rises significantly at about 4 months in males and 5 months in females. So, at 8 months the rats have been subjected to abnormal conditions for 3–4 months. The effect of these and the influence of sex on levels of antioxidant enzymes were investigated. Both factors, sucrose treatment and sex, were conducive to significant changes in those variables.Key words: antioxidant enzymes, gender influence, hypertriglyceridemia, hypertension, sucrose-fed rats.

Dietary protein source determines the degree of hypertension and renal disease in the Dahl salt-sensitive rat

Previous studies demonstrated that a whole-grain diet attenuated sodium-dependent hypertension and renal disease in Dahl salt-sensitive rats from the colony at the Medical College of Wisconsin (Dahl SS/Mcw rats) compared with rats maintained on a purified AIN-76A diet. The present experiments determined which component(s) of the grain diet prevented renal and cardiovascular disease. Male SS/Mcw rats were maintained on isocaloric diets identical to AIN-76A, except the source of protein (wheat gluten for casein), carbohydrate (wheat flour for sucrose), or fat (soybean oil for corn oil) was substituted in separate diets. Rats were maintained on the different diets from weaning and studied after 3 weeks on a high-salt (4.0% NaCl) diet. Substitution of the carbohydrate in the diet did not affect body weight, arterial pressure, or renal disease. Replacement of casein with wheat gluten significantly reduced body weight (258+/-7 versus 353+/-3 grams), mean arterial pressure (133+/-2 versus 153+/-2 mm Hg), and albumin excretion (9+/-1 versus 50+/-7 mg/d) to levels of rats fed the whole-grain diet (n=7 to 16/group). Replacement of the fat in the diet increased arterial pressure without affecting body weight or albumin excretion. The results of the present study indicate that dietary components other than sodium play an important role in the development of hypertension and renal disease in the Dahl SS/Mcw rat.

Impairment of glucose metabolism and energy transfer in the rat heart

The metabolic pathways involved in ATP production in hypertriglyceridemic rat hearts were evaluated. Hearts from male Wistar rats with sugar-induced hypertriglyceridemia were perfused in an isolated organ system. Mechanical performance, oxygen uptake and beat rate were evaluated under perfusion with different oxidizable substrates. Age- and weight-matched animals were used as control. The hypertriglyceridemic (HTG) hearts showed a decrease in the mechanical work and slight diminution in the oxygen uptake when perfused with glucose, pyruvate or lactate. No differences were found when perfused with palmitate, octanoate or beta-hydroxybutyrate. The glycolytic flux in HTG hearts was 2.4 times lower than in control hearts. Phosphofructokinase-I (PFK-I) was 16% decreased in HTG hearts, whereas pyruvate kinase activity did not change. The increased levels of glucose-6-phosphate in HTG heart, suggested a flux limitation by the PFK-I. Pyruvate dehydrogenase in its active form (PDHa) diminished as well. The PDHa level in the HTG hearts was restored to control values by dichloroacetate; however, this addition did not significantly improve the mechanical performance. Levels of ATP and phosphocreatine as well as total creatine kinase activity and the MB fraction were significant lower in the HTG hearts perfused with glucose. The data suggested that supply of ATP by glucose oxidation did not suffice to support cardiac work in the HTG hearts; this impairment was exacerbated by the diminution of the creatine kinase system output.

Effects of fish oil on hypertension, plasma lipids, and tumor necrosis factor-α in rats with sucrose-induced metabolic syndrome

Dietary fish oil rich in (n-3) fatty acids plays an important role in reducing abnormalities associated with the metabolic syndrome and mortality from coronary heart disease. We investigated the effects of dietary fish oil on the metabolic syndrome in a high-sucrose-fed rat model. The model was achieved by the administration of 30% sucrose in drinking water in male Wistar rats during 21 weeks. After the metabolic syndrome rat model was established, fish oil was administered during 6 weeks. The metabolic syndrome rats showed significant increases in body weight, systolic blood pressure, serum insulin, total lipids, triacylglycerols, cholesterol, free fatty acids, LDL, total proteins, albumin, and serum tumor necrosis factor-alpha (TNF-alpha). They also presented abdominal and epididymal fat accumulation and fatty liver. After fish oil diet administration, metabolic syndrome rats had a significant reduction in blood pressure, serum insulin, triacylglycerols, cholesterol, free fatty acids, and total lipids, but no change was observed in TNF-alpha concentration or fat accumulation. In conclusion, fish oil reversed the alterations on metabolic parameters and blood pressure exerted by sucrose administration, although it had no effect on TNF-alpha production and adiposity. This confirms the theory that the molecular etiology of the metabolic syndrome is multifactorial, as is the effect of n-3 polyunsaturated fatty acids (PUFAs) upon it, having complex and multifaceted actions.

Influence of diet and genetics on hypertension and renal disease in Dahl salt-sensitive rats

Experiments examined the influence of diet and genetics on hypertension and renal disease in inbred Dahl salt-sensitive (SS/Mcw) rats and consomic rats in which chromosomes 16 (SS.BN16) or 18 (SS.BN18) of the normotensive Brown Norway rat were inserted into the genetic background of the SS/Mcw. Dahl SS/Mcw breeders and offspring were randomly placed on a purified AIN-76A diet or a grain-based diet, and male offspring were screened for cardiovascular and renal phenotypes following 3 wk on a 4.0% NaCl diet. High-salt arterial blood pressure (162 +/- 5 mmHg, n = 10), urinary protein excretion (147 +/- 16 mg/day, n = 14), and albumin excretion (72 +/- 9 mg/day, n = 14) were significantly elevated in the Dahl SS/Mcw maintained on the purified diet compared with rats fed the grain-based diet. Rats fed the purified diet also exhibited significantly more renal glomerular and tubular damage than rats fed the grain diet. Moreover, feeding the purified diet to the parents led to a significant increase in blood pressure in the offspring, regardless of offspring diet. Similar dietary effects were observed in SS.BN16 and SS.BN18 rats. In rats fed the purified diet, substitution of chromosomes 16 or 18 led to a significant decrease in arterial blood pressure, albumin excretion, and protein excretion compared with the SS/Mcw. Chromosomal substitution did not, however, affect albumin or protein excretion in the consomic rats compared with the SS/Mcw when the rats were maintained on the grain diet. These data demonstrate a significant influence of diet composition on salt-induced hypertension and renal disease in the Dahl SS/Mcw rat.

Effect of troglitazone on vascular and glucose metabolic actions of insulin in high-sucrose-fed rats

In rats, diets high in simple sugar induce insulin resistance and alter vascular reactivity. The present study was designed to evaluate the effects of 5 weeks treatment with troglitazone on insulin sensitivity, regional hemodynamics, and vascular responses to insulin in chow-fed and high-sucrose-fed rats. Male rats were randomly divided in 4 groups to receive a regular chow diet in the absence (group 1) or presence of troglitazone (0.2% in food; group 2), or a sucrose-enriched diet in the absence (group 3) or presence of troglitazone (group 4) for 5 weeks. The rats were instrumented with Doppler flow probes and intravascular catheters to determine blood pressure, heart rate, and regional blood flows. Insulin sensitivity was assessed by the euglycemic hyperinsulinemic clamp technique. Glucose transport activity was examined in isolated muscles. Sucrose feeding was found to induce insulin resistance and to impair the insulin-mediated skeletal muscle vasodilation. Treatment with troglitazone was found to increase whole-body insulin sensitivity in sucrose- and chow-fed rats, but had no effect on skeletal muscle glucose transport activity measured in isolated muscles from both dietary groups. Changes in regional hemodynamics were observed in both dietary cohorts treated with troglitazone, and the hindquarter vasoconstrictor response to insulin noted in sucrose-fed rats was abolished by the treatment. The vascular effects of troglitazone, and its insulin-related attenuating effects on contractile tone, could have contributed, in part, to improve insulin action on peripheral glucose disposal, presumably by improving blood flow distribution and glucose delivery.

Induction of insulin resistance by high-sucrose feeding does not raise mean arterial blood pressure but impairs haemodynamic responses to insulin in rats

1. This study was undertaken to further investigate the effects of a sucrose-enriched diet on vascular function and insulin sensitivity in rats. 2. Male Sprague-Dawley rats were randomized to receive a sucrose- or regular rat chow-diet for 4 weeks. A first group of sucrose- and chow-fed rats was instrumented with pulsed Doppler flow probes and intravascular catheters to determine blood pressure, heart rate, regional blood flows and insulin sensitivity in conscious rats. Insulin sensitivity was assessed by the euglycemic hyperinsulinemic clamp technique. Glucose transport activity was examined in isolated muscles by using the glucose analogue [(3)H]-2-deoxy-D-glucose. A second group of sucrose- and chow-fed rats was used to obtain information regarding nitric oxide synthase (NOS) isozymes protein expression in muscles, and determine endothelin content in vascular tissues isolated from both dietary groups. 3. Sucrose feeding was found to induce insulin resistance, but had no effect on resting blood pressure, heart rate, or regional haemodynamics. This insulin resistance was accompanied by alteration in the vascular responses to insulin. Insulin-mediated skeletal muscle vasodilation was impaired, whereas the mesenteric vasoconstrictor response was potentiated in sucrose-fed rats. A reduction in eNOS protein content in muscle and an increase in vascular endothelin peptide were noted in these animals. Moreover, a reduction in insulin-simulated glucose transport activity was also noted in muscles isolated from sucrose-fed rats. 4. Together these data suggest that a cluster of metabolic and haemodynamic abnormalities occur in response to the intake of simple sugars in rats.

Differential blood pressure effects of oral glucose and intravenous L-arginine in healthy lean normotensive and obese hypertensive subjects

We investigated the role of insulin and glucose in the pathophysiology of hypertension associated with obesity. The comparative effects of an oral glucose load and of an L-arginine infusion on plasma glucose, plasma insulin and blood pressures (BP) were assessed in lean normotensive and in obese hypertensive males. Oral glucose (75 g in 1-2 min) induced a small but significant lowering of BP in lean normotensives, but failed to modify BP in obese hypertensives. L-arginine infusion (30 min, 500 mg/kg total dose) reduced BP; significantly greater reductions in systolic and diastolic BP were observed in obese hypertensives than in the control group. Both oral glucose and L-arginine induced greater increases in plasma insulin in obese hypertensives than in lean normotensives. Endothelial dysfunction which accompanies the insulin resistant state of obesity, glucose intolerance and hypertension, may account for the different BP effects induced by glucose and L-arginine in obese hypertensives and lean normotensives.

Insulin resistance and upper-normal glucose levels in hypertension: a review

Reduced insulin-mediated glucose disposal, indicative of insulin resistance, has been demonstrated in lean male hypertensives both with the hyperinsulinaemic euglycaemic clamp and the insulin suppression test. In lean hypertensives, insulin resistance was not accompanied by increases in fasting plasma insulin and glucose levels; but with modest hyperglycaemia and hyperinsulinaemia after a glucose load. Population studies (no stratification) reveal that: (1) insulin sensitivities vary widely in normotensives and hypertensives, (2) there are hypertensives and normotensives with similar degrees of insulin resistance, (3) not all hypertensives are insulin resistant, and (4) insulin resistance does not contribute to the blood pressure level of the hypertensive population. In large cross-sectional studies, the clustering of obesity, dyslipidaemia and type 2 diabetes is largely responsible for the observed associations between insulin or insulin resistance and hypertension. Recent studies indicate a role of glucose in blood pressure control. Glucose has been shown to elevate blood pressure in the presence of endothelial dysfunction and glucose values in the upper-normal range have been shown to be associated with increased cardiovascular mortality. Since endothelial dysfunction is present in hypertensives, dyslipidaemic, obese and in glucose intolerant individuals, lowering of high-normal glucose levels becomes a new, additional therapeutic target in the management of these patients. Hyperglycaemia together with endothelial dysfunction may account for the increased incidence of hypertension in obesity and diabetes mellitus. Because of the strong association between insulin resistance, hyperglycaemia and endothelial dysfunction, and the clustering of risk factors in these subjects, we propose the lowering of high normal glucose levels as part of the therapeutic strategy to prevent cardiovascular and metabolic disease.