Abnormalities of carbohydrate and lipid metabolism in Dahl rats

Supplementation of amino acids and organic acids prevents the increase in blood pressure induced by high salt in Dahl salt-sensitive rats

A high-salt (HS) diet leads to metabolic disorders in Dahl salt-sensitive (SS) rats, and promotes the development of hypertension. According to the changes in the metabolites of SS rats, a set of combined dietary supplements containing amino acids and organic acids (AO) were designed. The purpose of the present study was to evaluate the effect of AO supplementation on the blood pressure of SS rats after the HS diet and clarify the mechanism of AO by metabolomics and biochemical analyses. The results showed that AO supplementation avoided the elevation of blood pressure induced by the HS diet in SS rats, increased the renal antioxidant enzyme activities (catalase, superoxide dismutase, glutathione reductase, and glutathione S-transferase), reduced the H₂O₂ and MDA levels, and restored the normal antioxidant status of the serum and kidneys. AO also reversed the decrease in the nitric oxide (NO) levels and NO synthase activity induced by the HS feed, which involved the L-arginine/NO pathway. Metabolomics analysis showed that AO administration increased the levels of amino acids such as cysteine, glycine, hypotaurine, and lysine in the renal medulla and the levels of leucine, isoleucine, and serine in the renal cortex. Of note, lysine, hypotaurine and glycine had higher metabolic centrality in the metabolic correlation network of the renal medulla after AO administration. In conclusion, AO intervention could prevent HS diet-induced hypertension in SS rats by restoring the metabolic homeostasis of the kidneys. Hence, AO has the potential to become a functional food additive to improve salt-sensitive hypertension.

Mechanisms of Sinoatrial Node Dysfunction in Heart Failure With Preserved Ejection Fraction

BACKGROUND

The ability to increase heart rate during exercise and other stressors is a key homeostatic feature of the sinoatrial node (SAN). When the physiological heart rate response is blunted, chronotropic incompetence limits exercise capacity, a common problem in patients with heart failure with preserved ejection fraction (HFpEF). Despite its clinical relevance, the mechanisms of chronotropic incompetence remain unknown.

METHODS

Dahl salt-sensitive rats fed a high-salt diet and C57Bl6 mice fed a high-fat diet and an inhibitor of constitutive nitric oxide synthase (Nω-nitro-L-arginine methyl ester [L-NAME]; 2-hit) were used as models of HFpEF. Myocardial infarction was created to induce HF with reduced ejection fraction. Rats and mice fed with a normal diet or those that had a sham surgery served as respective controls. A comprehensive characterization of SAN function and chronotropic response was conducted by in vivo, ex vivo, and single-cell electrophysiologic studies. RNA sequencing of SAN was performed to identify transcriptomic changes. Computational modeling of biophysically-detailed human HFpEF SAN was created.

RESULTS

Rats with phenotypically-verified HFpEF exhibited limited chronotropic response associated with intrinsic SAN dysfunction, including impaired β-adrenergic responsiveness and an alternating leading pacemaker within the SAN. Prolonged SAN recovery time and reduced SAN sensitivity to isoproterenol were confirmed in the 2-hit mouse model. Adenosine challenge unmasked conduction blocks within the SAN, which were associated with structural remodeling. Chronotropic incompetence and SAN dysfunction were also found in rats with HF with reduced ejection fraction. Single-cell studies and transcriptomic profiling revealed HFpEF-related alterations in both the "membrane clock" (ion channels) and the "Ca2+ clock" (spontaneous Ca2+ release events). The physiologic impairments were reproduced in silico by empirically-constrained quantitative modeling of human SAN function.

CONCLUSIONS

Chronotropic incompetence and SAN dysfunction were seen in both models of HF. We identified that intrinsic abnormalities of SAN structure and function underlie the chronotropic response in HFpEF.

High Fructose-Induced Hypertension and Renal Damage Are Exaggerated in Dahl Salt-Sensitive Rats via Renal Renin-Angiotensin System Activation

Background

High‐fructose diet (HFr) induces hypertension and renal damage. However, it has been unknown whether the HFr‐induced hypertension and renal damage are exaggerated in subjects with salt sensitivity. We tested impacts of HFr in Dahl salt‐sensitive (DS) and salt‐resistant (DR) rats.

Methods and Results

Male DS and DR rats were fed control diet or HFr (60% fructose) with normal‐salt content. After 12 weeks, plasma and urinary parameters, renal histological characteristics, and renal expression of renin‐angiotensin system components were examined. Furthermore, effects of renin‐angiotensin system inhibitors were also examined in DS rats fed the HFr. HFr elevated blood pressure in DS rats but not in DR rats. HFr increased urinary albumin and liver type fatty acid binding protein excretions in both rats, but the excretions were exaggerated in DS rats. HFr increased plasma lipids and uric acid in both rats, whereas HFr increased creatinine clearance in DS rats but not DR rats. Although HFr decreased plasma renin activity in DS rats, HFr‐induced glomerular injury, afferent arteriolar thickening, and renal interstitial fibrosis were exaggerated in DS rats. HFr increased renal expression of angiotensinogen, renin, (pro)renin receptor, angiotensin‐converting enzyme, and angiotensin II type 1 receptor in DS rat, whereas HFr increased only angiotensin‐converting enzyme expression and decreased renin and angiotensin II type 1 receptor expressions in DR rats. Enalapril and candesartan attenuated the HFr‐induced hypertension, albuminuria, glomerular hyperfiltration, and renal damage in DS rats.

Conclusion

HFr‐induced hypertension and renal damage are exaggerated in DS rats via renal renin‐angiotensin system activation, which can be controlled by renin‐angiotensin system inhibitors.

Exercise training delays renal disorders with decreasing oxidative stress and increasing production of 20-hydroxyeicosatetraenoic acid in Dahl salt-sensitive rats

OBJECTIVE

Exercise training has antihypertensive and renoprotective effects in humans and rats. However, the effects of exercise training on renal disorders that occur with salt-sensitive hypertension remains unclear. The study aim was to investigate the effects and mechanisms of exercise training on renal function in a rat model of salt-sensitive hypertension.

METHODS

Six-week-old male Dahl salt-sensitive rats were divided into normal-salt (0.6% NaCl) diet, high-salt (8% NaCl) diet, and high-salt diet with exercise training groups. The high-salt diet with exercise training group underwent daily treadmill running for 8 weeks.

RESULTS

The high-salt diet induced severe hypertension and renal dysfunction. Exercise training significantly improved high-salt diet-induced urinary protein, albumin, and L-type fatty acid-binding protein excretion, and glomerulosclerosis but not renal interstitial fibrosis without changing blood pressure. Exercise training significantly attenuated high-salt diet-induced oxidative stress in the kidneys and decreased high-salt diet-stimulated xanthine oxidoreductase activity but not nicotinamide adenine dinucleotide phosphate oxidase activity. The high-salt diet did not change urinary excretion of 20-hydroxyeicosatetraenoic acid and decreased cytochrome P450 4A protein expression in the kidneys. Exercise training increased urinary 20-hydoroxyeicosatetraenoic acid excretion and renal cytochrome P450 4A protein expression.

CONCLUSION

Exercise training improved renal disorders without lowering blood pressure in Dahl salt-sensitive rats. Exercise training also decreased oxidative stress and increased 20-hydroxyeicosatetraenoic acid production in the kidneys. These results suggest that improvements in oxidative stress and 20-hydroxyeicosatetraenoic acid production may be potential mechanisms by which exercise training improved renal disorders in Dahl salt-sensitive rats.

Temporal Expression and Cellular Localization of PAPPA2 in the Developing Kidney of Rat

PAPPA2 is a metalloproteinase which cleaves insulin-like growth factor binding protein (IGFBP)-3 and IGFBP-5, and its role in pregnancy and postnatal growth is primarily studied. Using exclusion mapping, we reported a subcongenic (26-P) rat where a 0.71-Mbp region containing the pregnancy-associated plasma protein a2 (Pappa2) allele of salt-insensitive Brown Norway (BN) was introgressed into Dahl saltsensitive (SS) genetic background, resulting in the reduction of salt sensitivity. Pappa2 was differentially expressed in the adult kidney of 26-P and SS rats. Here, the expression and cellular localization of Pappa2 in embryonic and postnatal kidneys of 26-P and SS rats were examined. Pappa2 mRNA expression was 5-fold higher in the embryonic kidney (day 20.5) of the 26-P rat compared with the SS rat. Pappa2 mRNA expression progressively increased with the development of kidney, reaching a peak at postnatal day 5 before trending downward in subsequent stages of development in both strains. At all tested time points, Pappa2 remained higher in the 26-P compared with the SS rat kidney. Immunohistochemistry studies localized PAPPA2 in the ureteric bud (UB) and distal part of S-shaped body. PAPPA2 was colocalized with IGFBP-5 in the UB and Na⁺/K⁺/2Cl^- cotransporter-stained tubules, respectively. Future studies are needed to determine the role of Pappa2 in kidney development and mechanistic pathways involved in this process.

The protective role of hawthorn fruit extract against high salt-induced hypertension in Dahl salt-sensitive rats: impact on oxidative stress and metabolic patterns

In the present study, the renal-protective effect of hawthorn fruit extract (HW) on high-salt hypertension and its effect on metabolic patterns are determined. High salt causes hypertension in Dahl salt sensitive (SS) rats, while HW can effectively attenuate high-salt induced hypertension, and, various antihypertensive ingredients of HW have also been successfully identified using GC/MS. Of note, the biochemical assay indicates that HW significantly increases the concentration of nitric oxide (NO) and decreases the concentration of H2O2 and malonaldehyde. Especially, HW increases the activities of NO synthase and catalase in the renal medulla. Simultaneously, the renal cortex and medulla, harvested from SS rats, are used to perform the metabolomics analysis, and then, 11 and 8 differential metabolites are identified in the renal medulla and cortex with the HW gavage, respectively. All differential metabolites are then used to perform the pathway enrichment analysis. The results show that many metabolic pathways are enriched in both the renal medulla and cortex, especially those in the medulla including 23 enriched pathways. Therefore, it provides evidence that HW confers an antioxidant effect on high-salt induced hypertension and dramatically alters the metabolic patterns of SS rats, and the antihypertensive ingredients of HW also further indicate that it may be used as a nutritional supplemental therapeutic drug to protect against high-salt induced hypertension in the renal medulla.

Rat Models of Metabolic Syndrome

Metabolic syndrome is a complex disorder that comprises several other complex disorders, including obesity, hypertension, dyslipidemia, and diabetes. There are several rat models that encompass component features of MetS. Some models are inbred strains selected for one or more traits underlying MetS; others are population models with genetic risk for MetS traits, are induced by environmental stressors such as diet, are spontaneous monogenic mutant models, or are congenic strains derived from a combination of these models. Together they can be studied to identify the genetic and physiological underpinnings of MetS to identify candidate genes or mechanisms for study in human MetS subjects.

Macrophage-dependent impairment of α2-adrenergic autoreceptor inhibition of Ca2+ channels in sympathetic neurons from DOCA-salt but not high-fat diet-induced hypertensive rats

DOCA-salt and obesity-related hypertension are associated with inflammation and sympathetic nervous system hyperactivity. Prejunctional α₂-adrenergic receptors (α₂ARs) provide negative feedback to norepinephrine release from sympathetic nerves through inhibition of N-type Ca²⁺ channels. Increased neuronal norepinephrine release in DOCA-salt and obesity-related hypertension occurs through impaired α₂AR signaling; however, the mechanisms involved are unclear. Mesenteric arteries are resistance arteries that receive sympathetic innervation from the superior mesenteric and celiac ganglia (SMCG). We tested the hypothesis that macrophages impair α₂AR-mediated inhibition of Ca²⁺ channels in SMCG neurons from DOCA-salt and high-fat diet (HFD)-induced hypertensive rats. Whole cell patch-clamp methods were used to record Ca²⁺ currents from SMCG neurons maintained in primary culture. We found that DOCA-salt, but not HFD-induced, hypertension caused macrophage accumulation in mesenteric arteries, increased SMCG mRNA levels of monocyte chemoattractant protein-1 and tumor necrosis factor-α, and impaired α₂AR-mediated inhibition of Ca²⁺ currents in SMCG neurons. α₂AR dysfunction did not involve changes in α₂AR expression, desensitization, or downstream signaling factors. Oxidative stress impaired α₂AR-mediated inhibition of Ca²⁺ currents in SMCG neurons and resulted in receptor internalization in human embryonic kidney-293T cells. Systemic clodronate-induced macrophage depletion preserved α₂AR function and lowered blood pressure in DOCA-salt rats. HFD caused hypertension without obesity in Sprague-Dawley rats and hypertension with obesity in Dahl salt-sensitive rats. HFD-induced hypertension was not associated with inflammation in SMCG and mesenteric arteries or α₂AR dysfunction in SMCG neurons. These results suggest that macrophage-mediated α₂AR dysfunction in the mesenteric circulation may only be relevant to mineralocorticoid-salt excess. NEW & NOTEWORTHY Here, we identify a contribution of macrophages to hypertension development through impaired α₂-adrenergic receptor (α₂AR)-mediated inhibition of sympathetic nerve terminal Ca²⁺ channels in DOCA-salt hypertensive rats. Impaired α₂AR function may involve oxidative stress-induced receptor internalization. α₂AR dysfunction may be unique to mineralocorticoid-salt excess, as it does not occur in obesity-related hypertension.

Microbiotal-Host Interactions and Hypertension

Hypertension, or elevated blood pressure (BP), has been extensively researched over decades and clearly demonstrated to be caused due to a combination of host genetic and environmental factors. Although much research remains to be conducted to pin-point the precise genetic elements on the host genome that control BP, new lines of evidence are emerging to indicate that, besides the host genome, the genomes of all indigenous commensal micro-organisms, collectively referred to as the microbial metagenome or microbiome, are important, but largely understudied, determinants of BP. Unlike the rigid host genome, the microbiome or the "second genome" can be altered by diet or microbiotal transplantation in the host. This possibility is attractive from the perspective of exploiting the microbiotal composition for clinical management of inherited hypertension. Thus, focusing on the limited current literature supporting a role for the microbiome in BP regulation, this review highlights the need to further explore the role of the co-existence of host and the microbiota as an organized biological unit called the "holobiont" in the context of BP regulation.

Null mutation of the nicotinamide adenine dinucleotide phosphate-oxidase subunit p67phox protects the Dahl-S rat from salt-induced reductions in medullary blood flow and glomerular filtration rate

Null mutations in the p67(phox) subunit of nicotinamide adenine dinucleotide phosphate-oxidase confer protection from salt sensitivity on Dahl salt-sensitive rats. Here, we track the sequential changes in medullary blood flow (MBF), glomerular filtration rate (GFR), urinary protein, and mean arterial pressure in SSp67(phox) null rats and wild-type littermates during 21 days of 4.0% NaCl high-salt (HS) diet. Optical fibers were implanted in the renal medulla and MBF was measured in conscious rats by laser Doppler flowmetry. Separate groups of rats were prepared with femoral venous catheters and GFR was measured by the transcutaneous assessment of fluorescein isothiocyanate-sinistrin disappearance curves. Mean arterial blood pressure was measured by telemetry. In wild-type rats, HS caused a rapid reduction in MBF, which was significantly lower than control values by HS day-6. Reduced MBF was associated with a progressive increase in mean arterial pressure, averaging 170±5 mm Hg by HS salt day-21. A significant reduction in GFR was evident on day-14 HS, after the onset of hypertension and reduced MBF. In contrast, HS had no significant effect on MBF in SSp67(phox) null rats and the pressor response to sodium was blunted, averaging 150±3 mm Hg on day-21 HS. GFR was maintained throughout the study and proteinuria was reduced. In summary, when p67(phox) is not functional in the salt-sensitive rats, HS does not cause reduced MBF and salt-sensitive hypertension is attenuated, and consequently renal injury is reduced and GFR is maintained.

DPP-4 inhibitor linagliptin ameliorates cardiovascular injury in salt-sensitive hypertensive rats independently of blood glucose and blood pressure

Background

It remains to be elucidated whether dipeptidylpeptidase-4 (DPP-4) inhibitor can ameliorate cardiovascular injury in salt-sensitive hypertension. The present study was undertaken to test our hypothesis that linagliptin, a DPP-4 inhibitor, administration initiated after onset of hypertension and cardiac hypertrophy can ameliorate cardiovascular injury in Dahl salt-sensitive hypertensive rats (DS rats).

Methods

High-salt loaded DS rats with established hypertension and cardiac hypertrophy were divided into two groups, and were orally given (1) vehicle or (2) linagliptin (3 mg/kg/day) once a day for 4 weeks, and cardiovascular protective effects of linagliptin in DS rats were evaluated.

Results

Linagliptin did not significantly affect blood pressure and blood glucose levels in DS rats. Linagliptin significantly lessened cardiac hypertrophy in DS rats, as estimated by cardiac weight and echocardiographic parameters. Linagliptin significantly ameliorated cardiac fibrosis, cardiac macrophage infiltration, and coronary arterial remodeling in DS rats. Furthermore, linagliptin significantly mitigated the impairment of vascular function in DS rats, as shown by the improvement of acetylcholine-induced or sodium nitroprusside-induced vascular relaxation by linagliptin. These cardiovascular protective effects of linagliptin were associated with the attenuation of oxidative stress, NADPH oxidase subunits, p67^phox and p22 ^phox, and angiotensin-converting enzyme (ACE).

Conclusions

Our results provided the experimental evidence that linagliptin treatment initiated after the appearance of hypertension and cardiac hypertrophy protected against cardiovascular injury induced by salt-sensitive hypertension, independently of blood pressure and blood glucose. These beneficial effects of linagliptin seem to be attributed to the reduction of oxidative stress and ACE.

Role of 20-HETE in the impaired myogenic and TGF responses of the Af-Art of Dahl salt-sensitive rats

The present study examined whether 20-HETE production is reduced in the renal vasculature and whether this impairs myogenic or tubuloglomerular feedback (TGF) responses of the afferent arteriole (Af-Art). The production of 20-HETE was 73% lower in renal microvessels of Dahl salt-sensitive rats (SS) rats than in SS.5(BN) rats, in which chromosome 5 from the Brown Norway (BN) rat containing the CYP4A genes was transferred into the SS genetic background. The luminal diameter of the Af-Art decreased by 14.7 ± 1.5% in SS.5(BN) rats when the perfusion pressure was increased from 60 to 120 mmHg, but it remained unaltered in SS rats. Administration of an adenosine type 1 receptor agonist (CCPA, 1 μM) reduced the diameter of the Af-Art in the SS.5(BN) rats by 44 ± 2%, whereas the diameter of the Af-Art of SS rats was unaltered. Autoregulation of renal blood flow (RBF) and glomerular capillary pressure (PGC) was significantly impaired in SS rats but was intact in SS.5(BN) rats. Administration of a 20-HETE synthesis inhibitor, HET0016 (1 μM), completely blocked the myogenic and adenosine responses in the Af-Art and autoregulation of RBF and PGC in SS.5(BN) rats, but it had no effect in SS rats. These data indicate that a deficiency in the formation of 20-HETE in renal microvessels impairs the reactivity of the Af-Art of SS rats and likely contributes to the development of hypertension induced renal injury.

Analysis of metabolites in plasma reveals distinct metabolic features between Dahl salt-sensitive rats and consomic SS.13(BN) rats

Salt-sensitive hypertension is a major risk factor for cardiovascular disorders. Our previous proteomic study revealed substantial differences in several proteins between Dahl salt-sensitive (SS) rats and salt-insensitive consomic SS.13(BN) rats. Subsequent experiments indicated a role of fumarase insufficiency in the development of hypertension in SS rats. In the present study, a global metabolic profiling study was performed using gas chromatography/mass spectrometry (GC/MS) in plasma of SS rats (n=9) and SS.13(BN) rats (n=8) on 0.4% NaCl diet, designed to gain further insights into the relationship between alterations in cellular intermediary metabolism and predisposition to hypertension. Principal component analysis of the data sets revealed a clear clustering and separation of metabolic profiles between SS rats and SS.13(BN) rats. 23 differential metabolites were identified (P<0.05). Higher levels of five TCA cycle metabolites, fumarate, cis-aconitate, isocitrate, citrate and succinate, were observed in SS rats. Pyruvate, which connects TCA cycle and glycolysis, was also increased in SS rats. Moreover, lower activity levels of fumarase, aconitase, α-ketoglutarate dehydrogenase and succinyl-CoA synthetase were detected in the heart, liver or skeletal muscles of SS rats. The distinct metabolic features in SS and SS.13(BN) rats indicate abnormalities of TCA cycle in SS rats, which may play a role in predisposing SS rats to developing salt-sensitive hypertension.

Age-dependent salt hypertension in Dahl rats: fifty years of research

Fifty years ago, Lewis K. Dahl has presented a new model of salt hypertension - salt-sensitive and salt-resistant Dahl rats. Twenty years later, John P. Rapp has published the first and so far the only comprehensive review on this rat model covering numerous aspects of pathophysiology and genetics of salt hypertension. When we summarized 25 years of our own research on Dahl/Rapp rats, we have realized the need to outline principal abnormalities of this model, to show their interactions at different levels of the organism and to highlight the ontogenetic aspects of salt hypertension development. Our attention was focused on some cellular aspects (cell membrane function, ion transport, cell calcium handling), intra- and extrarenal factors affecting renal function and/or renal injury, local and systemic effects of renin-angiotensin-aldosterone system, endothelial and smooth muscle changes responsible for abnormal vascular contraction or relaxation, altered balance between various vasoconstrictor and vasodilator systems in blood pressure maintenance as well as on the central nervous and peripheral mechanisms involved in the regulation of circulatory homeostasis. We also searched for the age-dependent impact of environmental and pharmacological interventions, which modify the development of high blood pressure and/or organ damage, if they influence the salt-sensitive organism in particular critical periods of development (developmental windows). Thus, severe self-sustaining salt hypertension in young Dahl rats is characterized by pronounced dysbalance between augmented sympathetic hyperactivity and relative nitric oxide deficiency, attenuated baroreflex as well as by a major increase of residual blood pressure indicating profound remodeling of resistance vessels. Salt hypertension development in young but not in adult Dahl rats can be attenuated by preventive increase of potassium or calcium intake. On the contrary, moderate salt hypertension in adult Dahl rats is attenuated by superoxide scavenging or endothelin-A receptor blockade which do not affect salt hypertension development in young animals.

Differential predictors of insulin resistance in nondiabetic salt-resistant and salt-sensitive subjects

We studied the characteristics of insulin resistance in 19 normotensive and 25 hypertensive subjects who underwent an acute protocol for determination of salt-sensitivity of blood pressure. Hypertensive subjects were older and more obese, with higher creatinine, lipids, and aldosterone than normotensive volunteers. They also had higher glucose and insulin levels with a marked decrease in insulin sensitivity (HOMA2-S index). Once all participants were classified into salt-sensitive (SS) and salt-resistant (SR) groups, most of these differences were no longer present. In contrast, SS had classical characteristics of this phenotype (higher percentage of blacks, suppressed plasma renin, increased aldosterone-to-renin ratio, and blunted renin and aldosterone responses to changes in salt balance). Despite similar insulin levels, HOMA2-S was significantly lower in SS than SR. Salt-loading did not change HOMA2-S in SS or SR. In contrast, salt-depletion, by significantly increasing glucose and insulin of SR, decreased their HOMA2-S to the levels observed in SS. Correlates of insulin resistance in SR included age, triglycerides, body mass index, mean arterial pressure, aldosterone, and epinephrine. However, only body mass index and aldosterone remained as significant predictors in multivariate analyses. Correlates of insulin resistance in SS were mean arterial pressure, epinephrine, and norepinephrine, all remaining as significant predictors in multivariate modeling. Our data confirm that salt-sensitivity of blood pressure is associated with insulin resistance, suggest that salt restriction may be beneficial in SS but perhaps detrimental in SR subjects, and uncover possible differences in mechanisms of insulin resistance between SS and SR, with implications for pharmacological therapy.

Rat chromosome 8 confers protection against dyslipidemia caused by a high-fat/low-carbohydrate diet

BACKGROUND/AIMS

Recent studies have highlighted the importance of gene by diet interactions in contributing to risk factors of metabolic syndrome. We used a consomic rat panel, in which a chromosome of the Brown Norway (BN) strain is introgressed onto the background of the Dahl salt-sentitive (SS) strain, to test the hypothesis that these animals will be useful for dissecting gene by diet interactions involved in metabolic syndrome.

METHODS

We placed the parental SS and BN strains on a low-fat/high-carbohydrate (LF) or high-fat/low-carbohydrate (HF) diet for 22 weeks and measured several indices of metabolic syndrome. We then investigated the effect of diet in eight consomic rat strains.

RESULTS

We show that the HF diet resulted in significantly increased levels of fasting plasma cholesterol and triglycerides in the SS strain, with no effect in the BN. Both strains responded to the HF diet with slight increases in body weight. SSBN8 was the only consomic strain that resembled that of the BN, with low levels of fasting cholesterol and triglycerides even on the HF diet.

CONCLUSIONS

These results indicate that BN chromosome 8 harbors a gene or genes that confer protection against dyslipidemia caused by the HF diet.

Antihyperglycemic, hypolipidemic and antioxidant activities of ethanolic extract of Commiphora mukul gum resin in fructose-fed male Wistar rats

High fructose feeding (66 % of fructose) induces type-2 diabetes in rats, which is associated with the insulin resistance, hyperinsulinemia, hypertriglyceridemia and oxidative stress. The present study was undertaken to evaluate the effect of ethanol extract of Commiphora mukul gum resin (CMEE) on blood glucose, plasma insulin, lipid profiles, reduced glutathione, lipid peroxidation, protein oxidation and enzymatic antioxidants like superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase, glutathione-S-transferase in fructose-induced type-2 diabetic rats. A significant gain in body weight, hyperglycemia, hyperinsulinemia, increased lipid profiles, lipid peroxidation, protein oxidation and decreased reduced glutathione, activities of enzymatic antioxidants and insulin sensitivity (increased homeostasis assessment assay) were observed in high-fructose-induced diabetic rats. The administration of CMEE (200 mg/kg/day) daily for 60 days in high-fructose-induced diabetic rats reversed the above parameters significantly. CMEE has the ability to improve insulin sensitivity and delay the development of insulin resistance, aggravate antioxidant status in diabetic rats and may be used as an adjuvant therapy for patients with insulin resistance.

Effect of A-HRS on blood pressure and metabolic alterations in fructose-induced hypertensive rats

Fructose feeding induces a rise in blood pressure in normal rats that is associated with insulin resistance, hyperinsulinemia, hyperglycaemia, hypercholesterolaemia and hypertriglyceridaemia. We have examined the effect of chronic administration of A-HRS (100 and 300 mg kg⁻¹; p.o.) isolated from Hibiscus rosa sinensis (Malvaceae) on systolic blood pressure (SBP), vascular reactivity, serum glucose, triglycerides, cholesterol, uric acid and insulin in fructose-induced hypertension model. A-HRS treatment (100 and 300 mg kg⁻¹, p.o. for 6 weeks) reduced SBP, vascular reactivity changes to catecholamines and reversed the metabolic alterations induced by fructose (10%) treatment for 6 weeks. The cumulative concentration response curve (CCRC) of angiotensin II (Ang II) was shifted towards the right in rats treated with A-HRS using an isolated strip of ascending colon. The results suggest that A-HRS could prevent the development of high-blood pressure induced by a diet rich in fructose, probably by reversing the metabolic alterations induced by fructose. In conclusion, A-HRS has an antihypertensive action in a fructose model.

The exenatide analogue AC3174 attenuates hypertension, insulin resistance, and renal dysfunction in Dahl salt-sensitive rats

Background

Activation of glucagon-like peptide-1 (GLP-1) receptors improves insulin sensitivity and induces vasodilatation and diuresis. AC3174 is a peptide analogue with pharmacologic properties similar to the GLP-1 receptor agonist, exenatide. Hypothetically, chronic AC3174 treatment could attenuate salt-induced hypertension, cardiac morbidity, insulin resistance, and renal dysfunction in Dahl salt-sensitive (DSS) rats.

Methods

DSS rats were fed low salt (LS, 0.3% NaCl) or high salt (HS, 8% NaCl) diets. HS rats were treated with vehicle, AC3174 (1.7 pmol/kg/min), or GLP-1 (25 pmol/kg/min) for 4 weeks via subcutaneous infusion. Other HS rats received captopril (150 mg/kg/day) or AC3174 plus captopril.

Results

HS rat survival was improved by all treatments except GLP-1. Systolic blood pressure (SBP) was lower in LS rats and in GLP-1, AC3174, captopril, or AC3174 plus captopril HS rats than in vehicle HS rats (p < 0.05). AC3174 plus captopril attenuated the deleterious effects of high salt on posterior wall thickness, LV mass, and the ratio of LV mass to body weight (P ≤ 0.05). In contrast, GLP-1 had no effect on these cardiovascular parameters. All treatments reduced LV wall stress. GLP-1, AC3174, captopril, or AC3174 plus captopril normalized fasting insulin and HOMA-IR (P ≤ 0.05). AC3174, captopril, or AC3174 plus captopril improved renal function (P ≤ 0.05). Renal morphology in HS rats was associated with extensive sclerosis. Monotherapy with AC3174, captopril, or GLP-1 attenuated renal damage. However, AC3174 plus captopril produced the most effective improvement.

Conclusions

Thus, AC3174 had antihypertensive, cardioprotective, insulin-sensitizing, and renoprotective effects in the DSS hypertensive rat model. Furthermore, AC3174 improved animal survival, an effect not observed with GLP-1.

Effect of high fat loading in Dahl salt-sensitive rats

Salt sensitivity of blood pressure (BP) is speculated to be a characteristic in obesity-induced hypertension. To elucidate the influence of obesity on salt-sensitive hypertension, we examined the effect of fat loading on BP, renal damage, and their progression induced by salt excess in Dahl salt-sensitive (S) rats. High fat (HF: 45% fat diet: 8 weeks) diet increased BP with greater weight gain and visceral fat accumulation than low fat (10% fat) diet. In HF-fed rats, plasma glucose, plasma insulin, and urinary catecholamine increased, and urinary protein tended to be elevated. Moreover, excessive salt (8% salt diet: 8 weeks)-induced hypertension and proteinuria was accelerated in HF-fed rats. Therefore, fat loading increased BP in Dahl S rats possibly through insulin-resistance and sympathetic excitation. Moreover, fat loading accelerated salt-induced BP elevation and renal damage, suggesting excessive intake of both fat and salt, such as a civilized diet, exert the synergic harmful effects.

Effects of a high-salt diet on adipocyte glucocorticoid receptor and 11-beta hydroxysteroid dehydrogenase 1 in salt-sensitive hypertensive rats

High-salt diets decrease insulin sensitivity in salt-sensitive hypertensive rats, and glucocorticoids promote adipocyte growth and may have pathophysiological roles in the metabolic syndrome. The aim of this study was to clarify the relationship between high-salt diet and the adipocyte glucocorticoid hormones in salt-sensitive hypertensive rats. Six-week-old Dahl salt-sensitive (DS) hypertensive rats and salt-resistant (DR) rats were fed a high-salt diet or a normal-salt diet for 4 weeks. Fasting blood glucose (FBG), serum adiponectin, plasma insulin, and corticosterone in plasma and in visceral adipose tissues, 11beta-hydroxysteroid dehydrogenase 1 (11beta-HSD1) activities in adipose tissues and glucose uptake in isolated muscle were measured. Animals underwent an oral glucose tolerance test (OGTT). The expression of mRNA for glucocorticoid receptor (GR), 11beta-HSD1 and tumor necrosis factor-alpha (TNF-alpha) in adipose tissues were measured using a real-time PCR. A high-salt diet did not influence FBG; however, decreased 2-deoxy glucose uptake and plasma insulin during OGTT in DS rats. The high-salt diet increased significantly adipose tissue corticosterone concentration and 11beta-HSD1 activities, gene expression for GR, 11beta-HSD1 and TNF-alpha in adipose tissues in DS rats compared with DR rats (p<0.05). The high-salt diet did not influence plasma corticosterone and serum adiponectin concentration in DS and DR rats. These results suggest that changes in GR and 11beta-HSD1 in adipose tissue may contribute to insulin sensitivity in salt-sensitive hypertensive rats.

Vascular insulin resistance: a potential link between cardiovascular and metabolic diseases

The physiologic actions of insulin in the vasculature serve to couple regulation of metabolic and hemodynamic homeostasis. Insulin activation of the phosphatidylinositol-3-kinase (PI3K) pathway promotes glucose uptake in insulin-responsive tissues and nitric oxide (NO) production in the endothelium. NO induces vasodilation and inhibits platelet aggregation and vascular smooth muscle cell growth. In contrast, insulin activation of the mitogen-activated protein kinase (MAPK) leads to vasoconstriction and pathologic vascular cellular growth. In states of insulin resistance, insulin activation of PI3K is selectively impaired, whereas the MAPK pathway is spared and activated normally. In the endothelium, selective impairment of insulin-mediated NO production may contribute to the development of hypertension, endothelial dysfunction, atherogenesis, and insulin resistance. This article reviews experimental and clinical data elucidating the physiologic and pathophysiologic role of insulin in the vasculature and the mechanisms contributing to the development of vascular and metabolic diseases.

Role of the IRS-1 and/or -2 in the Pathogenesis of Insulin Resistance in Dahl Salt-Sensitive (S) Rats

Insulin resistance is a common finding in hypertensive humans and animal models. The Dahl salt-sensitive (S) rat is an ideal model of genetically predetermined insulin resistance and salt-sensitive hypertension. Along the insulin signaling pathway, the insulin receptor substrates 1 and 2 (IRS-1 and -2) are important mediators of insulin signaling. IRS-1 and/or IRS-2 genetic variant(s) and/or enhanced serine phosphorylation correlate with insulin resistance. The present commentary was designed to highlight the significance of IRS-1 and/or -2 in the pathogenesis of insulin resistance. An emphasis will be given to the putative role of IRS-1 and/or -2 genetic variant(s) and serine phosphorylation in precipitating insulin resistance.

Altered hyperlipidemia, hepatic steatosis, and hepatic peroxisome proliferator-activated receptors in rats with intake of tart cherry

Elevated plasma lipids, glucose, insulin, and fatty liver are among components of metabolic syndrome, a phenotypic pattern that typically precedes the development of Type 2 diabetes. Animal studies show that intake of anthocyanins reduces hyperlipidemia, obesity, and atherosclerosis and that anthocyanin-rich extracts may exert these effects in association with altered activity of tissue peroxisome proliferator-activated receptors (PPARs). However, studies are lacking to test this correlation using physiologically relevant, whole food sources of anthocyanins. Tart cherries are a rich source of anthocyanins, and whole cherry fruit intake may also affect hyperlipidemia and/or affect tissue PPARs. This hypothesis was tested in the Dahl Salt-Sensitive rat having insulin resistance and hyperlipidemia. For 90 days, Dahl rats were pair-fed AIN-76a-based diets supplemented with either 1% (wt:wt) freeze-dried whole tart cherry or with 0.85% additional carbohydrate to match macronutrient and calorie provision. After 90 days, the cherry-enriched diet was associated with reduced fasting blood glucose, hyperlipidemia, hyperinsulinemia, and reduced fatty liver. The cherry diet was also associated with significantly enhanced hepatic PPAR-alpha mRNA, enhanced hepatic PPAR-alpha target acyl-coenzyme A oxidase mRNA and activity, and increased plasma antioxidant capacity. In conclusion, physiologically relevant tart cherry consumption reduced several phenotypic risk factors that are associated with risk for metabolic syndrome and Type 2 diabetes. Tart cherries may represent a whole food research model of the health effects of anthocyanin-rich foods and may possess nutraceutical value against risk factors for metabolic syndrome and its clinical sequelae.

Important genetic checkpoints for insulin resistance in salt-sensitive (S) Dahl rats

Despite the marked advances in research on insulin resistance (IR) in humans and animal models of insulin resistance, the mechanisms underlying high salt-induced insulin resistance remain unclear. Insulin resistance is a multifactorial disease with both genetic and environmental factors (such as high salt) involved in its pathogenesis. High salt triggers insulin resistance in genetically susceptible patients and animal models of insulin resistance. One of the mechanisms by which high salt might precipitate insulin resistance is through its ability to enhance an oxidative stress-induced inflammatory response that disrupts the insulin signaling pathway. The aim of this hypothesis is to discuss two complementary approaches to find out how high salt might interact with genetic defects along the insulin signaling and inflammatory pathways to predispose to insulin resistance in a genetically susceptible model of insulin resistance. The first approach will consist of examining variations in genes involved in the insulin signaling pathway in the Dahl S rat (an animal model of insulin resistance and salt-sensitivity) and the Dahl R rat (an animal model of insulin sensitivity and salt-resistance), and the putative cellular mechanisms responsible for the development of insulin resistance. The second approach will consist of studying the over-expressed genes along the inflammatory pathway whose respective activation might be predictive of high salt-induced insulin resistance in Dahl S rats.

Variations in genes encoding the insulin receptor substrates -1 and/or -2 (IRS-1, -2) and/or genes encoding the glucose transporter (GLUTs) proteins have been found in patients with insulin resistance. To better understand the combined contribution of excessive salt and genetic defects to the etiology of the disease, it is essential to investigate the following question:

Question 1: Do variations in genes encoding the IRS -1 and -2 and/or genes encoding the GLUTs proteins predict high salt-induced insulin resistance in Dahl S rats?

A significant amount of evidence suggested that salt-induced oxidative stress might predict an inflammatory response that upregulates mediators of inflammation such as the nuclear factor- kappa B (NF-kappa B), the tumor necrosis factor-alpha (TNF-α) and the c-Jun Terminal Kinase (JNK). These inflammatory mediators disrupt the insulin signaling pathway and predispose to insulin resistance. Therefore, the following question will be thoroughly investigated:

Question 2: Do variations in genes encoding the NF-kappa B, the TNF-α and the JNK, independently or in synergy, predict an enhanced inflammatory response and subsequent insulin resistance in Dahl S rats in excessive salt environment?

Finally, to better understand the combined role of these variations on glucose metabolism, the following question will be addressed:

Question 3: What are the functional consequences of gene variations on the rate of glucose delivery, the rate of glucose transport and the rate of glucose phosphorylation in Dahl S rats?

The general hypothesis is that "high-salt diet in combination with defects in candidate genes along the insulin signaling and inflammatory pathways predicts susceptibility to high salt-induced insulin resistance in Dahl S rats".

Evidence that the etiology of the syndrome containing type 2 diabetes mellitus results from abnormal magnesium metabolism

Evidence is reviewed supporting the presence of an inherited structural defect in the plasma membranes of somatic cells of humans who have type 2 diabetes mellitus and sodium-sensitive essential hypertension. This magnesium-binding defect (MgBD) consists of a decreased content of tightly bound Mg2+ ion in the cell membrane and limits the amount of Mg2+ that enters the cell, some of which combines with ATP4-, produced by the cell, to form MgATP2-, the currency of metabolic energy. Consequently, in both prediabetes and overt diabetes, the intracellular concentration of the interdependent Mg2+ and MgATP2- ions is significantly less than normal. These 2 ions are required as cofactors and (or) substrates for some 300 enzyme systems in human metabolism, many of which are involved with insulin. Thus the decreased activities of particular ones of these enzyme systems due to the decreased intracellular [Mg2+] and its dependent [MgATP2-] are responsible for (i) insulin resistance and (ii) decreased insulin secretion and (or) production, the 2 pathophysiological processes required for the occurrence of type 2 diabetes mellitus. These 2 processes can account for all of the morbid symptoms associated with this disease. Thus, the decreased intracellular concentration of the interdependent Mg2+ and MgATP2- ions constitutes the etiology of genetic predisposition to type 2 diabetes mellitus and can be corrected by 2 identified peptide Mg2+-binding promoters that are derived from the carboxyl terminal of the tachykinin substance P and occur in normal blood plasma. Decreased intracellular [Mg2+] and [MgATP2-] can also result from a dietary deficiency of magnesium or from an abnormal accumulation of saturated fatty acids in cell membranes, which inhibits the entrance of Mg2+ into the cell; thus it is also the etiology not only of diabetes caused by magnesium deficiency, but also of the "lipotoxic" type 2 diabetes mellitus. Although these pathologies cannot be corrected by the Mg2+-binding promoters, they can be corrected, respectively, by dietary magnesium supplementation or by exercise plus dietary caloric and lipid restriction. Theoretically, the disease syndrome containing type 2 diabetes mellitus may involve approximately 30% of the population.

Genetic and dietary salt contributors to insulin resistance in Dahl salt-sensitive (S) rats

Insulin resistance has been extensively investigated during the past decade because of its proposed role in initiating a cluster of cardiovascular risk factors including hypertension. Insulin resistance is an inherited genetic trait that precedes hypertension in Dahl salt-sensitive (S) rats, and is not present in Dahl salt-resistant (R) rats. Owing to the co-existence of insulin resistance and salt sensitivity of blood pressure in Dahl S, but not R rats, Dahl S rats are used to elucidate the role of dietary salt as a potential link in exacerbating both phenotypes (insulin resistance and salt sensitivity). In light of available data, examining the impact of dietary salt on insulin resistance in Dahl S rats in terms of salt concentration and duration of exposure helps answer the following question: What percentage of dietary salt and for what duration of exposure would we expect an enhanced insulin resistance in Dahl S rats? This commentary gathers all available research done on insulin resistance in Dahl S rats in an attempt to unravel dietary salt contribution to insulin resistance in Dahl S rats.

Effect of dietary sodium on estrogen regulation of blood pressure in Dahl salt-sensitive rats

The effects of high-sodium (HS) and normal-sodium (NS) diets on ovarian hormone modulation of mean arterial pressure (MAP) were examined in Dahl salt-resistant (DR) and salt-sensitive (DS) rats. Ovariectomy increased MAP (OVX-Sham) to a greater extent in DS rats maintained for 2 wk on a HS (22 mmHg) compared with a NS (6 mmHg) diet. Ovariectomy had no effect on MAP in DR rats on NS but did increase MAP in rats on HS (10 mmHg) diets. On HS diets, glomerular filtration rate (GFR) was 36% less in the DS-Sham than DR-Sham animals; ovariectomy increased GFR in both strains by 1.4-1.5-fold; glomerular angiotensin II type 1 receptor (AT(1)R) densities were 1.6-fold higher in the DS-Sham than in the DR-Sham group; ovariectomy increased glomerular AT(1)R densities by 1.3-fold in DR rats but had no effect in DS rats; 17beta-estradiol (E(2)) downregulated adrenal AT(1)R densities in both strains on either diet; ovariectomy reduced estrogen receptor-alpha (ER-alpha) protein expression in the renal cortex by 40-50% although renal ER-alpha expression was 34% lower in DS than in DR rats. These observed effects of gonadectomy were prevented by E(2) treatment, suggesting that E(2) deficiency mediates the effects of ovariectomy on MAP, GFR, AT(1)R densities, and renal ER-alpha protein expression. In conclusion, ovariectomy-induced increases in MAP are augmented by HS diet in both strains, and this effect is not mediated by a reduction in GFR. Aberrant renal AT(1)R regulation and reduced renal ER-alpha expression are potential contributors to the hypertensive effects of E(2) deficiency in DS rats. These findings have implications for women with salt-sensitive hypertension and women who are E(2) deficient, such as postmenopausal women.

The T8590C polymorphism of CYP4A11 and 20-hydroxyeicosatetraenoic acid in essential hypertension

A role for a deficit in transport actions of 20-hydroxyeicosatetraenoic acid (20-HETE) in hypertension is supported by the following: (1) diminished renal 20-HETE in Dahl-S rats; (2) altered salt- and furosemide-induced 20-HETE responses in salt-sensitive hypertensive subjects; and (3) increased population risk for hypertension in C allele carriers of the T8590C polymorphism of CYP4A11, which encodes an enzyme with reduced catalytic activity. We determined T8590C genotypes in 32 hypertensive subjects, 25 of whom were phenotyped for salt sensitivity of blood pressure and insulin sensitivity. Urine 20-HETE was lowest in insulin-resistant, salt-sensitive subjects (F=5.56; P<0.02). Genotypes were 13 TT, 2 CC, and 17 CT. C allele frequency was 32.8% (blacks: 38.9%; whites: 25.0%). C carriers (CC+CT) and TT subjects were similarly distributed among salt- and insulin-sensitivity phenotypes. C carriers had higher diastolic blood pressures and aldosterone:renin and waist:hip ratios but lower furosemide-induced fractional excretions of Na and K than TT. The T8590C genotype did not relate to sodium balance or pressure natriuresis. However, C carriers, compared with TT, had diminished 20-HETE responses to salt loading after adjustment for serum insulin concentration and resetting of the negative relationship between serum insulin and urine 20-HETE to a 1-microg/h lower level of 20-HETE. The effect of C was insulin independent and equipotent to 18 microU/mL of insulin (Delta20-HETE= 2.84-0.054xinsulin-0.98xC; r(2)=0.53; F=11.1; P<0.001). Hence, genetic (T8590C) and environmental (insulin) factors impair 20-HETE responses to salt in human hypertension. We propose that genotype analyses with sufficient homozygous CC will establish definitive relationships among 20-HETE, salt sensitivity of blood pressure, and insulin resistance.

Comparative genomics for detecting human disease genes

Originally, comparative genomics was geared toward defining the synteny of genes between species. As the human genome project accelerated, there was an increase in the number of tools and means to make comparisons culminating in having the genomic sequence for a large number of organisms spanning the evolutionary tree. With this level of resolution and a long history of comparative biology and comparative genetics, it is now possible to use comparative genomics to build or select better animal models and to facilitate gene discovery. Comparative genomics takes advantage of the functional genetic information from other organisms, (vertebrates and invertebrates), to apply it to the study of human physiology and disease. It allows for the identification of genes and regulatory regions, and for acquiring knowledge about gene function. In this chapter, the current state of comparative genomics and the available tools are discussed in the context of developing animal model systems that reflect the clinical picture.

Genetic and dietary interactions: role of angiotensin AT1a receptors in response to a high-fructose diet

The renin-angiotensin system (RAS) has been implicated in the cardiovascular complications of diabetes. We showed that a high-fructose diet increases blood pressure and plasma angiotensin and impairs glucose tolerance. We investigated the role of angiotensin AT(1a) receptors in the development of fructose-induced cardiovascular and metabolic dysfunction. Male angiotensin AT(1a) knockout (AT1aKO) and wild-type (AT1aWT) mice with arterial telemetric catheters were fed a standard diet or one containing 60% fructose. Fructose increased mean arterial pressure (MAP) in AT1aWT but only during the dark phase (8% increase). In AT1aKO mice, fructose unexpectedly decreased MAP, during both light and dark periods (24 and 13% decrease, respectively). Analytical methods were used to measure systolic arterial pressure (SAP) and pulse interval (PI) variability in time and frequency domains. In fructose-fed AT1aWT mice, there was an increase in SAP variance and its low-frequency (LF) domain (11 +/- 3 vs. 23 +/- 4 mmHg(2), variance, and 7 +/- 2 vs. 17 +/- 3 mmHg(2), LF, control vs. fructose, P < 0.004). There were no changes in SAP variance in AT1aKO mice. Depressor responses to alpha(1)-adrenergic blockade were augmented in fructose-fed AT1a WT compared with AT1aKO mice. Fructose inhibited glucose tolerance with a greater effect in AT1aWT mice. Fructose increased plasma cholesterol in both groups (P < 0.01) and reduced ANG II in AT1aKO mice. Results document prominent interactions between genetics and diet with data showing that in the absence of angiotensin AT(1a) receptors, a fructose diet decreased blood pressure.

Isohumulones Derived from Hops Ameliorate Renal Injury via an Anti-Oxidative Effect in Dahl Salt-Sensitive Rats

Previous studies have reported that isohumulones, the bitter compounds in beer, improve insulin resistance and hyperlipidemia in several animal models. In this study, we examined whether isohumulones ameliorate renal injury. Dahl salt-sensitive hypertensive rats were fed a low-salt diet (LS), a high-salt diet (HS) or a high-salt diet containing 0.3% isohumulones (HS+IH) for 4 weeks. Urinary nitrite/nitrate (NOx) excretion was measured at 4 weeks along with blood pressure and urinary protein excretion. Renal injury was evaluated histologically and reactive oxygen species (ROS) and nitric oxide (NO) production in the renal cortex was visualized. Oxidative stress and NO synthase (NOS) expression were evaluated by immunohistochemical staining and Western blot analysis. Mean blood pressure was significantly decreased in the HS+IH group compared with the HS group at 4 weeks (158.1+/-8.7 vs. 177.5+/-3.7 mmHg; p<0.05). Isohumulones prevented the development of proteinuria in the HS+IH group compared with the HS group at 2 weeks (61.7+/-26.8 vs. 117.2+/-9.8 mg/day; p<0.05). Glomerulosclerosis and interstitial fibrosis scores were significantly decreased in the HS+IH group compared with the HS group (0.61+/-0.11 vs. 1.55+/-0.23, 23.7+/-6.8 vs. 36.1+/-3.5%; p<0.05 for both). In the HS group, increased ROS and decreased NO were observed in glomeruli in vivo. Isohumulones reduced the ROS production, leading to the restoration of bioavailable NO. Urinary NOx excretion was significantly increased in the HS+IH group compared with the HS group. Furthermore, renal nitrotyrosine was increased in the HS group compared with the LS group, and this effect was prevented by isohumulones. Renal NOS expression did not differ among the three groups. These results suggest that isohumulones may prevent the progression of renal injury caused by hypertension via an anti-oxidative effect.

Consomic strategies to localize genomic regions related to vascular reactivity in the Dahl salt-sensitive rat

Chromosomal substitution strains afford the opportunity to discover regions of the rat genome that contain genes related to cardiovascular traits with the long-range goal of linking these genes to physiological function. PhysGen (Programs for Genomic Applications) created a consomic panel of rats derived from the introgression of a single chromosome (> or =95% of the BN chromosome, one at a time) of the Brown Norway (BN/NHsdMcwi) rat onto the homogeneous genetic background of the Dahl salt-sensitive rat (SS/JrHsdMcwi). For 3 wk before the experiment, the rats were maintained on a low-salt diet (0.4% NaCl). The dose response of aortic rings from each strain of rat to phenylephrine, acetylcholine, sodium nitroprusside, and three different levels of tissue bath hypoxia (10, 5, and 0% O2) was measured and compared with the parental SS rat. To maximize the possibility that differences among the strains would become apparent, each strain of rat including the parental SS and BN was also studied after being maintained on a high-salt diet (4.0% NaCl) for 3 wk. If the response of the aortic ring from a consomic strain to these vasoactive substances was different from that of the SS parental strain, it was concluded that the introgressed chromosome contained a gene or genes that contributed to that difference. Because the BN chromosome is removed from its native background and the SS rat loses a native chromosome, it is also necessary to consider the contribution of changes in gene-to-gene interaction.

Impact of genomics on research in the rat

The need to translate genes to function has positioned the rat as an invaluable animal model for genomic research. The significant increase in genomic resources in recent years has had an immediate functional application in the rat. Many of the resources for translational research are already in place and are ready to be combined with the years of physiological knowledge accumulated in numerous rat models, which is the subject of this perspective. Based on the successes to date and the research projects under way to further enhance the infrastructure of the rat, we also project where research in the rat will be in the near future. The impact of the rat genome project has just started, but it is an exciting time with tremendous progress.

Effects of morin on blood pressure and metabolic changes in fructose-induced hypertensive rats

High fructose (HF) feeding induces a moderate increase in blood pressure in rats, which is associated with insulin resistance, hyperinsulinemia, and hypertriglyceridemia. In the present study, we examined the chronic effect of morin, a flavonoid isolated from medicinal plants, on blood pressure, lipid profiles, and serum insulin and glucose in HF-induced hypertensive rats. Rats were divided into control group and HF-fed group during the first three weeks of experiments. Then, rats were further divided into four groups and treated for 4 more weeks as follows: 1) control group; 2) morin-treated (intraperitoneal 5 mg/kg/d) control group; 3) HF-fed group; 4) morin-treated, HF-fed group (n=8, each group). Morin-treated HF-fed group showed lower systolic blood pressure (SBP) (132.0+/-2.5 mmHg vs. 142.8+/-2.2 mmHg, p<0.05), lower serum insulin level (1.21+/-0.27 vs. 2.73+/-0.30 microIU/dl, p<0.05), and lower plasma triglycerides (47.8+/-5.0 vs. 65.5+/-5.0 mg/dl, p<0.05) than those of HF-fed group. Morin treatment also suppressed mRNA expression of endothelin-1 (ET-1) in the thoracic aorta from HF-induced hypertensive rats. Moreover, decreased renal sodium excretion in HF-induced hypertensive rats was ameliorated by morin treatment. In conclusion, the results of this study demonstrate that morin has an anti-hypertensive effect in HF-induced hypertensive rats. This effect of morin may be associated with the suppression of serum insulin and plasma triglyceride level, with the down-regulation of ET-1 in the thoracic aorta, and with the partial amelioration of renal dysfunctions in HF-induced hypertensive rats.

Transforming growth factor-beta, 20-HETE interaction, and glomerular injury in Dahl salt-sensitive rats

This study examined the role of transforming growth factor-beta (TGF-beta) in altering the glomerular permeability to albumin (P(alb)) during hypertension development in Dahl salt-sensitive (Dahl S) rats and whether TGF-beta acts by inhibiting the glomerular production of 20-HETE. The results indicate that the renal expression of TGF-beta doubles in Dahl S rats fed a high-salt diet for 7 days, and this is associated with a marked rise in P(alb) from 0.19+/-0.04 to 0.75+/-0.01 and changes in the ultrastructure of the glomerular filtration barrier. Chronic treatment of Dahl S rats with a TGF-beta neutralizing antibody prevented the increase in P(alb) and preserved the structure of glomerular capillaries. It had no effect on the rise in blood pressure produced by the high-salt diet. In other studies, preincubation of glomeruli isolated from Sprague Dawley rats with TGF-beta1 (10 ng/mL) for 15 minutes increased P(alb) from 0.01+/-0.01 to 0.60+/-0.02. This was associated with inhibition of the glomerular production of 20-HETE from 221+/-11 to 3.4+/-0.5 mug per 30 minutes per milligram of protein. Pretreatment of Sprague Dawley glomeruli with a stable analog of 20-HETE, 20-hydroxyeicosa-5(Z), 14(Z)-dienoic acid, reduced baseline P(alb) and opposed the effects of TGF-beta to increase P(alb). These studies indicate that upregulation of the glomerular formation of TGF-beta may contribute to the development of proteinuria and glomerular injury early in hypertension development in Dahl S rats by increasing P(alb) through inhibition of the glomerular production of 20-HETE.

Angiotensin II-induced hypertension in mice caused an increase in insulin secretion

OBJECTIVE AND DESIGN

Insulin action was determined in a mouse model of human hypertension via chronic angiotensin II administration followed by a glucose tolerance test.

METHODS

Angiotensin II or saline was infused systemically into mice via osmotic pump for 2 or 4 weeks. In angiotensin II-treated mice versus saline controls we compared blood pressure, blood glucose, and serum insulin concentrations during an intravenous glucose tolerance test and assessed glucose transport and insulin signaling in muscle.

RESULTS

Blood pressure increased at 2 and 4 weeks following angiotensin II treatment. Mice treated with angiotensin II for 4 weeks cleared a glucose bolus faster than mice treated with saline despite similar basal serum insulin concentrations. Upon glucose administration, the increase in serum insulin was greater in angiotensin II-treated mice, 38.8+/-6.5 pmol/l, compared to saline-treated mice, 21.8+/-2.9 pmol/l, but only at 4 weeks of angiotensin II treatment while no difference was observed at 2 weeks of angiotensin II administration. At 4 weeks of angiotensin II treatment, insulin signaling in the liver and in the skeletal muscle was not affected, since both the number of insulin receptors and phosphorylation of Akt were unchanged. Also at 4 weeks of angiotensin II treatment, ex vivo soleus muscle did not exhibit any change in basal and insulin-stimulated glucose uptake.

CONCLUSIONS

This study suggests that long-term angiotensin II treatment for 4 weeks enhances glucose-stimulated insulin secretion in mice. Angiotensin II-induced hyperinsulinemia may play a role in the development of insulin resistance in patients with hypertension.

Consomic rat model systems for physiological genomics

A consomic rat strain is one in which an entire chromosome is introgressed into the isogenic background of another inbred strain using marker-assisted selection. The development and physiological screening of two inbred consomic rat panels on two genetic backgrounds (44 strains) is well underway. Consomic strains enable one to assign traits and quantitative trait loci (QTL) to chromosomes by surveying the panel of strains with substituted chromosomes. They enable the rapid development of congenic strains over a narrow region and enable one to perform F2 linkage studies to positionally locate QTL on a single chromosome with a fixed genetic background. These rodent model systems overcome many of the problems encountered with segregating crosses where even if linkage is found, each individual in the cross is genetically unique and the combination of genes cannot be reproduced or studied in detail. For physiologists, consomics enable studies to be performed in a replicative or longitudinal manner to elucidate in greater detail the sequential expression of genes responsible for the observed phenotypes of these animals. They often provide the best available inbred control strains for physiological comparisons with the parental strains and they enable one to assess the impact of a causal gene region in a genome by allowing comparisons of the effect of replacement of a specific chromosome on a disease susceptible or a resistant genomic background. Consomic rat strains are proving to be a unique scientific resource that can greatly extend our understanding of genes and their role in the regulation of complex function and disease.

Application of chromosomal substitution techniques in gene-function discovery

A consomic rat strain is one in which an entire chromosome is introgressed into the isogenic background of another inbred strain using marker assisted selection. The development and initial physiologic screening of two inbred consomic rat panels on two genetic backgrounds (44 strains) is well underway. The primary uses of consomic strains are: (1) to assign traits and quantitative trait loci (QTL) to chromosomes by surveying the panel of strains with substituted chromosomes; (2) to rapidly develop congenic strains over a narrow region using several approaches described in this review and perform F2 linkage studies to positionally locate QTL in a fixed genetic background. In addition, consomic strains overcome many of the problems encountered with segregating crosses where, even if linkage is found, each individual in the cross is genetically unique and the combination of genes cannot be reproduced or studied in detail. Consomic strains provide greater statistical power to detect linkage than traditional F2 crosses because of their fixed genetic backgrounds, and can produce sufficient numbers of genetically identical rats to validate the relationship between a trait and a particular chromosome. These strains allow studies to be performed in a replicative or longitudinal manner to elucidate in greater detail the sequential changes responsible for the observed phenotypes of these animals, and they enable one to assess the impact of a causal gene region in a genome by allowing comparisons of the effect of replacement of a specific chromosome upon a disease susceptible or resistant genomic background. Consomics can be used to quickly develop multiple chromosome substitution models to investigate gene-gene interactions of complex traits or diseases. Finally, they often provide the best available inbred control strain for particular physiological comparisons with the inbred parental strains. Consomic rat strains are proving to be a unique scientific resource that greatly extends our understanding of genes and complex normal and pathological function.

Antihypertensive effect of glucagon-like peptide 1 in Dahl salt-sensitive rats

BACKGROUND

Dahl salt-sensitive (Dahl S) rats exhibit many phenotypic traits associated with salt-sensitive hypertension in man. Specifically, they are salt-sensitive, insulin-resistant and hyperlipidemic. They also develop endothelial dysfunction, cardiac injury and glomerulosclerosis. Insulin resistance is linked to hypertension, renal and cardiac damage and endothelial dysfunction. Thus, an agent that has diuretic action and can improve insulin resistance, like recombinant glucagon-like peptide-1(7-36)amide (rGLP-1), may have an antihypertensive effect.

OBJECTIVE

To determine whether chronic administration of rGLP-1 attenuates the development of hypertension, endothelial dysfunction and/or hypertension-induced renal and cardiac end organ damage in Dahl S rats.

METHODS

Mean arterial pressure (MAP) and urinary excretion of protein and albumin were measured in Dahl S rats before and after they were fed a 8% NaCl diet and infused with rGLP-1 (1 micro g/kg per min, i.v.) or vehicle for 14 days. At the end of the study, the degree of renal and cardiac injury was histologically assessed and endothelium-dependent relaxing function was studied using aortic rings. In other rats, the effects of rGLP-1 on sodium and water balance and plasma glucose and insulin levels for the first 3 days following a step change in sodium intake from a 0.1% NaCl diet to 7.5 mEq/day were determined.

RESULTS

rGLP-1 significantly attenuated the development of hypertension in Dahl S rats (136 +/- 7 versus 174 +/- 6 mmHg). This was associated with reduction in proteinuria (46 +/- 7 versus 128 +/- 15 mg/day) and albuminuria (46 +/- 7 versus 86 +/- 18 mg/day) and improvement of endothelial function and renal and cardiac damage. rGLP-1 markedly increased urine flow and sodium excretion for the first 3 days following elevation in sodium intake. It had no significant effects on plasma glucose and insulin concentrations.

CONCLUSION

rGLP-1 has antihypertensive and cardiac and renoprotective effects in Dahl S rats fed a high salt diet. The antihypertensive effect of rGLP-1 in Dahl S rats is due mainly to its diuretic and natriuretic effects, rather than an effect to improve insulin-resistance.

Leaf methanol extract of Bidens pilosa prevents and attenuates the hypertension induced by high-fructose diet in Wistar rats

Chronic fructose treatment in rats has repeatedly been shown to elevate blood pressure in association with insulin resistance and hyperinsulinemia. The purpose of the current study was to investigate the effect of the leaf methanol extract of Bidens pilosa on systolic blood pressure (SBP) and plasma glucose, insulin, cholesterol, triglycerides and creatinine levels in rats with fructose-induced hypertension. Wistar rats that drank a 10% fructose solution for 3-6 weeks showed significant increase not only in plasma insulin and cholesterol levels but also in SBP. B. pilosa extract was able to prevent the establishment of hypertension and lower elevated blood pressure levels. The extract also reduced the highly elevated plasma insulin levels provoked by the high fructose diet. These results suggest that the leaf methanol extract of B. pilosa exerts its antihypertensive effect in part by improving insulin sensitivity.

High-salt diet enhances insulin signaling and induces insulin resistance in Dahl salt-sensitive rats

A high-salt diet, which is known to contribute to the pathogenesis of hypertension, is also reportedly associated with insulin resistance. We investigated the effects of a high-salt diet on insulin sensitivity and insulin signaling in salt-sensitive (Dahl-S) and salt resistant (Dahl-R) strains of the Dahl rat. Evaluation of hyperinsulinemic-euglycemic clamp studies and glucose uptake into the isolated soleus muscle revealed that salt loading (8% NaCl) for 4 weeks induced hypertension and significant insulin resistance in Dahl-S rats, whereas no significant effects were observed in Dahl-R rats. Despite the presence of insulin resistance, insulin-induced tyrosine phosphorylation of the insulin receptor and insulin receptor substrates, activation of phosphatidylinositol 3-kinase, and phosphorylation of Akt were all enhanced in Dahl-S rats fed a high-salt diet. The mechanism underlying this form of insulin resistance thus differs from that previously associated with obesity and dexamethasone and is likely due to the impairment of one or more metabolic steps situated downstream of phosphatidylinositol 3-kinase and Akt activation. Interestingly, supplementation of potassium (8% KCl) ameliorated the changes in insulin sensitivity in Dahl-S rats fed a high-salt diet; this was associated with a slight but significant decrease in blood pressure. Evidence presented suggest that there is an interdependent relationship between insulin sensitivity and salt sensitivity of blood pressure in Dahl-S rats, and it is suggested that supplementing the diet with potassium may exert a protective effect against both hypertension and insulin resistance in salt-sensitive individuals.

Antihypertensive effects of Dorstenia psilurus extract in fructose-fed hyperinsulinemic, hypertensive rats

We examined the effect of methanol/methylene chloride extract of Dorstenia psilurus given by gastric intubation on systolic blood pressure, plasma glucose, insulin, cholesterol, triglycerides and creatinine in rats with fructose-induced hypertension. Male Wistar rats in groups of 6 animals each were fed fructose-rich diets or standard chow for 3 weeks and treated with 100 mg/kg/day or 200 mg/kg/day of plant extract or vehicle for 3 subsequent weeks. Systolic blood pressure was measured every three days using the indirect tail cuff method. Systolic blood pressure was higher in fructose-fed rats (142+/-2 mm Hg, p < 0.01) compared with the controls (112+/-2 mm Hg), and was lower in Dorstenia psilurus-treated groups (127+/-2 and 119+/-1 mm Hg for the dose of 100 and 200 mg/kg, respectively) compared with the fructose-fed rats. Plasma insulin, cholesterol and triglycerides were higher on the fructose-rich diet compared with the controls. Plasma insulin and cholesterol were lower in the Dorstenia psilurus-treated groups. These results suggest that, Dorstenia psilurus treatment could prevent and reverse high blood pressure induced by a diet rich in fructose probably by improvement of plasma insulin levels. The plant extract might prove useful in the treatment and/or prevention of hypertension.