Insulin resistance and blood pressure in Dahl rats and in one-kidney, one-clip hypertensive rats

Insulin Resistance and High Blood Pressure: Mechanistic Insight on the Role of the Kidney

The metabolic effects of insulin predominate in skeletal muscle, fat, and liver where the hormone binds to its receptor, thereby priming a series of cell-specific and biochemically diverse intracellular mechanisms. In the presence of a good secretory reserve in the pancreatic islets, a decrease in insulin sensitivity in the metabolic target tissues leads to compensatory hyperinsulinemia. A large body of evidence obtained in clinical and experimental studies indicates that insulin resistance and the related hyperinsulinemia are causally involved in some forms of arterial hypertension. Much of this involvement can be ascribed to the impact of insulin on renal sodium transport, although additional mechanisms might be involved. Solid evidence indicates that insulin causes sodium and water retention, and both endogenous and exogenous hyperinsulinemia have been correlated to increased blood pressure. Although important information was gathered on the cellular mechanisms that are triggered by insulin in metabolic tissues and on their abnormalities, knowledge of the insulin-related mechanisms possibly involved in blood pressure regulation is limited. In this review, we summarize the current understanding of the cellular mechanisms that are involved in the pro-hypertensive actions of insulin, focusing on the contribution of insulin to the renal regulation of sodium balance and body fluids.

Renal metabolism and hypertension

Hypertension is a leading risk factor for disease burden worldwide. The kidneys, which have a high specific metabolic rate, play an essential role in the long-term regulation of arterial blood pressure. In this review, we discuss the emerging role of renal metabolism in the development of hypertension. Renal energy and substrate metabolism is characterized by several important and, in some cases, unique features. Recent advances suggest that alterations of renal metabolism may result from genetic abnormalities or serve initially as a physiological response to environmental stressors to support tubular transport, which may ultimately affect regulatory pathways and lead to unfavorable cellular and pathophysiological consequences that contribute to the development of hypertension.

Alkali supplementation as a therapeutic in chronic kidney disease: what mediates protection?

Sodium bicarbonate (NaHCO₃) has been recognized as a possible therapy to target chronic kidney disease (CKD) progression. Several small clinical trials have demonstrated that supplementation with NaHCO₃ or other alkalizing agents slows renal functional decline in patients with CKD. While the benefits of NaHCO₃ treatment have been thought to result from restoring pH homeostasis, a number of studies have now indicated that NaHCO₃ or other alkalis may provide benefit regardless of the presence of metabolic acidosis. These data have raised questions as to how NaHCO₃ protects the kidneys. To date, the physiological mechanism(s) that mediates the reported protective effect of NaHCO₃ in CKD remain unclear. In this review, we first examine the evidence from clinical trials in support of a beneficial effect of NaHCO₃ and other alkali in slowing kidney disease progression and their relationship to acid-base status. Then, we discuss the physiological pathways that have been proposed to underlie these renoprotective effects and highlight strengths and weaknesses in the data supporting each pathway. Finally, we discuss how answering key questions regarding the physiological mechanism(s) mediating the beneficial actions of NaHCO₃ therapy in CKD is likely to be important in the design of future clinical trials. We conclude that basic research in animal models is likely to be critical in identifying the physiological mechanisms underlying the benefits of NaHCO₃ treatment in CKD. Gaining an understanding of these pathways may lead to the improved implementation of NaHCO₃ as a therapy in CKD and perhaps other disease states.

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.

Sodium bicarbonate loading limits tubular cast formation independent of glomerular injury and proteinuria in Dahl salt-sensitive rats

Sodium bicarbonate (NaHCO₃) slows the decline in kidney function in patients with chronic kidney disease (CKD), yet the mechanisms mediating this effect remain unclear. The Dahl salt-sensitive (SS) rat develops hypertension and progressive renal injury when fed a high salt diet; however, the effect of alkali loading on kidney injury has never been investigated in this model. We hypothesized that NaHCO₃ protects from the development of renal injury in Dahl salt-sensitive rats via luminal alkalization which limits the formation of tubular casts, which are a prominent pathological feature in this model. To examine this hypothesis, we determined blood pressure and renal injury responses in Dahl SS rats drinking vehicle (0.1 M NaCl) or NaHCO₃ (0.1 M) solutions as well as in Dahl SS rats lacking the voltage-gated proton channel (Hv1). We found that oral NaHCO₃ reduced tubular NH₄⁺ production, tubular cast formation, and interstitial fibrosis in rats fed a high salt diet for 2 weeks. This effect was independent of changes in blood pressure, glomerular injury, or proteinuria and did not associate with changes in renal inflammatory status. We found that null mutation of Hv1 also limited cast formation in Dahl SS rats independent of proteinuria or glomerular injury. As Hv1 is localized to the luminal membrane of TAL, our data suggest that alkalization of the luminal fluid within this segment limits cast formation in this model. Reduced cast formation, secondary to luminal alkalization within TAL segments may mediate some of the protective effects of alkali loading observed in CKD patients.

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.

Reactive oxygen species as important determinants of medullary flow, sodium excretion, and hypertension

The physiological evidence linking the production of superoxide, hydrogen peroxide, and nitric oxide in the renal medullary thick ascending limb of Henle (mTAL) to regulation of medullary blood flow, sodium homeostasis, and long-term control of blood pressure is summarized in this review. Data obtained largely from rats indicate that experimentally induced elevations of either superoxide or hydrogen peroxide in the renal medulla result in reduction of medullary blood flow, enhanced Na(+) reabsorption, and hypertension. A shift in the redox balance between nitric oxide and reactive oxygen species (ROS) is found to occur naturally in the Dahl salt-sensitive (SS) rat model, where selective reduction of ROS production in the renal medulla reduces salt-induced hypertension. Excess medullary production of ROS in SS rats emanates from the medullary thick ascending limbs of Henle [from both the mitochondria and membrane NAD(P)H oxidases] in response to increased delivery and reabsorption of excess sodium and water. There is evidence that ROS and perhaps other mediators such as ATP diffuse from the mTAL to surrounding vasa recta capillaries, resulting in medullary ischemia, which thereby contributes to hypertension.

HV1 acts as a sodium sensor and promotes superoxide production in medullary thick ascending limb of Dahl salt-sensitive rats

We previously characterized a H(+) transport pathway in medullary thick ascending limb nephron segments that when activated stimulated the production of superoxide by nicotinamide adenine dinucleotide phosphate oxidase. Importantly, the activity of this pathway was greater in Dahl salt-sensitive rats than salt-resistant (SS.13(BN)) rats, and superoxide production was enhanced in low Na(+) media. The goal of this study was to determine the molecular identity of this pathway and its relationship to Na(+). We hypothesized that the voltage-gated proton channel, HV1, was the source of superoxide-stimulating H(+) currents. To test this hypothesis, we developed HV1(-/-) null mutant rats on the Dahl salt-sensitive rat genetic background using zinc-finger nuclease gene targeting. HV1 could be detected in medullary thick limb from wild-type rats. Intracellular acidification using an NH4Cl prepulse in 0 sodium/BaCl2 containing media resulted in superoxide production in thick limb from wild-type but not HV1(-/-) rats (P<0.05) and more rapid recovery of intracellular pH in wild-type rats (ΔpHI 0.005 versus 0.002 U/s, P=0.046, respectively). Superoxide production was enhanced by low intracellular sodium (<10 mmol/L) in both thick limb and peritoneal macrophages only when HV1 was present. When fed a high-salt diet, blood pressure, outer medullary renal injury (tubular casts), and oxidative stress (4-hydroxynonenal staining) were significantly reduced in HV1(-/-) rats compared with wild-type Dahl salt-sensitive rats. We conclude that HV1 is expressed in medullary thick ascending limb and promotes superoxide production in this segment when intracellular Na(+) is low. HV1 contributes to the development of hypertension and renal disease in Dahl salt-sensitive rats.

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.

Regulation of ENaC in mice lacking renal insulin receptors in the collecting duct

The epithelial sodium channel (ENaC) is one of the central effectors involved in regulation of salt and water homeostasis in the kidney. To study mechanisms of ENaC regulation, we generated knockout mice lacking the insulin receptor (InsR KO) specifically in the collecting duct principal cells. Single-channel analysis in freshly isolated split-open tubules demonstrated that the InsR-KO mice have significantly lower ENaC activity compared to their wild-type (C57BL/6J) littermates when animals were fed either normal or sodium-deficient diets. Immunohistochemical and Western blot assays demonstrated no significant changes in expression of ENaC subunits in InsR-KO mice compared to wild-type littermates. Insulin treatment caused greater ENaC activity in split-open tubules isolated from wild-type mice but did not have this effect in the InsR-KO mice. Thus, these results suggest that insulin increases ENaC activity via its own receptor affecting the channel open probability. To further determine the mechanism of the action of insulin on ENaC, we used mouse mpkCCDc14 principal cells. Insulin significantly augmented amiloride-sensitive transepithelial flux in these cells. Pretreatment of the mpkCCDc14 cells with phosphatidylinositol 3-kinase (LY294002; 10 μM) or mTOR (PP242; 100 nM) inhibitors precluded this effect. This study provides new information about the importance of insulin receptors expressed in collecting duct principal cells for ENaC activity.

High dietary salt does not significantly affect plasma 25-hydroxyvitamin D concentrations of Sprague Dawley rats

BACKGROUND

The Dahl salt-sensitive rat, but not the Dahl salt-resistant rat, develops hypertension and hypovitaminosis D when fed a high salt diet. Since the salt-sensitive rat and salt-resistant rat were bred from the Sprague Dawley rat, the aim of this research was to test the hypothesis that salt-resistant and Sprague Dawley rats would be similar in their vitamin D endocrine system response to high salt intake.

FINDINGS

Sprague Dawley, salt-sensitive, and salt-resistant rats were fed high (80 g/kg, 8%) or low (3 g/kg, 3%) salt diets for three weeks. The blood pressure of Sprague Dawley rats increased from baseline to week 3 during both high and low salt intake and the mean blood pressure at week 3 of high salt intake was higher than that at week 3 of low salt intake (P < 0.05). Mean plasma 25-hydroxyvitamin D concentrations (marker of vitamin D status) of Sprague Dawley, salt-sensitive, and salt-resistant rats were similar at week 3 of low salt intake. Mean plasma 25-hydroxyvitamin D concentrations of Sprague Dawley and salt-resistant rats were unaffected by high salt intake, whereas the mean plasma 25-hydroxyvitamin D concentration of salt-sensitive rats at week 3 of high salt intake was only 20% of that at week 3 of low salt intake.

CONCLUSIONS

These data indicate that the effect of high salt intake on the vitamin D endocrine system of Sprague Dawley rats at week 3 was similar to that of salt-resistant rats. The salt-sensitive rat, thus, appears to be a more appropriate model than the Sprague Dawley rat for assessing possible effects of salt-sensitivity on vitamin D status of humans.

The fructose-fed rat: a review on the mechanisms of fructose-induced insulin resistance and hypertension

The metabolic syndrome is an important public health concern that predisposes individuals to the development of cardiovascular disease and/or Type 2 diabetes. The fructose-fed rat is an animal model of acquired systolic hypertension that displays numerous features of the metabolic syndrome. This animal model is used to study the relationship between insulin resistance/compensatory hyperinsulinemia and the development of hypertension. Several mechanisms have been proposed to mediate the link between insulin resistance and hypertension. In this review, we have addressed the role of sympathetic nervous system overactivation, increased production of vasoconstrictors, such as endothelin-1 and angiotensin II, and prostanoids in the development of hypertension in fructose-fed rats. The roles of nitric oxide, impaired endothelium-dependent relaxation and sex hormones in the pathogenesis of the fructose-fed induced hypertensive rats have also been highlighted. More recently, increased formation of reactive oxygen species and elevated levels of uric acid have been reported to contribute to fructose-induced hypertension.

Role of angiotensin II and oxidative stress in vascular insulin resistance linked to hypertension

Insulin activation of the phosphatidylinositol 3-kinase (PI3K) pathway stimulates glucose uptake in peripheral tissues and synthesis of nitric oxide (NO) in the endothelium. Insulin resistance (IR) and hypertension frequently coexist, particularly among individuals with salt-sensitive hypertension. The mechanisms underlying this association are poorly understood. We investigated these mechanisms in a model of salt-sensitive hypertension in which we have previously shown that endothelial dysfunction is mediated by superoxide anion (O(2)(-)) linked to local ANG II. Dahl salt-sensitive rats were fed, for 6 wk, a normal salt diet (NS; 0.5% NaCl), high-salt diet (HS; 4% NaCl), HS plus the ANG II type 1 receptor (AT(1)R) blocker (ARB) candesartan (10 mg.kg(-1).day(-1)), or HS plus the antioxidant tempol (172 mg/l in drinking water). Hypertensive (mean arterial pressure: 145 +/- 4 vs. 102 +/- 5 mmHg in NS, P < 0.05) rats manifested increased aortic AT(1)R mRNA (210%) and protein (101%) expression and O(2)(-) production (104%) and impaired endothelium-dependent relaxation (EDR) to acetylcholine [maximal response (E(max)): 68 +/- 9 vs. 91 +/- 8% in NS, P < 0.05]. ARB or tempol normalized O(2)(-) and EDR despite that they did not normalize mean arterial pressure, which was reduced only 25%. Hypertensive rats manifested metabolic IR (36% reduction in the glucose infusion rate by insulin clamp), impaired NO-mediated insulin-induced EDR (E(max): 12 +/- 5 vs. 32 +/- 4% in NS, P < 0.05), and impaired insulin activation of PI3K/endothelial NO synthase. ARB or tempol improved insulin-mediated EDR, PI3K, Akt/ endothelial NO synthase phosphorylation, and metabolic IR (all P < 0.05). This study provides insight into the mechanisms that underlie the association between metabolic and hypertensive cardiovascular diseases and support the notion that O(2)(-) overproduction linked to tissue ANG II interferes with shared insulin signaling pathways in metabolic and cardiovascular tissues.

Multiple blood pressure loci on rat chromosome 13 attenuate development of hypertension in the Dahl S hypertensive rat

Previous studies have indicated that substitution of chromosome 13 of the salt-resistant Brown Norway BN/SsNHsdMcwi (BN) rat into the genomic background of the Dahl salt-sensitive SS/JrHsdMcwi (SS) rat attenuates the development of salt-sensitive hypertension and renal damage. To identify the regions within chromosome 13 that attenuate the development of hypertension during a high-salt diet in the SS rat, we phenotyped a series of overlapping congenic lines covering chromosome 13, generated from an intercross between the consomic SS-13BN rat and the SS rat. Blood pressure was determined in chronically catheterized rats after 2 wk of high-salt diet (8% NaCl) together with microalbuminuria as an index of renal damage. Four discrete regions were identified, ranging in size from 4.5 to 16 Mbp, each of which independently provided significant protection from hypertension during high-salt diet, reducing blood pressure by 20–29 mmHg. Protection was more robust in female than male rats in some of the congenic strains, suggesting a sex interaction with some of the genes determining blood pressure during high-salt diet. Among the 23 congenic strains, several regions overlapped. When three of the “protective” regions were combined onto one broad congenic strain, no summation effect was seen, obtaining the same decrease in blood pressure as with each one independently. We conclude from these studies that there are four regions within chromosome 13 containing genes that interact epistatically and influence arterial pressure.

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.

Salt-induced hypertension in WKY rats: prevention by alpha-lipoic acid supplementation

There is strong evidence that points to excess dietary salt as a major factor contributing to the development of hypertension. Salt sensitivity is associated with glucose intolerance and insulin resistance in both animal models and humans. In insulin resistance, impaired glucose metabolism leads to elevated endogenous aldehydes which bind to vascular calcium channels, increasing cytosolic [Ca2+]i and blood pressure. In an insulin resistant animal model of hypertension, spontaneously hypertensive rats (SHRs), dietary supplementation with lipoic acid lowers tissue aldehydes and plasma insulin levels and normalizes blood pressure. The objective of this study is to examine the effects of a high salt diet on tissue aldehydes, cytosolic [Ca2+]i and blood pressure in WKY rats and to investigate whether dietary supplementation with lipoic acid can prevent a salt induced increase in blood pressure. Starting at 7 weeks of age, WKY rats were divided into three groups of six animals each and treated for 10 weeks with diets as follows: WKY-normal salt (0.7% NaCl); WKY-high salt (8% NaCl); WKY-high salt + lipoic acid (8% NaCl diet + lipoic acid 500 mg/Kg feed). At completion, animals in the high salt group had elevated systolic blood pressure, platelet [Ca2+]i, and tissue aldehyde conjugates compared with the normal salt group and showed smooth muscle cell hyperplasia in the small arteries and arterioles of the kidneys. Dietary alpha-lipoic acid supplementation in high salt-treated WKY rats normalized systolic blood pressure and cytosolic [Ca2+]i and aldehydes in liver and aorta. Kidney aldehydes and renal vascular changes were attenuated, but not normalized.

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.

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.

Role of aldehydes in fructose induced hypertension

Aldehydes are formed in tissues of humans and animals as intermediates of glucose and fructose metabolism and due to lipid peroxidation. N-acetyl cysteine (NAC), an analogue of the dietary amino acid cysteine, binds aldehydes thus preventing their damaging effect on physiological proteins. We measured systolic blood pressure (SBP), platelet cytosolic free calcium [Ca2+]i and tissue aldehyde conjugates in fructose induced hypertensive Wistar-Kyoto (WKY) rats and examined the effect of NAC in the diet on these parameters. Animals age 7 weeks were divided into three groups of 6 animals each and were treated as follows: WKY-control (chow diet and normal drinking water); WKY-Fructose (chow diet and 4% fructose in drinking water); WKY-Fructose+NAC (1.5% NAC in chow diet and 4% fructose in drinking water). After 11 weeks, systolic blood pressure, platelet [Ca2+]i and kidney aldehyde conjugates were all significantly higher in fructose treated rats. NAC treatment prevented these changes. These results suggest that aldehydes may be the cause of fructose induced hypertension and elevated cytosolic free calcium.

Insulin resistance and risk factors for coronary heart disease

In this presentation an effort has been made to review the impact of resistance to insulin-mediated glucose uptake and/or hyperinsulinaemia on various metabolic end-points and clinical syndromes. Insulin resistance is present in the great majority of patients with states of glucose intolerance, but frank decompensation of glucose homoeostasis does not occur if individuals can maintain a state of compensatory hyperinsulinaemia. Although compensatory hyperinsulinaemia may prevent the development of NIDDM in insulin-resistant individuals, there is substantial evidence that insulin resistance and/or hyperinsulinaemia is associated with higher plasma concentrations of triglyceride, uric acid and plasminogen activator inhibitor 1 and with lower HDL cholesterol concentrations. Obesity, decreased physical activity and possibly cigarette smoking accentuate the degree of insulin resistance and its manifestations, and a genetic basis is also involved. Resistance to insulin-mediated glucose uptake and/or hyperinsulinaemia have been shown to be associated with high blood pressure, microvascular angina and CHD. Thus, resistance to insulin-mediated glucose uptake is a common phenomenon, which makes a major contribution to the aetiology and clinical course of common and serious diseases. Based on the above considerations, it is difficult to over-emphasize the health-related implication of a defect in insulin-mediated glucose uptake.

Angiotensin II increases glucose utilization during acute hyperinsulinemia via a hemodynamic mechanism

To determine whether hemodynamic changes can modulate insulin action in vivo, we administered angiotensin II (AII) to normal men under three separate, euglycemic conditions. First, in the presence of physiological hyperinsulinemia (approximately 115 microU/ml), infusion of AII at rates of 2, 10, and 20 ng/min per kg caused significant elevations of blood pressure, whole-body glucose clearance, and plasma insulin concentrations in an AII dose-dependent manner. Second, in the presence of plasma insulin concentrations that stimulate glucose transport maximally (approximately 5,000 microU/ml), AII infusions increased whole-body glucose clearance without enhancing glucose extraction across the leg. Third, in the presence of basal insulin concentrations (approximately 13 microU/ml), AII infusions had no effect on whole-body glucose turnover or leg glucose extraction. Thus, AII enhanced whole-body glucose utilization without directly stimulating glucose transport in a major skeletal muscle bed. To evaluate a possible hemodynamic mechanism for the effects of AII on glucose utilization, we measured blood flow to two areas that differ in their sensitivity to insulin: the kidneys and the leg. We found that AII redistributed blood flow away from the predominantly insulin-independent tissues of the kidney and toward the insulin-sensitive tissues of the leg during both sham and hyperinsulinemic glucose clamps. The redistribution of flow had no effect on whole-body glucose turnover when leg glucose uptake was unstimulated (sham clamps). However, when leg glucose uptake was activated by insulin, the redistribution of flow caused a net increase in whole-body glucose utilization. Our findings indicate that hemodynamic factors can modulate insulin action in vivo. Furthermore, our results suggest that variable activity of the renin-angiotensin system may contribute to inconsistencies in the association between insulin resistance and hypertension.