SHR/NDmcr-cp Research Articles

Abstract P171: Comparison Of Modulation Of Renal Arterial Tone By Perivascular Adipose Tissue Between Two Animal Models Of Metabolic Syndrome

Sex differences have recently been noticed in the regulation of arterial tone by perivascular adipose tissue (PVAT). In SHRSP.Z- Lepr fa /IzmDmcr (SHRSP.ZF) rats, an animal model of metabolic syndrome (MetS), we demonstrated that mesenteric and renal PVAT in female rats consistently have an enhancing effect on vasodilation at 23 weeks, an age by which the effect of PVAT is impaired in the male rats. This could explain the sex differences in the prevalence of cardiovascular complications in patients with MetS. Therefore, we determined whether the sex difference in PVAT response also occurs in another animal model of MetS, SHR/NDmcr-cp (SHR-cp) rats.Renal arteries were isolated from male and female 23-week-old SHR-cp rats, and ring preparations with and without PVAT were made. After a stable contraction was obtained by phenylephrine administration, vasodilation in response to acetylcholine was examined using organ bath methods.Vasodilation in arteries without PVAT from female rats was smaller than that in arteries without PVAT from male rats, and presence of PVAT in arteries from female rats increased vasodilation to the same level as that observed in arteries without PVAT from male rats. Furthermore, renal PVAT in male rats was shown to have an enhancing effect on vasodilation.The present study did not identify sex differences in renal PVAT-mediated modulation in SHR-cp rats because the enhancing effects of PVAT did not disappear in male SHR-cp rats, in contrast to that observed in male SHRSP.ZF rats at the same age. The difference in PVAT response in male rats between two MetS models may be due to differences in the severity of MetS symptoms, especially blood pressure, between the models.

Abstract 222: Impairment of Autonomic Function and Increased Aldosterone in Metabolic Syndrome Model Rats Mediates Circadian Blood Pressure Rhythms

[Aim] Metabolic syndrome (MetS) is significantly associated with abnormal blood pressure (BP) circadian rhythms, although the underlying mechanism(s) is unclear. Using SHR/NDmcr-cp (SHRcp), manifesting with hypertension, obesity, insulin resistance and dyslipidemia, we examined the mechanisms underlying abnormal circadian rhythms of BP in MetS. [Methods] (1)We surgically implanted telemetry devices in control SHR and SHRcp to monitor BP continuously. We performed a cross-spectral analysis, using a fast Fourier transformation algorithm, of arterial pulse waves to determine autonomic function and baroreceptor reflex function. Urine samples in dark (active) phase and light (inactive) phase were collected with metabolic cages to measure factors associated with blood pressure control. (2)SHRcp were orally administered azilsartan (1mg/kg/day), an AT1 receptor blocker, once daily at the beginning of the active phase, to examine the effects of azilsartan on the above mentioned parameters. [Results] (1)SHRcp exhibited non-dipper type hypertension, although SHR exhibited dipper-type hypertension. Compared with SHR, SHRcp showed an increased low frequency (LF) power of sBP and a decreased spontaneous baroreceptor reflex gain (sBRG). Thus, SHRcp was characterized by enhanced vascular sympathetic tone and impaired baroreflex function 24 hrs a day. Urine norepinephrine(NE) and aldosterone excretion levels were greater in SHRcp over 24 hrs than in SHR. (2)Azilsartan treatment once daily normalized BP in SHRcp over 24 hrs. Azilsartan had a greater hypotensive effect in SHRcp than in SHR, thus indicating the key role of hypertension in SHRcp. Azilsartan decreased LF of sBP, increased sBRG, and reduced urinary NE excretion levels in SHRcp. Azilsartan also reduced urinary aldosterone excretion over 24 hrs and serum aldosterone concentration, thus increasing urinary sodium excretion in SHRcp. [Conclusion] SHRcp, a model of MetS,exhibit non-dipper type hypertension, and thus they are suitable models for studying abnormal BP circadian rhythms. The mechanism of abnormal BP circadian rhythm in SHRcp was attributed to an impaired autonomic nervous system and aldosterone-induced sodium retention, which were both mediated by AT1 receptor.

Serial changes in adipocytokines and cardiac function in a rat model of the metabolic syndrome

Obesity is associated with high chronic cardiac workload due to the need to supply more blood to peripheral tissue, and frequently leads to left ventricular (LV) dysfunction. The present study examined serial changes in cardiac function in the SHR/NDmcr-cp (SHR/cp) strain, an experimental model of obesity plus hypertension and metabolic syndrome. Transthoracic echocardiography was used to define cardiac dimensions and function in male spontaneously hypertensive rats (SHR/lean), SHR/cp and Wistar-Kyoto rats. We also assessed age-related changes in plasma and LV adipocytokine levels in this model. Although there were no significant differences in LV end-diastolic diameter and end-systolic diameter among the three rat strains until 24weeks of age, these parameters were significantly higher and LV fractional shortening (%FS) was significantly lower in SHR/cp compared with SHR/lean at 32weeks of age. At the same age, pronounced interstitial fibrosis and infiltration of macrophages and T lymphocytes into the LV was noted in SHR/cp relative to the other strains. In the myocardium, adiponectin levels were significantly lower and resistin levels and the expression of proinflammatory cytokines (tumour necrosis factor-α and interleukin-6) were significantly higher in SHR/cp than SHR/lean at 32weeks of age. Using echocardiography, we demonstrated reduced systolic function in 32-week-old SHR/cp. Changes in myocardial cytokine concentrations could be involved in worsening of cardiac function in our animal model of metabolic syndrome.

Chronic Inhibition of 11β-Hydroxysteroid Dehydrogenase Type 1 Activity Decreases Hypertension, Insulin Resistance, and Hypertriglyceridemia in Metabolic Syndrome

Metabolic syndrome is a constellation of risk factors including hypertension, dyslipidemia, insulin resistance, and obesity that promote the development of cardiovascular disease. Metabolic syndrome has been associated with changes in the secretion or metabolism of glucocorticoids, which have important functions in adipose, liver, kidney, and vasculature. Tissue concentrations of the active glucocorticoid cortisol are controlled by the conversion of cortisone to cortisol by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). Because of the various cardiovascular and metabolic activities of glucocorticoids, we tested the hypothesis that 11β-HSD1 is a common mechanism in the hypertension, dyslipidemia, and insulin resistance in metabolic syndrome. In obese and lean SHR/NDmcr-cp (SHR-cp), cardiovascular, metabolic, and renal functions were measured before and during four weeks of administration of vehicle or compound 11 (10 mg/kg/d), a selective inhibitor of 11β-HSD1. Compound 11 significantly decreased 11β-HSD1 activity in adipose tissue and liver of SHR-cp. In obese SHR-cp, compound 11 significantly decreased mean arterial pressure, glucose intolerance, insulin resistance, hypertriglyceridemia, and plasma renin activity with no effect on heart rate, body weight gain, or microalbuminuria. These results suggest that 11β-HSD1 activity in liver and adipose tissue is a common mediator of hypertension, hypertriglyceridemia, glucose intolerance, and insulin resistance in metabolic syndrome.

Effects of Liver Hydrolysate on the Blood Glucose in Metabolic Syndrome Model Rats (SHR/NDmcr-cp)

Insulin resistance associated with visceral fat obesity has been suggested to be the pathological basis of metabolic syndrome. Many studies have demonstrated increased oxidant stress in diabetic patients and animal models of diabetes mellitus. In this study, the effect of liver hydrolysate administration on the blood glucose was examined in SHR/NDmcr-cp (SHR-cp) rats that show spontaneously occurring metabolic syndrome-like abnormalities. The SHR-cp rats were fed diets containing 5% liver hydrolysate for 12 weeks, and the fasting blood glucose and HbA1c were determined every 3 weeks. After administration of the liver hydrolysate-containing feed for 12 weeks, an oral glucose tolerance test was conducted and the plasma angiotensin II (AngII) concentrations were determined. The liver hydrolysate administration had no effect on the blood insulin levels in the oral glucose tolerance test, but significantly inhibited the d-glucose-induced increases of the blood glucose levels. Furthermore, the liver hydrolysate had almost no effect on the fasting blood glucose level, but tended to inhibit the increase of HbA1c. The plasma AngII concentration after the 12-week administration of liver hydrolysate remained significantly lower than that in the control group. These results indicate that a component of liver hydrolysate inhibits d-glucose-induced increase of the blood glucose level, and may improve insulin resistance. The angiotensin converting enzyme (ACE)-inhibiting effect and antioxidant effect of liver hydrolysate may be involved in this effect.

Diet modification and its influence on metabolic and related pathological alterations in the SHR/NDmcr-cp rat, an animal model of the metabolic syndrome

SHR/NDmcr-cp (SHR/NDcp) rats, which carry a nonsense mutation of the leptin receptor gene, are known to spontaneously develop hypertension, obesity and hyperlipidemia, and have therefore found use as an animal model of the metabolic syndrome and type 2 diabetes. However, some recent studies on SHR/NDcp rats revealed only mild elevation of blood glucose levels. To investigate whether metabolic factors including blood glucose and histopathological alterations of SHR/NDcp rats deteriorate with a diabetogenic diet, biochemical and histopathological examinations were conducted with animals fed normal or diabetogenic diets for 20 weeks. SHR/NDcp rats receiving the normal diet displayed obesity, hypertension, hyperlipidemia, and mild elevation of blood glucose and HbA1c levels. Urinary glucose excretion was noted in only 1 out of 6 animals. Histologically, macro- and micro-vesicular steatosis in the liver, glomerular and tubular damages in the kidney and islet hyperplasia mainly of beta cells in the pancreas were characteristically noted. In SHR/NDcp rats fed the diabetogenic diet, obesity was more severe, with higher blood glucose and HbA1c levels, increased numbers of animals with urinary glucose excretion, and more pronounced hepatic steatosis and renal tubular changes. However, elevation of blood glucose levels and urinary glucose excretion proved transient. These observations indicate that the diabetic state and associated histopathological alterations in SHR/NDcp rats are exacerbated by feeding a diabetogenic diet, but the effects are limited. Elevated islet function with compensative insulin secretion might be related to amelioration of the hyperglycemic state. Further diet modification could be needed to induce a more prominent and persistent diabetic state in SHR/NDcp rats.

Beneficial Effect of Coenzyme Q10 on Increased Oxidative and Nitrative Stress and Inflammation and Individual Metabolic Components Developing in a Rat Model of Metabolic Syndrome

Metabolic syndrome (MetS) is a group of cardiovascular risk factors, including visceral obesity, glucose intolerance, hypertension, and dyslipidemia. Increased oxidative and nitrative stress and inflammation and decreased endothelial function occur in an animal model of metabolic syndrome, SHR/NDmcr-cp (SHR/cp) rats. The present study investigated the effects of coenzyme Q10 (CoQ10), one of the important antioxidants, on the abnormal oxidative condition and characteristic components of metabolic syndrome in SHR/cp rats by maintaining them on a diet supplemented with 0.07% – 0.7% CoQ10 for 26 weeks. We determined serum levels of oxidatively modified low-density lipoprotein (Ox-LDL) and 8-hydroxy-2’-deoxyguanosine (8-OHdG) as oxidative stress markers, 3-nitrotyrosine as a nitrative stress marker, 3-chlorotyrosine as a marker of myeloperoxidase (MPO)-catalyzed oxidation and high-sensitivity C-reactive protein (hsCRP) as an inflammatory marker. The administration of CoQ10 significantly attenuated the increase of oxidative and nitrative stress markers and inflammatory markers in a dose-dependent manner. CoQ10 prevented the elevated serum insulin levels, although it did not affect the elevated glucose level and dyslipidemia. CoQ10 also reduced elevated blood pressure, but did not affect body weight gain. In addition, CoQ10 improved endothelial dysfunction in the mesenteric arteries. These findings suggest that the antioxidant properties of CoQ10 can be effective for ameliorating cardiovascular risk in MetS.

Peroxynitrite is Involved in the Dysfunction of Vasorelaxation in SHR/NDmcr-cp Rats, Spontaneously Hypertensive Obese Rats

SHR/NDmcr-cp (SHR-cp) rats display typical symptoms and features of the metabolic syndrome. We previously reported that endothelium-dependent relaxation decreases in the thoracic aortas of SHR-cp rats, despite increased nitric oxide (NO) production from the endothelium. In the present study, to search for the reasons for this contradiction, we investigated whether vascular abnormality could be reduced by treatment of SHR-cp rats with antihypertensive drugs; a calcium channel blocker (amlodipine), an alpha 2 and imidazoline receptor agonist (moxonidine), and an angiotensin II type 1 (AT1) receptor antagonist (telmisartan). Telmisartan but not amlodipine and moxonidine ameliorated the impairment of relaxation in response to acetylcholine and the increased protein expression of endothelium NO synthase in thoracic aortas. All three drugs significantly lowered the blood pressure. Telmisartan decreased the serum levels of lipid peroxide and 8-hydroxy-2'-deoxyguanosine, oxidative stress markers, and also the aortic levels of the protein expression of gp91, a component of NADPH oxidase, and 3-nitrotyrosine, a biomarker of peroxynitrite. These findings suggest that NADPH oxidase-derived superoxide, probably produced due to stimulation of AT1 receptors, reacts with NO to form peroxynitrite, and consequently decreases active NO, leading to attenuation of endothelium-dependent relaxation. Angiotensin receptor antagonists may be effective for preventing endothelial dysfunction in metabolic syndrome.

MECHANICAL BONE PROPERTIES OF OBESE MODEL SHR/NDmcr‐cp RATS

SUMMARY 1 High-blood pressure or diabetes may be related to the loss of bone mass or the development of osteoporosis. We examined the mechanical bone properties of the SHR/NDmcr-cp (SHR-cp) rat, an obese strain that develops hypertension, hyperlipidaemia and insulin-independent diabetes. 2 The mechanical properties of the femur of 22-week-old Wistar-Kyoto (WKY) and SHR-cp rats were measured by Peng's three-point bending procedure modified by Shintani. Femurs were then defatted and dried. After weighing, the dried bones were ashed and the ash was weighed. The values of the dry weight, ash weight and ash weight/dry weight (%) were used as a description of the physical parameters of the bone. 3 All values of stiffness, strength, toughness and ductility in SHR-cp were significantly lower than those of WKY rats (P < 0.05). The value of ash weight/dry weight (%) was lower in SHR-cp rats (P < 0.01). These results showed that bone fragility was greater in SHR-cp rats, indicative of osteopenia.

ABNORMALITIES OF NITRIC OXIDE‐MEDIATED VASORELAXATION IN A RAT MODEL OF METABOLIC SYNDROME: INVOLVEMENT OF PEROXYNITRITE FORMATION

SUMMARY 1 We reported previously that nitric oxide (NO)-mediated relaxation is impaired, despite an increase in NO production from the endothelium, in the thoracic aorta of SHR/NDmcr-cp (SHR-cp) rats, an animal model of the metabolic syndrome. In the present study, we investigated whether telmisartan, an angiotensin II receptor antagonist, can improve abnormal vasorelaxation responses. 2 Treatment with telmisartan (10 mg/kg per day, p.o.) for 8 weeks reduced elevated blood pressure in SHR-cp rats, but did not affect the increased bodyweight, serum triglyceride and glucose levels. Telmisartan restored impaired acetylcholine-induced relaxation. Both increased endothelial NO synthase protein expression in aortas and 3-nitrotyrosine content, evidence of peroxynitrite formation, were significantly suppressed by telmisartan. Serum levels of thiobarbituric acid-reactive substances, an index of oxidized lipids, were significantly decreased. 3 These results suggest that telmisartan can reduce the decline in NO bioavailability caused by peroxynitrite formation in the aortas of SHR-cp rats. We propose that antagonism of angiotensin II action may be effective in preventing vascular endothelial dysfunction in metabolic syndrome.

Salt-Induced Nephropathy in Obese Spontaneously Hypertensive Rats Via Paradoxical Activation of the Mineralocorticoid Receptor

Aldosterone is implicated in the pathogenesis of proteinuria and chronic kidney disease. We previously demonstrated the contribution of elevated serum aldosterone in the early nephropathy of SHR/NDmcr-cp (SHR/cp), a rat model of metabolic syndrome. In the present study, we investigated the effect of salt loading on renal damage in SHR/cps and explored the underlying mechanisms. SHR/cps fed a high-sodium diet for 4 weeks developed severe hypertension, massive proteinuria, and advanced renal lesions. High salt also worsened glomerular podocyte impairment. Surprisingly, selective mineralocorticoid receptor (MR) antagonist eplerenone dramatically ameliorated the salt-induced proteinuria and renal injury in SHR/cps. Although salt loading reduced circulating aldosterone, it increased nuclear MR and expression of aldosterone effector kinase Sgk1 in the kidney. Gene expressions of transforming growth factor-beta1 and plasminogen activator inhibitor-1 were also enhanced in the kidneys of salt-loaded SHR/cps, and eplerenone completely inhibited these injury markers. To clarify the discrepancy between decreased aldosterone and enhanced MR signaling by salt, we further investigated the role of oxidative stress, a putative key factor mediating salt-induced tissue damage. Interestingly, antioxidant Tempol attenuated the salt-evoked MR upregulation and Sgk1 induction and alleviated proteinuria and renal histological abnormalities, suggesting the involvement of oxidative stress in salt-induced MR activation. MR activation by salt was not attributed to increased serum corticosterone or reduced 11beta-hydroxysteroid dehydrogenase type 2 activity. In conclusion, sodium loading exacerbated proteinuria and renal injury in metabolic syndrome rats. Salt reduced circulating aldosterone but caused renal MR activation at least partially via induction of oxidative stress, and eplerenone effectively improved the nephropathy.

Elevated circulating levels of markers of oxidative-nitrative stress and inflammation in a genetic rat model of metabolic syndrome

Metabolic syndrome is a cluster of metabolic diseases that in essence greatly promotes progression of atherosclerosis. We used a genetic model of the metabolic syndrome, the SHR/NDmcr-cp (SHR/cp) rat, from 6 to 40 weeks of age to investigate whether systemic oxidative stress, a major cause of atherosclerosis, increases in this syndrome. Nine-week-old male rats already showed manifestations of metabolic syndrome, including heavier body weight, higher blood pressure and higher levels of serum glucose, insulin and various lipids compared to the age-matched Wistar Kyoto (WKY) rats used as a genetic control. These metabolic parameters gradually progressed with age. Likewise, the serum levels of oxidative stress markers, including lipid peroxides, which oxidatively modify low-density lipoprotein (LDL) and 8-hydroxydeoxyguanosine (8-OHdG), gradually increased in SHR/cp rats. The serum levels of 3-nitrotyrosine and 3-chlorotyrosine also persistently increased, indicating the involvement of peroxynitrite or myeloperoxidase-catalyzed oxidation. In addition, high-sensitivity C-reactive protein (hsCRP), an early marker of inflammation, temporarily increased in SHR/cp rats compared to WKY rats. These findings suggest that oxidative stress, as well as nitrative stress and inflammation, increases in the metabolic syndrome, which may contribute to the development of atherosclerosis.

DYSFUNCTION OF PURINERGIC REGULATION OF SYMPATHETIC NEUROTRANSMISSION IN SHR/NDMCR-CP (SHR-CP) RAT

1. The effect of 2-chloroadenosine (2CA), a P1 receptor agonist and beta,gamma-methylene ATP (betagamma mATP), a P2 receptor agonist, on the overflow of endogenous noradrenaline (NE) and the contractile response were examined in the electrically field-stimulated (EFS) (1 Hz) caudal artery obtained from Wistar-Kyoto (WKY) and SHR/NDmcr-cp (SHR-cp) rats. 2. Both 2CA and betagamma mATP reduced the EFS-evoked release of NE from the arteries of WKY. Also, 2CA significantly reduced the EFS-evoked contractile response in WKY, while it had no effect at all in SHR-cp. Betagamma mATP significantly reduced the EFS-evoked contractile response in both WKY and SHR-cp. Both 2CA and betagamma mATP did not affect the contractile response induced by NE at 1 micromol/L. 3. These results indicate that in the caudal arteries of SHR-cp, the P2 agonist but not the P1 agonist is functional in the prejunctional inhibitory regulation of adrenergic neurotransmission. This P1 dysfunction may play a role in the sympathetic hyperinnervation in metabolic syndrome.