A Moderately High Fat Diet Promotes Salt-Sensitive Hypertension in Obese Zucker Rats by Impairing Nitric Oxide Production

The objective of this research was to examine the contribution of a moderately high fat (MHF) diet to the development of salt-sensitive hypertension in obese Zucker rats. Lean and obese Zucker rats were fed either a MHF diet or a diet of standard rat chow (control diet) for 10 weeks. From week 4 through week 10, the drinking water was supplemented with 1% NaCl. Blood pressure was measured weekly, and urinary excretion of nitric oxide metabolites (NO_x) was determined at weeks 4 and 10. At week 10, renal nitric oxide synthase (NOS) activity was assessed in kidney homogenates. Blood pressures of obese, but not lean, rats on the MHF fat diet were significantly increased by salt-supplementation, whereas blood pressures of rats on the control diet were not appreciably affected. NO_x excretion was increased in response to salt-supplementation in rats on the control diet, with the effect being particularly dramatic in obese rats. After salt-supplementation, NO_x excretion by rats on the MHF diet was lower than rats on the control diet. In obese rats on the MHF diet, this decrease in NO production was accompanied by a reduction in renal NOS activity. These results indicate that obese rats are more inclined than lean rats to develop diet-induced hypertension in response to a moderately high fat, salt-supplemented diet. Furthermore, they suggest that MHF diet-induced defects in NO production may promote the salt-sensitivity of blood pressure in obese Zucker rats, which appear to require more NO to maintain blood pressure during a salt challenge.     

Upregulation of hypothalamic nitric oxide synthase gene expression in streptozotocin-induced diabetic rats

Summary Plasma arginine vasopressin (AVP) is known to be elevated in patients with uncontrolled insulin-dependent diabetes mellitus who have plasma hyperosmolality with hyperglycaemia. Although osmotic stimuli cause an increase in nitric oxide synthase (NOS) activity as well as synthesis of AVP and oxytocin in the paraventricular (PVN) and supraoptic nuclei (SON), it is not known whether NOS activity in the hypothalamus changes in the diabetic patients who have plasma hyperosmolality with hyperglycaemia caused by insulin deficiency. Expression of the neuronal (n) NOS gene in the PVN and SON in streptozotocin (STZ)-induced diabetic rats was investigated by using in situ hybridization histochemistry and NADPH-diaphorase histochemical staining. Four weeks after intraperitoneal (i. p.) administration of STZ, male Wistar rats developed hyperglycaemia and plasma hyperosmolality. The expression of nNOS gene and NADPH-diaphorase staining in the PVN and SON remarkably increased in STZ-induced diabetic rats compared to control rats. Three weeks after administration of STZ, the diabetic rats were subcutaneously treated with insulin for 1 week, which resulted in significant suppression of the induction of nNOS, AVP and oxytocin gene expression in the PVN and SON. Furthermore, the induction of nNOS gene expression in the PVN and SON was suppressed in STZ-induced diabetic rats treated with phlorizin and diet to normalize hyperglycaemia without insulin treatment. These results suggest that upregulation of nNOS gene expression as well as AVP and oxytocin gene expression in the PVN and SON in STZ-induced diabetic rats may be associated with hyperglycaemia and plamsa hyperosmolality. [Diabetologia (1998) 41: 640–648] Received: 16 September 1997 and in revised form: 9 February 1998     

Salt-Induced Cardiac Hypertrophy Is Independent of Blood Pressure and Endothelin in Obese,Heart Failure-Prone SHHF Rats

The interaction of salt sensitivity and obesity in development of cardiac hypertrophy is incompletely understood. The SHHF/Mcc-fa^cp (SHHF) rat model was used to examine the effect of high salt on cardiac hypertrophy and expression of endothelin (ET) and nitric oxide synthase (NOS) isoforms. Homozygous lean (+/+) and obese (fa^cp/fa^cp) SHHF were fed a low-salt diet (0.3% NaCl) for seven days followed by a high-salt diet (8.0% NaCl) for seven days. To assess the role of ET in mediating cardiac hypertrophy and gene expression with high salt, additional groups were treated with an ET_A/ET_B receptor antagonist (bosentan) while on high salt. Obese SHHF showed an increase in systolic blood pressure and cardiac hypertrophy in response to the high-salt diet. High salt resulted in decreased expression of preproET as well as all three NOS isoforms in the Obese, while cytokine induced NOS (iNOS) and neuronal NOS (nNOS) increased in Leans. Though the salt-sensitive component of the hypertension observed in the Obese was prevented by bosentan, cardiac hypertrophy still occurred and expression of all NOS isoforms remained lower in Obese compared to Lean. Endothelial NOS (eNOS) expression increased in the Lean with bosentan. These studies suggest that cardiac hypertrophy is independent of the level of hypertension and may be mediated by altered production of NOS isoforms in salt-sensitive, obese SHHF.     

Role of neuronal nitric oxide synthase and inducible nitric oxide synthase in intestinal injury in neonatal rats

AIM: To investigate the dynamic change and role of neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) in neonatal rat with intestinal injury and to define whether necrotizing enterocolitis (NEC) is associated with the levels of nitric oxide synthase (NOS) in the mucosa of the affected intestine tissue. METHODS: Wistar rats less than 24 h in age received an intraperitoneal injection with 5 mg/kg lipopolysaccharide (IPS). Ileum tissues were collected at 1, 3, 6, 12 and 24 h following LPS challenge for histological evaluation of NEC and for measurements of nNOS and iNOS. The correlation between the degree of intestinal injury and levels of NOS was determined. RESULTS: The LPS-injected pups showed a significant increase in injury scores versus the control. The expression of nNOS protein and mRNA was diminished after LPS injection. There was a negative significant correlation between the nNOS protein and the grade of median intestinal injury within 24 h. The expression of iNOS protein and mRNA was significantly increased in the peak of intestinal injury. CONCLUSION: nNOS and iNOS play different roles in LPS-induced intestinal injury. Caution should be exerted concerning potential therapeutic uses of NOS inhibitors in NEC.     

A moderately high fat diet promotes salt-sensitive hypertension in obese zucker rats by impairing nitric oxide production

The objective of this research was to examine the contribution of a moderately high fat (MHF) diet to the development of salt-sensitive hypertension in obese Zucker rats. Lean and obese Zucker rats were fed either a MHF diet or a diet of standard rat chow (control diet) for 10 weeks. From week 4 through week 10, the drinking water was supplemented with 1% NaCl. Blood pressure was measured weekly, and urinary excretion of nitric oxide metabolites (NO(x)) was determined at weeks 4 and 10. At week 10, renal nitric oxide synthase (NOS) activity was assessed in kidney homogenates. Blood pressures of obese, but not lean, rats on the MHF fat diet were significantly increased by salt-supplementation, whereas blood pressures of rats on the control diet were not appreciably affected. NO(x) excretion was increased in response to salt-supplementation in rats on the control diet, with the effect being particularly dramatic in obese rats. After salt-supplementation, NO(x) excretion by rats on the MHF diet was lower than rats on the control diet. In obese rats on the MHF diet, this decrease in NO production was accompanied by a reduction in renal NOS activity. These results indicate that obese rats are more inclined than lean rats to develop diet-induced hypertension in response to a moderately high fat, salt-supplemented diet. Furthermore, they suggest that MHF diet-induced defects in NO production may promote the salt-sensitivity of blood pressure in obese Zucker rats, which appear to require more NO to maintain blood pressure during a salt challenge.     

天麻酚类成分对脑缺血模型大鼠海马一氧化氮和一氧化氮合酶的影响

目的探讨天麻酚类成分对脑缺血大鼠海马NO和一氧化氮合酶(NOS)的影响。方法采用双侧颈总动脉永久性结扎法,造成大鼠脑缺血模型。造模6周后,SD大鼠40只随机分为5组,假手术组、模型组、尼莫地平组、天麻酚类成分高剂量组(高剂量组)和天麻酚类成分低剂量组(低剂量组),每组8只。给药3周后,比色法检测海马NO含量和NOS活性,免疫印记法检测大鼠海马NOS 3种亚型(nNOS,iNOS,eNOS)的表达。结果与假手术组比较,模型组大鼠海马NO含量、NOS活性及nNOS和iNOS表达明显升高,eNOS表达明显降低;与模型组比较,尼莫地平组和高剂量组大鼠海马NO含量、NOS活性及nNOS和iNOS表达明显降低,eNOS表达明显升高;低剂量组大鼠NOS活性和iNOS表达明显降低,差异有统计学意义(P<0.05,P<0.01)。结论天麻酚类成分对脑缺血大鼠海马NO损伤有保护作用。     

脓毒症时各型一氧化氮合酶在大鼠心脏中的表达及其可能机制

目的研究脓毒症时各型一氧化氮合酶(NOS)在心脏中的损伤作用及其机制。方法成年雄性Wistar大鼠腹腔注射脂多糖(LPS)制备脓毒症模型。应用多导生理仪监测大鼠心功能变化;用分光光度计法测定大鼠心肌组织NOS的活性;用RT-PCR和Western blot对大鼠心肌组织各型NOS的表达进行半定量分析。结果给予LPS后6h大鼠心肌收缩和舒张功能受损下降,心肌中iNOS的活性明显升高,eNOS和nNOS(合称cNOS)活性减弱;RT-PCR和Western blot结果显示,给予LPS后cNOS的表达减少,给予LPS后iNOS表达量明显增加。结论脓毒症时,iNOS、nNOS和eNOS的表达和活性发生改变;心肌细胞上iNOS表达及活性升高,这些变化可能在心功能降低中发挥作用。     

Accelerated gastric emptying of glucose in Zucker type 2 diabetic rats: role in postprandial hyperglycaemia

Summary Patients with early non-insulin-dependent diabetes mellitus (NIDDM) empty glucose solutions from their stomachs more rapidly than non-diabetic control subjects, and this exacerbates postprandial hyperglycaemia.To determine if accelerated gastric emptying occurred in a rat model of NIDDM and influenced postprandial hyperglycaemia, gastric emptying of glucose was measured, and the effect of slowing the gastric emptying rate on postprandial hyperglycaemia was observed. We tested eight male obese Zucker diabetic rats and eight age-matched lean Zucker controls at 10–13 weeks of age to measure gastric emptying of glucose (by gamma scintigraphy). Rats fasted overnight were gavaged with 30 % glucose at 1 ml/100 g body weight. Separately, six Zucker diabetic rats and six lean controls were tested for sensitivity to the inhibitory effects of cholecystokinin and secretin on gastric emptying. The diabetic rats emptied glucose significantly faster than controls (t_1/2 = 37.3 ± 1.5 vs 58.8 ± 2.3 min in controls), and aging exaggerated this differential. Camostat, a stimulant of cholecystokinin and secretin release, added to the glucose meal significantly slowed gastric emptying (t_1/2 = 123 ± 23 and 166 ± 19 min, diabetic vs lean, respectively), and significantly reduced postprandial hyperglycaemia in diabetic rats. Compared to Zucker lean controls, Zucker diabetic rats were as sensitive (cholecystokinin) or more sensitive (secretin) to gastrointestinal hormones that inhibit gastric emptying. The results demonstrate accelerated gastric emptying in a rat model of NIDDM, consistant with similar observations in humans with early NIDDM. These results also support the proposal that interventions to slow gastric emptying may improve glucose control in this disease. [Diabetologia (1997) 40: 136–142] Received: 11 July 1995 and in final revised form: 11 October 1996     

甲状腺激素对大鼠小脑,海马,嗅脑神经元型一氧化氮合酶基因表达的调节

目的　观察 15日龄大鼠小脑 ,海马 ,嗅脑一氧化氮 (NO)含量 ,一氧化氮合酶 (NOS)活性的变化及甲状腺激素对上述部位神经元型一氧化氮合酶 (nNOS)基因表达的调节。方法　采用丙基硫氧嘧啶 (PTU)给孕母鼠灌胃造成仔鼠甲减动物模型 ;采用NO ,NOS生化测定法及nNOSmRNA半定量逆转录聚合酶链反应 (RT PCR)法。结果　无论正常组还是甲减组 ,NO含量 ,NOS活性及nNOSmRNA转录均以小脑为最高 ,嗅脑次之 ,海马最低 (P <0 .0 5 ) ;正常组NO含量 ,NOS活性nNOSmRNA转录均高于甲减组 (P <0 .0 1)。结论　提示甲状腺激素对nNOS基因表达有上调作用 ,NO信号系统可能参与大鼠小脑 ,海马 ,嗅脑等区甲状腺激素缺乏所造成的脑损害过程。     

Subcellular distribution of nitric oxide synthase isoforms in the rat duodenum

AIM:To study the cell-type specific subcellular distribution of the three isoforms of nitric oxide synthase(NOS) in the rat duodenum.METHODS:Postembedding immunoelectronmicroscopy was performed,in which primary antibodies for neuronal NOS(nNOS),endothelial NOS(eNOS),and inducible NOS(iNOS),were visualized with protein A-gold-conjugated secondary antibodies.Stained ultrathin sections were examined and photographed with a Philips CM10 electron microscope equipped with a MEGAVIEW II camera.The specificity of t...     

糖尿病大鼠肾脏一氧化氮系统基因表达的研究

目的 研究糖尿病大鼠肾脏一氧化氮系统基因的表达。方法 观察了１２周ＳＴＺ－糖尿病大鼠肾脏皮质一氧化氮（ＮＯ）含量及一氧化氮合成酶（ＮＯＳ）活力,并应用ＲＴ－ＰＣＲ技术检测了肾脏皮质诱生型一氧化氮合成酶ｍＲＮＡ水平的改变。结果 糖尿病大鼠肾脏皮质ＮＯＳ活性及ｉＮＯＳ ｍＲＮＡ水平明显高于正常对照组（Ｐ〈０．０５）,然而ＮＯ含量却反而下降（Ｐ〈０．０５）。结论 糖尿病大鼠肾脏一氧化氮合成障碍,灭活加速     

Altered insulin-mediated and insulin-like growth factor-1-mediated vasorelaxation in aortas of obese Zucker rats

OBJECTIVE: Insulin and insulin-like growth factor-1 (IGF-1) have vasorelaxant effects in vivo, which is dependent on nitric oxide (NO) production. The aim of this study was to investigate the vasorelaxant responses mediated by insulin and/or IGF-1 in aortas of obese Zucker rats. METHODS: The thoracic aortas of eight lean and eight obese Zucker rats (6 months old) were isolated for vasorelaxation analysis. Insulin-induced and IGF-1-induced vasorelaxant responses were evaluated by the isometric tension of aortic rings in the organ bathes. The roles of phosphatidylinositol 3-kinase (PI3K) and nitric oxide synthase (NOS) in vasorelaxant responses were examined by treating selective inhibitors, such as wortmannin (an inhibitor of PI3K) and N (omega)-nitro-L-arginine methyl ester (L-NAME, a NOS inhibitor). In addition, the vascular responses to sodium nitroprusside (SNP), a direct vasodilator of vascular smooth muscle, were examined. RESULTS: The insulin-induced vasorelaxation in aortas of obese rats was significantly decreased, whereas the IGF-1-induced vasorelaxation was significantly increased, compared with that in lean rats. After the pre-administration of wortmannin or L-NAME, the altered insulin-induced or IGF-1-induced vasorelaxation was abolished. There was no significant difference in the SNP-induced vasorelaxation between lean and obese rats. CONCLUSION: Our findings suggested that the decreased insulin-mediated vasorelaxation in obese rats appeared to be counteracted by the increased IGF-1-mediated vasorelaxation. Furthermore, the NO-dependent pathway was involved in the altered vasorelaxant responses. However, the SNP-induced vasorelaxation was not changed in obese rats.     

Differential nNOS gene expression in salt-sensitive and salt-resistant Dahl rats.

BACKGROUND: Several indications exist to suggest that an impaired production of nitric oxide might have a role in the development of salt-sensitive hypertension. OBJECTIVE: To examine whether the gene expression of the nitric oxide synthases (NOS) is altered in the salt-sensitive Dahl rat compared with that in the salt-resistant Dahl rat. DESIGN AND METHODS: The abundance of NOS mRNA was measured by RNase protection assay in different organs of salt-resistant and salt-sensitive Dahl rats. In addition, the zonal expression of NOS genes in the kidney under salt load and salt restriction was determined. RESULTS: The abundance of endothelial NOS mRNA was similar between the salt-resistant and salt-sensitive Dahl rat strains in all organs. Inducible NOS mRNA was not detectable by RNase protection assay in any organ. Neuronal NOS (nNOS) mRNA expression, however, was about 50% lower in brain and kidney of salt-sensitive Dahl rats than in salt-resistant Dahl rats. Within the kidney, nNOS mRNA levels were significantly decreased in salt-sensitive Dahl rats compared with those in salt-resistant Dahl rats, in cortex, outer and inner medulla (50, 40 and 30%, respectively) under all dietary conditions. A comparison of renal nNOS gene expression in Dahl rats with that in salt-insensitive Sprague- Dawley rats revealed that the abundance of renal nNOS was similar in salt-sensitive Dahl and Sprague-Dawley rats, but was increased in salt-resistant Dahl rats relative to that in Sprague-Dawley rats. CONCLUSION: These data suggest that nNOS gene expression is increased in salt-resistant Dahl rats compared with that in salt-sensitive Dahl rats. This increased nNOS expression of the salt-resistant Dahl strain might play a part in compensating for a defect of renal salt excretion in the Dahl strains.     

The BBZ/Wor rat: clinical characteristics of the diabetic syndrome

Summary The BBZ/Wor rat is a model of obesity and autoimmune diabetes mellitus developed by crossing the BB/Wor and Zucker rats. We studied circulating glucose and insulin levels, islet morphology and lymphocyte subsets in lean and obese BBZ/Wor rats before and after the onset of diabetes, and studied the clinical course of diabetes in animals after interruption of exogenous insulin therapy. Lean BBZ/Wor rats developed insulin-dependent diabetes and died in ketoacidosis within 1 week after cessation of insulin injections. Diabetes also developed in obese rats, but these animals were not insulin-dependent and survived for months without insulin therapy. The islets of the lean diabetic rats revealed complete destruction of pancreatic beta cells and plasma insulin levels were virtually undetectable. In contrast, the islets of the obese rats revealed insulitis and substantial beta-cell loss, however autoimmune bete-cell destruction was incomplete, and residual beta cells were presumably responsible for the presence of measurable levels of plasma insulin and the long-term survival of obese diabetics without insulin therapy. Obese rats were hyperinsulinaemic, developed diabetes significantly earlier, and with a greater incidence than lean rats, suggesting a possible relationship between enhanced beta-cell metabolic activity and immune destruction. Obese males became diabetic more frequently and at an earlier age than obese females and lean rats of both sexes, suggesting a role for gender in the pathogenesis of diabetes. We conclude that the BBZ/Wor rat is a unique animal model for investigating the interaction of obesity, beta-cell metabolism, autoimmune insulitis and genetic predisposition to diabetes.     

Diminished Expression of Constitutive Nitric Oxide Synthases in the Kidney of Spontaneously Hypertensive Rat

In kidney, nitric oxide (NO) synthesized by nitric oxide synthase (NOS) regulates sodium and water excretion, and renal medullary blood flow. The expression of constitutive NOS, endothelial NOS (eNOS) and neuronal NOS (nNOS), were assessed in kidney of the spontaneously hypertensive rat (SHR) and the normotensive Wistar Kyoto (WKY) rat by Western blot analysis and immunocytochemistry. Neuronal NOS expression was observed in the cortex and eNOS was detected only in the inner medulla of both WKY and SHR. In SHR, expression of eNOS was attenuated to 35.1 ± 10.8%, while expression of nNOS was only 57.5 ± 5.7% of the levels seen in WKY rat. Immunocytochemical studies revealed decreased staining of nNOS in the macula densa, collecting ducts and in the glomerulus of SHR compared to WKY rat. Endothelial NOS immunoreactivity was restricted to vascular structures of the inner intima cells and smooth muscle cells, and was markedly reduced in the vasculature of SHR. The decreased renal blood flow observed in SHR may be linked to a diminished expression of eNOS and nNOS, underscoring the importance of these enzymes in the pathophysiology and maintenance of genetic hypertension.     

Different responsiveness in body weight and hepatic 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 1 mrna to 11beta-HSD inhibition by glycyrrhetinic acid treatment in obese and lean zucker rats

Tissue-specific dysregulation of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) activity in obese humans and animals may be associated with obesity and the metabolic syndrome. We investigated the effect of inhibition of 11beta-HSD with glycyrrhetinic acid (GE), an effective 11beta-HSD inhibitor, on body weight regulation in obese Zucker rats, which have a defect in the leptin receptor gene. GE (280 mg/kg/d) was administered in drinking water to 8-week-old male Zucker rats for 14 weeks. GE had no effect on food intake or weight gain, and did not affect hepatic 11beta-HSD1 and renal 11beta-HSD2 mRNA levels in obese rats. In contrast, average daily food intake and body weight on week 14 were significantly reduced by GE in lean rats (both P <.0001). Hepatic 11beta-HSD1 and renal 11beta-HSD2 mRNA levels were also significantly decreased by GE in lean rats (both P <.05). GE had no significant effect on plasma corticosterone levels in obese rats but lowered them in lean rats (P <.05). Plasma leptin levels declined in both GE-treated obese and lean rats (both P <.01). In conclusion, long-term GE treatment decreased weight gain in lean Zucker rats but not in obese Zucker rats. These findings suggest that the differing responses of 11beta-HSD1 to GE in obese and lean Zucker rats are closely associated with the different weight-gain responses. Furthermore, the weight-lowering effect of GE may require intact leptin receptors.     

Increased renal angiotensin II AT1 receptor function in obese Zucker rat

Angiotensin II (Ang II) via the activation of AT1 receptors and subsequent stimulation of the tubular sodium transporters increases sodium and water reabsorption in the proximal tubule. An enhanced tubular action of Ang II is implicated in obesity related hypertension; however, the mechanism of such a phenomenon is unknown. Present study was designed to determine the AT1 receptor numbers and function in the proximal tubule of obese and lean Zucker rats. Obese Zucker rats were hypertensive and hyperinsulinemic. The plasma renin activity was similar in the lean and obese rats. Angiotensin II stimulated the Na,H-exchanger (NHE) activity in the proximal tubule, but the stimulatory response was markedly greater in obese than in lean rats. Similarly, Ang II caused greater inhibition in cAMP accumulation in the proximal tubule of obese compared to lean rats. The (125I]sar-Ang II binding revealed a 100% increase in the AT1 receptor number in the brush border membrane (BBM) of obese compared to lean rats. The Western blot analysis revealed a 36-51% increase in the Gi(alpha)1 and Gi(alpha)3 in the BBM of obese compared to lean rats. We conclude that increases in the AT1 receptor number and abundance of the Gi(alpha) on BBM may be responsible for the enhanced signaling and subsequent greater stimulation of NHE by Ang II in proximal tubules of obese rats. The greater stimulation of NHE by Ang II may contribute to the increased tubular sodium reabsorption and to the hypertension in obese Zucker rats.