Inhibition of nitric oxide synthesis accentuates blood pressure elevation in hyperinsulinemic rats

NO levels in diabetes mellitus: Effects of l-NAME and insulin on LCAT, Na(+)/K(+) ATPase activity and lipid profile

OBJECTIVES

Diabetes mellitus (DM) is a chronic disease and one of the most important health problems. Several factors may be responsible for the complications of diabetes mellitus including alterations in the activities of sodium-potassium adenosine triphosphatase (Na(+)/K(+) ATPase) and lecithin:cholesterol acyltransferase (LCAT) and also levels of nitric oxide (NO). We have investigated the effects of alterations in serum NO levels on activities of erythrocyte membran Na/K ATPase and serum LCAT enzymes.

MATERIALS AND METHODS

The experiments were performed on male rats divided into four groups: group 1, control (standart diet); group 2, diabetic control (single dose of 65mg/kg of streptozotocin (STZ), i.p); group 3, STZ+insulin (8IU/kg/day s.c.); group 4 (STZ+l-NAME 5mg/kg/day orally).

RESULT

Streptozotocin-induced diabetic rats, showed a significant increase in blood glucose and serum cholesterol (C) and triglyceride (TG). Compared to the control group with diabetic group plasma LCAT concentrations and erythrocyte membrane Na(+)/K(+) ATPase were found to be decreased. Activities of Na(+)/K(+) ATPase and serum NO level were decreased with the administration of l-NAME. We observed that insulin was ameliorated in all parameters.

CONCLUSIONS

Serum NO levels is related to erythrocyte membrane Na(+)/K(+) ATPase activity. But serum NO levels did not affect the plasma LCAT activity and serum lipid profiles.

Exercise attenuates the premature cardiovascular aging effects of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2D) is an example of a disease process that results in decrements in function additional to those imposed by the inexorable 'primary aging' process. These decrements due to disease, rather than primary aging, can be termed 'secondary aging', and include the premature development (as early as adolescence) of asymptomatic preclinical cardiovascular abnormalities (e.g. endothelial dysfunction, arterial stiffness, diastolic dysfunction), as well as impaired exercise performance. These abnormalities are important, as they are associated with greater cardiovascular morbidity and mortality in people with and without T2D. A better understanding of the pathophysiology of secondary cardiovascular aging in people with T2D is warranted, and an evaluation of the benefits of existing treatments for these abnormalities is useful (e.g. exercise training). The focus of this review is to discuss the data relevant to the following key postulates: (a) T2D causes premature cardiovascular aging; (b) in contrast to primary cardiovascular aging, the premature cardiovascular aging of T2D may be modifiable with exercise. The exercise-focused perspective for this review is appropriate because impairments in exercise performance are markers of premature cardiovascular aging in T2D, and also because exercise training shows promise to attenuate some aspects of cardiovascular aging during the preclinical stage.

Chronic insulin infusion normalizes blood pressure and the gene expressions of angiotensin II type 1 receptor in fructose-fed rats

It remains open to debate whether hyperinsulinemia leads to the development of hypertension. We addressed this issue by investigating the effect of chronic insulin infusion on blood pressure and related parameters in hypertensive fructose-fed rats. Rats were given either normal chow or a fructose-rich diet, and insulin or saline was infused through mini-pumps in the same animals for 14 days. The chronic insulin infusion exerted no effect on the blood pressure of the chow-fed rats. Fructose feeding increased the blood pressure and levels of insulin, triglyceride and fatty acid. Insulin infusion augmented the hyperinsulinemia but normalized the blood pressure and plasma lipids. Plasma angiotensin II was elevated in the fructose-fed rats, while insulin infusion left it unchanged. The expression of angiotensin II type 1 receptor (AT1R) mRNA was doubled in both the aorta and epididymal fat of the fructose-fed rats, while that of angiotensin II type 2 receptor (AT2R) was unaltered. Insulin infusion completely rectified the over-expression of the AT1R gene. Our findings indicate that chronic insulin infusion exacerbates hyperinsulinemia while normalizing blood pressure and the gene expressions of AT1R in insulin-resistant fructose-fed rats, suggesting that endogenous hyperinsulinemia caused by insulin resistance is associated with the development of hypertension, whereas exogenous hyperinsulinemia attenuates hypertension probably due to amelioration of insulin resistance.

Chronic blockade of nitric oxide synthesis reduces adiposity and improves insulin resistance in high fat-induced obese mice

Genetic deletion of inducible nitric oxide synthase (NOS) in mice has been shown to improve high-fat diet (HFD)-induced insulin resistance. However, a pathophysiological role of endogenous nitric oxide (NO) in obesity-related insulin resistance remains controversial. To address this issue, we examined the metabolic phenotypes in HFD-induced obese mice with chronic blockade of NO synthesis by a NOS inhibitor, N(G)-nitro-l-arginine methyl ester (L-NAME). Six-week-old male C57BL/6j mice were provided free access to either a standard diet (SD) or a HFD and tap water with or without L-NAME (100 mg/kg.d) for 12 wk. L-NAME treatment significantly attenuated body weight gain of mice fed either SD or HFD without affecting calorie intake. L-NAME treatment in HFD-fed mice improved glucose tolerance and insulin sensitivity. HFD feeding induced inducible NOS mRNA expression, but not the other two NOS isoforms, in white adipose tissue (WAT) and skeletal muscle. L-NAME treatment up-regulated uncoupling protein-1 in brown adipose tissue of HFD-fed mice but down-regulated monocyte chemoattractant protein-1 and CD68 mRNAs levels in WAT. HFD feeding up-regulated leptin mRNA levels but conversely down-regulated adiponectin mRNA levels in WAT, but these effects were unaffected by L-NAME treatment. Moreover, L-NAME treatment also increased peroxisome proliferator-uncoupling protein-3 mRNA levels in skeletal muscles of HFD-fed mice. Increased urinary excretion of norepinephrine after HFD feeding was augmented in L-NAME-treated mice. Insulin-stimulated tyrosine phosphorylation of insulin receptor substrate-1 and serine phosphorylation of Akt/Akt2 in soleus muscle was markedly impaired in HFD-fed mice but reversed by L-NAME treatment. In conclusion, chronic NOS blockade by L-NAME in mice ameliorates HFD-induced adiposity and glucose intolerance, accompanied by reduced adipose inflammation and improved insulin signaling in skeletal muscle, suggesting that endogenous NO plays a modulatory role in the development of obesity-related insulin resistance.

The endocrine system in chronic nitric oxide deficiency

The experimental model of chronic inhibition of nitric oxide (NO) production has proven to be a useful tool to study cardiovascular and renal lesions produced by this type of hypertension, which are similar to those found in human hypertension. It also offers a unique opportunity to study the interaction of NO with the humoral systems, known to have a role in the normal physiology of vascular tone and renal function. This review provides a thorough and updated analysis of the interactions of NO with the endocrine system. There is special focus on the main vasoactive factors, including the renin-angiotensin-aldosterone system, catecholamines, vasopressin, and endothelin among others. Recent discoveries of crosstalk between the endocrine system and NO are also reported. Study of these humoral interactions indicates that NO is a molecule with ubiquitous function and that its inhibition alters virtually to all other known regulatory systems. Thus, hypothyroidism attenuates the pressor effect of NO inhibitor N-nitro-L-arginine methyl ester, whereas hyperthyroidism aggravates the effects of NO synthesis inhibition; the sex hormone environment determines the blood pressure response to NO blockade; NO may play a homeostatic role against the prohypertensive effects of mineralocorticoids, thyroid hormones and insulin; and finally, NO deficiency affects not only blood pressure but also glucose and lipid homeostasis, mimicking the human metabolic syndrome X, suggesting that NO deficiency may be a link between metabolic and cardiovascular disease.

Insulin resistance, hyperinsulinemia, and renal injury: mechanisms and implications

Most of the basic components of the metabolic syndrome, namely type 2 diabetes mellitus, hypertension, obesity, or low high-density lipoprotein cholesterol levels, apart from being major risk factors for cardiovascular disease have been also associated with an increased risk of chronic kidney disease. However, several epidemiologic studies conducted over the past years suggest that the central component of the syndrome, insulin resistance, as well as compensatory hyperinsulinemia are independently associated with an increased prevalence of chronic kidney disease. In addition, background studies support the existence of several pathways linking insulin resistance and hyperinsulinemia with kidney damage. Insulin per se promotes the proliferation of renal cells and stimulates the production of other important growth factors such as insulin-like growth factor-1 and transforming growth factor beta. Insulin also upregulates the expression of angiotensin II type 1 receptor in mesangial cells, thus enhancing the deleterious effects of angiotensin II in the kidney, and stimulates production and renal action of endothelin-1. Moreover, insulin resistance and hyperinsulinemia are associated with decreased endothelial production of nitric oxide and increased oxidative stress which have been also implicated in the progression of diabetic nephropathy. This review analyzes the above and other potential mechanisms, through which insulin resistance and hyperinsulinemia can contribute to renal injury.

Cardiometabolic Syndrome and Chronic Kidney Disease: What Is the Link?

The term metabolic syndrome or cardiometabolic syndrome describes the clustering of several cardiovascular and renal risk factors, including type 2 diabetes mellitus, central obesity, hypertension, and dyslipidemia. Over the past 15 years, several studies have examined the association between the metabolic/cardiometabolic syndrome or its central component, insulin resistance, with the presence of elevated urine albumin excretion. Intrarenal changes associated with the cardiometabolic syndrome result in elevated glomerular filtration rate, impaired pressure natriuresis, endothelial dysfunction related to changes in nitric oxide and, hence, impaired renal autoregulation and enhanced chronic inflammation. The aforementioned changes that occur in the cardiometabolic syndrome all contribute to the development of renal injury. While this review focuses on the epidemiology and mechanisms associated with vascular/renal injury, it must be remembered that prevention and treatment of kidney disease require a multifactorial approach. Weight loss through diet and exercise can reverse many of these pathophysiologic adaptations. Pharmacologic intervention should be aimed at achieving guideline goals and include insulin sensitizers to aid in tight glycemic control, lipid control, blockade of the renin-angiotensin-aldosterone system for blood pressure reduction, and anti-inflammatory therapies.

Role of exercise training on cardiovascular disease in persons who have type 2 diabetes and hypertension

Exercise training is an essential component in the medical management of patients who have type 2 diabetes and hypertension. Regular exercise improves the cardiovascular health of individuals who have these conditions through multiple mechanisms (Fig. 1). These mechanisms include improvements in endothelial vasodilator function,left ventricular diastolic function, arterial stiffness.systematic inflammation, and reducing left ventricular mass. Exercise training also reduces total and abdominal fat, which mediate improvements in insulin sensitivity and blood pressure, and possibly, endothelial function. Persons who are in a prediabetic stage or those who have the metabolic syndrome may be able to prevent or delay the progression to overt diabetes by adopting a healthier lifestyle, of which increasing habitual levels of physical activity isa vital component. Most persons who have diabetes and hypertension or are at risk for these conditions should be able to initiate an exercise program safely after appropriate medical screen-ing and the establishment of an individualized exercise prescription. Despite the increasing amount of evidence that shows the benefits of exercise training, this modality of prevention and treatment continues to be underused. Although patients' lack of knowledge of the benefits of exercise or lack of motivation contributes to this underuse, a lack of clear and specific guidelines from health care professionals also is an important factor. Clinicians need to educate patients about the benefits of exercise for managing their type 2 diabetes and assist in formulating specific advice for increasing physical activity. Specific instructions should be given to patients, rather than general advice, such as "you should exercise more often." Many cardiac re-habilitation and clinical exercise programs can accommodate patients who have type 2 diabetes and hypertension. Such programs can establish individualized exercise prescriptions and provide an environment that is conducive for "lifestyle change" that underlies long-term compliance to exercise and risk factor modification.

Aging and the role of reactive nitrogen species

The role of reactive oxygen species and its effects on aging has received considerable attention in the past 47 years since Dr. Denham Harman first proposed the "free radical theory of aging." Though not completely understood due to the incalculable number of pathways involved, the number of manuscripts that facilitate the understanding of the underlying effects of reactive radical species on the oxidative stress on lipids, proteins, and DNA and its contribution to the aging process increases nearly exponentially each year. More recently, the role of reactive nitrogen species, such as nitric oxide and its by-products--nitrate (NO3-), nitrite (NO2-), peroxynitrite (ONOO-), and 3-nitrotyrosine--have been shown to have a direct role in cellular signaling, vasodilation, and immune response. Nitric oxide is produced within cells by the actions of a group of enzymes called nitric oxide synthases. Presently, there are three distinct isoforms of nitric oxide synthase: neuronal (nNOS or NOS-1), inducible (iNOS or NOS-2), and endothelial (eNOS or NOS-3), and several subtypes. While nitric oxide (NO*) is a relative unreactive radical, it is able to form other reactive intermediates, which could have an effect on protein function and on the function of the entire organism. These reactive intermediates can trigger nitrosative damage on biomolecules, which in turn may lead to age-related diseases due to structural alteration of proteins, inhibition of enzymatic activity, and interferences of the regulatory function. This paper will critically review the evidence of nitration and the important role it plays with aging. Furthermore, it will summarize the physiological role of nitration as well as the mechanisms leading to proteolytic degradation of nitrated proteins within biological tissues.