Hypertension and associated metabolic abnormalities--the role of insulin resistance and the sympathoadrenal system

Insulin resistance and systemic hypertension

There is a complex relation among insulin sensitivity, hypertension, and endothelial function. Although there are few prospective data on the relation between insulin levels and the development of hypertension, there is some evidence that insulin resistance precedes the onset of established hypertension in high-risk patients. Because insulin is a vasodilator, it would need to activate a variety of other potential physiologic mechanisms to play a causal role in the pathogenesis of hypertension. There are changes in the arterial wall in patients with hyperinsulinemia, and characteristic decreases in elasticity of the arterial wall have been noted in hypertensive patients with insulin resistance. Hyperglycemia, hyperinsulinemia, and hypertriglyceridemia appear to jointly contribute to increased arterial stiffness. There are, however, ethnic and racial disparities in the association of insulin, insulin sensitivity, and blood pressure, as this relation is not strongly observed in the black population in the United States and elsewhere. This may reflect complex relations among obesity, diabetes, and hypertension, which are more common in patients with African ancestry, although recent evidence supports the probability that the differences are genetically determined. Whatever the precise mechanisms, clinical investigations demonstrate the benefit of early interventions to improve insulin sensitivity and control hypertension, as well as to reduce hypercholesterolemia. In particular, enhanced insulin sensitivity may improve hypertension and its subsequent damage to vessel walls.

Visceral obesity and insulin resistance are associated with plasma aldosterone levels in women

OBJECTIVE

Both obesity and insulin resistance increase the risk of hypertension and other cardiovascular diseases, but the mechanisms linking these abnormalities are unknown. The current study was undertaken to examine the effects of obesity, fat distribution, and insulin resistance on plasma levels of aldosterone and other adrenal steroids that might contribute to sequelae of obesity.

RESEARCH METHODS AND PROCEDURES

Twenty-eight normotensive premenopausal women and 27 normotensive men with a wide range of body fat underwent measurements of visceral adipose tissue by CT scan, total fat mass by dual energy X-ray absorptiometry, blood pressure, insulin sensitivity, and plasma levels of three adrenal steroid hormones.

RESULTS

Plasma aldosterone in women correlated directly with visceral adipose tissue (r=0.66, p<0.001) and inversely with insulin sensitivity (r=-0.67, p<0.001), and these associations were independent of plasma renin activity. There were no corresponding correlations in men. Plasma aldosterone was significantly correlated with plasma cortisol and dehydroepiandrosterone sulfate in women. Seventeen women and 15 men completed a weight-reduction regimen, losing an average of 15.1+1.2 kg. After weight loss, plasma aldosterone was significantly lower and insulin sensitivity higher; however, the correlations of aldosterone with visceral adipose tissue and insulin sensitivity in women persisted (p = 0.09 and 0.07, respectively). Although none of the women were hypertensive, blood pressure correlated with plasma aldosterone both before and after weight loss.

DISCUSSION

We conclude that visceral adiposity and insulin resistance are associated with increased plasma aldosterone and other adrenal steroids that may contribute to cardiovascular diseases in obese women.

1999 World Health Organization-International Society of Hypertension Guidelines for the management of hypertension. Guidelines sub-committee of the World Health Organization

The present Guidelines were prepared by the Guidelines Sub-Committee of the World Health Organization-International Society of Hypertension (WHO-ISH) Mild Hypertension Liaison Committee, the members of which are listed at the end of the text. These guidelines represent the fourth revision of the WHO-ISH Guidelines and were finalised after presentation and discussion at the 7th WHO-ISH Meeting on Hypertension, Fukuoka, Japan, 29th Sept-1st Oct, 1998. Previous versions of the Guidelines were published in Bull WHO 1993, 71:503-517 and J Hypertens 1993, 11:905-918.

Insulin resistance and hypertension

Insulin resistance, a common accompaniment of essential hypertension, increases cardiovascular risk both directly, and via its adverse effect on other cardiovascular risk factors. Decreasing insulin resistance by lifestyle modification including diet, weight loss, and physical exercise is an important component of therapy in all patients. With the exception of thiazide diuretics as monotherapy, the currently utilized classes of agent appear equally effective in lowering blood pressure in insulin resistant patients. Currently utilized agents do, however, differ substantially in their effect on insulin resistance and associated risk factors. Agents that diminish insulin resistance may have a rationale in treating insulin resistant patients with hypertension although a decisive recommendation about class of agent in this group of patients must await several prospective large scale trials currently underway. Lower intervention thresholds and lower therapeutic goals would appear to apply to hypertensive patients with insulin resistance especially in the presence of impaired glucose tolerance or overt diabetes mellitus.

Early phase insulin infusion and muscarinic blockade in obese and lean subjects

The effect of early phase insulin on postprandial levels of insulin, C-peptide, glucose, and glucagon was investigated in lean (n = 10) and obese (n = 12) subjects. Subjects underwent four conditions during ingestion of a meal (600 kcal): 1) saline infusion; 2) 10-min insulin infusion simultaneously with meal ingestion (0.24 U bolus, 15 mU. m(-2). min(-1)); 3) atropine infusion (0.4 mg/m(2) bolus, 0.4 mg. m(-2). h for 4 h); 4) insulin and atropine infusion. Blood samples were taken for 3.5 h. Insulin infusion had no effect on postprandial insulin levels in either population but significantly reduced postprandial glucose in the obese subjects (P < 0.05). Obese subjects with elevated postprandial glucose levels in the presence of muscarinic blockade exhibited a decline in glucose with insulin supplementation. Atropine reduced postprandial insulin levels in both groups, with a greater attenuation in the obese (P < 0.01), but postprandial glucose levels were also significantly reduced, suggesting that atropine inhibited gastric emptying. Thus the effects of muscarinic blockade on postprandial insulin levels cannot be evaluated. These data suggest that insulin supplementation during the preabsorptive time period may contribute to glucoregulation in the obese population.

Weight reduction and obesity

Obesity and hypertension are intimately linked. Weight loss lowers blood pressure and improves the blood pressure response to sodium restriction and antihypertensive medications. In addition to the effects of energy restriction, diets rich in fruits and vegetables (and hence potassium) and rich in low fat dairy products (and hence rich in calcium and magnesium), high in fiber, and low in saturated fat also lower blood pressure independent of sodium and energy content. These dietary modifications, along with weight loss are beneficial in patients only mildly overweight and, because of beneficial effects on other cardiac risk factors should be part of the therapeutic regimen in all obese hypertensive patients.

Chromium homeostasis in patients with type II (NIDDM) diabetes

The purpose of this study was to assess chromium handling in non-insulin dependent diabetic patients (NIDDM) compared to healthy volunteers. Chromium handling was evaluated using fasting blood and second morning void urine samples from 93 NIDDM patients and 33 healthy volunteers. Significant differences in chromium homeostasis were seen between patients and controls. NIDDM patients had mean levels of plasma chromium around 33% lower and urine values almost 100% higher than those found in health. Healthy volunteers showed a significant negative correlation between fasting levels of plasma chromium and insulin. This was not evident in NIDDM patients. In the early years of onset of NIDDM, plasma chromium values were inversely correlated with plasma glucose. This was lost in patients with diabetes of more than 2 years duration. We suggest large losses of chromium over many years may exacerbate an already compromised chromium status in NIDDM patients and might contribute to the developing insulin resistance seen in patients with type 2 diabetes.

Excess catecholamine syndrome. Pathophysiology and therapy

In addition to genetic factors, lifestyle has a predominant influence on primary hypertension and noninsulin-dependent diabetic mellitus (NIDDM). We initiated studies using radiotelemetry for characterizing molecular events linked with excess calorie intake and psychologic stress. An increased calorie intake was associated with raised (p < 0.05) systolic and diastolic blood pressure as well as heart rate independent of day-night cycle. Sympathetic activity was in excess when related to the unchanged motility. The hyperkinetic hypertension is expected to result in adverse remodeling of resistance vessels and to aggravate insulin resistance. To examine adverse effects of psychological stress, rats were subjected to intermittent food pellet feeding. Urinary catecholamines and cardiac norepinephrine stores were increased (p < 0.05). The depressed (p < 0.05) rate of Ca2+ uptake of sarcoplasmic reticulum is expected to contribute to cellular Ca2+ overload. These lifestyle influences strengthen the notion of an excess catecholamine syndrome which requires selective reduction of sympathetic outflow of the brain by I1-receptor agonists.

Genetics of Cd36 and the clustering of multiple cardiovascular risk factors in spontaneous hypertension

Disorders of carbohydrate and lipid metabolism have been reported to cluster in patients with essential hypertension and in spontaneously hypertensive rats (SHRs). A deletion in the Cd36 gene on chromosome 4 has recently been implicated in defective carbohydrate and lipid metabolism in isolated adipocytes from SHRs. However, the role of Cd36 and chromosome 4 in the control of blood pressure and systemic cardiovascular risk factors in SHRs is unknown. In the SHR. BN-Il6/Npy congenic strain, we have found that transfer of a segment of chromosome 4 (including Cd36) from the Brown Norway (BN) rat onto the SHR background induces reductions in blood pressure and ameliorates dietary-induced glucose intolerance, hyperinsulinemia, and hypertriglyceridemia. These results demonstrate that a single chromosome region can influence a broad spectrum of cardiovascular risk factors involved in the hypertension metabolic syndrome. However, analysis of Cd36 genotypes in the SHR and stroke-prone SHR strains indicates that the deletion variant of Cd36 was not critical to the initial selection for hypertension in the SHR model. Thus, the ability of chromosome 4 to influence multiple cardiovascular risk factors, including hypertension, may depend on linkage of Cd36 to other genes trapped within the differential segment of the SHR. BN-Il6/Npy strain.

Cardiovascular consequences of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS), a syndrome of hyperandrogenism and anovulation with numerous associated derangements, is typified by a substantially increased incidence of type 2 diabetes mellitus and coronary disease in mid-adult life. A marker of the disorder, and a potential determinant of the macroangiopathy, is insulin resistance. Thus, in addition to altered lipid metabolism, hypertension, hormonal derangements, obesity, and altered coagulation--all of which may contribute to the development of vascular disease--the insulin resistance and dysinsulinemia may underlie impaired fibrinolysis and related derangements within the vessel walls that may be modifiable by attenuation of insulin resistance and amelioration of hyperinsulinemia.

The sympathetic nervous system and baroreflexes in hypertension and hypotension

Blood pressure and blood volume are closely regulated by the interrelated actions of the sympathetic nervous system (SNS) and the renin-angiotensin-aldosterone system (RAAS). Reflex vasoconstriction caused by parallel SNS and RAAS activation is modulated by two interactive negative feedback systems called baroreflex. The aortic-carotid baroreflex systems respond to momentary changes in systolic blood pressure, adjusting the degree of SNS-dependent peripheral vasoconstriction and cardiac output to allow maintenance of a relatively constant perfusion pressure. Cardiopulmonary baroreflexes respond to momentary changes in cardiac filling, adjusting the degree of peripheral venoconstriction and venous return to maintain cardiac preload and stroke volume. Under normal conditions, each baroreflex system exhibits a degree of tonic negative feedback so that it can alter SNS output immediately, providing counterregulatory increases or decreases in pressure or volume to maintain homeostasis. The SNS is inappropriately active in obesity and hypertension and plays a causal or permissive role in all forms of chronic hypertension. If the negative feedback control exerted by the baroreflexes over the SNS and renin-angiotensin-aldosterone system (RAAS) were perfect, chronic hypertension would not occur. Activity of the baroreflexes, however, is chronically altered by maladaptive changes such as cardiac and vascular fibrosis and hypertrophy. Long-term increases in SNS and RAAS activity also exert ongoing deleterious effects on the heart and vasculature by directly facilitating further cardiac hypertrophy and arterial stiffening. These effects appear to contribute to a vicious cycle of chronic hypertension and target organ damage. Other syndromes of abnormal blood pressure (BP) control, including orthostatic hypotension and baroreflex failure are examples of abnormal baroreflex activity and SNS control.

Effects of different insulin infusion rates on heart rate variability in lean and obese subjects

The low-frequency to high-frequency ratio (LF/HF ratio) is an index of cardiac sympathovagal balance. We hypothesized that insulin might also stimulate the LF/HF ratio. Thus, 15 lean and 15 obese subjects were studied. Each subject underwent sequential hyperinsulinemic clamps (insulin infusion rate 0.50, 1, and 2 mU/kg x min) while the heart rate was recorded by the Holter technique continuously. Indirect calorimetry allowed determination of the respiratory quotient (Rq) and substrate oxidation. The leg blood flow (LBF), leg vascular resistance (LVR), and plasma norepinephrine concentration were also measured. In seven lean subjects, hyperinsulinemic clamps were repeated along with propranolol infusion (0.1 mg x kg(-1) as an intravenous bolus dose followed by continuous intravenous infusion of 0.5 mg x kg(-1) x min(-1) throughout the study). Lean subjects had better insulin action than obese subjects. Insulin infusion was associated with an increase of the deltaLF/HF ratio in both lean (P < .001 for time-dependent changes) and obese (P < .02 for time-dependent changes) subjects; however, the extent of insulin-mediated stimulation of the LF/HF ratio was greater in lean versus obese subjects. Insulin infusion did not significantly affect HF values in both groups. Independently of gender, body fat, changes in the plasma norepinephrine concentration, LBF, and LVR, the deltaLF/HF ratio at the end of the fastest insulin infusion (0.8 +/- 0.2 v 0.3 +/- 0.2, P < .04) was still greater in lean versus obese subjects. The deltaLF/HF ratio was also more stimulated during insulin versus insulin + propranolol infusion in lean subjects. In conclusion, insulin stimulates the LF/HF ratio in both lean and obese subjects and thus produces a shift in the cardiac autonomic nervous system activity toward sympathetic predominance.

Effect of hyperinsulinemia on renal function in a general Japanese population: the Hisayama study

BACKGROUND

Insulin resistance and hyperinsulinemia induce glomerular hypertension and hyperfiltration, which may result in glomerulosclerosis. However, the relationship between hyperinsulinemia and renal function is uncertain.

METHODS

To elucidate whether hyperinsulinemia plays a significant part in the initiation and development of renal dysfunction, we examined in 1988 the relationship between serum insulin and renal function on data from a cross-sectional community survey conducted among residents from Hisayama Town, Japan, who were aged 40 to 79 years old. A total of 1065 men (72.0% of the total population in the same age range) and 1381 women (79.0%) without renal failure (creatinine clearance of more than 30 ml/min) underwent a comprehensive examination, including a 75 g oral glucose tolerance test.

RESULTS

The correlation analysis showed that serum insulin, blood pressure, total cholesterol, low-density lipoprotein cholesterol, triglycerides, and body mass index were all negatively correlated with the reciprocal of serum creatinine level (P < 0.01), and alcohol intake was positively correlated (P < 0.05) in both sexes. High-density lipoprotein cholesterol and smoking habits were positively correlated (P < 0.05) in men. When the subjects were divided into quartiles based on the sum of fasting and two-hour postloading insulin levels, the averages of the reciprocal of serum creatinine were significantly lower in the fourth quartile (0.90 +/- 0.10 for men and 1.10 +/- 0.14 for women) compared with the lowest quartile (0.95 +/- 0.12 and 1.13 +/- 0.13, respectively) in both sexes (P < 0.05). In multiple regression analysis, the correlation between the sum of insulin levels and the reciprocal of serum creatinine remained significant even after controlling for age, sex, body mass index, blood pressure, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, alcohol intake, and smoking habits. We could not find appropriate correlations of creatinine clearance calculated by the Cockcroft-Gault formula with the covariates including serum insulin.

CONCLUSIONS

The findings of this study suggest that hyperinsulinemia is a significant relevant factor of renal function in the general population.

Hypertriglyceridemia, insulin resistance, and the metabolic syndrome

The metabolic syndrome consists of a cluster of metabolic disorders, many of which promote the development of atherosclerosis and increase the risk of cardiovascular disease events. Insulin resistance may lie at the heart of the metabolic syndrome. Elevated serum triglycerides commonly associate with insulin resistance and represent a valuable clinical marker of the metabolic syndrome. Abdominal obesity is a clinical marker for insulin resistance. The metabolic syndrome manifests 4 categories of abnormality: atherogenic dyslipidemia (elevated triglycerides, increased small low-density lipoproteins, and decreased high-density lipoproteins), increased blood pressure, elevated plasma glucose, and a prothrombotic state. Various therapeutic approaches for the patient with the metabolic syndrome should be implemented to decrease the risk of cardiovascular disease events. These interventions include decreasing obesity, increasing physical activity, and managing dyslipidemia; the latter may require the use of pharmacotherapy with cholesterol-lowering and triglyceride-lowering drugs.

Impaired vagal reflex activity in insulin-resistant rats

Insulin resistance, without frank diabetes, is associated with sudden cardiac death. We postulated that a potential mechanism for this association is autonomic dysfunction. Male Sprague-Dawley rats were randomized into one of two groups: (a) insulin resistant (IR; n = 15), or (b) control (n = 11). Animals were made insulin resistant with a fructose-rich diet, whereas control animals received standard rat chow. Four weeks after randomization, arterial pressure and baroreceptor reflex were assessed. Baroreflex sensitivity was defined as the heart-rate response to acute blood pressure changes caused by nitroprusside (0.5-18 micrograms) or phenylephrine (0.2-3 micrograms). To determine the role of vagal stimulation specifically, each animal was randomized to receive atropine sulfate (1 mg/kg) or vehicle (normal saline) before administration of phenylephrine. Mean arterial pressure and fasting insulin concentrations were increased in the insulin-resistant group, whereas there were no differences in body weight, fasting glucose concentrations, or resting heart rate. Phenylephrine increased arterial blood pressure to a maximum of 54 +/- 2 mm Hg for control and 45 +/- 6 mm Hg for IR, p = 0.7. The maximal heart-rate change response to the increased blood pressure was markedly blunted in IR as compared with control (-88 +/- 12 beats/min for IR vs. -238 +/- 18 beats/min for control; p < 0.001). Thus the baroreflex sensitivity (BRS) was threefold less in IR versus the control group (-1.8 +/- 0.2 vs. -4.6 +/- 0.7 beats/min/mm Hg; p = 0.001). Pretreatment with atropine sulfate decreased the BRS in both groups, eliminating the difference between groups (-0.96 +/- 0.5 beats/min/mm Hg for control and -0.56 +/- 0.3 beats/min/mm Hg for IR; p = 0.2). Thus atropine sulfate caused the phenylephrine-induced heart rate and arterial blood pressure response to be equal between groups. On the other hand, BRS to nitroprusside-induced blood pressure changes were similar between groups. Insulin resistance, without the confounding factors of obesity, diabetes, and significant hypertension, is associated with a large reduction in vagal activity, which occurs via attenuation in reflex activity. In contrast, the insulin-resistant syndrome does not affect baroreflex sensitivity via sympathetic reflex.

Special considerations in the therapy of diabetic hypertension

Patients with diabetes mellitus have an increased prevalence of hypertension and associated cardiovascular disease (CVD), including coronary and cerebrovascular disease. The risk of an individual of developing CVD is much greater when both diseases coexist and is further magnified by their frequent association with dyslipidemia, coagulation, platelet, and endothelial abnormalities. Metabolic abnormalities frequently associated with hypertension are insulin resistance, enhanced coagulation, and decreased fibrinolytic activity. Drug treatment of hypertension in diabetic subjects is fraught with potential difficulties, including altered efficacy of medications, possible side effects, worsening of glycemic control, and impairment of lipid metabolism. Because hypertension is a major contributor to morbidity and mortality in diabetes, it should be recognized and treated early and aggressively despite these difficulties. This article reviews the efficacy and side effects of the various classes of antihypertensive agents in patients with diabetes mellitus.

Blood pressure control, microalbuminuria and cardiovascular risk in Type 2 diabetes mellitus

Type 2 (noninsulin-dependent) diabetes mellitus (DM) affects about 3% of the UK population. Diabetes often coexists with a cluster of other potent cardiovascular risk factors, including hypertension, dyslipidaemia and increased tendency for thrombosis, and increases the risk of early death from cardiovascular causes by about threefold. Microalbuminuria or proteinuria also may be present, further increasing the risk of cardiovascular mortality. Cardiovascular risk factors must be treated aggressively in patients with Type 2 diabetes and control of blood pressure at 140/85 mm Hg or lower is a priority. The management of hypertension in patients from some ethnic groups demands special consideration because they have a high incidence of diabetes and hypertensive complications. Patients must be urged to adopt appropriate lifestyle changes in the first instance but additional drug treatment for hypertension is usually required. All the major classes of antihypertensive agents lower blood pressure in Type 2 diabetic patients but have different effects on metabolic risk factors in different ways. Low-dose thiazide diuretics, beta-blockers, calcium channel blockers and angiotensin converting enzyme (ACE) inhibitors have been shown to reduce cardiovascular risk. Individually, the effects of low-dose thiazide diuretics and beta-blockers on glucose and lipid metabolism is clinically insignificant, though in combination much larger metabolic effects are seen. ACE inhibitors and calcium channel blockers have no, or small, beneficial effects on glucose and lipid metabolism, while the greater beneficial effects of alpha1-blockers on lipid profiles may render them especially useful in the Type 2 diabetic patient. Long-acting calcium-channel blockers and ACE inhibitors protect renal function and are suitable as first line therapy in patients with microalbuminuria or proteinuria. Until results from the current batch of randomized, placebo-controlled trials comparing different classes of antihypertensive agents are available, the choice of antihypertensive agent is difficult. Addressing overall cardiovascular risk factors, rather than hypertension alone, is essential in the management of the hypertensive Type 2 diabetic patient.

Plasma leptin levels are associated with abnormal fibrinolysis in men and postmenopausal women

BACKGROUND

Leptin is a crucial mediator of satiety signals and energy balance, and its circulating levels are increased in obesity. It has recently been shown that plasma leptin levels in humans correlate with circulating insulin and to insulin secretion. This indicates that leptin may be an important link in metabolic consequences of the insulin resistance syndrome. Whether this includes abnormalities in fibrinolysis has not been studied.

METHODS AND RESULTS

Healthy subjects (n = 165; 85 men and 80 women) from the Northern Sweden MONICA population were investigated. Anthropometric measurements, oral glucose tolerance tests and sampling for plasma leptin, lipids, fibrinogen and fibrinolytic variables were made. Leptin levels were 342% higher in women than in men and were in both sexes strongly correlated to body mass index (BMI). After adjustments for age and BMI, leptin levels correlated significantly to pre/post glucoseload insulin levels in both sexes. After further adjustment for baseline insulin levels, leptin levels were in males significantly associated with increased waist circumference (P<0.001), low HDL cholesterol (P<0.05), low tPA activity (P<0.01) and high PAI-1 activity (P<0.001). In postmenopausal females, a significant association between leptin and low tPA activity/high PAI-1 activity was seen after adjustment for age and BMI (P<0.05). Conclusions. Circulating levels of leptin are associated with components of the insulin resistance syndrome, including defective fibrinolysis, in men and postmenopausal women. This suggests that leptin may be involved in the mediation of consequences of insulin resistance.

Plasma aldosterone, plasma lipoproteins, obesity and insulin resistance in humans

Aldosterone production in vitro can be affected by many hormones, autacoids, ions, and lipids, but regulation in humans is incompletely understood. We measured plasma aldosterone in adult subjects with a wide range of obesity and insulin resistance. Aldosterone levels correlated with measures of visceral obesity in one predominantly male cohort and in the women of a second cohort. In the same subjects, aldosterone correlated with insulin resistance. Aldosterone also correlated with plasma cortisol in men and women, and with DHEA-S in women. The data suggested that visceral fat stimulates adrenal steroidogenesis. We found that certain fatty acids stimulated aldosterone production in vitro by rat adrenal cells incubated with rat hepatocytes, but not adrenal cells alone. The results suggested that fatty acids from visceral adipocytes induce hepatic formation of an adrenal secretagogue. This may explain the correlation of plasma steroids with visceral obesity. Aldosterone may contribute to vascular diseases that complicate obesity.

Intracerebroventricular administration of bromocriptine ameliorates the insulin-resistant/glucose-intolerant state in hamsters

Bromocriptine, a potent dopamine D2 receptor agonist, suppresses lipogenesis and improves glucose intolerance and insulin resistance. Recent evidence suggests that bromocriptine may produce these effects by altering central nervous system (CNS) regulation of metabolism. To determine whether or not the CNS plays a critical role in these bromocriptine-mediated effects on peripheral metabolism, we compared the metabolic responses to bromocriptine when administered peripherally versus centrally in naturally obese and glucose intolerant Syrian hamsters. Male hamsters (BW 194 +/- 5 g) were treated with bromocriptine or vehicle either intraperitoneally (i.p., 800 microgram/animal) or intracerebroventricularly (i.c.v., 1 microgram/animal) daily at 1 h after light onset for 14 days while held on 14-hour daily photoperiods. Glucose tolerance tests (GTTs, 3 g glucose/kg BW) were conducted after treatment. Compared to control animals, bromocriptine i.p. significantly reduced weight gain (11.7 vs. -2.4 g) and the areas under the glucose and insulin GTT curves by 29 and 48%, respectively. Similarly, compared with vehicle-treated controls, bromocriptine i.c.v. at 1 microgram/animal substantially reduced weight gain (8.7 vs. -6.3 g), the areas under the glucose and insulin GTT curves by 31 and 44% respectively, and the basal plasma insulin concentration by 41% (p < 0.05). Furthermore, both treatments significantly improved insulin-mediated suppression of hepatic glucose production during a hyperinsulinemic-euglycemic clamp. Thus, daily administration of bromocriptine at a very low dose i.c.v. replicates the metabolic effects of bromocriptine administered i.p. at a much higher dose. This finding demonstrates for the first time that the CNS is a critical target of bromocriptine's metabolic effects.

Nontraditional cardiovascular risk factors

A number of newer, "nontraditional" cardiovascular risk factors have been identified based on recent studies of the pathogenesis of atherosclerosis and atherothrombotic cardiovascular events. These include chronic inflammation and its markers, such as C-reactive protein; homocysteine; oxidative stress or endothelial dysfunction; lipoprotein Lp (a); psychosocial factors, such as environmental stress and responsiveness to stress; plasma insulin levels and markers of insulin resistance; and activation of the renin-angiotensin system, which is in part a function of polymorphisms in genes for components of the system, such as angiotensinogen and the angiotensin II type 1 receptor. The strength of the associations of the newer risk factors with cardiovascular therapy are currently being tested. This review will briefly discuss evidence that these risk factors are related to cardiovascular disease.

Controlled study of the effect of angiotensin converting enzyme inhibition versus calcium-entry blockade on insulin sensitivity in overweight hypertensive patients: Trandolapril Italian Study (TRIS)

OBJECTIVE

The aim of this study was to evaluate the effect of trandolapril, an angiotensin converting enzyme inhibitor, on blood pressure, forearm blood flow and insulin sensitivity in comparison with nifedipine gastrointestinal therapeutic system.

PATIENTS AND METHODS

This is a multicentre, two-way parallel-group, open-label comparative study in 90 overweight hypertensive patients, who were randomly assigned to treatment for 8 weeks with either trandolapril or nifedipine. At baseline and after treatment, all patients underwent an oral glucose tolerance test, an evaluation of their metabolic profiles and a euglycaemic hyperinsulinaemic clamp test. In a subgroup of 18 patients, a forearm study was carried out.

RESULTS

Blood pressure fell by the second week of treatment and remained significantly reduced compared with baseline in both treatment groups. Plasma triglyceride levels were also significantly reduced after trandolapril therapy, but no significant changes occurred in the other metabolic parameters during treatment with either drug. During the euglycaemic hyperinsulinaemic clamp, whole-body glucose use was similar in the two treatment groups at baseline, and a moderate but statistically significant increase in insulin sensitivity was observed after trandolapril treatment (trandolapril: 5.0 +/- 0.2 versus 4.5 +/- 0.2 mg/kg per min; nifedipine: 4.1 +/- 0.3 versus 4.2 +/- 0.3 mg/kg per min; P < 0.05, versus baseline and trandolapril versus nifedipine treatment). Skeletal muscle glucose uptake was significantly higher after trandolapril than after nifedipine therapy (5.0 +/- 0.7 and 3.0 +/- 0.4 mg/min, respectively; P < 0.01). As forearm blood flow was similar in the two treatment groups at baseline and was unchanged after 8 weeks of therapy, skeletal muscle glucose extraction was significantly greater in the ACE inhibitor treated-group than in the nifedipine comparative group (trandolapril: baseline 21 +/- 2, treatment 24 +/- 3 mg/dl; nifedipine: baseline 18 +/- 3, treatment 16 +/- 2 mg/dl; P < 0.05, trandolapril versus nifedipine treatment).

CONCLUSIONS

During short-term treatment, ACE inhibition with trandolapril was able to moderately improve insulin sensitivity, in comparison with calcium blockade, and this effect appeared to be independent of the haemodynamic action of the drug.

Correlation of fasting serum C-peptide and insulin with markers of metabolic syndrome-X in a homogenous Chinese population with normal glucose tolerance

We surveyed 1447 men and 1800 women aged 30 years (mean 46.7 years) with normal glucose tolerance in Kin-Chen, Kinmen. Correlations of fasting serum insulin and C-peptide with various clinical and biochemical parameters were analyzed by multiple linear regression analysis. Women had significantly higher levels of insulin than men (98+/-43 vs. 91+/-43 pM, p<0.0001), yet they also had a more favorable cardiovascular risk profile. Insulin was positively associated with the female sex, height, body mass index, waist-to-hip ratio, serum triglyceride, total cholesterol, uric acid, and fasting plasma glucose, and was negatively associated with age, smoking, and high-density lipoprotein cholesterol. Independent correlates for C-peptide were similar to those of insulin, except for the addition of mean blood pressure and the exclusion of age and total cholesterol. Significant interaction of sex-body mass index (coefficient = -0.0051, p = 0.0232) was detected for C-peptide only. In conclusion, both fasting serum insulin and C-peptide are quantitatively associated with cardiovascular risk factors in this homogeneous Chinese population with normal glucose tolerance. The female sex is independently associated with higher insulin and C-peptide levels, and the strength of the positive association between the female sex and C-peptide reduces when the body mass index increases.

The kidney as part of the cardiovascular system

Renal vascular damage caused by arterial hypertension brings about changes in the systemic vascular function and structure. Nephrosclerosis appears to run in parallel with systemic atherosclerosis, accounting for the increased cardiovascular morbidity and mortality in hypertensive patients. Parameters indicating a change in renal function (increased serum creatinine concentration, proteinuria, and microalbuminuria) are independent predictors of increased cardiovascular morbidity and mortality and must therefore be considered in the classification of cardiovascular risk in hypertensive patients.

Microvascular function relates to insulin sensitivity and blood pressure in normal subjects

BACKGROUND

A strong but presently unexplained inverse association between blood pressure and insulin sensitivity has been reported. Microvascular vasodilator capacity may be a common antecedent linking insulin sensitivity to blood pressure. To test this hypothesis, we studied 18 normotensive and glucose-tolerant subjects showing a wide range in insulin sensitivity as assessed with the hyperinsulinemic, euglycemic clamp technique.

METHODS AND RESULTS

Blood pressure was measured by 24-hour ambulatory blood pressure monitoring. Videomicroscopy was used to measure skin capillary density and capillary recruitment after arterial occlusion. Skin blood flow responses after iontophoresis of acetylcholine and sodium nitroprusside were evaluated by laser Doppler flowmetry. Insulin sensitivity correlated with 24-hour systolic blood pressure (24-hour SBP; r=-0.50, P<0.05). Capillary recruitment and acetylcholine-mediated vasodilatation were strongly and positively related to insulin sensitivity (r=0.84, P<0.001; r=0.78, P<0.001, respectively), and capillary recruitment was inversely related to 24-hour SBP (r=-0.53, P<0.05). Waist-to-hip ratio showed strong associations with insulin sensitivity, blood pressure, and the measures of microvascular function but did not confound the associations between these variables. Subsequent regression analysis showed that the association between insulin sensitivity and blood pressure was not independent of the estimates of microvascular function, and part of the variation in both blood pressure (R2=38%) and insulin sensitivity (R2=71%) could be explained by microvascular function.

CONCLUSIONS

Insulin sensitivity and blood pressure are associated well within the physiological range. Microvascular function strongly relates to both, consistent with a central role in linking these variables.

Leptin is a risk marker for first-ever hemorrhagic stroke in a population-based cohort

BACKGROUND AND PURPOSE

Leptin, important for body weight regulation, may be involved in the pathogenesis of the insulin resistance syndrome, associated with cardiovascular disease. We tested to determine whether leptin is a risk marker for first-ever stroke in a nested case-referent study.

METHODS

We identified 113 patients with first-ever stroke (94 with ischemic and 19 with hemorrhagic stroke) who, before the stroke, had participated in population-based health surveys in northern Sweden. Referents were matched for sex, age, date and type of health survey, and geographic region. Blood pressure (BP), body mass index (BMI), and presence of smoking, diabetes, and hypertension were recorded. Total cholesterol, insulin, and leptin were analyzed in stored samples. Risk markers for first-ever stroke were analyzed by conditional logistic regression analysis.

RESULTS

Patients with hemorrhagic stroke had higher levels of BMI and systolic and diastolic BPs. Leptin levels were 72% and 59% higher in males and females, respectively, with hemorrhagic stroke versus referents. Patients with ischemic stroke more often had hypertension, diabetes mellitus, and higher fasting glucose and insulin levels. A diagnosis of hypertension and elevated systolic and diastolic BPs were significant risk markers for first-ever hemorrhagic stroke in univariate analysis. High leptin (OR=20.55; 95% CI, 1.12 to 376.7) levels together with hypertension (OR=16.28; 95% CI, 1.49 to 177.3) remained as significant risk markers in a multivariate model. The combination of high leptin and high systolic or diastolic BP were associated with a profoundly increased risk for hemorrhagic stroke (OR=22.11; 95% CI, 1.57 to 310.9). Diabetes, hypertension, and obesity (BMI >/=27), together with high levels of insulin, glucose, systolic and diastolic BP, were significant risk markers for first-ever ischemic stroke in univariate analysis. Hypertension (OR=2.10; 95% CI, 1.14 to 3.86) remained as an independent risk marker in a multivariate model.

CONCLUSIONS

Plasma leptin is strongly associated with an increased risk for first-ever hemorrhagic stroke, independent of other risk markers for cardiovascular disease. Leptin may be an important link in the development of cardiovascular disease in obesity.

From preadipocyte to adipocyte: differentiation-directed signals of insulin from the cell surface to the nucleus

An alarming rise in obesity, and the accompanying threat of type 2 diabetes mellitus and cardiovascular disease, have attracted worldwide attention. The pathogenic mechanism(s) underlying obesity remains obscure. However, new cellular and molecular insights about the development of adipose tissue, with respect to adipocyte number (hyperplasia) and size (hypertrophy), are occurring at a rapid pace. Specialized fibroblasts (preadipocytes) committed to the adipocyte lineage are present throughout life. Primary cell culture systems and immortalized cell line models of preadipocytes have advanced the study of adipocyte differentiation (adipogenesis). Differentiation-inducing cues are able to trigger a complex network of intracellular signaling pathways in the preadipocyte, allowing signals from cell-surface receptors to reach nuclear transcription factors that regulate the genetic program of adipocyte differentiation. The extracellular matrix environment of the preadipocyte, known to modulate adipogenesis, may act by altering some of these signaling events.

Lipid infusion lowers sympathetic nervous activity and leads to increased beta-cell responsiveness to glucose

We investigated the possible involvement of the autonomic nervous system in the effect of a long-term elevation of plasma free fatty acid (FFA) concentration on glucose-induced insulin secretion (GIIS) in rats. Rats were infused with an emulsion of triglycerides (Intralipid) for 48 hours (IL rats). This resulted in a twofold increase in plasma FFA concentration. At the end of infusion, GIIS as reflected in the insulinogenic index (DeltaI/DeltaG) was 2.5-fold greater in IL rats compared with control saline-infused rats. The ratio of sympathetic to parasympathetic nervous activities was sharply decreased in IL rats relative to controls. GIIS was studied in the presence of increasing amounts of alpha- and beta-adrenoreceptor agonists and antagonists. The lowest concentrations of the alpha2A-adrenoreceptor agonist oxymetazoline, which were ineffective in control rats, reduced GIIS in IL rats. At the dose of 0.3 pmol/kg, GIIS became similar in IL and control rats. The use of beta-adrenoreceptor agonist (isoproterenol) or antagonist (propranolol) did not result in a significant alteration in GIIS in both groups. GIIS remained as high in IL vagotomized rats as in intact IL rats, indicating that changes in parasympathetic tone were of minor importance. Altogether, the data show that lipid infusion provokes beta-cell hyperresponsiveness in vivo, at least in part through changes in alpha2-adrenergic innervation.

Troglitazone and vascular reactivity: role of glucose and calcium

We sought to determine whether insulin/insulin-like growth factor-1 (IGF-1) and an insulin-sensitizing agent, troglitazone, have additive vasodilatory effects and the possible involvement of intracellular Ca2+ ([Ca2+]i) and/or glucose utilization in these effects. Contractile responses to norepinephrine (NE) and potassium chloride (KCl), as well as relaxation to endothelium-dependent (acetylcholine [Ach]) and -independent (sodium nitroprusside [NaNP]) agents, were examined in rat tail artery rings in the presence of insulin/IGF-1 and/or troglitazone. Endothelium-intact tail artery rings stretched to 1 g tension were preincubated with troglitazone (3 micromol/L) and/or insulin/IGF-1 (100 nmol/L) prior to addition of graded doses of NE and KCI. A 90-minute exposure to troglitazone attenuated the maximal contraction to graded doses of NE and KCI (P<.0001). Incubation in glucose-free medium decreased the responses only to NE; troglitazone further attenuated the NE-induced contraction (P = .001). In submaximally precontracted endothelium-intact rings, troglitazone increased the relaxation both to NaNP (P<.0001) and to Ach (P = .001). Contraction experiments in depolarizing KCI (25 mmol/L) or Ca2+ -free buffer showed that troglitazone and insulin have a similar Ca2+ dependency. In conclusion, troglitazone, like insulin/IGF-1, attenuates responses to vasoactive agonists through a Ca2+ -dependent mechanism that may require the presence of glucose but is independent of insulin action and nitric oxide (NO) production.

Ionizing radiation and genetic risks. VI. Chronic multifactorial diseases: a review of epidemiological and genetical aspects of coronary heart disease, essential hypertension and diabetes mellitus

This paper provides a broad overview of the epidemiological and genetical aspects of common multifactorial diseases in man with focus on three well-studied ones, namely, coronary heart disease (CHD), essential hypertension (EHYT) and diabetes mellitus (DM). In contrast to mendelian diseases, for which a mutant gene either in the heterozygous or homozygous condition is generally sufficient to cause disease, for most multifactorial diseases, the concepts of genetic susceptibility' and risk factors' are more appropriate. For these diseases, genetic susceptibility is heterogeneous. The well-studied diseases such as CHD permit one to conceptualize the complex relationships between genotype and phenotype for chronic multifactorial diseases in general, namely that allelic variations in genes, through their products interacting with environmental factors, contribute to the quantitative variability of biological risk factor traits and thus ultimately to disease outcome. Two types of such allelic variations can be distinguished, namely those in genes whose mutant alleles have (i) small to moderate effects on the risk factor trait, are common in the population (polymorphic alleles) and therefore contribute substantially to the variability of biological risk factor traits and (ii) profound effects, are rare in the population and therefore contribute far less to the variability of biological risk factor traits. For all the three diseases considered in this review, a positive family history is a strong risk factor. CHD is one of the major contributors to mortality in most industrialized countries. Evidence from epidemiological studies, clinical correlations, genetic hyperlipidaemias etc., indicate that lipids play a key role in the pathogenesis of CHD. The known lipid-related risk factors include: high levels of low density lipoprotein cholesterol, low levels of high density lipoprotein cholesterol, high apoB levels (the major protein fraction of the low density lipoprotein particles) and elevated levels of Lp(a) lipoprotein. Among the risk factors which are not related to lipids are: high levels of homocysteine, low activity of paraoxonase and possibly also elevated plasma fibrinogen levels. In addition to the above, hypertension, diabetes and obesity (which themselves have genetic determinants) are important risk factors for CHD. Among the environmental risk factors are: high dietary fat intake, smoking, stress, lack of exercise etc. About 60% of the variability of the plasma cholesterol is genetic in origin. While a few genes have been identified whose mutant alleles have large effects on this trait (e.g., LDLR, familial defective apoB-100), variability in cholesterol levels among individuals in most families is influenced by allelic variation in many genes (polymorphisms) as well as environmental exposures. A proportion of this variation can be accounted for by two alleles of the apoE locus that increase (&epsi;4) and decrease (&epsi;2) cholesterol levels, respectively. A polymorphism at the apoB gene (XbaI) also has similar effects, but is probably not mediated through lipids. High density lipoprotein cholesterol levels are genetically influenced and are related to apoA1 and hepatic lipase (LIPC) gene functions. Mutations in the apoA1 gene are rare and there are data which suggest a role of allelic variation at or linked LIPC gene in high density lipoprotein cholesterol levels. Polymorphism at the apoA1--C3 loci is often associated with hypertriglyceridemia. The apo(a) gene which codes for Lp(a) is highly polymorphic, each allele determining a specific number of multiple tandem repeats of a unique coding sequence known as Kringle 4. The size of the gene correlates with the size of the Lp(a) protein. The smaller the size of the Lp(a) protein, the higher are the Lp(a) levels. (ABSTRACT TRUNCATED)

Identification of Cd36 (Fat) as an insulin-resistance gene causing defective fatty acid and glucose metabolism in hypertensive rats

The human insulin-resistance syndromes, type 2 diabetes, obesity, combined hyperlipidaemia and essential hypertension, are complex disorders whose genetic basis is unknown. The spontaneously hypertensive rat (SHR) is insulin resistant and a model of these human syndromes. Quantitative trait loci (QTLs) for SHR defects in glucose and fatty acid metabolism, hypertriglyceridaemia and hypertension map to a single locus on rat chromosome 4. Here we combine use of cDNA microarrays, congenic mapping and radiation hybrid (RH) mapping to identify a defective SHR gene, Cd36 (also known as Fat, as it encodes fatty acid translocase), at the peak of linkage to these QTLs. SHR Cd36 cDNA contains multiple sequence variants, caused by unequal genomic recombination of a duplicated ancestral gene. The encoded protein product is undetectable in SHR adipocyte plasma membrane. Transgenic mice overexpressing Cd36 have reduced blood lipids. We conclude that Cd36 deficiency underlies insulin resistance, defective fatty acid metabolism and hypertriglyceridaemia in SHR and may be important in the pathogenesis of human insulin-resistance syndromes.

Renal characteristics and effect of angiotensin suppression in oral contraceptive users

-The determinants of the increase in arterial blood pressure associated with the use of estrogen-progestogen oral contraceptives (OC) remain poorly known. The purpose of this study was to assess the renal characteristics and the role of the renin-angiotensin system in women with OC-associated hypertension. Urinary clearances of technetium-labeled diethylene triaminopentaacetic acid (glomerular filtration rate) and 131I-ortho iodohippurate (effective renal plasma flow) were estimated before and after acute administration of captopril in 38 women who became hypertensive while taking OC, 38 non-OC users with essential hypertension matched for age, body mass index, and level of blood pressure, and 38 normotensive women (19 with and 19 without OC). Plasma renin activity was higher in OC hypertensives when compared with those with essential hypertension, but captopril-induced changes in blood pressure and renal hemodynamics and function were similar in both groups. In addition, 24-hours urinary albumin excretion was increased in OC users when compared with nonusers with similar arterial blood pressure. In 13 hypertensive women followed up for 6 months after OC withdrawal, a decrease in plasma renin activity, blood pressure, and glomerular filtration rate but no significant change in urinary albumin excretion and captopril-induced changes in blood pressure and renal hemodynamics were observed. These results indicate that the use of OC is associated with an increased albuminuria and no evidence of a prominent role for the renin-angiotensin system in the maintenance of high blood pressure and renal hemodynamics when compared with non-OC users with essential hypertension.

Elevated serum semicarbazide-sensitive amine oxidase activity in non-insulin-dependent diabetes mellitus: correlation with body mass index and serum triglyceride

Previous clinical studies reported elevated semicarbazide-sensitive amine oxidase (SSAO) activity in insulin-dependent diabetes mellitus (IDDM), but there are not sufficient data about SSAO in non-insulin-dependent diabetes mellitus (NIDDM). The present study was conducted to investigate serum SSAO activity in NIDDM patients compared with nondiabetic and IDDM patients. Serum SSAO activity in 61 patients with diabetes (n = 34 NIDDM and n = 27 IDDM) and 36 controls was determined using 14C-benzylamine as a substrate. NIDDM and IDDM patients exhibited higher SSAO activity compared with controls ([mean +/- SD] NIDDM, 164.60+/-69.43 pmol/mg protein/h, P<.0001; IDDM, 143.91+/-72.45 pmol/mg protein/h, P<.002; control, 91.46+/-28.11 pmol/mg protein/h). There was a significant positive correlation between serum SSAO activity and the body mass index (BMI), body weight, hemoglobin A1c (HbA1c), fasting plasma glucose, and triglycerides. Within the control group, SSAO correlated with total cholesterol levels. The progression and severity of diabetic complications such as angiopathy may be exacerbated by cytotoxic metabolites (e.g., formaldehyde and hydrogen peroxide) formed by SSAO. These results reveal the possibility that elevated serum SSAO activity in association with obesity and hyperlipidemia may be a cardiovascular risk factor in diabetes mellitus.

Slower activation of insulin action in hypertension associated with obesity

OBJECTIVE

To determine whether kinetic abnormalities in the onset of insulin action contribute to the insulin resistance in obesity-associated hypertension.

DESIGN

We monitored the rate of increase in glucose infusion during 6 h of hyperinsulinemic (40 mU/m2 per min) euglycemic clamps in hypertensive and normotensive obese subjects. The two groups of hypertensive (n=9) and normotensive (n=9) subjects were matched for age (48+/-2 versus 45+/-5 years), sex (five males and four females versus four males and five females) and body mass index (42+/-3 versus 40+/-2 kg/m2).

RESULTS

In all subjects, the glucose infusion rate required to maintain euglycemia increased progressively during the clamp studies to achieve maximal, steady-state values within the fifth hour. During the first 2 h of the clamp, mean glucose infusion rate, the traditional approach to assessing insulin sensitivity, was lower in the hypertensive than in the normotensive obese patients (2.04+/-0.13 versus 3.29+/-0.41 mg/kg per min, respectively; P < 0.05). In contrast, the maximal steady-state glucose infusion rate, calculated as the mean value during the sixth hour of clamping, was similar in the hypertensive and in the normotensive obese patients (4.48+/-0.43 versus 4.81+/-0.45 mg/kg per min, respectively; NS). The time required to reach the half-maximal glucose infusion rate was greater in the hypertensive than normotensive obese patients (91+/-12 versus 38+/-5 min, respectively; P< 0.05).

CONCLUSION

In obesity, hypertension was associated with a slower rate of activation of the insulin effect on glucose metabolism, whereas the maximal steady-state insulin effects were not altered by elevated blood pressure. Thus, the link between obesity and hypertension may be associated with the kinetics of onset of insulin action.

Evaluation and treatment of hypertension in active individuals

Hypertension is a very common vascular disease. It is seen in adolescents, obese persons, postmenopausal women, and the elderly. A nonpharmacologic approach to treatment is a critical first step in management. The modalities include a diet low in salt and saturated fat, exercise, less than 2 ounces of alcohol daily, and abstinence from smoking. Dynamic (aerobic) exercise is effective in lowering blood pressure (BP) only if performed regularly. Weight reduction by diet must be combined with exercise if there is to be a reduction in BP. Strength training is not to be considered as an alternative to aerobic training for reducing BP. Antihypertensive mediation can be added to nonpharmacologic interventions for additional BP reduction. Beta-blockade is not a contraindication to exercise training.

Relationship between blood pressure, metabolic variables and blood flow in obese subjects with or without non-insulin-dependent diabetes mellitus

BACKGROUND

To assess the relationship between systemic blood pressure, metabolic variables and adipose tissue blood flow, we studied 55 subjects before and 36 subjects after an oral glucose load (100 g).

METHODS

The subjects were divided into four different groups: (a) young lean control subjects [age 31 +/- 1 years, mean +/- SE, BMI (body mass index) 22.7 +/- 0.4 kg m-2]; (b) young obese subjects (age 29 +/- 2 years, BMI 37.8 +/- 1.8 kg m-2); (c) middle-aged obese subjects (age 50 +/- 2 years, BMI 30.2 +/- 0.9 kg m-2); and (d) middle-aged obese non-insulin-dependent diabetic (NIDDM) subjects (age 54 +/- 2 years, BMI 30.0 +/- 0.7 kg m-2).

RESULTS

Groups 2-4 demonstrated a low fasting adipose tissue blood flow (ATBF) and the increase in ATBF after oral glucose was impaired. A further impairment was present in NIDDM subjects. Systolic and diastolic blood pressure were also increased in groups 2-4 and further so in group 4. Fasting glucose, lactate and free fatty acid (FFA) levels correlated positively with the systolic blood pressure, whereas ATBF correlated negatively with the diastolic blood pressure. Furthermore, in the NIDDM subjects fasting lactate correlated closely with both the systolic (r = 0.649, P = 0.01) and diastolic (r = 0.626, P = 0.013) blood pressure.

CONCLUSION

These data suggest a close relationship between insulin resistance and regulation of adipose tissue blood flow as well as blood pressure.

Hypertensive patients and diabetes: a high-risk population

Rising worldwide rates of diabetes mellitus heighten the need to maintain adequate metabolic control in diabetic patients and to control for other cardiovascular risk factors, such as lipid profile disturbances, high blood pressure, and smoking habits. This is especially the case in diabetic patients who also present with hypertension, a co-morbid state that is present in at least 50% of Type 1 and Type 2 diabetic patients. Cardiovascular disease is present in 75% of all diabetes-related deaths, and the concomitant condition of diabetes and hypertension is believed to act synergistically on elevating the risk for cardiovascular disease. A number of trials have demonstrated a greater incidence of cardiovascular disease end points in diabetic hypertensive patients than in diabetic normotensive patients. Furthermore, hypertension is associated not only with an increased risk for cardiovascular mortality but also for microvascular complications in patients with diabetes. Adequate treatment of high blood pressure is imperative in these patients. The effectiveness of antihypertensive treatment can be measured not only by the degree of reduction in blood pressure but also by assessment of the effects on urinary albumin excretion rate. It is assumed that the greater the reduction in urinary albumin excretion rate, the greater the renoprotective effect. Treatment choices should be evidence-based, i.e., physicians should concentrate not only on the treatment of hypertension but also on improving glycemic control and lipid profile disorders, when necessary. When viewed in this regard, angiotensin-converting enzyme inhibitors, low-dose diuretics, and in some cases beta-blockers, should be considered agents of choice in hypertensive diabetic patients.

Insulin-mediated growth in aortic smooth muscle and the vascular renin-angiotensin system

Insulin has been shown to directly affect blood vessel tone and to promote vascular hypertrophy, but the mechanism of these actions remains uncertain. Because angiotensin I (Ang I)-converting enzyme inhibitors have been shown to improve insulin action and to impede the progression of vascular hypertrophy in hypertensive animal models, it is possible that the vascular properties of insulin may be mediated through the tissue renin-angiotensin system (RAS). To evaluate this relationship, we first investigated the effect of insulin on components of the RAS using cultured rat vascular smooth muscle cells (VSMCs). Insulin treatment (1000 microU/mL) markedly increased angiotensinogen mRNA expression and angiotensinogen production. We next investigated the role of the RAS in insulin-mediated cell proliferation, using [3H]thymidine uptake. Studies were done both with insulin alone and in the presence of captopril (1x10(-7) to 10(-5) mol/L) and losartan (1x10(-9) to 10(-7) mol/L). [3H]Thymidine uptake was increased significantly by 1000 microU/mL insulin, and this stimulation was reduced by 1x10(-6) mol/L captopril (-38.8%, P<0.05) and by 1x10(-8) mol/L losartan (-37. 5%, P<0.05). Further studies showed that the degree of insulin-mediated [3H]thymidine uptake in VSMCs could be duplicated by 4x10(-10) mol/L Ang II. Losartan reduced the effects of both Ang II and insulin on [3H]thymidine uptake by about 40% to 45% of baseline (P<0.05). Captopril reduced insulin-mediated [3H]thymidine uptake but did not affect Ang II-mediated [3H]thymidine uptake. In summary, insulin induced significant stimulation of angiotensinogen expression and production and stimulated growth similar to that seen with Ang II in cultured rat VSMCs. Inhibition of Ang II production or its binding to the Ang II type 1 (AT1) receptor inhibited insulin-mediated growth in a fashion similar to that seen with inhibition of Ang II-mediated growth. Thus, insulin can modulate the vascular RAS, and the effect of insulin on vascular growth may be via direct effects on angiotensinogen expression and translation operative through both the AT1 receptor and the conversion of Ang I to Ang II.

Sympathetic activity in obese subjects with and without obstructive sleep apnea

BACKGROUND

Obese humans are reported to have increased muscle sympathetic nerve activity (MSNA). Obstructive sleep apnea (OSA) may also be accompanied by increased MSNA. Because there is a high prevalence of OSA in obese humans, it is possible that high MSNA reported in obese subjects may in fact reflect the presence of OSA in these subjects. We tested the hypothesis that obesity, per se, in the absence of OSA, is not accompanied by increased MSNA.

METHODS AND RESULTS

We measured MSNA in 25 healthy normal-weight subjects and 30 healthy sedentary obese subjects. All subjects were screened by history and examination to exclude subjects with OSA or hypertension. OSA was further excluded by overnight polysomnographic studies. Despite careful screening, polysomnography revealed that 1 of 25 normal-weight subjects and 9 of 30 obese subjects had occult OSA (P=0.015). MSNA was similar in normal-weight subjects (41+/-3 bursts per 100 heartbeats) and obese subjects without sleep apnea (42+/-3 bursts per 100 heartbeats, P=0.99). MSNA in the 9 obese subjects with occult OSA was 61+/-8 bursts per 100 heartbeats, which was higher than MSNA in normal-weight subjects without sleep apnea (P=0.02) and higher than MSNA in obese subjects without sleep apnea (P=0.02).

CONCLUSIONS

Obesity alone, in the absence of OSA, is not accompanied by increased sympathetic activity to muscle blood vessels.

Functional food science and the cardiovascular system

Cardiovascular disease has a multifactorial aetiology, as is illustrated by the existence of numerous risk indicators, many of which can be influenced by dietary means. It should be recalled, however, that only after a cause-and-effect relationship has been established between the disease and a given risk indicator (called a risk factor in that case), can modifying this factor be expected to affect disease morbidity and mortality. In this paper, effects of diet on cardiovascular risk are reviewed, with special emphasis on modification of the plasma lipoprotein profile and of hypertension. In addition, dietary influences on arterial thrombotic processes, immunological interactions, insulin resistance and hyperhomocysteinaemia are discussed. Dietary lipids are able to affect lipoprotein metabolism in a significant way, thereby modifying the risk of cardiovascular disease. However, more research is required concerning the possible interactions between the various dietary fatty acids, and between fatty acids and dietary cholesterol. In addition, more studies are needed with respect to the possible importance of the postprandial state. Although in the aetiology of hypertension the genetic component is definitely stronger than environmental factors, some benefit in terms of the development and coronary complications of atherosclerosis in hypertensive patients can be expected from fatty acids such as alpha-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid. This particularly holds for those subjects where the hypertensive mechanism involves the formation of thromboxane A2 and/or alpha 1-adrenergic activities. However, large-scale trials are required to test this contention. Certain aspects of blood platelet function, blood coagulability, and fibrinolytic activity are associated with cardiovascular risk, but causality has been insufficiently proven. Nonetheless, well-designed intervention studies should be initiated to further evaluate such promising dietary components as the various n-3 and n-6 fatty acids and their combination, antioxidants, fibre, etc. for their effect on processes participating in arterial thrombus formation. Long-chain polyenes of the n-3 family and antioxidants can modify the activity of immunocompetent cells, but we are at an early stage of examining the role of immune function on the development of atherosclerotic plaques. Actually, there is little, if any, evidence that dietary modulation of immune system responses of cells participating in atherogenesis exerts beneficial effects. Although it seems feasible to modulate insulin sensitivity and subsequent cardiovascular risk factors by decreasing the total amount of dietary fat and increasing the proportion of polyunsaturated fatty acids, additional studies on the efficacy of specific fatty acids, dietary fibre, and low-energy diets, as well as on the mechanisms involved are required to understand the real function of these dietary components. Finally, dietary supplements containing folate and vitamins B6 and/or B12 should be tested for their potential to reduce cardiovascular risk by lowering the plasma level of homocysteine.

Aldosterone in obesity

Plasma aldosterone levels were measured in adults whose body mass index ranged from lean to obese. Blood was drawn while subjects rested supine for 30-90 minutes. Aldosterone was higher in obese subjects, but could not be explained by renin or K+. The best predictors of plasma aldosterone were abdominal obesity measured as waist/hip ratio or by CT scan, and insulin resistance measured by insulin or oral glucose tolerance tests, or euglycemic clamp. In one cohort, these correlations were limited to women; in the other, they were also found in men. In the women with a strong correlation between aldosterone and visceral fat, aldosterone also correlated with cortisol and DHEA-S. The data are consistent with an effect of visceral fat on adrenal steroidogenesis. Visceral adipocytes have a high rate of triglyceride turnover, and their circulation drains directly to the liver. In an experiment based on these characteristics, rat hepatocytes responded to fatty acids by releasing an unidentified secretagogue that stimulated aldosterone production by rat adrenal glomerulosa cells. The clinical data suggest that aldosterone participates in hypertension associated with the "Insulin Resistance Syndrome". The adrenal in viscerally obese subjects may be driven by a secretagogue released from the liver by fatty acids from abdominal adipocytes.

Intracellular starvation in the insulin resistance syndrome and type II diabetes mellitus

Statistical associations of insulin resistance, type II diabetes, hypertension and hyperlipidemia have been well documented, but the pathophysiology of the 'insulin resistance syndrome' is unknown. This article explores the hypothesis that intracellular starvation plays a central role in the development of type II diabetes, hypertension and hyperlipidemia. According to this hypothesis, insulin resistance leads to inadequate intracellular glucose, which in turn leads to insufficient amounts of adenosine triphosphate needed for ion transfer, and to drive energy-requiring reactions. Indirect evidence supporting this hypothesis is presented. Intracellular starvation is also discussed as an alternative to the 'glucose hypothesis' to explain certain complications of diabetes.

Nephropathy and hypertension in diabetes

The treatment of the patient with diabetes, with or without hypertension, is complex and challenging. Hyperglycemic treatment should ideally not only control blood glucose, but also prevent the chronic complications and associated metabolic derangements that can lead to increased morbidity and mortality. Hypertensive treatment should not only decrease blood pressure, but also reduce the risk of macrovascular and microvascular disease. The use of antihypertensive agents that improve insulin resistance, dyslipidemia, glycemic control, and nephropathy is preferred whenever possible. The real key to success in the care of the hypertensive diabetic patient is adequate screening and appropriate, early treatment. Currently, there is ample evidence to support the use of intensive management with the goal of near-normalization of blood glucose levels in most patients with diabetes. Similarly, aggressive treatment of hypertension is the current standard. Accomplishing these goals helps to prevent the development of chronic diabetic complications, including nephropathy. ESRD need not be the inevitable outcome for individuals with early diabetic nephropathy. Interventions currently available that are targeted at the known modifiable risk factors underlying the development and progression of diabetic nephropathy offer the best hope for reducing the incidence and severity of this complication. Prevention of the complications of diabetes, including nephropathy, must be the goal for the future on behalf of all those who now have diabetes.

Familial hypertension, insulin, sympathetic activity, and blood pressure elevation

This study evaluated the effects of a positive family history of hypertension (FH+) on the contributions of sympathetic nervous system (SNS) activity and insulin to blood pressure elevation (BPE). The study design was longitudinal and evaluated BP, body mass index (BMI), and fasting plasma insulin and norepinephrine (NE) levels for 10 years in 557 young, nonobese Japanese men who were normotensive at entry. FH+ was defined as hypertension in first-degree relatives as verified by historical records or direct determination. BPE was defined as a > or = 10% rise in systolic and diastolic BP over entry levels during the 10-year period. In the total group FH+ was noted in 16%, and BPE occurred in 18% of normotensive subjects. When evaluated by FH, the prevalence of BPE was 33% in FH+ compared with 16% in FH- (P<0.05). BP levels were greater both at entry and at year 10 in the FH+ group. The absolute increment in plasma NE over 10 years was greater in the BPE group than in those without BPE (P<0.01). Of note, the rise in plasma NE levels in BPE individuals was identical in FH+ and FH- subjects. Plasma insulin increments were also greater in normotensive subjects with BPE than in normotensive subjects without BPE. However, compared with NE, development of hyperinsulinemia was more pronounced in the FH+ subjects. The results indicate that SNS hyperactivity may be a less genetically determined predictor of hypertension than is hyperinsulinemia. Because SNS changes in this initially normotensive population appeared more closely related to the development of hypertension than to hyperinsulinemia, environmental rather than genetic factors may be the main determinant of early BPE in nonobese normotensive subjects.

Lipids in hypertensive patients

Hypertension and hyperlipidemia are common and powerful risk factors for cardiovascular disease. Although they may coexist in the same individual by chance, the syndrome of insulin resistance is the common mechanism in many individuals, in whom there is a specific lipoprotein profile of small, dense, low-density lipoprotein particles, reduced plasma high-density lipoprotein cholesterol levels, and increased plasma triglycerides. This lipoprotein profile may be exacerbated by diuretics or beta-blockers. Initial management of the insulin resistance syndrome is by weight loss and dietary measures. Optimum antihypertensive and lipid-lowering drug strategy remains to be established.