Insulin sensitivity in the pathogenesis of hypertension and hypertensive complications

Sympathetic nervous system and hypertension: New evidences

Evidences collected in the past few years have strengthened the concept that the sympathetic nervous system plays a primary role in the development and progression of the hypertensive state, starting from the early stage, and in the hypertension-related cardiovascular diseases. Several pathophysiological mechanisms are involved. Among them the genetic background, the immune system in conjunction with sympathetic activation. The present review will briefly discuss the importance of the above mentioned mechanisms in the development of hypertension. The paper will also examine the sympathetic mechanisms underlying attended vs unattended blood pressure measurements as well as their role in resistant vs pseudo-resistant hypertension. Finally evidence from recent meta-analysis on the relevance of sympathetic nerve traffic activation in the pathogenesis of hypertension will be briefly discussed.

Chronic intrarenal insulin replacement reverses diabetes mellitus-induced natriuresis and diuresis

We showed recently that sustained natriuresis in type 1 diabetic dogs was attributed to the decrease in insulin rather than the hyperglycemia alone. The sodium-retaining action of insulin appeared to require hyperglycemia, and it completely reversed the diabetic natriuresis and diuresis. This study tested whether the sodium-retaining effect was attributed to direct intrarenal actions of insulin. Alloxan-treated dogs (D; n=7) were maintained normoglycemic using 24-h/d IV insulin replacement. After control measurements, IV insulin was decreased to begin a 6-day diabetic period. Blood glucose increased from 84±6 mg/dL to an average of 428 mg/dL on days 5 and 6, sodium excretion increased from 74±8 to 98±7 meq/d over the 6 days, and urine volume increased from 1645±83 to 2198±170 mL/d. Dir dogs (n=7) were subjected to the same diabetic regimen, but, in addition, insulin was infused continuously into the renal artery at 0.3 mU/kg per minute during the 6-day period. This did not affect plasma insulin. Blood glucose increased from 94±10 mg/dL to an average of 380 mg/dL on days 5 and 6, but sodium excretion averaged 76±5 and 69±8 meq/d during control and diabetes mellitus, respectively. The diuresis also was prevented. Glomerular filtration rate increased only in Dir dogs, and there was no change in mean arterial pressure in either group. This intrarenal insulin infusion had no effect on sodium or volume excretion in normal dogs. Intrarenal insulin replacement in diabetic dogs caused a sustained increase in tubular reabsorption that completely reversed diabetic natriuresis. Insulin plus glucose may work to prevent salt wasting in uncontrolled type 2 diabetes mellitus.

Healthy weight - healthy blood pressure

World Hypertension Day is an initiative of the World Hypertension League. This year's theme is "Healthy weight - healthy blood pressure". According to the World Health Organization, more than one billion people worldwide are reported to be overweight and more than 300 million people are obese. Obesity is linked to hypertension, kidney diseases and other cardiovascular diseases. Through World Hypertension Day, the World Hypertension League, in partnership with national and international organizations, aims to raise the awareness of obesity and hypertension. Simple manoeuvres such as eating healthy, being physically active, and changing nutritional and dietary behaviours are recommended.

Chronic glucose infusion causes sustained increases in tubular sodium reabsorption and renal blood flow in dogs

This study tested the hypothesis that inducing hyperinsulinemia and hyperglycemia in dogs, by infusing glucose chronically intravenously, would increase tubular sodium reabsorption and cause hypertension. Glucose was infused for 6 days (14 mg.kg(-1).min(-1) iv) in five uninephrectomized (UNX) dogs. Mean arterial pressure (MAP) and renal blood flow (RBF) were measured 18 h/day using DSI pressure units and Transonic flow probes, respectively. Urinary sodium excretion (UNaV) decreased significantly on day 1 and remained decreased over the 6 days, coupled with a significant, sustained increase in RBF, averaging approximately 20% above control on day 6. Glomerular filtration rate and plasma renin activity (PRA) also increased. However, although MAP tended to increase, this was not statistically significant. Therefore, the glucose infusion was repeated in six dogs with 70% surgical reduction in kidney mass (RKM) and high salt intake. Blood glucose and plasma insulin increased similar to the UNX dogs, and there was significant sodium retention, but MAP still did not increase. Interestingly, the increases in PRA and RBF were prevented in the RKM dogs. The decrease in UNaV, increased RBF, and slightly elevated MAP show that glucose infusion in dogs caused a sustained increase in tubular sodium reabsorption by a mechanism independent of pressure natriuresis. The accompanying increase in PRA, together with the failure of either RBF or PRA to increase in the RKM dogs, suggests the site of tubular reabsorption was before the macula densa. However, the volume retention and peripheral edema suggest that systemic vasodilation offsets any potential renal actions to increase MAP in this experimental model in dogs.

Pioglitazone, a thiazolidinedione derivative, attenuates left ventricular hypertrophy and fibrosis in salt-sensitive hypertension

Thiazolidinediones, which stimulate peroxisome proliferator-activated receptor gamma, have been shown to prevent cardiovascular injury. However, little is known about their effects on salt-sensitive hypertension. We thus investigated whether or not pioglitazone affects left ventricular (LV) hypertrophy in Dahl salt-sensitive rats, then compared its effects to those of an angiotensin II receptor blocker, candesartan. Rats were used at 16 weeks of age after they had been fed either a low-salt (0.3%; DSL) or high-salt (8%; DSH) diet for 10 weeks; some of the DSH rats were treated with pioglitazone (10 mg/kg/day) or candesartan (4 mg/kg/day). Both drugs decreased the elevated blood pressure in DSH rats, although it was still higher than in DSL rats. Both drugs decreased plasma insulin levels, but neither affected plasma glucose levels. The thiobarbituric acid reactive substance level in the LV was decreased by both drugs. LV hypertrophy evaluated by echocardiography in DSH rats was nearly normalized by both drugs, whereas only candesartan decreased LV diameter. In histological analysis, both drugs ameliorated LV fibrosis and myocardial cell hypertrophy. Both drugs decreased elevated gene expression levels of transforming growth factor-beta1 and collagen type I, although the pioglitazone action was slightly modest. The metalloproteinase activity was increased in DSH rats, but both drugs decreased this level. Taken together, these findings indicate that pioglitazone reduced LV hypertrophy and fibrosis in salt-sensitive hypertension. Improvement in blood pressure, insulin level, and oxidative stress may be associated with this beneficial action of pioglitazone.

Angiotensin II receptor blockers decreased blood glucose levels: a longitudinal survey using data from electronic medical records

Background

A beneficial effect on glucose metabolism is reported with angiotensin receptor blocker (ARB) treatment of hypertension. The effect on blood glucose level during the course of treatment with ARBs in clinical cases is uncertain. Our objectives were to survey the changes in glucose and HbA1c levels in patients with hypertension over a one-year period, and to study the correlations between these values and the time after the start of ARB therapy.

Methods

We conducted a retrospective longitudinal survey of blood glucose and HbA1c measurements in Japanese patients aged ≥20 years with newly diagnosed hypertension but without diabetes, who had received ARB monotherapy with candesartan cilexetil, losartan potassium, olmesartan medoxomil, telmisartan, or valsartan during the period from December 2004 to November 2005. Data including 2465 measurements of non-fasting blood glucose in 485 patients and 457 measurements of HbA1c in 155 patients were obtained from electronic medical records of Nihon University School of Medicine. Linear mixed effects models were used to analyze the relationship between these longitudinal data of blood examinations and covariates of patient age, sex, medication, and duration of ARB therapy.

Results

Casual blood glucose level was associated with the duration of treatment (P < 0.0001), but not with age, sex, or medication. Blood glucose level was significantly decreased during the periods of 0~3 months (P < 0.0001) and 3~6 months (P = 0.0081) compared with baseline, but was not significantly different between 6~12 months and baseline. There was no association between HbA1c level and covariates of sex, age, medication and duration of treatment.

Conclusion

Our findings provide new clinical evidence that the effects of ARBs on glucose metabolism may change during the course of treatment, suggesting a blood glucose-lowering effect in the short-term after the start of treatment.

Obesity, metabolic syndrome and sleep apnoea: all pro-inflammatory states

Obesity is associated with significant morbidity and mortality and is increasing in prevalence worldwide. Associated conditions include insulin resistance (IR), diabetes, hypertension and dyslipidaemia; a clustering of these has recently been termed as metabolic syndrome. Weight gain is a major predictor of the metabolic syndrome with waist circumference being a more sensitive indicator than body mass index as it reflects both abdominal subcutaneous adipose tissue and visceral adipose tissue (VAT). VAT has more metabolic activity and secretes a number of hormones and pro-inflammatory cytokines which are linked with the metabolic abnormalities listed above. Central obesity also increases the risk of obstructive sleep apnoea syndrome (OSAS), where the sleep disordered breathing may also independently lead to/or exacerbate IR, diabetes and cardiovascular risk. The contribution of OSAS to the metabolic syndrome has been under-recognized. The putative mechanisms by which OSAS causes or exacerbates these other abnormalities are discussed. We propose that activation of nuclear factor kappa B by stress hypoxia and/or by increased adipokines and free fatty acids released by excess adipose tissue is the final common inflammatory pathway linking obesity, OSAS and the metabolic syndrome both individually and, in many cases, synergistically.

Obesity and hypertension: two epidemics or one?

The association between obesity and hypertension is well documented, although the exact nature of this relation remains unclear. Sympathetic nervous and renin-angiotensin-aldosterone system activation appear to play an important role in the sodium and water retention, rightward shift in the pressure-natriuresis, and blood pressure elevation observed in obese individuals. Visceral obesity and the ectopic deposition of adipose tissue may be important in the activation of these systems and in the target organ damage that ensues. Weight loss is critical in the effective management of obesity hypertension and the accompanying target organ damage, although recidivism rates are high. However, prevention of weight gain should be the major priority for combating hypertension and its consequences in the future. The present review will provide an overview of our understanding of the etiology, pathophysiology, and treatment of obesity hypertension. Our focus is on the state of knowledge in humans. The potential role of abdominal obesity is considered throughout our review. We refer to relevant animal literature for supportive evidence and where little or no data in humans are available.

Insulin-exacerbated hypertension in captopril-treated spontaneously hypertensive rats: role of sympathoexcitation

Insulin excess exacerbates hypertension in spontaneously hypertensive rats (SHR). This study examined the relative contribution of the renin–angiotensin system and the sympathetic nervous system in this phenomenon. In SHR, daily subcutaneous injections of insulin were initiated either before short-term angiotensin-converting enzyme inhibition with captopril or after lifetime captopril treatment. Insulin treatment resulted in significant increases in mean arterial pressure and heart rate and captopril treatment lowered arterial pressure, but captopril did not lower arterial pressure more in the insulin-treated compared with control rats. To test the contribution of the sympathetic nervous system to this form of hypertension, each rat was intravenously infused with either a ganglionic blocker (i.e., hexamethonium) or a centrally acting α2-adrenergic receptor agonist (i.e., clonidine). Administration of either agent largely eliminated the differences in mean arterial pressure and heart rate between the insulin-treated and saline-treated SHR, irrespective of captopril treatment. These data indicate that in SHR, the ability of insulin to increase blood pressure is closely related to sympathoexcitation, which is unresponsive to blockade of angiotensin-converting enzyme.Key words: blood pressure, insulin, captorpil, hexamethonium, clonidine, rat.

[Glucose effectiveness and components of the metabolic syndrome in recently diagnosed hypertensive patients]

BACKGROUND

Glucose effectiveness (SG) is a parameter that indicates the glucose ability to clearing itself from the plasma independently of insulin's action. Our purpose was to analyze the cluster characteristics associated with the metabolic syndrome in a group of non-obese, recent-onset hypertensives and to test if there was a correlation with SG and the effectiveness of glucose at basal insulin point (GEZI).

PATIENTS AND METHOD

We studied 36 patients with mild hypertension with normal basal glucose levels. We determined plasma lipid subfractions, apolipoproteins and urate levels. An intravenous glucose tolerance test (TTGI) and minimal model analysis according to Bergman was performed and SG, GEZI and insulin sensitivity (SI) were calculated.

RESULTS

Patients with lower SG and GEZI had higher levels of total triglycerides (Tg) (r = 0.42; p = 0.01 and r = 0.48; p = 0.002, respectively) and triglycerides bind to VLDL (Tg-VLDL) (r = 0.40; p < 0.01 and r = 0.49; p = 0.002, respectively). When the cluster of metabolic syndrome was analyzed, SG was inversely related to uric acid levels and to the waist-hip index. However, SI was only related to the uric acid levels (r = 0.38; p = 0.01).

CONCLUSIONS

In non-obese, recently diagnosed hypertensive patients, the SG parameter seems to be an early marker for the development of metabolic syndrome.

Quinapril treatment restores the vasodilator action of insulin in fructose-hypertensive rats

1. Angiotensin-converting enzyme (ACE) inhibitors have been shown to improve insulin-resistance both experimentally and clinically. We therefore investigated the effects of quinapril, which has high tissue specificity for ACE, regarding the contribution of insulin to vascular contractions, as well as insulin sensitivity in a dietary rat model of insulin resistance. 2. Male Sprague-Dawley rats were divided into three groups: (i) rats fed normal chow (normal diet group); (ii) rats fed fructose-rich chow containing 40% fructose and 7% lard (fructose diet group); and (iii) rats fed fructose-rich chow plus quinapril (10 mg/kg per day; quinapril-treated group). 3. After 2 weeks, we evaluated systolic blood pressure, insulin sensitivity as assessed by steady state plasma glucose (SSPG) levels, response of aortic rings to phenylephrine (10-9 to 10-6 mol/L) in the presence or absence of insulin and the response of aortic rings to acetylcholine. 4. Feeding rats fructose-rich chow resulted in an elevation of blood pressure (P < 0.01) and SSPG levels (P < 0.01). Quinapril treatment significantly prevented increases in both blood pressure and SSPG, with a return to the levels seen in the normal diet group. 5. In the absence of insulin, the maximal contractile response to phenylephrine did not differ between the three groups. However, in the presence of insulin (100 mU/mL), the contractile response to phenylephrine (10-6 mol/L) was reduced by 22.8 +/- 1.2% in the normal diet group, although no insulin effects were observed in the fructose diet group (P < 0.01). Quinapril restored the inhibitory effect of insulin on phenylephrine-induced contractions. 6. In addition, the reduction in relaxation induced by acetylcholine in the fructose diet group was significantly reversed by quinapril treatment. 7. It is concluded that the fructose diet impairs the vasodilator effects of insulin as well as acetylcholine-induced relaxation in rat thoracic aortas. Quinapril prevented deterioration in the responses of the aortic rings, suggesting that ACE inhibitors may be useful for treating vascular insulin resistance.

Sleep disordered breathing--a new component of syndrome x?

Sleep disordered breathing (SDB) is a complication of obesity estimated to occur in about 4-6% of overweight individuals. These respiratory disturbances during sleep incorporate a number of conditions including snoring, upper airway resistance syndrome and obstructive sleep apnoea syndrome (OSAS). It is thought that as well as having deleterious effects on sleep quality these conditions may also promote cardiovascular and hormonal changes leading to an elevated blood pressure and an increased incidence of cardiovascular morbidity. Evidence reviewed here points to an alteration in sympathovagal balance, baroreceptor sensitivity, insulin resistance and leptin, growth hormone and lipid levels. Whether these changes are a consequence of the associated obesity or the SDB itself remains to be proven.

Predictors of target organ damage in hypertensive blacks and whites

The purpose of this study was to evaluate the association of the insulin resistance syndrome with both blood pressure and target organ damage in blacks and whites with essential hypertension. Eighty-two black and 63 white French Canadian patients were studied. None had diabetes, and antihypertensive medications had been discontinued for >/=1 week. Measurements included 24-hour blood pressure monitoring, fasting plasma lipids, insulin sensitivity determined with the Bergman minimal model, echocardiogram, microalbumin excretion, and inulin and lithium clearances. Compared with the white French Canadians, black patients had an attenuated nighttime reduction in blood pressure (P<0.02), increased cardiac dimensions (P<0.001), greater microalbumin excretion (P<0.05), increased inulin clearance (indicative of glomerular hyperfiltration; P<0.001), and decreased lithium clearance (indicative of increased sodium reabsorption in the proximal tubule; P<0.001). Blood pressure levels were not related to insulin resistance; although in blacks, the nighttime reduction in systolic blood pressure was inversely related to fasting plasma insulin (r=-0.18, P<0.04). In a stepwise multivariate analysis (including blood pressure levels and components of the insulin resistance syndrome as independent variables), race was the strongest predictor of left ventricular mass (r=0.53, P<0.000), relative wall thickness (r=0.49, P<0.000), and both inulin (r=0.53, P<0.000) and lithium (r=0.41, P<0.000) clearances. Nighttime systolic blood pressure was also a significant determinant of concentric left ventricular hypertrophy (r=0.37, P<0.000). In blacks, microalbumin excretion was related to insulin resistance. These observations are consistent with the hypothesis that there is a genetic contribution to cardiac hypertrophy, glomerular hyperfiltration, and sodium retention in blacks with essential hypertension.

Left ventricular mass is not related to insulin sensitivity in never-treated primary hypertension

OBJECTIVE

Insulin has been suggested to promote myocardial cell growth and the development of left ventricular (LV) hypertrophy. This study examines the possible relationship between LV mass and insulin sensitivity.

DESIGN

Previously untreated non-diabetic hypertensive patients.

PATIENTS

Fifty-one patients with mean age 51 +/- 8 years, body mass index (BMI) 25.9 +/- 3.2 kg/m2 and blood pressure 158/102 mmHg were included. LV mass was determined by echocardiography. Glucose metabolism was assessed by an euglycemic insulin clamp (40 mU/m2 body surface area/min).

RESULTS

Insulin sensitivity index (MI) and insulin clearance were inversely related to LV mass (r = -0.37, P < 0.01 and -0.33, P < 0.05, respectively) and LV mass indexed to height (r = -0.33, P < 0.05 and -0.29, P < 0.05, respectively). C-peptide and fasting insulin were related to LV mass (r = 0.33, P < 0.05 and r = 0.36, P < 0.01, respectively) and LV mass indexed to height (r = 0.30, P < 0.05 and r = 0.34, P < 0.05, respectively). In contrast, when LV mass was indexed by body surface area there was no longer a relation to MI, insulin clearance, C-peptide or fasting insulin. When adjusting for BMI in a multiple regression analysis, MI and LV mass no longer showed a relation. Indeed, MI, insulin clearance, C-peptide and insulin were all strongly related to weight and BMI.

CONCLUSION

Insulin sensitivity is related to body size in untreated hypertension. However, insulin sensitivity is not related to LV mass, if adjusting for body size. This does not support a direct growth-promoting effect of insulin on the myocardium. Insulin does not appear to be strongly involved in development of hypertensive LV hypertrophy.

Metabolic complications of obesity

The rising prevalence of obesity is accompanied by an increasing number of patients with the metabolic complications of obesity. The major complications come under the heading of the metabolic syndrome. This syndrome is characterized by plasma lipid disorders (atherogenic dyslipidemia), raised blood pressure, elevated plasma glucose, and a prothrombotic state. The clinical consequences of the metabolic syndrome are coronary heart disease and stroke, type 2 diabetes and its complications, fatty liver, cholesterol gallstones, and possibly some forms of cancer. At the heart of the metabolic syndrome is insulin resistance, which represents a generalized derangement in metabolic processes. Obesity is the predominant factor leading to insulin resistance, although other factors play a role. The mechanistic link between insulin resistance and the metabolic syndrome is complex. The relationship is modulated by yet other factors, such as physical activity, body fat distribution, hormones, and a person's genetic polymorphic architecture. A better understanding of the molecular basis of this relationship is needed to suggest new targets for prevention and treatment of the complications of obesity. In addition, understanding at the clinical level will lead to improved management of these complications.

Mechanisms of insulin resistance in rat models of hypertension and their relationships with salt sensitivity

Several lines of evidence suggest that insulin resistance and the resultant hyperinsulinaemia are causally related to hypertension. Insulin actions are initiated by binding to a high-affinity transmembrane protein receptor which is present in all mammalian cells. These effects are predominant in skeletal muscle, liver, and fat and involve a number of tissue-specific and biochemically diverse events. Less well known are effects of insulin occurring in tissues not usually considered as insulin targets, which are hypothetical contributors to the pro-hypertensive action of the hormone. These effects include activation of renal sodium reabsorption, stimulation of the sympathetic nervous system, growth-promoting activity on vascular smooth muscle cells, and modulation of transmembrane cation transport. Epidemiological investigations have implicated sodium intake in the pathogenesis of hypertension. Because of the sodium-retaining effects of insulin, it has been postulated that insulin resistance with associated hyperinsulinaemia may be critical for the pathogenesis of salt-sensitivity in essential hypertensive subjects. Insulin resistance is present also in strains of rats with genetic hypertension that can be utilized as models to study the molecular mechanisms of this abnormality. In the present article, we summarize the current knowledge of the mechanisms of insulin resistance in rat models of arterial hypertension in which decreased sensitivity to insulin occurs and propose a rationale hypothesis that links insulin resistance with salt-sensitivity and hypertension.

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.

Risk factors for cardiovascular disease and diabetes in two groups of Hispanic Americans with differing dietary habits

OBJECTIVE

The purpose of this study was to determine if Hispanic Seventh-Day Adventists (SDAs), who typically eat a diet lower in fat, saturated fat and protein, and higher in complex carbohydrates and dietary fiber than the usual omnivorous diet, exhibit lower risk factors for cardiovascular disease (CVD) and Type 2 diabetes compared to Hispanic Catholic omnivores.

METHODS

Anthropometric characteristics, dietary intake, blood pressure, serum lipids, glucose and insulin, as well as plasma ascorbic acid and vitamin E concentrations, were measured in two groups of Hispanic study participants residing in Denver, Colorado: 74 SDA study participants (x age: 42+/-1.5 y) and 45 Catholic participants (x age: 44+/-2.2 y).

RESULTS

The SDAs reported lower dietary intakes of total fat, saturated fat and cholesterol and higher relative intakes of carbohydrate and dietary fiber compared to their Catholic counterparts. The SDAs exhibited significantly lower body mass index (BMI = 27.2+/-0.6) and waist-to-hip ratios (WHR = 0.84+/-0.01) compared to the Catholics (BMI = 31.4+/-1.1; WHR = 0.88+/-0.01). The SDAs, compared to the Catholics, had lower fasting insulin (11.4+/-0.6 vs. 18.9+/-3.1 microu/ml) and glucose concentrations (88.6+/-1.1 vs. 104.1+/-5.4 mg/dl). The SDA Hispanics, compared to the Catholic Hispanics, exhibited significantly lower values for systolic blood pressure (SBP = 1102 vs. 118+/-3 mm Hg), serum total cholesterol (STC = 198+/-5 vs. 214+/-6 mg/dl) and serum triglycerides (TG = 152+/-12 vs. 232+/-27) and higher serum concentrations of high-density lipoprotein cholesterol (HDL-C = 44.7+/-1.3 vs. 39.1+/-1.4 mg/dl) and ascorbic acid (1.14+/-0.08 vs. 0.87+/-0.07 mg/dl). Low-density lipoprotein cholesterol (LDL-C) and vitamin E concentrations were not significantly different between groups, but the SDAs exhibited lower ratios of STC/HDL-C and LDL-C/HDL-C.

CONCLUSION

Hispanic American SDAs, who eat a plant-based diet, exhibit a more favorable blood lipid profile, lower blood pressure and lower risk for Type 2 diabetes compared to Hispanic American Catholics, who do not eat a plant-based diet.

Cardiovascular regulation during insulin infusion into the carotid or vertebral artery in dogs

OBJECTIVE

To test the hypothesis that insulin increases heart rate and arterial pressure via direct effects on the central nervous system.

METHODS AND DESIGN

Insulin was infused into the cerebral circulation of conscious dogs (n = 8) chronically instrumented for continuous infusions and measurement of arterial pressure, cardiac output, heart rate and other hemodynamic variables. In acute experiments, insulin was infused for 30 min into either a carotid or vertebral artery at several rates calculated to increase cerebral circulation insulin concentrations to levels in the physiological or pathophysiological range. It was infused with and without a simultaneous glucose infusion. During long-term experiments, insulin was infused into either a carotid or a vertebral artery for 4 days at 0.4 or 0.2 mU/kg per min, respectively.

RESULTS

Insulin infusion alone into the cerebral circulation produced no changes in any measured cardiovascular variable. A simultaneous glucose infusion also produced no changes in cardiovascular dynamics, except at the highest rate of infusion into the carotid artery. The changes seen at the highest rate of infusion are unlikely to be insulin-induced, since similar changes occurred when either glucose or saline was infused in the absence of any insulin infusion. Long-term insulin infusion (4 days) into carotid or vertebral arteries also produced no changes in any measured cardiovascular or renal variable.

CONCLUSIONS

These results provide no evidence that insulin, at physiological or pathophysiological concentrations, increases heart rate or arterial pressure by acting directly on the central nervous system, and suggest that sympathetic activation and tachycardia previously observed with systemic hyperinsulinemia may be secondary to peripheral actions of insulin.

Inhibitory action of insulin-sensitizing agents on calcium channels in smooth muscle cells from resistance arteries of guinea-pig

1. The actions of troglitazone, pioglitazone, metformin and bezafibrate, agents that improve insulin-resistance, on voltage-dependent Ca2+ channels in arterial smooth muscle cells were examined by use of the conventional and nystatin-perforated whole-cell clamp methods. Single cells were freshly isolated from resistance mesenteric arteries of guinea-pigs. The actions of these agents on 77 mM K+-induced contraction of the isolated arteries were also examined with the use of isometric tension recording. 2. The thiazolidinedione derivatives, troglitazone and pioglitazone, inhibited whole-cell Ca2+ currents in a dose-dependent manner with dissociation constants of 3.0 microM and 44.9 microM and Hill coefficients of 0.61 and 0.68, respectively. These two agents inhibited the 77 mM K+-induced contraction with similar potencies as those inhibiting the Ca2+ currents. Metformin and bezafibrate had no apparent effects on the Ca2+ current or high K+-induced contraction. 3. The inhibitory action of troglitazone on Ca2+ currents was not affected by the command potential, the holding potential, or the stimulation frequency, suggesting that its mode of the action differs from that of known organic Ca2+ channel antagonists. 4. The inhibitory action of troglitazone on Ca2+ currents was not affected by the addition of insulin to, or the removal of glucose from, the solutions. 5. In conclusion, the thiazolidinedione derivatives directly inhibited the voltage-dependent Ca2+ channels in a different manner from that of organic Ca2+ channel antagonists. This inhibitory action on Ca2+ channels was not a common feature of insulin-sensitizing agents.

Hypertension, hypertrophy, hormones, and the heart

Mild-to-moderate hypertension is common, and its natural history is reasonably well defined. The association of elevated blood pressure with left ventricular hypertrophy, insulin resistance, renal dysfunction, and increased propensity toward atherosclerotic cardiovascular disease and ventricular arrhythmias has been characterized. These associations, however, are not well predicted by the level of blood pressure elevation, suggesting some independence between blood pressure levels and cardiovascular complications. Although the reduction in pressure-related outcomes caused by therapeutic interventions (e.g., stroke) has been demonstrated, a similar reduction in many atherosclerotic outcomes has not been definitively demonstrated. The latter observation may be related to a number of factors but may be partly explained by the lack of direct correlation between blood pressure and cardiovascular outcome. This review attempts to update available information on the intermediating factors mitigating the relation among blood pressure, adverse cardiovascular outcome, and the treatment of hypertension.