Hyperinsulinemia. A link between hypertension obesity and glucose intolerance

Leucocyte sodium pump activity after meals or insulin in normal and obese subjects: cause for increased energetic efficiency in obesity?

As cellular sodium pumping is an energy consuming process and differences in the obese may account for their energetic efficiency, leucocyte sodium-22 efflux was studied in obese and normal volunteers both in the fasting state and after a test meal or infusion of glucose and insulin intravenously. The 22Na ouabain sensitive efflux rate constant was significantly higher in obese subjects than normal (mean (1 SD) 2.69 (0.40)/h v 2.35 (0.49)/h). Two hours after a 4.2 MJ (1000 kcal) meal there was an increase in the efflux rate constant from its fasting value in normal weight subjects (2.39 (0.33)/h to 2.71 (0.40)/h) but not in obese subjects (2.65 (0.54)/h to 2.61 (0.58)/h). The rise in ouabain sensitive efflux rates was significantly higher in normal than obese subjects. Both groups showed a rise in intracellular sodium concentrations. The euglycaemic clamp produced similar results. Feeding or infusion of insulin increases sodium pump activity more in normal than obese subjects. This difference may contribute to any defective dietary thermogenesis in obesity, which may lead to energetic efficiency and a tendency to gain weight.

Fructose-induced insulin resistance and hypertension in rats

To determine if hypertension could be produced in normal rats by feeding them a fructose-enriched diet, Sprague-Dawley rats were fed either normal chow or a diet containing 66% fructose as a percentage of total calories for approximately 2 weeks. At the end of this period systolic blood pressure had increased from 124 +/- 2 to 145 +/- 2 (SEM) mm Hg in the fructose-fed rats, whereas no change occurred in the control group. In addition, hyperinsulinemia and hypertriglyceridemia were associated with hypertension in fructose-fed rats. The addition of clonidine to the drinking water inhibited fructose-induced hypertension, but not the increase in plasma insulin or triglyceride concentration seen in fructose-fed rats. Thus, the metabolic changes associated with fructose-induced hypertension are unlikely to be secondary to an increase in sympathetic activity. Whether or not this is also true of the hypertension remains to be clarified.

A longitudinal study on the significance of environmental and individual factors associated with the development of essential hypertension

Altogether 379 men of the same age have been followed for more than 40 years, mainly as regards socioeconomic conditions during the first 10 years as well as cognitive ability measured at the ages of 10 and 20, education, income development, and psychosocial conditions in adulthood. At the age of 48 a health investigation was performed. In order to identify possible risk factors associated with the development of raised blood pressure 38 subjects with essential hypertension were compared with 155 men without any obvious mental or somatic diseases. No differences regarding socioeconomic conditions during childhood could be observed between the two groups. However, there was a very strong difference between father's education and the son's cognitive ability in the group with hypertension. The low income development for the group with hypertension can probably be explained partly by the lower cognitive ability. In the total group there was a positive correlation between IQ at the age of 10 and income at the age of 43 (r = 0.42; p less than 0.001). The hypertensive men were psychosocially disadvantaged with respect to divorce rate and job dissatisfaction, and furthermore they reported low physical activity during leisure time. Hypertensive men were more obese and had inferior respiratory function. The observation that a lower cognitive ability seems to be related to the development of hypertension is compatible with the observation that early mortality in this investigated group has a correlation of a low IQ with poor socioeconomic conditions in childhood.

Nonpharmacologic therapy of hypertension

At least seven nondrug therapies have been shown to reduce the blood pressure in some hypertensive patients. Although each has its detractors, I believe most should be utilized in the therapy of most hypertensives. Some, such as weight reduction for the obese, decreased saturated fat intake, regular isotonic exercise, and moderation of alcohol, can be enthusiastically advocated for everyone, since they may accomplish additional improvements in overall cardiovascular risk beyond their effect on blood pressure. Others such as moderate sodium restriction, adequate dietary sources of potassium, magnesium, and calcium, and relaxation therapy, can be helpful in at least some hypertensives and should be appropriately applied to the therapy of those who may benefit. To varying degrees, nondrug therapies should be included in the treatment of all patients with hypertension.

Relationship between blood pressure and plasma insulin in non-obese and obese non-diabetic subjects

In this study, we have measured plasma insulin at fasting and following an oral glucose load and blood pressure after glucose load in 367 (247 non-obese, 120 obese) normotensive and untreated mildly hypertensive subjects. Overall, there was no independent association between fasting plasma insulin levels and blood pressure values. After controlling for age and body weight, a significant relationship between postglucose plasma insulin levels and diastolic blood pressure was found. When non-obese and obese subjects were examined separately, significant relationships were identified between postglucose plasma insulin levels and both systolic and diastolic blood pressure values in the former but not in the latter. A comparison of sex-, age-, and weight-matched hyperinsulinaemic vs normoinsulinaemic subjects showed that the former had significantly higher values of blood pressure only if not obese. These results demonstrate that the plasma insulin response to glucose is independently correlated with blood pressure.

Elevated serum uric acid--a facet of hyperinsulinaemia

In a representative sample of the adult Jewish population in Israel (n = 1016) excluding known diabetic patients and individuals on antihypertensive medications, serum uric acid showed a positive association with plasma insulin response (sum of 1- and 2-hour post glucose load levels) in both males (r = 0.316, p less than 0.001) and females (r = 0.236, p less than 0.001). This association remained statistically significant in both sexes (p less than 0.001) after accounting by multiple regression analysis for age and major correlates of serum uric acid i.e. body mass index, glucose response (sum of 1- and 2-hour post load levels), systolic blood pressure and total plasma triglycerides. The net portion of the variance of serum uric acid attributable to insulin response was 12% in males and 8% in females, the total variance accountable by all these variables being 17% and 19% respectively. We conclude that elevated serum uric acid is a feature of hyperinsulinaemia/insulin resistance.

A role for insulin in the aetiology and course of hypertension?

It is proposed that abnormalities of glucose and insulin metabolism have a role in both the aetiology and the clinical course of hypertension. There is resistance to insulin-stimulated glucose uptake in patients with hypertension, which is associated with glucose intolerance and hyperinsulinaemia. Hyperinsulinaemia could contribute to hypertension by stimulating the activity of the sympathetic nervous system and kidney sodium and volume reabsorption. Glucose intolerance and hyperinsulinaemia have been identified as risk factors for coronary artery disease, and their presence may help explain why the frequency of this disease has not been reduced by treatment of hypertension. The fact that several antihypertensive drugs deleteriously affect glucose, insulin, and lipid metabolism makes it even more important to consider these factors in the treatment of high blood pressure.

Insulin resistance in essential hypertension

High blood pressure is prevalent in obesity and in diabetes, both conditions with insulin resistance. To test whether hypertension is associated with insulin resistance independently of obesity and glucose intolerance, we measured insulin sensitivity (using the euglycemic insulin-clamp technique), glucose turnover (using [3H]glucose isotope dilution), and whole-body glucose oxidation (using indirect calorimetry) in 13 young subjects (38 +/- 2 years [+/- SEM]) with untreated essential hypertension (165 +/- 6/112 +/- 3 mm Hg), normal body weight, and normal glucose tolerance. In the postabsorptive state, all measures of glucose metabolism were normal. During steady-state euglycemic hyperinsulinemia (about 60 microU per milliliter), hepatic glucose production and lipolysis were effectively suppressed, and glucose oxidation and potassium disposal were normally stimulated. However, total insulin-induced glucose uptake was markedly impaired (3.80 +/- 0.32 vs. 6.31 +/- 0.42 mg per minute per kilogram of body weight in 11 age- and weight-matched controls, P less than 0.001). Thus, reduced nonoxidative glucose disposal (glycogen synthesis and glycolysis) accounted for virtually all the defect in overall glucose uptake (1.19 +/- 0.24 vs. 3.34 +/- 0.44 mg per minute per kilogram, P less than 0.001). Total glucose uptake was inversely related to systolic or mean blood pressure (r = 0.76 for both, P less than 0.001). These results provide preliminary evidence that essential hypertension is an insulin-resistant state. We conclude that this insulin resistance involves glucose but not lipid or potassium metabolism, is located in peripheral tissues but not the liver, is limited to nonoxidative pathways of intracellular glucose disposal, and is directly correlated with the severity of hypertension.

Theory of the etiology of human toxemia of pregnancy: fetal hyperinsulinemia as a compensatory response to decreased uterine blood flow

Toxemia of pregnancy is a perplexing clinical problem that has defied accurate elucidation of its etiology because the disorder does not occur in undisturbed lower mammalian species that are currently used as animal models of reproductive physiology. We propose that toxemia of pregnancy occurs as the end stage human fetal-placental unit response to decreased maternal uterine blood flow, and that this fetal-placental unit response may be unique to the human species. The human fetus increases insulin secretion in response to progressive intrauterine asphyxia, which may result in decreased fetal-placental prostacyclin production (a vasodilator and inhibitor of platelet aggregation) and increased fetal-placental thromboxane A2 production (a vasoconstrictor). This could result in increased uteroplacental perfusion pressure, maternal hypertension, and increased maternal platelet aggregation. We also suggest that women who develop idiopathic toxemia of pregnancy are at increased risk for adult onset diabetes later on in life because they have a mild derangement in glucose-insulin homeostasis during their reproductive years that results in increased uterine vascular damage, that leads to decreased uterine blood flow, and ultimately the fetal hyperinsulinemia-prostaglandin pressor release mechanism. Therefore, prevention of toxemia may be possible by correction of mild derangements in glucose-insulin receptor homeostasis before conception occurs.

Diabetes induced by neonatal streptozotocin treatment in spontaneously hypertensive and normotensive rats

The development of non-insulin-dependent diabetes mellitus (NIDDM) induced by neonatal streptozotocin (STZ) treatment was compared between male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). The animals were intraperitoneally given 37.5, 50.0, 62.5, or 75.0 mg/kg of STZ at two days of age. At two days after STZ injection, plasma glucose was elevated in both groups of rats according to the dose of STZ, but the level was higher in SHR than in corresponding WKY. At ten days of age, plasma glucose in WKY returned to the similar level to that in vehicle-treated control irrespective of the doses of STZ, while in SHR it remained above control and its level was significantly higher than that in WKY. At 12 weeks of age, plasma glucose was within the control range in WKY, while in SHR it was markedly and dose-dependently elevated. The present study indicates that SHR are susceptible to NIDDM induced by neonatal STZ treatment. The difference in response to STZ between SHR and WKY was discussed.

Diabetes and atherosclerosis: an epidemiologic view

Diabetes is associated with changes in plasma lipids and lipoproteins into atherogenic direction. In IDDM these changes are small or absent if good metabolic control can be maintained. Diabetic nephropathy is, however, associated with the appearance of dyslipoproteinemia. In NIDDM plasma total and VLDL triglyceride levels are elevated, and HDL-cholesterol level is decreased, and this pattern of dyslipoproteinemia does not always respond to improved control of hyperglycemia. Abnormalities of lipoprotein metabolism, not reflected in conventional plasma lipid and lipoprotein level measurements, and glucosylation of lipoproteins and resulting alterations in lipoprotein catabolism may be of importance in the enhanced atherogenesis in diabetes. Both IDDM and NIDDM are associated with an increased frequency of hypertension, but the underlying mechanisms appear to be different. In IDDM hypertension is usually associated with the development of diabetic nephropathy and thus with a long duration of the disease. In NIDDM hypertension is often present already at the time of diagnosis, and also in IGT, the precursor stage of NIDDM, the prevalence of hypertension is already increased. Obesity explains only in part the high prevalence of hypertension in patients with NIDDM. Diabetes is known to be associated with multiple abnormalities in hemostatic factors and, although these abnormalities may contribute importantly to the increased risk of ASVD in diabetic patients, information about their real role is scanty and conflicting. The impact of general major risk factors for ASVD, elevated plasma cholesterol, elevated blood pressure, and smoking, on the risk of ASVD appears to be similar in diabetics and nondiabetics. Only a relatively small proportion of the excessive occurrence of ASVD in diabetics can, however, be explained by the effects of diabetes on the levels of general risk factors for ASVD. This proportion mediated through the effects of diabetes on risk factors is larger in female diabetics than in male diabetics. The major proportion of the excess of ASVD in diabetics remains, however, unexplained and must be due to effects of diabetes itself through mechanisms that are incompletely understood.

Effect of insulin excess and deficiency on norepinephrine turnover in rats

To examine whether insulin enhances norepinephrine (NE) turnover, an index of sympathetic nerve activity, the effects of excess insulin and streptozotocin (STZ) induced insulin deficiency were examined in Sprague-Dawley rats. Exogenous insulin caused hyperphagia and elevated (approximately 300%) urinary epinephrine excretion, but did not alter cardiac NE content or turnover. STZ-induced insulin deficiency caused hyperglycemia and hyperphagia, but also did not alter cardiac NE content or turnover. Insulin deficiency reduced hepatic NE content 18%, but did not affect NE turnover or content of kidney or spleen. These data do not support the hypothesis that insulin influences cardiac sympathetic nerve activity in rats.

Body mass, blood pressure, glucose, and lipids. Does plasma insulin explain their relationships?

Obesity, hypertension, a high plasma level of glucose, and some lipid abnormalities (high plasma levels of cholesterol and triglycerides) often occur in the same individuals. Some authors have postulated that the elevated levels of plasma insulin in obese individuals may explain this association. To explore this hypothesis further, the relationships between body mass index, fasting plasma glucose and insulin, blood pressure, serum lipids, and apoproteins were investigated in a group of 2144 healthy middle-aged men. Analysis of the data show that the associations between body mass index and blood pressure or lipid variables are largely independent of plasma glucose and insulin. Plasma glucose is strongly related to blood pressure in nonobese subjects. Plasma insulin is not associated with blood pressure independently of body mass index and plasma glucose; however, the simultaneous elevation of body mass index, plasma glucose, and insulin is strongly associated with blood pressure. The results also confirm that plasma insulin is positively related to triglycerides and negatively related to high density lipoprotein cholesterol independently of plasma glucose and body mass index.

Blood pressure changes in spontaneously hypertensive and normotensive rats with neonatal streptozotocin induced type 2 diabetes

We examined the blood pressure changes in hypertensive and normotensive rats with Type 2 diabetes induced by neonatal streptozotocin (STZ) treatment. STZ was intraperitoneally injected at 2 days of age with the dose of 25, 50 and 75 mg/kg for male spontaneously hypertensive rats (SHR) and with 75, 100, 125 and 150 mg/kg for male normotensive Wistar Kyoto rats (WKY). Blood pressure was measured by indirect tail-cuff method until 12 weeks of age. STZ-treated SHR, of which plasma glucose and glycosylated hemoglobin increased and body weight decreased with the dose of STZ, developed and maintained hypertension, same as did the vehicle-treated control SHR. On the other hand, STZ-treated WKY which developed only mild hyperglycemia lost body weight with the dose of STZ but the blood pressures rose slightly, these changes being correlated with the glycemic levels. The explanation for these differences between SHR and WKY remained to be elucidated.

Long-term effects of nifedipine on carbohydrate and lipid metabolism in hypertensive hemodialyzed patients

To evaluate long-term effects of nifedipine on carbohydrate and lipid metabolism, 15 hypertensive patients undergoing regular hemodialysis treatment were investigated before nifedipine therapy, after 3 and 9 weeks, and 2 weeks after stopping nifedipine therapy. Three weeks following the administration of nifedipine, both glucose and insulin concentrations decreased significantly from 102.1 +/- 2.6 to 94.9 +/- 2.2 mg/dl and from 19.9 +/- 2.9 to 13.9 +/- 1.7 microU/ml and also remained significantly lower after 9 weeks of nifedipine therapy. This effect was paralleled by a fall of noradrenaline and dopamine. Glucagon levels remained constant. Glucose tolerance tests performed during nifedipine medication and 2 weeks after stopping of nifedipine therapy did not differ significantly. An increase of pyruvate, citric acid cycle intermediates, and ketone bodies--but not of lactate--was registered during nifedipine medication. The observed effects were not completely abolished after the 2-week placebo phase. Our data indicate that nifedipine lowers serum glucose values despite decreased insulin and constant glucagon levels in hypertensive hemodialyzed patients. Considering additionally the behavior of catecholamines and organic acids, the effects could be explained by the improvement of peripheral glucose utilization.

The leucocyte sodium pump in healthy and obese subjects: the association of insulin with its activity

Leucocyte ouabain-sensitive 22Na+ efflux was studied in 35 normal and 12 obese subjects. This efflux rate constant was raised in the obese (2.72 +/- SEM 0.13 vs 2.31 +/- 0.08 h-1, P less than 0.006), indicating a higher activity of the sodium pump in vivo, There was a significant correlation between this efflux rate constant and fasting insulin level in both the whole population and in the normals alone (rs = 0.36, P less than 0.007, and rs = 0.40, P less than 0.009 respectively). A hyperinsulinaemic-euglycaemic clamp was performed on seven normal volunteers. After 2 h, there was a significant stimulation of the leucocyte efflux rate constant (from 2.86 +/- 0.17 to 3.33 +/- 0.18 h-1, P less than 0.01). In-vitro incubation of leucocytes with insulin produced a maximal stimulation of the Na+-K+-ATPase activity of about 35% at 2 h with half-maximal stimulation achieved at 46 mU/l. Insulin (100 mU/l) also stimulated the leucocyte ouabain-sensitive 22Na+ efflux rate constant in vitro by about 11% with or without 1 h of preincubation with the insulin. These findings may explain the hypokalaemic and sodium retaining effects of insulin in man; they may also partially explain the raised Na+ efflux rate constants in obesity.

Insulin as a potential factor influencing blood pressure in amputees

War-injured, bilateral above-knee amputees are known to be at increased risk for cardiovascular mortality. To evaluate possible risk factors, we compared blood pressures and plasma glucose and insulin responses to orally administered glucose in 19 above-knee amputees from the Vietnam War (mean age, 36 +/- 1 years) with those of 12 age-matched unilateral below-elbow amputees. Body composition by densitometry and maximal oxygen consumption during arm or leg exercise were also determined. Nine of 19 leg amputees were hypertensive compared with one of 12 arm amputees. Their 3-hour average insulin responses were markedly increased (260 +/- 60 microU/ml) compared with those of normotensive leg (125 +/- 24 microU/ml) and arm amputees (101 +/- 20 microU/ml), and their mean body fat content (37.2%) also was elevated compared with that in both of these groups (23.2 and 22.6%, respectively). A unique finding was that both insulin response and body fat content were strongly and independently correlated with diastolic blood pressure (r = 0.55, p less than 0.01, and r = 0.62, p less than 0.01, respectively). We conclude that insulin may be a major factor in blood pressure regulation in the maturity-onset obesity that develops following traumatic leg amputation in young, healthy men.

Blood pressure, insulin, and glycemia in nondiabetic subjects

The relation of blood pressure to fasting (basal) insulin and glycosylated hemoglobin (hemoglobin A1) was examined in 248 nondiabetic subjects (137 women and 111 men). None of the subjects was taking antihypertensive medication. There were statistically significant associations of systolic and diastolic blood pressure with insulin levels (r = 0.24, p less than 0.01; r = 0.30, p less than 0.01) and hemoglobin A1 levels (r = 0.28, p less than 0.001; r = 0.22, p less than 0.05) in women. These blood pressure indexes were also related to insulin levels in men (r = 0.23, p less than 0.05; r = 0.02, p less than 0.05). In a multiple regression analysis, the association between blood pressure and insulin level was diminished with an allowance for adiposity; however, it remained statistically significant. These data indicate that blood pressure is related to insulin levels in nondiabetic subjects and suggest that insulin may be a physiologic determinant of blood pressure.

Effect of past and concurrent body mass index on prevalence of glucose intolerance and type 2 (non-insulin-dependent) diabetes and on insulin response. The Israel study of glucose intolerance, obesity and hypertension

A representative sample (n = 2140) of the Israeli Jewish population aged 40-70 (excluding known diabetic patients), whose body mass index had been measured 10 years earlier, underwent an oral glucose tolerance test and redetermination of body mass index. Irrespective of weight changes, high concurrent and high past body mass index values (greater than or equal to 27) were associated with similarly increased rates of glucose intolerance as compared with body mass index values less than 27 at both time-points (rate ratio 1.76, 90% confidence limits 1.56-1.99). Glucose intolerance here includes borderline and impaired tolerance as well as Type 2 diabetes. The rate of Type 2 diabetes increased only with increasing past body mass index, while concurrent body mass index had no effect [rate ratios: 2.36 (1.48-3.75) and 1.99 (1.48-2.68) respectively for the medium-(23-26.9) versus-low (less than 23) and high- (greater than or equal to 27) versus-medium past body-mass-index categories]. Weight reduction was associated with only slightly reduced rate of glucose intolerance and had no effect on the rate of diabetes. Mean sum insulin (summed 1 and 2 h levels, mU/l) increased significantly with increasing concurrent body mass index (123, 150 and 190 in the low, medium and high categories) with no effect of past body mass index. It also increased significantly (p less than 0.001) in all concurrent body mass index categories from normal tolerance through borderline to impaired tolerance, and decreased significantly (p less than 0.001) in diabetes relative to impaired tolerance, although it remained above normal.(ABSTRACT TRUNCATED AT 250 WORDS)