Insulin resistance--not hyperinsulinemia--is pathogenic in essential hypertension

Aging-related cerebral microvascular degeneration is an important cause of essential hypertension

Blood pressure usually rises with age and most patients with essential hypertension are the elderly people. From the standpoint of physiology, the benefit of increasing blood pressure is to provide adequate oxygenation and nutrition to the brain and other critical organs. They suggest the rise of blood pressure is a compensation for critic organs' hypoperfusion. Brain is the most vulnerable organ to over decrease of blood pressure. It must work with constant and very high blood flow. It is located at the uppermost point of the circulatory system. And cerebral hypoperfusion can effectively raise systemic blood pressure. So we deduce that brain hypoperfusion is an important reason for increased blood pressure in the elderly people. Aging-related microvascular degeneration plays an important role in development of cerebral hypoperfusion. There is a close relationship between microvascular degeneration and essential hypertension. The degenerative changes in microcirculation are found in essential hypertension. Essential hypertension and microvascular degeneration may share similar risk factors. Thus, we hypothesize that aging-related cerebral microvascular degeneration is an important cause of essential hypertension.

Moderately obese, insulin-resistant women exhibit abnormal vascular reactivity to stress

To define the hemodynamic implications of insulin resistance (IR), we compared 10 normotensive, insulin-resistant women who had abnormal glucose tolerance tests with 10 age-matched healthy normotensive women with normal glucose tolerance tests with respect to mental arithmetic and handgrip responses. Hemodynamic variables obtained at baseline and during stress included heart rate, blood pressure, cardiac output, and systemic vascular resistance. The IR group weighed more (84 versus 66 kg). Screening BP was similar (123/72 versus 120/68 mm Hg, P=NS) between groups although baseline diastolic BP at testing day was higher in the IR group than control group (75 versus 65 mm Hg, P<.05). The IR group showed a significantly greater increase in systolic (18% versus 10%, P<.O1) and diastolic (24% versus 12%, P<.01) blood pressure responses to mental stress than the control group. During mental stress, the control group demonstrated increased cardiac output (1.4 L/min) and decreased systemic vascular resistance (-120 dyne x s x cm[-5]), whereas IR subjects demonstrated increased systemic vascular resistance (119 dyne x s x cm(-5); group difference, P<.02) with only a small increase in cardiac output (0.5 L/min). Handgrip also caused a greater increase in systemic vascular resistance in the IR group (252 versus 64 dyne x s x cm(-5), P<.05), with a correspondingly greater increase in blood pressure than control subjects. Baseline blood pressure was correlated with weight (r=.41, P<.02) and stress blood pressure with fasting insulin (r=.51, P<.001) and glucose-to-insulin ratio (r= -.55, P<.001). We conclude that insulin resistance is associated with an exaggerated blood pressure response to stress; an enhanced vasoconstriction to stress may mediate this response. This hyperreactivity may be a marker for future hypertension in obese, normotensive, hyperinsulinemic individuals.

Exploiting complementary therapeutic strategies for the treatment of type II diabetes and prevention of its complications

Impaired glycemic control in type II diabetes results from peripheral insulin resistance, hepatic insulin resistance, and a relative failure of beta cell function. Nutritional and pharmaceutical measures are now available for addressing each of these defects, presumably enabling a rational and highly effective clinical management of non-insulin-dependent diabetes mellitus. Peripheral insulin resistance, which usually responds to a very-low-fat diet, aerobic exercise training, and appropriate weight loss, can also treated with high-dose chromium picolinate, high-dose vitamin E, magnesium, soluble fiber, and possibly taurine; these measures appear likely to correct the diabetes-associated metabolic derangements of vascular smooth muscle, and thus lessen risk for macrovascular disease. Metformin's clinical efficacy is primarily reflective of reduced hepatic glucose output; this action should complement the benefits of peripheral insulin sensitizers. When these measures are not sufficient for optimal control, beta cell function can be boosted with second-generation sulfonylureas.

Up-regulation of IGF binding protein-1 as an anticarcinogenic strategy: relevance to caloric restriction, exercise, and insulin sensitivity

The mitotic rate of stem cells is a major determinant of cancer risk. Insulin-like growth factors (IGFs) are virtually obligate stimulants of cell turnover in nearly every tissue. IGF activity is subject to rapid modulation by hepatic release of IGF binding protein-1 (IGFBP-1), a factor whose synthesis is suppressed by insulin and increased by glucagon. Up-regulation of IGFBP-1 production can be expected to decrease IGF activity and thereby diminish cancer risk. Measures that sensitize peripheral tissues to insulin, and thereby down-regulate insulin secretion, can be expected to increase IGFBP-1 synthesis, provided that they do not unduly sensitize hepatocytes as well. Prolonged aerobic exercise and caloric restriction also increase IGFBP-1 production. Since IGF-1 suppresses hepatic synthesis of sex hormone binding globulin (SHBG), down-regulation of IGF activity will increase SHBG levels and thus diminish the availability of free sex hormones--an effect that should further decrease cancer risk in sex hormone-responsive tissues. These considerations rationalize many findings in animal and epidemiologic studies, and suggest that non-diabetic insulin resistance may be a significant cancer risk factor. Increased IGF activity associated with insulin resistance may also promote benign hyperplasias-most notably atherosclerosis. Hyperinsulinemia stimulates intimal hyperplasia indirectly, via IGF.

Up-regulation of intracellular signalling pathways may play a central pathogenic role in hypertension, atherogenesis, insulin resistance, and cancer promotion--the 'PKC syndrome'

The modern diet is greatly different from that of our paleolithic forebears' in a number of respects. There is reason to believe that many of these dietary shifts can up-regulate intracellular signalling pathways mediated by free intracellular calcium and protein kinase C, particularly in vascular smooth muscle cells; this disorder of intracellular regulation is given the name 'PKC syndrome'. PKC syndrome may entail either a constitutive activation of these pathways, or a sensitization to activation by various agonists. The modern dietary perturbations which tend to induce PKC syndrome may include increased dietary fat and sodium, and decreased intakes of omega-3 fats, potassium, calcium, magnesium and chromium. Insulin resistance may be both a cause and effect of PKC syndrome, and weight reduction and aerobic training should act to combat this disorder. PKC syndrome sensitizes vascular smooth muscle cells to both vasoconstrictors and growth factors, and thus promotes both hypertension and atherogenesis. In platelets, it induces hyperaggregability, while in the microvasculature it may be a mediator of diabetic microangiopathy. In vascular endothelium, intimal macrophages, and hepatocytes, increased protein kinase C activity can be expected to increase cardiovascular risk. Up-regulation of protein kinase C in stem cells may also play a role in the promotion of 'Western' fat-related cancers. Practical guidelines for combatting PKC syndrome are suggested.

Beta-cell function and replication in spontaneously hypertensive rats

We examined beta-cell function and replication in spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto rats (WKY). Rats were subjected to 90% pancreatectomy (Px) or sham operation at the age of 8 weeks, and islet function and regeneration were examined 4 weeks after surgery. Plasma glucose levels were higher in SHR than in WKY (509 +/- 38 v 325 +/- 109 mg/dL, P < .0001) 1 week after Px and throughout the experimental period. Plasma glucose responses to intravenous injection of glucose (0.5 g/kg body weight) were not different in the sham-operated animals of the two strains, whereas plasma insulin responses were greater in SHR than in WKY. No insulin responses to glucose were observed in either strain of Px rats. The insulin content of the remnant equivalent (6.7 +/- 2.1 v 4.2 +/- 0.4 micrograms, P < .05) and whole pancreas (156.7 +/- 10.7 v 123.8 +/- 23.5 micrograms, P < .01) in sham-operated rats was greater in SHR than in WKY. However, insulin content was lower (P < .05) in Px-SHR (1.0 +/- 0.2 microgram) than in Px-WKY (3.9 +/- 1.7 micrograms). Histological examination showed that fibrotic degeneration of islets was much greater in Px-SHR than in Px-WKY. These data strongly suggest that the beta cells of SHR were more vulnerable to reduction of islet mass than those of WKY. Our data also suggest that hyperinsulinemia and/or insulin resistance in SHR has a deleterious effect on beta-cell replication.

Reduction of free fatty acids may ameliorate risk factors associated with abdominal obesity

Experimental data as well as logical considerations suggest that the increased cardiovascular risk associated with abdominal obesity is mediated primarily by increased levels and flux of free fatty acids. Practical strategies for decreasing free fatty acid levels and/or flux may include: a very-low-fat, low-glycemic-index diet; promotion of insulin sensitivity (via exercise training, chromium, soluble fiber or drugs); anti-lipolytic agents; and stimulation of hepatic lipid oxidation with hydroxycitrate, carnitine and possibly fish omega-3s. Fortunately, many of these measures should also promote a leaner physique. Thus, even when abdominal obesity cannot be corrected, it may prove feasible to mitigate its dangers.

Hemostatic concomitants of syndrome X

The elevated risk factors classically associated with Syndrome X do not adequately explain the increased cardiovascular risk linked to insulin resistance. Considerable indirect evidence and more limited direct evidence suggests that increases in certain prognostically significant hemostatic variables--notably plasma fibrinogen, factor VII coagulant activity, and plasminogen activator inhibitor-1 levels--may be concomitants of Syndrome X. Increased platelet aggregability, and a reduced capacity of vascular endothelium for prostacyclin generation, may also be associated with insulin resistance. Large clinical studies, involving quantification of insulin sensitivity and measurement of hemostatic variables, are required to test this hypothesis. It is unlikely that hyperinsulinemia mediates the connections between insulin resistance and hemostatic variables (or indeed other risk factors in Syndrome X). In light of the remarkably broad impact of insulin resistance on cardiovascular risk factors, promotion of optimal insulin sensitivity should assume a central role in preventive cardiology.