17 beta-Estradiol attenuates voltage-dependent Ca2+ currents in A7r5 vascular smooth muscle cell line

Previous studies have shown that 17 beta-estradiol (beta-E2) has a direct acute inhibitory effect on vascular smooth muscle (VSM) contraction. To investigate the mechanisms underlying this phenomenon, we utilized whole cell patch-clamping techniques to study effects of beta-E2 on voltage-dependent Ca2+ channels in cultured VSM cells (VSMC). T- and L-type Ca2+ currents were characterized with ramp and pulse protocols in A7r5 cultured VSMC. T-type current, inactivated in < 100 ms, was reduced by Ba2+ and was comparatively little affected by isradipine. L-type current required higher voltages to activate, inactivated slowly, was greatly increased by Ba2+, and could be completely inhibited by 5 microM isradipine. beta-E2 (10 microM) significantly reduced peak L-type Ba2+ current and T-type Ca2+ current within 1-2 min, whereas alpha E2 (a hormonally inactive isomer of estradiol) caused significantly less reduction in both types of current. Vehicle (0.1% ethanol) had no significant effect on either current. The inhibitory effect of beta-E2 on voltage-dependent Ca2+ currents may contribute to previously demonstrated beta-E2 attenuation of VSM contraction.

Diabetes mellitus: a disease of abnormal cellular calcium metabolism?

Although the pathogenesis of the diabetes mellitus syndrome remains poorly understood, both insulin-dependent diabetes mellitus and non-insulin-dependent diabetes mellitus predispose the individual to a similar spectrum of complications, including hypertension, macrovascular and microvascular disease, cataracts cardiomyopathy, neuropathy, and premature aging, suggesting that these complications develop along a pathway common to both diabetic conditions. Yet not all diabetic persons are affected by all of these complications or to the same degree. What causes this marked variability in the clinical manifestations of the diabetes syndrome remains an enigma. Accumulating data from animal models of diabetes and from studying patients with diabetes reveal that intracellular calcium levels are increased in most tissues. The activities of the membrane, adenosine triphosphatase (ATPase) associated cation pumps, which determine intracellular calcium level (i.e., calcium-ATPase and [sodium + potassium]-ATPase), are also altered. The nature of the alteration is often tissue specific and may depend on the level of blood glucose or insulin, or both. In this review we discuss the potential contribution of these changes in intracellular calcium regulation, whether acquired or genetically determined, to the pathogenesis of the diabetes syndrome, to the abnormalities in insulin secretion and action (mainly in non-insulin-dependent diabetes), and to the complications of both diabetes syndromes. Altered intracellular calcium metabolism may represent a common, underlying abnormality linking the metabolic, cardiovascular, ocular, and neural manifestations of the diabetic disease process.

Increased platelet cytosolic calcium responses to low density lipoprotein in type II diabetes with and without hypertension

Non-insulin dependent diabetes mellitus (NIDDM) and hypertension are common diseases which are independently associated with insulin resistance/hyperinsulinemia, dyslysidemia, abnormalities of platelet function, and accelerated atherogenesis. The interaction of these independent risk factors is poorly understood. Recently, low density lipoprotein (LDL) receptors have been described, in platelets, and LDL elevates [Ca2+]i in these cells. In this study we have evaluated platelet [Ca2+]i responsiveness to LDL and arginine vasopressin (AVP) in NIDDM patients with (n = 28) and without (n = 13) concomitant hypertension, as well as in normal nondiabetic controls (n = 13). Platelet [Ca2+]i concentration-response curves to LDL for both NIDDM and hypertensive NIDDM were shifted significantly to the left when compared to the normotensive, nondiabetic controls. By contrast, no differences were seen in [Ca2+]i responses to 10 mumol/L AVP among any of the groups. To determine the possible role of hyperinsulinemia in this accentuated [Ca2+]i response to LDL, we measured basal and LDL-stimulated [Ca2+]i in platelets of normal volunteers after insulin treatment (0-100 mU/mL for 30 and 90 min). Insulin did not alter baseline or LDL-stimulated (150 mg/mL) platelet [Ca2+]i. Thus, an enhanced platelet [Ca2+]i response to LDL is characteristic of diabetes, independently of blood pressure. As such, it may also help to explain the enhanced platelet aggregation, endothelial dysfunction, and accelerated atherosclerosis of NIDDM.

Insulin resistance in hypertension: a focused review

The associations between insulin resistance, hyperinsulinemia, and hypertension are well recognized. The insulin resistance and hyperinsulinemia associated with hypertension is the result of increased renal tubular sodium reabsorption, increased sympathetic nervous system activity, and increased arterial wall smooth muscle reactivity. In insulin resistant states, intracellular calcium and sodium accumulation is thought to be the fundamental underlying abnormality. These is evidence that hyperinsulinemia is an independent risk factor for coronary artery disease. Therefore, therapeutic considerations in patients with insulin resistance should include nonpharmacologic methods for increasing insulin sensitivity as well as avoiding the deleterious effects on insulin action and lipid metabolism of various antihypertensive medications. Of the currently available antihypertensives therapies, the angiotensin-converting enzyme inhibitors, the alpha antagonists, and the calcium channel blockers are the most rational choices for treating patients with hypertension with evidence of coexisting insulin resistance.

Insulin attenuation of vasopressin-induced calcium responses in arterial smooth muscle from Zucker rats

Insulin attenuates agonist-induced vascular contractility of aortic rings and decreases vasopressin (AVP)-elicited increases in vascular smooth muscle cell (VSMC) intracellular calcium ([Ca2+]i). To determine if insulin's effects on AVP-induced [Ca2+]i responses are altered in an insulin-resistant and hypertensive state, we studied vascular smooth muscle calcium responses in VSMC derived from Zucker lean and obese rats. AVP concentration-response experiments revealed that VSMC derived from obese animals exhibited exaggerated [Ca2+]i responses over the range of 1 x 10(-10) to 1 x 10(-7) M AVP compared to lean controls (P < 0.05, by multiple analysis of variance). Insulin treatment (7 x 10(-7) M) decreased the [Ca2+]i response to 1 nM AVP by 66 +/- 8% and 71 +/- 9% in lean and obese VSMC, respectively. Similar decreases were observed with the 10 nM AVP stimulus (41 +/- 9% and 61 +/- 7%, for lean and obese, respectively). AVP receptor binding studies revealed that exaggerated [Ca2+]i responses in obese VSMC were not due to alterations in AVP-binding properties (no significant differences in ID50, Kd, or binding capacity in lean and obese VSMC preparations). In addition, insulin treatment (1 x 10(-7) M) resulted in no differences in AVP receptor-binding properties in either cell line. Therefore, exaggerated [Ca2+]i responses in obese VSMC are most likely due to a postreceptor abnormality. These abnormalities in VSMC [Ca2+]i metabolism preceed and may play a role in the development of hypertension in the Zucker obese rat. Although insulin resistance in Zucker obese rats has been demonstrated in several tissues, VSMC [Ca2+]i responses to AVP are, nonetheless, similarly attenuated by insulin in obese and lean VSMC preparations.

Sex-specific effects of an insulin secretagogue in stroke-prone hypertensive rats

Glyburide, an insulin secretagogue and an insulin-sensitizing agent, lowers blood pressure in normal male and female dogs when administered acutely. Because insulin resistance may contribute to spontaneous hypertension in rats, we sought to determine if long-term administration of glyburide (5 mg/kg per day by diet, age 5 weeks to 5 months) would lower blood pressure in male and female stroke-prone spontaneously hypertensive rats. Arterial (aortic) rings from these rats were incubated with insulin in vitro (100 mU/mL) 1 hour before and during phenylephrine-induced contraction to determine if long-term glyburide administration improves vascular sensitivity to the intrinsic vasodilator action of insulin. Glyburide, however, significantly increased blood pressures and ratios of heart weight to body weight in 5-month-old female rats (+20 mm Hg diastolic, P < .05), with no significant change noted in male rats (+4 mm Hg diastolic). Glyburide increased plasma insulin levels (twofold, P < .04) in female but not in male rats. Glyburide did not affect plasma glucose or catecholamine levels. After incubation with insulin, aortic to rings from glyburide-treated female rats demonstrated more than 40% greater contractile responsiveness the phenylephrine compared with aortic rings from control female rats (P < .04). This insulin-dependent increase in phenylephrine-induced contraction consisted of a reversal in the in vitro action of insulin, from attenuation to accentuation of such contraction (P < .05). This change was not seen in male rats. Neither gender, glyburide, nor insulin influenced acetylcholine-induced relaxation of phenylephrine-induced contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of Na+,K(+)-ATPase gene expression by insulin in vascular smooth muscle cells

Na+,K(+)-ATPase gene expression and activity and its modulation by insulin were investigated in vascular smooth muscle cells (VSMC). Messenger RNAs encoding for alpha 1- and alpha 2-isoforms of Na+,K(+)-ATPase were identified in a pure population of cultured VSMC (a7r5 cells). The predominant isoform in VSMC was alpha 1, but only alpha 2 was regulated by insulin. Insulin treatment of VSMC for 1 and 6 h caused significant increases in mRNA encoding the alpha 2-subunit of Na+,K(+)-ATPase (n = 7, P < .01). Under similar conditions, insulin had no effect on alpha 1-Na+,K(+)-ATPase mRNA levels. VSMC treated with insulin exhibited a significant stimulation of ouabain inhibitable ATPase activity (1 h insulin, n = 3, v control, n = 3, P < .025; 6 h insulin, n = 3, v control, n = 3, P < .05). Changes in insulin regulation of Na+,K(+)-ATPase gene expression in vascular smooth muscle may be an important factor in the development of hypertension in diabetes.

Hyperinsulinemia, insulin resistance, and hyperglycemia: contributing factors in the pathogenesis of hypertension and atherosclerosis

Subtle abnormalities of carbohydrate metabolism and overt diabetes mellitus are both associated with a substantial increase in the prevalence of hypertension and the accelerated development of atherosclerosis. Hypertension is also a presumed independent risk factor for atherosclerosis, although some of the atherogenic properties of hypertension may be related to the recently recognized subtle metabolic abnormalities commonly found in persons with essential hypertension. The results of epidemiologic studies suggest that the elevated fasting and postprandial insulin levels that often occur in patients with essential hypertension, as well as in patients with type II diabetes mellitus, are an independent risk factor for atherosclerotic cardiovascular disease. Elevated glucose levels in patients with diabetes and hypertension appear to contribute to the acceleration of atherosclerosis, perhaps through toxic effects on the vascular endothelium. Other cardiovascular risk factors that are accentuated in persons with carbohydrate intolerance and hypertension include abnormalities in platelet function, clotting factors, the fibrinolytic system, and dyslipidemia. The goals of both nonpharmacologic and pharmacologic therapy for patients with abnormal carbohydrate metabolism and hypertension are to decrease cardiovascular risk as well as lower blood pressure.

Vascular insulin abnormalities, hypertension, and accelerated atherosclerosis

There is accumulating evidence that insulin resistance, glucose intolerance, and hyperinsulinemia exist in people with high blood pressure, and it has been suggested that insulin resistance and hyperinsulinemia may be of great importance in the origin of hypertension and its ultimate clinical course. Of importance are the recent observations that persons with normal glucose tolerance, selected on the basis of hyperinsulinemia, had higher blood pressure than matched individuals with normoinsulinemia. Hypertension in in insulin-resistant states generally has been attributed to hyperinsulinemia, with resulting increases in sympathetic nervous system activity. However, recent data from our laboratory suggest that cellular insulin resistance rather than hyperinsulinemia per se may lead to hypertension. The basic tenet proposed in this article is that a deficiency of insulin at the cellular level represents a common mechanism that is involved in the development of hypertension in both type I and type II diabetes mellitus. Insulin has an important role in the modulation of cellular calcium metabolism. Decreased insulin action on vascular smooth muscle cells may contribute both to hypertension and to accelerated atherosclerosis. Recent observations suggest that an impaired cellular response to insulin predisposes to increased vascular smooth muscle tone (the hallmark of hypertension in the diabetic state). For example, recently reported studies from our laboratory demonstrate that insulin attenuates the vascular contractile response to phenylephrine, serotonin, and potassium chloride. Thus, it appears that insulin normally modulates (attenuates) vascular smooth muscle contractile responses to vasoactive factors, and insulin resistance should accordingly be associated with enhanced vascular reactivity.

Postpartum abnormalities of carbohydrate and cellular calcium metabolism in pregnancy induced hypertension

We have previously reported that young, primigravid, African-American women who developed preeclampsia exhibited insulin resistance (elevated fasting insulin:glucose ratios) and abnormal intracellular free calcium ([Ca2+]i) metabolism as early as the second trimester of pregnancy. To determine if these abnormalities persist postpartum (suggesting a genetic link), we evaluated the effects of an oral glucose load (50 g) on plasma and glucose insulin, basal platelet [Ca2+]i and platelet [Ca2+]i responses to arginine vasopressin (AVP). The study population consisted of nine, young, primigravid, African-American women at 43 +/- 12 weeks postpartum from pregnancy induced hypertensive (PIH) gestations and 10 age- and weight-matched African-American women who were 29 +/- 7 weeks postpartum from normal pregnancies. The PIH group consisted of five subjects who were preeclamptic and four subjects with gestational hypertension. Baseline fasting body weights, body mass indices, plasma glucose, plasma insulin, basal platelet [Ca2+]i, and platelet [Ca2+]i responses to AVP were similar in the postpartum PIH and control groups. The oral glucose load had no effect on basal platelet [Ca2+]i levels in either group. However, plasma glucose and insulin and platelet [Ca2+]i responses to AVP were accentuated at 30 min following an oral glucose load suggesting a subtle abnormality of carbohydrate and [Ca2+]i metabolism that persists in individuals with pregnancy induced hypertension. Long term studies involving African-American populations will be necessary to determine if these metabolic abnormalities are associated with an increased propensity to hypertension.

Effects of weight reduction on cellular cation metabolism and vascular resistance

The early stages of weight loss are associated with a reduction in blood pressure, and the mechanisms mediating this reduction remain unclear. Platelet free calcium levels, [Ca2+]i, have been reported to be elevated in essential hypertension and to decrease with pharmacological treatment of the hypertension. In the current study, 18 obese subjects had measurements of blood pressure, forearm blood flow, forearm vascular resistance, and both basal platelet [Ca2+]i and [Ca2+]i responses to vasopressin during 12 weeks on a very low calorie (3,360 kJ, or 800 kcal) diet. Weight reduction was associated with reduction in mean arterial blood pressure at 3-4 weeks. There were associated reductions in forearm vascular resistance and platelet [Ca2+]i as well as increases in forearm blood flow at 3-4 weeks of the diet. Increased forearm blood flow was correlated with weight loss. Vasopressin-induced platelet [Ca2+]i responses increased, which correlated with the reduction in mean arterial pressure at 7-8 weeks of weight loss. Assuming that platelet [Ca2+]i metabolism reflects vascular smooth muscle cell [Ca2+]i metabolism, the data suggest that blood pressure reduction after weight loss may be related to reduced vascular smooth muscle cell [Ca2+]i. The reason for the increased vasopressin-induced [Ca2+]i after weight reduction is unclear.

Calcium antagonists and atherosclerosis. The Multicenter Isradipine/Diuretic Atherosclerosis Study

The Multicenter Isradipine/Diuretic Atherosclerosis Study (MIDAS) is a double-blind, randomized, controlled clinical trial comparing the effects of isradipine and hydrochlorothiazide on the progression or regression of early carotid atherosclerosis in 883 hypertensive patients. Assessment of the outcome is by B-mode ultrasonographic measurement of early lesions (as reflected by intimal-medial wall thickening) at baseline and semiannually over 36 months. At baseline, the participants' mean age was 58.5 years. The study population was 78.6% male and 72.4% white. The average resting systolic and diastolic blood pressures were 149.8 and 96.5 mm Hg, respectively. Mean total serum cholesterol and low-density lipoprotein (LDL)-cholesterol levels were 216.2 mg/dL and 146.6 mg/dL, respectively. Risk factors for coronary artery disease were balanced at baseline between the two study groups. The mean maximum intimal-medial thickness at baseline (measured in the near and far walls of three segments for both carotid arteries) was 1.17 +/- 0.20 mm; the mean intimal-medial thickness of the single thickest lesion was 2.11 +/- 0.51 mm. Cross-sectional analyses show that intimal-medial thickness correlates independently with male gender, age, number of cigarettes smoked per day, levels of LDL cholesterol, systolic blood pressure, and white blood cell count. The MIDAS endpoint results will be available in 1993.

Carotid plaque associations among hypertensive patients

OBJECTIVE

To assess the relationship between cardiovascular risk factors and carotid plaque.

DESIGN

Hypertensive patients were screened for randomization into the Multicenter Isradipine Diuretic Atherosclerosis Study, a trial intended to determine if blood pressure control by isradipine as compared with hydrochlorothiazide will blunt the progression of carotid plaque (intima plus media thickness, 1.3 to 3.5 mm) in patients with serum cholesterol levels of less than 6.85 mmol/L (265 mg/dL) without insulin-dependent diabetes mellitus or estrogen therapy. Demographics of those who underwent B-mode ultrasound evaluations at common, bifurcation, and internal carotid artery sites to detect plaque were assessed from a southern and a northern site.

SETTING

Participants were from ambulatory outpatient clinics associated with medical schools.

PATIENTS

The initial screening included 1823 hypertensive volunteer patients who were between 40 and 83 years of age who had a diastolic pressure of 90 to 114 mm Hg (or < 90 mm Hg with treatment).

OUTCOME MEASURES

Complete data were collected on the variables of age, cholesterol, cigarette smoking, race, gender, and the presence of carotid plaque in 1126 patients.

RESULTS

All variables were significantly associated with carotid plaque (intima plus media thickness, > or = 1.3 mm). The adjusted percentage with plaque was 66.4% +/- 3.4% for blacks and 70.1% +/- 2.3% for whites at the southern site and 42.7% +/- 4.5% for blacks and 61.3% +/- 3.2% for whites at the northern site. The rate of plaque was 75.8% among cigarette smokers, despite a mildly elevated cholesterol level.

CONCLUSIONS

Although these 1126 cases do not constitute a random sample of patients, these data suggest that there may be regional differences in racial tendencies toward plaque among blacks.

Ambulatory blood pressure monitoring in a nonacademic setting. Effects of age and sex

Twenty-four-hour ambulatory blood pressure measurements (ABPM) are likely to eliminate the stress of visits and observer bias in office blood pressure (BP) recordings, allow consideration of the circadian variability in BP, and correlate well with target organ damage. To define the prevalence of "white coat" hypertension in a rural community to a nonacademic setting, and to assess age and sex related differences, we studied 131 patients who had more than two prior office diastolic BP measurements greater than 90 mm Hg and less than 115 mm Hg. Blood pressure was measured every 10 to 60 min for 24 h using the SpaceLabs 90207 device. Office BP readings were higher than ABPM in the group as a whole, in individual age groups, and in both sexes. The differences were more pronounced at night. Average differences between office and ambulatory BP ranged between 14.4 +/- 1.7/2.9 +/- 2.0 (ABPM at 10:00), and 33.8 +/- 2.3/22.8 +/- 1.5 mm Hg (systolic/diastolic +/- SE) (ABPM at 01:00). The nighttime drop in systolic BP was not apparent in subjects more than 65 years old. Women had a proportionately higher mean office BP than men (115.0 +/- 0.9 office v 110.2 +/- 1.3 mm Hg ABPM in women and 112.3 +/- 0.9 v 104.3 +/- 1.1 mm Hg in men) (P = .013), and the elderly did not display the relationship between ambulatory and office mean BP seen in younger subjects (r = 0.15, P = .30 v r = 0.36, P = .0004, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Antiatherosclerotic effects of calcium channel blockers

Hypertension is a constellation of abnormalities, including metabolic disorders. The current approach to treatment of hypertension should not be dictated solely by measures to lower blood pressure. It must also take into consideration the effect of antihypertensive drug treatment on the development of atherosclerosis and many other important factors. Evidence from rabbit models and cell cultures indicates that calcium channel blockers are antiatherogenic through a variety of mechanisms. In addition to preserving endothelial function, these agents inhibit the following: Platelet aggregation Migration of monocytes and smooth-muscle cells into the intima Incorporation of low-density lipoprotein cholesterol into these cells Matrix formation Calcium overload in atherosclerotic lesions However, additional studies are needed to delineate the antiatherogenic effects of these and other antihypertensive agents.

Insulin resistance, hyperinsulinemia, dyslipidemia, hypertension, and accelerated atherosclerosis

Hypertension is only one component of a multifaceted metabolic-hemodynamic complex that also includes obesity, subtle and overt glucose intolerance, dyslipidemia, enhanced vascular resistance and accelerated atherosclerosis. Results of a number of studies in the past 5 years have shown that even nonobese, nondiabetic individuals with hypertension display insulin resistance, which is located in peripheral tissues (primarily skeletal muscle), is limited to nonoxidative pathways of glucose disposal, and appears to be directly correlated with the severity of hypertension. Insulin resistance and associated hyperinsulinemia in hypertensive individuals are also associated with increased plasma triglyceride levels and decreased high-density lipoprotein concentrations, which likely contributes to enhanced atherosclerosis. Hyperinsulinemia may directly promote atherosclerosis by enhancing LDL-cholesterol accumulation in vessel walls, vascular smooth muscle migration, and proliferation, augmenting connective tissue synthesis in the vascular wall, and decreasing the regression of lipid plaques. The enhanced peripheral vascular resistance that characterizes insulin resistance/hyperinsulinemic states may be related to decreased vascular smooth muscle responses to insulin, which normally modulates (attenuates) vascular contractile responses to vasoactive agents.

Diabetes mellitus and hypertension

Diabetes mellitus and hypertension are common diseases that coexist at a greater frequency than chance alone would predict. Hypertension in the diabetic individual markedly increases the risk and accelerates the course of cardiac disease, peripheral vascular disease, stroke, retinopathy, and nephropathy. Our understanding of the factors that markedly increase the frequency of hypertension in the diabetic individual remains incomplete. Diabetic nephropathy is an important factor involved in the development of hypertension in diabetics, particularly type I patients. However, the etiology of hypertension in the majority of diabetic patients cannot be explained by underlying renal disease and remains "essential" in nature. The hallmark of hypertension in type I and type II diabetics appears to be increased peripheral vascular resistance. Increased exchangeable sodium may also play a role in the pathogenesis of blood pressure in diabetics. There is increasing evidence that insulin resistance/hyperinsulinemia may play a key role in the pathogenesis of hypertension in both subtle and overt abnormalities of carbohydrate metabolism. Population studies suggest that elevated insulin levels, which often occurs in type II diabetes mellitus, is an independent risk factor for cardiovascular disease. Other cardiovascular risk factors in diabetic individuals include abnormalities of lipid metabolism, platelet function, and clotting factors. The goal of antihypertensive therapy in the patient with coexistent diabetes is to reduce the inordinate cardiovascular risk as well as lowering blood pressure.

Hypertension in insulin-resistant Zucker obese rats is independent of sympathetic neural support

We have previously reported that insulin-resistant Zucker obese rats exhibit hypertension associated with impaired vascular smooth muscle (VSM) Ca2+ transport and proposed that this results from failure of insulin to regulate VSM Ca2+ transport in insulin resistance. However, hypertension in insulin-resistant states is generally attributed to hyperinsulinemia, with a consequent stimulation of sympathetic neural activity. Accordingly, the present study was conducted to determine whether the hypertension observed in Zucker obese rats compared with their lean controls was dependent on either increased sympathetic neural activity or exaggerated vascular reactivity. Intra-arterial blood pressure responses to ganglionic blockade with Ecolid (chlorisondamine chloride) and to graded intravenous injections of angiotensin II and norepinephrine were compared in 6- to 8-wk-old male Zucker rats and their lean controls (n = 10/group). The obese rats exhibited significant hypertension before ganglionic blockade (P less than 0.001), and this difference was largely sustained during ganglionic blockade (P less than 0.005). Furthermore, the obese rats exhibited greater pressor sensitivity to both angiotensin II and to norepinephrine during ganglionic blockade (P less than 0.01). Thus enhanced pressor sensitivity, independent of sympathetic neural activity, appears to support hypertension in Zucker obese rats.

Insulin attenuates vasopressin-induced calcium transients and a voltage-dependent calcium response in rat vascular smooth muscle cells

Insulin attenuates the contractile responses of vascular smooth muscle (VSM) to various agonists. Insulinopenic and insulin-resistant rats lack this normal attenuation of vascular contractile responses. To study this attenuating mechanism, the effects of insulin on calcium (Ca2+) responses of cultured VSM cells (a7r5) to arginine vasopressin (AVP) and membrane potential were investigated. Insulin (1 and 100 mU/ml) shifted AVP dose-response curves to the right, reducing relative potency of AVP by 16-fold and 220-fold, respectively. Responses to AVP were significantly attenuated within 30 min of insulin application. The AVP-elicited rise in [Ca2+]i was partially dependent upon extracellular Ca2+. AVP-elicited inward current was reduced by 90 min of insulin treatment (100 mU/ml), from a peak current of -103 +/- 27 pA (normal) to -37 +/- 15 pA (insulin treated). Peak voltage-dependent Ca(2+)-dependent inward current was unaffected by insulin; however, the current-voltage curve was shifted 16 +/-3 mV to the right by insulin. Thus, insulin may reduce VSM contractile responses by attenuating agonist-mediated rises in [Ca2+]i mediated, in part, by reductions in Ca2+ influx through both receptor- and voltage-operated channels.

Therapeutic approach to hypertension in the elderly

Hypertension is an important risk factor for cardiovascular disease in the elderly. This article addresses the factors that increasingly influence hypertension as age increases. In addition, the initial therapeutic approach to the elderly hypertensive patient should generally consist of a reduction in salt and caloric intake and increased exercise. Drug therapy should be initiated with lower doses of medication with special concern about orthostatic hypotension. The drug regimen should be made as simple as possible and be carefully explained to the patient. With these considerations in mind, hypertension in the geriatric patient can be effectively managed.

Is hypertension an insulin-resistant state? Metabolic changes associated with hypertension and antihypertensive therapy

In this review, the relationship between hypertension and abnormal carbohydrate metabolism is explored. A review of the current literature reveals that people with hypertension are also likely to suffer from insulin resistance, glucose intolerance, and hyperinsulinemia. Likewise, hypertension is prevalent in obese and diabetic patients. Deficiency of insulin at the cellular level may be a common mechanism in the development of hypertension in patients with type I or type II diabetes mellitus. Essential hypertension appears to be an insulin-resistant state. Insulin resistance may engender hypertension by increasing peripheral vascular resistance as well as by increasing salt retention at the level of the kidney. Therefore effective antihypertensive therapy should include agents that do not adversely affect carbohydrate metabolic abnormalities. Commonly used antihypertensive agents, such as thiazide, thiazide-like diuretics, and beta-blockers, are associated with glucose intolerance and increased insulin resistance. In contrast, angiotensin-converting enzyme inhibitors, calcium antagonists, and peripheral alpha-blockers (such as prazosin and terazosin) do not adversely affect glucose tolerance or insulin sensitivity. In addition, alpha-blockers have a positive effect on the serum lipid profile. The entire multifactorial cardiac risk profile must be considered when choosing therapeutic agents for conditions that have an impact on cardiovascular disease.

Diabetes and hypertension: a review

The basic mechanisms that initiate and sustain hypertension in type 2 diabetics are poorly understood. Contributing factors discussed in this review include obesity, insulin resistance, hyperinsulinemia, genetic factors, and abnormalities of cellular cation homeostasis. Also discussed are the features of hypertension in type 2 diabetic individuals that are reminiscent of the hemodynamic abnormalities characterizing hypertension in the elderly, including increased vascular reactivity and increased atherosclerotic vascular disease. This article reviews mechanisms by which hyperinsulinemia, insulin resistance, or both may lead to hypertension.

Epidemiologic and clinical aspects of insulin resistance and hyperinsulinemia

Epidemiologic studies have shown that insulin is a risk factor for coronary heart disease (CHD). Clinical studies have also demonstrated positive correlations between insulin and blood pressure, triglycerides, total cholesterol, fibrinogen, and plasminogen activator inhibitor. Moreover, there is an inverse correlation between insulin and high-density lipoprotein (HDL). These studies have provided evidence in support of the biologic plausibility of epidemiologic observations, but they have not clearly established insulin's role in the pathogenesis of human cardiovascular diseases (CVD) such as hypertension. In fact, there is considerable evidence that insulin resistance (abnormal nonoxidative glucose disposal), not hyperinsulinemia, is the primary insulin-related abnormality in human hypertension, and that hyperinsulinemia occurs as a response to insulin resistance. Skeletal muscle appears to be the primary site of insulin resistance in essential hypertension, although other organs, such as the kidneys and liver--key sites for cell and water homeostasis and lipoprotein regulation, respectively--may respond normally to insulin. Adipocytes also appear to be a site of insulin resistance. Thus, the putative interrelationship between hyperinsulinemia and insulin resistance, on the one hand, and with blood pressure and lipoproteins, on the other, is a complex one and may involve organ-specific insulin resistance. Altered cation transport is one of several mechanisms by which insulin resistance might raise blood pressure. The Na+, K(+)-ATPase and Ca(2+)-ATPase pumps are insulin sensitive. Thus, when insulin resistance is present, the activity of these pumps in the smooth muscle of the arterial wall might be reduced. This would lead to an intracellular accumulation of sodium and calcium, thereby sensitizing the vascular wall to pressor substances. Moreover, secondary hyperinsulinemia will occur, and insulin has been shown to stimulate sympathetic nervous system activity and to increase renal tubular absorption of sodium. Insulin is also a growth factor and therefore might have a trophic effect on the vessel wall, one that could initiate and/or sustain hypertension as well as atherosclerosis. Abnormal lipoprotein metabolism is yet another possible explanation for the accelerated atherosclerosis that has been observed in persons with abnormal carbohydrate tolerance and insulin resistance. Hyperinsulinemia and insulin resistance both play a role in the expression of elevated very-low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) levels as well as in the depression of HDL levels. Coronary risk reduction has been disappointing when blood pressure has been lowered with treatment regimens based on thiazide diuretics and/or beta blockers. Thiazides and some beta blockers may further impair tissue insulin sensitivity and often cause blood lipoprotein abnormalities.(ABSTRACT TRUNCATED AT 400 WORDS)