Cardiovascular risk factors in South America and the Caribbean

Facing the conclusion of the twentieth century, cardiovascular disease (CVD) remains a major cause of morbidity and a leading contributor to mortality worldwide. Developing countries, including those in South America and the Caribbean, contribute substantially to the global burden of CVD. Indeed, 8 to 9 million deaths attributable to CVD (63% of world total) occurred in developing countries in 1990, compared to 5.3 million deaths in developed nations. Over the next 25 years, it is projected that there will be a rise in CVD mortality rates in the developing countries, linked not only to demographic changes (expansion and aging of the population), but also to progressive urbanization and lifestyle modifications. As such, the ratio of deaths from CVD to deaths from infectious disease is likely to triple during the next 20 years in South America and the Caribbean. The identification of major risk factors and the implementation of control strategies (eg, community education and target of high risk individuals) have contributed to the fall in CVD mortality rates observed in industrialized nations. Most countries of South America and the Caribbean lack an efficient health care system, and the medical and socio-economic consequences of the projected rise in CVD will further strain financial resources. Therefore, appropriate strategies based on knowledge extrapolated from research among other populations should be initiated. The agenda of any lifestyle-related disease control program should include the promotion of healthy diet, exercise, and should encourage decreasing tobacco and alcohol usage.

Influence of age on contractile response to insulin-like growth factor 1 in ventricular myocytes from spontaneously hypertensive rats

Evidence suggests a pathophysiological role of insulin-like growth factor 1 (IGF-1) in hypertension. Cardiac function is altered with advanced age, similar to hypertension. Accordingly, the effects of IGF-1 on cardiac myocyte shortening and intracellular Ca(2+) were evaluated in hypertension at different ages. Ventricular myocytes were isolated from Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR), aged 12 and 36 weeks. Mechanical and intracellular Ca(2+) properties were examined by edge-detection and fluorescence microscopy. At 12 weeks, IGF-1 (1 to 500 ng/mL) increased peak twitch amplitude (PTA) and FFI changes (DeltaFFI) in a dose-dependent manner in WKY myocytes, with maximal increases of 27.5% and 35.2%, respectively. However, IGF-1 failed to exert any action on PTA and DeltaFFI in the age-matched SHR myocytes. Interestingly, at 36 weeks, IGF-1 failed to exert any response in WKY myocytes but depressed both PTA and DeltaFFI in a dose-dependent manner in SHR myocytes, with maximal inhibitions of 40.5% and 16.1%, respectively. Myocytes from SHR or 36-week WKY were less sensitive to norepinephrine (1 micromol/L) and KCl (30 mmol/L). Pretreatment with nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 micromol/L) did not alter the IGF-1-induced response in 12-week WKY myocytes but unmasked a positive action in 12-week SHR and 36-week WKY myocytes. L-NAME also significantly attenuated IGF-1-induced depression in 36-week SHR myocytes. In addition, the Ca(2+) channel opener Bay K8644 (1 micromol/L) abolished IGF-1-induced cardiac depression in 36-week SHR myocytes. Collectively, these results suggest that the IGF-1-induced cardiac contractile response was reduced with advanced age as well as with hypertension. Alterations in nitric oxide and intracellular Ca(2+) modulation may underlie, in part, the resistance to IGF-1 in hypertension and advanced age.

An update on perioperative management of diabetes

Surgery in the patient with diabetes mellitus is relatively common, as the numbers of persons with diabetes is increasing and diabetes predisposes to medical conditions that require surgical intervention. An estimated 25% of diabetic patients will require surgery, and advances in perioperative care of these patients allow them to safely undergo the most complicated surgical procedures. We will review issues of preoperative, intraoperative, and postoperative care of diabetic patients.

Insulin-like growth factor I as a cardiac hormone: physiological and pathophysiological implications in heart disease

Accumulating evidence has indicated that insulin-like growth factor-1 (IGF-1) plays a specific role in the intricate cascade of events of cardiovascular function, in addition to its well established growth-promoting and metabolic effects. IGF-1 is believed to mediate many effects of growth hormone (GH), IGF-1 promotes cardiac growth, improves cardiac contractility, cardiac output, stroke volume, and ejection fraction. In humans, IGF-1 improves cardiac function after myocardial infarction by stimulating contractility and promoting tissue remodeling. Furthermore, IGF-1 facilitates glucose metabolism, lowers insulin levels, increases insulin sensitivity, and improves the lipid profile. These data suggest an attractive therapeutic potential of IGF-1. Both clinically observed and experimentally induced impairments of cardiac function are also found to be associated with abnormal IGF-1 levels. IGF-1 and its binding proteins have been considered as markers for the presence of certain cardiac abnormalities, indicating that IGF-1 may be a risk factor for certain cardiac disorders. The present review will emphasize the role of IGF-1 in the regulation of cardiac growth and function, and the potential pathophysiological role of IGF-1 in cardiac function.

Effects of insulin and metformin on glucose metabolism in rat vascular smooth muscle

Glucose metabolism in vascular smooth muscle cells (VSMCs) is characterized by substantial lactate production even in fully oxygenated conditions. Insulin and metformin, an insulin-sensitizing agent, have direct effects on the vascular tissue metabolism. We investigated whether insulin or metformin can induce a switch in VSMC glucose metabolism from lactate production to pyruvate oxidation, by measuring lactate oxidation as determined by the conversion of [1-14C]-D,L-lactate to [1-14C]-pyruvate and subsequent oxidation to acetyl coenzyme A and 14CO2 by pyruvate dehydrogenase (PDH). Lactate oxidation was measured in control rat aortic cultured VSMCs incubated for 30 minutes in media with and without additional glucose compared with VSMCs cultured in the presence of insulin or metformin. The addition of glucose to VSMCs decreased lactate oxidation (4.6+/-1.7 v 9.6+/-2.4 pmol/cell/min, P < .001). In the absence of additional glucose, metformin decreased lactate oxidation in VSMCs compared with controls (4.9+/-1.4 v 9.6+/-2.4 pmol/cell/min, P < .01). Metformin in the presence of glucose caused the greatest decline in lactate oxidation (2.5+/-0.4 pmol/cell/min, P < .001). In contrast to the effects of metformin, insulin increased lactate oxidation both with (12.9+/-1.5 pmol/cell/min, P < .001) and without (17.9+/-4.4, P < .01) additional glucose. This suggests that insulin facilitates VSMC utilization of lactate as a source of pyruvate and energy production even during noncontractile periods.

Metformin but not glyburide prevents high glucose-induced abnormalities in relaxation and intracellular Ca2+ transients in adult rat ventricular myocytes

We have recently demonstrated that adult rat ventricular myocytes maintained in a high glucose (HG) culture medium exhibit abnormalities in excitation-contraction coupling similar to myocytes from diabetic rats. Metformin, an insulin-sensitizing biguanide, enhances peripheral insulin action and lowers blood pressure in hyperinsulinemic animals, but its direct impact on cardiac function is not fully understood. To examine the role of metformin on HG-induced cardiac dysfunction at the cellular level, normal adult ventricular myocytes were cultured for 1 day in a serum-free insulin-containing medium with either normal glucose (5.5 mmol/l glucose) or HG (25.5 mmol/l glucose) in the presence or absence of metformin or the sulfonylurea glyburide. Mechanical properties were evaluated using a high-speed video-edge detection system, and intracellular Ca2+ transients were recorded in fura-2-loaded myocytes. As previously reported, culturing myocytes in HG depresses peak shortening, prolongs time to 90% relengthening, and slows Ca2+ transient decay. Culturing cells with metformin (50 micromol/l) prevented the HG-induced abnormalities in relaxation without ameliorating depressed peak-shortening amplitudes. Incubation of the cells with metformin also prevented slower intracellular Ca2+ clearing induced by HG. However, the HG-induced relaxation defects were not improved by glyburide (50-300 micromol/l). Interestingly, metformin also improved HG-induced relaxation abnormalities in the absence of insulin, whereas it failed to protect against HG in the presence of the tyrosine kinase inhibitor genistein (50 micromol/l). These data demonstrate that, unlike glyburide, metformin provides cardioprotection against HG-induced abnormalities in myocyte relaxation, perhaps through tyrosine kinase-dependent changes in intracellular Ca2+ handling, independent of its insulin sensitizing action.

Augmentation of the inotropic response to insulin in diabetic rat hearts

Insulin participates in the modulation of myocardial function, but its inotropic action in diabetes mellitus is not fully clear. In the present study, we examined contractile responses to insulin in left-ventricular papillary muscles and ventricular myocytes isolated from hearts of normal or short-term (5-7 days) streptozotocin-induced (65 mg/kg) diabetic rats. Mechanical properties of papillary muscles and ventricular myocytes were evaluated using a force transducer and an edge-detector, respectively. Contractile properties of papillary muscles or cardiac myocytes, electrically stimulated at 0.5 Hz, were analyzed in terms of peak tension development (PTD) or peak twitch amplitude (PTA), time-to-peak contraction (TPT) and time-to-90% relaxation (RT90). Intracellular Ca2+ transients were measured as fura-2 fluorescence intensity change (deltaFFI). Insulin (1-500 nM) had no effect on PTD in normal myocardium, whereas it produced a positive inotropic response in preparations from diabetic animals, with a maximal increase of 11%. Insulin did not modify TPT or RT90 in either group. Further studies revealed that insulin enhanced cell shortening in diabetic but not normal myocytes, with a maximal increase of 21%. Consistent with its action on the mechanical properties of papillary muscles and cardiac myocytes, insulin also induced a dose-dependent increase in the intracellular Ca2+ transient in diabetic but not normal myocytes. Collectively, these data suggest that the myocardial contractile response to insulin may be altered in diabetes.

Interleukin-1beta-induced nitric oxide production in rat aortic endothelial cells: inhibition by estradiol in normal and high glucose cultures

Expression of inducible nitric oxide synthase (iNOS) and the resultant increased nitric oxide (NO) production are associated with septic shock, atherosclerosis, and cytokine-induced vascular injury. Estrogen is known to impact vascular injury and vascular tone, in part through regulation of NO production. In the current study, we examined the effect of physiological concentrations of estradiol on interleukin-1beta (IL-1beta)-induced NO production in rat aortic endothelial cells (RAECs). 17Beta-estradiol significantly decreased IL-1beta-induced iNOS protein levels and reduced NO production in RAECs. High glucose (25 mM) elevated the increase in IL-1beta-induced iNOS protein and NO production. Nevertheless, estradiol still inhibited IL-1beta-induced iNOS and NO production even in the presence of high glucose. These data suggest that estradiol may exert its beneficial effects in part by inhibiting induction of endothelial iNOS, a possible mechanism for the protective effect of estradiol against diabetes-associated cardiovascular complications.

Cardiovascular disease in the diabetic woman

The incidence of cardiovascular disease (CVD) with age is increasing in the United States, and elderly women constitute a disproportional component of the aging population. Elderly women also have a relatively high incidence of diabetes, which contributes to this relatively high CVD risk. Although CVD is less common in premenopausal women than in men, this difference begins to disappear after the onset of menopause, presumably related to decreased levels of female sex hormones (estrogen and/or progesterone). Diabetes mellitus removes the normal premenopausal gender-related differences in the prevalence of CVD by mechanisms that are not clearly defined, including metabolic and hemodynamic factors associated with diabetes. Dyslipidemia in diabetes mellitus consists of low high density lipoprotein cholesterol, elevated triglyceride levels, and a small, dense, more atherogenic low density lipoprotein particle (i.e. oxidized). Dyslipidemia interacts with associated hemodynamic (i.e. hypertension) and metabolic abnormalities (i.e. increased platelet aggregation and plasminogen activator inhibitor-1 levels) to promote CVD risks in diabetic women. Recent controlled trials underscore the critical importance of aggressively treating CVD risk factors, especially dyslipidemia, in women with diabetes.

Influence of age on inotropic response to insulin and insulin-like growth factor I in spontaneously hypertensive rats: role of nitric oxide

Insulin-like growth factor-1 (IGF-1) and insulin stimulate cardiac growth and contractility. Recent evidence suggests a relationship between essential hypertension, left ventricular hypertrophy, and circulating IGF-1 levels. Advanced age alters cardiac function in a manner similar to hypertension. The aim of this investigation was to evaluate the effects of IGF-1 and insulin on the force generating capacity of cardiac muscle in hypertension and the influence of age on this response. Contractile responses to IGF-1 and insulin were examined using papillary muscles from Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) at 10 and 25 weeks of age. Muscles were electrically stimulated at 0.5 Hz, and contractile properties, including peak tension development (PTD), time-to-peak tension, time-to-90% relaxation, and the maximal velocities of contraction and relaxation, were evaluated. PTD was similar in WKY and SHR myocardium at both age groups. At 10 weeks of age, IGF-1 (1-500 ng/ml) caused a dose-dependent increase in PTD in WKY but not SHR myocardium, whereas insulin (1-500 nM) had no effect on PTD in either group. At 25 weeks of age, the positive inotropic effect of IGF-1 was attenuated in the WKY group, and IGF-1 exerted no inotropic action in the SHR group. Pretreatment with the nitric oxide synthase inhibitor, N-omega-nitro-L-arginine methyl ester (L-NAME, 100 microM), did not alter the IGF-1-induced positive inotropic response in 10-week-old WKY myocardium, whereas it unmasked a positive inotropic action in muscles from age-matched SHR animals. At 25 weeks of age, L-NAME abolished IGF-1-induced a positive inotropic response in WKY myocardium, and did not unmask an IGF-induced inotropic response in SHR myocardium. Our results suggest that alterations in nitric oxide modulation of IGF-1-induced contraction may underlie resistance to this inotropic peptide with advancing age, and/or hypertension.

Special considerations in the therapy of diabetic hypertension

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

Insulin, cation metabolism and insulin resistance

There is considerable evidence that insulin and insulin-like growth factors regulate a number of important physiological functions in a variety of tissues, some not considered to be classically insulin sensitive. Impaired biological responses to insulin and related insulin-like growth factors are referred to as insulin resistance. Persons with insulin resistance often display clinical abnormalities other than impaired glucose tolerance, including central obesity, hypertension, dyslipidemia, microalbuminuria, and abnormal coagulation and fibrinolytic systems. The mechanisms leading to development of insulin resistance are not fully understood. However, in addition to abnormalities of phosphorylation processes, it appears that alterations in cellular cation metabolism contribute to diminished cellular actions of insulin (i.e., glucose transport and hemodynamic actions). This review focuses on known cellular cation abnormalities and associated insulin resistance and cardiovascular disease.

Obesity, hypertension, and vascular disease

Obesity, hypertension, and related metabolic and hemodynamic abnormalities contribute significantly to cardiovascular disease in westernized societies such as the United States. Both obesity and hypertension are more prevalent among minorities such as black and Hispanic populations. Obesity substantially increases the likelihood of hypertension, and weight reduction has been shown to be an effective hygienic measure in reducing blood pressure. There is accumulating evidence that central obesity, particularly obesity that is distributed in the paraomental (visceral) region, especially predisposes one to hypertension and related metabolic abnormalities that contribute cerebrovascular disease.

Troglitazone and vascular reactivity: role of glucose and calcium

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

Magnesium responsiveness to insulin and insulin-like growth factor I in erythrocytes from normotensive and hypertensive subjects

Depletion of intracellular free magnesium (Mg(i)) is a characteristic feature of insulin resistance in essential hypertension, but it is not clear to what extent low Mg(i) levels contribute to insulin resistance, result from it, or both. As insulin-like growth factor I (IGF-I) may improve insulin resistance, we investigated whether this peptide could similarly improve Mg(i) responsiveness to insulin in hypertension, and whether this effect was related to any direct IGF-I effect on Mg(i). 31P-Nuclear magnetic resonance spectroscopy was used to measure Mg(i) in erythrocytes from 13 fasting normotensive and 10 essential hypertensive subjects before and 30, 60, and 120 min after incubation with a physiologically maximal dose of insulin (200 microU/mL) and with different doses of recombinant human IGF-I (0.1-100 nmol/L). In normotensive subjects, IGF-I elevated Mg(i) (P < 0.05) in a dose- and time-dependent fashion, as did insulin (P < 0.05). However, in hypertensive subjects, maximal Mg(i) responses to insulin, but not to IGF-I, were blunted [insulin, 163+/-11 to 177+/-10 micromol/L (P=NS); IGF-I, 164+/-6 to 190+/-11.7 micromol/L (P < 0.05)]. Furthermore, for insulin, but not for IGF-I, cellular Mg(i) responsiveness was closely and directly related to basal Mg(i) levels (insulin: r=0.72; P < 0.01; IGF-I: r=0.18; P=NS). Lastly, blunted Mg(i) responses to insulin could be reversed by preincubation of hypertensive cells with IGF-I. We conclude that 1) both IGF-I and insulin stimulate erythrocyte Mg(i) levels; 2) cellular Mg(i) responses to insulin, but not to IGF-I, depend on basal Mg(i) levels, i.e. the higher the Mg(i) the greater the sensitivity to insulin; and 3) IGF-I potentiates insulin-induced stimulation of Mg(i) at doses that themselves do not raise Mg(i). These effects of IGF-I may underlie at least in part its ability to improve insulin sensitivity clinically. Together, these data support a role for IGF-I in cellular magnesium metabolism and emphasize the importance of magnesium as a determinant of insulin action.

Isradipine in prediabetic hypertensive subjects

OBJECTIVE

Investigators from the Multicenter Isradipine Diuretic Atherosclerosis Study (MIDAS) previously reported that the isradipine group had a higher incidence of cardiovascular disease (CVD) events than the diuretic group. The ultimate objective of the analyses presented here was to assess how indices of glycemia (specifically, serum glucose, serum insulin, and HbA1c) might have influenced the effects of the two agents on blood pressure control and CVD events.

RESEARCH DESIGN AND METHODS

Inclusion criteria included men and women > or = 40 years of age with ultrasonographically confirmed carotid atherosclerosis and a diastolic blood pressure of > 90 mmHg. Although insulin-dependent diabetic patients were excluded, the three glycemia indices had wide enough ranges to include patients who may be classified as prediabetic. A total of 883 patients were randomized either to the dihydropyridine calcium antagonist (CA) isradipine (2.5-5 mg twice a day) or to the diuretic hydrochlorothiazide (12.5-25 mg twice a day) and followed in double-blind fashion for 3 years.

RESULTS

Both treatment groups had achieved comparable control of diastolic blood pressure, and there were no statistically significant differences in any of the glycemia indices, either at baseline or during follow-up. However, the excess isradipine events were noted to be clustered among those patients with elevated baseline levels of HbA1c who also experienced greater blood pressure reductions during follow-up.

CONCLUSIONS

The increased cardiovascular risk associated with dihydropyridine CAs in prediabetic patients may be an explanation for the overall CA debate.

Comorbidity of hypertension and diabetes: the fosinopril versus amlodipine cardiovascular events trial (FACET)

Macrovascular disease is the major cause of mortality in persons with type 2 diabetes mellitus, and hypertension is an important factor contributing to this high prevalence. High blood pressure is about twice as common in persons with diabetes mellitus as in those without. Up to 75% of diabetes-related cardiovascular complications are attributed to hypertension. These observations are part of the rationale for recommendations for more aggressive lowering of blood pressure (to < 130/85 mm Hg) in persons with coexistent diabetes and hypertension. This may require therapy with a combination of antihypertensive agents. The Fosinopril versus Amlodipine Cardiovascular Events Trial (FACET), discussed herein, supports the case for combination therapy with an angiotensin-converting enzyme (ACE) inhibitor and a calcium antagonist in diabetic patients with hypertension.

Insulin potentiates platelet-derived growth factor action in vascular smooth muscle cells

Correlative studies have indicated that hyperinsulinemia is present in many individuals with atherosclerosis. Insulin resistance has also been linked to cardiovascular disease. It has proved to be difficult to decipher whether hyperinsulinemia or insulin resistance plays the most important role in the pathogenesis of atherosclerosis and coronary artery disease. In this study, we demonstrate that insulin increases the amount of farnesylated p21Ras in vascular smooth muscle cells (VSMC), thereby augmenting the pool of cellular Ras available for activation by platelet-derived growth factor (PDGF). In VSMC incubated with insulin for 24 h, PDGF's influence on GTP-loading of Ras was significantly increased. Furthermore, in cells preincubated with insulin, PDGF increased thymidine incorporation by 96% as compared with a 44% increase in control cells (a 2-fold increment). Similarly, preincubation of VSMC with insulin increased the ability of PDGF to stimulate gene expression of vascular endothelial growth factor 5- to 8-fold. The potentiating influence of insulin on PDGF action was abrogated in the presence of a farnesyltransferase inhibitor. Thus, the detrimental influence of hyperinsulinemia on the arterial wall may be related to the ability of insulin to augment farnesyltransferase activity and provide greater amounts of farnesylated p21Ras for stimulation by various growth promoting agents.

Diabetic vascular disease and hypertension

There is increasing evidence that essential hypertension is associated with a panoply of metabolic abnormalities. Included in these abnormalities are insulin resistance, dyslipidemia, enhanced coagulation, and decreased fibrinolytic activity, microalbuminuria, and platelet abnormalities and endothelial dysfunction. Visceral obesity appears to be the most common and predictive underlying factor for all of these metabolic abnormalities accompanying hypertension as well as increased cardiovascular disease (CVD) risk. As the prevalence of obesity is increasing, there is cause for concern that CVD increases will parallel this risk factor, particularly in especially high-risk populations, such as African-American women. Other important risk factors, such as increased oxidative stress, may require special therapeutic strategies, including the use of angiotensin-converting enzyme (ACE) inhibitors and angiotensin blockers as cornerstones of antihypertensive drug therapy.

Altered inotropic response to IGF-I in diabetic rat heart: influence of intracellular Ca2+ and NO

Normally, insulin-like growth factor I (IGF-I) exerts positive effects on cardiac growth and myocardial contractility, but resistance to its action has been reported in diabetes. This study was designed to determine whether IGF-I-induced myocardial contractile action is altered in diabetes as a result of an intrinsic alteration of contractile properties at the cellular level. Contractile responses to IGF-I were examined in left ventricular papillary muscles and ventricular myocytes from normal and short-term (5-7 days) streptozotocin-induced diabetic rats. Mechanical properties of muscles and myocytes were evaluated using a force transducer and an edge detector, respectively. Preparations were electrically stimulated at 0.5 Hz, and contractile properties analyzed include peak tension development (PTD) or peak twitch amplitude (PTA), time to peak contraction/shortening, and time to 90% relaxation/relengthening. Intracellular Ca2+ transients were measured as fura 2 fluorescence intensity changes. IGF-I (1-500 ng/ml) caused a dose-dependent increase in PTD and PTA in preparations from normal but not diabetic animals. IGF-I did not alter time to peak contraction/shortening or time to 90% relaxation/relengthening. Pretreatment with the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (100 microM) attenuated IGF-I-induced increases in PTD in normal myocardium but unmasked a positive inotropic action in diabetic animals. Pretreatment with Nomega-nitro-L-arginine methyl ester blocked IGF-I-induced increases in PTA in single myocytes. Consistent with its inotropic actions on muscles and myocytes, IGF-I induced a dose-dependent increase in Ca2+ transients in normal but not diabetic myocytes. These results suggest that the IGF-I-induced inotropic response is depressed in diabetes because of an intrinsic alteration at the myocyte level. Mechanisms underlying this alteration in IGF-I-induced myocardial response may be related to changes in intracellular Ca2+ and/or NO production in diabetes.

Obesity and cardiovascular disease

Obesity, diabetes mellitus, and hypertension are common, interrelated medical problems in Westernized, industrialized societies. These interrelated medical conditions are associated with an increased risk of cardiovascular disease and are more prevalent in several minority groups, including African-American and Hispanic populations. The associated cardiovascular risks of these problems are more thoroughly addressed in another review in this supplement. Obesity markedly enhances the development of Type 2 diabetes. Moreover, it enhances the cardiovascular risk associated with other risk factors, such as hypertension and dyslipidemia. Weight reduction in association with an aerobic exercise program improves metabolic abnormalities and reduces blood pressure in individuals with diabetes and hypertension.

Diabetes mellitus and cardiovascular disease in women

BACKGROUND

Coronary heart disease (CHD) is the leading cause of morbidity and mortality in women in the United States. Although CHD is less common in premenopausal women than in men, this difference begins to disappear after the onset of menopause, presumably related to reduced levels of female sex hormones.

RESULTS

An association between both a postmenopausal increase in blood pressure and CHD that coincide with loss of ovarian function suggests that estrogen and/or progesterone may be protective against hypertension and CHD. Diabetes removes the normal sex difference in the prevalence of CHD. Increased mortality in women with CHD and diabetes compared with women without diabetes has been observed in epidemiological studies.

CONCLUSIONS

Diabetes appears to obviate the protective effects of female sex hormones. Possible reasons for this catastrophic effect of diabetes in women are discussed.

Calcium and protein kinase C mediate high-glucose-induced inhibition of inducible nitric oxide synthase in vascular smooth muscle cells

Abnormal vascular smooth muscle (VSMC) proliferation is a key feature in diabetes-associated atherosclerotic disease. Since nitric oxide inhibits VSMC tone, migration, adhesion, and proliferation, we examined the effects of high glucose on IL-1beta-induced NO release from VSMCs in culture. Confluent smooth muscle cells, preincubated with either 5 mmol/L (mM) or 20 mmol/L (mM) glucose for 48 hours, were stimulated with IL-1beta. Nitrite was measured in the culture medium after 24 hours. IL-1beta-induced a 15-fold increase in NO production in normal glucose medium. Glucose (10 to 30 mmol/L (mM)) significantly reduced the response to IL-1beta. High glucose (20 mmol/L (mM)) inhibited IL-1beta-evoked NO production by approximately 50%. IL-1beta-stimulated [3H] citrulline-forming activity of the nitric oxide synthase (NOS) was also significantly lower in high-glucose-exposed cells, and this was reflected in diminished cellular levels of NOS protein. To assess the role of protein kinase C (PKC), membrane PKC activity was measured, and glucose (20 mmol/L (mM)) significantly increased it. Immunoblotting of the membranes revealed a glucose-induced increase in the PKC betaII isoform. 1,2-Dioctanoyl-glycerol, a PKC activator, mimicked the high-glucose effect on IL-1beta-induced NO release, while staurosporine, a PKC inhibitor, reversed it. The role of calcium in the glucose-mediated inhibition of cytokine-induced NO release was determined by treatment with BAPTA, an intracellular chelator of calcium. BAPTA partially reversed the inhibitory effects of glucose. Increasing intracellular calcium by A23187, an ionophore or thapsigargin, an inhibitor of endoplasmic reticulum Ca2+-ATPase, significantly decreased IL-1beta-induced NO release and NOS expression. These results indicate that glucose-induced inhibition of IL-1beta-stimulated NO release and NOS expression may be mediated by PKC activation and increased intracellular calcium.