Direct demonstration of insulin-like growth factor-I-induced nitric oxide production by endothelial cells

Fibroblast growth factor-2-induced cardioprotection against myocardial infarction occurs via the interplay between nitric oxide, protein kinase signaling, and ATP-sensitive potassium channels

Fibroblast growth factor-2 (FGF2) protects the heart from ischemia-reperfusion (I-R) injury via a vast network of protein kinases. In the heart, downstream effectors of these FGF2-triggered signals have not yet been identified. It is hypothesized that nitric oxide (NO) signaling and ATP-sensitive potassium (K(ATP)) channel activity are key effectors of protein kinases activated by FGF2-mediated cardioprotection. Hearts with a cardiac-specific overexpression of FGF2 (FGF2 Tg) were subjected to I-R injury in the absence or the presence of selective inhibitors of NO synthase (NOS) isoforms or sarcolemmal (sarcK(ATP)) and mitochondrial (mitoK(ATP)) K(ATP) channels. Multiple NOS isoforms are necessary for FGF2-mediated cardioprotection, and nitrite levels are significantly reduced in FGF2 Tg hearts upon inhibition of protein kinase C or mitogen-activated protein kinases. Likewise, sarcK(ATP) and mitoK(ATP) channels are important for cardioprotection elicited by endogenous FGF2. These findings suggest that FGF2-induced cardioprotection occurs via protein kinase-NOS pathways as well as K(ATP) channel activity.

Low serum IGF-1 is a risk factor for cardiac allograft vasculopathy in cardiac transplant recipients

BACKGROUND

Cardiac allograft vasculopathy (CAV) has an incidence of 43% at 8 years after heart transplantation with extremely limited treatment options and unclear pathogenesis. CAV constitutes a significant complication that limits the long-term survival of heart recipients. Insulin-like growth factor-1 (IGF-1) is associated with different cardiovascular diseases; however, its role in CAV pathogenesis remains unknown.

METHODS

Serum samples of 10 matched recipients with CAV and 10 with no-CAV were initially screened with a protein array. Subsequently, IGF-1- and IGF-binding protein-3 (IGFBP-3) were analyzed using enzyme-linked immunosorbent assay in 44 randomly selected CAV and 50 no-CAV patients at two time points.

RESULTS

The initial screening showed that IGF-1 and IGFBP-3 are differentially expressed in CAV compared with no-CAV patients (P=0.037 and P<0.0001, respectively). Subsequent enzyme-linked immunosorbent assay analyses indicated that serum IGF-1 protein concentrations were significantly lower in CAV patients (159.7±114 ng/mL) as compared with no-CAV patients (234.1±136 ng/mL; P=0.02). Serum IGFBP-3 protein concentrations were significantly lower in CAV (0.46±0.37 mg/L) as compared with no-CAV patients (1.03±0.73 mg/L; P=0.04). Multivariate logistic regression analyses showed that IGF-1 (odds ratio, 0.89; P=0.04) and IGFBP-3 (odds ratio, 0.09; P=0.03) are independent risk factors for CAV.

CONCLUSION

Low IGF-1 and IGFPB-3 serum concentrations are associated with CAV. The assessment of serum IGF-1 and IGFPB-3 might be beneficial in identifying cardiac allograft recipients who are prone to develop CAV. Moreover, IGF-1 might be a useful therapy that could protect cardiac allografts against CAV.

Effects of bench step exercise on arterial stiffness in post-menopausal women: contribution of IGF-1 bioactivity and nitric oxide production

OBJECTIVE

To examine the effect of bench step exercise on arterial pulse wave velocity (PWV) and the associated contribution of insulin-like growth factor (IGF)-1 bioactivity and nitric oxide (NO).

DESIGN

Twenty-six elderly (post-menopausal) women were randomly allocated to a bench step exercise group or a control group. The participants in the bench step exercise group practiced a 12-week home-based bench step exercise for 10-20min, 3 times daily (i.e., for a total of 140min/week at the intensity level of lactate threshold (LT)). In addition to conventional risk factors of atherosclerosis, PWV, IGF-1/IGF binding protein (IGFBP)-3 molar ratio (an index for IGF-1 bioactivity), and urinary nitrite/nitrate (NO(x)) excretion were measured before and after the intervention.

RESULTS

BMI, systolic blood pressure, fasting plasma glucose, low-density lipoprotein cholesterol, LT, and PWV were significantly improved in the bench step exercise group. A significant positive correlation between changes in PWV and IGF-1/IGFBP-3 molar ratio, and a significant negative correlation between changes in IGF-1/IGFBP-3 molar ratio and urinary NO(x) excretion were found in the bench step exercise group.

CONCLUSION

The bench step exercise leads to improvements in not only the classical risk factors of atherosclerosis but also the arterial stiffness in elderly women, partly through NO production via IGF-1 bioactivity.

Atherosclerotic Risk Factors and Premature Atherosclerosis in Acromegaly Before and After 48 Months of Octreotide-LAR Treatment

We studied premature atherosclerosis with carotid Doppler ultrasonography in active acromegaly before and after treatment. Patients (n = 27) with active acromegaly and 12 age-, gender-, and body mass index-matched healthy individuals were included in the study. Carotid intima–media thickness was decreased significantly in the inactive group after treatment (median: 0.6 mm, interquartile range [IQR]: 0.55-0.80]) when compared with the active group (median: 0.9 mm [IQR: 0.75-1.15], P < .0001), but there was no significant difference between the inactive and control groups. There was a correlation between homeostasis model of assessment–insulin resistance ( P = .01, r = .41) and growth hormone (GH; P < .0001, r = .46). In conclusion, premature atherosclerosis was demonstrated in active acromegaly patients probably as a consequence of insulin resistance and direct vascular effects of GH and/or insulin-like growth factor 1.

Increased IGF1 levels in relation to heart failure and cardiovascular mortality in an elderly population: impact of ACE inhibitors

OBJECTIVE

There are conflicting results regarding the association of circulating IGF1 with cardiovascular (CV) morbidity and mortality. We assessed the relationship between IGF1 levels and heart failure (HF), ischemic heart disease (IHD), and CV mortality in an elderly population taking into account the possible impact of angiotensin converting enzyme (ACE) inhibitors.

DESIGN AND METHODS

A total of 851 persons aged 66-81 years, in a rural Swedish municipality, were subjected to medical history, clinical examination, electrocardiography, echocardiography, and fasting plasma samples. They were then followed for 8 years.

RESULTS AND CONCLUSION

Patients on ACE inhibitors had higher IGF1 levels compared with those without ACE inhibitors. In patients on ACE inhibitors, higher IGF1 values were found in patients with an ejection fraction (EF) <40% compared with EF ≥40%, in patients with higher proBNP levels in quartile 4 vs 1, and in patients with IHD when compared to those without ACE inhibitors (P<0.001). In patients without ACE inhibitors, no relationship was found between IGF1 levels and HF or IHD. In multivariate regression, only ACE inhibitors, ECG changes characteristic for IHD, and gender had a significant impact on IGF1. Patients with higher IGF1 levels in quintiles 4 and 5 compared to quintiles 1 and 2 had a 50% higher risk for CV death (P=0.03). This was significant after adjustment for well-known CV risk factors and ACE inhibitors (P=0.03).

CONCLUSIONS

Our results show that treatment with ACE inhibitors in an elderly population is associated with increased IGF1 levels, especially in patients with impaired cardiac function or IHD. High IGF1 levels tend to be associated with an increased risk for CV mortality.

Myths and truths of growth hormone and testosterone therapy in heart failure

Heart failure is a chronic clinical syndrome with very poor prognosis. Despite being on optimal medical therapy, many patients still experience debilitating symptoms and poor quality of life. In recent years, there has been a great interest in anabolic hormone replacement therapy - namely, growth hormone and testosterone - as an adjunctive therapy in patients with advanced heart failure. It has been observed that low levels of growth hormone and testosterone have been associated with increased mortality and morbidity in patients with heart failure. Animal studies and clinical trials have shown promising clinical improvement with hormonal supplementation. Growth hormone has been shown to increase ventricular wall mass, decrease wall stress, increase cardiac contractility, and reduce peripheral vascular resistance, all of which might help to enhance cardiac function, resulting in improvement in clinical symptoms. Likewise, testosterone has been shown to improve hemodynamic parameters via reduction in peripheral vascular resistance and increased coronary blood flow through vasodilation, thereby improving functional and symptomatic status. To date, growth hormone and testosterone therapy have shown some positive benefits, albeit with some concerns over adverse effects. However, large randomized controlled trials are still needed to assess the long-term safety and efficacy.

The GH/IGF-1 Axis and Heart Failure

The growth hormone (GH)/insulin-like growth factor 1 (IGF-1) axis regulates cardiac growth, stimulates myocardial contractility and influences the vascular system. The GH/IGF-1 axis controls intrinsic cardiac contractility by enhancing the intracellular calcium availability and regulating expression of contractile proteins; stimulates cardiac growth, by increasing protein synthesis; modifies systemic vascular resistance, by activating the nitric oxide system and regulating non-endothelial-dependent actions. The relationship between the GH/IGF-1 axis and the cardiovascular system has been extensively demonstrated in numerous experimental studies and confirmed by the cardiac derangements secondary to both GH excess and deficiency. Several years ago, a clinical non-blinded study showed, in seven patients with idiopathic dilated cardiomyopathy and chronic heart failure (CHF), a significant improvement in cardiac function and structure after three months of treatment with recombinant GH plus standard therapy for heart failure. More recent studies, including a small double-blind placebo-controlled study on GH effects on exercise tolerance and cardiopulmonary performance, have shown that GH benefits patients with CHF secondary to both ischemic and idiopathic dilated cardiomyopathy. However, conflicting results emerge from other placebo-controlled trials. These discordant findings may be explained by the degree of CHF-associated GH resistance. In conclusion, we believe that more clinical and experimental studies are necessary to exactly understand the mechanisms that determine the variable sensitivity to GH and its positive effects in the failing heart.

All-cause mortality and serum insulin-like growth factor I in primary care patients

OBJECTIVE

Previous population-based studies provided conflicting results regarding the association of total serum insulin-like growth factor I (IGF-I) and mortality. The aim of the present study was to assess the relation of IGF-I levels with all-cause mortality in a prospective study.

DESIGN

DETECT (Diabetes Cardiovascular Risk-Evaluation: Targets and Essential Data for Commitment of Treatment) is a large, multistage, and nationally representative study of primary care patients in Germany. The study population included 2463 men and 3603 women. Death rates were recorded by the respective primary care physician. Serum total IGF-I levels were determined by chemiluminescence immunoassays and categorized into three groups (low, moderate, and high) according to the sex- and age-specific 10th and 90th percentiles.

RESULTS

Adjusted analyses revealed that men with low [hazard ratio (HR) 1.70 (95% confidence interval [CI] 1.05-2.73), p=0.03] and high [HR 1.76 (95% CI 1.09-2.85), p=0.02] IGF-I levels had higher risk of all-cause mortality compared to men with moderate IGF-I levels. The specificity of low IGF-I and high IGF-I levels increased with lower and higher cut-offs, respectively. No such association became apparent in women.

CONCLUSIONS

The present study revealed a U-shaped relation between IGF-I and all-cause mortality in male primary care patients.

Growth hormone and testosterone in heart failure therapy

IMPORTANCE OF THE FIELD

Heart failure is a progressive disease affecting millions of people worldwide. The disease carries a significantly high morbidity and mortality risk. There are multiple pharmaceutical options to decrease this risk and prolong survival; however, despite optimization of medical management, several patients still await heart transplant, the only definitive cure for heart failure. To slow the progression of disease preventing need for transplantation, improve clinical symptoms, and improve heart failure outcomes, there is a persistent need to discover new therapeutic strategies. Of interest, low growth hormone and testosterone levels have been associated with a worsening degree of heart failure. Many studies have begun to show a clinical improvement in heart failure symptoms when these levels are corrected with hormonal therapy. These findings, although mixed, are promising and indicate that both testosterone and growth hormone therapy should be considered as adjunctive therapy in advanced heart failure patients.

AREAS COVERED IN THIS REVIEW

This review discusses the physiology of both of these natural hormones, their therapeutic effects in heart failure and data from the published literature on studies using growth hormone or testosterone in patients with chronic heart failure. An extensive search of PubMed was conducted for topics on heart failure, growth hormone, insulin-like growth factor, testosterone, their physiology and pathophysiology, and trials in which they have been used as therapeutic interventions between 1989 and 2009.

WHAT THE READER WILL GAIN

The reader will gain an understanding of the intricate balance of both of these hormones in the disease state of heart failure. In addition, the trials conducted using these hormones in pharmacotherapy for heart failure are discussed along with proposed theories for interstudy variability.

TAKE HOME MESSAGE

Testosterone deficiency and growth hormone resistance are positively associated with a poor state of heart failure. Treatment of deficiency improves outcomes in heart failure; however, there is a significant paucity of data with regard to testosterone and heart failure as well as a significant amount of study variability with growth hormone and heart failure.

Association of serum IGF1 with endothelial function: results from the population-based study of health in Pomerania

OBJECTIVE

IGF1 mediates multiple physiological and pathophysiological responses in the cardiovascular system. The aim of this study was to analyze the association between serum IGF1 as well as IGF-binding protein 3 (IGFBP3) levels and endothelial function measured by flow-mediated dilation (FMD).

DESIGN

Cross-sectional population-based observational study.

METHODS

The study population comprised 1482 subjects (736 women) aged 25-85 years from the Study of Health in Pomerania. Serum IGF1 and IGFBP3 levels were determined by chemiluminescence immunoassays. FMD measurements were performed using standardized ultrasound techniques. FMD values below the sex-specific median were considered low.

RESULTS

In males, logistic regression analyses revealed an odds ratio (OR) of 1.27 (95% confidence interval (CI) 1.07-1.51; P=0.008) for decreased FMD for each decrement of IGF1 s.d. after adjustment for major cardiovascular confounders. In females, no significant relationship between serum IGF1 and FMD was found (OR 0.88, CI 0.74-1.05; P=0.147). After exclusion of subjects with the current use of antihypertensive medication, these findings were similar (males: OR 1.40, CI 1.12-1.75; P=0.003; females: OR 0.95, CI 0.77-1.16; P=0.595). There was no association between serum IGFBP3 levels and FMD in both sexes.

CONCLUSIONS

Low serum IGF1 levels are associated with impaired endothelial function in males. In women, serum IGF1 is not associated with endothelial function.

Effects of ACE-inhibition on IGF-1 and IGFBP-3 concentrations in older adults with high cardiovascular risk profile

OBJECTIVES

The present study evaluates the effects of a 6-month treatment with an ACE-inhibitor (ie, fosinopril) on serum concentrations of total IGF-1 and IGF binding protein (IGFBP)-3 in older adults at high risk for cardiovascular disease.

DESIGN

Data are from the Trial of Angiotensin Converting Enzyme Inhibition and Novel Cardiovascular Risk Factors (TRAIN) study, a double-blind, crossover, randomized, placebo-controlled trial.

SETTING

Participants were recruited from the communities of Winston Salem, NC, and Greensboro, NC.

PARTICIPANTS

Subjects > or = 55 years old with high cardiovascular disease risk profile.

INTERVENTION

The intervention consisted of 6-month administration of fosinopril vs. placebo.

MEASUREMENTS

Serum concentrations of total IGF-1 and IGFBP-3 were measured in 100 participants of the TRAIN study at baseline, 6-month and 12-month follow-up visits. Differences in total IGF-1 and IGFBP-3 concentrations were assessed using two-sided paired ttests.

RESULTS

The mean age of participants (47% women) was 66.5 (standard deviation 7.2) years. Serum concentrations of total IGF-1 were significantly higher after 6-month treatment with fosinopril compared to placebo (203.73 ng/mL vs 194.24 ng/mL; p=0.02): After ACE-inhibitor intervention, significantly higher serum IGFBP-3 concentrations compared to controls (4308.81 ng/mL vs 4086.93 ng/mL; p=0.03) were also reported.

CONCLUSIONS

A six-month treatment with fosinopril increases systemic levels of total IGF-1 and IGFBP-3 in older adults with high cardiovascular risk profile. This may represent a potential biological explanation to the beneficial effects of ACE-inhibition on stroke, ischemic heart disease and insulin resistance.

Muscle sympathetic nerve activity is related to a surrogate marker of endothelial function in healthy individuals

BACKGROUND

Evidence from animal studies indicates the importance of an interaction between the sympathetic nervous system and the endothelium for cardiovascular regulation. However the interaction between these two systems remains largely unexplored in humans. The aim of this study was to investigate whether directly recorded sympathetic vasoconstrictor outflow is related to a surrogate marker of endothelial function in healthy individuals.

METHODS AND RESULTS

In 10 healthy normotensive subjects (3 f/7 m), (age 37+/-11 yrs), (BMI 24+/-3 kg/m(2)) direct recordings of sympathetic action potentials to the muscle vascular bed (MSNA) were performed and endothelial function estimated with the Reactive Hyperaemia- Peripheral Arterial Tonometry (RH-PAT) technique. Blood samples were taken and time spent on leisure-time physical activities was estimated. In all subjects the rate between resting flow and the maximum flow, the Reactive Hyperemic index (RH-PAT index), was within the normal range (1.9-3.3) and MSNA was as expected for age and gender (13-44 burst/minute). RH-PAT index was inversely related to MSNA (r = -0.8, p = 0.005). RH-PAT index and MSNA were reciprocally related to time (h/week) spent on physical activity (p = 0.005 and p = 0.006 respectively) and platelet concentration (PLT) (p = 0.02 and p = 0.004 respectively).

CONCLUSIONS

Our results show that sympathetic nerve activity is related to a surrogate marker of endothelial function in healthy normotensive individuals, indicating that sympathetic outflow may be modulated by changes in endothelial function. In this study time spent on physical activity is identified as a predictor of sympathetic nerve activity and endothelial function in a group of healthy individuals. The results are of importance in understanding mechanisms underlying sympathetic activation in conditions associated with endothelial dysfunction and emphasise the importance of a daily exercise routine for maintenance of cardiovascular health.

Insulin-like growth factor-1 protects from vascular stenosis and accelerates re-endothelialization in a rat model of carotid artery injury

BACKGROUND

IGF-1 is a potent mitogen for vascular smooth muscle cells, but exerts protective effects on endothelial cells that may trigger antiatherogenic mechanisms.

OBJECTIVES

This study was designed to test the hypothesis that an IGF-1 excess following arterial injury prevents neointima formation and vascular stenosis.

METHODS

Rats were subjected to carotid balloon injury and treated with IGF-1 (1.2 mg kg(-1) per die) or saline for 10 days.

RESULTS

In IGF-1 treated animals, high tissue levels of eNOS, Akt and its phosphorylated form were found, confirming activation of IGF-1-dependent signaling pathways. IGF-1 markedly reduced neointima formation and post-injury arterial stenosis. IGF-1 exerted proliferative and anti-apoptotic effects in the media of injured carotids, but inhibited mitotic activity and induced apoptosis in the neointima. Furthermore, IGF-1 stimulated mobilization of progenitor endothelial cells and re-endothelialization of the injured arteries. L-NAME administration inhibited IGF-1 vasculoprotective effects.

CONCLUSIONS

IGF-1 attenuates post-injury carotid stenosis by exerting differential effects in the neointima and tunica media with regard to the key components of the response to injury. The data point to a novel role of IGF-1 as a potent vasculoprotective factor.

Gender differences in endothelial function in aortas from type 2 diabetic model mice

Type 2 diabetes mellitus is associated with high mortality and morbidity, mainly due to coronary artery disease and atherosclerosis, although female gender is a protective factor in the development of, for example, atherosclerosis and hypertension. Our main aim was to investigate gender differences in endothelial function in aortas from type 2 diabetic model mice. The nonfasting plasma glucose level was significantly elevated in diabetic mice (both males and females). The plasma insulin level was not different between controls and diabetics (either gender). The plasma adiponectin level was decreased by diabetes, and was lower in males. In control aortas (from males or females), the clonidine-induced relaxation was abolished by Akt-inhibitor treatment. In diabetic males (versus both control males and diabetic females): a) the clonidine- and insulin-induced endothelium-dependent aortic relaxations were impaired, but the acetylcholine (ACh)-induced and sodium nitroprusside (SNP)-induced aortic relaxations were not, b) the norepinephrine (NE)-induced aortic contractile response was enhanced, c) systemic blood pressure was elevated, and d) the clonidine-stimulated Ser-473 phosphorylation of Akt in the aorta was decreased. These results suggest that endothelial functions dependent on the Akt pathway are abrogated by type 2 diabetes only in male mice.

Role of IGF-1 in glucose regulation and cardiovascular disease

IGF-1 is a peptide hormone that is expressed in most tissues. It shares significant structural and functional similarities with insulin, and is implicated in the pathogenesis of insulin resistance and cardiovascular disease. Recombinant human IGF-1 has been used in Type 2 diabetes to improve insulin sensitivity and aid glycemic control. There is evidence supporting IGF-1 as a vascular protective factor and it may also be beneficial in the treatment of chronic heart failure. Further understanding of the effects of IGF-1 signaling in health and disease may lead to novel approaches to the prevention and treatment of diabetes and cardiovascular disease.

IGF system and peripheral arterial disease: relationship with disease severity and inflammatory status of the affected limb

OBJECTIVES

IGF-1 and its binding proteins are involved in the pathogenesis of atherosclerosis. We designed this study to unravel the relationship of the IGF system with peripheral arterial disease (PAD).

DESIGN

Case-control, cross-sectional study.

MEASUREMENTS

Serum levels of IGF-1, IGFBP-3 and acid labile subunit (ALS) were measured in 96 PAD patients and 89 controls. In 28 patients who underwent peripheral angiography, C-reactive protein (CRP), IGF-1, IGFBP-3 and ALS were measured in blood from femoral vein of the affected limb and aorta.

RESULTS

Compared to controls, PAD patients showed lower levels of IGFBP-3 (3569 +/- 115 vs. 3106 +/- 107 microg/l, P < 0.01), and ALS (12.2 +/- 0.5 vs. 8.3 +/- 0.5 mg/l, P < 0.01). In PAD, concentrations of IGFBP-3 and ALS were significantly lower in patients with ankle/brachial index less than median than in those with a less severe PAD. In the affected limb, CRP venous-arterial difference correlated negatively with that of IGF-1 (rho = -0.57, P < 0.01), and positively with that of IGFBP-3 (rho = 0.63, P < 0.01). At multivariate analysis, a high transfemoral gradient of CRP was independently associated with a low transfemoral gradient of IGF-1 (beta coefficient = -0.48, P < 0.01), and a high transfemoral gradient of IGFBP-3 (beta coefficient = 0.22, P < 0.05).

CONCLUSIONS

This study is the first to demonstrate that the systemic levels of IGF axis components are associated with the presence and severity of PAD, and that the inflammatory status of the ischaemic limb affects the transfemoral concentrations of IGF-1 and IGFBP-3. Due to the importance of IGF axis in modulating atherosclerotic plaque progression, our data may contribute to a better understanding of PAD pathophysiology.

Mitochondrial dysfunction and HIF1alpha stabilization in inflammation

Activation of murine-derived J774.A1 macrophages with interferon gamma and lipopolysaccharide leads to a progressive mitochondrial defect characterized by inhibition of oxygen consumption and a decrease in the generation of ATP by oxidative phosphorylation. These changes are dependent on the generation of nitric oxide (NO) by an inducible NO synthase that becomes a significant consumer of oxygen. Furthermore, in these activated cells there is a biphasic stabilization of the hypoxia-inducible factor HIF1alpha, the second phase of which is also dependent on the presence of NO. The mitochondrial defect and stabilization of HIF1alpha synergize to activate glycolysis, which, at its maximum, generates quantities of ATP greater than those produced by non-activated cells. Nevertheless, the amount of ATP generated is not sufficient to fulfil the energy requirements of the activated cells, probably leading to a progressive energy deficit with the consequent inhibition of cell proliferation and death.

The GH-IGF-I axis and the cardiovascular system: clinical implications

BACKGROUND

GH and IGF-I affect cardiac structure and performance. In the general population, low IGF-I has been associated with higher prevalence of ischaemic heart disease and mortality. Both in GH deficiency (GHD) and excess life expectancy has been reported to be reduced because of cardiovascular disease.

OBJECTIVE

To review the role of the GH-IGF-I system on the cardiovascular system.

RESULTS

Recent epidemiological evidence suggests that serum IGF-I levels in the low-normal range are associated with increased risk of acute myocardial infarction, ischaemic heart disease, coronary and carotid artery atherosclerosis and stroke. This confirms previous findings in patients with acromegaly or with GH-deficiency showing cardiovascular impairment. Patients with either childhood- or adulthood-onset GHD have cardiovascular abnormalities such as reduced cardiac mass, diastolic filling and left ventricular response at peak exercise, increased intima-media thickness and endothelial dysfunction. These abnormalities can be reversed, at least partially, after GH replacement therapy. In contrast, in acromegaly chronic GH and IGF-I excess causes a specific cardiomyopathy: concentric cardiac hypertrophy (in more than two-thirds of the patients at diagnosis) associated to diastolic dysfunction is the most common finding. In later stages, impaired systolic function ending in heart failure can occur, if GH/IGF-I excess is not controlled. Abnormalities of cardiac rhythm and of cardiac valves can also occur. Successful control of acromegaly is accompanied by decrease of the left ventricular mass and improvement of cardiac function.

CONCLUSION

The cardiovascular system is a target organ for GH and IGF-I. Subtle dysfunction in the GH-IGF-I axis are correlated with increased prevalence of ischaemic heart disease. Acromegaly and GHD are associated with several abnormalities of the cardiovascular system and control of GH/IGF-I secretion reverses (or at least stops) cardiovascular abnormalities.

Endothelial function and vascular oxidative stress in long-lived GH/IGF-deficient Ames dwarf mice

Hypopituitary Ames dwarf mice have low circulating growth hormone (GH)/IGF-I levels, and they have extended longevity and exhibit many symptoms of delayed aging. To elucidate the vascular consequences of Ames dwarfism we compared endothelial O2(-) and H2O2 production, mitochondrial reactive oxygen species (ROS) generation, expression of antioxidant enzymes, and nitric oxide (NO) production in aortas of Ames dwarf and wild-type control mice. In Ames dwarf aortas endothelial O2(-) and H2O2 production and ROS generation by mitochondria were enhanced compared with those in vessels of wild-type mice. In Ames dwarf aortas there was a less abundant expression of Mn-SOD, Cu,Zn-SOD, glutathione peroxidase (GPx)-1, and endothelial nitric oxide synthase (eNOS). NO production and acetylcholine-induced relaxation were also decreased in aortas of Ames dwarf mice. In cultured wild-type mouse aortas and in human coronary arterial endothelial cells treatment with GH and IGF significantly reduced cellular O2(-) and H2O2 production and ROS generation by mitochondria and upregulated expression of Mn-SOD, Cu,Zn-SOD, GPx-1, and eNOS. Thus GH and IGF-I promote antioxidant phenotypic changes in the endothelial cells, whereas Ames dwarfism leads to vascular oxidative stress.

The role of IGF-I and its binding proteins in the development of type 2 diabetes and cardiovascular disease

Patients with insulin resistance and type 2 diabetes have an excessive risk of cardiovascular disease (CVD); this increased risk is not fully explained by traditional risk factors such as hypertension and dyslipidaemias. There is now compelling evidence to suggest that abnormalities of insulin-like growth factor-I (IGF-I) and one of its binding proteins, insulin-like growth factor-binding protein-1 (IGFBP-1), occur in insulin-resistant states and may be significant factors in the pathophysiology of CVD. We reviewed articles and relevant bibliographies following a systematic search of MEDLINE for English language articles between 1966 and the present, using an initial search strategy combining the MeSH terms: IGF, diabetes and CVD. Our aim was first to review the role of IGF-I in vascular homeostasis and to explore the mechanisms by which it may exert its effects. We also present an overview of the physiology of the IGF-binding proteins, and finally, we sought to summarize the evidence to date describing the changes in the insulin/IGF-I/IGFBP-1 axis that occur in type 2 diabetes and CVD; in particular, we have focused on the potential vasculoprotective effects of both IGF-I and IGFBP-1. We conclude that this system represents an interesting and novel therapeutic target in the prevention of CVD in type 2 diabetes.

Localization of increased insulin-like growth factor binding protein-3 in diabetic rat penis: implications for erectile dysfunction

OBJECTIVES

Diabetes-induced erectile dysfunction (ED) is assumed to result from neurovascular abnormalities. However, the entire picture of the molecular mechanisms underlying ED has not yet been clarified. To elucidate the possible elements involved in ED in diabetes mellitus, we performed broad-scale gene expression profiling using cDNA array in the penis of streptozotocin-induced diabetic rats.

METHODS

Northern blot analysis was performed to examine the course of the mRNA expression encoded by the identified gene. Immunohistochemistry was performed to identify the cellular localization of the encoded protein.

RESULTS

Of the genes investigated, the expression level of insulin-like growth factor binding protein 3 (IGFBP-3) was greatly increased at 12 weeks after streptozotocin treatment. The levels of ErbB3 epidermal growth factor receptor-related proto-oncogene, G1/S-specific cyclin D2, hepatic neutral cholesteryl ester hydrolase precursor, UDP-galactose ceramide galactosyltransferase, and serine protease RNK-Met-1 were markedly decreased. Increased levels of IGFBP-3 mRNA were demonstrated as early as 2 weeks after induction of hyperglycemia. Increased IGFBP-3 protein was localized to the epithelium of the urethra, penile endothelium, and smooth muscle in the corpus cavernosum. Significant depletion of the smooth muscle density relative to the connective tissue was first observed in the penis of the 8-week diabetic rats, and a significant reduction in the intracavernous pressure was demonstrated only at 12 weeks after the induction of hyperglycemia.

CONCLUSIONS

These results suggest that the increased expression of IGFBP-3 during hyperglycemia might play an important role in the development of ED.

Applications of LDL-apheresis in nephrology

LDL-apheresis (LA) was originally used for familial hyperlipidemia, and then in Japan extended to use for the treatment of patients with peripheral arterial disease (PAD) and nephrotic syndrome due to steroid-resistant focal glomerular sclerosis (FGS). The reason why this treatment is applicable for these disorders is due to the fact that LA exerts its favorable effects beyond the lipid-lowering effect. The main underlying mechanisms, for example, in the case of LA application in patients with PAD are: (1) improvement of hemorheology, (2) improvement of endothelial dysfunction, (3) elevations of serum levels of NO and bradykinin, (4) increase in serum levels of vascular endothelial growth factor, and (5) reduction of adhesion molecules on monocytes. Furthermore, we have reported that LA could have anti-inflammatory effects because LA reduces serum levels of P-selectin, which is known to play an important role in the development of atherosclerosis as well as a reduction of serum C-reactive protein levels as standard biomarker of atherosclerosis. Massive proteinuria is also an important challenge in nephrology. The possible mechanisms besides removal of toxic lipids are the reduction of the vasoconstrictive prostanoid and thromboxane A2 (TXA2) and an improvement in macrophage function evidenced by a significant amelioration of interleukin-8 production by lipopolysaccharide-stimulated peripheral blood mononuclear cells. It is intriguing to note that in terms of pharmacodynamics, LA improves steroid and cyclosporine uptake into lymphocytes. Although there are no randomized controlled trials, it is clear that LA has various effects beyond lowering lipids. Making the device more concise and changing it into a whole blood adsorption type, we need to collect more clinical cases and to study the underlying mechanisms further.

Acute and chronic effects of growth hormone on renal regulation of electrolyte and water homeostasis

For decades, growth hormone (GH) has been known to influence electrolyte and water handling in humans and animals. However, the molecular mechanisms underlying the GH-induced anti-natriuretic and anti-diuretic effects have remained elusive. This review will examine the existing literature on renal electrolyte and water handling following acute and chronic GH-exposure. Renal responses to GH differ in acute and chronic models. Acute application of GH results in a reduced urinary electrolyte and water excretion, whereas the chronic effects of GH are more diverse, as this state likely represents a complex mixture of primary and secondary actions of GH as well as compensatory mechanisms. During chronic GH-exposure an initial sodium retaining state often occurs, followed by a normalization of the urinary sodium excretion, although extracellular volume expansion still persists. We recently described a possible mechanism by which GH acutely increases renal electrolyte and water reabsorption, by modulation of the kidney specific Na(+), K(+), 2Cl(-) co-transporter (NKCC2). The primary aim of this review is to investigate how GH-induced regulation of NKCC2 may be involved in the complex renal changes previously described during acute and chronic GH. We propose, that the GH-induced increase in NKCC2 activity may explain the initial water and sodium retention seen in a number of studies. Moreover, renal changes seen during prolonged GH-exposure may now be seen on the background of the acute stimulation of NKCC2. Additionally, GH also promotes renal acidification, thus influencing renal acid/base handling. The GH-induced renal acidification is partly compatible with changes in NKCC2 activity. Finally, we review the available data on changes in hormonal systems affecting tubular transport during acute and chronic GH-exposure.

Coronary flow reserve is impaired in patients with adult growth hormone (GH) deficiency

OBJECTIVE

Relationship between adult growth hormone deficiency (AGHD) and increased cardiovascular disease risk is very well known in hypopituitary patients treated with conventional hormone replacement therapy other than growth hormone (GH) administration. Endothelial dysfunction, an early and reversible event in pathogenesis of atherosclerosis, is associated with increased vascular smooth muscle tone, arterial stiffening and intima-media thickness (IMT). Coronary flow reserve (CFR) measurement by transthoracic Doppler echocardiography (TTDE) reflects coronary microvascular and endothelial functions, as a cheaper and an easy screening test. We have used TTDE to evaluate endothelial function and coronary microvascular function in AGHD.

DESIGN

Cross-sectional observational study.

PATIENTS

A total of 10 GH-deficient adults on conventional replacement therapy other than GH (4 males, 6 females; mean age 37 +/- 11 years) and 15 healthy subjects (7 males, 8 females; mean age 41 +/- 11 years) were studied. Patients and controls were all nonsmokers, normotensive and nondiabetic.

MEASUREMENTS

IGF-1, free T4, lipid profile, insulin, glucose, insulin resistance (IR), anthropometrical and physical parameters were recorded. CFR recordings and IMT measurements were performed using the Vivid 7 echocardiography device.

RESULTS

IMT were significantly higher in patients than controls (0.70 + 0.19 mm and 0.53 + 0.13 mm, respectively; P = 0.02). CFR was significantly lower in patients than in controls (1.96 +/- 0.35 and 2.62 +/- 0.45, respectively; P < 0.001). CFR was positively correlated with IGF-1 levels (r = 0.54, P = 0.005).

CONCLUSION

CFR is significantly lower in adults with GH deficiency than in controls. Direct correlation between CFR and IGF-1 concentrations suggests GH replacement could improve microvascular function and thereby could decrease cardiovascular morbidity and mortality in AGHD.

Hormone replacement therapy and vascular risk disorders in adult hypopituitarism

Adult patients with hypopituitarism are treated by the replacement of deficient hormones, although GH has not been substituted until March 2006 in Japan except for clinical trial. This study examines which hormonal status influences the prevalence of vascular risk disorders in hypopituitary adults. A sample of 263 adult patients with hypopituitarism was studied, among whom there were various hormonal status such as no deficiency, treated or untreated deficiency of each pituitary hormone. Analysis of adult patients with hypopituitarism showed that hypertension was more prevalent in the older than in younger patients and in male than in female patients. Hypercholesterolemia and hypertriglyceridemia were more prevalent in patients with TSH deficiency even with thyroxine substitution than those without TSH deficiency. Both obesity and hypertension were less prevalent in patients with treated ACTH deficiency than those without ACTH deficiency. Obesity was more prevalent in patients with treated vasopressin deficiency than those without vasopressin deficiency. These results provide evidence that glucocorticoid substitution in ACTH deficient adults was favorable to prevent obesity and hypertension but that the thyroxine substitution in TSH deficient adults appeared rather insufficient to prevent hyperlipidemia.

Effects of dynamic exercise on circulating IGF-1 and IGFBP-3 levels in patients with rheumatoid arthritis or ankylosing spondylitis

This study was performed to determine the effects of short-term dynamic exercise on serum insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding protein-3 (IGFBP-3) levels in the patients with rheumatoid arthritis (RA) and ankylosing spondylitis (AS). Patients with RA or AS and healthy controls were recruited. Dynamic treadmill exercise therapy was accomplished for 20 min/session with all of the participants. There were five sessions per week for 2 weeks. Morning stiffness duration, body pain, Stanford health assessment questionnaire, Ritchie articular index, Bath ankylosing spondylitis disease activity index (BASDAI), and Bath ankylosing spondylitis functional index (BASFI) were evaluated in the RA and AS patients. Laboratory assessments included: erythrocyte sedimentation rate, serum C-reactive protein, IGF-1, and IGFBP-3. Clinical and laboratory assessments were recorded at baseline and during exercise treatment on days 7 and 15. Twenty patients with RA, 15 with AS, and 14 healthy controls were included in this study. The pain evaluation, Ritchie, BASDAI, and BASFI scores were significantly improved by the exercise treatment in both patient groups. The important increases were found in circulating IGF-1 in RA (p < 0.001) and AS (p = 0.001) at the end of 2 weeks. In control individuals, serum IGF-1 levels showed a significant decline in the first week (p < 0.05). No significant changes were observed on serum IGFBP-3 levels. Our data suggest that serum IGF-1 levels are increased by the dynamic exercise program in RA and AS patients. The increased IGF-1 may play an important role in the beneficial effects of dynamic exercise therapy in these patients.

Evidence against the involvement of nitric oxide in the modulation of telomerase activity or replicative capacity of human endothelial cells

Telomerase, a reverse transcriptase involved in the maintenance of telomere function and cellular replicative capacity, is thought to be regulated by nitric oxide (NO). Here, we have used pharmacological tools and RNA interference to re-assess the role of NO in the regulation of telomerase and senescence of human umbilical vein endothelial cells. Acute or chronic treatment of these cells with the NO donors diethylenetriamine/NO (DETA-NO) or S-nitroso-N-acetylpenicillamine (SNAP) at concentrations which generated NO in the 1-300 nM range did not modulate telomerase activity. Similarly these agents did not affect cellular replicative capacity during long-term sub-cultivation. The NO synthase (NOS) inhibitor N(G)-monomethyl-L-arginine (1 mM) reduced basal levels of c-GMP by 50% but had no effect on telomerase activity or replicative capacity. Withdrawal of ascorbic acid increased the intracellular pro-oxidant capacity, reduced telomerase activity and increased the accumulation of senescent cells upon serial passage in culture. However, this shift to a more oxidative redox state did not unmask the putative capacity of NO to modulate telomerase or senescence. Infection of cells with a lentiviral vector expressing a small hairpin RNA targeted against endothelial NOS inhibited endogenous NO production completely but failed to affect the decrease of telomerase activity or the accumulation of senescent cells observed with passage in culture. Our findings suggest that physiological concentrations of NO do not modulate telomerase levels or replicative capacity of endothelial cells, regardless of their cellular oxidative status.

Insulin and IGF-I action on insulin receptors, IGF-I receptors, and hybrid insulin/IGF-I receptors in vascular smooth muscle cells

Insulin and insulin-like growth factor I (IGF-I) are known to affect cardiovascular disease. We have investigated ligand binding and the dose-response relationship for insulin and IGF-I on vascular smooth muscle cells (VSMCs) at the receptor level. VSMCs from rat thoracic aorta were serum starved, stimulated with IGF-I or insulin, lysed, immunoprecipitated, and analyzed by Western blot. d-[U-(14)C]Glucose accumulation and [6-(3)H]thymidine incorporation into DNA were also measured. Specific binding of both insulin and IGF-I was demonstrated, being higher for IGF-I. Both IGF-I receptor (IGF-IR) and insulin receptor (IR) beta-subunits were detected and coprecipitated after immunoprecipitation (IP) against either of the two. No coprecipitation was found after reduction of disulphide bonds with dithiotreitol before IP. After stimulation with 10(-10)-10(-9) M IGF-I, IP of the IGF-IR, or IR beta-subunit and immunoblot with anti-phosphotyrosine antibody, we found two distinct bands indicating phosphorylation of both the IGF-IR and the IR beta-subunit. Stimulation with 10(-10)-10(-9) M insulin and IP against the IGF-IR did not show phosphorylation of either beta-subunit, whereas after IP of the IR we found phosphorylation of the IR beta-subunit. [(14)C]Glucose accumulation and [(3)H]thymidine incorporation were elevated in cells stimulated with IGF-I at 10(-10)-10(-7) M, reaching maximum by 10(-9) M. Insulin stimulation showed measurable effects only at supraphysiological concentrations, 10(-8)-10(-7) M. In conclusion, coprecipitation of both the IGF-IR and the IR beta-subunit indicates the presence of hybrid insulin/IGF-I receptors in VSMC. At a physiological concentration, insulin activates the IR but does not affect either glucose metabolism or DNA synthesis, whereas IGF-I both activates the receptor and elicits biological effect.

Enhancement of cell attachment and tissue integration by a IKVAV containing multi-domain peptide

Laminin contains a number of cell binding motifs including IKVAV and some that bind heparin. We developed a multi-domain synthetic peptide, LA2, which combines IKVAV sequences with a heparin-binding domain with the goal of improving cell attachment to otherwise non-adherent substrates. LA2 was used to coat polystyrene, ethyl vinyl acetate (EVA), expanded polytetrafluoroethylene (ePTFE), polycarbonate, titanium and stainless steel. In cell attachment studies, LA2 dramatically increased cell attachment to polystyrene and EVA compared to uncoated counterparts or those coated with SIKVAV. Similar increases were observed on ePTFE and titanium. On polystyrene, LA2 enhanced the attachment of endothelial cells, smooth muscle cells, epithelial cells, myoblasts, and osteoblast progenitor cells. Following adhesion, the cells underwent proliferation to form confluent monolayers with phenotypic morphologies. Using osteoblast progenitor cells (MC3T3 cells) grown on LA2/polystyrene, the cells exhibited an increased production of a differentiation marker, alkaline phosphatase. In vivo, LA2 improved tissue integration into ePTFE when implanted subcutaneously in rats. After 2 weeks, cells had penetrated deep into the LA2 coated ePTFE implant whereas little cell penetration was found in uncoated grafts. The implant sites exhibited little inflammation or other untoward effects. The results indicated that the LA2 peptide improved cell adhesion and tissue integration and might be useful in a number of tissue engineering applications.

Beginning to end: cardiovascular implications of growth hormone (GH) deficiency and GH therapy

Both growth hormone (GH) and insulin-like growth factor I (IGF-I) are involved in heart development and in maintenance of cardiac structure and performance. Cardiovascular disease has been reported to reduce life expectancy in both GH deficiency (GHD) and GH excess. Patients with GHD suffer from a cluster of abnormalities associated with increased cardiovascular risk, including abnormal body composition, unfavorable lipid profile, increased fibrinogen and C-reactive protein levels, insulin resistance, early atherosclerosis and endothelial dysfunction, and impaired left ventricular (LV) performance (i.e., reduced diastolic filling and impaired response to peak exercise). Long-term GH replacement therapy reverses most of these abnormalities. More consistently, GH replacement reduces body fat and visceral adipose tissue, reduces low-density lipoprotein cholesterol and triglyceride levels, and improves endothelial function. GH replacement also reduces intima media thickness at major arteries and improves LV performance, but these results have been observed only in small series of patients treated on a short-term basis. This review discusses the roles of GHD and GH replacement therapy in the development of cardiovascular disease.

Bi-phasic activation of eNOS in response to uni-axial cyclic stretch is mediated by differential mechanisms in BAECs

We investigated the signaling mechanism of stretch-induced NO (Nitric oxide) production in bovine arterial endothelial cells (BAECs). BAECs cultured on an elastic silicone chamber coated with fibronectin were subjected to uni-axial cyclic stretch (1 Hz, 20% in length) and the amount of produced NO was measured by a cGMP assay. NO production increased in a bi-phasic manner and peaked at 5 min and 20 min after stretch onset. Correspondingly, the activities of endothelial nitric oxide synthase (eNOS) and Akt/PKB (measured by phosphorylation at serine 1,177 and serine 473, respectively), showed two peaks over time. Application of Gd(3+), a potent SA channel blocker, and depletion of external Ca(2+) exclusively inhibited the first peaks of eNOS and Akt activity, but exerted little effect on the second peak. On the other hand, the PI3K inhibitors, Wortmannin, LY294002, almost completely inhibited the second peak but not the first. These results suggest that up-regulation of eNOS in response to cyclic stretch was mediated by two distinct pathways, [Ca(2+)](i) increases via the SA channel in an early phase (partially Akt/PKB), and PI3K-Akt/PKB pathways in a late phase.

Insulin at physiological concentrations selectively activates insulin but not insulin-like growth factor I (IGF-I) or insulin/IGF-I hybrid receptors in endothelial cells

In muscle, physiologic hyperinsulinemia, presumably acting on endothelial cells (ECs), dilates arterioles and regulates both total blood flow and capillary recruitment, which in turn influences glucose disposal. In cultured ECs, however, supraphysiological (e.g. >or=10 nM) insulin concentrations are typically used to study insulin receptor (IR) signaling pathways and nitric oxide generation. IGF-I receptors (IGF-IRs) are more abundant than IR in ECs, and they also respond to high concentrations of insulin. To address whether IR mediates responses to physiologic insulin stimuli, we examined the insulin concentration dependence of IR and IGF-IR-mediated insulin signaling in bovine aortic ECs (bAECs). We also assessed whether insulin/IGF-I hybrid receptors were present in bAECs. Insulin, at 100-500 pM, significantly stimulated the phosphorylation of IRbeta, Akt1, endothelial isoform of nitric oxide synthase, and ERK 1/2 but not the IGF-IRbeta subunit. At concentrations 1-5 nm or greater, insulin dose-dependently enhanced the tyrosine phosphorylation of IGF-IRbeta, and this was inhibited by IGF-IR neutralizing antibody. In addition, immunoprecipitation of IRbeta pulled down the IGF-IRbeta, and the IRbeta immunocytochemically colocalized with IGF-IRbeta, suggesting that ECs have insulin/IGF-I hybrid receptors. We conclude that: 1) insulin at physiological concentrations selectively activates IR signaling in bAECs; 2) bAECs express IGF-IR and insulin/IGF-I hybrid receptors in addition to IR; 3) high concentrations of insulin (>or=1-5 nM) activate IGF-IR and hybrid receptors as well as IR; and 4) this crossover activation can confound interpretation of studies of insulin action in ECs when high insulin concentrations are used.

Alterations in the oxidant-antioxidant status in prepubertal children with growth hormone deficiency: effect of growth hormone replacement therapy

OBJECTIVE

Growth hormone deficiency (GHD) in adults is associated with increased oxidative stress determined by the underlying GH-IGF-1 axis alterations. Despite GHD being a common diagnosis in children with short stature, no data on the oxidant/antioxidant status are available in this age group. This study was designed to detect differences in oxidative stress parameters between prepubertal GH-deficient children and healthy controls. Furthermore, the effect of 12 months of conventional GH replacement (rGH) on oxidant-antioxidant status was evaluated in the GHD group only.

PATIENTS

Ten (nine males and one female) prepubertal children (mean age 9.1 +/- 1.3 years) with GHD were recruited and matched for sex and age (9.2 +/- 1.9 years) with 20 healthy controls (18 males and two females).

MEASUREMENTS

At study entry, lag phase, an index of susceptibility of low density lipoprotein (LDL) to in vitro oxidation, malondialdehyde (MDA) and vitamin E were measured in all subjects. These parameters were also evaluated in GH-deficient children after 12 months of rGH treatment.

RESULTS

The lag phase was significantly decreased in GH-deficient children compared to healthy controls (15.50 +/- 7.4 vs. 43.00 +/- 9.2 min; P = 0.0007), while MDA was significantly increased (1.33 +/- 0.38 vs. 0.46 +/- 0.10 nmol/mg; P = 0.0006). Vitamin E levels were significantly decreased (22.44 +/- 9.57 vs. 35.38 +/- 16.49 micromol/l; P = 0.001). IGF-1 and IGFBP-3 correlated directly to lag phase (r = 0.48; P = 0.01; r = 0.63, P = 0.002, respectively) and to vitamin E (r = 0.59, P = 0.003; r = 0.58, P = 0.006, respectively). By contrast, IGF-1 and IGFBP-3 correlated indirectly to MDA (r = -0.47, P = 0.01; r =-0.65, P = 0.002, respectively). After 1 year of rGH therapy, lag phase (39.32 +/- 15.24 min; P = 0.005) and vitamin E (34.9 +/- 7.7 micromol/l; P = 0.005) increased significantly, while MDA decreased significantly (0.71 +/- 0.42 nmol/mg; P = 0.005), reaching normal levels.

CONCLUSIONS

These data show that children with GHD have substantially increased oxidative stress parameters compared to healthy controls and demonstrate a normalization of these parameters after 1 year of rGH therapy.

Lack of iNOS induction in a severe model of transient focal cerebral ischemia in rats

Calcium-independent nitric oxide synthase (NOS) activity has been reported in ischemic brains and usually attributed to the inducible isoform, iNOS. Because calcium-independent mechanisms have recently been shown to regulate the constitutive calcium-dependent NOS, we proposed to confirm the presence of iNOS activity in our model of transient focal cerebral ischemia in rats. Our initial results showed that, in our model, ischemia induced an important increase in brain calcium concentration. Consequently, the determination of calcium-independent NOS activity required a higher concentration of calcium chelator than classically used in the NOS assay. In these conditions, calcium-independent NOS activity was not observed after ischemia. Moreover, our ischemia was associated with neither iNOS protein expression, measured by Western blotting, nor increased NO production, evaluated by its metabolites (nitrate/nitrite). Our results demonstrate that iNOS activity may be overestimated due to increased brain calcium concentration in ischemic conditions and also that iNOS is not systematically induced after cerebral ischemia.

Influence of growth hormone on cardiovascular health and disease

Experimental and clinical studies indicate that growth hormone (GH) and insulin-like growth factor-1 (IGF-1) are involved in heart development. Impaired cardiovascular function, as recently demonstrated, could potentially reduce life expectancy both in GH deficiency (GHD) and excess. Patients with childhood- or adult-onset GHD may have both cardiac structural and functional abnormalities, i.e. reduced cardiac mass, reduced diastolic filling, and impaired left ventricular response to peak exercise. In addition, GHD patients may present with an increase in vascular intima-media thickness and a higher occurrence of atheromatous plaques that can further aggravate the hemodynamic conditions and contribute to the increased cardiovascular and cerebrovascular risk. However, some evidence has been provided to show that cardiovascular abnormalities can be partially reversed after somatropin (recombinant GH) therapy in patients with GHD. Recently, somatropin administration was shown to induce improvement in hemodynamics and clinical status in some patients with heart failure. Although these data need to be confirmed in more extensive studies, such promising results open new perspectives for somatropin therapy. The role of GH secretagogues in heart failure is still unknown.

Endothelial function, carotid artery intima-media thickness, epicardial adipose tissue, and left ventricular mass and function in growth hormone-deficient adolescents: apparent effects of growth hormone treatment on these parameters

OBJECTIVE

The purpose of this study was to determine whether GH-deficient (GHD) adolescents have abnormalities of cardiac and vascular function detectable during the teenage years.

DESIGN/METHODS

Ten GHD children on GH treatment with a chronological age (CA) of 14.6 +/- 1.7 yr and 12 untreated GHD adolescents with a CA of 15.0 +/- 3.0 yr were studied. Cardiac mass and function, carotid artery intima-media thickness, flow-mediated endothelium-dependent vasodilation (percent change from baseline diameter during hyperemia), and hyperemia-induced blood flow increase of the brachial artery (percent change from baseline) and epicardial adipose tissue were evaluated by echocardiography. Fourteen healthy adolescents served as controls.

RESULTS

Untreated GHD adolescents present with a reduced left ventricular mass when compared with controls (P < 0.05) and a lower flow-mediated endothelium-dependent increase in the diameter of the brachial artery during hyperemia than both controls and treated GHD subjects (P < 0.02), whereas their epicardial adipose tissue is significantly higher than that of healthy controls (P < 0.02). Interventricular septum thickness, posterior wall thickness, left ventricular ejection fraction, and carotid artery intima-media thickness were similar in all three groups. Hyperemia-induced blood flow increase was greater in treated GHD adolescents than both untreated subjects and controls (P < 0.001). Body mass index correlated positively with epicardial adipose tissue in all three groups and with carotid intima-media thickness in treated and untreated GHD adolescents.

CONCLUSIONS

GHD adolescents have a reduced left ventricular mass and vascular abnormalities manifested by lower flow-mediated endothelium-dependent vasodilation. These findings together with an increase in epicardial adipose tissue, a good indicator of abdominal/visceral fat, may contribute to an increased cardiovascular risk in the long term. An improvement in endothelial function and a reduction in arterial stiffness appear to occur after GH replacement.

A physiogenomic approach to study the regulation of blood pressure

Several vasoregulatory systems including the renin-angiotensin system, sympathetic vasoregulation, and cytokine release have been studied extensively. The aim of the present study was to establish a physiogenomic screening model for differentially expressed genes in the regulation of blood pressure that might give a hint as to new vasoregulatory mechanisms. We induced acute hypotension in normotensive rats, assuming that vasoregulatory systems will counteract hypotension. Microarray transcriptome analysis was performed from kidneys 6 h after the induction of acute hypotension. The results were confirmed by real-time PCR. Six functionally known genes (Igfbp1, Xdh, Sult1a1, Mawbp, Por, and Gstm1) and two expressed sequence tages (BI277460 and AI411345) were significantly upregulated. Four of these genes (Igfbp1, Xdh, Por, and Gstm1) have well-characterized functions in the cardiovascular system. The proteins corresponding to Xdh, Por, and Gstm1 are involved in the metabolism of reactive oxygen species (ROS). Because ROS can mediate endothelial dysfunction, we measured the aortic dilatory capacity in thoracic aortic rings. Indeed, vasodilator potency to acetylcholine was largely diminished in hypotensive animals, whereas sodium nitroprusside induced equivalent vasodilations in normotensive and hypotensive animals. The vasodilator potency of the endothelium was partially restored by the superoxide scavenger tiron. Hence, acute hypotension induces a diminished vasodilator potency of the endothelium due to an accelerated degradation of nitric oxide by ROS. The present physiogenomic approach is capable of detecting vasoregulatory mechanisms and may provide deeper insight into the genetics and physiology of blood pressure regulation.

Insulin-like growth factors and coronary heart disease

Insulin-like growth factor-1 (IGF-I), the primary mediator of growth hormone (GH) effects, is an important regulator of cell growth, differentiation, and apoptosis. GH and IGF-I deficiency is known to be associated with premature atherosclerosis and elevated cardiovascular disease mortality. Recent evidence suggests that cardiovascular disease risk may also be elevated among apparently healthy individuals who have serum IGF-I levels in the low-normal range. In this review, we appraise the epidemiologic and clinical studies implicating low IGF-I level as a risk factor for incident myocardial infarction and other manifestations of coronary heart disease. Potential mechanisms that may underlie this association include beneficial effects of IGF-I on myocyte survival after ischemia, stability of atherosclerotic lesions, and endothelial function. We conclude that additional confirmatory data from prospective studies are needed to confirm low IGF-I level as an independent cardiovascular risk factor. However, if this finding is confirmed, this would support the rationale for intervention trials aimed at reducing cardiovascular disease morbidity and mortality among older adults by targeting the GH/IGF-I pathway.

Long-Term Monitoring of Insulin-Like Growth Factor I in Adult Growth Hormone Deficiency: A Critical Appraisal

Serum insulin-like growth factor I (IGF-I) levels predominantly reflect the hepatic effect of growth hormone (GH). Compared with serum GH levels, which reflect pulsatile GH secretion, serum IGF-I levels exhibit no major diurnal variation and thus provide a better estimate of integrated GH secretion in an individual patient. Measurement of serum IGF-I levels allows reliable identification of states of GH excess. In contrast, in a large proportion of adults with severe GH deficiency, serum IGF-I levels are within the normal range. Serum IGF-I levels increase markedly in response to GH administration and are often used as a surrogate variable for overall responsiveness to such treatment. Current data, however, suggest a poor relationship between changes in or levels of IGF-I and efficacy variables such as body composition, muscle function and well-being. The use of serum IGF-I as a guide during dose titration in the initial phase of treatment and during long-term monitoring of GH replacement therapy in adults, and its use as a safety marker or predictor of future morbidity and mortality are discussed here.

Calibration of NO sensors for in-vivo voltammetry: laboratory synthesis of NO and the use of UV?visible spectroscopy for determining stock concentrations

The increasing scientific interest in nitric oxide (NO) necessitates the development of novel and simple methods of synthesising NO on a laboratory scale. In this study we have refined and developed a method of NO synthesis, using the neutral Griess reagent, which is inexpensive, simple to perform, and provides a reliable method of generating NO gas for in-vivo sensor calibration. The concentration of the generated NO stock solution was determined using UV-visible spectroscopy to be 0.28+/-0.01 mmol L(-1). The level of NO(2) (-) contaminant, also determined using spectroscopy, was found to be 0.67+/-0.21 mmol L(-1). However, this is not sufficient to cause any considerable increase in oxidation current when the NO stock solution is used for electrochemical sensor calibration over physiologically relevant concentrations; the NO sensitivity of bare Pt-disk electrodes operating at +900 mV (vs. SCE) was 1.08 nA micromol(-1) L, while that for NO(2) (-) was 5.9 x 10(-3) nA micromol(-1) L. The stability of the NO stock solution was also monitored for up to 2 h after synthesis and 30 min was found to be the time limit within which calibrations should be performed.