The worrisome liaison between left ventricular systolic dysfunction and mitral annulus calcification in type 2 diabetes without coronary artery disease: data from the SHORTWAVE study

BACKGROUND AND AIM

Mitral annulus calcification (MAC) is a marker for coronary artery disease (CAD) and predicts poor outcome in the general population. No data are available on MAC in patients with type 2 diabetes. In these patients we assessed prevalence of MAC and the relation between MAC and left ventricular (LV) systolic function.

METHODS AND RESULTS

As many as 386 patients with type 2 diabetes without CAD were studied with Doppler echocardiography. LV systolic dysfunction was defined by analyzing 120 healthy subjects. Stress-corrected midwall shortening (sc-MS) and mitral annular peak systolic velocity (peak S') were considered as indexes of LV circumferential and longitudinal shortening and classified low if <89% and <8.5 cm/s, respectively (10th percentiles of controls). Patients who had MAC (107 = 28%) were older with longer duration of DM and were receiving more anti-hypertension medications than those who had not. At echocardiographic evaluation patients with MAC showed higher LV mass, larger left atrial volume (LAV), reduced sc-MS (88.4 ± 14.9 vs 92.6 ± 14.3%; p = 0.01) and peak S' (8.9 ± 2.2 vs 10.0 ± 2.0 cm/s; p < 0.001) than patients without MAC. Multiple logistic regression demonstrated older age (OR 1.03 [IC 1.01-1.06], p = 0.009), larger LAV (OR 1.19 [IC 1.11-1.28], p < 0.001) and combined reduction in sc-MS and peak S' (OR 3.00 [IC 1.57-5.72], p = 0.001) as independent factors associated with MAC.

CONCLUSIONS

MAC is detectable in one fourth of patients with type 2 diabetes without CAD and is mostly related to LV systolic dysfunction expressed as combined impairment of LV circumferential and longitudinal fibers, independent of age and LAV.

How can we monitor glycaemic variability in the clinical setting?

No universal consensus exists on how to express glycaemic variability. Among other parameters, standard deviation of blood glucose values, mean amplitude of glycaemic excursions (MAGE), the Low Blood Glucose Index (LBGI) and the High Blood Glucose Index (HBGI), which were subsequently combined into the Average Daily Risk Range (ADRR), mean of daily differences (MODD) and glycaemic variability index (GVI) are highlighted. The continuous glucose monitoring in research and clinical settings has been a great help for a comprehensive approach to circadian blood glucose evaluation and identification of individual patterns, mainly in type 1 diabetes, but recently also in type 2 diabetes. In everyday clinical practice the judicious use of self-monitoring of blood glucose in an educational setting involving the patient and the care team is an unreplaceable tool to effectively and safely guide behavioural and drug therapy.

Which patients should be evaluated for blood glucose variability?

Diabetes is characterized by glycaemic disorders that include both sustained chronic hyperglycaemia and acute fluctuations (i.e. glycaemic variability). Increasing attention is being paid to the role of glycaemic variability as a relevant determinant for diabetes control and prevention of its vascular complications. As a consequence, it is strongly suggested that a global antidiabetic strategy should be aimed at reducing to a minimum the different components of glycaemic control (i.e. HbA1c, fasting and postprandial glucose, as well as glycaemic variability). Subjects at risk of hypoglycaemia, subjects with postprandial hyperglycaemia and patients who need to adjust or start insulin seem to be the categories that require glycaemic variability monitoring. The analysis of blood glucose variability represents an additional tool in the global assessment of glycaemic control and can serve as a guide to the clinician in the management of therapy and for the patients both in the prevention of acute complications, in particular hypoglycaemia, and chronic disease, in particular macrovascular complications.

Management of hyperglycemia in type 2 diabetes: evidence and uncertainty

The panoply of treatment algorithms, periodically released to improve guidance, is one mean to face therapeutic uncertainty in pharmacological management of hyperglycemia in type 2 diabetes, especially after metformin failure. Failure of recent guidelines to give advice on the use of specific antidiabetic drugs in patients with co-morbidity may generate further uncertainty, given the frequent association of type 2 diabetes with common comorbidity, including, although not limited to obesity, cardiovascular disease, impaired renal function, and frailty. The Italian Association of Diabetologists (Associazione Medici Diabetologi, AMD) recognized the need to develop personalized treatment plans for people with type 2 diabetes, taking into account the patients' individual profile (phenotype), with the objective of the safest possible glycemic control. As not every subject with type 2 diabetes benefits from intensive glycemic control, flexible regimens of treatment with diabetes drugs (including insulin) are needed for reaching individualized glycemic goals. Whether personalized diabetology will improve the quality healthcare practice of diabetes management is unknown, but specific research has been launched.

Combined circumferential and longitudinal left ventricular systolic dysfunction in patients with type 2 diabetes mellitus without myocardial ischemia

BACKGROUND/OBJECTIVE

Left ventricular (LV) circumferential or longitudinal shortening may be impaired in patients with type 2 diabetes mellitus (DM). In the present study, patients with type 2 DM without myocardial ischemia and combined impairment of circumferential and longitudinal (C+L) shortening were studied to assess the prevalence and factors associated with this condition.

METHODS

Data from 386 patients with type 2 DM enrolled in the SHORTening of midWall and longitudinAl left Ventricular fibers in diabEtes study were analyzed. One hundred twenty healthy subjects were used to define C+L dysfunction. Stress-corrected midwall shortening and mitral annular peak systolic velocity were considered as indexes of C+L shortening and classified as low if <89% and <8.5 cm/s, respectively (10th percentiles of controls).

RESULTS

Combined C+L dysfunction was detected in 66 patients (17%). The variables associated with this condition were lower glomerular filtration rate (OR 0.98 [95% CI 0.96 to 0.99], greater LV mass (OR 1.05 [95% CI 1.02 to 1.08]), high pulmonary artery wedge pressure (OR 1.23 [95% CI 1.04 to 1.44]) and mitral annular calcifications (OR 3.35 [95% CI 1.71 to 6.55]). Considering the entire population, the relationship between stress-corrected midwall shortening and peak systolic velocity was poor (r=0.20), and the model was linear. The relationship was considerably closer and nonlinear in patients with combined C+L dysfunction (r=0.61; P<0.001), having the best fit by cubic function.

CONCLUSIONS

Combined C+L dysfunction was present in one-sixth of patients with type 2 DM without myocardial ischemia. This condition was associated with reduced renal function, worse hemodynamic status and structural LV abnormalities, and may be considered a preclinical risk factor for heart failure.

[Risk factors for heart failure in women: diabetes]

Diabetes mellitus has become increasingly prevalent in recent years, the most dramatic increase being observed in younger women. Diabetes is a multiplier of cardiovascular risk and decreases life expectancy more in women than in men. Diabetic women are less likely to achieve therapeutic targets for cardiovascular risk factors and to be optimally treated. They present more often with atypical symptoms that cause delays in timely recognition and management of cardiovascular disease. Diabetes is an independent risk factor for heart failure and is associated with a worse outcome in women than in men affected by heart failure. Despite the high prevalence of early asymptomatic ventricular dysfunction in diabetics observed in the DYDA and SHORTWAVE studies, female gender was neither a protective nor predisposing factor to ventricular dysfunction or heart failure. Among 1129 outpatients with heart failure, data from the Cardiovascular Epidemiologic Observatory of Trieste show a prevalence of diabetes of 39% in men and 28% in women. In this ongoing epidemiological study, a significantly better prognosis was observed in female than in male diabetics, whereas diabetic and non-diabetic women showed comparable mortality and hospital admission rates. These findings underscore the impact and effectiveness of strict follow-up and management in the high-risk female diabetic population.

Osteoprotegerin induces morphological and functional alterations in mouse pancreatic islets

Although serum osteoprotegerin (OPG) is significantly increased in diabetic subjects, its potential role in beta cell dysfunction has not been investigated. This study aimed to assess the effect of full-length OPG administered in vivo in mice on pancreatic islet structure and function and its interaction with the renin-angiotensin system (RAS). OPG-treated mice showed increased islet monocyte/macrophage infiltration, fibrosis and apoptosis with reduction of islet function. The remodeling of islet architecture was associated with increased pancreatic expression of components of the RAS, growth factor genes (transforming growth factor β and connective tissue growth factor) and inflammatory molecules (monocyte chemotactic protein-1 and vascular adhesion molecule type 1). Prevention of these changes with improvement of insulin secretion was observed in ramipril treated animals. Our data suggest that OPG might play an important role in promoting beta cell dysfunction and that the upregulation of the local RAS represents one possible mechanism responsible for the OPG-induced beta cell dysfunction.

Human full-length osteoprotegerin induces the proliferation of rodent vascular smooth muscle cells both in vitro and in vivo

BACKGROUND/AIMS

Since elevated plasma levels of osteoprotegerin (OPG) represent a risk factor for death and heart failure in patients affected by diabetes mellitus and coronary artery disease, this study aimed to elucidate potential roles of OPG in the pathogenesis of atherosclerosis.

METHODS AND RESULTS

Recombinant human full-length OPG, used at concentrations comparable to the elevated levels found in the serum of diabetic patients, significantly increased the proliferation rate of rodent vascular smooth muscle cells (VSMC). To mimic the moderate chronic elevation of OPG observed in diabetic patients, low doses (1 microg/mouse) of full-length human OPG were injected intraperitoneally every 3 weeks in diabetic apolipoprotein E (apoE)-null mice. The group of animals treated for 12 weeks with recombinant OPG showed a small increase in the total aortic plaque area at necropsy in comparison to vehicle-treated animals. Importantly, while no differences in the amount of interstitial collagen or the degree of macrophage infiltration were observed between OPG-treated and vehicle-treated apoE-null diabetic animals, a significant increase in the number of alpha-actin-positive smooth muscle cells was observed in the plaques of OPG-treated mice.

CONCLUSIONS

Our data suggest that OPG promotes VSMC proliferation and might be directly involved in pathogenetic aspects of atherosclerosis.

Linking diabetes and atherosclerosis

Cardiovascular diseases are the major causes of morbidity and mortality in people with diabetes. Macroangiopathy in diabetes is manifested by more accelerated and progressive atherosclerosis, which is more widely distributed. The pathogenesis of this accelerated atherosclerosis is multifactorial and includes very complex interactions. Several abnormalities - such as hyperglycemia, dyslipidemia, hypertension, endothelial dysfunction, renin-angiotensin system activation and chronic subclinical inflammation - all appear to play important roles in the development of diabetes-induced atherosclerosis. Treatment of the residual risk, other than glycemia, blood pressure and low-density lipoprotein cholesterol, remains important as the rate of diabetes increases worldwide. A synergistic multifactorial approach against both conventional cardiovascular risk factors and emerging risk factors, such as vasoactive systems, the AGE-RAGE axis, novel proteins, such as TRAIL, and the complement system, as well as oxidative stress and inflammation, may be a promising way to prevent macrovascular disease in diabetes. In this review we focus on the major causes and mechanisms of atherosclerotic disease in patients with diabetes and highlight emerging targets for therapeutic intervention.

Dose and time-dependent apoptotic effects by angiotensin II infusion on left ventricular cardiomyocytes

OBJECTIVE

To gain insight into the regulation of cardiac apoptosis we studied the dose-response and time-course effects of angiotensin II (Ang II) infusion on ventricular cardiomyocyte apoptosis and on the expression of Bax and Bcl-2 genes and proteins.

STUDY DESIGN AND METHODS

In the dose-response study, Ang II was infused subcutaneously at doses of 100, 200, 400, 800 and 1200 ng/kg per min for 14 days. In the time-course study, rats infused with Ang II at doses of 200 and 400 ng/kg per min were followed for 7 and 14 days. The cardiomyocyte apoptotic density was assessed by DNA end labelling (terminal deoxynucleotide nick-end labelling; TUNEL). Gene and protein expression of Bcl-2 and Bax were evaluated by reverse transcriptase-polymerase chain reaction and by Western blots.

RESULTS

Systolic blood pressure and left ventricular mass were increased in a dose-dependent manner in Ang II-infused rats. A statistically significant increase in the rate of cardiac apoptosis and pro-apoptotic changes of Bcl-2 and Bax gene and protein expression was observed when high doses of Ang II (800-1200 ng/kg per min) were infused. A positive correlation of apoptotic density with Bax and a negative correlation with Bcl-2 and Bcl-2/Bax ratio were found. Cardiac apoptosis was greatly influenced by the timing of Ang II infusion. Losartan-treated Ang II-infused rats exhibited normalized systolic blood pressure, left ventricular weight, apoptosis, and Bax and Bcl-2 levels.

CONCLUSIONS

Our results are consistent with the pathophysiological role of Ang II in induction of cardiac apoptosis, and explain the cardioprotective effect of Ang II receptor antagonists.

An increased osteoprotegerin serum release characterizes the early onset of diabetes mellitus and may contribute to endothelial cell dysfunction

Serum osteoprotegerin (OPG) is significantly increased in diabetic patients, prompting expanded investigation of the correlation between OPG production/release and glycemic levels. Serum levels of OPG, but not of its cognate ligand receptor activator of nuclear factor-kappaB ligand (RANKL), were significantly increased in type 2 diabetes mellitus patients compared with healthy blood donors. Serum OPG was also significantly elevated in a subgroup of recently diagnosed diabetic patients (within 2 years). The relationship between serum OPG and diabetes mellitus onset was next investigated in apoE-null and littermate mice. Serum OPG increased early after diabetes induction in both mouse strains and showed a positive correlation with blood glucose levels and an inverse correlation with the levels of free (OPG-unbound) RANKL. The in vitro addition of tumor necrosis factor-alpha to human vascular endothelial cells, but not human peripheral blood mononuclear cells, markedly enhanced OPG release in culture. In contrast, high glucose concentrations did not modulate OPG release when used alone or in association with tumor necrosis factor-alpha. Moreover, the ability of soluble RANKL to activate the extracellular signal-regulated kinase/mitogen-activated protein kinase and endothelial nitric-oxide synthase pathways in endothelial cells was neutralized by preincubation with recombinant OPG. Altogether, these findings suggest that increased OPG production represents an early event in the natural history of diabetes mellitus, possibly contributing to disease-associated endothelial cell dysfunction.

Systemic tumor necrosis factor-related apoptosis-inducing ligand delivery shows antiatherosclerotic activity in apolipoprotein E-null diabetic mice

BACKGROUND

Although in vitro studies have suggested that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) might be involved in vascular biology, its potential role in the pathogenesis and/or treatment of atherosclerosis has not been investigated.

METHODS AND RESULTS

Both recombinant human TRAIL and an adeno-associated virus vector expressing human TRAIL were used to deliver TRAIL in apolipoprotein E (apoE)-null mice in which diabetes mellitus was induced by destruction of islet cells with streptozotocin. Diabetes in apoE-null mice was associated with a significant increase in atherosclerotic plaque area and complexity in the aorta as assessed by a marked increase in interstitial collagen, cellular proliferation, and macrophage infiltration and a focal loss of endothelial coverage. Repeated intraperitoneal injections of recombinant human TRAIL and a single intravenous injection of adeno-associated virus-human TRAIL significantly attenuated the development of atherosclerotic plaques in apoE-null animals. TRAIL also markedly affected the cellular composition of plaque lesions by inducing apoptosis of infiltrating macrophages and increasing the vascular smooth muscle cell content. Moreover, TRAIL promoted the in vitro migration of cultured human aortic vascular smooth muscle cells but not of monocytes or macrophages. Conversely, TRAIL selectively induced apoptosis of human cultured macrophages but not of vascular smooth muscle cells.

CONCLUSIONS

Overall, data from the present study indicate that atherosclerosis in diabetic apoE-null mice is ameliorated by systemic TRAIL administration and that adeno-associated virus-mediated TRAIL gene delivery might represent an innovative method for the therapy of diabetic vascular diseases.

Anti-atherosclerotic and renoprotective effects of combined angiotensin-converting enzyme and neutral endopeptidase inhibition in diabetic apolipoprotein E-knockout mice

OBJECTIVE

To investigate the effects of the combined angiotensin-converting enzyme (ACE)/neutral endopeptidase (NEP) inhibitor omapatrilat on atherosclerosis and renal injury in a model of diabetes-associated accelerated atherosclerosis and renal injury.

DESIGN

The study was performed using diabetic apolipoprotein E-knockout (apo E-KO) mice, a model combining hyperlipidemia and hyperglycemia, which leads to accelerated atherosclerosis and renal injury.

METHODS

Diabetes was induced by the injection of streptozotocin in 6-week old apo E-KO mice. Diabetic animals received no treatment (n = 12) or treatment with the ACE/NEP inhibitor omapatrilat (30 mg/kg per day, via gavage, n = 12) or quinapril (10 mg/kg per day, in drinking water, n = 12) for 20 weeks. Non-diabetic apo E-KO mice (n = 12) served as controls.

RESULTS

Omapatrilat reduced atherosclerosis and protected the mice from renal structural injury and albuminuria. The protective effects were associated with tissue inhibition of aortic and renal ACE and NEP as well as a significant reduction in blood pressure. Omapatrilat had similar anti-atherosclerotic effects compared with the ACE inhibitor quinapril in association with an almost complete inhibition of aortic ACE activity by both drugs. Omapatrilat conferred superior renoprotection in the diabetic apo E-KO mouse compared with quinapril in the context of greater renal ACE inhibition by omapatrilat than seen with quinapril, additional renal NEP inhibition and a modestly enhanced antihypertensive response.

CONCLUSIONS

These studies demonstrate the anti-atherosclerotic and renoprotective effects of omapatrilat in diabetic apo E-KO mice, a model of accelerated atherosclerosis and renal injury. These effects were observed in association with the local inhibition of ACE and NEP at the tissue level in the aorta and kidney. These results suggest that the anti-atherosclerotic effect conferred by omapatrilat treatment in the diabetic apo E-KO mouse is predominantly mediated by its capacity to inhibit local vascular ACE. By contrast, in the kidney, local renal ACE and NEP inhibition and the superior antihypertensive effect of omapatrilat all contribute to the renoprotective effect conferred by omapatrilat treatment in the diabetic apo E-KO mouse.

Current perspective. Diabetic vascular disease: from endothelial dysfunction to atherosclerosis

Cardiovascular complications are the leading cause of death in diabetes. Over the past decade a number of studies have addressed the underlying mechanisms. Derangements of endothelial function, also referred to as endothelial dysfunction, have emerged to be the crucial early step in the development of atherosclerosis and are also involved in plaque progression and clinical emergence. Endothelial dysfunction is a condition of impaired endothelium-dependent vasodilation and most important of "endothelial activation", characterized by a proinflammatory, proliferative, and procoagulatory milieu that promotes initiation and complications of atherogenesis. A synergistic cross-talk among the conventional cardiovascular risk factors associated with diabetes contributes to disruption of endothelial integrity and accelerated atherosclerosis. This review will focus on the multifactorial nature of endothelial dysfunction in diabetes, the relationship between endothelial dysfunction, conventional cardiovascular risk factors and atherosclerosis, and the therapeutic options to improve endothelial function.

Genetic polymorphisms of the renin-angiotensin-aldosterone system and renal insufficiency in essential hypertension

OBJECTIVE

The renin-angiotensin-aldosterone system (RAAS) plays an important role in the control of renal function both in physiological and pathological conditions. The aim of the present study was to evaluate the relation between four genetic polymorphisms of the RAAS and renal insufficiency in a population of patients with essential hypertension living in north-east Italy.

DESIGN AND METHODS

Eighty-six hypertensive patients with renal insufficiency and 172 hypertensive patients without renal damage matched for age and hypertension duration to within 2 years were evaluated. Genotyping for insertion/deletion of angiotensin-converting enzyme (ACE I/D), angiotensinogen (AGT) M235T, angiotensin II type 1 receptor (AT1R) A1166C and aldosterone synthase (CYP11B2) -344C/T polymorphisms were performed using polymerase chain reaction, with further restriction analysis when required.

RESULTS

Each of the genetic polymorphisms of the RAAS genes was associated with renal failure; the adjusted odds ratios were 1.47 and 1.89 for ACE D allele, assuming a co dominant and a recessive mode of inheritance, respectively; 1.51 for AGT T235 allele assuming a co dominant, and 1.98 assuming a recessive, pattern of inheritance; 1.79 for AT1R C1166 allele considering a dominant pattern; and 3.89 for CYP11B2 -344C allele as a recessive effect. However, CYP11B2 genotypes were not in Hardy-Weinberg equilibrium among controls. The associations AGT TT-AT1R AC and CYP11B2 CC-ACE DD showed a possible positive interaction in the development of renal insufficiency among hypertensive subjects. The association AGT MM-AT1R AA and AGT MM-AT1R AA-CYP11B2 TT or TC combinations were associated with a reduced risk for renal failure.

CONCLUSIONS

Our findings suggest that in patients with essential hypertension an unfavorable genetic pattern of RAAS may contribute to the increased risk for the development of renal failure.

Connective tissue growth factor and cardiac fibrosis after myocardial infarction

The temporal and spatial expression of transforming growth factor (TGF)-beta(1) and connective tissue growth factor (CTGF) was assessed in the left ventricle of a myocardial infarction (MI) model of injury with and without angiotensin-converting enzyme (ACE) inhibition. Coronary artery ligated rats were killed 1, 3, 7, 28, and 180 days after MI. TGF-beta(1), CTGF, and procollagen alpha1(I) mRNA were localized by in situ hybridization, and TGF-beta(1) and CTGF protein levels by immunohistochemistry. Collagen protein was measured using picrosirius red staining. In a separate group, rats were treated for 6 months with an ACE inhibitor. There were temporal and regional differences in the expression of TGF-beta(1), CTGF, and collagen after MI. Procollagen alpha1(I) mRNA expression increased in the border zone and scar peaking 1 week after MI, whereas collagen protein increased in all areas of the heart over the 180 days. Expression of TGF-beta(1) mRNA and protein showed major increases in the border zone and scar peaking 1 week after MI. The major increases in CTGF mRNA and protein occurred in the viable myocardium at 180 days after MI. Long-term ACE inhibition reduced left ventricular mass and decreased fibrosis in the viable myocardium, but had no effect on cardiac TGF-beta(1) or CTGF. TGF-beta(1) is involved in the initial, acute phase of inflammation and repair after MI, whereas CTGF is involved in the ongoing fibrosis of the heart. The antifibrotic benefits of captopril are not mediated through a reduction in CTGF.

Glomerular permeability defect in hypertension is dependent on renin angiotensin system activation

BACKGROUND

The aim of the present study was to compare glomerular permeability alterations associated with experimental hypertension models known to have different effects on the circulating renin-angiotensin system (RAS).

METHODS

Five groups, 10 animals each, were studied. One group served as a nonhypertensive control. The other four groups of hypertensive animals were composed of spontaneously hypertensive rats, deoxycorticosterone acetate hypertensive rats, Goldblatt two-kidney, one-clip rats, and a group of Wistar rats infused with angiotensin II (200 ng/kg/min). Tail-cuff sphygmomanometric systolic blood pressure (BP), albumin permeability determined in isolated glomeruli exposed to oncotic gradients (P(alb)), glomerular filtration rate (GFR, iopamidol method), plasma renin activity (PRA), and albuminuria were evaluated.

RESULTS

Alterations in P(alb) and albumin excretion rate were more evident in the experimental models with an activation of the RAS despite similar levels of systolic BP and GFR. A positive correlation was found between P(alb) and albuminuria (r = 0.51; P < .001) and between systolic BP and albuminuria (r = 0.37; P < .01). No relation was found between systolic BP and P(alb).

CONCLUSIONS

The present study indicates that the activation of the RAS plays a significant role in the development of glomerular albumin permeability defects in hypertensive models and may contribute to the mechanisms that lead to target organ damage in hypertension.

Accelerated Nephropathy in Diabetic Apolipoprotein E-Knockout Mouse: Role of Advanced Glycation End Products

Hyperlipidemia not only may be relevant to cardiovascular disease in diabetes but may also play a role in the development and progression of diabetic nephropathy. Furthermore, there is increasing evidence that advanced glycation end products (AGE) play an important role in diabetic renal disease. The objectives of this study were first to characterize renal injury in diabetic apolipoprotein E knockout (apo E-KO) mice and second to explore the role of AGE in the development and progression of renal disease in this model. Diabetes was induced by injection of streptozotocin in 6-wk-old apo E-KO mice. Diabetic animals received no treatment or treatment with the inhibitor of AGE formation aminoguanidine (1 g/kg per d) or the cross-link breaker [4,5-dimethyl-3-(2-oxo2-phenylethyl)-thiazolium chloride] ALT-711, which cleaves preformed AGE (20 mg/kg per d) for 20 wk. Nondiabetic apo E-KO mice as well as nondiabetic and diabetic C57BL/6 mice served as controls. Compared with nondiabetic apo E-KO mice, induction of diabetes in apo E-KO mice resulted in accelerated renal injury characterized by albuminuria and glomerular and tubulointerstitial injury. These abnormalities were associated with increased expression of collagen type I and type IV and transforming growth factor-beta1 (TGF-beta1), increased alpha-smooth muscle actin immunostaining and macrophage infiltration, and increased serum and renal AGE. The two treatments, which attenuated renal AGE accumulation in a disparate manner, were associated with less albuminuria, structural injury, macrophage infiltration, TGF-beta1, and collagen expression. The accelerated renal injury that was observed in diabetic apo E-KO mice was attenuated by approaches that inhibit renal AGE accumulation.

Advanced glycation end product interventions reduce diabetes-accelerated atherosclerosis

Advanced glycation end product (AGE) formation may contribute to the progression of atherosclerosis, particularly in diabetes. The present study explored atherosclerosis in streptozotocin-induced diabetic apolipoprotein E-deficient (apoE-/-) mice that were randomized (n = 20) to receive for 20 weeks no treatment, the AGE cross-link breaker ALT-711, or the inhibitor of AGE formation aminoguanidine (AG). A sixfold increase in plaque area with diabetes was attenuated by 30% with ALT-711 and by 40% in AG-treated mice. Regional distribution of plaque demonstrated no reduction in plaque area or complexity within the aortic arch with treatment, in contrast to the thoracic and abdominal aortas, where significant attenuation was seen. Diabetes-associated accumulation of AGEs in aortas and plasma and decreases in skin collagen solubility were ameliorated by both treatments, in addition to reductions in the vascular receptor for AGE. Collagen-associated reductions in the AGEs carboxymethyllysine and carboxyethyllysine were identified with both treatments. Diabetes was also accompanied by aortic accumulation of total collagen, specifically collagens I, III, and IV, as well as increases in the profibrotic cytokines transforming growth factor-beta and connective tissue growth factor and in cellular alpha-smooth muscle actin. Attenuation of these changes was seen in both treated diabetic groups. ALT-711 and AG demonstrated the ability to reduce vascular AGE accumulation in addition to attenuating atherosclerosis in these diabetic mice.

Imatinib Attenuates Diabetes-Associated Atherosclerosis

OBJECTIVE

Diabetes is associated with accelerated atherosclerosis, the major factor contributing to increased mortality and morbidity in the diabetic population. The molecular mechanisms by which diabetes promotes atherosclerosis are not fully understood. Platelet-derived growth factor has been shown to play a major role in the pathology of vascular diseases, but whether it plays a role in atherosclerosis associated with diabetes remains unknown. The aims of this study were to assess whether platelet-derived growth factor-dependent pathways are involved in the development of diabetes-induced atherosclerosis and to determine the effects of platelet-derived growth factor receptor antagonism on this disorder.

METHODS AND RESULTS

Diabetes was induced by injection of streptozotocin in 6-week-old apolipoprotein E knockout mice. Diabetic animals received treatment with a tyrosine kinase inhibitor that inhibits platelet-derived growth factor action, imatinib (STI-571, 10 mg/kg per day), or no treatment for 20 weeks. Nondiabetic apolipoprotein E knockout mice served as controls. Induction of diabetes was associated with a 5-fold increase in plaque area in association with an increase in aortic platelet-derived growth factor-B expression and platelet-derived growth factor-beta receptor phosphorylation as well as other prosclerotic and proinflammatory cytokines. Imatinib treatment prevented the development of atherosclerotic lesions and diabetes-induced inflammatory cytokine overexpression in the aorta.

CONCLUSIONS

Tyrosine kinase inhibition with imatinib appears to be a novel therapeutic option to retard the development of atherosclerosis, specifically in the context of diabetes.

Improved islet morphology after blockade of the renin- angiotensin system in the ZDF rat

The renin-angiotensin system (RAS) has an important role in the endocrine pancreas. Although angiotensin II has significant effects on cell proliferation and apoptosis, the contribution of the RAS to changes in islet structure and function associated with type 2 diabetes is yet to be defined. This study examined the specific effects of RAS blockade on islet structure and function in diabetes. Thirty-six male Zucker diabetic fatty (ZDF) rats, 10 weeks of age, were randomized to receive the angiotensin-converting enzyme inhibitor perindopril (8 mg/l in drinking water; n = 12), irbesartan (15 mg/kg via gavage; n = 12), or no treatment (n = 12) for 10 weeks. Results were compared with lean littermates (ZL) (n = 12) studied concurrently. ZDF rats had increased intra-islet expression of components of the RAS correlating with increased intraislet fibrosis, apoptosis, and oxidative stress. Disordered islet architecture, seen in ZDF rats, was attenuated after treatment with perindopril or irbesartan. Islet fibrogenesis was also diminished, as measured by picrosirius staining and expression of collagens I and IV. Gene expression of transforming growth factor-beta1 was increased in the ZDF pancreas (ZL, 1.0 +/- 0.1; ZDF, 2.0 +/- 0.3; P < 0.05) and reduced after blockade of the RAS (ZDF + P, 1.3 +/- 0.2; ZDF + I, 1.5 +/- 0.1; vs. ZDF, both P < 0.05). Improvements in structural parameters were also associated with functional improvements in first-phase insulin secretion. These findings provide a possible mechanism for the reduced incidence of new-onset diabetes that has been observed in clinical trials of RAS blockade.

Irbesartan but not amlodipine suppresses diabetes-associated atherosclerosis

BACKGROUND

It remains controversial whether specific blockade of the renin-angiotensin system confers superior antiatherosclerotic effects over other antihypertensive agents in diabetes. Therefore, the aim of this study was to compare equihypotensive doses of the angiotensin II subtype 1 (AT1) receptor blocker irbesartan with the calcium antagonist amlodipine on diabetes-induced plaque formation in the apolipoprotein E (apoE)-null mouse and to explore molecular and cellular mechanisms linked to vascular protection.

METHODS AND RESULTS

Diabetes was induced by injection of streptozotocin in 6-week-old apoE-null mice. Diabetic animals were randomized to no treatment, irbesartan, or amlodipine for 20 weeks. Diabetes was associated with an increase in plaque area and complexity in the aorta in association with a significant increase in aortic AT1 receptor expression, cellular proliferation, collagen content, macrophage- and alpha-smooth muscle actin-positive cell infiltration, as well as an increased expression of platelet-derived growth factor-B (PDGF-B), monocyte chemoattractant protein-1 (MCP-1), and vascular cell adhesion molecule-1 (VCAM-1). Irbesartan but not amlodipine treatment attenuated the development of atherosclerosis, collagen content, cellular proliferation, and macrophage infiltration as well as diabetes-induced AT1 receptor, PDGF-B, MCP-1, and VCAM-1 overexpression in the aorta despite similar blood pressure reductions by both treatments.

CONCLUSIONS

Diabetes-associated atherosclerosis is ameliorated by AT1 receptor blockade but not by calcium channel antagonism, providing further evidence for the vascular renin-angiotensin system playing a pivotal role in the development and acceleration of atherosclerosis in diabetes.

Diabetes mellitus: a cardiovascular disease

Cardiovascular disease (CVD) is the major cause of morbidity and mortality in patients with diabetes mellitus (DM). The pathophysiology of CVD in diabetes involves traditional and novel cardiac risk factors, including hypertension, dyslipidemia, smoking, genetic factors, hyperglycemia, insulin resistance/hyperinsulinemia, metabolic abnormalities, oxidative/glycoxidative stress, inflammation, endothelial dysfunction, a procoagulant state and myocardial fibrosis. Specific vascular, myopathic and neuropathic alterations have been suggested to be responsible for the excessive cardiovascular morbidity and mortality in diabetes. These alterations manifest themselves clinically as coronary heart disease, congestive heart failure and/or sudden cardiac death. In order to contain the emerging epidemic of CVD in DM, diabetic patients should ideally have excellent glycemic control, a low normal blood pressure and low levels of low-density lipoprotein cholesterol, and be taking an angiotensin-converting enzyme inhibitor and aspirin, which may go some way to containing the emerging epidemic of CVD in DM.

A breaker of advanced glycation end products attenuates diabetes-induced myocardial structural changes

The formation of advanced glycation end products (AGEs) on extracellular matrix components leads to accelerated increases in collagen cross linking that contributes to myocardial stiffness in diabetes. This study determined the effect of the crosslink breaker, ALT-711 on diabetes-induced cardiac disease. Streptozotocin diabetes was induced in Sprague-Dawley rats for 32 weeks. Treatment with ALT-711 (10 mg/kg) was initiated at week 16. Diabetic hearts were characterized by increased left ventricular (LV) mass and brain natriuretic peptide (BNP) expression, decreased LV collagen solubility, and increased collagen III gene and protein expression. Diabetic hearts had significant increases in AGEs and increased expression of the AGE receptors, RAGE and AGE-R3, in association with increases in gene and protein expression of connective tissue growth factor (CTGF). ALT-711 treatment restored LV collagen solubility and cardiac BNP in association with reduced cardiac AGE levels and abrogated the increase in RAGE, AGE-R3, CTGF, and collagen III expression. The present study suggests that AGEs play a central role in many of the alterations observed in the diabetic heart and that cleavage of preformed AGE crosslinks with ALT-711 leads to attenuation of diabetes-associated cardiac abnormalities in rats. This provides a potential new therapeutic approach for cardiovascular disease in human diabetes.

Renal processing of albumin in diabetes and hypertension in rats: possible role of TGF-beta1

BACKGROUND/AIMS

Recent studies show that albuminuria may be the result of changes in post-glomerular cellular uptake and processing of albumin. This study aims to determine whether this processing is disrupted in diabetes and/or hypertension.

METHODS

Diabetes (d) was induced using streptozotocin in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) and studied after 8, 16 and 24 weeks of disease. Intact albumin excretion was determined by radioimmunoassay. Total albumin was determined by [(14)C]albumin. Lysosomal activity was determined by dextran sulfate desulfation. Renal TGF-beta1 and transforming growth factor-beta1 inducible gene-h3 mRNA (betaig-h3) expression was determined by real time RT-PCR.

RESULTS

SHR-c rats exhibited an increase in intact albuminuria without significant change in total albumin excretion (intact plus albumin-derived peptides). For WKY-d rats, intact albuminuria developed initially, followed by an increase in total albumin excretion primarily in the form of albumin peptides (peptiduria). SHR-d rats exhibited both increases in peptiduria and intact albuminuria. There was no increase in glomerular permeability at 24 weeks for polydisperse [(3)H]Ficoll in all groups. Increased renal TGF-beta1 and betaig-h3 expression was correlated with a decrease in dextran sulfate desulfation and increased intact albuminuria independent of peptiduria.

CONCLUSION

Increased albumin excretion in hypertension and/or diabetes is manifested in different forms independent of glomerular permeability.

Renal expression of angiotensin receptors in long-term diabetes and the effects of angiotensin type 1 receptor blockade

OBJECTIVE

The aims of this study were to assess the renal expression of angiotensin type 1 (AT1) and type 2 (AT2) receptors in diabetic spontaneously hypertensive rats (SHR) and the effect of AT1 receptor blockade on the expression of these receptors.

DESIGN

Diabetes was induced by injection of streptozotocin in SHRs. Irbesartan, an AT1 receptor antagonist, was given to diabetic SHRs for 32 weeks (15 mg/kg per day, n = 10). Diabetic (n = 10) and non-diabetic SHRs (n = 10) were studied concurrently. A separate group of control and diabetic Wistar-Kyoto (WKY) rats were also evaluated.

METHODS

Gene and protein expressions of the AT1 and AT2 receptor were assessed by reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry with specific antibodies andin vitro autoradiography with [125I]Sar(1), Ile(8) angiotensin II or [125I]CGP42112B.

RESULTS

Both AT1 and AT2 receptor mRNA levels in the kidney were reduced in diabetic SHRs compared to non-diabetic SHRs. Immunohistochemistry staining with specific antibodies showed a similar reduction in glomerular and tubulo-interstitial staining for both AT1 and AT2 receptors. Reduced binding for the AT1 and AT2 receptor was found in the kidney of diabetic SHRs. Diabetic SHRs developed albuminuria and had glomerular and tubulo-interstitial injury, which were prevented by treatment with irbesartan. Reduced expression of the AT1 receptor, but not the AT2 receptor, in diabetic SHRs was prevented by treatment with irbesartan. In diabetic WKY rats no such reduction in AT1 expression was observed, although there was a trend for reduced AT2 receptor expression.

CONCLUSIONS

These findings demonstrated that renal expression of both AT1 and AT2 receptor was reduced in long-term diabetic SHRs and that blockade of the AT1 receptor had disparate effects on expression of angiotensin II receptor subtypes.

Prevention of accelerated atherosclerosis by angiotensin-converting enzyme inhibition in diabetic apolipoprotein E-deficient mice

BACKGROUND

Atherosclerosis is a major complication of diabetes, but the mechanisms by which diabetes promotes macrovascular disease have not been fully delineated. Although several animal studies have demonstrated that inhibition of ACE results in a decrease in the development of atherosclerotic lesions, information about the potential benefits of these agents on complex and advanced atherosclerotic lesions as observed in long-term diabetes is lacking. The aim of this study was to evaluate whether treatment with the ACE inhibitor perindopril affects diabetes-induced plaque formation in the apolipoprotein E (apoE)-deficient mouse.

METHODS AND RESULTS

Diabetes was induced by injection of streptozotocin in 6-week-old apoE-deficient mice. Diabetic animals received treatment with perindopril (4 mg x kg(-1) x d(-1)) or no treatment for 20 weeks. Nondiabetic apoE-deficient mice were used as controls. Induction of diabetes was associated with a 4-fold increase in plaque area compared with nondiabetic animals. This accelerated atherosclerosis was associated with a significant increase in aortic ACE expression and activity and connective tissue growth factor and vascular cell adhesion molecule-1 expression. Perindopril treatment inhibited the development of atherosclerotic lesions and diabetes-induced ACE, connective tissue growth factor, and vascular cell adhesion molecule-1 overexpression in the aorta.

CONCLUSIONS

The activation of the local renin-angiotensin system in the diabetic aorta and the reduction in atherosclerosis with ACE inhibitor treatment provides further evidence that the renin-angiotensin system plays a pivotal role in the development and acceleration of atherosclerosis in diabetes.

Haemodynamics in microvascular complications in type 1 diabetes

Type 1 diabetes is commonly associated with microvascular complications. Most of the microvascular blood vessels are involved but those in the kidney, retina and large nerves exhibit the more significant pathology. Haemodynamic and metabolic factors both alone and through the activation of a common pathway contribute to the characteristic dysfunction observed in diabetic vasculopathy. The haemodynamic abnormalities in type 1 diabetes are characterized by increased systemic blood pressure and altered blood flow with subsequent activation of various vasoactive factors, which can contribute to the maintenance of the haemodynamic alterations and to the development and progression of the microvascular complications. These vasoactive factors include vasoconstrictors such as angiotensin II, and endothelin, as well as vasodilators such as nitric oxide (NO). Systemic hypertension and vasoactive factors independently and in interaction with the metabolic pathway activate intracellular second messengers, nuclear transcription factors and various growth factors which lead to the typical functional and structural alterations of diabetic microvascular complications. Therapeutic strategies involved in the management and prevention of diabetic complications currently include antihypertensive agents, particularly those that interrupt the renin-angiotensin system. Further understanding of the interactions among the vasoactive factors, the intracellular second messengers and the growth factors may help to identify novel strategies to influence the action of the vasoactive factors. These novel therapies, together with specific inhibitors of the metabolic pathway or the common pathway, may provide the possibility of preventing or even reversing the progression of diabetic microvascular complications.

Angiotensin type 2 receptor antagonism confers renal protection in a rat model of progressive renal injury

The role of the angiotensin type 2 (AT(2)) receptor in the pathogenesis of progressive renal injury has not been previously elucidated. The renal expression of the AT(1) and AT(2) receptors in subtotally nephrectomized rats (STNx) and the effects of AT(2) receptor blockade on renal injury were explored. Reduced renal expression of the AT(1) but not the AT(2) receptor was observed in STNx by reverse transcription-PCR, by in vitro autoradiography, and by immunohistochemical staining. The STNx rats were randomly assigned to AT(1) receptor antagonist valsartan, AT(2) receptor antagonist PD123319, or the combination of both for 4 wk. Increased proteinuria in STNx rats was reduced by PD123319 but to a lesser degree when compared with valsartan. Reduced gene and protein expression of the slit diaphragm protein nephrin was prevented by either valsartan or PD123319. Expression of osteopontin, proliferating cell nuclear antigen, and monocyte/macrophage infiltration was increased in STNx rats and was reduced by both AT(1) and AT(2) receptor antagonists. These effects of AT(2) receptor antagonism were observed in the presence of increased BP in STNx rats. These findings suggest that blockade of the AT(2) receptor alone confers a degree of renal protection; in particular, it seems that the combination of the AT(1) and AT(2) receptor antagonists may confer additive renal effects than either receptor antagonist as monotherapy.

Modulation of nephrin in the diabetic kidney: association with systemic hypertension and increasing albuminuria

OBJECTIVE

Nephrin, a cytoskeletal protein which localizes to the slit pore of podocytes, may play a role in proteinuria. This study examines the possible relationship between nephrin expression and albuminuria in normotensive and hypertensive diabetic rats.

METHODS

Streptozotocin diabetes was induced in both Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Diabetic and control animals were sacrificed and the kidneys obtained after 8, 16 and 24 weeks. The glomerular filtration rate (GFR) and albuminuria were also measured. Glycaemic control was assessed by measurement of plasma glucose and glycated haemoglobin (HbA1c). Nephrin gene expression was quantitated by real-time polymerase chain reaction (PCR) and localized by in situ hybridization. Nephrin protein expression was localized by immunohistochemistry and quantitated.

RESULTS

Following a transient rise at 8 weeks in the diabetic SHR (P < 0.05 versus control SHRs), nephrin gene expression, as determined by real-time PCR, was significantly decreased at 16 and 24 weeks (P < 0.05 versus control SHRs). In situ hybridization confirmed similar changes in nephrin gene expression, which were confined to the glomeruli. This reduction in glomerular nephrin gene expression was associated with increasing albuminuria at 16 and 24 weeks in diabetic SHRs. There were no significant changes in nephrin gene expression, either by real-time reverse transcription polymerase chain reaction or in situ hybridization, observed in normotensive diabetic WKY rats, in the context of much less albuminuria in this group. Immunohistochemistry for nephrin protein revealed a greater depletion in renal nephrin content in SHR than in WKY rats after 24 weeks of diabetes.

CONCLUSION

Reduction in renal nephrin gene and protein expression is closely associated with the development of albuminuria, as observed in an experimental model of diabetes and hypertension.

Treatment for diabetic nephropathy - a review of the recent patent literature

Diabetic nephropathy is now the leading cause of end-stage renal disease in the Western world. Renal disease develops secondary to long-standing hyperglycemia and hemodynamic alterations, which activate a common pathway that ultimately leads to the renal damage. Current strategies to treat diabetic nephropathy include optimization of glycemic control and treatment of glomerular and systemic hypertension. Although these strategies can slow the progression of proteinuria and decline in renal function, diabetic nephropathy remains a huge clinical problem. It is anticipated that future treatment modalities for preventing and treating diabetic nephropathy will involve drugs that modulate common pathogenetic pathways, possibly acting to inhibit both metabolic and hemodynamically induced forms of renal injury. These include inhibitors of growth factor and cytokine release or action, and inhibitors of intracellular second messengers. Although most of these agents have only been investigated in vitro, in animal experiments, or in relatively short-term human studies, these studies suggest that therapeutic strategies which involve a multifactorial approach may be more successful in the treatment of diabetic kidney disease than drugs which influence only one pathway.

Modulation of incipient glomerular lesions in experimental diabetic nephropathy by hypotensive and subhypotensive dosages of an ACE inhibitor

A glomerular permeability defect occurs early in the course of type 1 diabetes and precedes the onset of microalbuminuria and renal morphological changes. Recently, ACE inhibitors have been shown to prevent loss of glomerular membrane permselective function, but the mechanism of this nephroprotective effect is still being debated. The objective of the present study was to evaluate the effects of hypotensive and subhypotensive dosages of the ACE inhibitor quinapril ex vivo and of its active metabolite quinaprilat in vitro on the glomerular albumin permeability (P(alb)) defect in the early phases of experimental diabetes. For the ex vivo study, six groups of male Wistar rats were evaluated for 4 weeks. One group served as a nondiabetic control (C); the other five groups were rendered diabetic and included untreated diabetic rats (D) and diabetic rats receiving quinapril at the dosages of 5 (DQ1), 2.5 (DQ2), 1.25 (DQ3), and 0.625 (DQ4) mg. kg(-1). day(-1). Dosage-dependent effects of quinapril on systolic blood pressure and the glomerular filtration rate were observed. In contrast, control of P(alb) in isolated glomeruli exposed to oncotic gradients, proteinuria, and glomerular and tubular hypertrophy was obtained with subhypotensive dosages (DQ3 and DQ4 groups) of the ACE inhibitor. In the in vitro study, quinaprilat reduced P(alb) significantly in concentration ranges from 10(-6) to 10(-14) mol/l compared with results in control glomeruli. The effect on P(alb) may have occurred by mechanisms different from kidney ACE inhibitor. These study results indicated that ACE inhibitor treatment prevents the early onset of the P(alb) defect in experimental diabetes. This effect seemed to occur independently of systemic or glomerular hemodynamic changes and, at least partially, from kidney ACE inhibition.

Mechanics of the carotid artery wall and baroreflex sensitivity after acute ethanol administration in young healthy volunteers

The effects of ethanol administered orally (300 mg/kg in 250 ml of water) or intravenously (7.5 mg.min(-1).kg(-1) in 250 ml of saline over 40 min) on common carotid haemodynamics, wall mechanics and baroreflex sensitivity were compared with the effects of the intravenous infusion of 250 ml of saline. Ethanol or saline was administered to 10 healthy volunteers after 30 min of supine rest, and measurements were obtained 40 min (median; range 34-46 min) after administration. After ethanol administration, the plasma alcohol level rose from 0 to 0.3+/-0.07 g/l. Mean arterial blood pressure had risen slightly at 20 min, but was normalized by 40 min, the time at which the haemodynamic study was performed. Heart rate decreased after infusion of either saline or alcohol, but was unchanged after oral ethanol administration. Both oral and intravenous ethanol administration were associated with significant decreases in baroreflex sensitivity, carotid shear stress and blood velocity, compared with resting values, while the mean carotid artery diameter was increased, and blood viscosity and mean blood flow were unchanged. No changes were observed in these parameters after saline administration. Ethanol, administered either intravenously or orally, increased the stiffness of the carotid artery and decreased the pulsatility (systo-diastolic changes) of its diameter. A direct, statistically significant correlation was found between the decrease in shear stress and the decrease in baroreflex heart rate control sensitivity after both modes of alcohol administration, while no such correlation was found between the increase in the Peterson elastic modulus and the decrease in carotid diameter pulsatility on the one hand or the decrease in baroreflex sensitivity on the other. In conclusion, reduced shear stress associated with vasodilatation of the carotid artery wall may contribute to the decrease in baroreflex sensitivity observed after acute ethanol administration.

Haemoconcentration, shear-stress increase and carotid artery diameter regulation after furosemide administration in older hypertensives

The aim of the present study was to determine whether changes of carotid wall shear stress induced by changes in blood viscosity after diuretic administration cause carotid arterial dilatation in elderly hypertensives, as reported in the cat. Arterial wall shear rate (ultrasound technique, profilmeter FRP III), the systo-diastolic diameter (echotracking technique) and the mean blood flow velocity and volume of the common carotid artery, the blood viscosity (rotational viscometer) and the finger arterial blood pressure (Finapress Ohmeda) were measured in 12 young volunteers (aged 25+/-2 years) and in 12 elderly hypertensives (aged 80+/-4 years) treated with short-acting calcium antagonists up to 24h before the study, both at baseline and after intravenous furosemide infusion (0.5mg/min), when the haematocrit had increased by at least two percentage points. After furosemide administration the mean arterial blood pressure decreased and blood viscosity and carotid systolic shear stress increased in both groups. However, common carotid artery diameter increased only in the young controls but not in the elderly hypertensives. These data show that an increase in carotid shear stress caused by haemoconcentration induces carotid vasodilatation only in young healthy subjects, and not in elderly hypertensives. This effect may be related to impaired endothelium function and/or arterial wall mechanics.

Effects of prolonged high-altitude exposure on peripheral adrenergic receptors in young healthy volunteers

The regulation of adrenergic receptors during hypoxia is complex, and the results of published reports have not been consistent. In the present study blood cell adrenoceptor characteristics at sea level (SL) before and after prolonged exposure to high altitude (HA) were measured in seven trained young male lowlanders. Sympathoadrenal activity and clinical haemodynamic parameters were also evaluated before departure (SLB), after 1 week (HA1) and 4 weeks (HA4) at HA and 1 week after return to sea level (SLA). As compared to pre-departure sea level values, urinary norepinephrine excretion increased significantly during altitude exposure [SLB: 10.26 (3.04) microg x 3 h(-1); HA1: 23.2 (4.19) microg x 3 h(-1); HA4: 20.3 (8.68) microg x 3 h(-1)] and fell to pre-ascent values 1 week after return to sea level [SLA: 9 (2.91) microg x 3 h(-1)]. In contrast, mean urinary epinephrine levels did not increase over time at HA. Both systolic and diastolic blood pressures, as well as heart rate, were increased during HA exposure. The circadian blood pressure and heart rate rhythms were preserved during all phases of altitude exposure. Mean maximal binding (Bmax) of the alpha2-adrenoceptor antagonist [3H]rauwolscine to platelet membranes was significantly reduced (P < 0.001) after exposure to chronic hypoxia [SLB: 172.6 (48.5) fmol x mg(-1) protein versus SLA: 136.8 (56.1) fmol x mg(-1) protein] without change in the dissociation constant (K(D)). Neither the lymphomonocyte beta2-adrenoceptor Bmax [SLB: 38.5 (13.6) fmol x mg(-1) protein, versus SLA: 32.4 (12.1) fmol mg(-1) protein] nor the K(D) for [3H]dihydroalprenolol was affected by chronic hypoxia. Cyclic AMP (adenosine 3',5'-cyclic monophoshate) generation in lymphomonocytes by maximal isoproterenol stimulation was not modified after prolonged HA exposure. In conclusion, the down-regulation of alpha2-adrenoceptors appears to be an important component of the adrenergic system response to HA exposure.

Albumin permeability in isolated glomeruli in incipient experimental diabetes mellitus

AIMS/HYPOTHESIS

The pre-clinical phase of diabetic nephropathy is characterised by increased glomerular filtration rate and episodes of microalbuminuria. The cause of the microalbuminuria has been variably ascribed to alterations of the size or charge selective barriers of the glomerulus or both or as a consequence of the haemodynamic changes. Our aim was to investigate very early albumin permeability alterations in isolated glomeruli which were not subject to perfusion pressure.

METHODS

Isolated glomeruli were studied from 120 male Wistar rats, divided into three groups: streptozotocin-treated, streptozotocin-treated with insulin pellet implants, and controls. From each group ten animals were killed at 7, 14, 28, and 56 days after induction. Study variables included blood pressure, proteinuria, iopamidol clearance, albumin permeability and glomerular area. Subsequently, albumin permeability, proteinuria, and iopamidol clearance were determined in an additional group of 40 diabetic animals studied at 24, 72, 96, and 120 h after induction.

RESULTS

Albumin permeability increased steadily from induction in streptozotocin-treated animals, reaching a plateau at approximately 120 h. Glomerular filtration rate was shown to increase significantly at approximately 7 days and proteinuria correlated with it. Glomerular hypertrophy was observed both in streptozotocin-treated animals and in streptozotocin-treated rats with insulin pellet implants. Strict blood glucose control delayed the appearance of the permeability defect in isolated glomeruli and inhibited the increase in glomerular filtration in intact animals. It did not prevent glomerular hypertrophy.

CONCLUSION/INTERPRETATION

An albumin permeability defect exists early in isolated non-perfused glomeruli from streptozotocin-treated rats and seems to be independent of glomerular filtration rate alterations.

Regional and systemic haemodynamic response to aortography in hypertensives

OBJECTIVE

To study the effects of aortography and of aortic counterflow bolus injection per se on regional and systemic haemodynamics in hypertensives in comparison to normotensive matched controls.

DESIGN AND METHODS

Mean blood velocity (MBV) and pulsatility index (PI)--as an index of regional vascular resistance--by the Doppler technique, at the femoral, common carotid and brachial arteries, finger arterial pressure and electrocardiographic R-R' interval were monitored beat-by-beat, before, during and for 3 min following counterflow bolus injections into the abdominal aorta of 40 ml/2.6 s of iopamidol (I), iso-osmolar mannitol (M) and 0.9 N saline (S), in 11 hypertensive and nine normotensive patients.

RESULTS

After bolus injection of iopamidol, MBV increased to a peak at 35+/-5 s, both in normotensive (deltaMBV versus baseline +16.7+/-9.9 cm/s; P < 0.01) and in hypertensive subjects (deltaMBV versus baseline: +13.9+/-6.6 cm/s; P < 0.01). At the same time, the PI decreased both in normotensive (deltaPI versus baseline: -4.05+/-2.49; P < 0.01) and in hypertensive subjects (deltaPI versus baseline: -3.02+/-2.25; P < 0.01). After M boluses, the haemodynamic changes were of the same direction and magnitude as I for both groups, while after S the magnitude was approximately 50% lower. No significant differences were observed between normotensive and hypertensive subjects. In other vascular circulations, a 15% increase of the early diastolic backflow in the brachial artery, in phase with the femoral artery haemodynamic changes, was the only evidence of the procedure. Mean arterial pressure decreased and heart rate increased in phase with flow changes of the femoral artery.

CONCLUSIONS

(1) The regional flow and systemic pressure changes observed during aortography seem, at least partially, to be due to the hydrodynamic perturbation induced by bolus injection per se. (2) The physical and chemical properties of the contrast media and therefore the probable different shear-stress modifications induced by the fluid injected could explain why the haemodynamic changes were greater after I compared to S and were more similar to M. (3) Hypertensive subjects did not show a different vasoreactive response in comparison to normotensive subjects during aortography.

Control of glomerular hyperfiltration and renal hypertrophy by an angiotensin converting enzyme inhibitor prevents the progression of renal damage in hypertensive diabetic rats

OBJECTIVE

Glomerular hyperfiltration and renal hypertrophy are both considered important in the progression of diabetic nephropathy. The aim of this study was to compare the effects of an equivalent reduction in blood pressure produced by the angiotensin-converting enzyme (ACE) inhibitor spirapril (SPI) and an antihypertensive triple drug combination of hydralazine, reserpine and hydrochlorothiazide (HRH) on kidney function, proteinuria and renal structure in hypertensive diabetic rats.

DESIGN AND METHODS

Four groups of animals were evaluated in short-term and long-term studies. In both studies one group served as a non-diabetic hypertensive control (H). The other three groups were rendered diabetic and were allocated to one of the following groups: the first diabetic group received no specific therapy (HD), the second diabetic group was treated with SPI (HD-SPI) and the third diabetic group was treated with HRH (HD-HRH). In each of the two studies the systolic blood pressure (SBP), 24 h urinary total protein, glomerular filtration rate (GFR), glomerular area, proximal tubular area and glomerular sclerosis were evaluated.

RESULTS

The blood pressure reduction was equal in rats receiving either SPI or HRH. The GFR, proteinuria, glomerular area and tubular area were significantly increased in the HD group, both in the short-term and the long-term study. In the HD-SPI group the diabetic hyperfiltration and renal hypertrophy responses were prevented. In the HD-HRH group the GFR and proteinuria were slightly reduced in the later phases of diabetes, while the glomerular area and tubular area were not affected. Semiquantitative analysis of renal lesions showed that SPI was more effective than HRH in the prevention of the development of glomerulosclerosis.

CONCLUSIONS

The results of this study suggest that the control of early adaptive hyperfiltration and renal hypertrophy by SPI may be relevant in the prevention of glomerulosclerosis.