Acute hyperglycaemia causes elevation in plasma atrial natriuretic peptide concentrations in Type 1 diabetes mellitus

Prediction of gestational diabetes mellitus in the first trimester: comparison of maternal fetuin-A, N-terminal proatrial natriuretic peptide, high-sensitivity C-reactive protein, and fasting glucose levels

OBJECTIVE

We investigated the utility of maternal fetuin-A, N-terminal proatrial natriuretic peptide (pro-ANP), high-sensitivity C-reactive protein (hs-CRP), and fasting glucose levels at 11-14 gestation weeks for predicting pregnancies complicated by gestational diabetes mellitus (GDM).

SUBJECTS AND METHODS

This prospective cohort study included 327 low-risk pregnant women who completed antenatal follow-up at a tertiary research hospital between January and April 2014. Maternal blood samples were collected between 11-14 gestational weeks in the first trimester of pregnancy and then stored at -80 °C until further analyses. During follow-up, 29 (8.8%) women developed GDM. The study population was compared 1:2 with age- and body mass index-matched pregnant women who did not develop GDM (n = 59). Fasting plasma glucose (FPG) levels and serum fetuin-A, pro-ANP, and hs-CRP levels were measured using automated immunoassay systems.

RESULTS

There was a significant negative correlation between fetuin-A and hs-CRP (CC = -0.21, p = 0.047) and a positive correlation between FPG and hs-CRP (CC = 0.251, p = 0.018). The areas under the receiver operating characteristic curve for diagnosing GDM were 0.337 (p = 0.013), 0.702 (p = 0.002), and 0.738 (p < 0.001) for fetuin-A, hs-CRP, and FPG, respectively. The optimal cut-off values were > 4.65, < 166, and > 88.5 mg/dL for maternal hs-CRP, fetuin-A, and FPG, respectively.

CONCLUSION

Reduced fetuin-A, elevated hs-CRP, and FPG levels in women in the first trimester can be used for the early detection of GDM. Further research is needed before accepting these biomarkers as valid screening tests for GDM.

Chlorogenic acid attenuates glucotoxicity in H9c2 cells via inhibition of glycation and PKC α upregulation and safeguarding innate antioxidant status

A series of cardiovascular complications associated with hyperglycemia is a critical threat to the diabetic population. Here we elucidate the link between hyperglycemia and cardiovascular diseases onset, focusing on oxidative stress and associated cardiac dysfunctions. The contribution of advanced glycation end products (AGE) and protein kinase C (PKC) signaling is extensively studied. For induction of hyperglycemia, H9c2 cells were incubated with 33 mM glucose for 48 h to simulate the diabetic condition in in vitro system. Development of cardiac dysfunction was confirmed with the significant increase of lactate dehydrogenase (LDH) release to the medium and associated decrease in cell viability. Various parameters like free radical generation, alteration in innate antioxidant system, lipid peroxidation, AGE production and PKC α -ERK axis were investigated during hyperglycemia and with chlorogenic acid. Hyperglycemia has significantly enhanced reactive oxygen species (ROS- 4 fold) generation, depleted SOD activity (1.3 fold) and expression of enzymes particularly CuZnSOD (SOD1) and MnSOD (SOD2), increased production of AGE (2.18 fold). Besides, PKC α dependent ERK signaling pathway was found activated (1.43 fold) leading to cardiac dysfunction during hyperglycemia. Chlorogenic acid (CA) was found beneficial against hyperglycemia most probably through its antioxidant mediated activity. The outcome of this preliminary study reveals the importance of integrated approach emphasizing redox status, glycation and signaling pathways like PKC α - ERK axis for control and management of diabetic cardiomyopathy (DCM) and potential of bioactives like CA.

Maternal serum atrial natriuretic peptide (ANP) and brain-type natriuretic peptide (BNP) levels in gestational diabetes mellitus

OBJECTIVE

The aim of the study is to evaluate maternal serum atrial natriuretic peptide (ANP) and brain-type natriuretic peptide (BNP) levels in patients with getational diabetes mellitus compared with a control group.

METHODS

We have measured maternal serum ANP and BNP levels in 35 otherwise healthy and 45 gestational diabetic women between gestational week 24 and 28 referred to our unit in a cross-sectional study. Independent samples t-test or the Mann-Whitney U-test was used for comparison of two groups where appropriate.

RESULTS

Mean maternal serum homeostasis model assessment of insulin resistance (HOMA-IR), HbA1c, fasting glucose and insulin levels in gestational diabetes mellitus (GDM) group were significantly higher than the control group (p < 0.01). Mean maternal serum ANP and BNP levels of women with GDM were significantly lower than the control group (12.9 ± 9.9 versus 34.8 ± 16.9 pg/ml, p < 0.001; 416.6 ± 209.7 versus 629.7 ± 162.2 mg/dl, p < 0.001, respectively). Maternal serum ANP and BNP levels were negatively correlated with insulin levels, HbA1c and HOMA-IR values (p < 0.05).

CONCLUSIONS

Maternal serum ANP and BNP levels are significantly lower in patients with GDM. These biomarkers might be valuable in clinical setting for identifying high-risk women for developing diabetes during pregnancy.

New insights in (inter)cellular mechanisms by heart failure with preserved ejection fraction

Recently, a new paradigm for the development of heart failure with preserved ejection fraction (HFpEF) has been proposed, which identifies a systemic pro-inflammatory state induced by comorbidities as the origin of microvascular endothelial cell inflammation and subsequent concentric cardiac remodeling and dysfunction. This review further discusses the pivotal role of the inflamed endothelium in the pathogenesis of HFpEF-specific cardiac remodeling. The potential importance of reciprocal interactions of the endothelium with cardiac fibroblasts and cardiomyocytes and with the cardiac neurohumoral response in this cardiac remodeling process is outlined.

Metabolic actions of natriuretic peptides and therapeutic potential in the metabolic syndrome

Natriuretic peptides (NPs) are a group of peptide-hormones mainly secreted from the heart, signaling via c-GMP coupled receptors. NP are well known for their renal and cardiovascular actions, reducing arterial blood pressure as well as sodium reabsorption. Novel physiological functions have been discovered in recent years, including activation of lipolysis, lipid oxidation, and mitochondrial respiration. Together, these responses promote white adipose tissue browning, increase muscular oxidative capacity, particularly during physical exercise, and protect against diet-induced obesity and insulin resistance. Exaggerated NP release is a common finding in congestive heart failure. In contrast, NP deficiency is observed in obesity and in type-2 diabetes, pointing to an involvement of NP in the pathophysiology of metabolic disease. Based upon these findings, the NP system holds the potential to be amenable to therapeutical intervention against pandemic diseases such as obesity, insulin resistance, and arterial hypertension. Various therapeutic approaches are currently under development. This paper reviews the current knowledge on the metabolic effects of the NP system and discusses potential therapeutic applications.

Hyponatremia is associated with higher NT-proBNP than normonatremia after prolonged exercise

OBJECTIVE

To determine the incidence of and risk factors for exercise-associated hyponatremia (EAH) in cyclists completing a long-distance bike ride and to assess whether postexercise serum NT-proBNP concentration (brain natriuretic protein precursor) differed between riders with and without EAH.

DESIGN

Observational study.

SETTING

"Around the Bay in a Day" cycle event, October 2010.

PARTICIPANTS

One hundred thirty-nine cyclists prospectively enrolled, with 90 completing 210 or 250 km.

MAIN OUTCOME MEASURES

Body weight change and fluid intake during the event, and postevent serum sodium concentration ([Na+]) and NT-proBNP concentration ([NT-proBNP]).

RESULTS

Four riders (4.5%) were hyponatremic ([Na+] < 135 mmol/L). The lowest postride [Na+] was 126 mmol/L. Hyponatremia was associated with a mean weight gain of 3.4 kg (3.9% of total body weight). Significant negative correlations were found between postride [Na+] and change in weight (r = -0.34; P < 0.01) and fluid intake when expressed as total volume (r = -0.35; P < 0.01), mL/kg body weight (r = 0.33; P < 0.01), mL·kg·h (r = -0.27; P < 0.01), or mL/h (r = -0.29; P < 0.01). NT-proBNP concentrations levels in 3 of the 4 hyponatremic subjects were markedly elevated compared with eunatremic subjects matched for age, sex, distance ridden, training, and medical history.

CONCLUSIONS

Exercise-associated hyponatremia was found to occur in 4.5% of the study group and was associated with weight gain during a prolonged bike ride. Postride [Na+] varied inversely with weight change and with fluid intake. Three of 4 hyponatremic riders had significant elevations of [NT-proBNP]. These results support the hypothesis that overconsumption of hypotonic fluids in this setting is the most important cause of EAH.

The effect of diabetes on the diagnostic and prognostic performance of mid-region pro-atrial natriuretic peptide and mid-region pro-adrenomedullin in patients with acute dyspnea

Serum mid-regional pro-atrial natriuretic peptide (MR-proANP) and pro-adrenomedullin (MR-proADM) are novel biomarkers for acute heart failure (AHF). Like other AFH biomarkers, the performance of these tests are affected by the presence of clinical variables such as renal failure and obesity. In a substudy of the Biomarkers from Acute Heart Failure Study, we show that diabetes did not influence the performance of these markers with regards to AHF diagnosis or 90-day all cause death. However, in patients without AHF, increased MR-proADM alone was associated with the presence of diabetes.

B-type natriuretic peptide (BNP) affects the initial response to intravenous glucose: a randomised placebo-controlled cross-over study in healthy men

AIMS/HYPOTHESIS

B-type natriuretic peptide (BNP) is a hormone released from cardiomyocytes in response to cell stretching and elevated in heart failure. Recent observations indicate a distinct connection between chronic heart failure and diabetes mellitus. This study investigated the role of BNP on glucose metabolism.

METHODS

Ten healthy volunteers (25 ± 1 years; BMI 23 ± 1 kg/m(2); fasting glucose 4.6 ± 0.1 mmol/l) were recruited to a participant-blinded investigator-open placebo-controlled cross-over study, performed at a university medical centre. They were randomly assigned (sequentially numbered opaque sealed envelopes) to receive either placebo or 3 pmol kg(-1) min(-1) BNP-32 intravenously during 4 h on study day 1 or 2. One hour after beginning the BNP/placebo infusion, a 3 h intravenous glucose tolerance test (0.33 g/kg glucose + 0.03 U/kg insulin at 20 min) was performed. Plasma glucose, insulin and C-peptide were frequently measured.

RESULTS

Ten volunteers per group were analysed. BNP increased the initial glucose distribution volume (13 ± 1% body weight vs 11 ± 1%, p < 0.002), leading to an overall reduction in glucose concentration (p < 0.001), particularly during the initial 20 min of the test (p = 0.001), accompanied by a reduction in the initial C-peptide levels (1.42 ± 0.13 vs 1.62 ± 0.10 nmol/l, p = 0.015). BNP had no impact on beta cell function, insulin clearance or insulin sensitivity and induced no adverse effects.

CONCLUSIONS/INTERPRETATION

Intravenous administration of BNP increases glucose initial distribution volume and lowers plasma glucose concentrations following a glucose load, without affecting beta cell function or insulin sensitivity. These data support the theory that BNP has no diabetogenic properties, but improves metabolic status in men, and suggest new questions regarding BNP-induced differences in glucose availability and signalling in various organs/tissues.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01324739

FUNDING

The study was funded by Jubilée Fonds of the Austrian National Bank (OeNB-Fonds).

Diabetic neuropathy and heart failure: role of neuropeptides

Cardiovascular autonomic neuropathy (CAN), in which patients present with damage of autonomic nerve fibres, is one of the most common complications of diabetes. CAN leads to abnormalities in heart rate and vascular dynamics, which are features of diabetic heart failure. Dysregulated neurohormonal activation, an outcome of diabetic neuropathy, has a significant pathophysiological role in diabetes-associated cardiovascular disease. Key players in neurohormonal activation include cardioprotective neuropeptides and their receptors, such as substance P (SP), neuropeptide Y (NPY), calcitonin-gene-related peptide (CGRP), atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). These neuropeptides are released from the peripheral or autonomic nervous system and have vasoactive properties. They are further implicated in cardiomyocyte hypertrophy, calcium homeostasis, ischaemia-induced angiogenesis, protein kinase C signalling and the renin-angiotensin-aldosterone system. Therefore, dysregulation of the expression of neuropeptides or activation of the neuropeptide signalling pathways can negatively affect cardiac homeostasis. Targeting neuropeptides and their signalling pathways might thus serve as new therapeutic interventions in the treatment of heart failure associated with diabetes. This review discusses how neuropeptide dysregulation in diabetes might affect cardiac functions that contribute to the development of heart failure.

Long-term treatment with atrial natriuretic peptide inhibits ATP production and insulin secretion in rat pancreatic islets

Atrial natriuretic peptide (ANP) levels correlate with hyperglycemia in diabetes mellitus, but ANP effects on pancreatic islet β-cell insulin secretion are controversial. ANP was investigated for short- and long-term effects on insulin secretion and mechanisms regulating secretion in isolated rat pancreatic islets. A 3-h incubation with ANP did not affect basal or glucose-stimulated islet insulin secretion. However, 7-day culture of islets with 5.5 mM glucose and ANP (1 nM - 1 μM) markedly inhibited subsequent glucose (11 mM)-stimulated insulin secretion; total islet insulin content was not affected. Following ANP removal for 24 h, the islet insulin-secretory response to glucose was restored. The insulin-secretory response to other insulin secretagogues, including α-ketoisocaproic acid, forskolin, potassium chloride, and ionomycin were also markedly inhibited by chronic exposure to ANP. However, the combination of potassium chloride and α-ketoisocaproic acid was sufficient to overcome the inhibitory effects of ANP on insulin secretion. The glucose-stimulated increases in islet ATP levels and the ATP/ADP ratio were completely inhibited in ANP 7-day-treated islets vs. control; removal of ANP for 24 h partially restored the glucose response. ANP did not affect islet glycolysis. ANP significantly increased levels of islet activated hormone-sensitive lipase and the expression of uncoupling protein-2 and peroxisome proliferator-activated receptor-δ and -α. Although islet ANP-binding natriuretic peptide receptor-A levels were reduced to 60% of control after 7-day culture with ANP, the ANP-stimulated cGMP levels remained similar to control islet levels. Thus, long-term exposure to ANP inhibits glucose-stimulated insulin secretion and ATP generation in isolated islets.

The atrial natriuretic peptide and guanylyl cyclase-A system modulates pancreatic beta-cell function

Atrial natriuretic peptide (ANP) and its guanylyl cyclase-A (GC-A) receptor are being involved in metabolism, although their role in the endocrine pancreas is still greatly unknown. The aim of this work is to study a possible role for the ANP/GC-A system in modulating pancreatic beta-cell function. The results presented here show a direct effect of the GC-A receptor in regulating glucose-stimulated insulin secretion (GSIS) and beta-cell mass. GC-A activation by its natural ligand, ANP, rapidly blocked ATP-dependent potassium (K(ATP)) channel activity, increased glucose-elicited Ca(2+) signals, and enhanced GSIS in islets of Langerhans. The effect in GSIS was inhibited in islets from GC-A knockout (KO) mice. Pancreatic islets from GC-A KO mice responded to increasing glucose concentrations with enhanced insulin secretion compared with wild type (WT). Remarkably, islets from GC-A KO mice were smaller, presented lower beta-cell mass and decreased insulin content. However, glucose-induced Ca(2+) response was more vigorous in GC-A KO islets, and basal K(ATP) channel activity in GC-A KO beta-cells was greatly diminished compared with WT. When protein levels of the two K(ATP) channel constitutive subunits sulfonylurea receptor 1 and Inward rectifier potassium channel 6.2 were measured, both were diminished in GC-A KO islets. These alterations on beta-cell function were not associated with disruption of glucose tolerance or insulin sensitivity in vivo. Glucose and insulin tolerance tests were similar in WT and GC-A KO mice. Our data suggest that the ANP/GC-A system may have a modulating effect on beta-cell function.

Atrial natriuretic peptide promotes pancreatic islet beta-cell growth and Akt/Foxo1a/cyclin D2 signaling

The adult differentiated insulin-secreting pancreatic islet beta-cell experiences slow growth. This study shows that atrial natriuretic peptide (ANP) stimulates cell proliferation and [(3)H]thymidine incorporation in INS-1E glucose-sensitive rat beta-cell line cells and isolated rat islet DNA. In addition, cGMP, the second messenger of natriuretic peptide receptors (NPR) A and B, stimulated islet DNA biosynthesis. The NPR-A receptor was expressed in INS-1E cells and islets. ANP-stimulated INS-1E cell DNA biosynthesis was blocked by preincubation with LY294002 (50 microM), an inhibitor of phosphatidylinositol 3'-kinase (PI3K). An indicator of cell cycle progression, cyclin D2 mRNA was increased by 2- to 3-fold in ANP- or 8-Br-cGMP-treated INS-1E cells and islets, and these responses were inhibited by LY294002. ANP and 8-Br-cGMP stimulated the phosphorylation of Akt and Foxo1a in INS-1E cells and islets, and LY294002 inhibited these responses. In contrast, ANP reduced the levels of phospho-ERK in INS-1E cells. Pancreas duodenum homeobox-1 (PDX-1) is essential for pancreas development, insulin production, and glucose homeostasis, and ANP increased PDX-1 mRNA levels by 2- to 3-fold in INS-1E cells and islets. The levels of glucokinase mRNA in islets and INS-1E cells were also increased in response to ANP. The evidence suggests that pancreatic beta-cell NPR-A stimulation results in activation of a growth-promoting signaling pathway that includes PI3K/Akt/Foxo1a/cyclin D2. These data support the conclusion that the activation of Akt by ANP or 8-Br-cGMP promotes cyclin D2, PDX-1, and glucokinase transcription by phosphorylating and restricting Foxo1a activity.

Heart failure in the diabetic patient

This review examines the extent of the increased rate of heart failure (HF) in the diabetic patient, along with the possible causes for this increase and the poor prognosis associated with HF. Also reviewed are the therapies that are available for the treatment of diabetic HF and whether intensifying the use of these therapies might improve the worsened clinical outcomes for the patient who has diabetes.

Atrial natriuretic peptide increases urinary albumin excretion in people with normoalbuminuric type-2 diabetes

BACKGROUND

Atrial natriuretic peptide (ANP) is elevated in patients with type-2 diabetes and microalbuminuria. The purpose of this study is to evaluate if ANP increases Urinary Albumin Eaxcretion Rate (UAER) in type-2 diabetes.

METHODS

Eight normoalbuminuric diabetic subjects underwent a randomised single blind study of 60 min intravenous infusion of ANP or vehicle. Eight non-diabetic controls underwent ANP infusion alone. Seven normoalbuminuric type-2 diabetes subjects received further ANP infusions during euglycaemia and during hyperglycaemia.

RESULTS

ANP increased urinary sodium (191.3 +/- 80.7 to 529.2 +/- 263.4 mumol/min, mean +/- SD, and P < 0.001) and UAER (72.2 +/- 73.4 to 224.9 +/- 182.9.5 mug/min, and P < 0.01) in diabetic subjects. In controls, UAER did not change significantly (P = 0.16); however, the natriuretic response to ANP was similar to diabetic subjects (P = 0.98). Hyperglycaemic did not enhance the albuminuric response to ANP (P = 0.88).

CONCLUSION

ANP increases UAER in normoalbuminuric type-2 diabetic subjects.

Participation of glucose transporters on atrial natriuretic peptide-induced glucose uptake by adult and neonatal cardiomyocytes under oxygenation and hypoxia

Natriuretic peptides, beside their endocrine actions, have paracrine functions which include regulating glucose uptake and metabolism. Atrial natriuretic peptide (ANP) actions are mediated by cGMP which is implicated in the metabolic adaptation of glucose metabolism to oxygen deprivation in the heart. Although, it has been reported that ANP increases glucose uptake, cGMP decreases it. The aim of the present paper was to evaluate the role of the glucose transporters 1 and 4 (GLUTS), in glucose uptake produced by ANP in fatty acid-dependent adult cardiomyocytes and glucose-dependent neonatal cardiomyocytes under oxygenation and hypoxia, which reverts adult metabolism to glucose-dependent. We also explored if the calcium-calmodulin complex participates in ANP-induced increase in glucose uptake. Neonatal cells had a higher glucose uptake than adult cells and GLUT 1 participated in basal uptake in both cell types. Hypoxia increased glucose uptake in adult cardiomyocytes but not in neonatal cells and this increase in glucose uptake was mediated by GLUT4. ANP increased glucose uptake in both adult and neonatal myocytes, under oxygenation and hypoxia, and GLUT4 favored this increase. Neonatal cells were less sensitive to ANP. Trifluoperazine, a calcium-calmodulin blocker, inhibited the ANP-induced increase in glucose uptake. This suggests that ANP promotes GLUT 4 calcium-mediated recruitment to the cell membrane. In conclusion, glucose uptake regulation is one of the paracrine metabolic effects of ANP in adult and neonatal cardiomyocytes under oxygenation and hypoxia. This effect of this peptide could explain the beneficial effects found in the internal medicine and surgical fields.

Alterations in atrial natriuretic peptide and its receptor levels in long-term, streptozotocin-induced, diabetes in rats

Diabetes mellitus (DM) shows a markedly increased incidence of cardiovascular pathology that leads to hypertension, endothelial macro- and microangiopathy, diabetic nephropathy, and myocardial infarction. Atrial natriuretic peptide (ANP), is a 28 amino acid peptide hormone synthesized mainly by the heart atria and ventricles. It has potent diuretic and natriuretic properties. In this article the effect of long-term DM on blood plasma, kidney, and heart atrial and ventricular ANP concentrations were evaluated in streptozotocin (STZ)-induced 8-month diabetic and control rats by using radioimmunoassay (RIA). Moreover, ANP receptors in STZ-induced, 8-month diabetic rat kidneys were studied by receptor autoradiography. In addition, the expression of ANP concentrations in the kidney of diabetic and control rats was evaluated by means of immunohistochemistry. Body weight loss and increased blood glucose levels were used as indices of DM in the STZ-induced diabetic rats. Our results showed significantly higher ANP concentrations in diabetic plasma (P < 0.05), kidney (P < 0.01), heart atria (P < 0.05), and ventricles (P < 0.01) compared to controls. We also demonstrated a significant decrease in ANP receptors in the outer cortex (P < 0.05), juxtaglomerular medulla (P < 0.05), and papilla (P < 0.05) of 8-month diabetic rat kidneys compared to controls. The observed increase in ANP levels in plasma and kidney could play a role in the development of diabetic nephropathy: probably by reducing the levels of ANP receptors in diabetic kidney. Furthermore, the role of ANP in the STZ-induced diabetic heart merits additional study.

Elevated plasma concentrations of atrial and brain natriuretic peptide in type 1 diabetic subjects

BACKGROUND

The intravenous infusion of atrial (ANP) and brain (BNP) natriuretic peptides have been shown to increase urinary albumin excretion in type 1 diabetes.

AIMS

To measure plasma ANP and BNP concentrations in patients with type 1 diabetes and to examine the parameters associated with elevated plasma concentrations. Methods We measured plasma ANP and BNP concentrations, UAER, HbA1C systolic blood pressure, and left ventricular mass index. Plasma ANP and BNP were also measured in non-diabetic control subjects for comparison.

RESULTS

Using multivariate regression analysis plasma ANP correlated positively with HbA1C (1.9 + 0.47, p = 0.0002), UAER (0.37 + 0.05, p = 0.00001), SBP (1.26 + 0.5, p = 0.01) and LVMI (00.46 + 0.25, p = 0.07). BNP was positively related with LVMI (0.95 + 0.4, p = 0.02), and UAER (0.56 + 0.08, p = 0.001).

CONCLUSIONS

Plasma concentrations of ANP and BNP are elevated in some patients with type 1 diabetes. Plasma ANP concentrations are closely related to UAER and elevated plasma concentrations are associated with poor glycaemic control and systemic hypertension. Plasma BNP concentration is related to LVMI.

Differential autocrine modulation of atrial and ventricular potassium currents and of oxidative stress in diabetic rats

The autocrine modulation of cardiac K(+) currents was compared in ventricular and atrial cells (V and A cells, respectively) from Type 1 diabetic rats. K(+) currents were measured by using whole cell voltage clamp. ANG II was measured by ELISA and immunofluorescent labeling. Oxidative stress was assessed by immunofluorescent labeling with dihydroethidium, a measure of superoxide ions. In V cells, K(+) currents are attenuated after activation of the renin-angiotensin system (RAS) and the resulting ANG II-mediated oxidative stress. In striking contrast, these currents are not attenuated in A cells. Inhibition of the angiotensin-converting enzyme (ACE) also has no effect, in contrast to current augmentation in V cells. ANG II levels are enhanced in V, but not in A, cells. However, the high basal ANG II levels in A cells suggest that in these cells, ANG II-mediated pathways are suppressed, rather than ANG II formation. Concordantly, superoxide ion levels are lower in diabetic A than in V cells. Several findings indicate that high atrial natriuretic peptide (ANP) levels in A cells inhibit RAS activation. In male diabetic V cells, in vitro ANP (300 nM-1 muM, >5 h) decreases oxidative stress and augments K(+) currents, but not when excess ANG II is present. ANP has no effect on ventricular K(+) currents when the RAS is not activated, as in control males, in diabetic males treated with ACE inhibitor and in diabetic females. In conclusion, the modulation of K(+) currents and oxidative stress is significantly different in A and V cells in diabetic rat hearts. The evidence suggests that this is largely due to inhibition of RAS activation and/or action by ANP in A cells. These results may underlie chamber-specific arrhythmogenic mechanisms.

Alterations in atrial natriuretic peptide and its receptors in streptozotocin-induced diabetic rat kidneys

In this study the effect of diabetes mellitus on atrial natriuretic peptide (ANP) receptors in streptozotocin- (STZ-) induced diabetic rat kidneys was studied. Moreover, plasma ANP concentration was evaluated in diabetic and control rats by using radioimmunoassay. In addition, the expression of ANP in the kidneys of control and diabetic rats was evaluated by immunohistochemistry. Body-weight loss and increased glucose levels were used as indices of diabetes mellitus in the STZ-induced rats. There was a significant loss in the body weight of the diabetic rats compared to controls. The efficacy of STZ administration was confirmed by rising blood glucose levels, which were significantly higher in diabetic rats compared to controls. Plasma ANP concentration was significantly greater in the diabetic rats in comparison with controls. Moreover, our immunohistochemical results show that the expression of ANP in diabetic rats was higher than that in age-matched controls. ANP was observed in the cells lining the proximal convoluted tubules in the cortex. The distribution and levels of ANP receptors in the kidneys of diabetic rats and age-matched controls were investigated using quantitative receptor autoradiography. Our results demonstrate significant decrease in ANP receptors in the kidneys of the diabetic rats compared to controls. The significant decrease was found in the juxtaglomerular medulla, inner medulla, and the papillae. The decrease in ANP receptors observed in the diabetic kidneys could have pathological consequences resulting in renal resistance to ANP in diabetes.

Screening for heart disease in diabetic subjects

BACKGROUND

The prevalence of left ventricular hypertrophy (LVH), coronary artery disease, and subclinical cardiomyopathy in diabetic patients without known cardiac disease is unclear. We sought the frequency of these findings to determine whether plasma brain natriuretic peptide (BNP) could be used as an alternative screening tool to identify subclinical LV dysfunction.

METHODS

Asymptomatic patients with diabetes mellitus without known cardiac disease (n = 101) underwent clinical evaluation, measurement of BNP, exercise stress testing, and detailed echocardiographic assessment. After exclusion of overt dysfunction or ischemia, subclinical myocardial function was sought on the basis of myocardial systolic (Sm) and diastolic velocity (Em). Association was sought between subclinical dysfunction and clinical, biochemical, exercise, and echocardiographic variables. RESULTS; Of 101 patients, 22 had LVH and 16 had ischemia evidenced by exercise-induced wall motion abnormalities. Only 4 patients had abnormal BNP levels; BNP was significantly increased in patients with LVH. After exclusion of LVH and coronary artery disease, subclinical cardiomyopathy was identified in 24 of 66 patients. Subclinical disease could not be predicted by BNP.

CONCLUSIONS

Even after exclusion of asymptomatic ischemia and hypertrophy, subclinical systolic and diastolic dysfunction occurs in a significant number of patients with type 2 diabetes. However, screening approaches, including BNP, do not appear to be sufficiently sensitive to identify subclinical dysfunction, which requires sophisticated echocardiographic analysis.

Osmoregulation of atrial myocytic ANP release: osmotransduction via cross-talk between L-type Ca2+ channel and SR Ca2+ release

Hyperosmolality has been known to increase ANP release. However, its physiological role in the regulation of atrial myocytic ANP release and the mechanism by which hyperosmolality increases ANP release are to be defined. The purpose of the present study was to define these questions. Experiments were performed in perfused beating rabbit atria. Hyperosmolality increased atrial ANP release, cAMP efflux, and atrial dynamics in a concentration-dependent manner. The osmolality threshold for the increase in ANP release was as low as 10 mosmol/kgH2O (approximately 3%) above the basal levels (1.55 +/- 1.71, 17.19 +/- 3.11, 23.15 +/- 5.49, 54.04 +/- 11.98, and 62.00 +/- 13.48% for 10, 20, 30, 60, and 100 mM mannitol, respectively; all P < 0.01). Blockade of sarcolemmal L-type Ca2+ channel activity, which increased ANP release, attenuated hyperosmolality-induced increases in ANP release (-13.58 +/- 4.68% vs. 62.00 +/- 13.48%, P < 0.001) and cAMP efflux but not atrial dynamics. Blockade of the Ca2+ release from the sarcoplasmic reticulum, which increased ANP release, attenuated hyperosmolality-induced increases in ANP release (13.44 +/- 7.47% vs. 62.00 +/- 13.48%, P < 0.01) and dynamics but not cAMP efflux. Blockades of Na+-K+-2Cl- cotransporter, Na+/H+ exchanger, and Na+/Ca2+ exchanger had no effect on hyperosmolality-induced increase in ANP release. The present study suggests that hyperosmolality regulates atrial myocytic ANP release and that the mechanism by which hyperosmolality activates ANP release is closely related to the cross-talk between the sarcolemmal L-type Ca2+ channel activity and sarcoplasmic reticulum Ca2+ release, possibly inactivation of the L-type Ca2+ channels.

Cardiac gene expression of natriuretic substances is altered in streptozotocin-induced diabetes during angiotensin II-induced pressure overload

OBJECTIVE

To gain insight into the cardiac adaptive mechanisms in diabetes, we studied whether angiotensin II (Ang II) alters expression of the atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP) and adrenomedullin (AM) genes in the left ventricle of the diabetic rat heart.

METHODS

Diabetes was induced by streptozotocin (STZ; 60 mg/kg body weight intravenously). During the last 24 h of 2.5 or 7 weeks of treatment of male Wistar rats with STZ or vehicle, Ang II (33 microg/kg per h) was administered via osmotic minipumps.

RESULTS

Diabetes was associated with an increased left ventricular weight to body weight (LV/BW) ratio, an index of left ventricular hypertrophy, at week 7 but not at week 2.5, and with increased ANP mRNA content at 2.5 weeks, but not with altered expression of the AM and BNP genes. Mean arterial pressure and LV/BW ratio were increased by Ang II in all groups except in the 7-week diabetic group. Levels of ANP mRNA were increased fourfold (P < 0.001) and threefold (P < 0.05) by Ang II at 2.5 and 7 weeks in control animals, respectively, and 11-fold (P < 0.001) and sevenfold (P < 0.001) at 2.5 and 7 weeks in diabetic animals, respectively. Ang II increased ventricular concentrations of BNP mRNA in control and diabetic animals at 2.5 weeks (1.3-fold, P < 0.001; and 1.6-fold, P < 0.001) and at 7 weeks (1.3-fold, P < 0.05; and 1.8-fold, P < 0.001), respectively. Left ventricular levels of adrenomedullin mRNA were increased by treatment with Ang II for 24 h in 2.5-week diabetic animals.

CONCLUSION

Ang II markedly increased the levels of natriuretic peptide mRNAs in the left ventricle of normal and diabetic rat hearts, whereas it increased adrenomedullin mRNA levels only in 2.5-week diabetic rats and failed to cause hypertension in 7-week diabetic rats. Left ventricular levels of ANP and BNP mRNA were increased by Ang II in diabetic animals more than the additive effects of diabetes and Ang II alone, showing that Ang II induced an amplified response with respect to cardiac concentrations of ANP and BNP in diabetes.

Heart failure: the frequent, forgotten, and often fatal complication of diabetes

There is a high frequency of heart failure (HF) accompanied by an increased mortality risk for patients with diabetes. The poor prognosis of these patients has been explained by an underlying diabetic cardiomyopathy exacerbated by hypertension and ischemic heart disease. In these patients, activation of the sympathetic nervous system results in increased myocardial utilization of fatty acids and induction of fetal gene programs, decreasing myocardial function. Activation of the renin-angiotensin system results in myocardial remodeling. It is imperative for physicians to intercede early to stop the progression of HF, yet at least half of patients with left ventricular dysfunction remain undiagnosed and untreated until advanced disease causes disability. This delay is largely because of the asymptomatic nature of early HF, which necessitates more aggressive assessment of HF risk factors and early clinical signs. Utilization of beta-blockade, ACE inhibitors, or possibly angiotensin receptor blockers is essential in preventing remodeling with its associated decline in ventricular function. beta-Blockers not only prevent, but may also reverse, cardiac remodeling. Glycemic control may also play an important role in the therapy of diabetic HF. The adverse metabolic side effects that have been associated with beta-adrenergic inhibitors in the diabetic patient may be circumvented by use of a third-generation beta-blocker. Prophylactic utilization of ACE inhibitors and beta-blockers to avoid, rather than await, the need to treat HF should be considered in high-risk diabetic patients.

Brain natriuretic peptide increases urinary albumin and alpha-1 microglobulin excretion in Type 1 diabetes mellitus

Atrial natriuretic peptide (ANP) increases urinary albumin excretion in Type 1 diabetes mellitus (DM). Brain natriuretic peptide (BNP) is structurally and functionally related to ANP, but its effect on urine albumin excretion rate (UAER) is unknown.

AIMS

To compare the albuminuric effects of intravenous infusion of ANP and BNP, and to assess the effect of both peptides on tubular protein excretion.

METHODS

Eight subjects with Type 1 DM were randomised to a three leg, double blind, and placebo controlled study. On each study day, subjects were euglycaemic clamped and subsequently water loaded (20 mL/kg orally, plus urine losses) to steady state diuresis. When in steady state, creatinine clearance was estimated in three separate 1 hour periods. At the end of the first period, a 1 hour intravenous infusion of either placebo, ANP 0.025 microg/kg/min, or BNP 0.025 microg/kg/min was administered. There followed a 1 hour recovery period. Urine was collected at 15 min intervals for estimation of urine albumin (ACR) and alpha1 microglobulin creatinine ratio (MCR). Results were analysed by anova.

RESULTS

Creatinine clearance was similar on the three study days, and was unaltered by any infusion. ACR was unaltered by placebo (1.3 +/- 0.5-1.2 +/- 0.4 mg/mmol, mean +/- SD, p = 0.81), but increased compared to placebo with infusion of both ANP (1.2 +/- 0.4-9.8 +/- 8.4 mg/mmol, P = 0.0004), and BNP (1.1 +/- 0.4-13.4 +/- 8.6 mg/mmol, P = 0.0001). The MCR was unaltered by placebo infusion (P = 0.89), but increased compared with placebo after infusion of ANP (5.4 +/- 0.9-12.3 +/- 4.2 mg/mmol, P < 0.0001), and BNP (5.4 +/- 0.8-12.1 +/- 2.5 mg/mmol, P < 0.0001).

CONCLUSIONS

Intravenous infusion of BNP and ANP both increase the urine excretion of albumin and the tubular protein alpha1 microglobulin, independent of creatinine clearance.