Ebru Arioglu

The influence of diabetes on cardiac β-adrenoceptor subtypes

Despite the significant developments in the treatment of diabetes mellitus, diabetic patients still continue to suffer from cardiac complications. The increase of cardiac adrenergic drive may ultimately contribute to the development and progression of diabetic cardiomyopathy. β-Adrenoceptors play an important role in the regulation of heart function. However, responsiveness of diabetic heart to β-adrenoceptor agonist stimulation is diminished. The chronotropic responses mediated by β1-subtype, which is mainly responsible for cardiac effects of catecholamines are decreased in the atria of diabetic rats. The expression of cardiac β1-subtype is significantly decreased in diabetic rats as well. β2-Adrenoceptors also increase cardiac function. Although the expression of this subtype is slightly decreased in diabetic rat hearts, β2-mediated chronotropic responses are preserved. On the other hand, functional β3-adrenoceptor subtype was characterized in human heart. Interestingly, stimulation of cardiac β3-adrenoceptors, on the contrary of β1- and β2-subtypes, mediates negative inotropic effect in human ventricular muscle. Cardiac β3-adrenoceptors are upregulated in experimental diabetes as well as in human heart failure. These findings suggest that each β-adrenoceptor subtype may play an important role in the pathophysiology of diabetes-induced heart disease. However, it is still not known whether the changes in the expression and/or responsiveness of β-adrenoceptors are adaptive or maladaptive. Therefore, this review outlines the potential roles of these receptor subtypes in cardiac pathologies of diabetes.

Diabetes decreases mRNA levels of calcium-release channels in human atrial appendage

Patients with chronic diabetes mellitus usually develop reductions in rate and force of cardiac contractions. Since calcium-release channels (ryanodine receptors (RyRs) and inositol 1,4,5-trisphosphate receptors (IP3Rs)) play integral roles in effecting these processes, we rationalize that alterations in their expression may underlie these defects. To test this hypothesis, right atrial appendages were obtained from diabetic (65.0 ± 4.5 years) and nondiabetic (56.2 ± 2.6 years) patients undergoing coronary arterial by-pass grafting and reverse transcription-polymerase chain reactions were used to compare steady state levels of mRNA encoding the three major isoforms of RyRs and IP3Rs. In this study we did not detect either RyR1 or RyR3 in human atrial appendage. When compared with nondiabetic patients, mRNA encoding RyR2 from diabetic patients decreased by 74.2 ± 6.2% (p< 0.01). Diabetes also significantly decreased steady-state levels of mRNA encoding the IP3Rs in human atrial appendage. IP3R1 decreased by 24.2 ± 4.6%, IP3R2 decreased by 63.0 ± 4.6% and IP3R3 decreased by 55.5 ± 6.5%. Since a reduction in steady-state mRNA is usually indicative of a decrease in protein levels, these data suggest that the decrease in chronotropy and inotropy seen in chronic diabetic patients may be due in part to a decrease in expression of calcium-release channels. (Mol Cell Biochem 263: 143-150, 2004).Patients with chronic diabetes mellitus usually develop reductions in rate and force of cardiac contractions. Since calcium-release channels (ryanodine receptors (RyRs) and inositol 1,4,5-trisphosphate receptors (IP3Rs)) play integral roles in effecting these processes, we rationalize that alterations in their expression may underlie these defects. To test this hypothesis, right atrial appendages were obtained from diabetic (65.0 ± 4.5 years) and nondiabetic (56.2 ± 2.6 years) patients undergoing coronary arterial by-pass grafting and reverse transcription-polymerase chain reactions were used to compare steady state levels of mRNA encoding the three major isoforms of RyRs and IP3Rs. In this study we did not detect either RyR1 or RyR3 in human atrial appendage. When compared with nondiabetic patients, mRNA encoding RyR2 from diabetic patients decreased by 74.2 ± 6.2% (p< 0.01). Diabetes also significantly decreased steady-state levels of mRNA encoding the IP3Rs in human atrial appendage. IP3R1 decreased by 24.2 ± 4.6%, IP3R2 decreased by 63.0 ± 4.6% and IP3R3 decreased by 55.5 ± 6.5%. Since a reduction in steady-state mRNA is usually indicative of a decrease in protein levels, these data suggest that the decrease in chronotropy and inotropy seen in chronic diabetic patients may be due in part to a decrease in expression of calcium-release channels. (Mol Cell Biochem 263: 143–150, 2004)

The effects of chronic trimetazidine treatment on mechanical function and fatty acid oxidation in diabetic rat hearts

Clinical and experimental evidence suggest that increased rates of fatty acid oxidation in the myocardium result in impaired contractile function in both normal and diabetic hearts. Glucose utilization is decreased in type 1 diabetes, and fatty acid oxidation dominates for energy production at the expense of an increase in oxygen requirement. The objective of this study was to examine the effect of chronic treatment with trimetazidine (TMZ) on cardiac mechanical function and fatty acid oxidation in streptozocin (STZ)-diabetic rats. Spontaneously beating hearts from male Sprague-Dawley rats were subjected to a 60-minute aerobic perfusion period with a recirculating Krebs-Henseleit solution containing 11 mmol/L glucose, 100 muU/mL insulin, and 0.8 mmol/L palmitate prebound to 3% bovine serum albumin (BSA). Mechanical function of the hearts, as cardiac output x heart rate (in (mL/min).(beats/min).10-2), was deteriorated in diabetic (73 +/- 4) and TMZ-treated diabetic (61 +/- 7) groups compared with control (119 +/- 3) and TMZ-treated controls (131 +/- 6). TMZ treatment increased coronary flow in TMZ-treated control (23 +/- 1 mL/min) hearts compared with untreated controls (18 +/- 1 mL/min). The mRNA expression of 3-ketoacyl-CoA thiolase (3-KAT) was increased in diabetic hearts. The inhibitory effect of TMZ on fatty acid oxidation was not detected at 0.8 mmol/L palmitate in the perfusate. Addition of 1 mumol/L TMZ 30 min into the perfusion did not affect fatty acid oxidation rates, cardiac work, or coronary flow. Our results suggest that higher expression of 3-KAT in diabetic rats might require increased concentrations of TMZ for the inhibitory effect on fatty acid oxidation. A detailed kinetic analysis of 3-KAT using different concentrations of fatty acid will determine the fatty acid inhibitory concentration of TMZ in diabetic state where plasma fatty acid levels are increased.

Decreased expression of β1- and β2-adrenoceptors in human diabetic atrial appendage

BackgroundUsing the streptozotocin-induced diabetic rat model, we have recently showed that the expression and function of β1-adrenoreceptor were decreased in the diabetic rat heart. However, the effect of diabetes on expression of β-adrenoreceptors in human cardiac tissue remains undefined. Therefore, the focus of the present study was to investigate the effect of diabetes on mRNA encoding β1- and β2-ARs in human atrial tissues.MethodsRight atrial appendages from five diabetic (mean age 65 ± 4.5; 4 female, 1 male) and five nondiabetic patients (mean age 56.2 ± 2.8; 4 male, 1 female) undergoing coronary artery bypass grafting were collected and assayed using reverse transcriptase-polymerase chain reaction (RT-PCR) for their mRNA content. No patient from these two groups suffered from acute myocardial infarction and/or failure. All diabetic patients received insulin for at least two years and had been diagnosed as diabetics for at least five years.ResultsWhen compared with levels in nondiabetics, steady state levels of mRNA encoding β1-adrenoreceptor decreased by 69.2 ± 7.6 % in diabetic patients while β2-adrenoreceptor mRNA decreased by 32.2 ± 5.5 % (p < 0.001).ConclusionsOur findings show a decreased expression of β1- and β2-adrenoreceptors in human diabetic atrial appendage.

Role of Beta-3-Adrenoceptor in Catecholamine-Induced Relaxations in Gastric Fundus from Control and Diabetic Rats

The contribution of β-adrenoceptor subtypes to the catecholamine-mediated relaxations in gastric fundus from control and streptozotocin (STZ)-induced diabetic rats were investigated. Isolated organ bath studies and molecular techniques were used to characterize the β-adrenoceptor subtypes mediating relaxation of rat gastric fundus. Isoprenaline-mediated relaxation was not significantly changed by nadolol (β1-/β2-adrenoceptor antagonist; 1 µmol/l) but only shifted to the right by SR59230A (3-(2-ethylphenoxy)-1-[[(1S)-1,2,3,4-tetrahydronaphth-1-yl]amino]-(2S)-2-propanol oxalate salt, 0.1–1 µmol/l), a selective β3-adrenoceptor antagonist, in a competitive manner. Relaxant responses to noradrenaline were antagonized in a concentration-dependent manner by SR59230A (0.1–1 µmol/l), but not by metoprolol (selective β1-adrenoceptor antagonist; 0.1–1 µmol/l) and ICI-118551 (1-[2,3-(dihydro-7-methyl-1Hinden- 4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride, selective β2-adrenoceptor antagonist; 0.1–1 µmol/l). SR59230A (1 µmol/l) also caused a significant rightward shift in fenoterol-induced relaxation while ICI-118551 (1 µmol/l) did not have any effect. Selective β3-adrenoceptor agonist, BRL37344 ([4-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]phenoxy]acetic acid), caused biphasic relaxation which was not affected by nadolol (1 µmol/l). SR59230A (1 µmol/l) abolished only the first phase of BRL37344 response. β1-, β2- and β3-adrenoceptor mRNA expressions have been detected in a similar intensity in gastric fundus from control rats. Experimental diabetes caused a significant decrease in Emax and pD2 values of isoprenaline and noradrenaline. Diabetes also reduced Emax but not pD2 value of the first component of BRL37344-induced relaxation response. The band intensity of mRNA transcript of β3-adrenoceptor was reduced in diabetics while no alteration has been found for β1- and β2-adrenoceptor mRNA transcripts between groups. These results show that functional β-adrenoceptor subtype involved in catecholamine-mediated relaxations is β3-adrenoceptor, and its function and mRNA expression are decreased in diabetes.

Acetylsalicylic acid protects erectile function in diabetic rats

We aimed to evaluate the effect of acetylsalicylic acid (ASA) treatment on diabetes‐induced erectile dysfunction. Adult male Sprague–Dawley rats were divided into four groups as follows: (i) control (C), (ii) diabetic (D), (iii) ASA‐treated control (C+ASA) and (iv) ASA‐treated diabetic (D+ASA) groups. In groups 2 and 4, diabetes was induced by injection of 35 mg kg−1 streptozotocin. ASA (100 mg kg−1 day−1, orally) was administrated to rats in groups 3 and 4 for 8 weeks. Both intracavernosal pressure (ICP) and mean arterial blood pressure (MAP) were measured in in vivo studies. In organ bath, the relaxation responses to acetylcholine (ACh), electrical field stimulation (EFS) and sodium nitroprusside were tested in corpus cavernosum (CC) strips. The mRNA expression for neuronal nitric oxide synthase (nNOS) was calculated using reverse transcription polymerase chain reaction technique. In in vivo experiments, diabetic rats displayed reduced ICP/MAP values, which were normalised with ASA treatment. The relaxant response to high‐dose ACh and EFS at low frequencies (1–8 Hz) in CC strips from the D+ASA group were significantly higher when compared to the D group. Treatment with ASA normalised the raised mRNA expressions of nNOS in diabetic penile tissues. ASA may be involved in mRNA of protein synthesis of NO released from nonadrenergic and noncholinergic cavernosal nerve in diabetes.

The effect of diabetes mellitus on α1-adrenergic receptor subtypes in the bladder of rats.

OBJECTIVE To detect the possible alterations on density or sensitivity of α1-adrenergic subtypes in diabetic bladder by reverse transcriptase-polymerase chain reaction technology and in vitro studies. METHODS Experimental diabetes was induced by administration of streptozotocin with a single injection through the tail vein. Rats were divided into control and diabetic groups. Contractile responses of bladder strips from each group were obtained for postassium chloride, adenosine triphosphate, and electrical field stimulation (0.5-32 Hz) in organ bath. Electrical field stimulation responses of strips were evaluated in the presence of PPADS (nonselective P2 antagonist), atropine (cholinergic antagonist), 5 MU (α-1a-adrenergic antagonist), BMY-7378 (α-1d-adrenergic antagonist), and finally CED (α-1b-adrenergic antagonist). mRNA expression of α1-adrenergic subtypes was determined for each group. RESULTS The difference between contractile responses related to electrical field stimulation with incubation with PPADS, atropine, 5 MU, BMY-7378, and CED, respectively, was not significant in the control and diabetic groups (P > .05). The electrical field stimulation responses of strips at 0.5-2 Hz without incubation were significantly different between the control and diabetic groups (P < .05). The contractile responses of strips with PPADS + atropine + 5 MU and BMY-7378 incubations in the diabetic group were significantly lower than in the control group in all doses (P < .05), The mRNA expression of α-1a-adrenergic in the diabetic group was significantly lower than in the control group (P < .05). No change was found in the expression of mRNA of α-1b-adrenergic. CONCLUSION These results support the probability of changes in presynaptic and autonomic receptor sensitivity. We believe that α-1a-adrenergic and α-1d-adrenergic subtypes should be kept in mind in the treatment of diabetic cystopathy.