Coronary microvascular disease: the next frontier for Cardiovascular Research

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Systemic, pulmonary and coronary haemodynamic actions of the novel dopamine receptor agonist in awake pigs at rest and during treadmill exercise Z1046

1. In view of the potential therapeutic application of specific dopamine receptor agonists in the treatment of hypertension and left ventricular dysfunction, we investigated the cardiovascular actions of the novel mixed D1/D2 dopamine receptor agonist Z1046 in awake pigs at rest and during treadmill exercise. 2. Thirteen swine were chronically instrumented under sterile conditions for measurement of systemic, pulmonary, and coronary haemodynamics. Regional blood flows were determined with the radioactive microsphere technique. 3. Z1046 (1, 10, 100 μg kg-1, i.v.) produced dose-dependent reductions in central aortic blood pressure (up to 27 ± 3%, P ≤ 0.05) in awake resting pigs which was accompanied by only minimal reflex activation of the sympathetic nervous system. The hypotensive response was principally the result of peripheral vasodilatation (system vascular resistance decreased up to 35 ± 4%, P ≤ 0.05), which was located in the cerebral, coronary, renal, mesenteric, adrenal, splenic and skeletal muscular vascular beds (vascular resistance decreased up to 30-40% after the highest dose in these beds). Only in the cerebral and mesenteric bed was the vasodilatation sufficiently large to overcome the decrease in blood pressure and result in an increased blood flow; the vasodilatation in the coronary bed was most likely due to autoregulation as neither coronary blood flow nor myocardial oxygen demand were changed significantly by Z1046. The systemic vasodilatation that was caused by the highest i.v. dose (100 μg kg-1) was accompanied by transient and minor increases in heart rate (15 ± 5%, P ≤ 0.05) and cardiac output (15 ± 5%, P ≤ 0.05) whereas after 10 μg kg-1, i.v., a slight decrease in cardiac output also contributed to the hypotension. Z1046 had no effect on pulmonary vascular resistance. 4. The systemic vasodilator responses to Z1046 (100 μg kg-1, i.v.) were sustained during treadmill exercise (2-4 km h-1 which produced heart rates of up to 233 ± 10 beats min-1), but with increasing treadmill speed attenuation of the exercise-induced increase in heart rate (-11 ± 3%, P ≤ 0.05) and hence cardiac output (-10 ± 3%, P ≤ 0.05) (as stroke volume was not altered by Z1046) contributed significantly to a lower aortic blood pressure (-20 ± 3%, P ≤ 0.05). Z1046 had no effect on pulmonary vascular resistance during exercise. 5. Oral administration of Z1046 (0.5, 1.5 mg kg-1) produced a fall in central aortic blood pressure (up to 15 ± 3%, P ≤ 0.05), which developed gradually during the first 90 min and lasted up to 4 h after administration, again with negligible changes in heart rate and LVdP/dt(max). 6. Neither non-selective α- and β-adrenoceptor blockade, nor selective α2-adrenoceptor blockade altered the vasodilator actions of Z1046, but non-selective α- and β-adrenoceptor blockade abolished the cardiac responses to dopamine receptor stimulation, suggesting that its cardiac actions were principally caused by D2-receptor-mediated inhibition of catecholamine release, whereas the vasodilator response was probably the result of vascular D1-receptor stimulation. 7. In conclusion, the novel dopamine receptor agonist Z1046 is an effective blood pressure lowering agent that elicits minimal reflex activation of the sympathetic nervous system in awake resting pigs. Systemic vasodilatation was not affected by combined α- and β-adrenoceptor blockade, which is consistent with a predominantly D1 receptor-dependent vasodilator mechanism. The hypotensive effect is maintained during treadmill exercise during which systemic vasodilatation and a lower cardiac output both contribute to the blood pressure lowering actions of Z1046. The cardiovascular profile of this orally active compound warrants further investigation of this class of drugs in experimental and clinical hypertension.</p

Systemic, pulmonary and coronary haemodynamic actions of the novel dopamine receptor agonist in awake pigs at rest and during treadmill exercise Z1046

1. In view of the potential therapeutic application of specific dopamine receptor agonists in the treatment of hypertension and left ventricular dysfunction, we investigated the cardiovascular actions of the novel mixed D1/D2 dopamine receptor agonist Z1046 in awake pigs at rest and during treadmill exercise. 2. Thirteen swine were chronically instrumented under sterile conditions for measurement of systemic, pulmonary, and coronary haemodynamics. Regional blood flows were determined with the radioactive microsphere technique. 3. Z1046 (1, 10, 100 μg kg-1, i.v.) produced dose-dependent reductions in central aortic blood pressure (up to 27 ± 3%, P ≤ 0.05) in awake resting pigs which was accompanied by only minimal reflex activation of the sympathetic nervous system. The hypotensive response was principally the result of peripheral vasodilatation (system vascular resistance decreased up to 35 ± 4%, P ≤ 0.05), which was located in the cerebral, coronary, renal, mesenteric, adrenal, splenic and skeletal muscular vascular beds (vascular resistance decreased up to 30-40% after the highest dose in these beds). Only in the cerebral and mesenteric bed was the vasodilatation sufficiently large to overcome the decrease in blood pressure and result in an increased blood flow; the vasodilatation in the coronary bed was most likely due to autoregulation as neither coronary blood flow nor myocardial oxygen demand were changed significantly by Z1046. The systemic vasodilatation that was caused by the highest i.v. dose (100 μg kg-1) was accompanied by transient and minor increases in heart rate (15 ± 5%, P ≤ 0.05) and cardiac output (15 ± 5%, P ≤ 0.05) whereas after 10 μg kg-1, i.v., a slight decrease in cardiac output also contributed to the hypotension. Z1046 had no effect on pulmonary vascular resistance. 4. The systemic vasodilator responses to Z1046 (100 μg kg-1, i.v.) were sustained during treadmill exercise (2-4 km h-1 which produced heart rates of up to 233 ± 10 beats min-1), but with increasing treadmill speed attenuation of the exercise-induced increase in heart rate (-11 ± 3%, P ≤ 0.05) and hence cardiac output (-10 ± 3%, P ≤ 0.05) (as stroke volume was not altered by Z1046) contributed significantly to a lower aortic blood pressure (-20 ± 3%, P ≤ 0.05). Z1046 had no effect on pulmonary vascular resistance during exercise. 5. Oral administration of Z1046 (0.5, 1.5 mg kg-1) produced a fall in central aortic blood pressure (up to 15 ± 3%, P ≤ 0.05), which developed gradually during the first 90 min and lasted up to 4 h after administration, again with negligible changes in heart rate and LVdP/dt(max). 6. Neither non-selective α- and β-adrenoceptor blockade, nor selective α2-adrenoceptor blockade altered the vasodilator actions of Z1046, but non-selective α- and β-adrenoceptor blockade abolished the cardiac responses to dopamine receptor stimulation, suggesting that its cardiac actions were principally caused by D2-receptor-mediated inhibition of catecholamine release, whereas the vasodilator response was probably the result of vascular D1-receptor stimulation. 7. In conclusion, the novel dopamine receptor agonist Z1046 is an effective blood pressure lowering agent that elicits minimal reflex activation of the sympathetic nervous system in awake resting pigs. Systemic vasodilatation was not affected by combined α- and β-adrenoceptor blockade, which is consistent with a predominantly D1 receptor-dependent vasodilator mechanism. The hypotensive effect is maintained during treadmill exercise during which systemic vasodilatation and a lower cardiac output both contribute to the blood pressure lowering actions of Z1046. The cardiovascular profile of this orally active compound warrants further investigation of this class of drugs in experimental and clinical hypertension.</p

Transmural Heterogeneity of Myofilament Function and Sarcomeric Protein Phosphorylation in Remodeled Myocardium of Pigs with a Recent Myocardial Infarction

Aim: Transmural differences in sarcomeric protein composition and function across the left ventricular (LV) wall have been reported. We studied in pigs sarcomeric function and protein phosphorylation in subepicardial (EPI) and subendocardial (ENDO) layers of remote LV myocardium after myocardial infarction (MI), induced by left circumflex coronary artery ligation. Methods: EPI and ENDO samples were taken 3 weeks after sham surgery (n = 12) or induction of MI (n = 12) at baseline (BL) and during β-adrenergic receptor (βAR) stimulation with dobutamine. Isometric force was measured in single cardiomyocytes at various [Ca2+] and 2.2 μm sarcomere length. Results: In sham hearts, no significant transmural differences were observed in myofilament function or protein phosphorylation. Myofilament Ca2+-sensitivity was significantly higher in both EPI and ENDO of MI compared to sham hearts. Maximal force was significantly reduced in MI compared to sham, but solely in ENDO cells. A higher passive force was observed in MI hearts, but only in EPI cells. The proportion of stiff N2B isoform was higher in EPI than in ENDO in both sham and MI hearts, and a trend toward increased N2B-proportion appeared in MI EPI, but not MI Endo. Analysis of myofilament protein phosphorylation did not reveal significant transmural differences in phosphorylation of myosin binding protein C, desmin, troponin T, troponin I (cTnI), and myosin light chain 2 (MLC-2) both at BL and during βAR stimulation with dobutamine infusion. A significant increase in MLC-2 phosphorylation was observed during dobutamine only in sham. In addition, the increase in cTnI phosphorylation upon dobutamine was twofold lower in MI than in sham. Conclusion: Myofilament dysfunction is present in both EPI and ENDO in post-MI remodeled myocardium, but shows a high degree of qualitative heterogeneity across the LV wall. These heterogeneous transmural changes in sarcomeric properties likely contribute differently to systolic vs. diastolic global LV dysfunction after MI

Higher-order Singular Value Decomposition Filter for Contrast Echocardiography

Assessing the coronary circulation with contrast-enhanced echocardiography has high clinical relevance. However, it is not being routinely performed in clinical practice because the current clinical tools generally could not provide adequate image quality. The contrast agent’s visibility in the myocardium is generally poor, impaired by motion and non-linear propagation artifacts. The established multi-pulse contrast schemes (MPCS) and the more experimental singular value decomposition (SVD) filter also fall short to solve these issues. Here, we propose a scheme to process AM/AMPI echoes with higher-order singular value decomposition (HOSVD) instead of conventionally summing the complementary pulses. The echoes from the complementary pulses form a separate dimension in the HOSVD algorithm. Then, removing the ranks in that dimension with dominant coherent signals coming from tissue scattering would provide the contrast detection. We performed both in vitro and in vivo experiments to assess the performance of our proposed method in comparison with the current standard methods. A flow phantom study shows that HOSVD on AM pulsing exceeds the contrast-to-background ratio (CBR) of conventional AM and an SVD filter by 10dB and 14dB, respectively. In vivo porcine heart results also demonstrate that, compared to AM, HOSVD improves CBR in open-chest acquisition (up to 19dB) and contrast ratio in closed-chest acquisition (3dB)

Reduced nitric oxide bioavailability impairs myocardial oxygen balance during exercise in swine with multiple risk factors

In the present study, we tested the hypothesis that multiple risk factors, including diabetes mellitus (DM), dyslipidaemia and chronic kidney disease (CKD) result in a loss of nitric oxide (NO) signalling, thereby contributing to coronary microvascular dysfunction. Risk factors were induced in 12 female swine by intravenous streptozotocin injections (DM), a high fat diet (HFD) and renal artery embolization (CKD). Female healthy swine (n = 13) on normal diet served as controls (Normal). After 5 months, swine were chronically instrumented and studied at rest and during exercise. DM + HFD + CKD swine demonstrated significant hyperglycaemia, dyslipidaemia and impaired kidney function compared to Normal swine. These risk factors were accompanied by coronary microvascular endothelial dysfunction both in vivo and in isolated small arteries, due to a reduced NO bioavailability, associated with perturbations in myocardial oxygen balance at rest and during exercise. NO synthase inhibition caused coronary microvascular constriction in exercising Normal swine, but had no effect in DM + HFD + CKD animals, while inhibition of phosphodiesterase 5 produced similar vasodilator responses in both groups, indicating that loss of NO bioavailability was principally responsible for the observed coronary microvascular dysfunction. This was associated with an increase in myocardial 8-isoprostane levels and a decrease in antioxidant capacity, while antioxidants restored the vasodilation to bradykinin in isolated coronary small arteries, suggesting that oxidative stress was principally responsible for the reduced NO bioavailability. In conclusion, five months of combined exposure to DM + HFD + CKD produces coronary endothelial dysfunction due to impaired NO bioavailability, resulting in impaired myocardial perfusion at rest and during exercise.</p

Cardiorenal disease connection during post-menopause: The protective role of estrogen in uremic toxins induced microvascular dysfunction

Female gender, post-menopause, chronic kidney disease (CKD) and (CKD linked) microvascular disease are important risk factors for developing heart failure with preserved ejection fraction (HFpEF). Enhancing our understanding of the interrelation between these risk factors could greatly benefit the identification of new drug targets for future therapy. This review discusses the evidence for the protective role of estradiol (E2) in CKD-associated microvascular disease and related HFpEF. Elevated circulating levels of uremic toxins (UTs) during CKD may act in synergy with hormonal changes during post-menopause and could lead to coronary microvascular endothelial dysfunction in HFpEF. To elucidate the molecular mechanism involved, published transcriptome datasets of indoxyl sulfate (IS), high inorganic phosphate (HP) or E2 treated human derived endothelial cells from the NCBI Gene Expression Omnibus database were analyzed. In total, 36 genes overlapped in both IS- and HP-activated gene sets, 188 genes were increased by UTs (HP and/or IS) and decreased by E2, and 572 genes were decreased by UTs and increased by E2. Based on a comprehensive in silico analysis and literature studies of collected gene sets, we conclude that CKD-accumulated UTs could negatively impact renal and cardiac endothelial homeostasis by triggering extensive inflammatory responses and initiating dysregulation of angiogenesis. E2 may protect (myo)endothelium by inhibiting UTs-induced inflammation and ameliorating UTs-related uremic bleeding and thrombotic diathesis via restored coagulation capacity and hemostasis in injured vessels

Myocardial perfusion MRI shows impaired perfusion of the mouse hypertrophic left ventricle

There is growing consensus that myocardial perfusion deficits play a pivotal role in the transition from compensated to overt decompensated hypertrophy. The purpose of this study was to systematically study myocardial perfusion deficits in the highly relevant model of pressure overload induced hypertrophy and heart failur