Research Doctorate - Doctor of Philosophy (PhD) / There is no consistency between studies of mammalian autonomic systems controlling the coronary circulation, particularly with respect to vagal cholinoceptor activity. Therefore, integrated autonomic control of regional coronary blood flow and conductance was investigated in chronically prepared awake sheep, and compared with data from this laboratory found in the awake dog. Coronary blood flow was measured simultaneously in the circumflex (Cx), right (R) and anterior descending (AD) beds by pulsed Doppler probes. Heart rate (HR) was controlled over the range of 100 to 180 beats/min by atrioventricular pacing. Baroreflex responses were evoked by elevating upper-body aortic pressure (Pa) using an external aortic occluder at HR of 150 and 180 beats/min. Specific agonists determined that effective populations of α-, β-adrenoceptors and cholinoceptors exist in all three coronary beds. Cholinoceptors (ch) and β-adrenoceptors (β) evoke vasodilatation, whereas α-adrenoceptors (α) evoke vasoconstriction. By contrast, electrical vagal stimulation constricts all 3 coronary beds, an effect blocked by methscopolamine. Pacing the heart upward raised baroreflex and metabolic activity and a differential rise in coronary conductance where Cx was greatest followed by R then AD. Block of ch, β and α alone, and together, at different HR revealed that, 1. in all 3 beds an underlying ch constrictor effect is balanced by the summed dilator effects of β, plus a probable α-enhanced vagal, vasointestinal peptide (VIP) interaction mechanism, 2. the net effects summate to enhance flow and conductance in Cx, but not in R and AD. At high HR, there is some waning of the neural mechanisms but raising and sustaining Pa at constant HR can recruit these mechanisms in each bed indicating ch, β and α/VIP, are baroreflex dependent even at the highest physiological HR. Therefore, differences do exist between species, for in particular baroreflex evoked cholinoceptor effects in the mammalian coronary circulation. They are vasoconstrictor in sheep, and vasodilator in the dog. These species differences specify successful alternatives in the evolution of reflex systems to meet the demand for coronary blood flow.

Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 6 uppsatser.

The effect of hypoxemia on coronary autoregulation was investigated in nine anesthetized, open-chest dogs. The anterior descending coronary artery (LAD) was cannulated and perfused with normoxic arterial blood and with moderately hypoxic blood (0₂ content = 10 + 1 ml 0₂ /dl). LAD blood flow was measured as perfusion pressure was varied from 140 to 40 mmHg. At perfusion pressures at and above 40 mmHg, hypoxemia significantly increased LAD flow. During normoxia, the autoregulatory closed-loop gain (Gc) was significantly greater than zero at perfusion pressures from 60 to 120 mmHg. During hypoxemia, Gc was greater than zero only at perfusion pressures from 80 to 100 mmHg. During hypoxemia, LAD blood flow increased sufficiently to maintain oxygen delivery and consumption constant, but the range and potency of autoregulation was attenuated.

No description available.

The objective of this thesis is to investigate the pathophysiology of the coronary slow phenomenon (CSFP). The experimental work of this thesis has taken a 'bedside to benchtop' approach with clinical observations made in the second chapter guiding the application of basic research techniques in subsequent chapters. Chapter 1 ; The CSFP is a disorder of the coronary microcirculation ; hence chapter 1 specifically reviews the current understanding of this vascular territory and concludes with a summary of the clinical disorders affecting it, concentrating on the CSFP. Chapter 2 ; investigated the angiographic response of the CSFP to a calcium channel blocking agent with antianginal efficacy in this disorder ( mibefradil ). Mibefradil administration was associated with an acute improvement of coronary flow indices which occurred despite background vasodilator therapy with conventional calcium channel antagonists. Chapter 3 ; investigated the in vitro response of human microvessels to mibefradil in comparison to conventional calcium channel blockers. Mibefradil was found to be a more potent agent both in terms of vasodilatation and the prevention of vasoconstriction. Both findings support the clinical observations and point to its selective action on the calcium T channel subtype as a potential mechanism. Chapter 4 ; examined the expression of T type calcium channels at the level of the microvasculature and compared T channel expression in CSFP patients and controls. T channels were found to be expressed at two or more orders of magnitude greater than the L channels. No difference in T channel expression between patients and controls was found. Chapter 5 ; examined the vasomotor reactivity of isolated subcutaneous arterial microvessels to various vasoactive substances between controls and CSFP patients. CSFP patients were found to have a selective hyper reactivity to endothelin. Chapter 6 ; examined plasma endothelin levels in CSFP patients and controls and the relationship between endothelin levels and angina frequency in the CSFP cohort. A small but statistically significant elevation of endothelin-1 was present in patients with the CSFP. A positive association between plasma endothelin fluctuation and angina frequency was also found in the CSFP cohort but not between absolute endothelin levels and angina symptoms. / Thesis (Ph.D.)-- The University of Adelaide, School of Medical Sciences, 2006.

The objective of this thesis is to investigate the pathophysiology of the coronary slow phenomenon (CSFP). The experimental work of this thesis has taken a 'bedside to benchtop' approach with clinical observations made in the second chapter guiding the application of basic research techniques in subsequent chapters. Chapter 1 ; The CSFP is a disorder of the coronary microcirculation ; hence chapter 1 specifically reviews the current understanding of this vascular territory and concludes with a summary of the clinical disorders affecting it, concentrating on the CSFP. Chapter 2 ; investigated the angiographic response of the CSFP to a calcium channel blocking agent with antianginal efficacy in this disorder ( mibefradil ). Mibefradil administration was associated with an acute improvement of coronary flow indices which occurred despite background vasodilator therapy with conventional calcium channel antagonists. Chapter 3 ; investigated the in vitro response of human microvessels to mibefradil in comparison to conventional calcium channel blockers. Mibefradil was found to be a more potent agent both in terms of vasodilatation and the prevention of vasoconstriction. Both findings support the clinical observations and point to its selective action on the calcium T channel subtype as a potential mechanism. Chapter 4 ; examined the expression of T type calcium channels at the level of the microvasculature and compared T channel expression in CSFP patients and controls. T channels were found to be expressed at two or more orders of magnitude greater than the L channels. No difference in T channel expression between patients and controls was found. Chapter 5 ; examined the vasomotor reactivity of isolated subcutaneous arterial microvessels to various vasoactive substances between controls and CSFP patients. CSFP patients were found to have a selective hyper reactivity to endothelin. Chapter 6 ; examined plasma endothelin levels in CSFP patients and controls and the relationship between endothelin levels and angina frequency in the CSFP cohort. A small but statistically significant elevation of endothelin-1 was present in patients with the CSFP. A positive association between plasma endothelin fluctuation and angina frequency was also found in the CSFP cohort but not between absolute endothelin levels and angina symptoms. / Thesis (Ph.D.)-- The University of Adelaide, School of Medical Sciences, 2006.

No description available.

We hypothesized that the interaction between tumor necrosis factor alpha(TNF)/nuclear factor-kappaB (NFkB) via activation of IKK may amplify one anotherresulting in the evolution of vascular disease and insulin resistance associated withdiabetes. The interaction between TNFa and monocyte chemoattractant protein-1 (MCP-1) may contribute to the evolution of vascular inflammation and endothelial dysfunctionin coronary arterioles in type 2 diabetes. To test this hypothesis, endothelium-dependent(ACh) and –independent (SNP) vasodilation of isolated, pressurized coronary arterioles(40-100 μm) from mLeprdb (heterozygote, normal), Leprdb (homozygote, diabetic) andLeprdb mice null for TNF (dbTNF-/dbTNF-) were examined. Although dilation of vesselsto SNP was not different between Leprdb and mLeprdb mice, dilation to ACh was reducedin Leprdb mice. The NFkB antagonist, MG-132, IKK inhibitor, sodium salicylate(NaSal), or Anti-MCP-1 partially restored endothelium-dependent coronary arteriolardilation in Leprdb mice. Protein expression of IKK and IKK were higher in Leprdb thanin mLeprdb mice. The expression of IKK, but not the expression of IKK was increasedin dbTNF-/dbTNF- mice. Leprdb mice showed increased insulin resistance, but NaSal improved insulin sensitivity. Protein expression of TNFa, NFkB, phosphorylation ofIKK and JNK were greater in Leprdb mice, but NaSal attenuated protein expression ofthem in Leprdb mice. The ratio of phosphorylated IRS-1 at Ser307 (pIRS-1)/IRS-1protein expression was elevated in Leprdb mice; both NaSal and JNK inhibitor SP600125reduced pIRS-1/IRS-1 in Leprdb mice. MG-132 or neutralization of TNF reducedsuperoxide production in Leprdb mice. Anti-MCP-1 attenuated superoxide productionand protein expression of nitrotyrosine (N-Tyr), which is an indicator of peroxynitriteproduction, in isolated coronary arterioles of Leprdb mice. Immunostaining resultsshowed that expression of MCP-1 and vascular cellular adhesion molecule-1 (VCAM) isco-localized with endothelial cells and macrophages. Anti-TNFa or anti-MCP-1markedly reduced macrophage infiltration and the number of MCP-1 positive cells.Neutralization of TNFa or anti-MCP-1 reduced the expression of adhesion molecules. Inconclusion, our results indicate that the interaction between NFkB and TNFa signalinginduces activation of IKKb. In addition, TNFa and TNFa-related signaling, includingthe expression of MCP-1 and adhesion molecules, further exacerbates oxidative stressleading to endothelial dysfunction in type 2 diabetes.

We hypothesized that the interaction between tumor necrosis factor alpha(TNF)/nuclear factor-kappaB (NFkB) via activation of IKK may amplify one anotherresulting in the evolution of vascular disease and insulin resistance associated withdiabetes. The interaction between TNFa and monocyte chemoattractant protein-1 (MCP-1) may contribute to the evolution of vascular inflammation and endothelial dysfunctionin coronary arterioles in type 2 diabetes. To test this hypothesis, endothelium-dependent(ACh) and –independent (SNP) vasodilation of isolated, pressurized coronary arterioles(40-100 μm) from mLeprdb (heterozygote, normal), Leprdb (homozygote, diabetic) andLeprdb mice null for TNF (dbTNF-/dbTNF-) were examined. Although dilation of vesselsto SNP was not different between Leprdb and mLeprdb mice, dilation to ACh was reducedin Leprdb mice. The NFkB antagonist, MG-132, IKK inhibitor, sodium salicylate(NaSal), or Anti-MCP-1 partially restored endothelium-dependent coronary arteriolardilation in Leprdb mice. Protein expression of IKK and IKK were higher in Leprdb thanin mLeprdb mice. The expression of IKK, but not the expression of IKK was increasedin dbTNF-/dbTNF- mice. Leprdb mice showed increased insulin resistance, but NaSal improved insulin sensitivity. Protein expression of TNFa, NFkB, phosphorylation ofIKK and JNK were greater in Leprdb mice, but NaSal attenuated protein expression ofthem in Leprdb mice. The ratio of phosphorylated IRS-1 at Ser307 (pIRS-1)/IRS-1protein expression was elevated in Leprdb mice; both NaSal and JNK inhibitor SP600125reduced pIRS-1/IRS-1 in Leprdb mice. MG-132 or neutralization of TNF reducedsuperoxide production in Leprdb mice. Anti-MCP-1 attenuated superoxide productionand protein expression of nitrotyrosine (N-Tyr), which is an indicator of peroxynitriteproduction, in isolated coronary arterioles of Leprdb mice. Immunostaining resultsshowed that expression of MCP-1 and vascular cellular adhesion molecule-1 (VCAM) isco-localized with endothelial cells and macrophages. Anti-TNFa or anti-MCP-1markedly reduced macrophage infiltration and the number of MCP-1 positive cells.Neutralization of TNFa or anti-MCP-1 reduced the expression of adhesion molecules. Inconclusion, our results indicate that the interaction between NFkB and TNFa signalinginduces activation of IKKb. In addition, TNFa and TNFa-related signaling, includingthe expression of MCP-1 and adhesion molecules, further exacerbates oxidative stressleading to endothelial dysfunction in type 2 diabetes.

Platelets have been shown to be a main contributor to thrombus formation in stenotic arteries leading to acute coronary syndromes. It is thought that increased activation and adhesion of platelets under variable shear and complex flow conditions contribute to thrombosis. The objective of this work was to evaluate the relationship between asymmetric stenosis hemodynamics and platelet adhesion using in-vitro models developed to properly simulate physiological conditions. In this study, platelet rich plasma was circulated through stenotic and straight coronary artery models. Adhesion results were obtained by post-perfusion fluorescent labelling and imaging of adhered platelets. Analysis of platelet area coverage has shown maximum adhesion occurs in the distal region of the stenosis. Most likely this is due to increased exposure time of platelets to the wall of the recirculation zone following the stenosis and that exposure being directly after a period of high shear stress. This result gives us a better understanding of the importance of both shear and flow conditions in coronary artery thrombosis.