The molecular basis of small vessel constriction in endothelin-1 models and peripheral arterial disease.
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Date
2013
Authors
Rajopadhyaya, Kanchani
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Wilson, David Peter Murray
Beltrame, John Francis
Fitridge, Robert A.
Beltrame, John Francis
Fitridge, Robert A.
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Abstract
Peripheral artery disease (PAD) affects 20% of people over the age of 65 years and the prevalence increases with age. Predominately affecting the lower limbs, PAD causes chronic ischaemic leg pain, reduced quality of life, and increased risk of death by heart attack and stroke. It is well established vascular disease is a large vessel, atherothrombotic disorder, however the importance of vasospasm and/or increased vascular tone is less well recognized, particularly in the microvasculature. Current vasodilatory medical therapies have focused on extracellular Ca²⁺ entry or specific receptor blockade. Targeting subcellular enzymes to attenuate general agonist-mediated vasoconstriction has not yet been implemented. Although specific agonists, such as endothelin-1 (ET-1), have been implicated in PAD, whether chronic exposure to these vasoconstrictors causes altered receptor profiles of circulating hormones have not been identified. The direct contractile responses of diseased human microvessels to specific agonists also remain unclear. We used 1) a rat model to identify the acute temporal activation of PKC and ROK during rapid and sustained ET-1-mediated vasoconstriction 2) a rat model of chronically elevated ET-1-meditated vasoconstriction to identify altered receptor profiles to specific agonists and 3) human subcutaneous arteries from patients with PAD to identify their functional and biochemical properties compared to age-matched non-PAD patients. We report that PKC and ROK inhibition in large caudal and small mesenteric rat arteries are effective in attenuating acute ET-1-mediated vasoconstriction in both the rapid and sustained phases of constriction. Chronically elevated ET-1 in a healthy rat model blunts the acute contractile response to the thromboxane A₂ mimetic, U46619 but does not change the vascular response to exogenously added ET-1, the α₁-adrenergic agonist, phenylephrine and serotonin receptor activation. In human subcutaneous arteries we identified an increased maximum contractile response to serotonergic and α₁-adrenergic receptor activation in PAD vs non-PAD patients, while vascular responses to K⁺₋ mediated activation of voltage-gated Ca²⁺ channels, thromboxane A₂, and ET-1 receptor activation were unchanged. Altered vascular reactivity was independent from the abundance and Ser1177-dependent and Thr855-dependent activation state of eNOS and myosin phosphatase, respectively. We identified, patients with PAD have more 5HT2A receptors than patients with no symptomatic PAD, suggesting a possible mechanism for increased contractile responses to serotonin receptor activation. These data suggest 1) subcellular targets that block the inhibition of myosin phosphatase may be valuable in attenuating the vasoconstrictor response to several agonists, and provide additional benefit to specific receptor blockade, 2) while elevated ET-1 is a strong marker of vascular disease, it may have less direct impact on vascular reactivity, 3) decreased contractile responses to thromboxane A₂ following chronic ET-1 infusion is most likely caused by down regulation of thromboxane A₂ receptors, which could have important implications for patients on antiplatelet agents, 4) blockade of enhanced serotonin and α₁-adrenergic vasoconstriction may be beneficial in improving subcutaneous microvascular blood flow in patients with PAD
School/Discipline
School of Medical Sciences
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Medical Sciences, 2013
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Copyright material removed from digital thesis. See print copy in University of Adelaide Library for full text.
Copyright material removed from digital thesis. See print copy in University of Adelaide Library for full text.