Local neural and endothelial-mediated control of the rabbit central ear artery: Changes with chronic nerve stimulation, X-radiation and acrylamide poisoning


This thesis examines the neural and endothelium-mediated control of the rabbit isolated central ear artery. The preparation was also used as a model to investigate the plasticity of vascular sympathetic transmission following long term stimulation in vivo, and the pathological changes produced in local control mechanisms following x-irradiation and acrylamide poisoning. Calcitonin gene-related peptide- and substance P-like immunoreactive perivascular nerve fibres were localised and shown to be of sensory origin. Exogenous calcitonin gene-related peptide exhibited endothelium-independent relaxant responses and inhibitory postjunctional actions, but no prejunctional neuromodulation on the release of noradrenaline. Somatostatin-like immunoreactivity was also localised in perivascular nerves, and exogenous somatostatin had inhibitory neuromodulatory actions both pre- and postjunctionally in the rabbit ear artery. Neuropeptide Y appears to be colocalised with noradrenaline and adenosine 5'-triphosphate in sympathetic nerves in the rabbit ear artery. Exogenous neuropeptide Y inhibited the release of noradrenaline prejunctionally, as well as potentiated contractile responses postjunctionally. Plasticity of local control mechanisms in the rabbit ear artery was examined following chronic cold exposure, which is known to increase activity in sympathetic nerves. Preparations taken from young adult and aged cold-stressed animals showed that there was an age-related difference in the ability of the sympathetic transmission to adapt to chronic cold stress. Up to six weeks after exposure to a single dose of x-radiation, damage to perivascular nerves, endothelial cells, smooth muscle cells and fibroblasts were observed in the rabbit ear artery. The tissue content of noradrenaline was reduced, but neuropeptide Y and calcitonin gene-related peptide levels were unaltered. X-irradiation-induced changes in local neural, endothelium-mediated and direct smooth muscle responses in the rabbit ear artery are discussed. Acrylamide poisoning did not alter the tissue content of noradrenaline, neuropeptide Y or calcitonin gene-related peptide in the rabbit ear artery. Although actions mediated by the peptides examined were unaffected, sympathetic cotransmission as well as endothelium-dependent relaxant responses were attenuated

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