The goals of this proposal relate to the action of alpha1 adrenergic receptors in smooth muscle with particular emphasis on mechanisms by which catecholamines induce desensitization of alpha1 receptor-mediated responses. Desensitization refers to loss in responsiveness of a tissue after prolonged exposure to an agonist drug or hormone. We have demonstrated that several adaptations in blood vessels contribute to desensitization of alpha1 receptor-mediated smooth muscle contraction after prolonged exposure to catecholamines. this application proposes to investigate further the molecular basis underlying these changes in function. We have found that prolonged activation of alpha receptors induces the endothelium of vascular smooth muscle to release enhanced amounts of endothelial derived relaxing factor (EDRF); the alpha receptor subtype on endothelial cells (alpha1A vs alpha1B; or alpha2) which transduces this effect will be determined. The explanation for the enhanced release of EDRF induced by catecholamines will be sought by determining the expression of the nitric oxide synthase gene in endothelial cells in response to catecholamines to determine if catecholamines induce nitric oxide synthase as has been found to occur for various cytokines. The pathophysiological significance of enhanced release of EDRF induced by catecholamines will be determined in two rat models, one of pheochromocytoma (a norepinephrine-secreting tumor) and after prolonged infusions of vasopressors commonly used in the treatment of cardiovascular shock. We have found that prolonged alpha1 adrenergic receptor stimulation leads to down-regulation of protein kinase C in vascular smooth muscle; the mechanism for changes in expression of various protein kinase C isoforms found in smooth muscle will be determined. Potential alterations in the turnover of protein kinase C isozymes and the expression of their genes in desensitized smooth muscle cells will be sought. We will investigate the effects of prolonged activation of alpha1 receptors on expression of alpha1B receptors in cultured rat aorta smooth muscle cells. Based on our preliminary data, additional studies relating to the action of alpha1 receptors are proposed. Activation of protein kinase C in smooth muscle cells leads to enhanced expression of alpha1 receptors; we propose to determine the basis for this important regulatory change by investigation of the structure of the 5' regulatory region of the alpha1B adrenergic receptor gene. Stimulation of alpha1 receptors leads to activation of expression of the c-fos gene in rat aorta. We propose to investigate the role of desensitization of smooth muscle contraction on adrenergic receptor- mediated induction of expression of c-fos and the effects of EDRF on this response. These latter studies have implications for the effects of alpha1 agonists and angiotensin II on smooth muscle cell growth.
Showing the most recent 10 out of 28 publications
