(Hypertension. 1997;30:295-300.)
© 1997 American Heart Association, Inc.
Articles |
Stimulation of Imidazoline Receptors Inhibits Proliferation of Human Coronary Artery Vascular Smooth Muscle Cells
From the Division of Neurobiology, Department of Neurology & Neuroscience, Cornell University Medical College, New York City, NY.
Abstract Vascular smooth muscle cells of rat aorta express imidazoline receptors whose stimulation, by drugs or an endogenous ligand, agmatine, inhibits serum-stimulated proliferation. We investigated whether imidazoline receptors are expressed in human vascular smooth muscle cells if their stimulation is antiproliferative. Cultured human coronary artery vascular smooth muscle cells express a nonadrenergic binding site for 3H-idazoxan and an imidazoline receptor–binding protein as revealed by immunocytochemical and immunoblot analyses with a specific antibody. Idazoxan and agmatine dose-dependently inhibited serum-stimulated proliferation of these cells as measured by the incorporation of 3H-thymidine (IC50: 5 and 70 µmol/L, respectively) and serum-stimulated expression of proliferating cell nuclear antigen and cell numbers. The agents inhibited proliferation of human and rat (aorta) smooth muscle cells stimulated by either norepinephrine (6560±440 disintegrations per minute norepinephrine versus 3345±220 norepinephrine and idazoxan), angiotensin II (7680±335 disintegrations per minute angiotensin II versus 3769±450 angiotensin II and idazoxan), or platelet-derived growth factor (IC50: 3 µmol/L for idazoxan and 40 µmol/L for agmatine), indicating inhibition of mitosis mediated by G-protein or receptor tyrosine kinase pathways. We conclude that human vascular smooth muscle cells express imidazoline-receptors whose activation inhibits proliferation by interacting at a distal step in an intracellular signal cascade common to G-protein and receptor tyrosine kinase mitogenic pathways. Agmatine, synthesized in endothelium, may act as a paracrine regulator of vascular smooth muscle cell proliferation through imidazoline receptors, and agents acting at this site may be useful in treating vascular hyperplasia.
Key Words: muscle, smooth • angioplasty • receptors, imidazoline • proliferation
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