Regulation of protein synthesis by α1-adrenergic receptor subtypes in cultured rabbit aortic vascular smooth muscle cells

To investigate the role of the sympathetic nervous system in maintenance and remodeling of vascular smooth muscle, we have examined regulation of protein synthesis by α 1 -adrenergic receptors (α 1 -AR) in cultured rabbit aortic vascular smooth muscle cells (VSMC). Stimulation of postconfluent cultures (passages 2-6) in serum-free growth medium with the α-AR agonist phenylephrine (PE, 30 μM) increases protein synthesis, measured as [ 3 H]leucine incorporation into protein (146 ± 5%, p ≤ 0.001) and total protein content (117 ± 2%, p ≤ 0.001). PE treatment does not affect cellular proliferation or [ 3 H]thymidine incorporation into DNA. PE-stimulated protein synthesis is evident within 24 h, sustained over 96 h, concentration-dependent, and saturable. PE-elicited responses are completely inhibited by the α-AR antagonist prazosin but not by the α 2 -AR antagonist yohimbine or the β-AR antagonists propranolol and atenolol ; the β-AR agonist isoproterenol is ineffective. Competition with [ 3 H]prazosin occupancy of α 1 -AR and agonist-elicited [ 3 H]leucine incorporation by subtype-selective receptor antagonists (WB4101 and 5-methylurapidil, α 1A ; chloroethylclonidine, α 1B ) demonstrates that these cells express a majority of α 1B -AR (75%) relative to α 1A -AR (25%), which elicit protein metabolism in proportion to their relative abundances. These results indicate that α 1B -AR predominate in coupling to metabolic responses, in contrast to previous reports that contractile responses in this tissue are preferentially mediated by α 1A -AR.