Alpha1D-adrenergic receptors and mitogen-activated protein kinase mediate increased protein synthesis by arterial smooth muscle.

Catecholamines may influence vascular smooth muscle cell (SMC) growth and vascular hypertrophic diseases. We previously demonstrated that stimulation of alpha1-adrenoceptors (AR) causes hypertrophy of vascular SMCs in vitro and in situ. Here, we used adult rat aorta SMCs that express alpha1D- and alpha1B-ARs (but not alpha1A-ARs) in vitro to examine the mechanisms and alpha1-AR subtypes involved. Norepinephrine (NE) increased protein synthesis and content in a time- and dose-dependent manner. To identify the responsible alpha1-AR subtype, we first documented the selectivity of two alpha1-AR subtype antagonists, BMY 7378 (alpha1D-AR antagonist) and chloroethylclonidine (CEC; alpha1B-AR antagonist), using Rat-1 fibroblasts stably transfected with the three different rodent alpha1-AR cDNAs. NE dose-dependently increased protein synthesis in each cell line. In alpha1D fibroblasts, BMY 7378 inhibited growth and protected alpha1D-ARs from CEC alkylation while having little blocking or protecting effect on the growth induced by stimulation of fibroblasts that express alpha1A- or alpha1B-ARs. In rat aorta SMCs, pretreatment with CEC in the presence of BMY 7378 to protect alpha1D-ARs had no effect on NE-induced protein synthesis. BMY 7378 inhibited the SMC growth response with a pKb of 8.4. NE caused rapid and transient p42-p44 mitogen-activated protein kinase (MAPK) activation that was alpha1D-AR dependent. Furthermore, NE caused tyrosine phosphorylation of multiple cellular proteins, phosphorylation of Raf-1, and stimulation of c-fos mRNA expression in aorta SMCs. The selective MAPK kinase inhibitor PD 98059 inhibited NE-induced protein synthesis and MAPK activation with IC50 values of 2.3 and 1.6 microM, respectively. These data demonstrate that SMC growth induced by NE is mediated by alpha1D-ARs that couple to activation of the MAPK cascade.