Activation by α₁-adrenergic Agonists of the progression phase in the proliferation of primary cultures of smooth muscle cells in mouse and rat aorta

The effects of catecholamines on the competence and progression phases in the proliferation of vascular smooth muscle cells (SMCs) in mouse and rat were investigated in primary cultures. α,β-Adrenergic agonists such as epinephrine and norepinephrine, and the α-adrenergic agonist, phenylephrine, stimulated proliferation of primary cultured SMCs, whereas the α₂-adrenergic agonist, clonidine, and β-adrenergic agonist, isoproterenol, did not. The stimulating effect of epinephrine was maximal at 0.54 μM and was then decreased at higher concentrations. The α-adrenergic antagonist, phentolamine, and α₁-adrenergic antagonist, prazosin, inhibited epinephrine-induced SMC proliferation, while the α₂-adrenergic antagonist, yohimbine, and β-adrenergic antagonist, propranolol, did not. In primary cultured and synchronized SMCs at the G₀ phase, norepinephrine accelerated the rate of SMC proliferation, but did not change the starting time of DNA synthesis and proliferation. These results show that catecholamines activate the progression phase in primary cultured aortic SMCs α₁-adrenergic receptors.