Abstract
The effect of epinephrine was tested on the proliferation of rat arterial smooth muscle cells (SMC) in secondary cultures. Epinephrine added daily to the culture medium caused a striking stimulation of growth. The effect increased with time and was dose-dependent. Maximal stimulation was observed at a concentration of 10(-5) M and after 72 hours. At higher concentrations (10(-3) M) epinephrine exhibited toxic effects on SMC. When SMC were maintained quiescent by deprivation of serum, the subsequent addition of epinephrine required serum to significantly enhance growth. This growth stimulation increased with serum concentration (from 0.1% to 10%). All the adrenergic agonists tested were found to stimulate SMC growth, with an activity classified by decreasing order as follows: norepinephrine greater than epinephrine greater than isoproterenol. Finally, this mitogenic response of SMC to catecholamines was specific since it could be blocked by adrenergic blocking agents, phentolamine being more efficient than propranolol in that connection. The results suggest that epinephrine and other catecholamines may act as growth factors for aortic SMC, at least in rat, mostly through adrenoreceptors.
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