Alpha 2-adrenergic stimulation promotes preadipocyte proliferation. Involvement of mitogen-activated protein kinases.

Primary cultures of rat preadipocytes were shown to express alpha 2- and beta-adrenoreceptors when maintained in serum-deprived medium. alpha 2-Adrenoreceptor stimulation led to an increase in cell number, whereas beta-adrenoreceptor stimulation was without effect. On 3T3-F442A clones stably transfected with the human alpha 2-C10 gene and expressing a physiologically related number of alpha 2-adrenoreceptors to overexpression, the proliferative effect of alpha 2-adrenoreceptor agonist UK14304 was proportional to the level of alpha 2-adrenoreceptor expressed in individual clones and required alpha-2 adrenoreceptor stimulation. Analysis of the signaling pathway linked to alpha 2-adrenoreceptor activation showed that the mitogenic effect was adenylyl cyclase- and protein kinase C-independent. It was pertussis toxin-sensitive, implying the involvement of pertussis toxin-sensitive G proteins. The activation of the mitogen-activated protein kinase pathway was increased after alpha 2-adrenoreceptor stimulation in both 3T3-F442 clones and rat preadipocytes and inhibited by pertussis toxin treatment. So, catecholamines are involved in the control of white preadipocyte proliferation through the alpha 2-adrenoreceptor activation, linked to the mitogen-activated protein kinase pathway.