Direct actions of adrenergic agents on rat anterior pituitary cells

We studied the effects of adrenergic agents on the five main cell types of the rat anterior pituitary by monitoring the changes of the cytosolic free Ca2+] (Ca2+]i) in single cells that were identified by multiple sequential primary immunocytochemistry at the end of the Ca2+ measurements. Adrenaline (100 nM) increased Ca2+]i in 30% of the cells. Responses were most prominent in somatotrophs and corticotrophs (40-65% of the cells responded) whereas the other three cell types, lactotrophs, thyrotrophs and gonadotrophs, gave poorer responses. Selective agonists and antagonists revealed the presence of both alpha1- and beta-adrenergic receptors. Alpha1-receptors dominated in corticotrophs, beta-receptors in somatotrophs. The alpha1-adrenergic responses increased with culture of the cells. The beta-adrenergic responses were mediated by cAMP and consisted of stimulation of Ca2+ entry through L-type voltage-gated channels. Stimulation of alpha1-receptors released Ca2+ from intracellular stores in corticotrophs and induced cAMP-independent Ca2+ entry in somatotrophs. The effects of alpha1-agonists were additive with those of the releasing factors growth hormone-releasing hormone (GHRH) and corticotropin releasing factor (CRF) whereas those of the beta-agonists were not. Our results suggest that direct effects of plasma catecholamines on AP cells may contribute to the hormonal response to stress.