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 sequent ial primary immunocytochemistry at the end of the Ca2+ measurements. Adrena line (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 gonadotro phs, gave poorer responses. Selective agonists and antagonists revealed the presence of both alpha (1)- and beta -adrenergic receptors. alpha (1)-Rece ptors dominated in corticotrophs, beta -receptors in somatotrophs. The alph a (1)-adrenergic responses increased with culture of the cells. The beta -a drenergic responses were mediated by cAMP and consisted of stimulation of C a2+ entry through L-type voltage-gated channels. Stimulation of alpha (1)-r eceptors released Ca2+ from intracellular stores in corticotrophs and induc ed cAMP-independent Ca2+ entry in somatotrophs. The effects of alpha (1)-ag onists were additive with those of the releasing factors growth hormone-rel easing hormone (GHRH) and corticotropin releasing factor (CRF) whereas thos e of the beta -agonists were not. Our results suggest that direct effects o f plasma catecholamines on AP cells may contribute to the hormonal response to stress.