[Action principles of hormones and neurotransmitters (author's transl)]

Membrane-bound receptors for hormones and neurotransmitters can be coupled to other membrane components which generate intracellular signals triggering the cellular response to the hormonal stimulus. For various hormonal factors, the occurrence of receptor subclasses has been established which are bound to different cellular signal-generating systems. Whereas one group of receptors (e.g., beta-adrenergic ones) is linked to adenylate cyclase in a stimulatory manner, other receptors (e.g., alpha 2-adrenergic ones) are linked to this enzyme in an inhibitory manner, and a third group (e.g., alpha 1-adrenergic receptors) is linked to changes in phosphatidylinositol metabolism, calcium distribution and cyclic GMP metabolism. It is not clear whether one given receptor can be linked only to one signal-generating system or whether one type of receptor can be linked to two different signal systems in one cell.