1. A widespread, and maybe universal, response to stimulation of α-adrenoceptors is inositol lipid hydrolysis: the receptor-coupled event is probably hydrolysis of phosphatidylinositol 4,5-bisphosphate. This reaction generates two second messenger molecules.
2. Inositol 1,4,5-trisphosphate may be responsible for the intracellular mobilization of Ca2+ that has long been recognized as a major mediator of the effects of α-receptor activation. In addition, the released 1,2-diacylglycerol probably contributes to control of cell function through activation of protein kinase C.