Second messengers regulating the level of free intracellular calcium and the level of phosphorylation (kinase activities) transduce within the cells the mechanical and biochemical (endocrine, paracrine and autocrine) signals detected by the arterial wall. In arterial smooth muscle cells two signalling pathways produce opposite functional and structural effects: the breakdown of phosphoinositol leading to an increase in intracellular calcium level, and the cyclic guanosine monophosphate (GMP) pathway resulting in a decrease in calcium level. The arterial cyclic GMP pathway is predominantly under control of the endothelial function to secrete no rather than influenced by the atrial natriuretic factor. These two intracellular second messenger pathways are involved not only in the regulation of motricity, but also in the control of arterial wall trophicity, including hypertrophy, hyperplasia and collagen hypersecretion. Inactivation of the cyclic GMP pathway and activation of phosphoinositol breakdown predominate in vascular adaptation to the ageing process.