PHYSIOLOGICAL ADAPTATIVE MECHANISMS DURING ORTHOSTATISM - ROLE OF THE SYMPATHETIC NERVOUS-SYSTEM AND PHARMACOLOGICAL IMPLICATIONS

The main physiological adaptative systems occuring during orthostatism are discussed. The nervous mechanisms and especially baroreceptor pathways allow a rapid adaptation to the new hemodynamic conditions whereas hormones (mainly vasopressin) are involved later. The role of baroreflex and cardiocirculatory mechanisms is explained by the description of adaptative mechanisms in giraffe, an animal with its brain so far above the ground. The changes in adrenoceptor receptivity and the adaptative homeostatic mechanisms of the autonomic nervous system during orthostatism in human are discussed. Their characterization might allow to propose new pharmacological approaches for the treatment of orthostatic hypotension.