Humoral regulation of the orthostatic reaction

A tilt-table test was performed on 12 untrained subjects to evaluate the humoral adaptation to postural change. The observed peripheral reaction with a reversible short-term rise of norepinephrine (NE) and plasma renin activity (PRA) allowed us to divide the syndrome of the orthostatic dysregulation into a hyponoradrenergic and hypernoradrenergic type. This classification can be helpful for the clinical evaluation and therapy of orthostatic lability. The central excessive stimulation of the antidiuretic (ADH) and adrenocorticotropic hormone (ACTH) follow-ing orthostatic symptoms such as weakness or dizziness was not completely reversible within the observation period of 30 min. The ADH and ACTH increase was not different between the hypo- and the hypernoradrenergic type of dysregulation but was the most sensitive indicator of orthostatic lability: 41% of all subjects showed a hypernoradrenergic orthostatic dysregulation with pronounced NE response and alpha 2-adrenoceptor down-regulation. By use of antiembolism stockings (AES) or dihydroergotamine (DHE) this rate decreased to 16%. This was associated with a significantly reduced NE and PRA response and a diminished alpha 2-adrenoceptor number.