ATRIAL-NATRIURETIC-PEPTIDE IN MULTIPLE SYSTEM ATROPHY

Central nervous system feedback loops centered on hypothalamic neurons control atrial natriuretic peptide (ANP). We evaluated the ANP respon se to arterial hypotension, isotonic blood volume expansion, and incre ase in plasma osmolality in 14 patients with multiple system atrophy ( MSA). Seven of the patients were characterized by a lack of vasopressi n response to hypotension (MSA type B), suggesting chronic sinoaortic denervation, and seven by a preserved response (MSA type A). Orthostat ic hypotension decreased ANP in controls and type A patients, whereas ANP in type B was not affected. Isotonic saline infusion increased ANP and diuresis in controls and type A patients, whereas it did not affe ct ANP in type B. Osmotic load increased plasma osmolality and vasopre ssin in controls and MSA patients and ANP in controls and type A but n ot in type B patients. In MSA patients with altered afferent control o f vasopressin, ANP secretion is not stimulated by blood volume expansi on, osmotic load, or blood pressure, suggesting that afferent excitato ry control plays a role in the release of ANP.