THE SYMPATHETIC NERVOUS-SYSTEM AND THE PHYSIOLOGICAL CONSEQUENCES OF SPACEFLIGHT - A HYPOTHESIS

Many of the physiologic consequences of weightlessness and the cardiov ascular abnormalities on return from space could be due, at least in p art, to alterations in the regulation of the autonomic nervous system. In this article, the authors review the rationale and evidence for an autonomic mediation of diverse changes that occur with spaceflight, i ncluding the anemia and hypovolemia of weightlessness and the tachycar dia and orthostatic intolerance on return from space. This hypothesis is supported by studies of two groups of persons known to have low cat echolamine levels: persons subjected to prolonged bedrest and persons with syndromes characterized by low circulating catecholamines (Bradbu ry-Eggleston syndrome and dopamine beta-hydroxylase deficiency). Both groups exhibit the symptoms mentioned. The increasing evidence that au tonomic mechanisms underlie many of the physiologic consequences of we ightlessness suggests that new pharmacologic approaches (such as admin istration of beta-blockers and/or sympathomimetic amines) based on the se findings may attenuate these unwanted effects.