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Effects of exposure to simulated microgravity on neuronal catecholamine release and blood pressure responses to norepinephrine and angiotensinWe tested the hypothesis that exposure to microgravity reduces the neuronal release of catecholamines and blood pressure responses to norepinephrine and angiotensin. Eight men underwent 30 days of 6 degrees head-down tilt (HDT) bedrest to simulate exposure to microgravity. Plasma norepinephrine and mean arterial blood pressure (MAP) were measured before and after a cold pressor test (CPT) and graded norepinephrine infusion (8, 16 and 32 ng/kg/min) on day 6 of a baseline control period (C6) and on days 14 and 27 of HDT. MAP and plasma angiotensin II (Ang-II) were measured during graded Ang-II infusion (1, 2 and 4 ng/kg/min) on C8 and days 16 and 29 of HDT. Baseline total circulating norepinephrine was reduced from 1017ng during the baseline control period to 610 ng at day 14 and 673ng at day 27 of HDT, confirming a hypoadrenergic state. An elevation of norepinephrine (+178 ng) to the CPT during the baseline control period was eliminated by HDT days 14 and 27. During norepinephrine infusion, similar elevations in plasma norepinephrine (7.7 pg/ml/ng/kg/min) caused similar elevations in MAP (0.12 mmHg/ng/kg/min) across all test days. Ang-II infusion produced higher levels of plasma Ang-II during HDT (47.3 pg/ml) than during baseline control (35.5 pg/ml), while producing similar corresponding elevations in blood pressure. While vascular responsiveness to norepinephrine appears unaffected, impaired neuronal release of norepinephrine and reduced vascular responsiveness to Ang-II might contribute to the lessened capacity to vasoconstrict after spaceflight. The time course of alterations indicates effects that occur within two weeks of exposure.
Document ID
20040172676
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Convertino, V. A.
(Air Force Research Laboratory Brooks Air Force Base, Texas 78235-5104, United States)
Ludwig, D. A.
Gray, B. D.
Vernikos, J.
Date Acquired
August 22, 2013
Publication Date
April 1, 1998
Publication Information
Publication: Clinical autonomic research : official journal of the Clinical Autonomic Research Society
Volume: 8
Issue: 2
ISSN: 0959-9851
Subject Category
Aerospace Medicine
Distribution Limits
Public
Copyright
Other
Keywords
NASA Center HQS
Non-NASA Center
NASA Discipline Cardiopulmonary

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