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Evidence for Increased Beta-Adrenoreceptor Responsiveness Induced by 14 Days of Simulated Microgravity in HumansWe studied hemodynamic responses to alpha and beta receptor agonists in 8 healthy men ( 38+- 2 yrs) before and after 14 days of 6 degree head-down tilt (HDT) to test the hypothesis that increased adrenergic responsiveness is induced by prolonged exposure to microgravity. Immediately following a 30-min baseline period, a steady-state infusion of isoproterenol (ISO) was used to assess beta 1- and beta 2-adrenergic responsiveness. ISO was infused at three graded constant rates of 0.005, 0.01 and 0.02 ug/kg/min. After heart rate and blood pressure had been allowed to return to baseline levels following ISO infusion graded infusion of phenylephrine (PE) was used to assess responsiveness of alpha I-vascular receptors. PE was infused at three graded constant rates of 0.25, 0.50 and 1.00 ug/kg/min. Each infusion interval for both drugs was 9 min. During the infusions, constant monitoring of beat-to-beat blood pressure and heart rate was performed and leg blood flow was measured with occlusion plethysmography at each infusion level. The slopes calculated from linear regressions between ISO and PE doses and changes in heart rate, blood pressure, and leg vascular resistance for each subject were used to represent alpha- and beta- adrenoreceptor responsiveness. Fourteen days HDT increased the slopes of heart rate (1056 +- 107 to 1553 +- 83 beats/ug/kg/min; P= 0.014) and vasodilation (-469ft +- 111 to -l446 +- 309 PRU/ug/kg/min; P =0.0224) to ISO infusion. There was no alteration in blood pressure or vascular resistance responses to PE infusion after HDT. Our results provide evidence that microgravity causes selective increases in beta 1- and beta 2-adrenergic responsiveness without affecting alpha 1-vascular responses.
Document ID
19980008320
Acquisition Source
Ames Research Center
Document Type
Contractor Report (CR)
Authors
Convertino, Victor A. (Armstrong Lab. Brooks AFB, TX United States)
Polet, Jill L. (Armstrong Lab. Brooks AFB, TX United States)
Engelke, Keith A. (Armstrong Lab. Brooks AFB, TX United States)
Hoffler, G. W. (Armstrong Lab. Brooks AFB, TX United States)
Lane, Lynda D. (Armstrong Lab. Brooks AFB, TX United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1996
Subject Category
Aerospace Medicine
Report/Patent Number
AD-A328721
NASA/CR-96-206732
NAS 1.26:206732
AL/AO/JA-1996-0041
Funding Number(s)
CONTRACT_GRANT: NAG2-408
CONTRACT_GRANT: NASA Order W-181568
CONTRACT_GRANT: NAS10-10286
PROJECT: AF Proj. 7755
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
Keywords
CARDIOVASCULAR SYSTEM

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