Accession Number : ADA328721

Title :   Evidence for Increased Beta-Adrenoreceptor Responsiveness Induced by 14 Days of Simulated Microgravity in Humans,

Corporate Author : ARMSTRONG LAB BROOKS AFB TX AEROSPACE MEDICINE DIRECTORATE

Personal Author(s) : Convertino, Victor A. ; Polet, Jill L. ; Engelke, Keith A. ; Hoffler, G. W. ; Lane, Lynda D.

PDF Url : ADA328721

Report Date : 1996

Pagination or Media Count : 8

Abstract : We 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.

Descriptors :   *CARDIOVASCULAR SYSTEM, SIMULATION, MONITORING, HUMANS, AMINES, DOSAGE, EXPOSURE(PHYSIOLOGY), RESPONSE(BIOLOGY), DRUGS, SPACE FLIGHT, HEART RATE, RESISTANCE(BIOLOGY), AUTONOMIC NERVOUS SYSTEM, BLOOD PRESSURE, LEGS, VASOCONSTRICTING, INFUSIONS, AUTONOMIC AGENTS, SYMPATHOMIMETIC AGENTS, ISOPROTERENOL, PLETHYSMOGRAPHY.

Subject Categories : Anatomy and Physiology
      Medicine and Medical Research
      Nuclear Physics & Elementary Particle Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE