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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

WISE-2005: adrenergic responses of women following 56-days, 6° head-down bed rest with or without exercise countermeasures

¹Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Canada; ²School of Kinesiology, University of Western Ontario, London, Canada; ³Explorations Fonctionnelles Vasculaires, Centres Hospitaliers Universitaires d'Angers, Angers, France; and ⁴Unité Médecine et Physiologie Spatiale, Centres Hospitaliers Universitaires Trousseau, Tours, France

Submitted 15 March 2007 ; accepted in final form 26 September 2007

We tested the hypotheses that women completing 56 days, 6° head-down bed-rest (HDBR) would have changes in sensitivity of cardiovascular responses to adrenergic receptor stimulation and that frequent aerobic and resistive exercise would prevent these changes. Twenty-four women, eight controls, eight exercisers (lower body negative pressure treadmill and flywheel resistance exercise), and eight receiving nutritional supplement but no exercise were studied in baseline and during administration of the β-agonist isoproterenol (ISO) and the - and β-agonist norepinephrine (NOR). In the control and nutrition groups, HDBR increased heart rate (HR) and reduced stroke volume (SV), and there was a significantly greater increase in HR with ISO after HDBR. In contrast, the HR and SV of the exercise group were unchanged from pre-HDBR. After HDBR, leg vascular resistance (LVR) was greater than pre-HDBR in the exercise group but reduced in control and nutrition. LVR was reduced with ISO and increased with NOR. Changes in total peripheral resistance were similar to those of LVR but of smaller magnitude, perhaps because changes in cerebrovascular resistance index were directionally opposite to those of LVR. There were no changes in sensitivity of the vascular resistance responses to adrenergic stimulation. The HR response might reflect a change in sensitivity or a necessary response to the reduction in SV after HDBR in control and nutrition groups. The reduced peripheral vascular resistance after HDBR might help to explain orthostatic intolerance in women. Exercise was an effective countermeasure to the HDBR effects.

vascular resistance; norepinephrine; microgravity; cardiac output