Submitted on March 15, 2007
Accepted on September 26, 2007
WISE-2005: Adrenergic responses of women following 56-days, 6o head-down bed rest with or without exercise countermeasures
Heather Edgell1, Kathryn A Zuj1, Danielle K Greaves1, J. Kevin Shoemaker2, Marc-Antoine Custaud3, Pascaline Kerbeci4, Philippe Arbeille5, and Richard L. Hughson6*
1 Applied Health Sciences, University of Waterloo, Waterloo, Canada
2 Kinesiology, University of Western Ontario, London, Canada
3 Medicine, CHU Angers, Angers, France
4 Unite Medecine et Physiologie Spatiale, CHU Trousseau, France
5 Unite Med & Physiol Spatiale, University Hospital Trousseau, TOURS, France
6 Applied Health Sciences, University of Waterloo, Waterloo, Canada; Cardiorespiratory + Vascular Dynamics Laboratory, University of Waterloo, Faculty of Applied Health Sciences, Waterloo, Canada
* To whom correspondence should be addressed. E-mail: hughson{at}uwaterloo.ca.
We tested the hypotheses that women completing 56-days, 6o 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. 24 women, 8 controls, 8 exercisers (lower body negative pressure treadmill and flywheel resistance exercise), and 8 receiving nutritional supplement but no exercise were studied in baseline and during administration of the 
-agonist isoproterenol (ISO) and the 
- and -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.
