Exposure to weightlessness causes deconditioning of the cardiovascular system, resulting in hypotension (abnormally low blood pressure), but the specific mechanisms involved in this process are unknown. In an animal model, Dr. Mohamed A. Bayorh is exploring overproduction of nitric oxide and prostacyclin as causes of cardiovascular deconditioning, and he is testing ways to inhibit their release in an attempt to lessen hypotension.
Mohamed A. Bayorh, Ph.D.
Morehouse School of Medicine
Exposure to microgravity or simulated microgravity in humans causes cardiovascular deconditioning with orthostatic hypotension and tachycardia. Postflight orthostatic intolerance is a dramatic physiologic consequence of human adaptation to microgravity made inappropriate by a sudden return to normal gravity. Loss of appropriate cardiovascular reflexes contributes to the cardiovascular deconditioning, but the specific mechanisms remain uncertain. The endothelium is now recognized to play a critical role in the regulation of vascular resistance and blood pressure through the release of nitric oxide and/or prostacyclin. The objective of the proposed studies is to test the hypothesis that the post-suspension hypotension in rats following simulated microgravity involves elevated levels of prostacyclin and/or nitric oxide and, thus, can be attenuated by specific inhibitors of these vasodilatory factors. Using the 30o tail-suspended (hindlimb-unloaded) rat model, the roles of prostacyclin and nitric oxide in post-suspension hypotension are being evaluated. For the coming year we will continue to examine gender differences in the post-suspension hypotensive response.