Volume 5, Number 2 March/April 1997
Aerospace Technology Development
ATS WITH HIGH BLOOD PRESSURE
flying on a recent Space Shuttle mission may help scientists better understand how
calcium helps maintain human health. Drs. David McCarron and Daniel Hatton, hypertension
specialists from the Oregon Health Sciences University, Portland, are examining calcium's
role in blood pressure regulation. Calcium has long been recognized as a critical
mineral in normal development and the function of bone and muscle.
"A large body of evidence indicates that problems in the way the body processes calcium also can lead to hypertension," Hatton said. "This flight experiment will help us clarify the role calcium levels play in this condition."
Hypertension affects more than 50 million Americans and contributes to heart attack, stroke and kidney disease. It costs the nation's health care system billions of dollars annually, McCarron said. Dietary calcium seems to have its greatest effect on blood pressure when calcium demands on the body are highest.
McCarron and Hatton were among the first to propose that adequate dietary calcium is essential for normal cardiovascular function. They have tested their hypothesis in studies with humans and rats with normal and elevated blood pressures. The model for their studies is the "Spontaneously Hypertensive Rat," which is genetically predisposed to calcium-related high blood pressure. It is thought that space flight causes an increase of bone loss from the skeleton and a decrease in intestinal absorption of dietary calcium. The study of this animal model enables investigators to determine how dietary calcium modifies calcium metabolism and blood pressure in space.
NASA and the National Institutes of Health (NIH) are interested in how changes in gravity affect calcium metabolism because the loss of bone mass during space flight may cause osteoporosis in astronauts earlier than Earth-bound people. Bones, which support the body against gravity's pull, shed calcium into the blood and out of the body because bones are not weight-bearing in space. The shedding process begins immediately upon leaving Earth's gravity and seems to continue for the entire time in microgravity. An astronaut's mass in supporting bones drops 8 to 10 times faster than the corresponding loss of bone mass for aging people on Earth after just a few months.
The experiment, known as NIH-R4, included rats on both high-calcium and low-calcium diets. Scientists are conducting tests on the rats to discern how different calcium intakes affected blood pressure and cardiovascular functioning in microgravity. NASA's Ames Research Center is the experiment developer. For more information, see the NIH-R4 home page at: http://weboflife.arc.nasa.gov/EXPLORATIONS/MISSIONS/nihr4.html
For more information about NIH-R4, contact Dr. Daniel Hatton
at Oregon Health Sciences University.
Call 503/494-8464,E-mail: hattond@ohsu.edu
Please mention you read about it in Innovation.
