By Hoppe, Kathryn
Science News , Vol. 142, No. 16
Shuttle experiments probe basic physiology
Some fundamental questions about life on Earth may best be answered in space, as NASA researchers continue to expand our medical knowledge with a broad range of life sciences experiments shuttled into orbit.
The most recent biomedical mission, Spacelab J, launched 20 studies into space for eight days last month. Astronauts kept busy conducting experiments on themselves and caring for a menagerie that included two carp, four pregnant frogs, 30 fertilized chicken eggs, 180 hornets, and more than 7,600 fruit flies.
While investigators still need time to analyze the data from this latest venture, results from earlier flights have already raised new questions, prompting scientists to reexamine some traditional theories about how the human body functions, says Ronald J. White of NASA's life sciences division in Washington, D.C.
NASA's first Spacelab Life Sciences mission (SLS-1) carried 18 investigations into orbit for a nine-day flight in June 1991. After more than a year of analysis, researchers gathered this August at the World Space Congress in Washington, D.C., to discuss their results.
Unlike previous biomedical studies, SLS-1 was designed so that scientists could monitor and compare the long-term health of their astronaut subjects for several months before and after, as well as during, the actual flight. These studies revealed new details about the physiological changes that occur as the human body adapts to different gravitational environments (SN: 8/1/92, p.70).
Other investigations focused on the 29 white rats flown aboard the SLS-1 mission. Many of these experiments probed adaptations of the so-called antigravity muscles, which support the body and maintain posture in Earth's gravity.
One of the most unexpected results revealed that muscle cells in space do not process energy in the same way they do on the ground, White says.
In Earth's gravity, muscle cells use both fatty acids and carbohydrates for fuel, explains Kenneth M. Baldwin, a physiologist at the University of California, Irvine. Using biochemical tests, Baldwin and his co-workers determined that, in space, muscles appear to lose their ability to process fatty acids and thus rely more on carbohydrates for fuel.
This change in energy processing came as a "big surprise" to the researchers, says Baldwin, who adds that the study provided only a few hints as to the causes of the switch. He believes further studies may reveal details that could lead to alterations in astronauts' diets.
Related investigations provided new details about previously studied effects such as muscle atrophy -- the loss of mass and strength that occurs when muscles remain inactive. In the past, astronauts have lost muscle mass in response to the absence of gravitational stress in space, but such changes remain difficult to measure in humans.
The rat's higher metabolic rate causes these effects to occur faster, making short-term changes easier to study. During the nine days of SLS-1, Baldwin and his co-workers found that the rats lost as much as 25 percent of the mass in their antigravity muscles. Muscles used primarily for locomotion atrophied less. After returning to Earth, the rats regained muscle mass slowly: It took twice as long to regain mass as to lose it.
These and related studies highlight the need to counteract the effects of space travel so that astronauts can readapt more easily to life on the ground. Baldwin believes future astronauts may prevent atrophy by adding new exercises to their daily routine. Astronauts should "do the equivalent of pumping iron" while in space, he says.
Baldwin plans future studies to investigate the relationship between lost muscle mass and the loss of muscle function in space, as well as the biochemical signals that control atrophy. …