The use of a hyperoxic environment in the cabins of space vehicles increases the risk of toxic effects of hyperoxic exposure. Simulated and actual space-flight studies have demonstrated decreases in the red blood cell mass. However, it was not clear if these decreases were due to hyperoxia. Studies on animals and humans exposed to oxygen under high pressure indicated that hemolysis could develop due to peroxidation of unsaturated fatty acids in red blood cell membrane. The Skylab flights provided an opportunity to study the effects of hyperoxic exposure on the metabolism of red blood cells. The objective of experiment M114 was to determine the metabolic and cell membrane changes that occur in the human red blood cell as a result of exposure to weightlessness and the spacecraft environment.
During the Gemini and Apollo missions, blood samples were retrieved only during the pre- and postflight periods, limiting study of the red blood cell system. In the Skylab program, blood samples were collected during all phases of the flight. The approach of Skylab experiment M114 was to analyze peroxidation of red blood cell lipids, enzymes of red blood cell metabolism, and levels of 2,3-diphosphoglyceric acid and adenosine triphosphate (ATP) to determine if changes in these variables could be related to hemolysis and subsequent decrease in red blood cell mass. In addition, hemoglobin determination was made on blood samples by using the cyanmethemoglobin method.
On Skylab 2, 3 and 4, no evidence of lipid peroxidation, a biochemical effect known to be associated with irreversible cell damage, was observed. In addition, changes in observed glycolytic intermediates and enzymes provided evidence of red blood cell damage. The mean data from Skylab 2 indicated an in-flight increase in hexokinase, pyruvate kinase, and glyceraldehyde phosphate dehydrogenase. Postflight there was a significant decrease of phosphofructokinase. Skylab 3 mean data indicated significant in-flight decreases of hexokinase, phosphoglyceric acid kinase, and acetylcholinesterase, and increases in pyruvate kinase. The Skylab 4 mean data indicated significant change only in phosphofructokinase during the early in-flight phase of the mission. The most consistent change noted was a decrease in phosphofructokinase, an enzyme susceptible to the effects of oxygen that is thought to be at the center of the Pasteur effect (the shift from anaerobic glycolysis to respiration, brought about by the presence of oxygen).