Abstract
The skeletal system of living organisms has evolved on earth under 1G gravity. It has been reported that the bone density in astronauts and experimental animals decreases significantly during prolonged space flight and that the disorder is due to a decrease in bone formation rather than an increase in bone resorption. The main purpose of our space experiment was to examine morphologically and biochemically the mechanism of suppression of bone growth under microgravity using chick embryos flown in a space shuttle. In the original plan, our space experiment had been scheduled to be conducted in 1987. But, the accident of the space shuttle “Challenger” hampered our scheduled time line. During that time, Vellinger conducted a space experiment in 1989 using 2- and 9-day-old chick embryos, which was very similar to our research proposal but a more primitive one. He has reported that all of the 2-day-old embryos died, implying the importance of 1G gravity in the initial development of the embryos. To confirm his results, we planned to ship 0-day-old eggs in a shuttle with turning the eggs twice a day. Turning of eggs is essential for the normal development of embryos at least on the ground, in particular at an early stage of development, but this procedure was omitted in the Vellinger's experiment. We examined whether 1G gravity and turning of eggs in space are necessary for an early stage development of chick embryos using 0-day-old fertilized eggs. The effect of microgravity on bone formation and muscle development was examined morphologically and biochemically using 7- and 10-day-old embryos.
