Space flight and insulin-like growth factor-I signaling in rat osteoblasts.

The primary culture of rat osteoblasts was treated with 1alpha,25 dihydroxyvitamin D(3) and fixed with guanidine isothiocyanate solution during a space shuttle flight. The mRNA levels were analyzed by quantitative reverse transcription-polymerase chain reaction. Microgravity decreased the mRNA levels of insulin-like growth factor-I (IGF-I) and increased reciprocally the IGF-I receptor mRNA levels, as compared to the ground (1 x g) control. Microgravity completely suppressed the mRNA expression of the insulin receptor substrate-1, the postreceptor signaling molecule of IGF-I. Microgravity might deteriorate the action and signaling of IGF-I in rat osteoblasts.