THE EFFECTS OF SPACEFLIGHT ON MESSENGER-RNA LEVELS FOR CYTOKINES IN PROXIMAL TIBIA OF OVARIECTOMIZED RATS

Background: Bone resorption was elevated in ovariectomized rats during a 14-d orbital spaceflight over and above that caused by gonadal horm one deficiency (2). Locally produced cytokines are believed to have an important role in normal as well as abnormal bone resorption. Methods : The purpose of the present study in the same rats was to determine w hether spaceflight results in altered expression of cytokines in cance llous bone. The mRNA levels for selected cytokines were determined in proximal tibial metaphysis using ribonuclease (RNase) protection assay s. Results: The message for interleukin 1 receptor antagonist, interle ukins 1 alpha, 10, and 12, macrophage migration inhibitory factor, and tumor necrosis factor-alpha was below the limit of detection for all groups. Interleukin 6 and transforming growth factor-beta(2) were expr essed in bone but the mRNA levels for these cytokines were not altered by either ovariectomy or spaceflight. There was a tendency for interl eukin-1 beta message to be increased following ovariectomy (OVX) and t his tendency achieved statistical significance following spaceflight. Finally, spaceflight resulted in an increase in the message level for interferon gamma in OVX rats. In summary, spaceflight results in incre ases in mRNA levels of two cytokines in OVX rats which have been shown to increase bone resorption.