EFFECTS OF MODELED MICROGRAVITY CONDITIONS ON RAT INTESTINAL TRANSIT

Exposure to microgravity leads to modifications of several physiological processes whose mechanisms are not clearly understood. This study aimed to determine whether modeled microgravity conditions performed with a three dimensional clinostat (Random Positioning Machine, RPM) influence intestinal transit in the rat and the expression of enzymes involved in this process and gastrointestinal homeostasis: the inducibile isoform of nitric oxide synthase (iNOS), ciclooxygenase (COX-1, 2), ICAM-1 and heat shock proteins (HSP 70 and 90). Rats, individually housed, were studied in 3 groups: RPM, kept in a semicylinder fixed on the RPM and two control groups: one kept immobilized in a semicylinder on the floor of RPM (CG), to rule out a possible effect of immobilization stress and another with animals kept in a stan- dard cage (CC). The present study shows that RPM reduced rat intestinal transit and that this effect could be medi- ated by an increase of iNOS, ICAM 1 and Hsp 70 expression as well as by a reduction of COX-2 expression. While we could not rule out a role of immobilization stress, data on intestinal iNOS and HSP 70 as well as HSP 90 in stom- ach support the idea that RPM reduced intestinal transit in the rat, a process with an important role in some adap- tive mechanisms.