Effects of simulated weightlessness on the intestinal mucosal barrier of rats

This study employed a rat tail-suspension model to investigate the effects of simulated weightlessness on the intestinal mucosal barrier. Twenty-four Wistar rats were randomly divided into control (CON), 14-day tail-suspension (SUS-14d), and 21-day tail-suspension (SUS-21d) groups (n = 8 per group). Expression of occludin and zonula occludins-1 (ZO-1), proteins of the tight junction (TJ), in the intestinal mucosa was measured by immunohistochemical analysis, Western blotting, and mRNA fluorescent quantitation PCR. Plasma concentrations of diamine oxidase (DAO) and d-lactate were determined using an enzymatic spectrophotometric assay. Expression of occludin and ZO-1 was reduced in the SUS-14d and SUS-21d groups as compared to the CON group, with lowest expression observed in the SUS-21d group (P < 0.01). Examination by transmission electron microscopy (TEM) of the jejunal epithelium revealed increased intercellular space, decreased TJ and desmosome densities, and destruction of microvilli in the SUS-14d and SUS-21d groups. Plasma DAO and d-lactate concentrations in the SUS-21d group were higher than those in SUS-14d group and significantly higher than those in the CON group (P < 0.01). In all three groups, the expression of occludin and ZO-1 was found to correlate negatively with DAO (P < 0.01) and d-lactate (P < 0.01) concentrations. It is concluded that simulated weightless results in down-regulation of expression of TJ proteins in the rat intestinal mucosa. Simulated weightlessness is proposed to increase intestinal permeability through damage to the TJ.