[Ultrastructure of the submandibular glands in rats kept in weightlessness]

Submandibular salivary glands of male rats weighing 330-350 g were examined after space flight and ground-based control study. Light microscopy was carried out using hematoxylin-eosin staining and PAS-reaction. Electron microscopy was performed using glutaraldehyde and osmium tetroxide fixation and contrasting according to Reynolds. Light microscopy revealed no destructive changes in the gland parenchyma; differences between flight and control rats remained within physiological limits. Electron microscopy of acinar cells of flight animals showed chromatin condensation, darkening of cells and nuclei, appearance of electron-dense vacuoles, fragmentation fo the granular endoplasmatic reticulum as well as enlargement of interstitial spaces, lumens of acini and intercellular canaliculi, loosening of basal membranes, and thinning of capillary walls. Electron microscopy of acinar cells of control rats demonstrated chromatin condensation in nuclei and fragmentation of the GER. Thus, both animal groups exhibited ultrastructural signs of inhibition of the synthesis and excretion of salivary protein. In addition, flight animals showed increased excretion and, probably, secretion of water and electrolytes. Examinations of granulocytes revealed enlargement of secretory granules in both animal groups, the largest granules being seen in flight animals. They also showed mitochondrial swelling which was most significant in control rats. After the ground-based study cells of the striated compartment also displayed a very distinct mitochondrial swelling which may reduce the reabsorption capacity and enhance salivation of the compartment. However the mechanism of these changes seems to be different from that underlying changes after real space flight.