KovariI H., F. KovariI, V. ZiZkovsky, J. Velek: Developmental Changes oj Trimeric GTP-binding Protein in Porcine Brain and Immune System. Acta vet. Bmo 1998,67: 15-20. We studied developmental changes of membrane trimeric alpha subunits of GTP-binding proteins (G proteins), i.e. G alpha (q/ll), G alpha (s) and G alpha (i I ,2) in porcine brain cortex, thymus and spleen on fetal day 92 (FD 92) and 110 (FD 110, newborn), postnatal day 60 (PD 60), and in adult animals. We used immunochemical techniques ELISA or Western blotting with rabbit antibodies against synthetic C-terminal dekapeptides of G alpha subunits prepared by us. In control tests no cross reactivity of G alpha-antisera was detected by ELISA method. Brain cortex was characterized by age-dependent marked decline of G alpha (qlll) and slight decrease of both G alpha (s) and G alpha (i 1,2). In thymus, higher levels of G alpha (q/ll) were estimated on FD 92 which was similar to those on FD 110 and in both thymus and spleen G alpha (s) increased with age. We observed age-induced elevation of G alpha ( i I ,2) subunit in thymus, whereas spleen G alpha ( i 1,2) levels were similar. When summarized. opposite courses of developmental levels of G alpha subunits in brain cortex and lymphoid organs were demonstrated, i.e. brain-dependent decrease and lymphoid tissue-dependent increase as a function of age. These data can represent molecular changes and tissue specifities of differentiation and maturation in the porcine organism. Thymus, spleen, G-alpha subunit, G protein