ROUTE OF ADMINISTRATION MAY DETERMINE THE BIOLOGICAL EFFECTS OF RU-41,740 (BIOSTIM) - TRAPPING OF TC-99M-LABELED HUMAN ALBUMIN COLLOIDS IN MICE

Experiments have been conducted in mice to examine whether treatment w ith the immunostimulating drug RU 41,740 (Biostim) may change the dist ribution of i.v. injected radiolabelled human albumin colloids. It was observed that a single i.p. injection of Biostim (1 ng - 1000 mug) si gnificantly enhanced trapping of the particles in spleen and lungs. Th e effect, which was dose-dependent, was most pronounced in the lungs w here more than a 10-fold increase could take place. On the contrary, o ral administration of Biostim caused a dose-dependent decrease of coll oid trapping in the lungs. Further experiments showed that oral admini stration of Biostim resulted in the appearance of soluble factors in t he blood which inhibited the phagocytic activity of lung macrophages, for example, sera from such mice inhibited lung colloid trapping when injected into new hosts. I.p. administration of Biostim, however, resu lted in the appearence of factors in the blood which enhanced phagocyt osis of lung macrophages. Our conclusion is that the biological activi ty of Biostim in vivo may be highly dependent on its route of administ ration.