COMPARATIVE-STUDIES ON EFFECTS OF ALL-TRANS-RETINOIC ACID AND ALL-TRANS-RETINOYL-BETA-D-GLUCURONIDE ON THE DEVELOPMENT OF FETAL MOUSE THYMUS IN AN ORGAN-CULTURE SYSTEM

The thymus is a target organ of retinoid teratogens. Retinoids with a generally reduced teratogenic potency should therefore also exert redu ced adverse effects on thymus development. The effects of all-irans-re tinoic acid (a-tRA) and all-trans-retinoyl-beta-glucuronide (a-tRAG) o n the in vitro development of thymic lobes of 15-day-old mouse foetuse s were compared in an organ culture system. Both compounds were added to the medium at concentrations ranging from 10(-7) to 10(-5) M. The c ulture period was 6 days. The investigations showed a concentration-de pendent effect of both substances on the proliferation of the lymphati c cells. At 10(-5) M the number of thymocytes was significantly reduce d to values of about 70% of the controls by either of the retinoids (P less than or equal to 0.05). Results of flow cytometry showed signifi cant differences concerning the differentiation markers CD4 and CD8 af ter the culture period. The presence of 10(-6) M a-tRA induced a signi ficant increase in the percentages of CD4(+)CD8(-) cells and a signifi cant decrease of CD4(+)CD8(+) cells. At 10(-5) M a-tRA an additional s ignificant increase in the percentages of CD4(-)CD8(-) cells was found . In contrast, after treatment with a-tRAG, percentages of these popul ations were in the same range as the controls. Light and electron micr oscopic investigations revealed a depletion of lymphatic cells and an increase of intracytoplasmic vacuoles in the thymic epithelial cells a t 10(-6) and 10(-1) M of either retinoid. HPLC analyses revealed a rem arkable degree of retinoid isomerization and (in the case of a-tRAG) o f hydrolysis. Compared with the culture medium, retinoids were accumul ated in the thymic lobes. Possibly a-tRAG acts by way of limited hydro lysis to retinoic acid.