Enzymatic and morphological response of the thymus to drugs in normal and zinc-deficient pregnant rats and their fetuses

Summary In the thymus of normally fed pregnant rats the plasma membrane enzymes dipeptidyl peptidase IV (DPP IV) and alkaline phosphatase (alP) were found in cortical and medullary lymphocytes (thymocytes). Plasma membrane aminopeptidase A (APA) and adenosine monophosphate hydrolysing phosphatase (AMPP) were present in cortical reticular cells. In medullary reticular cells, aminopeptidase M (APM), -glutamyl transferase (GGT), adenosine triphosphate (ATPP) and thiamine pyrophosphate (TPPP) cleaving phosphatases were detected. Medullary reticular cells did not contain APA. Lysosomal DPP I and II, acid phosphatase, acid -d-galactosidase, -d-N-acetylglucosaminidase, -d-glucuronidase and non-specific esterases occurred especially in macrophages at the corticomedullary junction. The 21-day-old fetal thymus showed a similar reaction pattern as the maternal organ except for APA which was absent before birth.—After treatment of the pregnant rats with valproic acid (VPA), salicylic acid (SA), streptozotocin (ST) and retinoic acid (RA) APA showed an increase in activity in the thymic cortex. In addition, ST and RA induced AMPP, ATPP and TPPP activity in cortical reticular cells up to the same pattern as in medullary reticular cells. After ethanol (ET) administration severe damages occurred. The thymic cortex was free of DPP IV-positive lymphocytes; the medullary reticular cells showed reduced or no GGT and occasionally an increased APM activity. Dexamethasone (DEXA) given to normal or zinc-deficient rats produced the most severe lesions; thymocytes with DPP IV activity were completely absent in the cortex and medulla. In Zn-deficient pregnant rats similar alterations were observed as after ET. When the drugs were applied to Zn-deficient pregnant rats, the alterations resembled those observed after drug treatment alone. In all cases of severe thymus degeneration, i.e. ET and DEXA treatment and Zn-deficiency, the number of macrophages and activities of lysosomal hydrolases in macrophages and reticular cells were increased; the lysosomal hydrolases were often homogeneously distributed over the cortex. Cell contacts between reticular cells and lymphocytes were reduced. Vacuoles occurred within the reticular cells.—The fetal thymus was reduced in size and the number of macrophages and the activities of their lysosomal enzymes were increased after Zn-deficiency, DEXA treatment and Zn-deficiency combined with ET administration.Supported by the Deutsche Forschungsgemeinschaft (Sfb 174)