Administration of cyclosporine a (CyA) to rats from birth: increased mortality and NK activity

Neonatal DA and LEW rats received 15, 7.5, and 3.75 mg/Kg of CyA or saline subcutaneously 3x each week for 1-12 weeks. In animals receiving 15 and 7.5 mg/Kg a significant (p<0.05-0.01) decrease in body weight was observed by 1 and 2 weeks, respectively. Most animals given 15 mg/Kg died by 4 weeks. Rats receiving 7.5 and 3.75 mg/Kg survived but weighed less (p<0.05) than controls at 2 and 5 weeks, respectively. Morphologically, rats receiving CyA exhibited decreased cellularity in their thymic cortex as well as medulla and spleen white pulp. In addition, there was also a significant decrease in total number of cells harvested from each organ. Rats receiving the 7.5 and 3.75 mg/Kg dose had 1.5-2x more LGLs in their peripheral blood (PBL) and spleen (SPL) then controls after 6-12 weeks. In addition, their PBL and spleen cells were 2-3x more effective than controls in causing 51Cr release from YAC-1 target cells. Also, SPL cells stained with propidium iodide from the 3.75 mg/Kg group demonstrated a 1.5-2x increase in cells within the S phase of their cell cycle by flow cytometry. Thus, prolonged administration of CyA may have selective enhancing effects on certain lymphoid compartments and subpopulations of neonatal rats as well as a selective toxic effects on neonatal rat development