Effects of exposure period of acetylsalicylic acid, paracetamol and isopropanol on L929 cytotoxicity.

An established fibroblast cell line, L929, was exposed to three substances-acetylsalicylic acid, isopropanol and paracetamol-for 24 hr, 72 hr or 13 days. The effective concentration that caused 50% inhibition of cell growth (EC(50)) was calculated for both the 24- and 72-hr exposures using three assays-total protein (TP), neutral red uptake (NR) and enzymatic conversion of MTT to formazan. The methods determining the viability of the cells were more sensitive than measurement of total protein. Cells exposed for 13 days continued to proliferate during the entire period, although at a reduced rate, and never attained the density of the control. The relative toxic effect of the substances varied considerably as a consequence of the duration of the exposure period.