Effect of pre-incubation of cells with 1 μM actinomycin on the stimulation of AA release by tamoxifen. The cells were pre-incubated for 2-h in the presence of 1 μM actinomycin. During the 2-h pre-incubation, the % AA released by incubation with the control MEM/BSA and MEM/BSA containing actinomycin was 4.2 ± 0.21(4) and 4.3 ± 0.11(4) respectively. Each bar gives the mean value and the brackets give the SEM. (□) = MEM/BSA; (■) = MEM/BSA containing 8 μM tamoxifen. The data recorded are the sum of the AA released during the 2-h pre-incubation plus the average of the subsequent 6-h incubation. They are representative of three separate experiments with similar results.