Problems concerning the quality of DNA measurements on Feulgen-stained imprints. A study of five fixation techniques.

Feulgen-stained rat liver imprints were investigated, and hepatocytes, lymphocytes and granulocytes were measured. Additionally, chicken erythrocytes placed on the slides were measured as an external DNA standard. The imprints were treated according to five different fixation protocols. The measured integrated optical density (IOD) was normalized according to the leukocytes and afterwards scaled according to the diploid hepatocytes. The mean IOD, coefficient of variation (CV), standard error of the mean (SEM) and IOD ratios of distinct cell groups were calculated. The CV of the IOD for hepatocytes was slightly better for air-dried preparations. It was larger for leukocytes than for hepatocytes and worst for chicken erythrocytes. The SEM of hepatocytes did not show remarkable differences between the fixation groups; in general it was near 1%. In all cases the IOD ratios of 2c, 4c and 8c hepatocytes reasonably well followed the expected ratio of 1:2:4 except for wet, formalin-fixed hepatocytes (3.8). The ratios of leukocytes to 2c hepatocytes were about 1.0 for air-dried preparations but considerably lower (0.85) for wet fixation in formalin. The IOD ratios of chicken erythrocytes to 2C hepatocytes varied from 0.33 to 0.35. The deviation of the ratios of single specimens from the estimated mean of a fixation group are described.