Abstract
The effect of colchicine and colcemid (1 Γ 10^β6^ M) on the blastogenic response of human lymphocytes to concanavalin A was studied in vitro by three different methods. (a) Measurement of [^3^H]thymidine ([^3^H]dThd) incorporation which was strongly suppressed by the drugs. (b) Volume spectroscopy showing that the growth of cellular and nuclear volume was only moderately affected by the drugs during the first two days of culture: in drugβtreated cultures, 25% of the cells responded by measureable growth of their nuclear volume as compared to 30% in untreated cultures. After two days, however, growth stagnated in drugβtreated cultures, and cell division never occurred. (c) Flow cytofluorometry, showing that in drugβtreated cultures the number of cells measurably increasing their DNA content, i.e. entering Sβphase, was about 60% of that in untreated cultures. However, the drugs caused a majority of the responding cells to stop DNA synthesis before completing Sβphase. This effect could not fully account for the strong suppression of the [^3^H]dThd incorporation indicating that colchicine and colcemid caused a malfunction of the [^3^H]dThd assay. It is concluded that colchicine and colcemid do not significantly inhibit initiation of a blastogenic response indicating that microtubuli, which are known to be affected by these drugs, are not essential for the triggering of blastogenesis.