Measurement of the S-phase duration in normal and abnormal human endometrium by in vitro double labelling with bromodeoxyuridine and tritiated thymidine.

The duration of the S phase of the cell cycle (ts) in the glands and stroma of normal, hyperplastic, and malignant endometrium was measured in vitro using a double labelling technique. Endometrial organ cultures were incubated sequentially in tritiated thymidine (3HTdR) and bromodeoxyuridine (BrdU) each for 1 h. Labelled cells were visualized in tissue sections using 3HTdR autoradiography and immunohistochemistry with an anti-(BrdU) antibody. Three populations of cells, single labelled with either 3HTdR or BrdU, and double labelled cells, were easily identified and ts was calculated from both the rate of influx into, and efflux out of S. There were no significant differences in ts in the different tissue types or between influx and efflux in the glands. However, in the stroma ts calculated from the rate of efflux was significantly shorter than that calculated from the rate of influx, suggesting that during the cell culture period the rate of cell efflux from S was greater than influx. This is the opposite to what would be expected in an exponentially growing cell population and suggests that there may be an effect from the culturing conditions.