To elucidate the relationship of
estrogen-depleted condition to apoptosis and
tumor regression, 7,12-dimethylbenz[a]
anthracene-induced
mammary cancers of Sprague-Dawley rats were ovariectomized or treated with the anti-estrogenic agent
epitiostanol after which proliferative activity and the incidence of apoptosis were investigated using the nick end labeling method,
agarose gel electrophoresis of
DNA, electron microscopy, the
BrdU-labeling method and mitotic count.
Tumor regression was found after 7-day treatment, and apoptosis induced by the agent on the 3rd day was clearly shown in both
agarose gel electrophoresis of
DNA and electron microscopy, which are two major methods used to judge apoptosis. The incidence of apoptosis revealed by the nick end labeling method reached its maximum, about threefold the control level, on the 3rd day of
epitiostanol treatment compared with control
tumors (P < 0.01). The incidence of the cells incorporating
BrdU reached its maximum of 9.7% on the 2nd day of the treatment, while the incidence in
tumors without treatment was 7.5% (P < 0.05). Subsequently, the incidence of apoptosis was reduced after 7-day treatment, and the incidence of
BrdU-positive cells was significantly reduced to about 3% after 5-day treatment. The incidence of mitosis did not change until the 3rd day of the treatment and was reduced after 5-day treatment. Similarly, chronological changes of the incidences of
BrdU-labeled cells, apoptotic cells and mitosis were observed in the
tumors after
ovariectomy.
BrdU-labeled apoptotic bodies were detected in the
tumors on the 3rd day in
epitiostanol-treated rats that received a 6-hr bolus of
BrdU before sacrifice.(ABSTRACT TRUNCATED AT 250 WORDS)