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Alternate fluctuations of leucine and thymidine incorporation by mammary tumors in rats during the estrous cycle.

1977; National Institutes of Health; Volume: 37; Issue: 9 Linguagem: Inglês

Chung Lee, John J. Murphy, Cheryl A. Diamond, Nancy S. Rafferty, Ryoichi Oyasu,

Estrogen and related hormone effects

Summary Rates of [3H]leucine and [3H]thymidine incorporation by 7,12-dimethylbenz(a)anthracene-induced rat mammary tumors were examined during different days of the host9s estrous cycle. Actively growing tumors were surgically removed from regularly 5-day-cycling hosts and were cut into 1 to 2-cu mm pieces for incubation. The incubation was carried out in 4 ml of Medium 199 containing either [3H]leucine for 2 hr or [3H]thymidine for 1 hr at 37° under 95% O2 and 5% CO2. By scintillation counting the rate of [3H]leucine incorporation was the highest at proestrus and dropped significantly to its lowest point on the next day at estrus. During the remaining 3 days of the cycle at metestrus, diestrus 1, and diestrus 2, the rate increased slightly but was still significantly lower than that observed at proestrus. Unlike [3H]leucine incorporation, the rate of [3H]thymidine incorporation was the lowest at proestrus and remained low at estrus. The rate began to rise by metestrus, peaked at diestrus 1, and declined by diestrus 2. Rates of [3H]thymidine incorporation correlated significantly with tissue mitotic counts, which also peaked at diestrus 1. Radioactivities in the acid-soluble fraction of the incubated tissues were not significantly different for either labeled precursors throughout the estrous cycle. Autoradiographic studies of tissues collected after incubation with [3H]thymidine showed that silver grains were localized over cell nuclei. The data indicate that the growth of 7,12-dimethylbenz(a)anthracene-induced mammary tumors in rats during the estrous cycle is associated with a peak of [3H]leucine incorporation at proestrus and a wave of [3H]thymidine incorporation during metestrus-diestrus.