Comparison of ovariectomy and retinyl acetate on the growth of established 7,12-dimethylbenz[a]anthracene-induced mammary tumors in the rat
Gandilhon, P.; Melancon, R.; Djiane, J.; Kelly, P.A.
Journal of the National Cancer Institute 69(2): 447-451
1982
ISSN/ISBN: 0027-8874 PMID: 6287078 Document Number: 193035
Prolonged exposure to retinyl acetate (RA) in the diet inhibits the development of 7,12-dimethylbenzanthracene (DMBA)-induced mammary cancers in rats. The effectiveness of RA was examined when given 6 mo. after the administration of DMBA. Non-inbred female Sprague-Dawley rats with DMBA-induced mammary tumors were divided into 3 groups and treated for 4 wk as follows: Group 1 served as controls, group 2 was ovariectomized, and group 3 received 328 mg RA/kg diet. Ovariectomy (OVX) markedly reduced the number and size of the tumors. RA administration failed to induce any significant regression in tumor number but significantly retarded tumor growth when compared to tumor growth in group 1 controls. The levels of estradiol, progestin and prolactin (PRL) receptors were significantly reduced after OVX, whereas only the levels of PRL receptors declined significantly after RA administration. Circulating progesterone concentrations were not affected in the RA-treated group but the plasma PRL level was significantly increased. If treatment with RA is delayed until 6 mo. after carcinogen administration, the protective effect of RA can still be observed although its effectiveness is less dramatic than when it is administered earlier.