Modulation of estrogen action in the rat pituitary and mammary glands by dietary energy consumption

We are investigating the mechanisms through which estrogens induce developm ent of prolactin (PRL)-producing pituitary tumors and mammary carcinomas in rats and how these mechanisms are affected by dietary energy consumption. The hypothesis under examination is that dietary energy restriction inhibit s tumorigenesis in estrogen-responsive tissues by altering cellular respons iveness to estrogenic hormones. In the Fischer 344 (F344) rat strain; a 40% restriction of energy consumption virtually abolishes development of estro gen-induced pituitary tumors. Inhibition of pituitary tumorigenesis in the F344 strain by energy restriction results from modulation of estrogen regul ation of cell survival, not cell proliferation. In contrast, energy restric tion has no inhibitory effect on estrogen-induced pituitary tumor developme nt in the ACI rat strain. However, energy restriction markedly inhibits ind uction of mammary carcinomas in female ACI rats treated with 17 beta-estrad iol. Data presented herein indicate that dietary energy restriction modulat es the responsiveness of specific cell populations to estrogenic hormones a nd thereby inhibits estrogen-induced tumorigenesis in a manner specific to both rat strain and tissue.