Tamoxifen and norethisterone: effects on plasma cholesterol and total body calcium content in the estrogen-deficient rat.

It is important that drugs which are used to protect bone from the osteoporotic effects of estrogen deficiency should not affect plasma lipids adversely. Effects of a) norethisterone acetate and b) tamoxifen citrate on plasma cholesterol and on bone conservation in rats with normal plasma 17B-estradiol and in rats made estrogen-deficient with the LHRH agonist, buserelin are reported. Tamoxifen halved total plasma cholesterol (p < 0.01), whereas norethisterone did not lower plasma cholesterol. Furthermore tamoxifen fully protected bone from estrogen-deficiency osteopenia whereas norethisterone conserved bone less well. Reductions in cholesterol elicited by tamoxifen were similar in estrogen-deficient rats and in rats with normal ovarian function. This is the first report in the rat that tamoxifen has lipid-lowering actions. It is suggested the rat may be useful for future investigations of the lipid-lowering mechanisms of tamoxifen.