Raloxifene, tamoxifen, nafoxidine, or estrogen effects on reproductive and nonreproductive tissues in ovariectomized rats

Abstract

For the first time, four well-characterized compounds from four distinct chemical classes were directly compared for efficacy and potency in hone, uteri, lipids, and adipose tissues in an ovariectomized model with 6 month old rats. Five weeks of oral dosing confirmed that ethynyl estradiol, tamoxifen, and raloxifene are potent inhibitors of the loss in volumetric bone mineral density (BMD, mg/cc) induced by ovariectomy, as measured by computed tomography. In the metaphysis of distal femora from ovariectomized rats, analysis showed a significant 12-20% decrease (P< 0.01) in the BMD. Linear regression analysis was used to calculate half-maximal efficacious doses for ethynyl estradiol ED(50) =0.04mg /kg, which was threefold more potent than tamoxifen, which in turn was threefold more potent than raloxifene, which was more efficacious than nafoxidine. In the uterus, raloxifene had minimal effects on the endometrium and smaller effects on uterine eosinophil peroxidase activity than nafoxidine, tamoxifen, or estrogen, respectively. Estrogen was the most potent in reducing cholesterol levels in ovariectomized rats, whereas tamoxifen and nafoxidine were more effective than raloxifene in blocking gain in body weight. Distinct compounds had advantages in the management of bone, uterine, serum cholesterol, and adipose tissues after ovariectomy. The distinct pattern of pharmacological effects may be best understood in terms of their respective chemical structure, specifically estrogens, benzothiophenes (raloxifene), dihydronapthylenes (nafoxidine), and triphenylethylenes (tamoxifen). These data point to advantages of separate compounds in the management of bone, uterine, serum cholesterol, and adipose tissues after estrogen deficiency, and show that the benzothiophene raloxifene has potentially important advantages over estrogen, tamoxifen, or nafoxidine in the uterus.