Effects of estradiol and dihydrotestosterone on osteoblast gene expression in osteopenic ovariectomized rats

Because androgens increase bone formation and estrogens inhibit bone resorption, there is a potential therapeutic use for a combined treatment of these hormones to preserve bone. We investigated the effect of dihydrotestosterone (DHT) and estradiol, alone and in combination, on the mRNA levels of genes expressed during osteoblast development in osteopenic ovariectomized (ovx) rats: 40 animals were ovx and administered vehicle or 80 mg/kg body weight DHT at 15 weeks postovariectomy. At 19 weeks postovariectomy, the rats were administered vehicle or 20 mg/kg body weight estradiol for 1 week. The treatment groups were as follows: (1) vehicle + vehicle, (2) DHT + vehicle, (3) vehicle + estradiol, and (4) DHT + estradiol. Fasting blood and urine samples were collected at 15, 17, 19, and 20 weeks postovariectomy for bone biochemical analyses. On completion of both procedures, the long bones were removed and total RNA extracted. Combined DHT and estradiol treatment increased the mRNA (P < 0.001) and serum levels of alkaline phosphatase (ALP) (P < 0.01) compared to control rats. These data suggest that combined DHT and estradiol treatment stimulates osteoblasts at an early stage of their development when ALP is expressed.