The high-affinity estrogen receptor antagonist ICI 182,780 has no effect on bone growth in young male rats

Estrogens have profound effects on the processes of bone formation and turn over in females. The physiological role of this class of hormones on bone m etabolism in males is less certain. The purpose of this study was to determ ine the effect of the high affinity estrogen receptor antagonist ICI 182,78 0 on tibial growth in normal male rats. The effects of ICI 182,780 on growi ng male rats were compared to orchiectomy, which prevents the synthesis of estrogens as well as androgens. Neither orchiectomy nor ICI 182,780 had an effect on body weight gained. Orchiectomy decreased longitudinal bone growt h at the proximal tibial metaphysis and radial bone growth at the tibia-fib ula synostosis. In contrast, ICI 182,780 had no effect on either endochondr al or intramembranous bone growth. These findings suggest that androgens ar e more important than estrogens in determining peak bone mass in male rats.