Morphometric analysis of the pelvis in mice treated neonatally with tamoxifen

The pelves of male and female C57BL/Tw mice given five daily injection of 100 micrograms tamoxifen, 50 micrograms dihydrotestosterone (DHT), or 2 micrograms diethylstilbestrol (DES) from the day of birth were examined morphometrically and histomorphometrically. Total areas of the pelvis, ilium, ischium, and pubis were significantly smaller in neonatally tamoxifen-treated mice than in the controls. There was no significant difference in length of the ischium between tamoxifen-treated and control mice of both sexes. However, lengths of ilium and pubis, and widths of ilium, pubis, and ischium in tamoxifen-treated male and female mice were significantly smaller than in the respective controls. In contrast, neonatal treatment with DHT or DES did not affect the shape of the pelvis of either sex. In the neonatally tamoxifen-treated females, the number of osteoblasts and osteoclasts per 200 microns trabecular surface length and per 10,000 microns2 subperiosteal area of pubic bone section was smaller than in the controls. Inhibition of ossification persisted in the junction of the pubis and ischium of pelves treated with tamoxifen in vitro. These results suggest that neonatally administered tamoxifen mainly retards the growth of the ilium and pubis in mice by changing the activities of osteoclasts and osteoblasts, and that tamoxifen acts directly on the neonatal mouse pubis to inhibit its ossification.