Abstract
Studies were carried out to clarify the effects of 17β-estradiol on tibia histo-morphometry in chick embryos. Varying levels of 17β-estradiol (0, 20, 40, or 80μg) were injected every other day from the 10th to 18th day of incubation into the air chamber of eggs. On the 20th day of incubation, right tibiae were excised and diaphyseal cross sections were examined by light microscopy. Morphological differences were quantified using a computerlized histomorphometric technique. The administration of two higher doses of 17β-estradiol caused significant increase in histomorphometric indices of bone formation. Total bone area, measured at middiaphysis, greatly increased in the 17β-estradiol-treated embryos compared to controls receiving the vehicle alone. This increase was associated with marked increase in bone volume, expressed as percentage of the bone matrix area. The number and areas of periosteal osteoblasts were remarkably enhanced in the 17β-estradiol-treated group. 17β-Estradiol treatment did not affect the two histomorphometric indices of bone resorption, nuclei number and area of osteoclast. Exogenous 17β-estradiol would thus appear to induce periosteal osteoblast differentiation and stimulate bone formation in the chick embryo tibia.
