Abstract
Osteoblasts and osteoclasts on the medullary bone surface in the femurs of laying hens treated with tamoxifen (an antiestrogen) were examined with an electron microscope while an egg was in the magnum or in the shell gland of the oviduct. Most osteoblasts on the medullary bone surface of non-treated hens having an egg in the magnum were characterized by well developed cytoplasm containing a large endoplasmic reticulum and Golgi complexes. And osteoclasts which were distributed very sparsely on the bone surface did not possess ruffled borders. After tamoxifen treatment, however, many osteoblasts had poorly developed cell organelles, but osteoclasts had well developed cytoplasm and extended ruffled borders adjacent to the bone surface. When an egg was in the shell gland, many osteoblasts in both tamoxifen-treated and non-treated hens showed poorly developed cytoplasm, but the osteoclasts had well developed cytoplasm and ruffled borders.
These results indicate that osteoblastic bone formation is suppressed and osteoclastic bone resorption is accelerated by tamoxifen treatment while an egg is in the magnum, and that effects of tamoxifen may not be detected in osteoblasts and osteoclasts while an egg is in the shell gland. Therefore, it is suggested that estrogen stimulates the bone formative functions of osteoblasts and prevents the bone resorptive functions of osteoclasts during the egg laying cycles.
