Studies were undertaken to assess the chicken embryo and newly hatched chicken as models for studying the effects of bone-active agents. Initially, 1,25-dihydroxycholecaliferol (1,25[OH]2D3), sodium fluoride (NaF), parathyroid extract, epidermal growth factor, and prostaglandin E2, were tested for lethality over a broad dose range. One or 3 injections of 1,25(OH)2D3 into the yolk sac of chicken embryos resulted in death of embryos given greater than 0.1 ng/injection, whereas 0.01 ng was tolerated by the embryos. Administering 1,25(OH)2D3 intraperitoneally to newly hatched chickens as a single injection or weekly for 3 weeks resulted in no deaths at doses up to 50 ng. One or 3 IV injections of less than 400 micrograms were tolerated by the embryo. Giving chickens feed and water containing 2.4 g of NaF/kg was lethal but no deaths occurred when chickens were given feed containing less than 1.2 g of NaF/kg. Mortality associated with the administration of epidermal growth factor to embryos was inconsistent, in that death occurred in embryos given a single injection of greater than 250 ng, but no deaths occurred in embryos given 3 injections at similar doses. Parathyroid extract and prostaglandin F2 were not lethal when administered to embryos and chickens in a single-injection or multiple-injection regimen. Overall, lethality in chicken embryos given a particular agent reflected the dose of bone-active agent injected, rather than the number of injections. Three of the bone-active agents were selected to characterize their microscopic bone effects in chicken embryos and chickens. Administration of 1,25(OH)2D3 to embryos on day 14 at doses of 100, 10, 1, and 0.1 ng led to subperiosteal hyperosteoidosis in all 5 of the tibiotarsi examined from the high-dose (100 ng) group necropsied on day 18 of incubation. Three of 5 of the tibiotarsi from the 10-ng treatment group were similarly affected. Bone effects were noticed in chickens hatched from the aforementioned treatment groups or in chickens given 1,25(OH)2D3 intraperitoneally and examined at 3 and 6 weeks of age. Administration of NaF to chicken embryos on the 10, 12th, and 14th days of incubation via the IV route at doses of 160, 80, 40 and 20 micrograms/embryo led to subperiosteal hyperosteoidosis in tibiotarsi from 3 of 10 embryos (examined at 18 days of incubation) from the 2 high-dose groups. Tibiotarsi of chickens from this treatment group were microscopically normal at 3 weeks after hatching. When newly hatched chickens were given a diet containing NaF at dosages of 1.2 g/kg, 0.6 g/kg, and 0.3 g/kg, a dose-dependent increase in osteoid was seen at 3 and 6 weeks. In addition, cortical thinning and expansion of the medullary canal were observed only at 3 weeks. In contrast to the effects observed with 1,25(OH)2D3 and NaF, parathyroid extract caused no microscopic bone alterations when given to embryos or chickens. Overall, the bone alterations in the embryo were attributed to increased subperiosteal osteoid formation and defective mineralization. These findings were consistent with known effects of NaF and 1,25(OH)2D3 on bone, and they establish the chicken embryo as a sensitive model for studying bone-active agents.

A study was undertaken to determine which arteries supply the periosteum of the normal adult canine tibia. The vessels were found to arise from locations distinct from the muscular vascularization. The venous drainage of the tibial periosteum had a satellite relationship with the arteries. On the surface of the periosteum, the vessels formed rectangular patterns. All surfaces of the distal end of the tibia seemed to have less distinct anastomoses of the transverse periosteal twigs, compared with the proximal end of the tibia.

Healing of cancellous bone graft donor sites in the proximal tibial metaphysis of 12 healthy adult dogs was studied histologically. Cancellous bone was curetted from the metaphysis of the proximal end of the tibia, via a 1-cm diameter circular opening in the medical cortex. A hematoma and fibrovascular tissue filled the bone defect at 2 weeks. At 4 and 8 weeks, endosteal callus, composed initially of cartilage and woven bone and later of lamellar bone, filled the marrow cavity. At 12 weeks, the normal structural arrangement of lamellar bone and hematopoietic marrow was reestablished in the marrow cavity. The medial cortex defect was filled only with lamellar trabecular bone. It was concluded that, in adult dogs, a second cancellous bone graft could be collected from the proximal portion of the tibial metaphysis 12 weeks or more after an initial collection.