LONG-TERM GROWTH HORMONE-RELEASING FACTOR ADMINISTRATION ON GROWTH-HORMONE, INSULIN-LIKE GROWTH-FACTOR-I CONCENTRATIONS, AND BONE HEALING IN THE BEAGLE

Twelve 11 month old male Beagles were assigned to two treatment groups : a control group (saline) and a group receiving human growth hormone( GH)-releasing factor (hGRF) [1-29]NH2 (25 mu g/kg, SC, TID), Treatment was started 6 days prior to surgery (day 1) and continued until necro psy (3 dogs per group/day) on d 29 or 58. Two porous polyethylene rods were surgically implanted on the lateral diaphysis of the femoral sha ft and a 3 mm hole was drilled through the cortex between the two impl ants of each dog on day 1, Blood and urine were collected on d -6, 27 and 56. Human GRF injections produced a significant (P < 0.05) increas e in GH release following each injection. An increase in GH response w as also observed (P < 0.05) over time. The concentration of insulin-li ke growth factor-1 (IGF-1) increased for 5 weeks and then reached a pl ateau, None of the hematologic or urine measured parameters was affect ed by the treatment (P > 0.05). Albumin, calcium, and protein concentr ations were higher (P < 0.05) on d 27 and 56 in GRF-treated animals. H istological sections of the onlay sites showed that bony ingrowth tend ed to be greater into the porous polyethylene material in GRF-treated animals than the controls at d 28 and 57, while no difference was obse rved in the degree of periosteal bone formation around the implants at either time period (P > 0.05), Bone formation into the cortical defec t was greater in the GRF-treated dogs when compared to controls at day 57 only. In conclusion, chronic hGRF [1-29]NH2 treatment in Beagle do gs produced an increased GH response over time and increased IGF-1 con centrations, It also appeared to promote bony ingrowth into a porous p olyethylene onlay and into a bony deficit.