Effects of a Four-day Spaceflight and Recombinant Human Growth Hormone on Cancellous Bone Microarchitecture in Femoral Head of Rapidly Growing Male Rats

Spaceflight results in reduced bone accrual and muscle atrophy in growing rodents. Some studies suggest that the detrimental effects of spaceflight are due, in part, to impaired growth hormone (GH) signaling. An experiment flown aboard STS-41 (October 6–10, 1990) evaluated the efficacy of recombinant human growth hormone (rhGH) in ameliorating the detrimental effects of spaceflight on the musculoskeletal system in male Sprague Dawley rats. The rats were 39 days old at launch and sacrificed following the 4–day flight. Ground controls (n=11/treatment group) and flight animals (n=8/treatment group) were treated with rhGH or excipient delivered using osmotic pumps implanted subcutaneously one day prior to launch. For the present examination, cancellous bone in the femoral head was evaluated using X-ray microtomography (microcomputed tomography), a technology not available when the study was performed. Spaceflight resulted in lower cancellous bone volume fraction, connectivity density, trabecular thickness and trabecular number, and higher trabecular separation. rhGH had no independent effect on cancellous bone architecture and there were no spaceflight by rhGH interactions. These findings suggest that a short interval of microgravity during rapid growth was sufficient to reduce accrual of cancellous bone and alter bone microarchitecture at an important weight bearing skeletal site. Additionally, increasing growth hormone levels was ineffective in preventing cancellous osteopenia in flight animals and did not increase cancellous bone volume fraction in ground controls.