ASGSB 1998 Annual Meeting Abstracts

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GROWTH RATE VARIABILITY OF LAMELLAR BONE IN RATS EXPOSED TO MACROGRAVITY (2G+).    T.G. Bromage¹, I. Smolyar², S.B. Doty³, and E. Holton⁴. ¹Hunter College, NY, ²NOAA-NODC, Silver Springs, MD, ³Hospital for Special Surgery, NY, ⁴NASA-Ames, Moffett Field, CA.

We have previously reported on the circadian growth rate variability of bone lamellae formed on exposure to microgravity (0G), pointing to a reduction in bone formation of the midshaft humerus from ca. 300 gm male Harlan (Sprague/Dawley) rats flown on the 9-day SLS-1 Space Shuttle mission (STS-40). Here, the midshaft tibiae of ca. 300 gm male Wistar rats were examined for variability of bone growth rate and relative bone density owing to 1G (control), 2G, and 3G exposure for 14 days: a protocol following that of the 14 day Cosmos 2044 biosatellite mission.

Embedded polished 60-80 micron thick sections were imaged by both polarizing light microscopy (PLM) and backscattered electron microscopy in the SEM (BSE-SEM). PLM images of endosteal lamellae were obtained and subjected to image processing. Resulting binary images were passed to a quantification program for measurements of the widths between adjacent lamellae. Same fields of view were also imaged in BSE-SEM imaging mode at 20 kV, 500 pa, and a 15 mm working distance for grey level analysis of relative bone density.

Quantitative analyses indicate increased daily growth rates in rats exposed to 2G+. The average lamellar formation rate, in microns per day, was as follows: Vivarium Control, 4.7; On Center Axis Control, 4.6; 2G, 6.1; 3G, 6.6. BSE imaging revealed density dependent differences owing to macrogravity. The grey level histogram of lamellar bone formed during exposure to 2G contains a greater proportion of less dense bone than the 1G control. The peak bone density is shifted slightly toward lower bone density and the overall average density is 5-10% less than for 1G controls. Further research will be required to determine whether the combination of increased growth rate and lowered bone density is a result of a mineral balance or bone matrix perturbation in the presence of increased loading, or, a normal adaptation to elevated strain combined with a lag in bone mineralization/maturation owing to the rapidity of matrix formation.

Research funded by NASA (NAG5-6606) and NSF (SBR-9512373).

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