Mechanical stimulation of intervertebral disc cells by cyclic hydrostatic pressure

Objective. To examine the effects of hydrodynamic cyclic loading on intervertebral disc cell biosynthesis. Design. With the use of a piston-chamber pressure vessel, hydrodynamic pressure was applied to intervertebral disc cells in monolayer culture. Background. The influence of compression on intervertebral disc cells has been examined in a number of previous studies. However, in most cases, hydrostatic pressure was used at low levels, and in none were high, hydrodynamic pressures at varying frequencies applied to intervertebral disc cells. Methods. Cells were harvested from porcine intervertebral discs. After digestion, the cells were plated and grown to confluence in culture flasks, and then trypsinized and reattached to 35mm culture dishes. By the means of cyclic, hydrodynamic loading, the cells were exposed to varied pressures and frequencies for 20 minutes a day for 3 and 7 days. Following the 2nd and 6th day of loading, [3H]-proline was used to label the cells and they were incubated overnight to allow incorporation of the isotope. After loading on the 3rd and 7th day, the medium was removed and both cells and medium were frozen separately waiting analysis. By scintillation, the incorporated and released [3H]-proline into and by the cells could be determined, and these values were normalized by DNA(ug). Results. As reported previously, mechanical stimulation inhibited disc degeneration versus the Control. The treatment of 1Hz and 5MPa for both the 3 and 7 day trial caused the least ratio of collagen released, and for the 3 day trial, this treatment had the highest average of incorporated collagen, though for the 7 day trial this was not the case. Also, there appears to be a possible shift in biosynthesis near the frequency of 8Hz as this is where the cells began to increase degeneration after decreasing from the Control to 1Hz. It is believed that a detailed examination of frequencies from 1 to 15Hz should be conducted at constant pressure to determine the point of singularity.