The effect of hydrostatic pressure on intervertebral disc metabolism

Study Design. By the use of pressure vessels, hydrostatic pressure was appl ied to intervertebral disc cells cultured in an alginate. Objective. To test the hypothesis that hydrostatic pressure directly affect s the synthesis of collagen and proteo-glycan by the intervertebral disc ce lls. Summary of Background Data. The influence of compression (both hydrostatic and mechanical) on chondrocyte metabolism was examined in a number of earli er studies. However, in most of these studies, articular car tilage, not in tervertebral disc, was used, and in none of these was hydrostatic pressure applied to intervertebral disc cells cultured in alginate. Methods. Fresh cells were harvested from the lumbar intervertebral discs of dogs. Before their suspension in an alginate gel system, the cells were pl ated and expanded until they reached confluence. Then, by use of the algina te gel system, the cells were exposed (for up to 9 days) to specific values of hydrostatic pressure inside two Stainless steel pressure vessels. One v essel was kept at 1 MPa and the other at atmospheric pressure. The effects of 1 MPa were compared against atmospheric pressure by measuring the incorp oration of [H-3]-proline and [S-35]-sulfate into collagen and proteoglycans , respectively, for the anulus cells and nucleus cells separately, and by d etermining whether this incorporation was reflected by changes in the level s of mRNA for aggrecan and Types I and II collagen. Results. Comparisons with atmospheric pressure yielded the following findin gs: 1) In the incorporation studies, the nucleus and anulus cells exhibited a differential response to a hydrostatic pressure of 1 MPa. Collagen and p roteoglycan syntheses were stimulated in the nucleus cells and inhibited in the anulus cells. 2) There was no significant increase in cell proliferati on, as measured by DNA content, at 1 MPa for either the anulus or nucleus c ells. 3) The mRNA levels of collagen (Col 1A1 and Col 2A1) and aggrecan inc reased at 1 MPa in both the nucleus and anulus cells. Conclusions. Hydrostatic pressure directly affects the synthesis of collage n and proteoglycan by the intervertebral disc cells.