Effects of hydrostatic pressure on matrix synthesis in different
regions of the intervertebral disc.
Ishihara, Hirokazu, Donal S McNally, Jill P. G. Urban, and Andrew C.
Hall.
University Laboratory of Physiology, Oxford, United Kingdom OX1
3PT
APStracts 2:0521A, 1995.
The intervertebral disc is routinely subjected to compressive loads
which alter with posture and muscle activity, and which can produce
pressures >2MPa in human lumbar discs in vivo30,31. We measured
the effect of load on hydrostatic pressures in bovine caudal discs.
With increase in applied load, pressure increased linearly in the
nucleus and inner annulus. The resting pressure measured after
slaughter (0.19+.05 MPa) and the pressure at failure (34MPa,
estimated from the vertebrae/ disc segment failure load of 7430+590N)
define the limits which can occur in vivo. Since hydrostatic pressure
influences matrix synthesis in articular cartilage, we have examined
the effects of pressures in the range 1-10MPa applied for 20 secs. or
2 hrs., on proteoglycan synthesis in bovine caudal and human lumbar
intervertebral discs in vitro. In the nucleus pulposus and inner
annulus of bovine discs application of hydrostatic pressure in the
range 1-7.5 MPa for only 20 secs. stimulated matrix synthesis over
the following 2 hrs. at atmospheric pressure. The maximum stimulation
in the bovine discs was seen in the inner annulus after application
of 2.5MPa where proteoglycan synthesis rates doubled. Exposure to
2.5MPa also stimulated synthesis in the nucleus pulposus of human
discs taken at surgery, whereas 7.5MPa inhibited synthesis in 5/6
specimens. With 2 hrs. continuous exposure to the same levels of
pressure, no stimulation was seen in the nucleus of bovine discs and
significant stimulation was only observed at 5.0MPa in the inner
annulus. Exposure to 10 MPa for either 20 secs. or 2 hrs. inhibited
proteoglycan synthesis in these regions of the discs. In contrast in
the outer annulus, where loading does not lead to a rise hydrostatic
pressure in vivo, there was no significant response to hydrostatic
pressure over the range of 1-10 MPa in bovine or human discs.
Received 31 May 1994; accepted in final form 26 October 1995.
APS Manuscript Number A553-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95