Effects of nicotine on the intervertebral disc: an experimental study in rabbits.

Clinically, we have observed that a large proportion of patients presenting with low back pain as the chief complaint are smokers. It was therefore postulated that smoking might affect the intervertebral disc. We investigated the histological and functional effects of nicotine on intervertebral discs in rabbits. Rabbits were implanted subcutaneously with minipumps for the delivery of 200 microg/ml nicotine for 4 or 8 weeks. The selected dose produced blood nicotine levels equivalent to those found in heavy smokers (30 cigarettes/day). Nicotine injection caused necrosis and fibrous tissue and vitreous formation in the nucleus pulposus of the intervertebral disc, as well as hypertrophy of the fibrous ring, with partial cracks and detachment. Measurement of collagen and proteoglycan production in intervertebral discs showed reduced synthesis of these proteins in nicotine-treated rabbits compared with the control findings. Our results indicated that the harmful effects of nicotine on the integrity of the intervertebral disc might be mediated by the direct effect of nicotine, or indirectly, by causing vasoconstriction of the vascular network surrounding the intervertebral discs.