Mechanism of Intervertebral Disc Degeneration Caused by Nicotine in Rabbits to Explicate Intervertebral Disc Disorders Caused by Smoking

Abstract

STUDY DESIGN: The effects of nicotine on intervertebral discs in rabbits were studied experimentally. OBJECTIVES: To investigate the effects of nicotine on the vascular buds in rabbits for elucidating the mechanism of nicotine-induced vertebral disc degeneration. BACKGROUND DATA: Several groups have suggested that cigarette smoking is associated with low back pain, but the exact mechanism is not yet fully understood. METHODS: The pump was filled with a diluted nicotine solution, then implanted under the skin of rabbits for 8 weeks. This model was designed to maintain blood nicotine concentration at approximately 110 ng/mL. Rabbits receiving physiologic saline were used as control animals. RESULTS: Nicotine treatment resulted in necrosis and hyalinization of the nucleus pulposus in all rabbits. The anulus fibrosus showed a disturbance of the pattern of overlapping laminae with and without clefts and separation. These resulted in changes indicative of stenosis of vascular buds and perivascular calcification. Nicotine treatment resulted in hypertrophy of vascular walls, necrotic changes in endothelial cells, and narrowing of the vascular lumen. Nicotine treatment resulted in delineation of vascular buds in the vicinity of the vertebral endplate and a reduction of their numbers. However, the control animals showed a dense vascular network. The number of vascular buds decreased in nicotine treatment. CONCLUSION: The authors believe that both reduction in the density of vascular buds and narrowing of the vascular lumen result in decreased oxygen tension, leading to decreased synthesis of proteoglycan and collagen, thus facilitating degeneration of the disc.