RESUMEN
Clinically it had been noticed that a large proportion of patients presenting with low back pain are smokers. Therefore, in this experimental study the histological effects of nicotine on the lumbar intervertebral discs of the rabbits was investigated. Eighteen rabbits were divided equally into 3 groups, Group I [a and b]; as control. Group 2 injected intraperitoneally by 5000 ng/kg nicotine daily for 4 weeks. Group 3 injected intraperitoneally by 5000 ng/kg nicotine daily for 8 weeks. The selected dose produced blood nicotine levels equivalent to those found in heavy smokers [30 cigarettes / day]. Light and electron microscopic studies revealed that nicotine injection showed a variety of histological changes, which were not observed in the control group. This includes appearance of spaces within the nucleus pulposus and separation from the adjacent fibrous lamellae in the annulus fibrosus. Also loss of the regularity of the multilayered structure of the annulus fibrosus, and excessive inclusions associated with vacuoles which continue with the rough endoplasmic reticulum within the chondrocytes. Disc degeneration was more marked in rabbits injected with nicotine for 8 weeks [G3] than in those injected for 4 weeks [G2]. It could be concluded that the disc degeneration is more common among smokers and is correlated with the duration of exposure to nicotine