Degeneration of intervertebral discs due to smoking: experimental assessment in a rat-smoking model.

We have investigated the intervertebral discs of rat-smoking models to demonstrate that smoking is a cause of degenerative intervertebral disc disease. A smoking box was developed for this study. We exposed 8-week-old rats to indirect tobacco smoke inhalation. Each rat was forced to inhale the smoke from one cigarette per hour. The mean blood nicotine level of rodents exposed to cigarette smoke corresponds to about twice that of ordinary human smokers. Histological and immunological studies were then performed to assess the effects of smoking for varying periods of time. After 8 weeks, the chondrocytes in the disordered annulus fibrosus layer tended to grow larger and attain a rounder form than normal chondrocytes. The interleukin-1beta level in the 8-week smoking group was significantly higher than that of the control group. Tobacco smoke inhalation increased local production and release of inflammatory cytokines and resultant decomposition of chondrocyte activity.