Aged vocal folds have been reported to have dense collagen deposition and decreased hyaluronic acid (HA) in the lamina propria. These characteristics are thought to contribute to vocal problems that occur with age (presbyphonia). To restore better viscoelasticity to aged vocal folds, an intervention that might increase HA and decrease collagen production from aged vocal fold fibroblasts would appear to be a potentially useful approach. Our previous in vitro study has revealed that basic fibroblast growth factor (bFGF) consistently stimulates HA production and decreases collagen production from aged rat vocal fold fibroblasts. The present in vivo study examined the effects of intracordal injection of bFGF into aged rats' vocal folds in terms of restoration of HA and collagen distribution in the lamina propria. We injected bFGF transorally into the lamina propria of (unilateral) vocal folds. The injection was repeated 4 times weekly, and rats were painlessly sacrificed 1 week, 1 month, and 2 months after the final injection. Histologic examination revealed that bFGF significantly increased the HA content of the lamina propria up to 2 months, but showed no effect on collagen, even after 2 months. Because it might take longer for excessive collagen to be degraded, further studies are necessary to clarify the long-term effect on collagen. A drug delivery system for bFGF also needs to be developed to maximize its effect in the future. The present study suggested at least a positive effect of bFGF in restoring the HA content in the aged vocal fold lamina propria.
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