THE EFFECT OF ULTRASOUND ON COLLAGEN-SYNTHESIS AND FIBROBLAST PROLIFERATION IN-VITRO

Ultrasound has been applied therapeutically to accelerate connective t issue healing although there is little direct scientific evidence to s upport its use. This investigation was conducted to determine the effe cts of ultrasound on the rate of collagen synthesis and cell prolifera tion using cultured fibroblasts derived from Achilles tendons of neona tal rats. Ultrasound (intensity = 0.4 W . cm(-2): frequency = 1 MHz) w as applied to experimental cells growing as monolayers in culture flas ks. Ultrasound had no effect on the rate of collagen synthesis by cont rol fibroblasts over a period of 9 d. The addition of vitamin C to cul ture media stimulated collagen synthesis to the same extent in both co ntrol and ultrasound-treated cultures. Partial digestion of cell matri ces with collagenase (used to simulate injury) resulted in an approxim ately 20% increase in the rate of collagen synthesis. Synthesis was fu rther increased with ultrasound treatment (50-67%). For example, after a single ultrasound treatment, the rate of collagen synthesis was 3.0 +/- 0.4 pg .mu g(-1) DNA . h(-1) in cultures treated with collagenase , compared with 1.8 +/- 0.3 pg .mu g(-1) DNA . h(-1) in collagenase-tr eated cultures not treated with ultrasound and 1.4 +/- 0.3 pg .mu g(-1 ) DNA . h(-1) in controls. Ultrasound applied to preconfluent cultures resulted in significant increases in the rate of thymidine incorporat ion and DNA content. Three daily ultrasound treatments caused a 100% i ncrease in the rate of thymidine incorporation and a 28% increase in D NA content. The results indicate that ultrasound stimulates collagen s ynthesis in tendon fibroblasts in response to an injury of the connect ive tissue matrix and that ultrasound stimulates cell division during periods of rapid cell proliferation.