Mammalian interstitial collagenases (E.C.3.4.24.7) are considered as key initiators of collagen degradation in periodontal diseases. However, the cellular sources of collagenases present in gingival crevicular fluid have not been completely clarified. Resident fibroblasts and epithelial cells as well as infiltrating neutrophils and monocyte/macrophages are potential sources of the enzymes. We have recently found significant differences in tetracycline inhibition between human neutrophil and fibroblast interstitial collagenases. To address the cellular source of collagenase present in gingival crevicular fluid in 2 distinct periodontal diseases, we studied the tetracycline inhibition of collagenase in gingival crevicular fluid of patients with localized juvenile periodontitis and adult periodontitis. Gingival crevicular fluid samples were collected from deep (greater than 5 mm) periodontal pockets and assayed for collagenase in the presence of 0-1000 microM doxycycline as well as a chemically modified tetracycline devoid of antimicrobial activity (4-de-dimethylaminotetracycline). The drug concentration required to inhibit 50% of collagenase activity (IC50) in localized juvenile periodontitis gingival crevicular fluid was 280 microM for doxycycline and 470 microM for 4-de-dimethylaminotetracycline. Significantly lower values, 10-20 microM, were obtained for collagenase in gingival crevicular fluid of patients with adult periodontitis. We propose that systemic tetracycline levels are efficient inhibitors of collagenase in gingival crevicular fluid in affected sites of patients with adult periodontitis but not of patients with localized juvenile periodontitis and that the fibroblast type interstitial collagenase is the predominant collagenase type in gingival crevicular fluid in affected sites of patients with localized juvenile periodontitis and the neutrophil collagenase in adult periodontitis gingival crevicular fluid.(ABSTRACT TRUNCATED AT 250 WORDS)