Collagen production rates following acute lung damage induced by butylated hydroxytoluene

Abstract

Treatment of mice intraperitoneally with butylated hydroxytoluene (BHT) results in the formation of a diffuse, dose-dependent lung lesion. At high doses of BHT, pulmonary flbrosis becomes evident. The rate of collagen production was measured in vitro in normal and BHT-damaged lung tissue by quantitating the formation of acid-insoluble [ 3H]hydroxyproline from [ 3H]proline at 1, 2, 3 and 4 hr of incubation. Collagen production was elevated 2 days after BHT (400 mg/kg) and reached a maximum rate of 150 pmoles · (mg dry wt) −1· hr −1 at day 7. The rate then declined but was still significantly above control levels of 57 pmoles · (mg dry wt) −1 · hr −1 at day 14. Expressing these data as a percentage of total protein synthesis committed to collagen demonstrated a specific stimulation of collagen synthesis. A maximum level of 1.5% of total protein synthesis was committed to collagen 7 days after BHT. Control mice committed 0.6% to collagen synthesis. Both the maximum and control percentages of collagen synthesis were the same as those previously reported in vivo following BHT (400 mg/kg). Doses of BHT as low as 200 mg/kg produced a significant increase in both the in vitro rate and percentage of pulmonary collagen synthesis. Only at doses of BHT of 300 mg/kg or greater could the deposition of excess collagen be detected as an increase in total lung hydroxyproline. There was a linear dose-response relationship between BHT and the rate of collagen synthesis. Pulmonary DNA synthesis, another index of lung damage, exhibited a steep, non-linear dose-response relationship with BHT. These data show that increases in the rate and percentage of collagen production are readily detected at levels of lung damage which do not result in the deposition of a measurable excess of hydroxyproline and that in vitro rates of collagen synthesis are, therefore, a sensitive index of lung damage which may be used to extrapolate to “non-toxic” dosage levels. This study also shows that the percentage of protein synthesis devoted to collagen is the same in vivo and in vitro in both normal and BHT-damaged lung tissue.