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Type III procollagen N-peptides (PIIINPs) are believed to be released in stoichiometric amounts as type III collagen molecules are secreted from cells. We hypothesized that if the human lung actively produces type III collagen a detectable transpulmonary gradient in PIIINPs would exist in normal individuals that might be altered following a pulmonary insult. PIIINPs were therefore measured by radioimmunoassay in serum taken simultaneously from the pulmonary artery (PA) and left ventricle/aorta (LV) in 11 patients undergoing routine cardiac catheterisation. Mean PIIINP levels +/- SEM in LV were 66.8 +/- 5.4 micrograms.ml-1 and 59.9 +/- 4.1 micrograms.ml-1 in PA (p less than 0.04). In 6 patients, repeat measurements taken 4 h after cardiopulmonary bypass revealed a significant fall in PA values to 43.8 +/- 2.6 micrograms.ml-1 (p less than 0.001) and abolition of the transpulmonary gradient. These results suggest the adult human lung actively synthesis type III collagen and that, in the short term, cardiopulmonary bypass inhibits this process.

Bronchoalveolar lavage fluid from patients with systemic sclerosis was analysed for evidence of pulmonary vascular leakage, inflammatory cell influx, and enhanced type III collagen synthesis. Eighteen patients with systemic sclerosis and computed tomographic evidence of fibrosing alveolitis were compared with 16 patients with a normal scan. The albumin concentration in lavage fluid was higher in all patients than in normal volunteers. Patients with an abnormal computed tomogram as a group had increased proportions of all inflammatory cell types, whereas those with a normal scan had increased neutrophils only. Increased lavage type III procollagen peptides were found in all patients with an abnormal computed tomogram and eight of those with a normal scan. These results suggest that pulmonary vascular leakage and neutrophil influx may be early pathological features of lung disease in systemic sclerosis and frequently associated with enhanced collagen production. Thus lavage of patients with systemic sclerosis may identify lung inflammation and altered collagen metabolism early in the evolution of fibrosing alveolitis.