Increased serum angiotensin I-converting enzyme activity in patients with mixed connective tissue disease and pulmonary hypertension.

The relationship between serum angiotensin I-converting enzyme (ACE) activity, a possible marker of pulmonary endothelial injury, and the occurrence of pulmonary hypertension (PH) in patients with mixed connective tissue disease (MCTD) was investigated. Before corticsteroid therapy, the mean serum ACE level was 26.4 +/- 14.0 mU/ml in patients with MCTD and PH (n = 6), 16.8 +/- 4.1 mU/ml in patients with MCTD but without PH (n = 18), 16.8 +/- 4.1 mU/ml in patients with undifferentiated connective tissue disease (n = 14), and 16.5 +/- 3.9 mU/ml in controls (n = 18). No significant difference in the enzyme activity was found among the groups. However, 4 patients with MCTD showed increased ACE levels (> 28.3 mU/ml), and all of them had PH. Our results suggest that elevation of serum ACE activity may be related to the occurrence of PH in patients with MCTD.