Brain natriuretic peptide (BNP), a family of peptides with structural and biologic homologies to previously identified atrial natriuretic peptide (ANP), has been found in human cardiac tissue and plasma. To examine the secretion mechanism of these peptides, we have studied the relationship between their plasma concentrations and hemodynamic parameters before and at 0.5 and 24 hours after percutaneous transvenous mitral commissurotomy (PTMC) in 14 patients with mitral stenosis. We have also investigated the validity of measuring plasma natriuretic peptides as a means for estimating changes in hemodynamic parameters after PTMC. The procedure decreased left atrial pressure (p < 0.01) with an elevation in left ventricular end-diastolic pressure (p < 0.05). Plasma ANP levels decreased significantly after PTMC (before, 64.1 +/- 33.7 fmol/ml; at 0.5 hour, 58.9 +/- 27.7 fmol/ml; at 24 hours, 45.7 +/- 18.3 fmol/ml; p < 0.01), whereas plasma BNP levels remained unchanged after the procedure (before, 5.3 +/- 1.5 fmol/ml; at 0.5 hour, 5.6 +/- 1.9 fmol/ml; at 24 hours, 5.0 +/- 1.9 fmol/ml; p = NS). There was a significant relationship between basal plasma ANP and left atrial pressure (r = 0.88; p < 0.001), and changes in plasma ANP were correlated with those in left atrial pressure (r = 0.69; p < 0.01). Basal plasma BNP was significantly correlated with basal left ventricular end-diastolic pressure (r = 0.65; p < 0.05) but not with the other measured hemodynamic parameters or with plasma volume.(ABSTRACT TRUNCATED AT 250 WORDS)