The present study describes the concentration and molecular form of atrial natriuretic peptide (ANP) in Holstein dairy cattle with mild (bacterial endocarditis; BEC) or severe (dilated cardiomyopathy; DCM) heart failure. Significant increases in plasma concentration of ANP were observed in cattle with DCM (73.3 +/- 16.02 pmol/l, n = 4, P less than 0.01) and BEC (20.6 +/- 3.45 pmol/l, n = 7, P less than 0.05), when compared with those in control cattle (14.5 +/- 1.84 pmol/l, n = 12). The concentration of ANP in cattle with DCM was significantly (P less than 0.01) higher compared with that in cattle with BEC. Plasma concentration of ANP correlated significantly with right atrial pressure (r = 0.95, P less than 0.01) and left ventricular end-diastolic pressure (r = 0.84, P less than 0.01). Gel-permeation chromatography of ANP in plasma and the right atrium from control and cattle with BEC revealed a single peak corresponding to the elution position of authentic human ANP(99-126) in plasma, and two peaks corresponding to those of authentic human ANP(99-126) and pro-ANP in the atrial extract. In cattle with DCM, however, peaks corresponding to the elution positions of authentic human beta-ANP and/or pro-ANP were detected in addition to the peak corresponding to ANP(99-126). The content of ANP in the right atrium of cattle with DCM was significantly (P less than 0.05) increased compared with that in control cattle and those with BEC. The present study therefore suggests that the synthesis and secretion of ANP might be stimulated by atrial distention induced by increased atrial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)