Changes in myocardial and circulating atrial natriuretic peptide following thorax irradiation in rat

The effect of thoracic irradiation on plasma and myocardial atrial natriuretic peptide (ANP) was studied in rat. The animals were irradiated with a dose of 20 Gy to the heart. After, 1, 12, 26 and 52 weeks, plasma ANP concentration and ANP in atrial and ventricular myocardium were determined. Plasma ANP levels were increased to 140% of control values from 3 months onwards and remained elevated for the next 9 months. Atrial ANP concentrations remained unaltered in the first 6 months post-treatment, but became reduced after 1 year to 37% of control values. Ventricular ANP concentration in irradiated rats rose 20-fold within 3 months, remained at that level up to 6 months and fell to six times control values at 1 year. An inverse relationship between plasma and atrial ANP concentration was found, while plasma and ventricular ANP concentrations were positively correlated. The results obtained in the present study suggest that in radiation-induced heart disease, plasma ANP concentration can be used as a marker for early stage cardiac dysfunction.