Alterations of atrial natriuretic peptide in cardiomyocytes and plasma of rats after different intensity exercise.

To characterize the effect of long-term exercise training at different intensities on endocrine structure and function of the heart, plasma atrial natriuretic peptide (ANP) levels, expression of ANP in cardiomyocytes, and ultrastructure of cardiomyocytes were examined by radioimmunoassay, immunohistochemistry and transmission electron microscopy in Sprague-Dawley rats trained on a treadmill at different intensities for 8 weeks. The plasma ANP increased gradually with increasing exercise intensity. The immunoreactivity of ANP in cardiomyocytes increased in the moderate- and high-intensity exercise group and decreased in the exhaustive exercise group. The ANP electron-dense granules and the quantity and volume of mitochondria increased in moderate and high-intensity exercise group. The ANP electron dense granules decreased and the mitochondria tumefied in the exhaustive exercise group. The changes of plasma ANP have a tendency of increasing gradually with increase in exercise intensity. Moderate and high-intensity exercise increases ANP synthesis and storage in cardiomyocytes and induces adaptive changes in the ultrastructure of cardiomyocytes. The decrease of ANP immunoreactivity in cardiomyocytes after exhaustive exercise is probably the result of massive depletion and induces damaging changes in the ultrastructure of cardiomyocytes.