EFFECT OF ENDURANCE TRAINING ON ATRIAL-NATRIURETIC-PEPTIDE GENE-EXPRESSION IN NORMAL AND HYPERTROPHIED HEARTS

We studied the effects of physical endurance training on atrial natriuretic peptide (ANP) gene expression in beagle dogs, Wistar rats, and spontaneously hypertensive rats (SHR). The dogs underwent a gradually increased running training up to 40 km/day on a treadmill for 55 wk while the nontrained sibling control dogs were kept in their cages throughout the study. Endurance training caused a significant 13% (P < 0.05) increase in ventricular hypertrophy but did not change plasma immunoreactive (ir)-ANP levels at rest or ventricular ANP mRNA or irANP levels. When normotensive Wistar rats ran up to 2,200 m/day for 8 wk, no significant change was seen in ventricular hypertrophy or in plasma or ventricular irANP levels at rest compared with nontrained controls. However, endurance training caused a 2.2-fold increase in epicardial ANP mRNA levels (P < 0.05). In the SHR strain, running training up to 900 m/day for 31 wk increased ventricular hypertrophy of trained SHR by 7% (P < 0.01) and caused a concomitant 1.6- to 1.7-fold elevation in ventricular irANP and ANP mRNA levels (P < 0.01-0.001) compared with nontrained SHR. In contrast, changes in atrial ANP mRNA or irANP levels in response to training were small in all three protocols. This study shows that in the normal heart induction of ANP synthesis by endurance training is not associated with ventricular hypertrophy. Moreover, the common stimulus for ventricular ANP synthesis induced by both chronic pressure overload and physical training may be mechanical stretching of cardiac myocytes, because endurance training further stimulated ANP synthesis in hypertrophied ventricles in SHR.