Protective effect of atrial natriuretic peptide on electrical-field-stimulated rat ventricular strips during hypoxia

We have previously shown that atrial natriuretic peptide reduces lactate accumulation in non-beating rat ventricular myocardium exposed to hypoxic conditions, and that hypoxia induces release of atrial natriuretic peptide from isolated rat atrial tissue. In these studies we suggested that atrial natriuretic peptide may be physiologically important for protection of the myocardium during periods of oxygen deficit. In the present study, we used isolated strips of rat right ventricle, contracted by electrical-field-stimulation, as a model of a beating myocardium. After contraction stabilization, hypoxic conditions were introduced through aeration with 20% O2, held for 20 or 30 min., and then interrupted by reoxygenation with 95% O2. The contractile force was recorded and the percentage regain of the contractions after reoxygenation was considered as an indication of the amount of cell damage induced during the period of hypoxia. The results show that after 30 min. of hypoxia and subsequent reoxygenation, ventricular strips treated with atrial natriuretic peptide (0.1 microM) recovered 67.9 +/- 2.8% of the prehypoxic force of contraction; control strips from the same ventricle regained 44.9 +/- 4.4% (P = 0.015) of their initial contractile activity. After 20 min. of hypoxia followed by reoxygenation, a ventricular strip incubated together with an atrium regained 78.6 +/- 2.4% of the prehypoxic force of contraction as compared to a 60.2 +/- 2.7% regain (P = 0.002) for the control strip. We conclude that atrial natriuretic peptide protects the working ventricular myocardium during hypoxia, which further supports our previously reported suggestion that the effect on myocardial metabolism is physiologically relevant during situations of oxygen deficit in heart muscle.