Abstract

In this study, cardiac performance and circulating immunoreactive atrial natriuretic peptide (Ir-ANP) were measured during sustained exercise to examine the relationship between cardiac filling, heart rate and circulating ANP. 15 trained males (27.6+-1 yr) were studied during 2 exercise sessions. Initially, VO2max was determined. On a separate occasion subjects performed 150 min of continuous exercise at 70-74 of max. heart rate, with radionuclide angiography performed at rest and every 50 min, in conjunction with Ir-ANP, blood pressure and heart rate measurements. During maximal exercise subjects reached a VO2max of 47.9+-2.1 ml/kg/min. Ir-ANP increased from 9.8+-1.1 pg/ml at rest to 45.2+-6.6 pg/ml at maximal exercise. Ir-ANP remained elevated (28.9+-3.4 pg/ml) 3 min after exercise. During prolonged exercise, left ventricular end-diastolic filling decreased significantly between 50 and 150 min, with progressive rise in heart rate observed between 50 (141+-8 b/min) and 150 minutes (154+-3 b/min). No change in left ventricular end-systolic counts, or arterial blood pressure were observed throughout the exercise period. Ir-ANP was elevated significantly during prolonged exercise, increasing from 9.4+-1.7 at rest, to 19.2+-3.4 after 50 min, 17.8+-4.3 pg/ml after 100 min of exercise, and 23.5+-2.1 pg/ml by 150 min of exercise. We conclude that during prolonged exercise the pattern of circulating Ir-ANP levels cannot be sufficiently explained by a progressive upward drift in heart rate and is dissociated from cardiac filling. Verf.-Ref.