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. Fifteen well-trained male subjects (mean age = 27.6±1 years) were studied during two exercise sessions. Initially, graded exercise to maximum was performed to determine maximal oxygen consumption (V̇O2 max). On a separate occasion subjects performed 150 minutes of continuous exercise at 70-74% of the maximal heart rate, with radionuclide angiography performed at rest and every 50 minutes, in conjunction with Ir-ANP, blood pressure and heart rate measurements. During maximal exercise subjects reached a V̇O2 max of 47.9±2.1 ml/kg/min. Ir-ANP increased from 9.8±l.lpg/ml at rest to 45.2±6.6 pg/ml at maximal exercise. Ir-ANP remained elevated (28.9±3.4 pg/ml) 3 minutes after exercise (p<0.05). During prolonged exercise, left ventricular end-diastolic filling decreased significantly between 50 and 150 minutes (p < 0.05), with progressive rise in heart rate observed between 50 (141±8 beats/minute) and 150 minutes (154±3 beats/ min; p < 0.05). 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 minutes, 17.8±4.3 pg/ml after 100 minutes of exercise (p < 0.05), and 23.5±2.1 pg/ml by 150 minutes of exercise. A weak correlation (r = 0.33) was observed between heart rate and Ir-ANP throughout the exercise session. 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. Factors in addition to cardiac filling and heart rate may be important determinants of ANP concentration during prolonged exercise.
Key words
Atrial natriuretic peptide - exercise
