EXERCISE INCREASES THE CIRCULATING CONCENTRATION OF THE N-TERMINUS OF THE ATRIAL-NATRIURETIC-FACTOR PROHORMONE IN NORMAL INDIVIDUALS

Recently two peptides consisting of amino acids (aa) 1 to 30 and 31 to 67 of the N-terminus of the 126 aa prohormone of atrial natriuretic factor (proANF), as well as atrial natriuretic factor (ANF, aa 99 to 126; C-terminus), were found to have vasodilatory and natriuretic properties. These peptides, as well as ANF, circulate in humans as part of the N-terminus of the prohormone. To determine the effect of graded exercise on the circulating concentrations of the N-terminus and C-terminus of the ANF prohormone in normal persons, 12 healthy individuals (mean age 45 +/- 2 years) were evaluated before, for 2 hours after, and during bicycle exercise at a work loads of 25, 50, 75, 100, 125, 150, and 175 W. Both the N- and C-terminus of the ANF prohormone were released simultaneously with graded exercise in direct proportion to the intensity of the work load, measured objectively via maximal oxygen consumption (VO2max), respiratory quotient, and heart rate. Both the N-terminus and C-terminus of the ANF prohormone had strong positive correlations (p < 0.001) with blood pressure, heart rate, VO2max, and respiratory quotient. Following exercise, the C-terminus returned to preexercise levels within 30 minutes, while the N-terminus remained significantly elevated at 30 and 60 minutes postexercise, reflecting the longer half-life of the N-terminus in the circulation.