RELATIONSHIP BETWEEN ATRIAL-NATRIURETIC-PEPTIDE AND PLASMA-VOLUME DURING GRADED-EXERCISE WITH WATER IMMERSION

To assess the relationship between atrial natriuretic peptide (ANP) an d the reduction in plasma volume (PV) during exercise, we measured cha nges in PV and ANP in seven male volunteers during treadmill exercise in air (AE) and with water immersion (WE) together with time control s tudies of rest in air and in water. Blood samples were collected from a catheter in the antecubital vein at exercise intensities of 32, 49, 65, and 78% of peak oxygen consumption (Vo(2)). Plasma ANP in AE incre ased significantly from the resting value [15 +/- 1 (SE) pg/ml] only a t 78% of peak Vo(2) (29 +/- 5 pg/ml), whereas ANP in WE increased sign ificantly at exercise levels of >49% of peak Vo(2) and reached 68 +/- 9 pg/ml at 78% of peak Vo(2). Although PV in AE and WE decreased signi ficantly with Vo(2) of > 49% of peak Vo(2) (P < 0.01), the decrease fr om the resting value in WE was significantly greater than that in AE o f >65% of peak Vo(2) (P < 0.01) and the decreases at 78% of peak Vo(2) were -9.7 +/- 0.8 and -6.1 +/- 1.7%, respectively. The difference in the decrease in PV between AE and WE at corresponding Vo(2) correlated strongly with that in the increase in ANP (r = -0.97; P < 0.01). Thes e results are consistent with the hypothesis that ANP may be involved in the fluid shift from the intra- to extravascular space during exerc ise.