Schmidt, W., A. Bub, M. Meyer, T. Weiss, D. Schneider, N. Maassen, and W. G. Forssmann. Is urodilatin the missing link in exercise-dependent renal sodium retention? J. Appl. Physiol. 84(1): 123-128, 1998.The purpose of the present study was to investigate the behavior of plasma atrial natriuretic peptide [ANP-(99126)] concentration ([ANP]) and renal urodilatin [Uro; ANP-(95126)] excretion during and after exercise and their possible effects on renal Na⁺ retention. Ten male subjects performed a cycle ergometer test for 60 min at 60% of maximum workload. Blood and urine samples were collected before, during, and up to 24 h after exercise. During exercise, plasma [ANP] and renal Uro excretion were oppositely affected: whereas [ANP] increased from 46.5 ± 5.1 to 124.1 ± 10.6 pg/ml, urinary Uro excretion decreased from 120.8 ± 16.0 to 49.5 ± 9.8 fmol/min and remained at a lower level until 1 h after exercise. Glomerular filtration rate showed lowest values during exercise (from 164.9 ± 15.3 to 75.8 ± 10.1 ml/min), and urine flow and the fractional excretion rate of Na⁺ (FE_Na⁺) and Cl () had their nadir during the first hour after exercise. Positive relationships were observed between Uro excretion and FE_Na⁺ (P < 0.05) and , whereas a tendency toward a negative correlation was obtained between [ANP] and FE_Na⁺. It seems possible that Uro may be, among other factors, involved in the exercise-related regulation of renal Na⁺ retention. The specific roles Uro and ANP play during exercise, however, remain to be investigated.