Effect of exercise on plasma renin substrate.

Effects of physical exercise on plasma renin substrate (RS) and plasma renin activity (PRA) levels were studied during short-term and prolonged exercise. Six healthy male volunteers performed a dynamic exercise test with exercise levels of 50, 100, 150, and 200 W for 4 min at each level. Measured with direct radioimmunoassay (RIA), which measures both intact RS and des-angiotensin I-RS (des-A I-RS), a significant increase in RS was seen during short-term exercise. RS measured with indirect (enzymatic) assay, which measures intact RS only, did not change, whereas PRA increased significantly. During prolonged exercise, a 75-km cross-country ski race, PRA increased more than two fold in ten healthy males participating in the study. Measured with direct RIA, RS increased by 22%, the corresponding increase in RS measured enzymatically was 10%. The increases in RS were not significant, however. It is concluded that the increased consumption of RS by rising PRA during exercise is counterbalanced by increased synthesis or release of RS by the liver or extrahepatic tissue. During prolonged exercise, liver production rate of RS apparently reaches a plateau which can be sustained for at least 7-8 h.