Free and sulfate-conjugated catecholamines during exercise in man.

The study examined the plasma concentration of free and sulfate-conjugated norepinephrine (NE) and epinephrine (E) at rest and after vigorous bicycle exercise. Free and total catecholamines were measured by a modified radioenzymatic assay using external standards. This assay was less costly and, in subjects with normal renal function, plasma levels were highly comparable to those obtained using internal standards. Exercise was associated with a predictable rise in plasma free NE and E concentration, which correlated with the hemodynamic changes, and a significant decrease in the levels of catecholamine sulfate conjugates. There was an inverse relationship between the degree of conjugation and the free levels of NE and E both at rest and after exercise. This suggests that the degree of conjugation is another factor determining the concentration of free amines in plasma.