Inhibitors of dopamine-beta-hydroxylase in human plasma

There are two types of endogenous inhibitors of DBH in human plasma. One is sensitive to copper, or N-ethyl-maleimide, and is dialyzable. The other is not sensitive to copper, maleimide, or dialysis. Both types can be counteracted by diluting the plasma, thus eliminating the need for inactivators during the assay of plasma.