In the classic definition, hormones are secretory products of the ductless glands, which are released in catalytic amounts into the blood stream and transported to specific target cells (or organs), where they elicit physiologic, morphologic and biochemical responses.
What is meant by catalytic amount? Does it mean that amount required for catalysis? I know only renin which is catalytic and act as an enzyme, and many other hormones are non enzymatic so why the term catalytic is used in general sense?