What is meant by "catalytic amount of a hormone"?
The writer obviously means “small amount”, and has chosen his words badly as hormones do not themselves catalyse reactions. 

The idea he is probably trying to convey is that a few molecules of hormone binding to their receptor can cause changes to many molecules within the target cell. This often (generally?) involves catalysis within the cell produced by the receptor activating an enzyme, so one can understand the line of thought leading to the misuse of this term.