Question

How can the same hormone have different effects on different cells?

Answer 1

An hormone is not different from most other molecules. To have an effect on a cell it binds to a (more or less specific) receptor, located either on the plasma membrane or inside the cell, and it initiates an intracellular cascade of events1.

There are several ways an hormone can have different effects:

there can be multiple receptors for the same hormone. For instance, prolactin can bind to two receptors, called prolactin receptor (PRL-R) short and long form. The short form of the receptor has been shown to lack the ability to promote milk protein genes transcription (See Lesueur et al., PNAS - 1991).

the same receptor can be coupled to different intracellular pathways in different cell types / physiological conditions, thus resulting in different effects.

each cell type/tissue expresses a set of protein that will interact in a different manner with the intracellular cascade promoted by the hormone.

an hormone can interact with receptors for other molecules. For instance allopregnanolone, a metabolite of progesterone, is a potent agonist of the GABA-A receptor, giving it anxiolitic properties