Peter Fuller from the Hudson Institute of Medical Research, gave an interesting talk this morning at the 9th Aldosterone and ENaC in Health and Disease: The Kidney and Beyond Conference. His talk focuses on the evolution of the mineralocorticoid receptor in vertebrates. For animals living on land, the receptor responds mainly to the hormone aldosterone. The receptor can also bind the stress hormone cortisol and the sex hormone progesterone, although progesterone binding inhibits the receptor.
Interestingly, in teleost fish (ray-finned fish) the receptor is actually activated by progesterone. It is thought that the switch to activation by aldosterone coincided with the transition to land in terrestrial vertebrates as aldosterone functions to retain sodium (and also water) in the body.