**4. Conclusions**

GH is a pleiotropic hormone produced mainly in the pituitary gland and the placenta, although the molecular forms of the hormone depend on the territory where they are

produced. From an evolutionary point of view, GH comes from a common gene with PRL, from which it diverged millions of years ago, this may explain why GH and PRL share some physiological actions. All GH genes have five exons separated by four introns. Although GH has traditionally been considered a product of pituitary expression, today we know that the hormone can be produced in practically any territory and cell, the brain, retina, and gonads being particularly important. Currently, we can consider GH as a true prohormone, given the large number of forms that can be generated by proteolytic processing, both in the pituitary itself and in the tissues, processing that is tissue and sexspecific. Although it has been considered that only the classic GH-N can be generated in the pituitary, GH N-glycosylated products have been identified in this gland, suggesting that they may have similarities with placental GH-V. Regarding this, a new placental variant has been identified, GH-V2, which seems to play important roles, even antagonistic to those of pituitary GH-N. The original ancestral GH has undergone many structural changes throughout evolution, which has allowed the number of actions of the hormone to increase as the complexity of organisms increases. This leads to the fact that its initial effect as merely a growth hormone has been increased in a species-specific way.
