**3. Facts and perspectives**

It is now clear that pituitary secretion of GH is mainly subject to a tonic inhibitory control exerted by SS, contrary to what was thought after the discovery of GHRH. Therefore, only the factors that can inhibit the production of SS will be responsible for the release of GH induced by GHRH, whose synthesis and release into the portal circulation are inhibited by SS. All this was identified in the last decade of the last century. However, the great complexity of the hypothalamus, in terms of the large number of existing neuronal types that can release very different compounds, suggests that more neurotransmitters with the capacity to act on the SS and, consequently, on the hypothalamic-somatotropic axis can still be identified, although, logically, their actions will always be more secondary than those of the factors that have been described in this chapter.
