Somatotropin (Growth Hormone) is secreted by the somatotroph cells within theanterior pituitary gland.
Some of GH's characteristics are:
It is the most abundant pituitary hormone (10-15%)
It is a small protein (21 kd and 91 amino acids)
Structurally resembles prolactin - which suggests some functional overlap. So it has some of the activity of prolactin in addition to stimulating lactation; in addition, it also stimulates some level of growth of the epithelial cells and breast tissue.
Half life (t1/2) = 20-25 min; the half life is increased when bound to plasma proteins for transport.