The liver synthesizes and secretes at least three important hormones:
Insulin-like Growth Factor-1 (IGF-1)
Angiotensinogen
Thrombopoietin
Insulin-like Growth Factor 1
This protein of 70 amino acids was once called somatomedin because it, not growth hormone, is the immediate stimulus for growth of the body.
Growth hormone released from the anterior lobe of the pituitary
binds to receptors on the surface of liver cells.
This stimulates the synthesis and release of IGF-1 from them.
Many cells have receptors for IGF-1, especially cells in the bone marrow in the cartilaginous growing regions of the long bones.
Binding of IGF-1 to cells with receptors for it stimulates them to move from G1 of the cell cycle to S phase and on to mitosis.
The levels of IGF-1 in the blood are highest during the years of puberty which is, of course, a time of rapid growth. Occasionally children are found that have stunted growth because they have inherited mutant genes for the growth hormone (GH) receptor. Recombinant human IGF-1 has been successfully used to treat them.
This protein is released into the blood where it serves as the precursor for angiotensin. How angiotensin is manufactured, and the role it plays in maintaining blood pressure is described in the discussion of the kidney hormone renin.
Thrombopoietin is a protein of 332 amino acids. It stimulates precursor cells in the bone marrow to differentiate into megakaryocytes. Megakaryocytes generate platelets, essential to blood clotting.
A segment of thrombopoietin, manufactured by recombinant DNA technology, is now available for human therapy. It already shows promise in quickly restoring normal platelet counts in patients who have undergone chemotherapy.