The Role of GH
Growth hormone activity controls protein synthesis, immune system regulation, glucose metabolism and fat metabolism.
GH increases the breakdown of stored fat, increases the release of fatty acids into the bloodstream and the cellular uptake and burning of free fatty acids as fuel. GH decreases the body’s use of glucose, decreases the formation of glycogen and increases the availability of amino acids by increasing the transport of amino acids across the cell membrane. GH is a major factor in protein synthesis because it increases the tissue availability of amino acids and it increases tissue RNA levels. GH increases the body’s nitrogen retention, increases the retention of sodium, potassium, and phosphorus, increases renal blood flow and filtration, and increases collagen synthesis, cartilage growth, skeletal growth and muscle growth.
Some of the physiologic effects of GH are mediated by a peptide called IGF-1, which is created by the liver from GH. IGF-1 binds to IGF-1 cell membrane receptors where it promotes the cellular uptake of glucose and amino acids and enhances protein synthesis by activating the same pathways as insulin.
Growth Hormone has the following direct and indirect effects on the body:
1. Growth hormone has an anti-insulin effect and a direct action on carbohydrate and lipid metabolism. GH spares glucose utilization, and increases the availability of free fatty acids by promoting fat mobilization in tissues (lipolysis). The effects of increasing fatty acid utilization and decreasing glucose utilization can be beneficial in countering hypoglycemia. Conversely, the anti-insulin effect of GH can also cause high blood sugar when GH is given in pharmacological doses in the form of GH injections. Elevation of blood sugar is one of the most common side effects seen in individuals receiving GH injections.
2. The indirect actions of GH are mediated by several growth factors of which IGF-1 is the most well known. IGF-1 promotes protein synthesis and cell proliferation in both skeletal and soft tissues. IGF-1 has an insulin-like effect so, through IGF-1 activity, GH promotes amino acid uptake by the cells and increases cellular protein synthesis. The end result of GH’s direct and indirect effects on carbohydrate, lipid, and protein metabolism is a decrease in body fat and an increase in lean body mass. So people get thinner and stronger.
3. GH is required for the growth of children. Children with low levels of GH are short and when GH is extremely low dwarfism occurs.
4. GH maintains the health and strength of bones and GH decline will result in osteoporosis, which can even occur in young people who have GH deficiency.
5. GH maintains muscle mass and strength and when GH declines in old age both men and women lose their muscles. This effect is often seen in aging.
6. GH maintains the health of the skin. In aging, when GH declines, people have sagging of skin on their upper arms, face and neck. Also the skin becomes thin and fragile, age spots appear and wrinkling occurs.
7. GH increases calcium absorption from the gut.