Arginine

Semi-essential amino acid – substrate of NO synthase (nitric oxide) for widening of the blood vessels. Important for immune function and wound healing.

What arginine does in the body

Arginine comes from food and from the body's own production: the cells of the small intestine make citrulline, which the kidneys convert into arginine. Arginine is a building block of proteins and the starting material for several pathways. The NO synthases split it into nitric oxide (NO) and citrulline; NO relaxes the smooth muscle of the vessel wall so that the vessels widen, inhibits platelet clumping, serves nerve cells as a messenger and immune cells as a weapon against pathogens. Arginase splits arginine in the urea cycle of the liver into urea and ornithine; ornithine gives rise to proline for collagen and polyamines for cell division – both are needed for wound healing. Together with glycine, arginine is also the starting material for creatine, the energy store of the muscles.

Low arginine – what happens in the body?

When little arginine is available, the vessel walls produce less NO: the vessels widen less well, and blood flow can decrease, especially in small vessels. Immune cells, particularly T cells, multiply less well when arginine is lacking, and less proline and fewer polyamines are available for wound healing. Low values occur when consumption rises – after surgery, injuries, burns and with severe infections, when immune cells produce more arginase and break down arginine –, when the gut or kidneys provide or convert less citrulline, and with low protein intake.

High arginine – what happens in the body?

More arginine in the blood does not automatically mean more NO: the NO synthases are usually already sufficiently supplied with arginine, and how much NO is produced depends mainly on their activity and on inhibitors such as ADMA. Temporarily higher values are found after protein-rich meals. Markedly raised values arise when arginase is missing in the liver – in a rare inherited disorder of the urea cycle, argininaemia; arginine then accumulates, ammonia can rise and the nervous system is put under strain.

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