Arginine residues in proteins can be deiminated by PAD enzymes to form citrulline, which is a post-translational modification process called citrullination. This is important in fetal development, is part of the normal immune process, as well as the control of gene expression, but is also significant in autoimmune diseases.:275 Another post-translational modification of arginine involves methylation by protein methyltransferases.

Arginine is the immediate precursor of nitric acid (NO), an important signaling molecule that can act as a second messenger, as well as an intercellular messenger that regulates vasodilation, and also has functions in the immune system’s reaction to infection.

Arginine is also a precursor for urea, ornithine, and agmatine; is necessary for the synthesis of creatine; and can also be used for the synthesis of polyamines (mainly through ornithine and to a lesser degree through agmatine, citrulline, and glutamate.) The presence of asymmetric dimethylarginine (ADMA), a close relative, inhibits the nitric oxide reaction; therefore, ADMA is considered a marker for vascular disease, just as L-arginine is considered a sign of a healthy endothelium.
Intravenously administered arginine is used in growth hormone stimulation tests because it stimulates the secretion of growth hormone.

A meta-analysis showed that L-arginine reduces blood pressure with pooled estimates of 5.4 mmHg for systolic blood pressure and 2.7 mmHg for diastolic blood pressure.

Supplementation with L-arginine reduces diastolic blood pressure.
Lengthens pregnancy for women with gestational hypertension, including women with high blood pressure as part of pre-eclampsia. It did not lower systolic blood pressure or improve weight at birth.

Brain tissue of deceased schizophrenics shows altered Arginine metabolism. Assays also confirmed significantly reduced levels of γ-aminobutyric acid (GABA), but increased glutamate/GABA ratio in the schizophrenia cases.