In the liver, pyridoxine is essential for glucose production from amino acids via its role as coenzyme for the transaminase enzymes. Pyridoxine is also needed by the liver and muscles to make stored glycogen available for glucose production, and to synthesize niacin from the amino acid tryptophan. In red blood cells, pyridoxine is needed for hemoglobin synthesis, and regulates its oxygen affinity. Additionally, steroid hormone action is modulated by pyridoxine at the receptor level. In the nervous system, pyridoxine is needed to synthesize several neurotransmitters, such as serotonin (from tryptophan), taurine, dopamine, norepinephrine, histamine and gamma-aminobutyric acid (GABA). Many experimental and clinical observations support the fact that adequate amounts of dietary vitamin B6 are required to maintain normal nervous system function.