Adrenal Medulla and Catecholamines

Adrenal Medulla and Catecholamines

• The adrenal medulla is considered a neuro-endocrine unit, as it is part of the sympathetic nervous system and produces catecholamine hormones.
• The catecholamine hormones produced by the adrenal medulla are dopamine, norepinephrine, and epinephrine.

Control of Catecholamines

• The release of catecholamines from the adrenal medulla is stimulated by low levels of catecholamines in the body.
• Elevated levels of catecholamines in the body inhibit the release of catecholamines from the adrenal medulla.

Biosynthesis of Catecholamines

• Catecholamines are synthesized from the amino acid tyrosine by chromaffin cells (pheochromocytes) in the adrenal medulla.
• Chromaffin cells are also found in extramedullary tissues such as the heart, liver, kidney, gonads, sympathetic fibers, and CNS.
• The main differences between catecholamines produced by the adrenal medulla and those produced by extramedullary tissues are:
  • Epinephrine is the main product of the adrenal medulla, while norepinephrine is the main product of extramedullary tissues.
  • Catecholamines produced by the adrenal medulla are transported by blood circulation to act on other tissues, while those produced by extramedullary tissues act locally.
• The sequential steps for converting tyrosine into epinephrine are:
  • Ring hydroxylation.