A 21-amino
acid peptide that circulates in the plasma,
but its source is not known. Endothelin-3 has been found in
tall concentrations in the
brain and may regulate
significant functions in
neurons and astrocytes, such as proliferation and development. It
also is found throughout the
gastrointestinal tract and in the
lung and kidney. (n eng j med 1995;333(6):356-63)