<P> TRH is produced by the globe in medial neurons of the paraventricular nucleus . At the beginning, it is synthesized as a 242 - amino acid precursor polypeptide that contains 6 copies of the sequence - Gln - His - Pro-Gly -, flanked by Lys - Arg or Arg - Arg sequences . </P> <P> To produce the mature form, a series of enzymes are required . First, a protease cleaves to the C - terminal side of the flanking Lys - Arg or Arg - Arg . Second, a carboxypeptidase removes the Lys / Arg residues leaving Gly as the C - terminal residue . Then, this Gly is converted into an amide residue by a series of enzymes collectively known as peptidylglycine - alpha - amidating monooxygenase . Concurrently with these processing steps, the N - terminal Gln (glutamine) is converted into pyroglutamate (a cyclic residue). These multiple steps produce 6 copies of the mature TRH molecule per precursor molecule for human TRH (5 for mouse TRH). </P> <P> Following secretion, TRH travels across the median eminence to the anterior pituitary gland via the hypophyseal portal system where it stimulates the release of thyroid - stimulating hormone from cells called thyrotropes . </P> <P> TRH can also be detected in other areas of the body including the gastrointestinal system and pancreatic islets, as well as in the brain . </P>

How does thyrotropin releasing hormone travel from the hypothalamus to the pituitary gland