Synthesis, Secretion, and Transport of Peptide Hormones

Abstract

Peptide hormones are composed of polypeptide chains with a size ranging from three to hundreds of amino acids. Peptide hormone synthesis involves several steps occurring in the nucleus and cytoplasm of secretory cells, including gene transcription into the precursor nuclear ribonucleic acid, posttranscriptional modifications of the precursor messenger ribonucleic acid transcript, translation of the mature messenger ribonucleic acid, and cotranslational and posttranslational modifications of the hormonal peptide. Synthesis of peptide hormones is regulated at one or more of the above-mentioned biosynthetic steps in order to meet the secretory requirements of endocrine glands. Once they are synthesized, peptide hormones are packaged into secretory granules until appropriate stimuli result in their secretion into the extracellular space. Secretion is not uniform, but rather follows pulsatile patterns and rhythmic changes which, in association with feedback mechanisms, ensure that hormone production is adequate and prevent the excessive release of hormones. Most peptide hormones are water soluble and therefore do not require carrier proteins to circulate in the blood stream. This property results in rapid hormone degradation by plasma proteases and a shorter half-life and duration of action compared to other types of hormones, such as steroid and thyroid hormones.