Veterinary Physiology-III

Peptide hormone

PEPTIDE HORMONES

• Most hormones are peptide in nature and are composed of aminoacids. Like other proteins, they are synthesized on ribosomes where their specific aminoacids sequence is determined (translated) by a specific messenger RNA sequence. The nucleotide sequences of the mRNA are transcribed from specific nucleotide sequences in the DNA. The proteins are then released and transported into the rough endoplasmic reticulum. The initial protein formed is larger than the active hormone and is called preprohormone.
• In the interior of RER, pre portion of the hormone is cleaved to form prohormone. This in turn transported in the transport vesicles to the golgi bodies where they may be altered (e.g) sulphated or combined with carbohydrate moieties and the hormone is in its final form within the Golgi apparatus.
• Vesicles containing the hormone and possibly other products (proteolytic enzymes) are then pinched off the terminal cisternae of golgi bodies. These secretory vesicles are distributed within the cytoplasm. Protein hormones are stored within the gland until needed for release. Although some of the hormones are secreted continuously, most are excreted by a process of exocytosis of granules in response to specific signals. Exocytosis requires ATP and Ca²⁺