Lipotropin
Lipotropin is the name for two hormones produced by the cleavage of pro-opiomelanocortin. The anterior pituitary gland produces the pro-hormone POMC, which is then cleaved again to form adrenocorticotropin and β-lipotropin.
β-Lipotropin
β-Lipotropin is a 90-amino acid polypeptide that is the carboxy-terminal fragment of POMC. It was initially reported to stimulate melanocytes to produce melanin. It was also reported to perform lipid-mobilizing functions such as lipolysis and steroidogenesis. However, no subsequent studies have been published that support these early findings and no receptor has been identified for β-lipotropin.β-Lipotropin can be cleaved into smaller peptides. In humans, γ-lipotropin, β-MSH, and β-endorphin, are all possible fragments of β-lipotropin. β-endorphin is the predominant opioid of the anterior human and rat pituitary gland. Birdsall and Hulme demonstrated that the C-fragment of lipotropin has a high affinity for opiate receptors in the brain, and the binding was reversed by naloxone, a classical antagonist of the opiates. Alongside this, Feldberg found that β-endorphin administered in cat ventricles was 100 times more potent than morphine as an analgesic agent and the analgesia persisted for several hours. Feldberg concluded that β-endorphin was the most potent analgesic agent known.
β-Lipotropin is found in essentially equimolar concentrations to that of corticotropin. Evidence shows that β-Lipotropin is metabolized into endorphins that can greatly affect mood and behavior and is thus regarded as a prohormone.
γ-Lipotropin
γ-lipotropin is the amino-terminal peptide fragment of β-lipotropin. In humans, it has 56 amino acids. Gamma lipotropin is identical to the first 56 amino acid sequences of β-lipotropin. It can be cleaved to β-melanocyte stimulating hormone.In sheep, gamma-lipotropic hormone is a 58-amino-acid long pituitary polypeptide formed from the first 58 residues of beta-lipotropic hormone. The carboxyl-terminal of gamma-lipotropic hormone is identical to the structure of beta-melanophore-stimulating hormone.
Use in pain relief
β-endorphin has been determined to have an analgesic effect. It produces effectssimilar to or characteristic of morphine.