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 (β-endorphin) has a high affinity for opiate receptors in the brain, and the binding was reversed by naloxone, a classical antagonist of the opiates (Bradbury et al. 1976a). Alongside this, Feldberg found that β-endorphin administered in cat ventricles was 100 times more potent than morphine as an analgesic agent (Feldberg & Smyth 1976, 1977) 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 ==