What Is the LPH Hormone and What Does It Do?

Lipotropin (LPH) is a polypeptide hormone produced in the anterior pituitary gland. It is derived from a larger parent molecule and was initially named for its presumed ability to mobilize fats. LPH exists in two primary forms, beta-lipotropin and gamma-lipotropin, which differ in size and origin from the parent molecule.

Origin of LPH from Proopiomelanocortin (POMC)

Lipotropin originates from a large precursor protein known as proopiomelanocortin (POMC), which is synthesized in the anterior pituitary gland, hypothalamus, and skin cells. POMC itself has no single function; instead, it is a raw material. Through enzymatic cleavage, enzymes cut the POMC chain at specific points to release various smaller, active peptide hormones.

From the single POMC protein, the body can generate several distinct hormones, each with its own job. Among these products are LPH and adrenocorticotropic hormone (ACTH), which is involved in the stress response. The specific hormones produced from POMC can vary depending on the tissue and enzymes present, allowing for a tailored release of signals.

The creation of LPH from POMC is a regulated process. The initial cleavage of POMC splits it into multiple pieces, one of which is beta-lipotropin (β-LPH). This 90-amino acid polypeptide is one of the final large fragments released from the POMC precursor. Its production in the pituitary occurs in roughly equal amounts to ACTH, highlighting their shared origin.

LPH’s Dual Functions: Intrinsic Activity and Precursor Role

Lipotropin was first investigated for its direct biological activities, such as lipolysis (the breakdown of fats) and steroidogenesis (the creation of steroid hormones). Early research suggested LPH could stimulate the release of fatty acids into the bloodstream for use as energy. This proposed action on fat metabolism is what originally earned the hormone its name.

Despite these initial findings, the direct functions of LPH are not its primary purpose. Research has not strongly supported these early observations, and no exclusive receptor for LPH has been identified. Its direct effects, like stimulating pigment cells, are weak compared to other hormones designed for that task.

The main significance of LPH is its role as a prohormone, an intermediate molecule that is processed to create other, more potent hormones. Beta-lipotropin is a precursor that can be cleaved into smaller peptides, including endorphins and melanocyte-stimulating hormones (MSH). Its metabolism into these other molecules is its most impactful contribution to bodily function.

How LPH Gives Rise to Endorphins

Beta-lipotropin (β-LPH), the 90-amino acid chain derived from POMC, contains the entire sequence for the opioid peptide beta-endorphin. Through enzymatic cleavage, the tail end of the β-LPH molecule is cut away, releasing this 31-amino acid fragment. This process transforms a larger, less active molecule into a smaller, highly specific signaling molecule.

Endorphins are the body’s natural painkillers, modulating pain perception, reducing stress, and contributing to feelings of well-being. When released, beta-endorphin binds to the same opiate receptors in the brain targeted by drugs like morphine. Studies found that beta-endorphin administered into the brain was significantly more potent as an analgesic agent than morphine, with effects that lasted for several hours.

The generation of beta-endorphin from β-LPH is a pathway for managing the body’s response to pain and stress. Since β-LPH is produced and stored in the pituitary gland, it provides a ready reservoir that can be quickly metabolized into endorphins. This system allows the body to deploy its pain-relieving substances in response to injury or intense physical exertion.

The Link Between LPH and Melanocyte-Stimulating Hormones

Lipotropin also serves as a source for melanocyte-stimulating hormones (MSH). The amino acid sequences for certain forms of MSH are embedded within the larger LPH molecules. For instance, gamma-lipotropin (γ-LPH) is a 56-amino acid peptide that contains the sequence for gamma-MSH (γ-MSH) and can be cleaved to release it.

Melanocyte-stimulating hormones are recognized for regulating pigmentation by acting on cells called melanocytes, stimulating them to produce melanin. This function explains why β-LPH itself has weak melanocyte-stimulating activity, as it contains an MSH sequence. However, the cleaved MSH molecules are far more potent in this role.

The functions of MSH extend beyond skin pigmentation to influence a range of physiological processes. These include:

• Regulating appetite and energy balance
• Possessing anti-inflammatory properties
• Playing a role in sexual arousal
• Influencing other neurological functions