The melanocortin system is a family of five G-protein-coupled receptors: MC1R through MC5R. They respond to endogenous melanocortin peptides such as α-MSH, β-MSH, γ-MSH, and ACTH, but each receptor sits in a different tissue context and serves a different biological role.

MC1R is most associated with pigmentation. MC3R and MC4R play major roles in appetite and central signaling. MC2R is linked to adrenal cortisol biology. MC5R shows up in exocrine tissue contexts. Together they create a receptor map that explains why related melanocortin compounds can produce very different biological outcomes.

Melanotan 2 is comparatively broad across melanocortin receptors, which helps explain its pigmentation profile. PT-141 is more focused on MC3R and MC4R, which puts it deeper inside central nervous system signaling rather than skin-focused melanogenesis. KPV is different again: it comes from the α-MSH sequence, but much of its anti-inflammatory interest is framed as receptor-independent NF-κB modulation rather than classical melanocortin agonism.

That is why receptor maps matter. Without them, it is easy to assume compounds with similar ancestry should behave the same way when in reality they activate different tissues and signaling circuits.

One of the most studied pieces of the melanocortin system is the MC4R-AgRP axis. Agouti-related protein acts as an inverse agonist at MC3R and MC4R, pushing appetite upward. That is one reason melanocortin biology frequently shows up in both hormonal and metabolic research conversations.

Understanding the receptor map clarifies why PT-141 can be relevant to central signaling, why Melanotan 2 has pigmentation consequences, and why KPV is often treated as a separate anti-inflammatory story despite its sequence heritage.