Receptor pharmacology
Everything MT-II does, good and bad, follows from a single fact: it is a full agonist at four of the five melanocortin…
One key, four locks: the pharmacology of non-selectivity
Everything MT-II does, good and bad, follows from a single fact: it is a full agonist at four of the five melanocortin receptors. This unit unpacks what that means, how tightly it binds each receptor, and why the one receptor it skips is its most important safety feature.
Understanding the binding profile turns MT-II from a mysterious "tanning drug" into a predictable piece of pharmacology, where every effect maps to a receptor and every receptor maps to a tissue.
Key terms
The binding profile
MT-II does not act at all five receptors equally. As a broad melanocortin agonist it drives the pigment receptor (MC1R) strongly, acts at the brain and metabolic receptors (MC3R, MC4R, MC5R), and has little action at the adrenal receptor (MC2R), which is tuned to ACTH rather than MSH-type ligands. Those differences in receptor activity shape which effects dominate at a given exposure.
Read the row left to right and the whole drug makes sense. The darkest cell is MC1R, the pigment receptor, so tanning is the headline effect. The near-empty cell is MC2R, which is why MT-II does not behave like a stress hormone. The mid-range cells (MC3R, MC4R, MC5R) are the receptors behind the appetite, sexual, and glandular effects people report as "side effects."
AdvancedWhy sparing MC2R matters so much
MC2R is the receptor for ACTH, the hormone that drives the adrenal glands to make cortisol. A melanocortin agonist that hit MC2R would risk Cushing-like effects: high cortisol, blood-sugar disruption, and more. MT-II binds four of the five melanocortin receptors but not MC2R, which recognises ACTH rather than the MSH peptides, and that gap is the single most important reason its side-effect profile, while broad, does not include adrenal steroid overload.