Receptor pharmacology
Everything MT-II does, good and bad, follows from a single fact: it is not selective for the pigment receptor.
One key, four locks: the pharmacology of non-selectivity
Everything MT-II does, good and bad, follows from a single fact: it is not selective for the pigment receptor. This unit unpacks what that means, which tissues carry melanocortin receptors, and why no number can be put on how tightly MT-II holds any of them.
Understanding the receptor map turns MT-II from a mysterious "tanning drug" into a predictable piece of pharmacology, where every effect maps to a tissue. What it does not do is turn it into a measured one.
Key terms
The receptor profile
A dermatology reference sums MT-II up in one line: it mimics melanocortin peptides non-selectively. In skin the relevant receptor is MC1R, the signal on melanocytes that responds to alpha-MSH by switching on eumelanin synthesis. Everything else MT-II does follows from the same message reaching melanocortin receptors elsewhere in the body.
That second column is the honest part of this page. It is common to see a tidy grid of MT-II affinities, one number per receptor, presented as settled pharmacology. No such grid exists in the published record this course is built on, so this course prints none. What can be said is qualitative: the molecule carries the universal melanocortin message, it acts in skin, and it plainly reaches tissues far from skin.
AdvancedWhy no affinity number appears in this unit
The affinity constants for this chemical series live in a 1995 paper that could not be obtained. What surfaces in its place, in databases, is a curated record of sub-nanomolar values against a ligand identifier that cannot be matched to melanotan II rather than to one of the position-7 antagonist analogues the paper is actually about. That is the classic trap: a real number attached to the wrong molecule. A course that wants an affinity figure needs the primary pharmacology read in full first, and until then the honest statement is that none exists.