GLP-1, GIP and glucagon receptors, explained

What a receptor is

A receptor is a protein that sits in the outer membrane of a cell. One end faces outside, where a signal molecule can attach to it. The other end faces inside, where it passes the message on. A good picture is a lock in a door: the right molecule fits, and the door sends a message.

What an agonist is

An agonist is a compound that fits the lock and turns it, so the receptor is switched on. A compound that fits but does not turn it is called an antagonist. The natural signal molecules are agonists too. The synthetic compounds studied in research are built to fit the same locks.

The three receptors

• The GLP-1 receptor, named after glucagon-like peptide-1, the natural molecule that binds to it.
• The GIP receptor, named after glucose-dependent insulinotropic polypeptide.
• The glucagon receptor, named after the hormone glucagon.

Why peptides suit receptor research

The natural molecules that bind these receptors are themselves peptides. That makes peptides a natural fit for building compounds that interact with them. Tirzepatide is described as acting on the first two receptors, and retatrutide on all three. Our posts on each compound explain the difference.

How laboratories measure activity

A common method is to grow cells that carry one receptor, add the compound, and measure the signal the cell produces inside. All three of these receptors raise a small messenger molecule called cyclic AMP, so a rise in cyclic AMP is a direct readout of receptor activity. Comparing the rise at different concentrations shows how strongly a compound acts.

A common mix-up

GLP-1 and glucagon sound alike but are different molecules that act on different receptors. Glucagon-like peptide-1 was named for its similarity to glucagon, not because the two do the same job. When a paper says the GLP-1 receptor, it means the one named for glucagon-like peptide-1, not the glucagon receptor.

Research use only

Pep Pantry products are sold for laboratory research by adults. They are not for human or veterinary use. This article describes the science for laboratory readers only.