cerulein

You might think this is just a fancy, alternative spelling for the color blue (cerulean), but you'd be missing a letter and a whole lot of chemistry. Cerulein is a noun that refers to a powerful substance originally discovered in a surprising place: the skin of the Australian green tree frog.

In the medical world, cerulein is a "secretagogue," which is a fancy way of saying it tells your organs to start secreting digestive fluids. It mimics gut hormones that signal your pancreas and gallbladder to get to work. However, in a completely different laboratory—one dealing with fabrics—cerulein can also refer to a dye used to color wool and silk, often yielding greenish-blue or olive tones.

Cerulein (also spelled caerulein) is a valid English word with two distinct meanings depending on whether you are talking to a biologist or a textile chemist.

In biochemistry and medicine, cerulein is a specific peptide (a short chain of amino acids). It was famously isolated from the skin of Ranoidea caerulea, the Australian green tree frog. It is chemically very similar to cholecystokinin (and related gut peptides), hormones humans produce to aid digestion. Because it is so effective at stimulating the release of digestive enzymes and bile (and at contracting the gallbladder), clinicians have historically used cerulein stimulation as a diagnostic tool to test pancreatic function. In research, it is frequently used to induce pancreatitis in animal models to help scientists study the disease.

In the context of organic chemistry and dyeing, cerulein is a dye derived from heating gallein with concentrated sulfuric acid. Despite the name sounding like "sky blue," this dye often produces olive-green or grayish-blue shades and is used on fabrics like calico, wool, and silk.

It is important not to confuse *cerulein (the noun for the drug or dye) with cerulean (the adjective for the color of the deep blue sky). While they both come from the Latin word caeruleus*, meaning dark blue or azure, they are used in very different ways today.

So whether you are analyzing the chemistry of frog skin or dyeing a vintage wool coat, cerulein is a potent agent of change.