Dynorphin B

Where it comes from

Made in

The same neurons as dynorphin A, cut from the end of prodynorphin

Sent out by

With dynorphin A

Acts on

• Kappa receptors
• Developing heart cells in culture

What it does

• Acts like dynorphin A at kappa receptors, and was purified from the same pituitary extracts ¹
• Reported to push stem cells towards heart muscle, a finding one independent study did not confirm ³
• The partner half of big dynorphin, and the half that does not disturb cell membranes ²

In medicine

• No medicine copies it. The approved kappa agonists, nalfurafine and difelikefalin, act at the receptor it shares with dynorphin A, so nothing distinguishes it at the bedside
• It is not measured in practice. Because it begins with the same seven residues as dynorphin A, it was separated from it only when the peptide was purified in its own right in 1982 ¹

Beyond the body’s own use

• Nothing containing it is in trials, and no analogue of it has been given to a person
• The one claim made for it beyond opioid signalling is cardiac: it was reported to drive embryonic stem cells towards heart muscle through a nuclear opioid route, a line of work that stayed with one laboratory ³
• What distinguishes it from dynorphin A is largely what it does not do. In lipid vesicles dynorphin A and big dynorphin leak the membrane and dynorphin B does not, which is how the non-opioid toxicity of this family was pinned on the longer peptides ²