Relaxin-1

Where it comes from

Made in

Decidua, trophoblast and prostate, at low levels

Sent out by

Unknown

Acts on

• Uterus and cervix, presumably

What it does

• Arose when the ancestral relaxin gene duplicated in the catarrhine primates, about 44 to 30 million years ago, and the pair survives only in the apes ¹
• Acts like relaxin-2 at the receptor; relaxin-2 does the circulating work ²
• Its transcripts turn up in decidua, trophoblast and prostate, the same places as relaxin-2, and no separate function has been shown ³

In medicine

• Nothing is measured or treated with it: no assay used in care separates H1 from H2 relaxin
• A fusion transcript joining RLN1 to RLN2 has been reported in prostate cancer, which is the only clinical thread so far ⁴

Beyond the body’s own use

• It is studied as a question in evolution rather than as a hormone: why a duplicate kept for 30 million years has no job of its own
• All the human work on relaxin, from pregnancy physiology to the heart failure trials, has used relaxin-2 or its synthetic form, so this gene is read from sequence and tissue expression rather than from experiments ²