Relaxin-2

Where it comes from

Made in

Corpus luteum of the ovary; the placenta and decidua; in men, the prostate

Sent out by

Highest in the first trimester, under hCG; in the menstrual cycle, after ovulation

Acts on

• Arteries and kidney (vasodilation)
• Heart
• Pelvic ligaments and cervix
• Fibroblasts (less collagen)

What it does

• Raises cardiac output and kidney blood flow in early pregnancy ⁴
• Softens the cervix and pelvic ligaments toward birth
• Reduces scarring in heart, kidney and lung in animals ⁴

In medicine

• Serelaxin, the synthetic form, was infused for 48 hours in acute heart failure. The second large trial, in 6,545 patients, found no reduction in cardiovascular death at 180 days and none in worsening heart failure at day 5 ¹
• The European regulator refused it a marketing authorisation in January 2014 and confirmed the refusal on re-examination that May, so no relaxin medicine is approved ²
• Relaxin is not measured in pregnancy care, and nothing is given to replace it

Beyond the body’s own use

• An oral agonist at the relaxin receptor has been through a 24-week trial in 375 people with chronic heart failure: it was tolerated and moved haemodynamic measures, with no effect on outcomes yet tested ³
• A long-acting relaxin fusion has reached mid-stage trials in heart failure with pulmonary hypertension; neither it nor the oral agonist is approved
• The idea that relaxin loosens joints, or softens old scar tissue, comes from pregnancy physiology and animal work; no trial has given it to people for either ⁴