relaxin

Relaxin is a peptide hormone belonging to the relaxin/insulin-like family of peptides. In humans, the gene family includes RLN1 and RLN2, which encode relaxin-1 and relaxin-2; RLN3 encodes relaxin-3. Relaxin is produced mainly by the corpus luteum of the ovary during pregnancy and, in placental mammals, by the placenta; in men and nonpregnant individuals, smaller amounts are produced by tissues such as the prostate.

Relaxin exerts its effects by binding to relaxin family peptide receptors, primarily RXFP1 and RXFP2, which are G protein-coupled receptors. A related peptide, relaxin-3, binds RXFP3 mainly in the brain.

Physiological roles in pregnancy include remodeling of reproductive tissues, cervical ripening, and pelvic ligament laxity to facilitate parturition. Relaxin also has vasodilatory effects, increases renal blood flow, and influences angiogenesis and extracellular matrix remodeling. Its heart- and kidney-related effects have been studied in nonpregnant individuals.

Historically, relaxin was described in 1926 by Frederick Hisaw as a substance in the ovarian extracts that relaxed the uterus. In medicine, recombinant human relaxin-2 (serelaxin) was evaluated for acute heart failure, but large trials did not demonstrate a clear, durable benefit and regulatory approval has not been obtained in major markets.

Overall, relaxin is a multifunctional peptide with reproductive, cardiovascular, and connective tissue remodeling roles, with distinct peptides in the family acting via different receptors.