Relaxin

Relaxin is a protein hormone of about 6000 Da first described in 1926 by Frederick Hisaw. Relaxin is a protein hormone of about 6000 Da first described in 1926 by Frederick Hisaw. The relaxin-like peptide family belongs in the insulin superfamily and consists of 7 peptides of high structural but low sequence similarity; relaxin-1 (RLN1), 2 (RLN2) and 3 (RLN3), and the insulin-like (INSL) peptides, INSL3, INSL4, INSL5 and INSL6. The functions of relaxin-3, INSL4, INSL5, INSL6 remain uncharacterised. In the female, it is produced by the corpus luteum of the ovary, the breast and, during pregnancy, also by the placenta, chorion, and decidua. In the male, it is produced in the prostate and is present in human semen. Structurally, relaxin is a heterodimer of two peptide chains of 24 and 29 amino acids linked by disulfide bridges, and it appears related to insulin. Relaxin is produced from its prohormone, 'prorelaxin', by splitting off one additional peptide chain reaction. In females, relaxin is produced mainly by the corpus luteum, in both pregnant and nonpregnant females. Relaxin levels rise to a peak within approximately 14 days of ovulation, and then decline in the absence of pregnancy, resulting in menstruation. Relaxin may be involved in the vital process of decidualisation, working alongside steroid hormones to allow the endometrium to prepare for implantation. During the first trimester of pregnancy, levels rise and additional relaxin is produced by the decidua. Relaxin's peak is reached during the first trimester (14-weeks) and at delivery. Relaxin mediates the hemodynamic changes that occur during pregnancy, such as increased cardiac output, increased renal blood flow, and increased arterial compliance. It also relaxes other pelvic ligaments. It is believed to soften the pubic symphysis. In males, relaxin enhances motility of sperm in semen. In the cardiovascular system, relaxin works mainly by activating the nitric oxide pathway. Other mechanisms include activation of NFκB leading to vascular endothelial growth factor (VEGF) and matrix metalloproteinases transcription.