Relaxin is a hormone produced by the female body during pregnancy. Among other things, it affects the connective tissue, changing its properties to make it more stretchy and thereby prepare for childbirth. In addition, medicine uses relaxin to treat heart disease.
What is relaxin?
Relaxin is a peptide hormone that participates in various processes in the human body. Peptide hormones are hormones that are insoluble in fat. They consist of amino acids that are linked by a peptide bond. In this type of bond, two amino acids are linked by the carboxyl group of one amino acid fusing with the amino group of the other. In the process, they split off water. In this way, long amino acid chains can be formed that fold in space due to their biochemical properties. Only in this way do proteins acquire their characteristic three-dimensional structure. The shape of the macromolecule is not arbitrary, but has a decisive influence on how the hormone functions. Relaxin is similar in structure to the hormone insulin, which regulates blood sugar. Insulin and relaxin are similar in their building blocks: they consist of two amino acid chains. In each case, two disulfide bridges connect the two amino acid chains.
Function, action, and roles
Medicine discovered relaxin primarily in its role as a pregnancy hormone. A woman’s body produces relaxin after the fertilized egg has nested in the lining of the uterus. The hormone changes the properties of the connective tissue: among other things, relaxin alters the structure of the cells in the canal of the cervix. Due to hormonal stimulation, the passage widens and thus prepares the female body for childbirth. In addition, Relaxin dilates the cervix. Without these adjustments, natural childbirth would not be possible. However, Relaxin also leads to some unpleasant side effects. Pregnant women often suffer from water retention. Relaxin provides one reason for this: it manipulates the settings of the receptors that control volume in body tissues as well as osmosis. During pregnancy, therefore, the normal fluid balance is upset and additional water is stored between the individual cells: The tissue swells. The feet and calves are particularly often affected by this, as the fluid in the legs has to fight both osmotic regulation and gravity. Pregnant women may find the water retention uncomfortable or even suffer from pain due to the intense pressure; however, it is not directly harmful to their health. Recent findings show that the functions of Relaxin are more diverse than initially assumed. Increasingly, medicine is also using the hormone specifically to treat diseases, for example after acute heart failure. Three variants of the peptide hormone are now known to science. Both relaxin-1 and serelaxin (relaxin-2) play a role in pregnancy. Relaxin-3, on the other hand, appears to be involved in neuronal processes and has a slightly lower mass in comparison.
Formation, occurrence, properties, and optimal levels
Relaxin is formed primarily in the ovaries, in the corpus luteum. The corpus luteum is the empty follicle after ovulation – in a sense, the shell that contained a single egg. The corpus luteum is thus a part of the ovary. Without fertilization of the egg, the corpus luteum degenerates into the corpus albicans a few days after ovulation. It owes its name to the whitish, scar-like surface. However, if a sperm fertilizes the egg, the corpus luteum does not develop into the corpus albicans, but into the corpus luteum graviditatis. In this process, the hormone chorionic gonadotropin stimulates the transformation. The corpus luteum graviditatis is mainly responsible for relaxin synthesis. The natural sciences also refer to the starting material for the synthesis of relaxin as a precursor. This is a precursor of the actual hormone. From the precursor, enzymes cleave off two amino acid chains, which in the further course of synthesis are transformed into the final hormone. The corpus luteum graviditatis also produces progesterone. Progesterone stimulates the growth of the endometrium, thereby preparing it for implantation of the egg. During pregnancy, progesterone interrupts the maturation process of the remaining follicles in the ovaries.In this way, no further ovulation can occur until the pregnancy is terminated and normal hormonal balance is restored.
Diseases and disorders
Medicine has long suspected a number of connections between relaxin and various diseases. For example, it hopes that a variant of relaxin, serelaxin (relaxin-2), will provide better treatment options for acute heart failure. Serelaxin causes several hemodynamic changes in the human body even in the absence of pregnancy; among other things, it causes the kidneys, lungs and other organs to receive better blood flow. Physicians therefore use serelaxin to alleviate the symptoms of heart patients – for example, in the regeneration phase after acute heart failure or in heart failure. Research has also established a link between relaxin and cancer. A substance similar to relaxin could therefore promote tumor growth and tissue destruction. The relaxin receptor also appears to be involved in the development of metastases. However, the exact processes are very complex; numerous other substances are also involved in these reactions. In addition to the physical responses to relaxin, there also appear to be psychological effects of the hormone. Research suggests that relaxin, along with other hormones, contributes to the development of postpartum depression and other psychological disorders that may be triggered by pregnancy and childbirth.
