Relaxin: What is it? How is it controlled? Functions and Consequences of Elevated and Low Levels of this Hormone

It is a hormone produced by the ovary and placenta with important effects on the female reproductive system and during pregnancy.

Relaxin is a heterodimer of two peptide chains of 24 and 29 amino acids joined by disulfide bridges. Relaxin belongs to the same family of hormones as insulin.

Relaxin is produced from its prohormone, ” prorelaxin “, by excising an additional peptide chain reaction.

Relaxin function

The effects of relaxin are best described during the female reproductive cycle and pregnancy.

The levels of relaxin in the circulation increase after ovulation, during the second half of the menstrual cycle. At this stage, it is thought that it relaxes the wall of the uterus by inhibiting contractions, and also prepares the lining of the uterus for pregnancy. If pregnancy does not occur, relaxin levels decrease again.

Relaxin during pregnancy

During pregnancy, relaxin levels are at their highest point in the first trimester. At this time, it is believed to promote the implantation of the developing fetus in the wall of the uterus and the growth of the placenta.

At the beginning of pregnancy, relaxin also inhibits contractions in the wall of the uterus, to prevent premature labor. Relaxin can regulate the cardiovascular and renal systems of the mother to help them adapt to the increased demand for oxygen and nutrients for the fetus, and to process the resulting waste products.

In preparation for labor, relaxes the ligaments of the pelvis and softens and widens the cervix. Towards the end of pregnancy, relaxin promotes the rupture of the membranes surrounding the fetus and the growth, opening and softening of the cervix and vagina to aid in the birth process.

Although its function is extremely important to facilitate delivery, it can also involve a series of negative effects during pregnancy. It can, for example, result in a greater possibility of contractures, especially in the lower back, pelvic and knees.

Relaxin in men

In men, relaxin is secreted from the prostate gland and can be detected in semen, but it is not usually found in the bloodstream.

Other functions

Relaxin reduces tissue fibrosis in the kidney , heart, lungs and liver, and promotes wound healing. Tissue fibrosis is the formation of hard tissue as a result of inflammation that can cause scarring and loss of organ function.

In addition, relaxin can influence blood pressure by relaxing blood vessels; promote the growth of new blood vessels; and it is also anti-inflammatory. All these properties could make it a potential therapeutic target for the treatment of certain diseases.

How is relaxin controlled?

The production of relaxin by the ovary during the menstrual cycle is stimulated by the luteinizing hormone of the pituitary gland, and its release during pregnancy is also stimulated by the human chorionic gonadotropin of the placenta.

It is not clear if relaxin can feed back into the pituitary or the fetus to affect luteinizing hormone or human chorionic gonadotropin levels and thus control its own release.

It carries out its actions on the reproductive system and other organs by activating specific receptors in these tissues.

What happens if there are elevated levels of relaxin?

Disorders of relaxin secretion have not been described in detail. Studies have suggested that high levels of circulating relaxin in the mother are associated with premature birth, most likely through its effects on the rupture of the fetal membranes and the opening of the cervix.

What happens if there are low levels of relaxin?

There is some evidence that low levels of relaxin may contribute to a condition known as scleroderma , where the skin thickens and hardens. This is caused by the development of fibrosis and scarring of the skin, which also occurs in the lung, stomach and blood vessels.