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 essential 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 a different peptide chain reaction.

Relaxin function

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

The relaxin levels 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 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. It is believed to promote the implantation of the developing fetus in the uterus wall and the growth of the placenta.

At the beginning of pregnancy, relaxin inhibits contractions in the uterus wall 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 process the resulting waste products.


In preparation for labor, it 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 essential to facilitate delivery, it can also involve adverse 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 due to inflammation that can cause scarring and loss of organ function.

In addition, relaxin can influence blood pressure by relaxing blood vessels, promoting the growth of new blood vessels, and being anti-inflammatory. These properties could make it a potential therapeutic target for treating 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 the human chorionic gonadotropin also produces its release during pregnancy placenta.

It is unclear if relaxin can feedback into the pituitary or the fetus to affect luteinizing hormone or human chorionic gonadotropin levels and thus control its release.

It acts 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 relaxin levels 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.