Progesterone

Progesterone is a steroid and sex hormone that is created endogenously (by our own bodies). It is the primary hormone in the steroid class progestogens. Although widely known to play a large role in the menstrual cycle and pregnancy, scientists are just beginning to understand the enormous range of effects progesterone can have on the human body and its many systems. The word progesterone comes from the Latin pro-, meaning "for," and gest-, referring to pregnancy (as in "gestation"). It is commonly called the "pregnancy hormone." Progestins are a synthetic form of progesterone that differ in molecular makeup from the progesterone created by our bodies. Progestins are used by pharmaceutical companies in medications and contraceptives and are purposefully created to differ in molecular structure from progesterone since it is not possible to patent a chemical as it exists in nature.

Role in the Menstrual Cycle
At the beginning of a woman's cycle, the hypothalamus begins to secrete Gonadotropin Releasing Hormone (GnRH), stimulating the pituitary to create Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH), which travel to the ovaries. FSH causes the ovaries to stimulate the maturation process of follicles. Several follicles, each of which stores an egg, begin to grow as they mature, and in the process releasing estrogen. This estrogen produces a negative feedback during the first 10 days of the cycle that tells to the pituitary to inhibit the release of LH. It is important to note that low levels of estrogen will inhibit the release of LH from the pituitary, while high levels will stimulate it.

As estrogen continues to rise due to the maturing follicles, is also causes FSH levels to fall steadily (low estrogen triggers the release of FSH). Around day 10 of the cycle, estrogen levels reach a threshold which stops the negative feedback loop and begins a positive one resulting in the secretion of LH by the pituitary. The resulting spike in LH triggers the most mature follicle to release an egg (or oocyte); this is known as ovulation.

After ovulation, the empty follicle will begin to die. This dying follicle is called a corpus luteum. As the corpus luteum degrades, it secretes estrogen, inhibin, and progesterone. Inhibin provides a negative feedback to the pituitary to suppress the production of FSH. Progesterone provides a similar feedback to prohibit the release of GnRH, which in turn decreases the levels of LH and FSH. It also stimulates endometrial growth (the lining of the uterus).

As the corpus luteum degenerates, it will secrete fewer and fewer hormones, and progesterone, estrogen, and inhibin will steadily decrease. This decrease in progesterone allows for the secretion of GnRH to begin again, and the cycle repeats again, unless the egg becomes fertilized. If the egg is not fertilized, the decreasing levels of progesterone can no longer maintain the lining of the uterine wall, so the wall dies and sheds out of the body, resulting in menstruation.

Progesterone only exists in high levels during the second half of the menstrual cycle, the Luteal Phase.

Bio-Identical Progesterone & BHRT
Many functional medicine doctors have begun supplementing imbalanced hormone levels with bio-identical hormone replacement therapy (BHRT). The term bio-identical distinguishes these hormone supplements from the often used synthetic derivatives created by pharmaceutical companies. The use of the latter is widely known and highly conventional among mainstream medicine, whereas BHRT is most often only heard of in functional or integrative medicine. Bio-identical hormone supplements are identical in molecular structure to the natural hormones your body creates. A practitioner who uses BHRT will likely measure your hormone levels via saliva or blood sample, and prescribe your hormones through a compounding pharmacy. Bio-identical progesterone is made from yams and can be taken as a transdermal cream, pill, or vaginal gel.

Progesterone as a Neurosteroid
Progesterone not only plays a major role in female reproduction, but has many other important roles in both males and females. One such role is as a powerful neurosteroid. Neurosteroids are steroids synthesized in the brain that regulate the excitability of neurons. It has been shown to be important in myelin repair in rodents in the sciatic nerve. In one study, the administration of progesterone to the site of brain lesions led to the regeneration of new myelin sheaths. Neurosteroids can have powerful effects on both pain perception and inflammation, and research has suggested that female sex hormones like progesterone play a key role in modulating chronic pain. Progesterone has been shown in mice to prevent neurodegeneration, increase muscle strength, and enhance respiratory activity. The same study showed that progesterone blocks pro-inflammatory mediators, lessened Iba1+ microglial cells, and decreased symptoms of brain inflammation in mice. It also reduced the production of nitric oxide and TNF-α. Progesterone is neuroprotective, anti-inflammatory, and promyelinating, and could present great benefits for neurological illnesses.

It suppresses the inflammatory response to lipopolysaccharides by inhibiting IL-6 and IL-8.